UBC Theses and Dissertations

UBC Theses Logo

UBC Theses and Dissertations

Size-assortative mating in threespine sticklebacks from two sites on the Salmon River, British Columbia Borland, Marjory 1986

Your browser doesn't seem to have a PDF viewer, please download the PDF to view this item.

Item Metadata

Download

Media
831-UBC_1986_A6_7 B57.pdf [ 4.29MB ]
Metadata
JSON: 831-1.0096679.json
JSON-LD: 831-1.0096679-ld.json
RDF/XML (Pretty): 831-1.0096679-rdf.xml
RDF/JSON: 831-1.0096679-rdf.json
Turtle: 831-1.0096679-turtle.txt
N-Triples: 831-1.0096679-rdf-ntriples.txt
Original Record: 831-1.0096679-source.json
Full Text
831-1.0096679-fulltext.txt
Citation
831-1.0096679.ris

Full Text

SIZE-ASSORTATIVE MATING IN THREESPINE STICKLEBACKS FROM TWO SITES ON THE SALMON RIVER, BRITISH COLUMBIA by MARJORY BORLAND B.Sc.,Simon Fraser University,1982 A THESIS SUBMITTED IN PARTIAL FULFILLMENT OF THE REQUIREMENTS FOR THE DEGREE OF MASTER OF SCIENCE in THE FACULTY OF GRADUATE STUDIES (Department of Zoology) We accept t h i s thesis as conforming to the required standard THE UNIVERSITY OF BRITISH COLUMBIA October 1986 c Marjory Borland, 1986 In presenting t h i s thesis i n p a r t i a l f u l f i l m e n t of the requirements for an advanced degree at the University of B r i t i s h Columbia, I agree that the Library s h a l l make i t f r e e l y available for reference and study. I further agree that permission for extensive copying of t h i s thesis for scholarly purposes may be granted by the head of my department or by his or her representatives. I t i s understood that copying or publication of t h i s thesis for f i n a n c i a l gain s h a l l not be allowed without my written permission. Department of The University of B r i t i s h Columbia 1956 Main Mall Vancouver, Canada V6T 1Y3 DE-6 (3/81) i i ABSTRACT S i z e - a s s o r t a t i v e m a t i n g was s t u d i e d i n f r e s h w a t e r G a s t e r o s t e u s a c u l e a t u s f r o m two s i t e s on t h e S almon R i v e r , B r i t i s h C o l u m b i a . I n t h e u p p e r r i v e r f e m a l e s t e n d t o be l a r g e r t h a n m a l e s b u t i n t h e l o w e r r i v e r f e m a l e s a r e g e n e r a l l y s m a l l e r t h a n m a l e s . M a l e s i z e i s s i m i l a r i n b o t h a r e a s . The h y p o t h e s i s t e s t e d was t h a t f e m a l e s i z e i n f l u e n c e s m a le mate c h o i c e . F r e s h w a t e r m a l e s f r o m t h e two a r e a s showed a p r o n o u n c e d d i f f e r e n c e i n mate p r e f e r e n c e w i t h r e s p e c t t o f e m a l e s i z e . I n c h o i c e t e s t s , m a l e s f r o m t h e u p p e r r i v e r f a v o u r f e m a l e s l a r g e r t h a n t h e m s e l v e s , w h e r e a s l o w e r r i v e r m a l e s f a v o u r f e m a l e s s m a l l e r t h a n t h e m s e l v e s . D i f f e r e n c e s i n c o u r t s h i p b e h a v i o u r a l s o e x i s t b e t w e e n m a l e s f r o m t h e two s i t e s . A f t e r an i n i t i a l a s s e s s m e n t p e r i o d , t h e r e l a t i v e f r e q u e n c i e s a n d o c c u r r e n c e o f some m a l e b e h a v i o u r p a t t e r n s a r e s t r o n g l y a s s o c i a t e d w i t h e i t h e r t h e r e l a t i v e s i z e o r g e n e t i c t y p e o f t h e f e m a l e . O t h e r b e h a v i o u r s a r e i n d e p e n d e n t o f t h e s i z e o r t y p e o f f e m a l e c o u r t e d . Lower S a l m o n m a l e s a p p e a r t o be c o n s t r a i n e d f r o m c h o o s i n g l a r g e r , a n d t h e r e f o r e more f e c u n d , f e m a l e s by t h e p r e s e n c e d u r i n g t h e b r e e d i n g s e a s o n o f t h e m a r i n e f o r m o f t h r e e s p i n e s t i c k l e b a c k . The . m a r i n e f o r m o f G. A c u l e a t u s i s anadromous a n d a s a d u l t s a r e a d a p t e d t o a p e l a g i c , m a r i n e e x i s t e n c e . They r e p r e s e n t a d i s c r e t e a n d d i f f e r e n t g e n e - p o o l f r o m t h e f r e s h w a t e r f o r m . F e m a l e s o f t h e m a r i n e f o r m a r e c o n s i s t e n t l y t h e l a r g e s t s t i c k l e b a c k f e m a l e s e n c o u n t e r e d i n t h e l o w e r r i v e r . L ower S a l m o n m a l e s c l e a r l y d i s t i n g u i s h b e t w e e n m a r i n e a n d f r e s h w a t e r f e m a l e s a n d t o some e x t e n t t h i s d i s c r i m i n a t i o n i s r e l a t e d t o f e m a l e s i z e . The a b s e n c e o f t h i s c o n s t r a i n t i n t h e u p p e r r i v e r a l l o w s u p p e r r i v e r m a l e s t o i n c r e a s e t h e i r r e p r o d u c t i v e p o t e n t i a l by p r e f e r e n t i a l l y m a t i n g w i t h t h e l a r g e s t a n d most f e c u n d f e m a l e s i n t h e i r a r e a . i v TABLE OF CONTENTS ABSTRACT i i L I S T OF TABLES v i L I S T OF FIGURES v i i i ACKNOWLEDGEMENTS i x I n t r o d u c t i o n 1 M a t e r i a l s a n d M e t h o d s 9 S t u d y s i t e s 9 L i t t l e C a m p b e l l R i v e r 9 Salmon R i v e r 12 C o l l e c t i o n a n d M a i n t e n a n c e o f F i s h 12 M a l e B e h a v i o u r 16 O b s e r v a t i o n a n d R e c o r d i n g P r o c e d u r e s 17 D a t a A n a l y s i s 19 E x p e r i m e n t a l P r o t o c o l s 20 L i t t l e C a m p b e l l R i v e r p r e l i m i n a r y s t u d y 20 Salmon R i v e r S t u d y 21 Mate S e l e c t i o n E x p e r i m e n t s 21 F r e s h w a t e r M a t e S e l e c t i o n E x p e r i m e n t s 21 F r e s h w a t e r v s Anadromous Mate S e l e c t i o n 22 C o u r t s h i p B e h a v i o u r 22 1) C o u r t s h i p c y c l e s 25 2) E a r l y C o u r t s h i p B e h a v i o u r 26 3) Uncommon C o u r t s h i p B e h a v i o u r s 26 (a) F i r s t R e s p o n s e 27 (b) N e s t M a i n t e n a n c e a f t e r I n i t i a l A p p r o a c h ... 27 ( c ) G l u e i n g a n d C r e e p i n g T h r o u g h 27 (d ) N e s t M a i n t e n a n c e a f t e r F e m a l e f o l l o w s t o N e s t 27 R e s u l t s 28 F e m a l e S i z e S u r v e y 28 F e c u n d i t y A n a l y s i s 31 Mate S e l e c t i o n E x p e r i m e n t s 38 L i t t l e C a m p b e l l p r e l i m i n a r y s t u d y 38 Salmon R i v e r s t u d y 39 M a t e S e l e c t i o n E x p e r i m e n t s 39 F r e s h w a t e r v s Anadromous S e l e c t i o n E x p e r i m e n t s ... 41 Summary 42 C o u r t s h i p B e h a v i o u r E x p e r i m e n t s 43 C o u r t s h i p c y c l e s 43 E a r l y C o u r t s h i p B e h a v i o u r 46 Uncommon C o u r t s h i p B e h a v i o u r s 53 F i r s t R e s p o n s e 53 N e s t M a i n t e n a n c e a f t e r I n i t i a l A p p r o a c h 53 G l u e i n g a n d C r e e p i n g t h r o u g h 57 N e s t M a i n t e n a n c e a f t e r F e m a l e f o l l o w s t o N e s t .... 57 Summary 63 D i s c u s s i o n 65 R e f e r e n c e s c i t e d 76 A p p e n d i x 1 82 L I S T OF TABLES T a b l e 1. L i t t l e C a m p b e l l R i v e r b r e e d i n g popn 28 T a b l e 2. Salmon R i v e r b r e e d i n g p o p u l a t i o n s 32 T a b l e 3. C o r r e l a t i o n c o - e f f i c i e n t s r e f e m a l e s i z e a n d egg number 37 T a b l e 4. Number o f t r i a l s r e s u l t i n g i n n e s t e n t r y 39 T a b l e 5. Number o f a n a l y z e d c o u r t s h i p t r i a l s 43 T a b l e 6. C o u r t s h i p c y c l e s a n d p r o b a b i l i t y o f n e s t e n t r y ... 44 T a b l e 7. C o m p a r i s o n o f c o u r t s h i p w i t h i n S almon R i v e r p o p u l a t i o n s (A) 47 T a b l e 8. C o m p a r i s o n o f c o u r t s h i p w i t h i n Salmon R i v e r p o p u l a t i o n s (B) . . .- 48 T a b l e 9. C o m p a r i s o n o f c o u r t s h i p b e t w e e n Salmon R i v e r p o p u l a t i o n s 49 T a b l e 10. C o m p a r i s o n o f c o u r t i n g w i t h m a r i n e f e m a l e 51 T a b l e 11. C o m p a r i s o n o f c o u r t i n g w i t h own a n d m a r i n e p o p u l a t i o n 52 T a b l e 12. C o m p a r i s o n o f n e s t m a i n t e n a n c e a f t e r i n i t i a l a p p r o a c h t o own f e m a l e s 54 T a b l e 13. C o m p a r i s o n a f t e r i n i t i a l a p p r o a c h t o own a n d m a r i n e f e m a l e 55 T a b l e 14. C o m p a r i s o n b e t w e e n p o p u l a t i o n s a f t e r i n i t i a l a p p r o a c h t o m a r i n e f e m a l e 56 T a b l e 15. C o m p a r i s o n b e t w e e n p o p u l a t i o n s r e g l u e i n g a n d c r e e p i n g 58 T a b l e 16. C o m p a r i s o n o f g l u e i n g a n d c r e e p i n g b e t w e e n f e m a l e t y p e s 59 T a b l e 17. C o m p a r i s o n o f n e s t m a i n t e n a n c e a f t e r f o l l o w by own f e m a l e 60 T a b l e 18. C o m p a r i s o n o f n e s t m a i n t e n a n c e a f t e r f o l l o w by m a r i n e f e m a l e 61 T a b l e 19. C o m p a r i s o n o f n e s t m a i n t e n a n c e a f t e r f o l l o w by own a n d m a r i n e f e m a l e 62 v i i i L I S T OF FIGURES F i g u r e 1. L i t t l e C a m p b e l l R i v e r s h o w i n g c o l l e c t i o n s i t e . .. 10 F i g u r e 2. Salmon R i v e r s h o w i n g c o l l e c t i o n s i t e s 1-4 13 F i g u r e 3. Salmon R i v e r b r e e d i n g p o p u l a t i o n s , 1984 29 F i g u r e 4. Salmon R i v e r b r e e d i n g p o p u l a t i o n s 1983 33 F i g u r e 5. Salmon R i v e r b r e e d i n g p o p u l a t i o n s 1982 35 i x ACKNOWLEDGEMENTS T h i s s t u d y r e c e i v e d f i n a n c i a l s u p p o r t f r o m t h e N a t u r a l S c i e n c e s a n d E n g i n e e r i n g R e s e a r c h C o u n c i l a n d t h e I n s t i t u t e o f A n i m a l R e s o u r c e E c o l o g y , U n i v e r s i t y o f B r i t i s h C o l u m b i a . I p a r t i c u l a r l y want t o t h a n k my s u p e r v i s o r , J . D . M c P h a i l , f o r d i r e c t i n g my a t t e n t i o n t o an i n t r i g u i n g p r o b l e m a n d f o r h i s u n f a i l i n g g u i d a n c e a n d s u p p o r t t h r o u g h o u t t h i s s t u d y . D r . Nancy R e i d p r o v i d e d v a l u a b l e a s s i s t a n c e i n s e l e c t i n g t h e s t a t i s t i c a l t e s t s a p p r o p r i a t e t o t h e a n a l y s i s o f my d a t a . To my f e l l o w s t u d e n t s , my t h a n k s f o r t h e i r a c c e p t a n c e a n d h e l p a n d my g r a t i t u d e , i n p a r t i c u l a r , t o P a t r i c k L a v i n f o r p a t i e n t l y a n s w e r i n g a l l my q u e s t i o n s a b o u t t h e m y s t e r i e s o f p r e p a r i n g a t h e s i s on a c o m p u t e r a n d t o E r i c T a y l o r f o r r e a d i n g a n d o f f e r i n g h e l p f u l s u g g e s t i o n s on t h e o r i g i n a l d r a f t . L a s t , b u t n o t l e a s t I want t o e x p r e s s my a p p r e c i a t i o n t o my f a m i l y a n d f r i e n d s f o r t h e i r s u p p o r t a n d e n c o u r a g e m e n t . R o s s B o r l a n d p r e p a r e d t h e maps a n d my h u s b a n d a n d b e s t buddy A l a s t a i r h e l p e d me i n ways t o o numerous t o m e n t i o n . 1 INTRODUCTION A r e t h e r e b e n e f i t s t o be d e r i v e d f r o m b e i n g d i s c r i m i n a t i n g i n t h e c h o i c e o f a mate? I n t u i t i v e l y , i t seems p l a u s i b l e t h a t mate c h o i c e s h o u l d be a common f e a t u r e i n t h e s e x u a l b e h a v i o u r o f a n i m a l s . As B e r v e n ( 1 9 8 1 ) p o i n t e d o u t , h o w e v e r , u n t i l r e c e n t l y o n l y t h r e e p a t t e r n s o f m a t i n g a s s o c i a t i o n s h a v e commonly been c o n s i d e r e d : m a l e - m a l e c o m p e t i t i o n f o r c o n t r o l o f f e m a l e s , m a l e c o n t r o l o f r e s o u r c e s e s s e n t i a l t o f e m a l e s a nd mate c h o i c e by f e m a l e s . The f o u r t h p a t t e r n o f m a t i n g a s s o c i a t i o n , m a l e mate c h o i c e , i s l e s s w e l l s t u d i e d e x c e p t i n monogamous m a t i n g s y s t e m s where m a l e s c o n t r i b u t e a s u b s t a n t i a l p a r e n t a l e f f o r t . S i n c e male s t i c k l e b a c k s c a n r e a r t h e c l u t c h e s o f s e v e r a l f e m a l e s w i t h l i t t l e more e f f o r t t h a n t h a t i n v o l v e d i n c a r i n g f o r o n e , D a l y a n d W i l s o n ( l 9 8 3 ) c o n s i d e r e d t h a t t h r e e s p i n e s t i c k l e b a c k s d i d n o t f a l l w i t h i n t h i s , f o u r t h c a t e g o r y From a r e v i e w o f t h e e v i d e n c e f o r f e m a l e mate c h o i c e i n a n i m a l s i t seems t h a t , i n many g r o u p s , t h e r e may be b o t h i m m e d i a t e a n d l o n g - t e r m b e n e f i t s t o f e m a l e s t h a t e x e r c i s e mate c h o i c e . F o r i n s t a n c e , i n some b i r d s , f e m a l e s may c h o o s e on t h e b a s i s o f t h e m a l e s ' d e m o n s t r a t e d s k i l l a s a p r o v i d e r s i n c e c o u r t s h i p f e e d i n g makes an i m p o r t a n t c o n t r i b u t i o n t o f e m a l e r e p r o d u c t i v e s u c c e s s by i n c r e a s i n g egg s i z e a n d s u b s e q u e n t f l e d g i n g s u c c e s s ( N i s b e t , 1 9 7 3 ) . S i m i l a r l y , i n i n s e c t s , t h e c h o i c e o f a m a l e w h i c h p r o v i d e s a l a r g e n u p t i a l g i f t may i n c r e a s e a f e m a l e ' s f e c u n d i t y a n d a l l o w h e r t o a v o i d e x p o s u r e t o p r e d a t o r s ( T h o r n h i l l , 1 9 8 0 ) . W i t h i n a s p e c i e s , l a r g e r m a l e s may be p r e f e r r e d by f e m a l e s 2 b e c a u s e t h e y a r e more e f f e c t i v e d e f e n d e r s o f s c a r c e r e s o u r c e s t h a n s m a l l e r m a l e s . E x a m p l e s a r e t h e d e f e n c e o f s u i t a b l e b u r r o w s by f i d d l e r c r a b s ( C h r i s t y , 1 9 8 3 ) , l o w - p r e d a t i o n o v i p o s i t i o n s i t e s by b u l l f r o g s ( H o w a r d , 1978) a n d h i g h - q u a l i t y t e r r i t o r i e s by b l a c k b i r d s ( S e a r c y , 1 9 7 9 ) . I n f i s h , f e m a l e s c u l p i n s a p p a r e n t l y c h o o s e l a r g e r m a l e s b e c a u s e t h e y a r e l e s s l i k e l y t o abandon n e s t s i t e s t h a n s m a l l e r m a l e s and t h u s i n c r e a s e t h e p r o b a b i l i t y t h a t t h e e g g s w i l l h a t c h (Downhower & B r o w n , 1 9 8 0 ) . I n a monogamous c i c h l i d f i s h m a l e s i z e a f f e c t s b r e e d i n g s u c c e s s i n two ways: l a r g e r m a l e s h o l d n e s t s i t e s l e s s s u s c e p t i b l e t o d e s t r u c t i v e wave a c t i o n and t h e y o u n g o f l a r g e r m a l e s grow f a s t e r t h a n t h e y o u n g o f s m a l l e r m a l e s due t o t h e p r o t e c t i o n p r o v i d e d by t h e l a r g e m a l e d u r i n g f e e d i n g ( P e r r o n e , 1 9 7 8 ) . T h u s , f e m a l e s c h o o s e m a l e s t h a t c a n make t h e most s u b s t a n t i a l c o n t r i b u t i o n t o t h e i r r e p r o d u c t i v e s u c c e s s . I n c o n t r a s t t o f e m a l e s , m a l e s a p p e a r t o l o s e r e l a t i v e l y l i t t l e by i n d i s c r i m i n a t e m a t i n g . W i t h t h e e x c e p t i o n o f monogamous s p e c i e s , t h e b e n e f i t s t o m a l e s o f m a t i n g o f t e n a n d i n d i s c r i m i n a t e l y u s u a l l y o u t w e i g h any l o s s e s ( i . e . s p e r m w a s t a g e ) a n d c o n s e q u e n t l y i t i s o f t e n assumed t h a t m a l e s show l i t t l e mate p r e f e r e n c e ( B a t e m a n , 1 9 4 8 ) . The m a l e s o f some s p e c i e s , h o w e v e r , show a s t r o n g p r e f e r e n c e f o r l a r g e r , a n d t h e r e f o r e more f e c u n d , f e m a l e s . F o r e x a m p l e , m a l e i s o p o d s t e n d t o m o n o p o l i z e t h e l a r g e s t f e m a l e s i n a p o p u l a t i o n . S i n c e t h e l a r g e r f e m a l e s a r e c l o s e r t o o v i p o s i t i o n t h a n s m a l l f e m a l e s , t h e s e m a l e s a p p a r e n t l y s a v e t i m e w h i c h may t h e n be u t i l i z e d i n s e a r c h i n g f o r o t h e r f e m a l e s ( M a n n i n g , 1 9 7 3 ) . I n f r o g s , 3 f e c u n d i t y i s p o s i t i v e l y c o r r e l a t e d w i t h body s i z e , c o n s e q u e n t l y m a l e s t h a t mate p r e f e r e n t i a l l y w i t h l a r g e f e m a l e s a l m o s t t r i p l e t h e number o f eggs f e r t i l i z e d i n a s i n g l e m a t i n g ( B e r v e n , 1981) and t h u s i n c r e a s e t h e number o f e g g s f e r t i l i z e d p e r u n i t o f r e p r o d u c t i v e e f f o r t . S i m i l a r a r g u m e n t s c a n be made f o r p u p f i s h ( L o i s e l l e , 1982) and Mormon c r i c k e t s (Gwynne, 1 9 8 1 ) . S u c h a s s o r t a t i v e m a t i n g i s commonly a s c r i b e d t o p r e f e r e n c e , b u t t h e f a c t o r s t h a t d e t e r m i n e mate c h o i c e r a r e l y a r e known. When c h o o s i n g a mate t h e a n i m a l may u s e e i t h e r t h e p r e s e n c e o f t h e b e n e f i t i t s e l f o r some c l u e i n t h e b e h a v i o u r o r a p p e a r a n c e of t h e p r o s p e c t i v e mate t h a t p r e s a g e s t h e p o t e n t i a l b e n e f i t . D i s c r i m i n a t i o n may be a c q u i r e d i n some s p e c i e s by i m p r i n t i n g , o r e a r l y e x p e r i e n c e may be i m p o r t a n t ( C o o k e a n d M c N a l l y , 1 9 7 5 ) . T h e s e a l t e r n a t i v e s , h o w e v e r , a r e n o t a v a i l a b l e t o a s h o r t - l i v e d s p e c i e s t h a t u s u a l l y e x p e r i e n c e s b u t a s i n g l e b r e e d i n g s e a s o n . I n t h i s c a s e , i f v a r i a b i l i t y e x i s t s i n t h e q u a l i t y o f m a t e s , d i s c r i m i n a t i n g a n i m a l s s h o u l d be f a v o u r e d by n a t u r a l s e l e c t i o n o v e r i n d i s c r i m i n a t e o n e s . I n many f i s h , f e m a l e s c o n t i n u e t o grow a f t e r s e x u a l m a t u r i t y a nd t h u s t h e number o f p r o g e n y a f e m a l e c a n p r o d u c e i n c r e a s e s a s body s i z e i n c r e a s e s . C o n s e q u e n t l y , i n f i s h , we m i g h t e x p e c t m a l e c h o i c e o f m a t e s t o be s t r o n g l y i n f l u e n c e d by t h e s i z e , a n d p e r h a p s a g e , o f t h e f e m a l e . R e p r o d u c t i v e t h e o r y ( T r i v e r s , 1972) p r e d i c t s t h a t i f one sex makes a s u b s t a n t i a l l y h i g h e r i n v e s t m e n t i n p a r e n t a l c a r e t h a n t h e o t h e r s e x , t h e n mate c h o i c e s h o u l d be more a p p a r e n t i n t h e h i g h e r - i n v e s t i n g s e x . The t h r e e s p i n e s t i c k l e b a c k , 4 G a s t e r o s t e u s a c u l e a t u s , h a s s e v e r a l a t t r i b u t e s t h a t s u g g e s t t h a t m a l e s o f t h i s s p e c i e s may e x e r c i s e a p r e f e r e n c e i n t h e i r s e l e c t i o n o f m a t e s . R e p r o d u c t i v e m a l e s c o m p e t e f o r s u i t a b l e n e s t s i t e s a n d many m a l e s a r e a p p a r e n t l y e x c l u d e d f r o m m a t i n g b e c a u s e s u i t a b l e t e r r i t o r i e s a r e i n s h o r t s u p p l y . Once a m a l e e s t a b l i s h e s a t e r r i t o r y he b u i l d s a n e s t a n d c o u r t s m a t u r e f e m a l e s w h i c h t e n d t o come s y n c h r o n o u s l y t o t h e s p a w n i n g a r e a ( K y n a r d , 1 9 7 9 ) . The m a l e u s u a l l y m a t e s s e v e r a l t i m e s i n a s i n g l e r e p r o d u c t i v e c y c l e a n d t h u s n e s t s n o r m a l l y c o n t a i n e g g s f r o m s e v e r a l f e m a l e s . The m a l e t h e n c e a s e s c o u r t i n g a n d s w i t c h e s i n t o t h e p a r e n t a l p h a s e . D u r i n g t h i s p h a s e he g u a r d s a n d t e n d s t h e e g g s a n d l a t e r t h e y o u n g f r y . T h i s p a r e n t a l p h a s e l a s t s b e t w e e n t e n and f o u r t e e n d a y s ; d u r i n g t h i s t i m e t h e m a l e i s n o t a v a i l a b l e f o r r e p r o d u c t i v e a c t i v i t i e s . I n c o n t r a s t , f e m a l e s t i c k l e b a c k s e x p e r i e n c e a much s h o r t e r r e p r o d u c t i v e t u r n - a r o u n d t i m e t h a n m a l e s a n d u s u a l l y p r o d u c e a new b a t c h o f m a t u r e e g g s w i t h i n a few d a y s ( W o o t t o n , 1 9 7 3 ) . T h i s a s y m m e t r y i n t h e r e p r o d u c t i v e t u r n - a r o u n d t i m e o f t h e s e x e s means t h a t a s t h e r e p r o d u c t i v e s e a s o n p r o c e e d s m a l e s become a l i m i t i n g r e s o u r c e f o r f e m a l e s . C o n s e q u e n t l y f e m a l e s m i g h t be e x p e c t e d t o c o m p e t e f o r m a l e s ( K y n a r d , 1979) a n d m a l e s may h a v e a c h o i c e o f s e v e r a l f e m a l e s . U n d e r t h e s e c i r c u m s t a n c e s m a l e s m i g h t be e x p e c t e d t o c h o o s e t h e l a r g e r , more f e c u n d , f e m a l e s . T h i s s h o u l d be e s p e c i a l l y t r u e i n a r e a s where c o u r t s h i p -a s s o c i a t e d r i s k s f a v o u r r a p i d c l u t c h b u i l d - u p . I n s o u t h w e s t e r n B r i t i s h C o l u m b i a , G . a c u l e a t u s o c c u r s f r o m t h e h e a d w a t e r s t o t h e mouths o f low g r a d i e n t r i v e r s . I n t h e s e 5 r i v e r s t h e s t i c k l e b a c k s o f t e n show a s t r i k i n g d i s c r e p a n c y i n f e m a l e body s i z e b e t w e e n h e a d w a t e r s a n d l o w e r r e a c h e s - t h e h e a d w a t e r f e m a l e s a r e u s u a l l y l a r g e r ( J . D . M c P h a i l , p e r s o n a l c o m m u n i c a t i o n ) . S i g n i f i c a n t l y , m a l e s do n o t show t h i s p a t t e r n ; m a l e s a r e t h e same s i z e i n b o t h t h e u p p e r a n d l o w e r r e a c h e s o f t h e s e s t r e a m s . T h i s s u g g e s t s t h a t f o o d a v a i l a b i l i t y i s n o t a c a u s a t i v e f a c t o r , u n l e s s m a l e s and f e m a l e s e x p l o i t d i f f e r e n t f o o d r e s o u r c e s , o r h a v e s t r i k i n g l y d i f f e r e n t e n e r g y r e q u i r e m e n t s and t h i s seems u n l i k e l y . A p o s s i b l e e x p l a n a t i o n f o r t h e d i s c r e p a n c y i n s i z e b e t w e e n h e a d w a t e r and l o w e r r e a c h f e m a l e s i s t h a t f e m a l e s i z e i n f l u e n c e s m a l e mate p r e f e r e n c e . I f t h i s i s t r u e , t h e n some f a c t o r , o r f a c t o r s , must f a v o u r m a l e s t h a t c h o o s e l a r g e f e m a l e s i n h e a d w a t e r a r e a s b u t n o t i n l o w e r a r e a s . T h u s , a p r i m a r y a i m o f t h i s s t u d y was t o d e t e r m i n e i f f e m a l e s i z e i n f l u e n c e s m a l e mate c h o i c e . To p l a c e t h i s s t u d y i n an e c o l o g i c a l c o n t e x t m a l e s were c o m p a r e d f r o m two l o c a l i t i e s : a l o c a t i o n on t h e u p p e r S a l m o n R i v e r w here many f e m a l e s a r e l a r g e r t h a n m a l e s a n d a s i t e on t h e l o w e r S almon R i v e r where most o f t h e f e m a l e s a r e s m a l l e r t h a n m a l e s . T h u s , t h e s i z e d i s t r i b u t i o n o f m a t u r e f e m a l e s a t b o t h s i t e s i s s k e w e d : a t t h e l o w e r s i t e i n t h e d i r e c t i o n o f s m a l l f e m a l e s a n d i n t h e u p p e r s i t e i n t h e d i r e c t i o n o f l a r g e f e m a l e s . T h i s means t h a t , a t b o t h s i t e s , m a l e s p o t e n t i a l l y h a v e a c h o i c e o f e i t h e r l a r g e o r s m a l l f e m a l e s , b u t t h e r e l a t i v e f r e q u e n c y o f l a r g e a n d s m a l l f e m a l e s d i f f e r s s t r i k i n g l y b e t w e e n t h e s i t e s . B e c a u s e m a l e s s h o u l d o n l y show a p r e f e r e n c e f o r a p a r t i c u l a r s i z e o f f e m a l e i f t h e r e i s some r e p r o d u c t i v e g a i n 6 associated with th i s size, I also investigated the relationship between female length and fecundity. In addition, since size in f i s h i s usually related to age, I attempted to age breeding females by means of o t o l i t h s . To test my aging and fecundity techniques I used a preliminary study s i t e on the nearby L i t t l e Campbell River. I also used t h i s upper Campbell population for a p i l o t study to determine i f I could experimentally examine the influence of female size on male mate choice. The results from t h i s L i t t l e Campbell p i l o t study indicate that in some populations of freshwater sticklebacks the males do show a preference for mating with the largest available females. The question then arises as to whether th i s i s a general phenomenon. If i t i s , then the presence of predominately small females in the,lower reaches of streams i s a puzzle that needs an answer. A possible, and e v o l u t i o n a r i l y interesting, explanation i s that the lower Salmon River i s invaded annually by a breeding population of anadromous marine sticklebacks(to break up the monotonous rep e t i t i o n of the description 'anadromous marine' the terms anadromous and marine w i l l be used interchangeably to refer to t h i s form). The anadromous form of Gasterosteus i s considerably larger than the freshwater form and anadromous and freshwater females in the lower river barely overlap in their size d i s t r i b u t i o n s (Fig. 3). The taxonomic status of the anadromous and freshwater forms of G. aculeatus i s not clear; however,the two forms d i f f e r in a number of inherited morphological characters (Hagen, 1967). In body shape the anadromous form appears to be adapted to a pelagic l i f e whereas 7 the freshwater form i s deeper-bodied and adapted to stream l i f e . These d i f f e r e n c e s i n body shape are i n h e r i t e d and a s s o c i a t e d with major d i f f e r e n c e s i n s u s t a i n e d and bu r s t swimming performance ( T a y l o r and McPhail,1986). The anadromous form a l s o has 30-35 l a t e r a l p l a t e s , whereas 3-7 p l a t e s are d i a g n o s t i c f o r the freshwater form. There are a l s o d i f f e r e n c e s between the forms i n g i l l - r a k e r number and d o r s a l and anal ray numbers; the anadromous form i s f u r t h e r d i s t i n g u i s h e d by being a s i l v e r y c o l o u r and having a caudal k e e l . Hagen (1967) s t u d i e d the anadromous and freshwater forms i n the L i t t l e Campbell r i v e r and concluded that they conformed to Mayr's (1963) d e f i n i t i o n of b i o l o g i c a l s p e c i e s . He observed that they were p a r a p a t r i c a l l y d i s t r i b u t e d w i t h i n the stream but connected by a narrow h y b r i d zone.' He concluded that no gene flow o c c u r r e d through t h i s zone. In the lower Salmon River there i s no c l e a r evidence of a h y b r i d zone but the two forms c o - e x i s t throughout the lower r i v e r d u r i n g the breeding season; t e r r r i t o r i a l males and g r a v i d females of both forms are r e g u l a r l y c o l l e c t e d i n the same t r a p samples. In c o n t r a s t to the lower r i v e r , only the freshwater form of G. a c u l e a t u s occurs i n the upper Salmon r i v e r . The primary purposes of the t h e s i s are to document the d i f f e r e n c e i n female s i z e between the upper and lower Salmon R i v e r and to i n v e s t i g a t e whether d i f f e r e n c e s i n female s i z e i n f l u e n c e male mate c h o i c e . I p o s t u l a t e t h a t , s i n c e the anadromous form i s absent, i n the upper r i v e r males w i l l show a p r e f e r e n c e f o r the most 8 f e c u n d ( l a r g e s t ) f e m a l e s . A c o r o l l a r y h y p o t h e s i s i s t h a t i n the lower reaches of the r i v e r , where the anadromous form i s p r e s e n t , f r e s h w a t e r males w i l l p r e f e r s m a l l e r f e m a l e s . These hypotheses a r e based on two w e l l - s u p p o r t e d a s s u m p t i o n s : 1) That the anadromous and f r e s h w a t e r forms of G a s t e r o s t e u s r e p r e s e n t two d i s c r e t e gene p o o l s t h a t a r e adapted t o two s t r i k i n g l y d i f f e r e n t ways of l i f e (Heuts 1947; Munzing 1963; Hagen 1967; B e l l 1984), and 2) t h a t h y b r i d s between such d i f f e r e n t forms w i l l be l a r g e l y i n t e r m e d i a t e i n morphology, p h y s i o l o g y and b e h a v i o u r and c o n s e q u e n t l y i l l - a d a p t e d t o e i t h e r p a r e n t a l way of l i f e (Hagen 1967; Bentzen and M c P h a i l 1984; Y o s h i h a r u and Tamura 1984). S i n c e anadromous s t i c k l e b a c k s a r e , u s u a l l y , l a r g e r than f r e s h w a t e r s t i c k l e b a c k s , I h y p o t h e s i z e t h a t female s i z e i s used by males as a p r i m a r y c l u e about female genotype. I f t h i s i s t r u e then the d i f f e r e n c e s i n female s i z e between the upper and lower r i v e r may not be f o r t u i t o u s but may be due t o male p r e f e r e n c e s c o n f e r r i n g an advantage upon d i f f e r e n t s i z e s of females i n the two p a r t s of the r i v e r . T h i s p r e d i c t s t h a t males from the upper and lower p a r t s of the Salmon R i v e r s h o u l d behave d i f f e r e n t l y t o l a r g e and s m a l l f e m a l e s . Males i n the lower r i v e r must d i s t i n g u i s h between two k i n d s of females and a r e l i a b l e g u i d e t o d i s t i n g u i s h i n g the two k i n d s of females i s s i z e . C o n s e q u e n t l y , I p r e d i c t t h a t , i n c h o i c e s i t u a t i o n s , upper Salmon males w i l l choose the l a r g e s t a v a i l a b l e female, whereas, i n the same s i t u a t i o n , Lower Salmon males w i l l respond d i f f e r e n t l y and choose females s m a l l e r than t h e m s e l v e s . 9 MATERIALS AND METHODS Study s i t e s The t h r e e s p i n e s t i c k l e b a c k , G.aculeatus, i s found i n most low g r a d i e n t streams and r i v e r s i n the lower F r a s e r V a l l e y , B r i t i s h Columbia. In such r i v e r s the s p e c i e s occurs from headwaters to r i v e r mouth. The f o l l o w i n g account d e s c r i b e s the p h y s i c a l c o n d i t i o n s i n two F r a s e r V a l l e y r i v e r s : the L i t t l e Campbell River which was the s i t e of the i n i t i a l p i l o t study, and the Salmon River from which two p o p u l a t i o n s were s e l e c t e d f o r the main study. L i t t l e Campbell R i v e r The L i t t l e Campbell River i s l o c a t e d i n the southwest p o r t i o n of B r i t i s h Columbia. I t i s approximately 26 k i l o m e t e r s long and flows west i n t o Semiahmoo Bay near White Rock ( F i g . 1 ) . Farms and pasture l a n d border the r i v e r f o r much of i t s l e n g t h and low deciduous brush and second growth c o n i f e r s cover the banks. The upper reaches of the r i v e r are slow-running due to beaver dams and i t tends to f i l l w i th grasses and water weeds i n l a t e summer. The s u b s t r a t e i s s o f t mud and the water i s t e a -c o l o u r e d . 10 F i g u r e 1. L i t t l e Campbell R i v e r showing c o l l e c t i o n s i t e , ( adapted from Hagen, 1967) 1 2 S a l m o n R i v e r T h e p h y s i c a l a s p e c t s o f t h e S a l m o n R i v e r a r e s i m i l a r t o t h o s e o f t h e L i t t l e C a m p b e l l R i v e r . I t a l s o l i e s t o t h e s o u t h o f t h e F r a s e r R i v e r a n d f l o w s f o r a p p r o x i m a t e l y 40 k i l o m e t e r s n o r t h w e s t b e f o r e e m p t y i n g i n t o B e d f o r d C h a n n e l o f t h e F r a s e r R i v e r n e a r F o r t L a n g l e y ( F i g . 2 ) . T h e u p p e r S a l m o n R i v e r h a s a s l i g h t g r a d i e n t b u t i n t h e l o w e r r e a c h e s i t b e c o m e s a t y p i c a l l o w - g r a d i e n t m e a n d e r i n g r i v e r . F o r t h e p u r p o s e s o f t h i s s t u d y t h e U p p e r r i v e r w a s c o n s i d e r e d t o e n d a t R a w l i s o n C r e s c e n t b e t w e e n M c M i l l e n P a r k a n d t h e f l a t s . L i k e t h e L i t t l e C a m p b e l l R i v e r , i n s l o w - m o v i n g s t r e t c h e s w i t h n u t r i e n t - r i c h s o f t m u d s u b s t r a t e , t h i s r i v e r t e n d s t o b e c o m e w e e d - c h o k e d . T h e s e a r e a s a r e f a v o u r e d b y b o t h f r e s h w a t e r a n d a n a d r o m o u s s t i c k l e b a c k s d u r i n g t h e s p a w n i n g s e a s o n . C o l l e c t i o n a n d M a i n t e n a n c e o f F i s h T h e s t i c k l e b a c k s u s e d i n t h i s s t u d y w e r e c o l l e c t e d f r o m A p r i l t h r o u g h t o J u l y 1 9 8 4 b y m i n n o w t r a p s s e t a t s i t e s 1 -4 a l o n g a 2 0 k m s t r e t c h o f t h e S a l m o n R i v e r ( F i g 2 ) . S i t e 4 i s i n t h e l o w e r r i v e r i n a n a r e a o c c u p i e d b y b o t h f r e s h w a t e r a n d a n a d r o m o u s s t i c k l e b a c k s . S i t e s 1-3 a r e i n t h e u p p e r r i v e r : t h i s a r e a i s a b o v e t h e m a x i m u m p e n e t r a t i o n o f t h e a n a d r o m o u s f o r m . F i s h f r o m t h e u p p e r ( s i t e s 1 - 3 ) a n d l o w e r ( s i t e 4 ) r i v e r w e r e p l a c e d i n s e p a r a t e c o n t a i n e r s a n d t r a n s p o r t e d d i r e c t l y t o t h e l a b o r a t o r y . H e r e t h e y w e r e k e p t i n a c o n t r o l l e d e n v i r o n m e n t a l 13 F i g u r e 2 . S a l m o n R i v e r s h o w i n g c o l l e c t i o n s i t e s 1 -4 . 14 <=>A!_M C f s l 15 chamber u n d e r a n a t u r a l p h o t o p e r i o d a n d t e m p e r a t u r e r e g i m e . H i g h l y c o l o u r e d m a l e s o f t h e f r e s h w a t e r f o r m f r o m t h e two a r e a s ( h e r e a f t e r c a l l e d u p p e r a n d l o w e r S a l m o n f i s h ) were i n s t a l l e d i n 170 L g l a s s a q u a r i a ( i n t e r i o r d i m e n s i o n s 122cm l o n g ; 30cm w i d e ; 52cm d e e p ) . E a c h t a n k was d i v i d e d i n two by a p a r t l y - t r a n s p a r e n t p a r t i t i o n . T h i s gave e a c h m a l e a t e r r i t o r y r o u g h l y e q u i v a l e n t t o t h a t f o u n d i n t h e w i l d , i . e . 55cm b e t w e e n n e s t c e n t r e s ( W o o t t o n , 1 9 7 2 ) . P a r t o f t h e p a r t i t i o n i n e a c h t a n k was t r a n s p a r e n t t o a l l o w i n t e r a c t i o n b e t w e e n t h e m a l e s w i t h o u t t h e r i s k o f i n j u r y i n a g g r e s s i v e e n c o u n t e r s . The f i s h w ere f e d a d i e t o f f i n e l y s h r e d d e d l i v e r a n d l i v e b r i n e s h r i m p n a u p l i i ( A r t e m i a ) . A l l t r i a l s were r u n a t l e a s t two h o u r s a f t e r f e e d i n g . E a c h m a l e was p r o v i d e d w i t h a r o u n d n e s t i n g pan ( d i a m e t e r 20cm) c o n t a i n i n g mud f r o m t h e s i t e where he was c o l l e c t e d . N e s t i n g m a t e r i a l was s c a t t e r e d o v e r t h e 7cm t h i c k l a y e r o f washed r i v e r g r a v e l t h a t c o v e r e d t h e a q u a r i u m b o t t o m . I n t h i s way u n i f o r m t e r r i t o r y s i z e a n d n e s t s i t e q u a l i t y were m a i n t a i n e d . M a l e s were d i s c o u r a g e d f r o m b u i l d i n g e l s e w h e r e i n t h e t a n k a n d t h e n e s t i n g pan was l o c a t e d i n a s i m i l a r p l a c e i n e a c h t e r r i t o r y . T r i a l s began when t h e m a l e s c o m p l e t e d n e s t c o n s t r u c t i o n , i . e . a f t e r t h e y p e r f o r m e d " c r e e p i n g - t h r o u g h " b e h a v i o u r (Van I e r s e l , 1 9 5 3 ) . B l a c k p l a s t i c c u r t a i n s were a r r a n g e d o v e r e a c h t a n k so t h a t l i g h t was d i r e c t e d downward. T h i s a l l o w e d t h e o b s e r v e r t o r e m a i n i n shadow. F l o a t i n g d u c k w e e d (Lemna) a n d p l a n t s ( E l o d e a ) w e r e a d d e d t o d i f f u s e t h e l i g h t . O n l y t h e f r o n t o f t h e t a n k was 16 k e p t a l g a e - f r e e f o r o b s e r v a t i o n a l p u r p o s e s . The m a l e s r e a d i l y h a b i t u a t e d t o t h e p r e s e n c e o f t h e o b s e r v e r a n d were o n l y d i s t u r b e d by sudden movements. B e c a u s e i t i s d i f f i c u l t t o i n d u c e w i l d - c a u g h t f e m a l e s t o become g r a v i d u n d e r l a b o r a t o r y c o n d i t i o n s f r e s h l y c a u g h t f e m a l e s f r o m e a c h a r e a were u s e d i n a l l t r i a l s . The f e m a l e s were a c c l i m a t i z e d t o l a b o r a t o r y l i g h t a n d t e m p e r a t u r e c o n d i t i o n s i n s e p a r a t e communal t a n k s u n t i l t h e t e m p e r a t u r e d i f f e r e n c e b e t w e e n s t o r a g e a n d e x p e r i m e n t a l t a n k s was l e s s t h a n 2 °C. S i z e m e a s u r e m e n t s were made o n l y a f t e r t h e c o m p l e t i o n o f a t r i a l . T h i s k e p t d i s t u r b a n c e t o a minimum. M a l e B e h a v i o u r A b r i e f d e s c r i p t i o n o f t h e r e c o r d e d b e h a v i o u r s i s g i v e n b e l o w : 1. Z i g - z a g - M a l e a d v a n c e s t o f e m a l e i n an a l t e r n a t i n g s e r i e s o f a p p r o a c h e s a n d r e t r e a t s . 2. B u t t - Any l u n g e d i r e c t e d a t t h e d i s t e n d e d a b d o m i n a l r e g i o n o f t h e f e m a l e , mouth open o r s h u t . 3. A g g r e s s i o n - B i t i n g , ramming, f i n , s p i n e o r t a i l p u l l i n g a n d c h a s i n g . A l s o any a t t e m p t e d a g g r e s s i o n t o t h e m ale i n t h e a d j o i n i n g t e r r i t o r y . 4. N e s t M a i n t e n a n c e - m a l e g a t h e r s n e s t m a t e r i a l a n d a d d s i t t o t h e n e s t t h e n p o k e s , b o r e s and f a n s . 5. G l u e i n g - A f t e r a d d i t i o n o f n e s t m a t e r i a l t h e m a l e swims o v e r t h e n e s t f r o m e n t r a n c e t o e x i t r e l e a s i n g an a d h e s i v e g l u e f r o m t h e g e n i t a l p o r e . 1 7 6. C r e e p i n g T h r o u g h - M a l e p u s h e s t h r o u g h t h e n e s t f r o m e n t r a n c e t o e x i t , p r o d u c i n g a t u n n e l . 7. L e a d / F o l l o w - M a l e swims t o n e s t a n d f e m a l e f o l l o w s . 8. Show - When male and f e m a l e r e a c h t h e n e s t , t h e m a l e t u r n s on h i s s i d e a n d p o k e s h i s s n o u t w i t h a j e r k y m o t i o n i n t o t h e n e s t e n t r a n c e . 9. Swim - M a l e swims o r r e m a i n s m o t i o n l e s s i n t h e w a t e r . The f o c u s o f t h e m a l e ' s a t t e n t i o n ( i . e . l a r g e f e m a l e , s m a l l f e m a l e , n e i g h b o u r i n g m a l e ) was a l s o r e c o r d e d f o r e a c h b e h a v i o u r . T h i s g ave a t w o - d i g i t c o d e . O b s e r v a t i o n a nd R e c o r d i n g P r o c e d u r e s M a te s e l e c t i o n a n d c o u r t s h i p b e h a v i o u r e x p e r i m e n t s were c a r r i e d o u t w i t h a s many d i f f e r e n t a n i m a l s a s p o s s i b l e . G e n e r a l l y m a l e s w i t h n e s t s were n o t t e s t e d more t h a n once i n a d a y ; h o w e v e r , i n t h e few c a s e s w here m a l e s were t e s t e d t w i c e i n a day t h e y were a l l o w e d a t h r e e h o u r b r e a k b e t w e e n t e s t s . T e s t s w e r e n o t c o n d u c t e d c o n s e c u t i v e l y on a d j o i n i n g t e r r i t o r i e s b e c a u s e t h e w a t c h i n g m a l e became o v e r l y a g g r e s s i v e a n d t e n d e d t o k i l l o r s e v e r e l y damage f e m a l e s . G r a v i d f e m a l e s were n e v e r t e s t e d t w i c e w i t h t h e same m a l e . To a s s u r e r e a d i n e s s t o c o u r t , o n l y m a l e s t h a t h a d e x h i b i t e d " c r e e p i n g - t h r o u g h " b e h a v i o u r were u s e d i n t e s t s . F e m a l e s were c h e c k e d f o r " d e g r e e o f g r a v i d i t y " a n d o n l y f e m a l e s t h a t e x h i b i t e d a n o t i c e a b l e b u l g i n g o f t h e abdomen were u s e d i n t r i a l s . 18 P a i r s o f f e m a l e s were i n t r o d u c e d i n t o a m a l e ' s t e r r i t o r y t h r o u g h a c l e a r p l e x i g l a s s r e l e a s i n g box f i t t e d w i t h a p u l l s t r i n g - o p e r a t e d t r a p d o o r . I n most e x p e r i m e n t s , f e m a l e s t h a t e n t e r e d t h e n e s t were p r e v e n t e d f r o m s p a w n i n g by p i n c h i n g t h e i r c a u d a l p e d u n c l e w i t h l o n g b l u n t f o r c e p s . T h i s a p p a r e n t l y s i m u l a t e d m ale ' n i p p i n g ' b e h a v i o u r w h i c h c a u s e s t h e f e m a l e t o l e a v e t h e n e s t w i t h o u t d e p o s i t i n g h e r e g g s . I f e g g s were d e p o s i t e d i n t h e n e s t t h e y were removed by t h e o b s e r v e r t o p r e v e n t t h e m a l e f r o m p r o c e e d i n g i n t o t h e p a r e n t a l p h a s e . M a l e s q u i c k l y r e p a i r e d t h e i r n e s t s a f t e r s u c h a d i s t u r b a n c e . S i n c e m a l e s were n o t a l l o w e d t o r e t a i n an egg c l u t c h t h e y u s u a l l y a b a n d o n e d t h e i r n e s t s w i t h i n 2-3 weeks. They were t h e n r e p l a c e d by n e w l y - c a u g h t m a l e s b e c a u s e t h e f o r m e r n e v e r a t t e m p t e d t o b u i l d e l s e w h e r e i n t h e t e r r i t o r y . The t o t a l number o f m a l e s u s e d i n t h e t r i a l s was : Lower S a l m o n = 19, U p p e r S a l m o n =19. B e h a v i o u r a l d a t a were r e c o r d e d on a h a n d - h e l d e l e c t r o n i c d a t a c o l l e c t i o n d e v i c e (MORE = M i c r o p r o c e s s o r R e c o r d i n g E q u i p m e n t ) . E v e n t s were r e c o r d e d by p r e s s i n g d i f f e r e n t k e y s f o r t h e d i f f e r e n t b e h a v i o u r s . The m a l e was t h e f o c a l a n i m a l f o r r e c o r d i n g p u r p o s e s . R e c o r d i n g began when f e m a l e s were r e l e a s e d i n t o t h e t a n k s a n d t e r m i n a t e d when a f e m a l e e n t e r e d t h e n e s t , a p r e - s e t t i m e h a d e l a p s e d , o r t h e t r i a l was s t o p p e d b e c a u s e t h e m a l e was d a m a g i n g t h e f e m a l e . The MORE was i n t e r f a c e d w i t h a PDP11 c o m p u t e r f o r d a t a r e t r i e v a l . D a t a a n a l y s i s was c a r r i e d o u t u s i n g t h e M i n i t a b s t a t i s t i c a l c o m p u t i n g p a c k a g e on a Dec Vax 11/750 c o m p u t e r . 19 D a t a A n a l y s i s The d a t a on commonly o c c u r r i n g c o u r t s h i p a n d t e r r i t o r i a l b e h a v i o u r s were a n a l y s e d u s i n g t h e MINITAB INC. 1983 s t a t i s t i c a l p a c k a g e ( U n i v . P a r k , P A ) . S i n c e t h e a s s u m p t i o n s o f t h e t - t e s t c o u l d n o t be met ( d i s t r i b u t i o n was n o n - n o r m a l ) a non -p a r a m e t r i c t e s t was u s e d i n t h e a n a l y s i s - t h e M a n n - W h i t n e y U t e s t , c o r r e c t e d f o r t i e s . T h i s t e s t i s t h e n o n - p a r a m e t r i c t e s t most s e n s i t i v e t o d i f f e r e n c e s i n c e n t r a l t e n d e n c y , t h e r e f o r e i t was c h o s e n t o t e s t w h e t h e r t h e two i n d e p e n d e n t s a m p l e s came f r o m t h e same s t a t i s t i c a l p o p u l a t i o n . The t e s t u s e d t o d e t e r m i n e w h e t h e r e a c h d i s t r i b u t i o n f i t s a t h e o r e t i c a l c u m u l a t i v e f r e q u e n c y d i s t r i b u t i o n was t h e K o l m o g o r o v - S m i r n o v one s a m p l e 2-t a i l e d g o o d n e s s - o f - f i t t e s t . T i m e s t o e g g - d r o p a f t e r c o u r t s h i p d a t a were a n a l y s e d u s i n g t h e W i l c o x o n m a t c h e d - p a i r s s i g n e d - r a n k s t e s t . D a t a on i n f r e q u e n t c o u r t s h i p b e h a v i o u r s were a n a l y s e d u s i n g t h e C h i - s q u a r e p r o b a b i l i t y t e s t (MINITAB) F e c u n d i t y d e t e r m i n a t i o n s were a n a l y s e d u s i n g r e g r e s s i o n a n a l y s i s (MINITAB) an d c o v a r i a n c e a n a l y s i s (MTS MIDAS, Fox and G u i r e , 1 9 7 6 ) . The d a t a f r o m f i e l d c o l l e c t i o n s made t o c h e c k w h e t h e r t h e p o p u l a t i o n s e x a m i n e d were s i g n i f i c a n t l y d i f f e r e n t w i t h r e s p e c t t o s i z e w e r e t e s t e d u s i n g t h e t - t e s t w h e r e a s t h e t e s t u s e d f o r g o o d n e s s - o f - f i t i n t h e mate s e l e c t i o n e x p e r i m e n t s was t h e b i n o m i a l t e s t ( M I N I T A B ) . I n a l l t e s t s t h e n u l l h y p o t h e s i s i s t h a t t h e r e a r e no d i f f e r e n c e s b e t w e e n t h e p o p u l a t i o n s and t h e l e v e l o f a c c e p t a n c e i s 5 p e r c e n t . 20 E x p e r i m e n t a l P r o t o c o l s L i t t l e C a m p b e l l R i v e r p r e l i m i n a r y s t u d y I n t h e s p r i n g o f 1982 a s a m p l e o f m a t u r e m a l e s a nd f e m a l e s was c o l l e c t e d f r o m a s i n g l e s i t e i n t h e u p p e r r e a c h e s o f t h e r i v e r . T h i s s a m p l e was m e a s u r e d f o r s t a n d a r d l e n g t h a n d t h e r e s u l t s a n a l y s e d t o d e t e r m i n e t h e mean l e n g t h o f b o t h s e x e s ( T a b l e 1 ) . To e s t a b l i s h a c o r r e l a t i o n b e t w e e n f e m a l e s i z e a n d c l u t c h s i z e , g r a v i d f e m a l e s were m e a s u r e d ( S L ) a n d t h e number o f m a t u r e e g g s d e t e r m i n e d . W o o t t o n ( 1 9 7 3 ) e s t a b l i s h e d t h a t s i z e a n d q u a l i t y o f eg g s was n o t s i g n i f i c a n t l y d i f f e r e n t b e t w e e n l a r g e a n d s m a l l f i s h , c o n s e q u e n t l y t h e s e f a c t o r s were n o t m e a s u r e d i n t h e p r e s e n t s t u d y . A g r o u p o f m a l e s t i c k l e b a c k s was m a i n t a i n e d i n t h e l a b o r a t o r y a n d a l l o w e d t o e s t a b l i s h t e r r i t o r i e s . M a te s e l e c t i o n t r i a l s were t h e n c a r r i e d o u t by s i m u l t a n e o u s l y i n t r o d u c i n g two p r e - t e s t e d f e m a l e s i n t o t h e m a l e ' s t e r r i t o r y . I n t h e s e t e s t s one f e m a l e was a l w a y s a t l e a s t 10mm l a r g e r t h a n t h e o t h e r f e m a l e . Thus m a l e s were g i v e n a c h o i c e b e t w e e n two s i z e s o f f e m a l e s f r o m t h e i r own p o p u l a t i o n . No d i s t i n c t i o n was made w i t h r e s p e c t t o f e m a l e s i z e r e l a t i v e t o male s i z e , h o w e v e r , many f e m a l e s were l a r g e r t h a n any o f t h e m a l e s ( T a b l e 1 ) . S u c h l a r g e f e m a l e s may be s e v e r a l y e a r s o l d , o r t h e y may ha v e a c h i e v e d l a r g e s i z e by d e l a y i n g m a t u r i t y u n t i l t h e i r s e c o n d summer. I n l i g h t o f t h i s p o s s i b i l i t y , an a t t e m p t was made t o age t h e b r e e d i n g f e m a l e s f r o m t h e i r o t o l i t h s . O t o l i t h s were e x a m i n e d f r o m s a m p l e s o f f e m a l e s c o l l e c t e d i n t h e s p r i n g o f 1982 and 1983 21 a n d f r o m f i s h r a i s e d i n t h e l a b o r a t o r y ( D a t a a n d methods a r e l i s t e d i n A p p e n d i x 1 ) . S a lmon R i v e r S t u d y M a te S e l e c t i o n E x p e r i m e n t s I n t h e mate s e l e c t i o n e x p e r i m e n t s a p a i r o f f e m a l e s was s i m u l t a n e o u s l y i n t r o d u c e d i n t o a m a l e ' s t e r r i t o r y i n a c l e a r p l e x i g l a s s r e l e a s i n g box f i t t e d w i t h a t r a p d o o r o p e r a t e d by a p u l l s t r i n g . The f e m a l e s were r e l e a s e d when t h e y were swimming n o r m a l l y a n d t h e m a l e s h a d n o t i c e d t h e i r p r e s e n c e . T h i s c o n f i n e m e n t was b r i e f , n e v e r more t h a n t h r e e m i n u t e s . N i n e t e e n m a l e s f r o m e a c h p o p u l a t i o n were u s e d a l o n g w i t h e i g h t y - t w o l o w e r a n d e i g h t y - t h r e e u p p e r S a l m o n f e m a l e s . A t r i a l was c o n s i d e r e d s u c c e s s f u l when a f e m a l e f o l l o w e d t h e m a l e t o h i s n e s t , e n t e r e d i t a n d t h e m a l e r a p i d l y p r o d d e d t h e f e m a l e ' s d i s t e n d e d abdomen t o i n d u c e s p a w n i n g . I f t h e r e was no e n t r y i n 25 m i n u t e s t h e f e m a l e s were r e m o v e d . The s u c c e s s f u l t r i a l s w ere s c o r e d on a Yes/No b a s i s w i t h r e s p e c t t o w h e t h e r t h e f e m a l e w h i c h e n t e r e d t h e n e s t was l a r g e r o r s m a l l e r t h a n t h e m a l e . F r e s h w a t e r M a t e S e l e c t i o n E x p e r i m e n t s T r i a l s i n w h i c h m a l e s were g i v e n a c h o i c e b e t w e e n two s i z e s o f g r a v i d f e m a l e s were c a r r i e d o u t b o t h w i t h i n a n d b e t w e e n u p p e r a n d l o w e r S a l m o n r i v e r p o p u l a t i o n s . As f a r a s p o s s i b l e I t r i e d 22 t o e n s u r e t h a t one f e m a l e was l a r g e r a nd one f e m a l e s m a l l e r t h a n t h e t r i a l m a l e . F r e s h w a t e r v s Anadromous Mate S e l e c t i o n To a s c e r t a i n i f m a t i n g w o u l d o c c u r b e t w e e n f o r m s , t r i a l s w ere c a r r i e d o u t b e t w e e n m a l e s f r o m b o t h g r o u p s o f f r e s h w a t e r m a l e s a n d s i n g l e m a r i n e f e m a l e s . I n a d d i t i o n a s m a l l number o f t r i a l s w ere c a r r i e d o u t i n w h i c h m a l e s f r o m t h e l o w e r Salmon were p r e s e n t e d s i m u l t a n e o u s l y w i t h b o t h a f r e s h w a t e r a n d a m a r i n e f e m a l e . C o u r t s h i p B e h a v i o u r F o r a s u c c e s s f u l c o u r t s h i p t o o c c u r t h e r e h a s t o be a c o r r e c t i n t e r - c h a n g e o f s i g n a l s b e t w e e n t h e s e x e s . T h e s e s i g n a l s a r e g r a d e d i n some f i s h s p e c i e s b u t i n o t h e r s t h e m a i n a c t i o n p a t t e r n s o f c o u r t s h i p b e h a v i o u r b e h a v e a s d i g i t a l s i g n a l s ( i . e . t h e y a r e e i t h e r on o r o f f , B a r l o w , 1 9 6 9 ) . I n s u c h s p e c i e s i n d i v i d u a l a c t i o n s a r e s u f f i c i e n t l y n o n - g r a d e d a s t o a p p e a r a l i k e a t e a c h p e r f o r m a n c e b u t t h e f i s h r e s p o n d s t o d i f f e r e n c e s i n t h e s i t u a t i o n by c h a n g i n g t h e f r e q u e n c y o f o c c u r r e n c e o f t h e u n i t s ( B a r l o w a n d G r e e n , 1970; B a y l i s , 1 9 7 6 ) . The l a t t e r i s more common i n s p e c i e s w h i c h do n o t f o r m a l a s t i n g p a i r b o n d s u c h a s G. a c u l e a t u s . M c P h a i l and Hay (1983) f o u n d d i f f e r e n c e s i n m ale c o u r t s h i p i n t h e i n i t i a l a p p r o a c h t o t h e f e m a l e w h i c h p r o v i d e d e v i d e n c e t h a t p o s i t i v e a s s o r t a t i v e m a t i n g e x i s t s b e t w e e n p a r a p a t r i c f r e s h w a t e r a n d m a r i n e p o p u l a t i o n s . 23 T h i s s e c t i o n a d d r e s s e s t h e q u e s t i o n o f w h e t h e r f e m a l e s i z e i n f l u e n c e s m a le c o u r t i n g b e h a v i o u r i n two f r e s h w a t e r p o p u l a t i o n s , one o f w h i c h i s s y m p a t r i c d u r i n g t h e b r e e d i n g s e a s o n w i t h a m a r i n e p o p u l a t i o n . E a c h e x p e r i m e n t a l m a l e ( s e l e c t e d a t random) was p r e s e n t e d w i t h a c h o i c e o f two e q u a l l y g r a v i d f e m a l e s o f d i f f e r e n t s i z e s ( S L ) a n d a l l o w e d t o c o u r t . T r i a l s w i t h m a r i n e f i s h were c o n d u c t e d w i t h a s i n g l e f e m a l e . M a l e c o u r t i n g b e h a v i o u r was r e c o r d e d on t h e MORE e v e n t r e c o r d e r w i t h r e s p e c t t o t h e i n t e r a c t i o n s w i t h e a c h f e m a l e a n d t h e a d j o i n i n g m a l e a n d a l s o b e h a v i o u r p e r f o r m e d a l o n e . N i n e t e e n u p p e r a n d l o w e r Salmon m a l e s , s e v e n t y - s i x l o w e r S almon a n d s e v e n t y - s e v e n u p p e r S almon f e m a l e s a n d t h i r t y - e i g h t m a r i n e f e m a l e s were u s e d i n t h e c o u r t s h i p t r i a l s . The f o l l o w i n g c r i t e r i a d e t e r m i n e d w h e t h e r a t r i a l w o u l d be i n c l u d e d i n t h e d a t a a n a l y s i s : 1. The m a l e had t o e x h i b i t c o u r t s h i p b e h a v i o u r t o b o t h f e m a l e s ( i . e . z i g - z a g , b u t t , a g g r e s s i o n ) . 2. M a l e c o u r t s h i p h a d t o be v i g o r o u s ( > 0.5 z i g z a g p e r s e c . ) . 3. A l l f e m a l e s h a d t o r e s p o n d t o t h e m a l e by f o l l o w i n g t o t h e n e s t e n t r a n c e i . e . show w i l l i n g n e s s t o mate. A t r i a l was e n d e d when one o f t h e f o l l o w i n g e v e n t s o c c u r r e d : 1. A f t e r b o t h f e m a l e s h a d been l e d t o t h e n e s t t h e 24 m a l e e n g a g e d i n a d a m a g i n g a g g r e s s i v e a t t a c k w h i c h l a s t e d l O s e c s . o r more on e i t h e r f e m a l e . 2. A p p r o x i m a t e l y 25 m i n u t e s h ad e l a p s e d - a s e q u e n c e was n e v e r i n t e r r u p t e d . C h o i c e o f t h e s e c r i t e r i a was b a s e d on my e x p e r i e n c e t h a t most s u c c e s s f u l t r i a l s were c o m p l e t e d q u i c k l y , a n d t h a t once a m a l e became i n t e n s e l y a g g r e s s i v e f u r t h e r r e s p o n s e f r o m t h e f e m a l e was u n l i k e l y . I n a l l t r i a l s t h e t i m e u n i t f o r r e c o r d i n g was 0.1 s e e s , a n d n i n e b e h a v i o u r s were r e c o r d e d . The m a l e b e h a v i o u r s r e c o r d e d i n t h e c o u r t s h i p e x p e r i m e n t s w e r e : 1. Z i g - z a g s t o f e m a l e . 2. B u t t s f e m a l e . 3. E n g a g e s i n a g g r e s s i v e b e h a v i o u r . 4. P e r f o r m s n e s t m a i n t e n a n c e b a h a v i o u r . 5. G l u e s n e s t m a t e r i a l . 6. C r e e p s t h r o u g h n e s t . 7. L e a d s f e m a l e t o n e s t a n d f e m a l e f o l l o w s . 8. Shows n e s t e n t r a n c e t o f e m a l e . 9. Swims o r h o v e r s . The f o c u s o f t h e m a l e ' s a t t e n t i o n f o r e a c h b e h a v i o u r was r e c o r d e d . C o m b i n e d , t h e d a t a were r e c o r d e d a s a two d i g i t c o d e . 1. L a r g e f e m a l e . 25 2. S m a l l f e m a l e . 3. O t h e r m a l e . 4. A l o n e . T h u s , f o r e x a m p l e , 1.2 r e p r e s e n t s z i g z a g b e h a v i o u r t o t h e s m a l l e r f e m a l e . The f o l l o w i n g t r i a l s w ere i n c l u d e d i n t h e d a t a a n a l y s i s : 1. N i n e t e e n t r i a l s w i t h l o w e r Salmon m a l e s and f e m a l e s . 2. N i n e t e e n t r i a l s w i t h u p p e r Salmon m a l e s and f e m a l e s . 3. E l e v e n t r i a l s w i t h l o w e r Salmon m a l e s and m a r i n e f e m a l e s . 4. S i x t e e n t r i a l s w i t h u p p e r S almon m a l e s a n d m a r i n e f e m a l e s . A n a l y s i s i n t h i s s e c t i o n a d d r e s s e s t h r e e d i f f e r e n t a s p e c t s of. t h e c o u r t s h i p s e q u e n c e : 1) C o u r t s h i p c y c l e s C o u r t s h i p s s o m e t i m e s b r e a k o f f a f t e r t h e f e m a l e f o l l o w s t h e m a l e t o t h e n e s t ; t h e m a l e t h e n a p p r o a c h e s t h e f e m a l e a g a i n and t h e c o u r t s h i p b e g i n s anew. T h e s e s e q u e n c e s a r e r e g a r d e d a s s e p a r a t e c o u r t s h i p c y c l e s ( v a n den Assem, 1 9 6 7 ) . T y p i c a l l y , c o n s u m m a t i o n t a k e s p l a c e i n t h e f i r s t few c y c l e s . An a n a l y s i s o f t h e s u c c e s s r a t e , w i t h r e s p e c t t o t h e d i f f e r e n t p o t e n t i a l m a t e s , was c a r r i e d o u t f o r f r e s h w a t e r m a l e s f r o m b o t h t h e u p p e r and l o w e r S almon p o p u l a t i o n s . 26 2) E a r l y C o u r t s h i p B e h a v i o u r The e a r l y s t a g e s o f c o u r t s h i p a r e t h e o r e t i c a l l y t h e most i m p o r t a n t d e t e r m i n a n t o f w h e t h e r a c o u r t s h i p w i l l p r o c e e d t o m a t i n g . The a s s u m p t i o n i s t h a t , w i t h i n t h e c o n s t r a i n t s o f p h y s i o l o g i c a l f a c t o r s , r i s k s a s s o c i a t e d w i t h c o u r t s h i p s e l e c t f o r a r a p i d e x c h a n g e o f s i g n a l s . C o n s e q u e n t l y , i t i s t o t h e a d v a n t a g e o f b o t h s e x e s t o b r e a k o f f an i n a p p r o p r i a t e p a i r i n g r a p i d l y . T h r e e commonly o c c u r r i n g i n i t i a l b e h a v i o u r s were e x a m i n e d : t h e f r e q u e n c y a n d d u r a t i o n o f b o u t s o f z i g - z a g g i n g , b u t t i n g a n d a g g r e s s i v e b e h a v i o u r . T h e s e b e h a v i o u r s were t h e n d i v i d e d by t h e l e n g t h o f t h e o b s e r v a t i o n p e r i o d t o g i v e a r e l a t i v e ( p e r s e c . ) e s t i m a t e o f e a c h b e h a v i o u r . T h u s , a mean number o f b o u t s p e r t r i a l s e c o n d a n d a mean b o u t l e n g t h ( i n s e c o n d s ) was o b t a i n e d . C o m p a r i s o n s were t h e n made o f c o u r t s h i p s i n v o l v i n g m a l e s o f t h e u p p e r a n d l o w e r r i v e r p o p u l a t i o n s when c o u r t i n g f e m a l e s o f t h e i r own a n d t h e an a d r o m o u s m a r i n e p o p u l a t i o n s . 3) Uncommon C o u r t s h i p B e h a v i o u r s F i v e b e h a v i o u r s d i d n o t i n v a r i a b l y o c c u r d u r i n g c o u r t s h i p . T h e s e w e r e : f i r s t r e s p o n s e t o f e m a l e ; n e s t m a i n t e n a n c e a f t e r i n i t i a l a p p r o a c h t o f e m a l e ; " g l u e i n g " a n d " c r e e p i n g t h r o u g h " d u r i n g c o u r t s h i p ; a n d n e s t m a i n t e n a n c e a f t e r f o l l o w t o n e s t by f e m a l e . . T h e s e b e h a v i o u r s were r e c o r d e d e i t h e r a s o c c u r r i n g o r n o t o c c u r r i n g a n d t h e i r f r e q u e n c i e s were c o m p a r e d between t h e m a l e s o f t h e u p p e r a n d l o w e r Salmon p o p u l a t i o n s u s i n g t h e C h i -27 s q u a r e t e s t . They were c o r r e c t e d f o r c o n t i n u i t y s i n c e t h e c o m p a r i s o n s i n v o l v e 2x2 c o n t i n g e n c y t a b l e s ( S o k a l & R o h l f , l 9 8 l ) . ( a ) F i r s t R e s p o n s e The m a l e s o f t h e two p o p u l a t i o n s were c o m p a r e d w i t h r e s p e c t t o t h e i r f i r s t r e s p o n s e t o a g r a v i d f e m a l e - w h e t h e r z i g z a g , b u t t o r a g g r e s s i o n . (b) N e s t M a i n t e n a n c e a f t e r I n i t i a l A p p r o a c h The p r e s e n c e o r a b s e n c e o f n e s t m a i n t e n a n c e a f t e r an i n i t i a l a p p r o a c h was r e c o r d e d and a c o m p a r i s o n made, a s b e f o r e , b e t w e e n t h e t a r g e t p o p u l a t i o n s . ( c ) G l u e i n g a n d C r e e p i n g T h r o u g h T h e s e b e h a v i o u r s a r e a c o n s t a n t f e a t u r e o f t h e c o u r t s h i p s e q u e n c e a n d a s t r o n g i n d i c a t i o n t h a t a m a l e i s w i l l i n g t o p r o c e e d w i t h a c o u r t s h i p s e q u e n c e . A c o m p a r i s o n was made t o d e t e c t a n y d i f f e r e n c e s i n t h e s e b e h a v i o u r s b e t w e e n p o p u l a t i o n s a n d b e t w e e n p o t e n t i a l m a t e s . (d) N e s t M a i n t e n a n c e a f t e r F e m a l e f o l l o w s t o N e s t O b s e r v a t i o n showed t h a t t h i s b e h a v i o u r d i d n o t i n v a r i a b l y o c c u r a f t e r a " f o l l o w " a n d a c o m p a r i s o n was made t o d e t e c t d i f f e r e n c e s i n o c c u r r e n c e . 28 RESULTS F e m a l e S i z e S u r v e y The u p p e r L i t t l e C a m p b e l l R i v e r i s c h a r a c t e r i z e d by a f r e s h w a t e r s t i c k l e b a c k p o p u l a t i o n i n w h i c h t h e s i z e d i s t r i b u t i o n o f f e m a l e s i s skewed i n f a v o u r o f l a r g e m a t u r e f e m a l e s ( T a b l e 1 ) . T a b l e 1 Body s i z e ( s t a n d a r d l e n g t h ) i n t h e 1982 L i t t l e C a m p b e l l R i v e r G . a c u l e a t u s b r e e d i n g p o p u l a t i o n F e m a l e s M a l e s X(mm) 50.9. 45.1 S.E. 0.39 0.37 Range 41.3-63.4 39.6-52.4 n 127 53 I n t h i s p o p u l a t i o n t h e m a j o r i t y o f t h e b r e e d i n g f e m a l e s a r e l a r g e r t h a n t h e t e r r i t o r i a l m a l e s . T h e r e a r e , h o w e v e r , some m a t u r e f e m a l e s t h a t a r e s m a l l e r t h a n t h e m a l e s . S a m p l e s o f g r a v i d f e m a l e s t a k e n f r o m t h e h e a d w a t e r s o f t h e n e a r b y Salmon R i v e r show t h a t h e r e t h e f e m a l e s i z e a l s o o v e r l a p s m a l e s i z e ( F i g . 3 , T a b l e 2 ) . T h u s , m a l e s p o t e n t i a l l y c a n c h o o s e mates f r o m a r a n g e o f s i z e s . The m a r i n e f o r m d o e s n o t c o - e x i s t w i t h t h e f r e s h w a t e r f o r m i n e i t h e r o f t h e s e l o c a t i o n s . S i m i l a r s a m p l e s , t a k e n f r o m t h e l o w e r r e a c h e s o f t h e S almon R i v e r i n d i c a t e t h a t h e r e f e m a l e s i z e r a n g e d o e s n o t o v e r l a p t h a t o f m a l e s t o t h e same d e g r e e a s i n t h e u p p e r r i v e r . I n t h e l o w e r 29 F i g u r e 3. Salmon R i v e r b r e e d i n g p o p u l a t i o n s , 1984. Females - Standard length (mm) Males - Standard length (mm) 10 — 5 — 10 — 5 — 38 40 45 50 55 60 65 Lower Salmon - freshwater 70 .c o d 10 _ 5 — 38 40 45 50 55 60 65 Upper Salmon - freshwater 70 10 — 10 5 — 38 40 45 50 55 60 65 Lower Salmon - freshwater 38 40 45 50 55 60 65 Upper Salmon - freshwater 70 38 40 45 50 55 60 65 70 38 40 45 50 55 60 65 70 Lower Salmon - anadromous Lower Salmon - anadromous CO o 31 r i v e r , m a l e a n d f e m a l e s i z e s more c l o s e l y c o n f o r m ( F i g 3 ) . I t i s i n t h i s l o w e r r i v e r a r e a t h a t t h e f r e s h w a t e r a n d a n a d r o m o u s , m a r i n e f o r m s of G a s t e r o s t e u s c o - e x i s t d u r i n g t h e b r e e d i n g s e a s o n . The f e m a l e s f r o m t h e u p p e r S almon a r e l a r g e r t h a n t h o s e f r o m t h e l o w e r r i v e r ( p < 0.005, 1 - t a i l ) . I n c o n t r a s t , t h e mean s i z e o f b r e e d i n g m a l e s f r o m t h e two s i t e s i s n o t d i f f e r e n t , n o r do f r e s h w a t e r m a l e s d i f f e r i n mean s i z e b e t w e e n t h e L i t t l e C a m p b e l l a n d t h e S a l m o n s i t e s (p > 0.11, 2 - t a i l ) . The a n a d r o m o u s , m a r i n e p o p u l a t i o n i n t h e l o w e r S almon R i v e r c o n t a i n s m a l e s a n d f e m a l e s o f s i m i l a r s i z e s . T h i s s i z e c o r r e s p o n d s t o t h e s i z e r a n g e o f t h e l a r g e s t f e m a l e s i n t h e u p p e r r i v e r b u t d o e s n o t o v e r l a p , t o any e x t e n t t h e s i z e o f f r e s h w a t e r s t i c k l e b a c k s i n t h e l o w e r r i v e r ( F i g . 3 ) . The mean s i z e o f t h e anadromous f i s h i s c o n s i d e r a b l y l a r g e r t h a n t h a t o f e i t h e r p o p u l a t i o n o f f r e s h w a t e r f i s h (p < 0.005, 1 - t a i l ) . S a m p l e s t a k e n f r o m t h e same l o c a t i o n s i n t h e S almon R i v e r i n p r e v i o u s y e a r s ( p r o v i d e d by J . D . M c P h a i l ) show t h a t t h e s e r e l a t i v e s i z e d i f f e r e n c e a r e c o n s i s t e n t e v e n t h o u g h means v a r y somewhat f r o m y e a r t o y e a r ( F i g 4 & 5, T a b l e 2 ) . F e c u n d i t y A n a l y s i s S a m p l e s o f f r e s h w a t e r s t i c k l e b a c k s o b t a i n e d f r o m t h e u p p e r and l o w e r Salmon R i v e r s i t e s a nd f r o m t h e L i t t l e C a m p b e l l R i v e r a s w e l l a s anadromous s a m p l e s f r o m t h e l o w e r S almon R i v e r were a n a l y s e d t o d e t e r m i n e t h e c o r r e l a t i o n b e t w e e n f e m a l e s i z e a nd egg number i n g r a v i d f e m a l e s . A p o s i t i v e c o r r e l a t i o n b e t ween egg number and f e m a l e s i z e . i s a p p a r e n t i n a l l p o p u l a t i o n s 32 Table 2 Mean si z e of breeding Salmon r i v e r sticklebacks (U.S."lower Salmon, U.S.«upper Salmon). 1984 Males L.S. U.S. Marine X 48.3 46.8 62.1 S.E. 0.86 0.44 0.79 Range 41.5-55.0 41.5-56.8 54.0-65.1 n 21 53 17 Fema1es X 49.7 53.9 64.2 S.E. 0.63 0.56 0.57 Range 37.5-64.6 39.2-69.8 53.0-69.1 n 103 129 38 1983 Males X 44.4 44.1 57.2 S.E. 0.35 0.55 0.39 Range 40.1-47.3 40.1-46.5 55.0-59.4 n 32 15 15 Females "X 43.5 48.5 58. 1 S.E. 0.40 0.96 0.35 Range 38.4-54.0 38.5-57.6 53.3-63.4 n 7 1 23 36 1982 Males X 45.8 44.4 58.0 S.E. 1.002 1.001 0.73 Range 37.0-52.0 38.0-52.0 52.0-63.0 n 48 45 17 Fema1es x" 44 . 1 47.2 58.0 S.E. 1.002 1.003 1.001 Range 35.0-55.0 35.0-62.0 54.0-64.0 n 74 88 2G 33 F i g u r e 4. Salmon R i v e r b r e e d i n g p o p u l a t i o n s 1983. Females - Standard length (mm) Males - Standard length (mm) 10 — 5 -38 40 45 50 55 60 65 Lower Salmon - freshwater d 10 5 -10 -38 40 45 50 55 60 65 Lower Salmon - anadromous 10 — 5 — 70 10 — 5 — 38 40 45 50 55 60 65 70 Upper Salmon - freshwater 10 — 5 — 38 40 45 50 55 60 65 Lower Salmon - freshwater 70 38 40 45 50 55 60 65 Upper Salmon - freshwater 70 70 ' 3840 45 50 55 60 65 70 Lower Salmon - anadromous CO 4=» 35 F i g u r e 5. Salmon R i v e r b r e e d i n g p o p u l a t i o n s 1982. Females - Standard length (mm) Males - Standard length (mm) T a b l e 3 C o r r e l a t i o n between female s l z e M o g t r a n s f o r m e d ) and egg number 1n f o u r s t i c k l e b a c k p o p u l a t i o n s . L o c a t i o n Range Mean SL(mm) Mean *eggs ( s e ) ( s e . ) L i t t l e Campbell - f.w. 31 35.8-62.5 51.0 ( 1 .28 ) 84 (5.11) 0.775 Lower Salmon f.w. 21 37.6-59.1 47. 1 ( 1 . 17) 125 (7.72 ) 0. 7J7 Upper Salmon - f.w. 19 44.9-69.8 59.9 ( 1 .26) 204 (44.52) 0.7 13 37 Lower Salmon - marine 27 57.5-68.8 64 .2 (0.50) 3" 1B (11.27) 0.54 1 38 ( T a b l e 3) a n d i s c o n s i s t e n t w i t h t h e r e l a t i o n s h i p f o u n d i n o t h e r s t u d i e s ( H a g e n , 1967; W o o t t o n , 1 9 7 3 ) . The n a r r o w s i z e r a n g e o f a n a dromous f e m a l e s p r o b a b l y a c c o u n t s ' f o r t h e l o w e r c o r r e l a t i o n i n t h a t s a m p l e . C o - v a r i a t e a n a l y s i s o f t h e s i z e - f e c u n d i t y r e g r e s s i o n c u r v e s o f t h e f o u r p o p u l a t i o n s showed t h a t t h e s l o p e s o f t h e r e g r e s s i o n l i n e s were s i m i l a r i n t h e f r e s h w a t e r Salmon R i v e r p o p u l a t i o n s b u t d i f f e r e d f r o m t h o s e o f t h e L i t t l e C a m p b e l l R i v e r a n d t h e m a r i n e s t i c k l e b a c k p o p u l a t i o n i n t h e l o w e r S a l m o n . S i n c e t h e s l o p e s o f t h e r e g r e s s i o n l i n e s d i f f e r e d , f u r t h e r a n a l y s i s o f t h e s e r e s u l t s was n o t u n d e r t a k e n . M a te S e l e c t i o n E x p e r i m e n t s L i t t l e C a m p b e l l p r e l i m i n a r y s t u d y The p o s t u l a t e t h a t m a l e s , when p r e s e n t e d w i t h a c h o i c e , s h o u l d c h o o s e t h e l a r g e r o f two g r a v i d f e m a l e s was s u p p o r t e d i n t h i s s t u d y . I n t w e n t y s u c c e s s f u l t r i a l s ( i . e . t h o s e e n d i n g i n n e s t e n t r y ) L i t t l e C a m p b e l l m a l e s c h o s e t h e l a r g e r o f t h e two f e m a l e s i n 75% o f t h e c a s e s (p < 0.05, 1 - t a i l B i n o m i a l t e s t ) . I t p r o v e d d i f f i c u l t t o age s t i c k l e b a c k s r e l i a b l y f r o m o t o l i t h s ( A p p e n d i x 1) so t h e r e i s no i n d e p e n d e n t c h e c k on w h e t h e r l a r g e r f e m a l e s a r e o l d e r o r m e r e l y f a s t e r g r o w i n g t h a n t h e s m a l l e r f e m a l e s . 39 Salmon River study Mate Select ion Experiments When given the choice of two sizes of apparently equally gravid females, upper and lower Salmon males tended to court d i f f e r e n t sized females. Lower Salmon males appear to prefer females that are smaller than themselves, whereas the upper Salmon males c l e a r l y prefer females larger than themselves (Table 4). Table 4. Number of successful courtships(i.e.nest entries) ordered by female size r e l a t i v e to male s i z e . Probability values are derived from the Binomial T e s t ( 1 - t a i l ) . (L.S.=lower Salmon; U.S.=upper Salmon) Population Number Nest Entry Q>C* Q<cf Probability Male Female of t r i a l s (% success) ~ Values L.S. L.S. 36 8 1 7 p<0.05 (25%) U.S. U.S. 37 6 6 0 p<0.05 (17%) L.S. U.S. 8 5 1 4 p>0.05 U.S. L.S. 9 5 5 0 p<0.05 Due to the s t r i c t c r i t e r i o n set in t h i s test that both females be equally responsive ( i . e . attempt to enter the nest) the proportion of successful courtships was not high. In a number of cases one female quickly entered the nest before the other had time to respond. However, according to observations made by other observers in the wild (Kynard, 1979; A.Brett, 40 p e r s . comm.) n o r m a l l y t h e p r o p o r t i o n o f c o u r t s h i p s w h i c h end i n n e s t e n t r y i s n o t h i g h . L i ( 1 9 7 6) a r g u e d t h a t few m a l e c o u r t s h i p s w i l l l e a d t o s p a w n i n g due t o t h e h i g h i n c i d e n c e d u r i n g c o u r t s h i p o f n e s t - d i r e c t e d d i s r u p t i v e b e h a v i o u r by n e i g h b o u r i n g m a l e s . T h i s d i s r u p t i v e b e h a v i o u r was v e r y a p p a r e n t i n t h i s s t u d y a s t h e n e i g h b o u r i n g m a l e s d i s p l a y e d a g g r e s s i v e a n d c o u r t i n g b e h a v i o u r a t t h e t e r r i t o r y b o u n d a r y w h i l e c o u r t s h i p was i n p r o g r e s s . The r e s u l t s show t h a t l o w e r Salmon R i v e r m a l e s p r e f e r t o mate w i t h f e m a l e s s m a l l e r t h a n t h e y a r e ; i n o n l y one c a s e o u t o f e i g h t d i d t h e t h e m ale d i r e c t h i s c o u r t s h i p t o a f e m a l e t h a t was l a r g e r t h a n he was. I n t h i s p a r t i c u l a r c a s e b o t h f e m a l e s were l a r g e r b u t t h e m ale c o u r t e d t h e s m a l l e r o f t h e two f e m a l e s . I n t h e u p p e r S a l m o n p o p u l a t i o n s i x s u c c e s s f u l t r i a l s were c o n d u c t e d where one f e m a l e was l a r g e r a n d one s m a l l e r t h a n t h e m a l e . I n a l l c a s e s t h e l a r g e r f e m a l e e n t e r e d t h e n e s t . I n t h e b e t w e e n - p o p u l a t i o n t r i a l s , i n a l l c a s e s ( f i v e ) , u p p e r S a l m o n m a l e s o n l y l e d l o w e r Salmon f e m a l e s t h a t were l a r g e r t h a n t h e y were t o t h e n e s t . The r e s u l t w i t h l o w e r S a l m o n m a l e s was t h e r e v e r s e , w i t h b u t one e x c e p t i o n . I n t h i s c a s e b o t h f e m a l e s were l a r g e r t h a n t h e m a l e a n d i t was t h e s m a l l e r o f t h e two f e m a l e s t h a t went t o t h e n e s t . L a r g e f e m a l e s o c c a s i o n a l l y i n t e r r u p t e d a c o u r t s h i p i n v o l v i n g a s m a l l e r f e m a l e by n i p p i n g a t h e r ; h o w e v e r , t h i s was n o t a r e g u l a r f e a t u r e o f c o u r t s h i p . I t a p p e a r e d o n l y when t h e two f e m a l e s were c r o w d e d t o g e t h e r i n a c o r n e r o f t h e a q u a r i u m by t h e m a l e . 41 F r e s h w a t e r v s Anadromous S e l e c t i o n E x p e r i m e n t s T e s t s were c a r r i e d o u t u s i n g m a l e s f r o m b o t h f r e s h w a t e r g r o u p s . The p u r p o s e was t o a s c e r t a i n i f f r e s h w a t e r m a l e s w o u l d c o u r t a nadromous f e m a l e s . B e c a u s e , i n n a t u r e , u p p e r S almon m a l e s do n o t e n c o u n t e r anadromous f e m a l e s t h e y may t r e a t them s i m p l y a s u n u s u a l l y l a r g e f e m a l e s . I n d e e d , u p p e r S almon m a l e s c o u r t e d a n d l e d m a r i n e f e m a l e s t o e n t e r t h e n e s t i n t h e i r n o r m a l f a s h i o n ( 8 / 2 3 t r i a l s , s u c c e s s 3 4 . 8 % ) . I n c o n t r a s t , l o w e r Salmon m a l e s l e d t h e m a r i n e f e m a l e s t o t h e n e s t i n a m e a n d e r i n g f a s h i o n . A m e a n d e r i n g l e a d i n G a s t e r o s t e u s i s u s u a l l y a s s o c i a t e d w i t h c o u r t s h i p s i n w h i c h t h e male i s n o t r e a d y t o spawn ( W i l z , l 9 7 0 ) . I n t h i s c a s e , h o w e v e r , i f t h e f e m a l e r e a c h e d t h e n e s t e n t r a n c e n o r m a l c o u r t s h i p b e h a v i o u r was r e s u m e d ( s h o w i n g , p r o d d i n g e t c . ) a n d t h e f e m a l e e n t e r e d ( 4 / 1 5 t r i a l s , s u c c e s s 2 6 . 7 % ) . T h e s e t r i a l s w e r e r e c o r d e d a n d a n a l y s e d f o r b e h a v i o u r a l d i f f e r e n c e s . Hay a n d M c P h a i l ( 1 9 7 5 ) c o n d u c t e d e x t e n s i v e e x p e r i m e n t a l work on m a l e mate s e l e c t i o n i n c o - e x i s t i n g p o p u l a t i o n s o f f r e s h w a t e r a n d a n adromous s t i c k l e b a c k s . My s a m p l e t r i a l s c o n f i r m t h e f i n d i n g s o f t h e s e s t u d i e s : f r e s h w a t e r m a l e s t e n d t o mate w i t h f e m a l e s of t h e i r own f o r m ( i n 3/4 s u c c e s s f u l t r i a l s ) . I n one t r i a l , d i r e c t i n t e r f e r e n c e by a f e m a l e was o b s e r v e d . An a n a dromous f e m a l e was c h a s e d o f f by a l a r g e l o w e r S almon f r e s h w a t e r f e m a l e . T h i s f r e s h w a t e r f e m a l e t h e n resumed c o u r t s h i p w i t h t h e m a l e . I n t h e s u c c e s s f u l t r i a l s where t h e f r e s h w a t e r f e m a l e was s m a l l e r t h a n t h e anadromous f e m a l e t h e r e was no i n t e r f e r e n c e a n d t h e m ale a d d r e s s e d most o f h i s c o u r t s h i p 42 b e h a v i o u r t o t h e f r e s h w a t e r f e m a l e . U n f o r t u n a t e l y t h e s a m p l e i s s m a l l . Summary The mate s e l e c t i o n e x p e r i m e n t s s u g g e s t t h a t f r e s h w a t e r m a l e s t i c k l e b a c k s i n t h e S a l m o n R i v e r do n o t mate r a n d o m l y w i t h r e g a r d t o f e m a l e s i z e . M a l e s f r o m t h e u p p e r a n d l o w e r r i v e r e x h i b i t d i f f e r e n t p r e f e r e n c e s w i t h r e s p e c t t o r e l a t i v e f e m a l e s i z e . T h e s e p r e f e r e n c e s a r e n o t a b s o l u t e a nd u n d e r e x p e r i m e n t a l c o n d i t i o n s i n t e r - p o p u l a t i o n a n d i n t e r - f o r m p a i r i n g s a r e p o s s i b l e . When g i v e n a c h o i c e , h o w e v e r , t h e f r e s h w a t e r m a l e s f r o m t h e two a r e a s show p r e f e r e n c e s f o r d i f f e r e n t s i z e d f e m a l e s . U p p e r Salmon R i v e r m a l e s mate more o f t e n w i t h f e m a l e s t h a t a r e l a r g e r t h a n t h e y a r e , w h e r e a s l o w e r S almon m a l e s mate most o f t e n w i t h f e m a l e s s m a l l e r t h a n t h e m s e l v e s . 43 C o u r t s h i p B e h a v i o u r E x p e r i m e n t s The f o l l o w i n g t r i a l s were i n c l u d e d i n t h e d a t a a n a l y s i s : 1. N i n e t e e n t r i a l s w i t h l o w e r S almon m a l e s a n d f e m a l e s . > 2. N i n e t e e n t r i a l s w i t h u p p e r Salmon m a l e s a n d f e m a l e s . 3. E l e v e n t r i a l s w i t h l o w e r S almon m a l e s a n d m a r i n e f e m a l e s . 4. S i x t e e n t r i a l s w i t h u p p e r S a l m o n m a l e s a n d m a r i n e f e m a l e s . The t r i a l s c h o s e n f o r a n a l y s i s were c h a r a c t e r i z e d by v i g o r o u s c o u r t s h i p a n d f o l l o w i n g t o t h e n e s t by b o t h f e m a l e s , b u t t h e y d i d n o t n e c e s s a r i l y end i n n e s t e n t r y ( T a b l e 5 ) . T a b l e 5. C o u r t s h i p t r i a l s u s e d i n b e h a v i o u r a n a l y s i s . N o t e t h a t n o t a l l t r i a l s e n d e d i n n e s t e n t r y . ( L . S . = l o w e r S a l m o n , U.S.=upper S a l m o n ) L.S.x L.S. U.S.x U.S. L.S.x M a r . U.S.x Mar. N e s t e n t r y 7 ( 3 7 % ) 1 4 ( 7 4 % ) . 4 ( 3 6 % ) 8 ( 5 0 % ) No n e s t e n t r y 1 2 ( 5 3 % ) 5 ( 2 7 % ) 7 ( 5 4 % ) 8 ( 5 0 % ) T o t a l 19 19 11 16 C o u r t s h i p c y c l e s T a b l e 6 shows t h e number o f c o u r t s h i p c y c l e s a n d t h e p r o b a b i l i t y o f a f e m a l e e n t e r i n g t h e n e s t on e a c h s u c c e s s i v e c y c l e . The d a t a i n d i c a t e t h a t t h e h i g h e s t number o f n e s t e n t r i e s o c c u r d u r i n g t h e f i r s t f i v e c o u r t s h i p c y c l e s . The t o t a l Table 6 Successive courtship cycles and the pr o b a b i l i t y a female w i l l enter the nest in each c y c l e f s l z e code: 1 *fema1e>ma1e, 2=fema1e<ma1e; L.S. = 1ower Salmon, U.S.•upper Salmon; tota1«number of females Interacting with male at the beginning of each cycle: P=probabt11ty of entry, C.P.=Cumulative p r o b a b i l i t y of entry). Popn. Size Cycle 1 Cycle 2-5 Cycle 6-10 Cycle > 10 code Male Female Total Entry P. C P . Total Entry P. C P . Total Entry P. CP. Total Entry P. C P . L.S.L.S. 1 17 0 0.00 0.00 11 1 0.09 0.09 4 0 0.00 0.09 0 0 0.000.09 2 21 1 0.05 0.05 10 3 0.30 0.19 S 1 0.16 0.24 4 1 0.25 0.29 U.S. U.S. 1 33 1 0.03 0.03 15 9 0.60 0.30 5 2 0.40 0.36 3 2 0.67 0.42 2 5 0 0.00 0.00 5 0 0.00 0.00 3 0 0.00 0.00 0 0 0.00 0.00 L.S. Marine 1 10 0 0.00 0.00 9 2 0.22 0.20 4 1 0.25 0.30 3 1 0.33 0.40 • t o U.S. Marine 1 16 1 0.06 0.06 14 6 0.4 3 0.44 4 1 0.25 0.50 2 0 O.OO 0.50 _ > 45 column shows the numbers of females r e m a i n i n g i n a c t i v e i n t e r a c t i o n w i t h the male at the b e g i n n i n g of each c o u r t s h i p c y c l e . In the Salmon r i v e r f r e s h w a t e r p o p u l a t i o n s the l e s s p r e f e r r e d m a t e s d a r g e females i n the lower Salmon and s m a l l females i n the upper Salmon) d i d not p e r s i s t i n t o the l a t e r c y c l e s ; t h i s c o u l d be due to l a c k of s t i m u l a t i o n or i n c r e a s e d a g g r e s s i o n by the male , or b o t h . Upper Salmon m a l e s , i n i n t e r a c t i o n w i t h l a r g e females from t h e i r own area and females of the anadromous p o p u l a t i o n , had a h i g h e r p r o b a b i l i t y of l e a d i n g females to the nest i n the e a r l i e r c y c l e s than d i d males from the lower Salmon p o p u l a t i o n . G e n e r a l l y , the upper Salmon males approach females sooner and c o u r t more v i g o r o u s l y than do lower Salmon m a l e s . The s i m i l a r i t y i n the u l t i m a t e p r o b a b i l i t y of nest e n t r y of the anadromous females was due more to the p e r s i s t e n c e of the anadromous female than to the c o u r t s h i p of the lower Salmon m a l e s . C h a r a c t e r i s t i c a l l y , lower Salmon males a v o i d e d l e a d i n g anadromous females to the nest by meandering ( i . e . p r o l o n g i n g the l e a d / f o l l o w sequence ; Mann-Whitney U - t e s t , p = 0 . 0 0 9 ) . Upper Salmon males c o u r t anadromous marine females more v i g o r o u s l y than do lower Salmon m a l e s ; c o n s e q u e n t l y , anadromous females have a h i g h e r p r o b a b i l i t y of r e a c h i n g the nest i n the e a r l i e r c o u r t s h i p c y c l e s when c o u r t e d by upper Salmon m a l e s . 46 E a r l y C o u r t s h i p B e h a v i o u r The e a r l y s t a g e s o f c o u r t s h i p p r o v e d t o be t h e most i m p o r t a n t d e t e r m i n a n t o f w h e t h e r a c o u r t s h i p w o u l d p r o c e e d t o n e s t e n t r y . The f i r s t r e s p o n s e o f m a l e s o f b o t h p o p u l a t i o n s t o t h e a p p e a r a n c e o f a f e m a l e - l i k e o b j e c t i s t o a p p r o a c h t h e f e m a l e e i t h e r d i r e c t l y o r w i t h z i g - z a g c o u r t s h i p movements. T h i s o c c u r s r e g a r d l e s s o f t h e s u i t a b i l i t y o f t h e mate ( C h i - s q u a r e , p > 0 . 0 5 ) . T h i s f i r s t i n s p e c t i o n t h e n d e t e r m i n e s t h e s u b s e q u e n t a c t i o n s o f t h e m a l e . M a l e s f r o m t h e l o w e r S a l m o n , t h a t c o - e x i s t w i t h a b r e e d i n g p o p u l a t i o n o f anadromous m a r i n e s t i c k l e b a c k s , e x h i b i t q u a n t i t a t i v e d i f f e r e n c e s i n t h e i n i t i a l s t a g e s o f c o u r t s h i p o f t h e i r own f e m a l e s d e p e n d i n g on t h e s i z e o f f e m a l e c o u r t e d ( T a b l e 7 ) . Z i g - z a g b o u t s a r e more v i g o r o u s ( p = 0.022) a n d more p r o l o n g e d ( p = 0.025) t o t h e s m a l l e r f e m a l e o f a p a i r a n d a g g r e s s i v e b o u t s a r e c o r r e s p o n d i n g l y d i r e c t e d c h i e f l y a t t h e l a r g e r f e m a l e (p = 0 . 0 0 0 1 ) . I n c o n t r a s t , t h e b e h a v i o u r o f u p p e r S a l m o n m a l e s t o d i f f e r e n t s i z e s o f f e m a l e s f r o m t h e i r own p o p u l a t i o n d o e s n o t d i f f e r . H o w e v e r , i n t r i a l s w here t h e u p p e r S a l m o n m a l e i s p r e s e n t e d w i t h two f e m a l e s (one l a r g e r a n d one s m a l l e r t h a n t h e m a l e ) t h e z i g - z a g b e h a v i o u r he d i r e c t s t o t h e l a r g e r f e m a l e i s more v i g o r o u s (p = 0 . 0 1 3 ) . T h e r e i s no d i f f e r e n c e i n a g g r e s s i o n ( T a b l e 8 ) . The l o w e r Salmon d a t a a r e c o n s i s t e n t w i t h t h o s e i n T a b l e 7. U p p e r a n d l o w e r Salmon m a l e s a l s o d i f f e r i n t h e e a r l y s t a g e s o f t h e i r c o u r t s h i p o f l a r g e f e m a l e s . Lower Salmon m a l e s r e d u c e t h e i r z i g - z a g g i n g (p = 0.057) and a r e more a g g r e s s i v e ( p 47 Table 7 Comparison of early courtship behaviour (21g-zagging, butting, aggression) by males of two Salmon River freshwater populations to d i f f e r e n t sizes of females from th e i r own popul at lon( s 1 ze code-. *l»larger female . #2«smaller female). The values are medians, the p r o b a b i l i t y values are derived from Mann-Whitney U tests, and s i g n i f i c a n t differences are indicated by an as t e r i s k . Lower Salmon males Upper Salmon males Female Size # 1 *2 (n=19) (n=19) Probab i l l t y the behaviour is the same Female Size * 1 #2 (n=19) (n=19) Probabi1i ty the behaviour is the same Zig-zag bouts 0.0089 0.0186 p«0.0228-per second Zig-zag bout 3.2266 4.0000 p*0.0255* length(seconds) Butting bouts 0.0059 00056 p=0.4655 per second Butting bout 3.2667 3.5000 p=0.4425 length(seconds) Aggressive bouts 0.0164 0.0042 p=0.0001" per second Aggressive bout 4.8167 3.3000 p=0.0024» 1ength(seconds) 0.0129 0.0150 p=0.4305 3.2070 2.8670 p=0.8153 0.0130 0.0130 p=1.0000 2.5670 2.5250 p=0.6721 0.0060 0.0080 p=0.726 1 3.6140 4.2500 p=0.4391 48 Table 8 Comparison of early courtship behaviour (zig-zagging. butting, aggression) by males of two Salmon River freshwater populations to females which are l a r g e r d f l ) and smaller(#2) than* the male. The values are medians, the p r o b a b i l i t y values are derived from Mann-Whitney U tests, and s i g n i f i c a n t difference are indicated by an aster i sk. Lower Salmon n.^ies Relative P r o b a b i l i t y Female Size (n«12) (n»12) the behaviour is the same Upper Salmon males Relative Probability Female Size * 1 #2 (n«9) (n»9) the behaviour is the same Zig-zag bouts 0.0073 0.0216 per second Zig-zag bout 3.2759 4.0551 length(seconds ) Butting bouts 0.0045 0.0045 per second Butting bout 3.4958 2.6500 1ength(seconds) Aggressive bouts 0.1529 0.0037 per second Aggressive bout 5.1917 3.5000 1ength(seconds ) p-0.0327-p=0.3123 p=0.7508 p=0.0885 p=0.0262" p=0.0111" 0.0239 0.0057 p=0.0134* 3.3833 3.9444 p=0.7239 0.0154 0.0024 p=0.0521 3.3000 2.3000 p=0.1853 0.0103 0.0065 p-0.1333 4.8571 7.4600 p=0.4529 49 Table 9 Comparison of early courtship behaviour(zig-zagging,butt1ng.aggression) between males of two Salmon River freshwater populations to two d i f f e r e n t sizes of females from their own populations. The values are medians, the pr o b a b i l i t y values are derived from Mann-Whitney U tests, and s i g n i f i c a n t differences are indicated by an as t e r i s k . Large Females Sma11 Fema1es Lower Upper Pr o b a b i l i t y Salmon Salmon the behaviour (n=19) (n=19) 1s the same Lower Upper Probability Salmon Salmon the behaviour (n=19) (n=19) is the same Zig-zag bouts 0.0089 0.0129 p=0.0577 per second Z1g-zag bout 3.2266 3.2070 p=0.8267 1ength(seconds) Butting bouts 0.0059 0.0130 p=0.0850 per second Butting bout 3.2667 2.5670 p=0.2736 1ength(seconds ) Aggressive bouts 0.0164 0.0060 p=0.0173* per second Aggressive bout 4.8167 3.6140 p=0.0069* 0.0186 0.0150 p=0.3732 4.0000 2.8670 p=0.0173* 0.0056 0.0130 p=0.0356' 3.5000 2.5250 p=0.1700 0.0042 0.0080 p=0.1793 3.3000 4.2500 p=0.2736 1ength(seconds) 50 = 0.017) o v e r l o n g e r p e r i o d s (p = 0.006) when c o u r t i n g l a r g e f e m a l e s t h a n when c o u r t i n g s m a l l f e m a l e s ( T a b l e 9 ) . Upper Salmon m a l e s , h o w e v e r , s p e n d l e s s t i m e i n z i g - z a g g i n g when c o u r t i n g s m a l l f e m a l e s t h a n when c o u r t i n g l a r g e f e m a l e s (p 0.017) C o m p a r i s o n s o f t h e s e same e a r l y c o u r t s h i p b e h a v i o u r s when m a l e s o f t h e two p o p u l a t i o n s c o u r t a n adromous f e m a l e s a g a i n show d i f f e r e n c e s i n t h e v i g o u r a n d d u r a t i o n o f c o u r t s h i p b e h a v i o u r b e t w e e n u p p e r a nd l o w e r S almon m a l e s . U p p e r Salmon m a l e s c o u r t a n a dromous f e m a l e s more v i g o r o u s l y (p = 0 . 0 0 5 3 ) , f o r l o n g e r p e r i o d s ( p = 0.0004) a n d a r e l e s s a g g r e s s i v e (p = 0.0218) t h a n a r e l o w e r Salmon m a l e s ( T a b l e 1 0 ) . I n t e r e s t i n g l y , a n a dromous f e m a l e s s t i m u l a t e more v i g o r o u s z i g - z a g g i n g f r o m m a l e s o f b o t h f r e s h w a t e r p o p u l a t i o n s t h a n do l a r g e f e m a l e s f r o m t h e i r own p o p u l a t i o n s . T h i s d i f f e r e n c e , h o w e v e r , i s . s t a t i s t i c a l l y s i g n i f i c a n t o n l y i n l o w e r S almon m a l e s (p = 0.045, T a b l e 1 1 ) . Lower s a l m o n m a l e s a l s o t e n d t o a v o i d d i r e c t a g g r e s s i v e e n c o u n t e r s w i t h a n adromous f e m a l e s (p = 0 . 0 0 0 6 ) ; h o w e v e r , a n a d r o m o u s f e m a l e s a p p a r e n t l y s t i m u l a t e t h e U p p e r S a l m o n m a l e s t o more v i g o r o u s b o u t s o f a g g r e s s i o n (p = 0.0188, T a b l e 1 1 ) . I n g e n e r a l , b o u t l e n g t h o f any b e h a v i o u r i s n o t d i f f e r e n t b e t w e e n m a l e s o f t h e two f r e s h w a t e r p o p u l a t i o n s . B o u t l e n g t h seems t o be o f a f a i r l y r e g u l a r d u r a t i o n f o r i n d i v i d u a l f i s h b u t l a r g e m a l e s a r e a b l e t o s u s t a i n l o n g e r b o u t s t h a n s m a l l m a l e s . The r e g u l a r i t y o f ' b u t t i n g ' b e h a v i o u r by t h e m a l e s o f t h e two f r e s h w a t e r p o p u l a t i o n s a p p e a r s t o i n d i c a t e t h a t t h i s b e h a v i o u r i s i n d e p e n d e n t o f f e m a l e s i z e o r t y p e . 51 T a b l e 10 Comparison of e a r l y c o u r t s h i p b e h a v i o u r ( z i g - z a g g i n g , b u t t i n g , a g g r e s s i o n ) by f r e s h w a t e r males of two Salmon R i v e r p o p u l a t i o n s t o Salmon R i v e r marine f e m a l e s . The v a l u e s a r e medians, the p r o b a b i l i t y v a l u e s a r e d e r i v e d from Mann-Whitney U t e s t s , and s i g n i f i c a n t d i f f e r e n c e s a r e i n d i c a t e d by an a s t e r i s k . Marine f e m a l e s Lower Salmon males Upper Salmon males P r o b a b i l i t y t h e b e h a v i o u r (n=11) (n=16) i s the same Z i g - z a g b o u t s per second Z i g - Z a g bout 1 e n g t h ( s e c o n d s ) B u t t i n g b o u t s per second B u t t i n g bout 1 e n g t h ( s e c o n d s ) A g g r e s s i v e b o u t s per second A g g r e s s i v e bout 1 e n g t h f s e c o n d s ) 0.0136 1.3300 0.0020 1.3300 0.0480 5.0000 0.0435 4.2150 0.0015 0.8350 0 0245 4 . 10O0 p=0.0053" p=0.0004-p=1.0000 p=06392 p=0.021B" p=0.7298 52 T a b l e 11 Comparison of e a r l y c o u r t s h i p b e haviour ( 2 i g - z a g g i n g . b u t t i n g , a g g r e s s i o n ) by f r e s h w a t e r males of two Salmon R i v e r p o p u l a t i o n s to l a r g e and small f e m a1 e s ( r e 1 a t i v e to t h e i r own s i z e ) of" t h e i r own p o p u l a t i o n and to females of the Salmon R i v e r marine p o p u l a t i o n . The v a l u e s a r e medians, the p r o b a b i l i t y v a l u e s a r e d e r i v e d from Mann-Whitney U t e s t s , and s i g n i f i c a n t d i f f e r e n c e s a r e i n d i c a t e d by an a s t e r i s k . Lower Salmon male: Upper Salmon males La r g e female Female of P r o b a b i l i t y Large female Female of P r o b a b i l i t y of own popn. mar.popn. the behaviour of own popn. mar.popn. the behaviour (n=12) (n«11) i s the same (n»9) (n=16) i s the same 2 i g - z i g bouts 0.0073 p e r second Z i g - z a g bout 3.3759 l e n g t h ( s e c o n d s ) B u t t i n g bouts 0.0045 p e r second B u t t i n g bout 3.4958 1e n g t h ( s e c o n d s ) A g g r e s s i v e bouts 0.1529 p e r second A g g r e s s i v e bout 5.1917 ) e n g t h ( s e c o n d s ) 0.013S p=0.0455' 1.3300 p=0.0743 0.0020 1.3300 0.0480 5.0000 p=0.3401 p=0.0794 p = 0 . 0 0 0 6 " p=0.6891 0.0239 3.8333 0.0154 3.3000 0.0103 4.857 1 0.0435 p=0.0949 4.2150 p=0.590" 0.0015 p=0.0949 0.8350 p=0.O579 0 . 0 2 J 5 p = 0 . 0 1 8 8 ' 4.1000 p=0.9549 53 Uncommon C o u r t s h i p B e h a v i o u r s  F i r s t R e s p o n s e Upper a n d Lower m a l e s were c o m p a r e d w i t h r e s p e c t t o t h e i r f i r s t r e s p o n s e t o a g r a v i d f e m a l e - w h e t h e r t h i s r e s p o n s e was " z i g - z a g " , " b u t t " o r a g g r e s s i o n . No d i f f e r e n c e was e v i d e n t i n t h e i n i t i a l a p p r o a c h t o t h e d i f f e r e n t s i z e s o f f e m a l e o r t o t h e a n adromous m a r i n e f e m a l e s ( C h i - s q u a r e , p > 0 . 0 5 ) . The f i r s t r e s p o n s e a p p e a r s t o be e x p l o r a t o r y . N e s t M a i n t e n a n c e a f t e r I n i t i a l A p p r o a c h The p r e s e n c e of f e m a l e s a l m o s t a l w a y s i n i t i a t e d an a p p r o a c h by t h e m a l e . T h i s o f t e n w o u l d be f o l l o w e d by a r e t u r n t o t h e n e s t a n d a b o u t o f n e s t m a i n t e n a n c e . A f t e r t h e i n i t i a l a p p r o a c h t h e r e was no d i f f e r e n c e i n t h e f r e q u e n c y o f n e s t m a i n t e n a n c e w i t h r e s p e c t t o f e m a l e s i z e by m a l e s f r o m e i t h e r t h e u p p e r o r l o w e r S almon R i v e r ( p > 0.25, T a b l e 1 2 ) . Lower Salmon m a l e s , h o w e v e r , p e r f o r m e d n e s t m a i n t e n a n c e much l e s s f r e q u e n t l y a f t e r an i n i t i a l a p p r o a c h t o an a n a d r o m o u s m a r i n e f e m a l e (p < 0.005, T a b l e 13) t h a n a f t e r an i n i t i a l a p p r o a c h t o t h e i r own f e m a l e s . T h e r e was no d i f f e r e n c e i n t h e r e a c t i o n o f u p p e r Salmon m a l e s t o e i t h e r t h e i r own o r anadromous f e m a l e s (p > 0 . 2 5 ) . U p p e r Salmon m a l e s , h o w e v e r , p e r f o r m n e s t m a i n t e n a n c e a c t i v i t i e s more f r e q u e n t l y a f t e r an i n i t i a l a p p r o a c h t o an a nadromous f e m a l e t h a n do l o w e r Salmon m a l e s (p < 0.05, T a b l e 1 4 ) . T a b l e 12 Comparison of f r e q u e n c y of nest maintenance, a f t e r i n i t i a l approach to f emale, between males of two f r e s h w a t e r p o p u l a t i o n s . Females are from the male's own p o p u l a t i o n and the c a t e g o r i e s " l a r g e " and " s m a l l " a r e r e l a t i v e to the s i z e of the c o u r t i n g male. Lower Salmon males Upper Salmon males Large Small c h i - s q u a r e Large Small c h i - s q u a r e female female v a l u e and female female v a l u e and probab i 1 1 t y probab 1 1 i ty Nest maintenance 15 No nest maintenance 13 13 0.54 df = 1 p>0.25 12 13 0. 12 df = 1 p>0.25 T a b l e 13 Comparison of f r e q u e n c y of nest maintenance, a f t e r I n i t i a l approach to f emale, between males of two f r e s h w a t e r p o p u l a t i o n s d u r i n g c o u r t s h i p . Females a r e from t h e i r own p o p u l a t i o n and the mar'ine p o p u l a t l o n ( a n a s t e r i s k i n d i c a t e s a s i g n i f i c a n t d i f f e r e n c e ) . Lower Salmon males Upper Salmon males Lower Marine c h i - s q u a r e Salmon female v a l u e and female p r o b a b i l i t y Upper Marine c h i - s q u a r e Salmon female v a l u e and female p r o b a b i l i t y Nest maintenance 28 No n e s t maintenance 10 7.91 df « 1 p<0.005' 25 13 11 0.04 df « 1 5 p>0.25 T a b l e 14 Comparison of f r e q u e n c y of nest maintenance, a f t e r I n i t i a l approach to f emale, between males of two f r e s h w a t e r p o p u l a t i o n s d u r i n g c o u r t s h i p of marine fema1es(an a s t e r i s k i n d i c a t e s a s i g n i f i c a n t d1f f e r e n c e ). Marine females Lower Salmon ma 1 es Upper Salmon ma 1 es c h i - s q u a r e v a l u e and p r o b a b i 1 1 t y Nest maintenance No nest maintenance 11 4 .49 df * 1 p<0.05" 57 G l u e i n g a n d C r e e p i n g t h r o u g h U p p e r Salmon m a l e s " g l u e " more d u r i n g c o u r t s h i p t h a n l o w e r S a lmon m a l e s r e g a r d l e s s o f w h e t h e r t h e f e m a l e i s o f t h e i r own p o p u l a t i o n (p < 0.05, T a b l e 15) o r f r o m t h e anadromous p o p u l a t i o n ( p < 0 . 0 0 2 5 ) . The f r e q u e n c y o f " c r e e p i n g t h r o u g h " a p p e a r s t o be i n d e p e n d e n t of f e m a l e t y p e ( p > 0.1, T a b l e 1 5 ) . T h e r e i s no d i f f e r e n c e i n t h e f r e q u e n c y o f " g l u e i n g " o r " c r e e p i n g t h r o u g h " by e i t h e r p o p u l a t i o n o f m a l e s when c o u r t i n g t h e two f o r m s o f f e m a l e (p > 0.25, T a b l e 1 6 ) . N e s t M a i n t e n a n c e a f t e r F e m a l e f o l l o w s t o N e s t Lower Salmon m a l e s p e r f o r m n e s t m a i n t e n a n c e more f r e q u e n t l y when f o l l o w e d t o t h e n e s t by a s m a l l f e m a l e t h a n when f o l l o w e d by a l a r g e one (p < 0.05, T a b l e 1 7 ) . I n u p p e r S almon m a l e s t h i s b e h a v i o u r i s i n d e p e n d e n t o f f e m a l e s i z e (p > 0.25, T a b l e 1 7 ) . A f t e r an anadromous f e m a l e f o l l o w s t o t h e n e s t t h e r e i s no d i f f e r e n c e b e t w e e n m a l e s o f t h e two p o p u l a t i o n s w i t h r e s p e c t t o n e s t m a i n t e n a n c e (p > 0.25, T a b l e 1 8 ) . A f t e r f o l l o w i n g t o t h e n e s t , a n a d r o m o u s f e m a l e s s t i m u l a t e l o w e r S a l m o n m a l e s t o more n e s t m a i n t e n a n c e t h a n l a r g e f e m a l e s o f t h e i r own p o p u l a t i o n (p < 0.025, T a b l e 1 9 ) . O b s e r v a t i o n , h o w e v e r , showed t h a t t h e r e was a q u a l i t a t i v e d i f f e r e n c e i n t h i s b e h a v i o u r . N e s t m a i n t e n a n c e was p e r f o r m e d i n an a g i t a t e d m anner, much l i k e a d i s p l a c e m e n t a c t i v i t y , a n d a f t e r a m e a n d e r i n g l e a d t o t h e n e s t . T h i s b e h a v i o u r was n o t d i f f e r e n t i n t h e u p p e r S almon m a l e s (p > 0.1) n o r were t h e s e m a l e s T a b l e 15 Comparison of the f r e q u e n c y of " g l u e i n g " and " c r e e p i n g - t h r o u g h " between males of the upper and lower Salmon when c o u r t i n g t h e i r own fe m a l e s and females of the marine popu I a11on( an a s t e r i s k i n d i c a t e s a s i g n i f i c a n t d i f f e r e n c e ) . Female of own p o p u l a t i o n Female of marine p o p u l a t i o n Lower Upper c h i - s q u a r e Salmon Salmon v a l u e and male male p r o b a b i l i t y Lower Upper c h i - s q u a r e Salmon Salmon v a l u e and male male p r o b a b i l i t y G l u e i n g No g l u e i n g 12 13 3 .85 df = 1 p<0.05* 12 6.01 df «1 p<0.0025* C r e e p i n g 5 9 1.81 2 7 1.92 df=1 „ df*1 No c r e e p i n g 14 10 p>0.10 9 9 p>0.10 T a b l e 16 Comparison of f r e q u e n c y of " g l u e i n g " and "creep 1ng-through" d u r i n g c o u r t s h i p between f r e s h w a t e r males from two Salmon r i v e r p o p u l a t i o n s when c o u r t i n g females of t h e i r own p o p u l a t i o n and marine females. Lower Salmon males Upper Salmon males Lower Marine Salmon female fema1e c h i - s q u a r e Upper Marine c h i - s q u a r e v a l u e and Salmon female v a l u e and p r o b a b i l i t y female p r o b a b i l i t y G l u e i n g No g l u e i n g 12 0.29 df = 1 p>0.25 13 12 0. 18 df = 1 p>0.25 C r e e p i n g No c r e e p i n g 14 0. 26 df = 1 p>0.25 10 0.05 df = 1 p>0.25 60 T a b l e 17 Comparison of f r e q u e n c y of nest maintenance*, a f t e r the female f o l l o w s t o n e s t , between males of two f r e s h w a t e r p o p u l a t i o n s . C o u r t s h i p i s of d i f f e r e n t s i z e d females from the male's own p o p u l a t i o n and the c a t e g o r i e s " l a r g e " and " s m a l l " a r e r e l a t i v e t o male s i z e . An a s t e r i s k i n d i c a t e s a s i g n i f i c a n t d i f f e r e n c e . Lower Salmon males Upper Salmon males Large Smal1 female female c h i - s q u a r e Large Small c h i - s q u a r e v a l u e and female female v a l u e and p r o b a b i l i t y p r o b a b i l i t y Nest maintenance No nest maintenance 14 11 3.89 df =1 p<0.05* 12 9 0.43 df = 1 10 p>0.25 T a b l e 18 Comparison of f r e q u e n c y of nest maintenance, a f t e r female f o l l o w s t o n e s t , between males of two f r e s h w a t e r p o p u l a t i o n s . C o u r t s h i p 1s of marine females. Marine females Lower Salmon Upper Salmon c h i - s q u a r e v a l u e males males and p r o b a b i l i t y Nest maintenance 8 10 0.31 df =1 No nest maintenance 3 6 p>0.25 62 T a b l e 19 Comparison of nest maintenance, a f t e r female f o l l o w s to nest, between males of two f r e s h w a t e r p o p u l a t i o n s . C o u r t s h i p i s of l a r g e f emales from t h e i r own p o p u l a t i o n s and marine females. An a s t e r i s k i n d i c a t e s a s i g n i f i c a n t d i f f e r e n c e . Lower Salmon males Upper Salmon males L a r g e Marine c h i - s q u a r e Large female female v a l u e and female p r o b a b i 1 i ty Marine c h i - s q u a r e female v a l u e and probab i 1 i ty Nest maintenance No n e s t maintenance 14 6.11 df * 1 p<0.025* 12 10 2.29 df = 1 p>0. 1 Comparison as above w i t h small females. Smal 1 fema1e Mar 1ne fema1e Smal 1 female Mar i ne fema1e Nest maintenance No nest maintenance 1 1 8 0.66 9 df = 1 3 p>0.25 10 10 0.80 df •= 1 p>0.25 63 d i f f e r e n t i n t h e i r c o u r t s h i p s o f anadromous m a r i n e f e m a l e s c o m p a r e d t o s m a l l f e m a l e s o f t h e i r own p o p u l a t i o n s ( p > 0 . 2 5 ) . Summary The c o u r t s h i p e x p e r i m e n t s c l e a r l y i n d i c a t e t h a t t h e r e a r e q u a n t i t a t i v e d i f f e r e n c e s i n c o u r t s h i p b e h a v i o u r b e t w e e n m a l e f r e s h w a t e r s t i c k l e b a c k s f r o m t h e u p p e r a nd l o w e r S almon R i v e r . G e n e r a l l y , h o w e v e r , t h e c o u r t s h i p s e q u e n c e o f male f r e s h w a t e r s t i c k l e b a c k s i s t h e same. The f i r s t r e s p o n s e o f t h e m a l e i n v o l v e s an i n i t i a l i n s p e c t i o n o f an a p p r o a c h i n g f e m a l e . The r e s u l t o f t h i s i n s p e c t i o n d e c i d e s - t h e s u b s e q u e n t c o u r s e o f c o u r t s h i p . U s u a l l y t h e m a l e r e t u r n s t o t h e n e s t a n d t h e r e a b o u t o f n e s t m a i n t e n a n c e b e h a v i o u r f o l l o w s . I n e n c o u n t e r s w i t h a n a dromous m a r i n e f e m a l e s , h o w e v e r , l o w e r S almon m a l e s r e d u c e n e s t a c t i v i t y r e l a t i v e t o t h e i r own f e m a l e s , w h e r e a s u p p e r S a l m o n m a l e s i n c r e a s e n e s t a c t i v i t y r e l a t i v e t o t h e i r own f e m a l e s . . The f r e q u e n c y o f " g l u e i n g " a n d " c r e e p i n g - t h r o u g h " a p p e a r s t o be i n d e p e n d e n t o f f e m a l e t y p e i n b o t h f r e s h w a t e r p o p u l a t i o n s . The f r e q u e n c y o f c o u r t s h i p e v e n t s a f t e r t h e i n i t i a l a p p r o a c h , h o w e v e r , a r e d e p e n d e n t on f e m a l e s i z e . A f t e r t h e i n i t i a l b o u t o f n e s t m a i n t e n a n c e , t h e c l a s s i c z i g - z a g c o u r t s h i p b e g i n s a n d f e m a l e s o f t h e a p p r o p r i a t e s i z e e l i c i t more z i g - z a g c o u r t s h i p a n d l e s s a g g r e s s i o n t h a n o t h e r f e m a l e s . I n t h e l a t e r c o u r t s h i p s t a g e s l o w e r Salmon m a l e s p e r f o r m n o r m a l n e s t a c t i v i t y more f r e q u e n t l y when f o l l o w e d t o t h e n e s t by s m a l l ( r e l a t i v e t o t h e m a l e ) f e m a l e s ; i n c o n t r a s t , n e s t a c t i v i t y i s a b n o r m a l w i t h an anadromous m a r i n e f e m a l e . U p p e r Salmon 64 males prefer to mate with larger females than lower Salmon males. Lower Salmon males appear to avoid courting, and are more aggressive to, females larger than they are. 65 DISCUSSION My r e s u l t s d e m o n s t r a t e t h a t , r e l a t i v e t o f e m a l e s i z e , m a t i n g i s n o t random i n f r e s h w a t e r s t i c k l e b a c k p o p u l a t i o n s f r o m t h e u p p e r a n d l o w e r S a l m o n R i v e r . I n t h e l o w e r r i v e r m a t i n g may o c c u r b e t w e e n m a r i n e and f r e s h w a t e r s t i c k l e b a c k s b u t m o r p h o l o g i c a l e v i d e n c e i n d i c a t e s t h a t s u c h m a t i n g s a r e r a r e ( J . D . M c P h a i 1 , p e r s . c o m m . ) . The r e s u l t s o f l a b o r a t o r y e x p e r i m e n t s p e r m i t i n f e r e n c e s a b o u t n a t u r a l s i t u a t i o n s ; h o w e v e r , i t i s n o t known f o r c e r t a i n t h a t f r e s h w a t e r m a l e s i n n a t u r e e v e r h a v e a c h o i c e b e t w e e n f e m a l e s . T h e r e a r e , h o w e v e r , some i n d i c a t i o n s t h a t t h i s i s p o s s i b l e . U n d e r n e a r - n a t u r a l c o n d i t i o n s i n a man-made pond I o b s e r v e d u p p e r S a l m o n f e m a l e s t i c k l e b a c k s a p p r o a c h m a l e t e r r i t o r i e s i n g r o u p s . I n a d d i t i o n , m a r i n e and f r e s h w a t e r f e m a l e s a r e commonly t a k e n t o g e t h e r i n t r a p s i n t h e l o w e r r i v e r . T h e s e o b s e r v a t i o n s a g r e e w i t h t h e r e p o r t s o f o t h e r w o r k e r s ( K y n a r d , 1 9 7 9 ; A . B r e t t , p e r s . comm.). One m a t i n g o b s e r v e d i n t h e p o nd i n v o l v e d one l a r g e a n d two s m a l l f e m a l e s . They a p p r o a c h e d t h e m a l e ' s t e r r i t o r y s i m u l t a n e o u s l y . The m a l e a p p r o a c h e d a n d d i r e c t e d most o f h i s z i g - z a g c o u r t s h i p t o t h e l a r g e f e m a l e . A f t e r a b r i e f b o u t o f c o u r t s h i p , i n v o l v i n g no a g g r e s s i o n , t h e f e m a l e f o l l o w e d t o t h e n e s t , e n t e r e d and spawned. The s m a l l e r f e m a l e s a l s o f o l l o w e d , s l i g h t l y b e h i n d t h e l a r g e r f e m a l e , a n d w a i t e d n e a r t h e n e s t e n t r a n c e u n t i l t h e m a t i n g was c o m p l e t e d . The m a l e t h e n c h a s e d t h e s m a l l f e m a l e s o f f . The n e s t was c o l l e c t e d a n d f o u n d t o c o n t a i n f i v e c l u t c h e s o f e g g s a t v a r i o u s s t a g e s o f d e v e l o p m e n t i n c l u d i n g ' w r i g g l e r s ' . 66 T h i s s u g g e s t s t h a t t h e m ale was c l o s e t o s w i t c h i n g i n t o t h e p a r e n t a l p h a s e , y e t e v e n a t t h i s l a t e s t a g e i n t h e c o u r t s h i p p h a s e t h e m a l e a p p a r e n t l y shows a p r e f e r e n c e f o r l a r g e f e m a l e s . T h e r e a r e c l e a r d i f f e r e n c e s i n f e m a l e s i z e b e t w e e n t h e s t i c k l e b a c k p o p u l a t i o n s o f t h e u p p e r and l o w e r S almon R i v e r . The mean s i z e o f b o t h m a l e s a n d f e m a l e s v a r i e s somewhat f r o m y e a r t o y e a r b u t t h e t r e n d i s t h e same - b r e e d i n g f e m a l e s i n t h e u p p e r r i v e r a r e on a v e r a g e l a r g e r t h a n b r e e d i n g m a l e s , w h e r e a s t h e r e v e r s e i s t r u e i n t h e l o w e r r i v e r . I f t h i s d i f f e r e n c e i n f e m a l e s i z e were due t o f o o d a v a i l a b i l i t y , t h e n m a l e s s h o u l d show a s i m i l a r d i f f e r e n c e . They do n o t . I t i s p o s s i b l e t h a t m a l e s a n d f e m a l e s f r o m t h e d i f f e r e n t p a r t s o f t h e r i v e r e x p l o i t d i f f e r e n t f o o d s . T h i s seems u n l i k e l y s i n c e no f e e d i n g d i f f e r e n c e s were o b s e r v e d i n t h e l a b o r a t o r y a n d t h e s t o m a c h c o n t e n t s o f w i l d c a u g h t f i s h show r o u g h l y t h e same mix o f b e n t h i c o r g a n i s m s i n b o t h s e x e s . A l s o , Hagen ( 1 9 6 7 ) e x a m i n e d s t o m a c h c o n t e n t s f r o m t h e n e a r b y L i t t l e C a m p b e l l R i v e r and showed t h a t f r e s h w a t e r s t i c k l e b a c k s o f b o t h s e x e s f e d on b e n t h i c o r g a n i s m s . I n a d d i t i o n , B e n t z e n (1982) f o u n d t h a t b e n t h i c s t i c k l e b a c k s i n E n o s L a k e , B r i t i s h C o l u m b i a , e x h i b i t e d no s e x u a l d i m o r p h i s m i n t h e i r f e e d i n g b e h a v i o u r . A t p r e s e n t t h e q u e s t i o n o f w h e t h e r t h e / f e m a l e s i n t h e u p p e r S a lmon R i v e r a r e on a v e r a g e o l d e r t h a n t h o s e i n t h e l o w e r r i v e r c a n n o t be a n s w e r e d . The p r o b l e m s a s s o c i a t e d w i t h a g e i n g s t i c k l e b a c k s a r e , so f a r , i n t r a c t a b l e . O t h e r w o r k e r s h a v e a t t e m p t e d t o age s t i c k l e b a c k s f r o m o t o l i t h s ; h o w e v e r , no one h a s v e r i f i e d a g e s by c h e c k i n g them a g a i n s t f i s h o f known age and 67 b r e e d i n g c o n d i t i o n . My own e x p e r i e n c e was t h a t s t i c k l e b a c k o t o l i t h s a r e n o t d i f f i c u l t t o r e a d b u t a r e e x t r e m e l y d i f f i c u l t t o i n t e r p r e t ( A p p e n d i x 1). Blouw and Hagen (1981) w o r k i n g w i t h A p e l t e s came t o a s i m i l a r c o n c l u s i o n . The f a c t t h a t l a r g e f e m a l e s i n t h e u p p e r r i v e r may be o l d e r t h a n s m a l l f e m a l e s i n t h e l o w e r r i v e r makes l i t t l e d i f f e r e n c e t o t h e b a s i c h y p o t h e s i s t h a t f e m a l e s i z e i s a m a j o r component i n m ale mate p r e f e r e n c e . H o w e v e r , i n a r e a s s u c h a s t h e u p p e r S a l m o n , i f t h e s i z e r a n g e o f m a t u r e f e m a l e s s i m p l y r e f l e c t e d a g r e a t e r l i k e l i h o o d o f f e m a l e s s u r v i v i n g f o r s e v e r a l s p a w n i n g s e a s o n s , we w o u l d e x p e c t r e l a t i v e l y few f e m a l e s i n t h e l a r g e s t s i z e c l a s s . T h i s i s n o t s o . I n b o t h t h e u p p e r Salmon a n d u p p e r L i t t l e C a m p b e l l t h e r e a r e a s many, a n d s o m e t i m e s more, l a r g e f e m a l e s t h a n t h e r e a r e s m a l l f e m a l e s . T h i s s t r o n g l y s u g g e s t s t h a t i n t h e s e p o p u l a t i o n s a good p r o p o r t i o n o f t h e f e m a l e s a r e d e l a y i n g m a t u r i t y . T h i s r a i s e s t h e q u e s t i o n o f how g e n e r a l t h i s phenomenon i s i n t h e t h r e e s p i n e s t i c k l e b a c k . S e x u a l s i z e d i m o r p h i s m i n G . a c u l e a t u s , i f i t o c c u r s a t a l l , i s u s u a l l y i n f a v o u r o f l a r g e r f e m a l e s ( J . D . M c P h a i l , p e r s . c o m m . ) . T h i s i s c o n s i s t e n t w i t h t h e e x p e c t a t i o n t h a t , i f a l l e l s e i s e q u a l , m a l e s t i c k l e b a c k s s h o u l d a t t e m p t t o mate w i t h t h e l a r g e s t f e m a l e s p o s s i b l e . Where m a r i n e and f r e s h w a t e r G a s t e r o s t e u s o c c u r t o g e t h e r , a s i n t h e l o w e r Salmon R i v e r , t h e f r e s h w a t e r f e m a l e s a r e g e n e r a l l y s m a l l e r t h a n t h e m a l e s . T h u s , i t a p p e a r s t h a t t h e p r e s e n c e o f t h e m a r i n e f o r m i n t h e l o w e r r i v e r s i g n i f i c a n t l y a l t e r s t h e s e l e c t i v e f o r c e s o p e r a t i n g on f e m a l e s i z e . S i n c e m a l e s i n t h e u p p e r and 68 lower river are the same size, the presence of the marine form apparently has not affected male si z e . The reproductive success of a mating pair may be affected by the extent to which their genotypes and their capacities to extend reproductive e f f o r t , especially in parental care, complement one another, that i s , on their 'genetic complementarity' (Halliday,1983). If the males of the upper and lower areas of the Salmon River are choosing females, how do they recognize a suitable mate? I suggest that the primary clue males use to assess the s u i t a b i l i t y of a potential mate i s s i z e . In the upper Salmon, males choose the largest, and therefore the most fecund, females. In contrast, the lower Salmon males choose small females. Again, they use size as a clue but for a d i f f e r e n t reason. Here size i s a r e l i a b l e clue to female genome and thus size discrimination acts as an i s o l a t i n g mechanism preventing matings between sticklebacks from two d i f f e r e n t gene pools that are adapted to two s t r i k i n g l y d i f f e r e n t environments. Presumably, hybrids re s u l t i n g from mating between marine and freshwater types w i l l be at a disadvantage. They are morphologically intermediate (Hagen, 1967) and consequently probably not well adapted to either parental habitat. Bentzen (1982) showed that hybrids between a sympatric pair of Gasterosteus species were intermediate in trophic morphology and also intermediate in feeding performance. His comparison involved benthic and limnetic sticklebacks from Enos Lake, B r i t i s h Columbia; however, the marine and freshwater forms in the Salmon River d i f f e r in equivalent d e t a i l s of trophic 69 morphology ( i . e . l e n g t h and spacing of g i l l r a k e r s ) . Consequently, i t i s reasonable to assume that h y b r i d s between these forms would a l s o be intermediate i n feeding e f f i c i e n c y . In Japan, Yoshiharu and Tamura (1984) found that fanning e f f i c i e n c y was reduced i n F1 h y b r i d s between marine and freshwater G a s t e r o s t e u s . Reduced fanning e f f i c i e n c y may w e l l r e s u l t i n reduced r e p r o d u c t i v e success. The p o i n t of r e f e r e n c e males use to d i s t i n g u i s h s i z e i s s p e c u l a t i v e , but using t h e i r own s i z e f o r comparison i s a p o s s i b i l i t y . P a r a l l e l swimming a l o n g s i d e the females, and swimming near the females with the head o r i e n t e d towards them, i s a common f e a t u r e of the e a r l y c o u r t s h i p p e r i o d . T h i s may serve to gauge the r e l a t i v e s i z e of a p o t e n t i a l mate. P a r a l l e l swimming i s common i n other t e r r i t o r i a l f i s h such as c i c h l i d s and appears to be used to assess a r i v a l ' s s t r e n g t h at the t e r r i t o r i a l boundaries (Fryer and l i e s , 1972). In red deer, p a r a l l e l walking occurs before male-male encounters ( C l u t t o n -Brock et a l . , 1979) and may serve a s i m i l a r f u n c t i o n . The demonstration that i n Gasterosteus mating i s not random pr o v i d e s necessary, but not s u f f i c i e n t , evidence that male mate ch o i c e occurs i n s t i c k l e b a c k s . There i s a conceptual d i f f i c u l t y with the term "mate c h o i c e " . The r a t i o n a l e i n t h i s t h e s i s r e s t s on the d e f i n i t i o n p r o v i d e d by H a l l i d a y (1983), "Mate c h o i c e may be o p e r a t i o n a l l y d e f i n e d as any p a t t e r n of behaviour, shown by members of one sex, that leads to t h e i r being more l i k e l y to mate with c e r t a i n members of the opp o s i t e sex r a t h e r than o t h e r s . " As H a l l i d a y argues, the e v o l u t i o n a r y consequences do 70 not depend on whether a t r u e p r e f e r e n c e i s i n v o l v e d , but on whether d i f f e r e n c e s i n b e h a v i o u r a r e c o r r e l a t e d w i t h d i f f e r e n c e s i n r e p r o d u c t i v e s u c c e s s . C l u t t o n - B r o c k and Harvey (1979) p o i n t out t h a t the d i r e c t assessment of d i f f e r e n c e s i n r e p r o d u c t i v e s u c c e s s i s o f t e n u n a t t a i n a b l e ; however, we can make i n f e r e n c e s i f t h e r e i s e v i d e n c e t h a t the t r a i t s b e i n g c o n s i d e r e d "show a c l o s e l y d e s i g n e d f i t t o some problem p r e s e n t e d by the a n i m a l ' s environment". Non-random mating c o u l d a l s o r e s u l t from c i r c u m s t a n c e s o t h e r than male mate c h o i c e ( e . g . male-male c o m p e t i t i o n or female mate c h o i c e ) . In G a s t e r o s t e u s , however,male c o u r t s h i p i s c o n s p i c u o u s and w e l l d e s c r i b e d . For t h i s reason t h i s s tudy c o n c e n t r a t e s on male c o u r t s h i p . Geographic v a r i a t i o n i n c o u r t s h i p b e h a v i o u r i s known t o o c c u r i n o t h e r f i s h s p e c i e s ( B a l l i n , 1972) and, i n some c a s e s , c o u r t s h i p d i f f e r e n c e s can be c o r r e l a t e d w i t h d i f f e r e n c e s i n s i z e between the p o p u l a t i o n s (de Boer,1981). L i l e y (1966) p r e d i c t e d t h a t s e l e c t i o n w i l l f a v o u r the e a r l y sequences of c o u r t s h i p b e h a v i o u r because t h i s p r o v i d e s the most e c o n o m i c a l means of mate d i s c r i m i n a t i o n . My r e s u l t s show t h a t , a f t e r an i n i t i a l i n s p e c t i o n which i s a p r e l u d e t o a l l c o u r t s h i p , pronounced d i f f e r e n c e s between upper and lower r i v e r males do occur e a r l y i n c o u r t s h i p . Salmon R i v e r males v a r y t h e i r c o u r t s h i p depending on female s i z e . In c h o i c e s i t u a t i o n s the z i g - z a g bouts of lower Salmon males a r e more v i g o r o u s and p r o l o n g e d when c o u r t i n g s m a l l e r f e m a l e s . In a d d i t i o n , they d i r e c t t h e i r a g g r e s s i v e bouts c h i e f l y t o l a r g e r females. In c o n t r a s t , upper Salmon males d i r e c t more z i g - z a g s per u n i t time 71 to females l a r g e r than they are and the s m a l l e r females are v i r t u a l l y ignored. There i s no d i f f e r e n c e i n upper Salmon males in the amount of a g g r e s s i o n they d i s p l a y to e i t h e r s i z e of female. The a n a l y s i s of c o u r t s h i p c y c l e s i n d i c a t e s that i n c h o i c e s i t u a t i o n s , i n both p o p u l a t i o n s , u n s u i t a b l e mates do not p e r s i s t i n t o the l a t e r c y c l e s . T h i s may be due to e i t h e r a l a c k of s t i m u l a t i o n , or i n c r e a s e d a g g r e s s i o n , or both. The vigour of the a g g r e s s i o n shown to l a r g e females by lower Salmon males may r e f l e c t the f a c t t h a t , in t h i s area, there i s a great d e a l at stake i n the choice of a s u i t a b l y - s i z e d mate. Males from the d i f f e r e n t areas on the Salmon River a l s o show d i f f e r e n c e s i n t h e i r c o u r t s h i p of marine females. The l a r g e marine females have a remarkable e f f e c t on the upper Salmon males. In t h e i r presence, upper Salmon males z i g - z a g more v i g o r o u s l y , and f o r longer p e r i o d s , than do lower Salmon males under s i m i l a r circumstances. However, upper Salmon males a l s o i n c r e a s e t h e i r r a t e of a g g r e s s i v e a t t a c k s . The lower Salmon males, i n c o n t r a s t , appear to reduce both t h e i r c o u r t s h i p and a g g r e s s i v e behaviour i n the presence of marine females. A f t e r the i n i t i a l encounter they perform l e s s nest maintenance behaviour and they p r o l o n g the l e a d / f o l l o w sequence by l e a d i n g the female i n a meandering f a s h i o n . Marine females are g e n e r a l l y at the upper s i z e l i m i t f o r upper Salmon freshwater females. Perhaps, upper Salmon males p e r c e i v e marine females as a super-normal s t i m u l u s . T h i s causes not only a q u a n t i t a t i v e change i n the r a t e of z i g - z a g g i n g but a q u a l i t a t i v e change in male c o u r t s h i p , p a r t i c u l a r l y i n behaviours that may s i g n a l 72 parental competence. It was not possible to quantify the vigour of nest maintenance behaviour, but i t was apparent to the observer that i t increased in the presence of a marine female. From the time a male becomes aware of the presence of a female to the point where leading begins i s p o t e n t i a l l y a period of assessment and stimulation. In species where the male performs a l l the parental care, demonstrations of parental competence are common. In giant water bugs the males brood eggs that are attached to their backs by females, and they perform "push-ups" to aerate the eggs during incubation (Smith,1979). This "push-up" behaviour i s also a feature of courtship and is performed even though no eggs are yet attached to the male's back. The metabolic costs associated with the e f f o r t , and the oxygen depletion involved in t h i s behaviour, suggest that i t i s an important part of the courtship sequence. S i m i l a r l y , during courtship, male mouth-brooding c i c h l i d s often lower the f l o o r of the mouth with what appears to be the same motion used in egg-r o l l i n g during incubation (personal experience). This also may be a parental competence display. If nest maintenance behaviour during courtship i s a display of parental competence in sticklebacks, then differences in t h i s behaviour between males from the upper and lower river imply that they have di f f e r e n t preferences for female si z e . After the i n i t i a l approach to females of their own population, both upper and lower Salmon males usually return to their nest and perform a bout of nest maintenance behaviour. In the presence of marine females lower Salmon males, after an i n i t i a l approach, perform 73 t h i s b e h a v i o u r much l e s s f r e q u e n t l y than they do t o t h e i r own fe m a l e s . In c o n t r a s t , upper Salmon males do not d i f f e r i n t h i s r e s p e c t compared t o t h e i r performance when c o u r t i n g t h e i r own fe m a l e s . The f r e q u e n c y of " g l u e i n g " and " c r e e p i n g - t h r o u g h " i n both p o p u l a t i o n s appears t o be independent of female s i z e . A f t e r a female f o l l o w s t o the n e s t , males o f t e n p e r f o r m another bout of n e s t maintenance and then r e t u r n t o show the w a i t i n g female the n e s t e n t r a n c e . T h i s second bout of nest maintenance i s performed most f r e q u e n t l y by lower Salmon males when a s m a l l female i s p r e s e n t a t the nes t e n t r a n c e . T h i s nest a c t i v i t y i s abnormal when a marine female f o l l o w s t o the nest and t h i s abnormal b e h a v i o u r o f t e n r e s u l t s i n the p a r t i a l d e s t r u c t i o n of the n e s t . Upper Salmon males show no d i f f e r e n c e s i n t h i s b e h a v i o u r when c o u r t i n g d i f f e r e n t s i z e s , or t y p e s , of fem a l e s . To summarize, the comparison of c o u r t s h i p a c t i v i t i e s of upper and lower Salmon males suggest t h a t , a f t e r the i n i t i a l a ssessment, the r e l a t i v e f r e q u e n c i e s of some b e h a v i o u r p a t t e r n s a r e s t r o n g l y a s s o c i a t e d w i t h e i t h e r the r e l a t i v e s i z e or genome of the female. Other k i n d s of b e h a v i o u r seem t o be independent of the type of female c o u r t e d . ' G e n e r a l l y , males d i f f e r most i n t h e i r z i g - z a g and a g g r e s s i v e b e h a v i o u r s , b o t h i n number of bouts per u n i t time and i n the l e n g t h of the b o u t s . The Mann-Whitney t e s t used f o r the comparisons i s a c o n s e r v a t i v e t e s t of d i f f e r e n c e s between s t a t i s t i c a l p o p u l a t i o n s and a l s o t a k e s i n t o account the magnitude of the i n d i v i d u a l d i f f e r e n c e s . The fr e q u e n c y of o c c u r r e n c e of some o t h e r b e h a v i o u r s t h a t were 7 4 c o m p a r e d a l s o s h o w e d t h a t t h e m a l e s d i f f e r e d i n t h e i r r e s p o n s e w i t h r e g a r d t o n e s t m a i n t e n a n c e b e h a v i o u r . T h u s , m a l e s o f t h e t w o f r e s h w a t e r s t i c k l e b a c k p o p u l a t i o n s i n t h e S a l m o n R i v e r d i f f e r i n t h e i r b e h a v i o u r a l c h a r a c t e r i s t i c s . T h e o r i g i n o f t h e s e d i f f e r e n c e s i s s p e c u l a t i v e . M a r i n e s t i c k l e b a c k s a p p a r e n t l y i n v a d e d f r e s h w a t e r r e p e a t e d l y ( B e l l , 1 9 8 4 ) . T h e m o s t r e c e n t i n v a s i o n s s t a r t e d a f t e r t h e g l a c i a l r e t r e a t a b o u t 1 2 , 0 0 0 y e a r s a g o . P r e s u m a b l y , t h e a n a d r o m o u s m a r i n e f o r m d i s p e r s e d p o s t g l a c i a l l y f r o m i c e - f r e e a r e a s a n d i n d e p e n d e n t l y p e n e t r a t e d f r e s h w a t e r i n m a n y a r e a s . T h e s e i n v a s i o n s g a v e r i s e t o t h e f r e s h w a t e r f o r m o f G a s t e r o s t e u s . T h e f r e s h w a t e r f o r m t h e n e v o l v e d t o e x p l o i t l o c a l e n v i r o n m e n t a l c o n d i t i o n s ( L a v i n a n d M c P h a i l , 1 9 8 5 ) . C o n t i n u i n g i n c u r s i o n s o f a n a d r o m o u s s t i c k l e b a c k s d u r i n g t h e b r e e d i n g s e a s o n w o u l d d i l u t e t h e s e l o c a l a d a p t a t i o n s i f g e n e f l o w o c c u r r e d b e t w e e n r e s i d e n t a n d m a r i n e s t i c k l e b a c k s . D o b z h a n s k y ( 1 9 5 1 ) p o i n t e d o u t t h a t , i f h y b r i d s a r e a t a d i s a d v a n t a g e r e l a t i v e t o t h e " p u r e " p a r e n t a l f o r m , p r e - m a t i n g m e c h a n i s m s s h o u l d d e v e l o p t h a t p r e v e n t g e n e f l o w . T h e s e m e c h a n i s m s s h o u l d d e v e l o p i n a r e a s o f c o n t a c t b u t n o t i n a r e a s o f a l l o p a t r y . I h a v e a l r e a d y d i s c u s s e d p o s s i b l e d i s a d v a n t a g e s o f h y b r i d s b e t w e e n t h e a n a d r o m o u s a n d f r e s h w a t e r s t i c k l e b a c k s . C o n s e q u e n t l y , t h e c o n d i t i o n s n e c e s s a r y f o r r e i n f o r c i n g s e l e c t i o n t o o c c u r a p p e a r t o e x i s t i n t h e S a l m o n R i v e r . H a g e n ( 1 9 6 7 ) s t a t e d t h a t m a r i n e a n d f r e s h w a t e r s t i c k l e b a c k s i n t h e L i t t l e C a m p b e l l R i v e r w e r e r e p r o d u c t i v e l y i s o l a t e d a n d t h u s t h a t t h e y f u l f i l l e d M a y r ' s ( 1 9 6 3 ) b i o l o g i c a l s p e c i e s d e f i n i t i o n ; h o w e v e r H a g e n c o u l d f i n d n o e v i d e n c e o f 75 e t h o l o g i c a l i s o l a t i n g m e c h a n i s m s . R e c e n t l y M c P h a i l a n d Hay ( 1 9 8 3 ) d e m o n s t r a t e d t h a t t h e r e a r e d i f f e r e n c e s i n m a l e c o u r t s h i p b e h a v i o u r b e t w e e n t h e f r e s h w a t e r a n d m a r i n e s t i c k l e b a c k s i n t h e L i t t l e C a m p b e l l R i v e r . A l t h o u g h p o s i t i v e a s s o r t a t i v e m a t i n g c l e a r l y o c c u r s i n t h i s s y s t e m ( H a y , 1 9 6 9 ) , m i s m a t i n g s s t i l l o c c u r b e c a u s e f e m a l e s do n o t d i s c r i m i n a t e s t r o n g l y b e t w e e n m a l e t y p e s ( H a g e n , 1967) I n t h e S a l m o n R i v e r , my r e s u l t s s t r o n g l y s u g g e s t t h a t e t h o l o g i c a l d i f f e r e n c e s e x i s t b e t w e e n m a l e s f r o m t h e l o w e r a n d u p p e r r i v e r . T h i s i s c o n s i s t e n t w i t h a r e i n f o r c i n g s e l e c t i o n a r g u m e n t . A p p a r e n t l y , f r e s h w a t e r m a l e s i n t h e l o w e r S a l m o n R i v e r d i s t i n g u i s h b e t w e e n a n a d r o m o u s m a r i n e a n d f r e s h w a t e r f e m a l e s on t h e b a s i s o f s i z e . I n c o n t r a s t t o l o w e r S a l m o n m a l e s , u p p e r r i v e r m a l e s do n o t f a c e t h e same c o n s t r a i n t s on m a t i n g w i t h l a r g e f e m a l e s . I n t h i s a r e a t h e r e a r e no a n a d r o m o u s m a r i n e f e m a l e s , t h u s t h e r e i s no p e n a l t y a t t a c h e d t o m a t i n g w i t h a f e m a l e l a r g e r t h a n o n e s e l f . R e l a x a t i o n o f t h i s c o n s t r a i n t a l l o w s u p p e r r i v e r m a l e s t o i n c r e a s e t h e i r r e p r o d u c t i v e p o t e n t i a l by d e v e l o p i n g a p r e f e r e n c e f o r t h e l a r g e s t f e m a l e s i n t h e i r own p o p u l a t i o n . 76 REFERENCES CITED A s h l e y , K.W. and D . L . G a r l i n g , J r . 1980. I m p r o v e d methods f o r p r e p a r i n g p e c t o r a l s p i n e s e c t i o n s o f c h a n n e l c a t f i s h f o r age d e t e r m i n a t i o n . The P r o g r e s s i v e F i s h - C u l t u r a l i s t 4 2:80-81 . B a l l i n , P . J . 1972. G e o g r a p h i c v a r i a t i o n i n c o u r t s h i p b e h a v i o u r o f t h e g u p p y , P o e c i l i a r e t i c u l a t a . M.Sc. T h e s i s , D e p t . o f Z o o l o g y , U n i v . B . C . 135 pp. B a r l o w , G.W. 1969. E f f e c t o f r e l a t i v e s i z e o f mate on c o l o r p a t t e r n s i n a m o u t h b r e e d i n g c i c h l i d f i s h , T i l a p i a m e l a n o t h e r o n . Commun. i n Behav. B i o l . 4:71-78. B a r l o w , G.W. a n d R . F . G r e e n . 1970. The p r o b l e m s o f a p p e a s e m e n t an d o f s e x u a l r o l e s i n t h e c o u r t s h i p b e h a v i o u r o f t h e b l a c k c h i n m o u t h b r e e d e r , T i l a p i a m e l a n o t h e r o n ( P i s c e s : C i c h l i d a e ) . B e h a v i o u r 3 6 : 8 4 - 1 1 5 . Bateman, A . J . 1948. I n t r a - s e x u a l s e l e c t i o n i n D r o s o p h i l a . H e r e d i t y 2:349-368. B a y l i s , J.R. 1976. A q u a n t i t a t i v e s t u d y of^ l o n g - t e r m c o u r t s h i p : 1. E t h o l o g i c a l i s o l a t i o n b e t w een s y m p a t r i c p o p u l a t i o n s o f t h e M i d a s c i c h l i d , C i c h l a s o m a c i t r i n e l l a , a n d t h e a r r o w c i c h l i d C . z a l i o s u m . B e h a v i o u r 5 9 : 5 9 - 6 9 . B e l l , M.A. 1984. E v o l u t i o n a r y p h e n e t i c s a n d g e n e t i c s . The t h r e e s p i n e s t i c k l e b a c k , G a s t e r o s t e u s a c u l e a t u s , a n d r e l a t e d s p e c i e s , pp.431-458 i n E v o l u t i o n a r y G e n e t i c s o f F i s h e s , B . J . T u r n e r ( e d . ) , P l e n u m P r e s s , New Y o r k , 636 pp. B e n t z e n , P. 1982. S p e c i a l i z a t i o n f o r a l t e r n a t e t r o p h i c n i c h e s by two f o r m s o f t h r e e s p i n e s t i c k l e b a c k G a s t e r o s t e u s , c o -e x i s t i n g i n Enos L a k e , V a n c o u v e r I s l a n d . M.Sc. T h e s i s , D e p t . o f Z o o l o g y , U n i v . B . C . B e n t z e n , P. a n d J.D. M c P h a i l . 1984. E c o l o g y and e v o l u t i o n o f s y m p a t r i c s t i c k l e b a c k s ( G a s t e r o s t e u s ) : s p e c i a l i z a t i o n f o r a l t e r n a t i v e t r o p h i c n i c h e s i n t h e E n o s L a k e s p e c i e s p a i r . C an. J . Z o o l . 6 2 : 2 2 8 0 - 2 2 8 6 . 77 B e r v e n , K.A. 1981. M a t e c h o i c e i n t h e wood f r o g : Rana s y l v a t i c a . E v o l u t i o n 3 5 : 7 0 7 - 7 2 2 . B l a c k e r , R.W. 1974. R e c e n t a d v a n c e s i n o t o l i t h s t u d i e s i n Sea F i s h e r i e s R e s e a r c h , F . R . H a r d e r - J o n e s ( e d . ) , E l e k S c i e n c e , L o n d o n . B l o u w , D.M. a n d D.W.Hagen 1981. E c o l o g y o f t h e f o u r s p i n e s t i c k l e b a c k A p e l t e s q u a d r a c u s w i t h r e s p e c t t o a p o l y m o r p h i s m f o r d o r s a l s p i n e number. Can. J . Z o o l . 59: 1677-1692. B o e r , B.A. d e , 1981. I n f l u e n c e o f p o p u l a t i o n d e n s i t y on t e r r i t o r i a l , c o u r t i n g a nd s p a w n i n g b e h a v i o u r o f male C h r o m i s c y a n e a ( P o m a c e n t r i d a e ) . B e h a v i o u r 7 7 : 9 9 - 1 2 0 . B r o w n , L. 1981. P a t t e r n s o f f e m a l e c h o i c e i n m o t t l e d s c u l p i n s ( C o t t i d a e , T e l e o s t e i ) . A n i m . B e h a v . 2 9 : 3 7 5 - 3 8 2 . Campana, S.E. a n d J . D . N e i l s o n . 1982. D a i l y g r o w t h i n c r e m e n t s i n o t o l i t h s o f t h e s t a r r y f l o u n d e r ( P l a t i c h t h y s s t e l l a t u s ) an d t h e i n f l u e n c e s o f some e n v i r o n m e n t a l v a r i a b l e s i n t h e i r p r o d u c t i o n . Can. J . F i s h . A q u a t . S c i . 3 9 : 9 3 7 - 0 4 2 . C h r i s t y , J.H. 1983. F e m a l e c h o i c e i n t h e r e s o u r c e - d e f e n c e m a t i n g s y s t e m o f t h e Sand F i d d l e r c r a b , Uca p u g i l a t o r . B e h a v . E c o l . S o c i o b i o l . 1 2:169-180. C o o k e , F. a n d C M . M c N a l l y . 1975. M a t e s e l e c t i o n a n d c o l o u r p r e f e r e n c e i n l e s s e r snow g e e s e . B e h a v i o u r 5 3 : 1 5 1 - 1 7 0 . C l u t t o n - B r o c k , T.H. a n d P.H.Harvey 1979. C o m p a r i s o n a n d a d a p t i o n . P r o c . R. S o c . L o n d . B . 2 0 5 : 5 4 7 - 5 6 5 . C l u t t o n - B r o c k , T.H., S.D. A l b o n , R.M.Gibson a n d F . E . G u i n n e s s . 1979. The l o g i c a l s t a g : a d a p t i v e a s p e c t s o f f i g h t i n g i n r e d d e e r ( C e r v u s e l a p h u s L . ) . A n i m . B e h a v . 2 7 : 2 1 1 - 2 2 5 . D a l y , M. a n d M . W i l s o n . 1983. S e x , E v o l u t i o n a nd B e h a v i o u r , 2nd e d i t . M c M a s t e r U n i v e r s i t y , W i l l a r d G r a n t P r e s s , B o s t o n . 402 pp. 78 D o b z h a n s k y , T. 1951. G e n e t i c s a n d t h e o r i g i n o f s p e c i e s . 3 r d e d . C o l u m b i a U n i v e r s i t y P r e s s , New Y o r k . Downhower, J . F . and L . B r o w n . 1980. M a t e p r e f e r e n c e s o f f e m a l e m o t t l e d s c u l p i n s : C o t t u s b a i r d i . A n i m . B e h a v . 28 : 7 28-734. F o x , D.J. a n d K . E . G u i r e . 1976. D o c u m e n t a t i o n f o r MIDAS. S t a t i s t i c a l R e s e a r c h L a b o r a t o r y , U n i v e r s i t y o f M i c h i g a n , Ann A r b o u r , MI. F r y e r , G. a n d T . D . I l e s . 1972. The c i c h l i d f i s h e s o f t h e g r e a t l a k e s o f A f r i c a : t h e i r b i o l o g y a n d e v o l u t i o n . O l i v e r a n d B o y d , E d i n b u r g h . 641 pp. Gwynne, D.T. 1984. S e x u a l s e l e c t i o n a n d s e x u a l d i f f e r e n c e s i n Mormon c r i c k e t s ( O r t h o p t e r a : T e t t i g o n i d a e , A n a b r u s s i m p l e x ). E v o l u t i o n 3 8 : 1 0 1 1 - 1 0 2 2 . Hagen, D.W. 1967. I s o l a t i n g M e c h a n i s m s i n t h r e e s p i n e s t i c k l e b a c k s ( G a s t e r o s t e u s ) . J . F i s h . R e s . Bd. Canada 24: 1637-1692. H a l l i d a y , T.R. 1983. The s t u d y o f mate c h o i c e , I n Mate C h o i c e , P a t r i c k B a t e s o n ( e d . ) , C a m b r i d g e U n i v . P r e s s , C a m b r i d g e . 275 p p . Hay, D.E. 1969. Mate s e l e c t i o n i n t h e t h r e e s p i n e s t i c k l e b a c k G a s t e r o s t e u s . M.Sc. T h e s i s , D e p t . o f Z o o l o g y . U n i v . B . C . 74pp. Hay, D.E. a n d J.D. M c P h a i l . 1975. M a t e s e l e c t i o n i n t h r e e s p i n e s t i c k l e b a c k s ( G a s t e r o s t e u s ) . C a n . J . Z o o l . 5 3 : 4 4 1 - 4 5 0 . H e u t s , M.J. 1946. P h y s i o l o g i c a l i s o l a t i n g m e c h a n i s m s a n d s e l e c t i o n w i t h i n t h e s p e c i e s G a s t e r o s t e u s a c u l e a t u s L. N a t u r e , L o n d . 158:839-840. Howard, R.D. 1978. The e v o l u t i o n o f m a t i n g s t r a t e g i e s i n b u l l f r o g s . Rana c a t e s b i a n a . E v o l u t i o n 3 2 : 8 5 0 - 8 7 1 . 79 I e r s e l , J . J . v a n 1953. An a n a l y s i s o f p a r e n t a l b e h a v i o u r o f t h e m a l e t h r e e s p i n e d s t i c k l e b a c k ( G a s t e r o s t e u s a c u l e a t u s L . ) . B e h a v i o u r S u p p l . 3:1-159. J o n e s , J . W . and H.B.N.Hynes. 1950. The age a n d g r o w t h o f G a s t e r o s t e u s a c u l e a t u s , P y g o s t e u s p u n q i t i u s and S p i n a c h i a  v u l g a r i s , a s shown by t h e i r o t o l i t h s . J . A n i m . E c o l . 19:59-73. K y n a r d , B.E. 1979. B r e e d i n g b e h a v i o u r o f a l a c u s t r i n e p o p u l a t i o n o f t h r e e s p i n e s t i c k l e b a c k s ( G a s t e r o s t e u s a c u l e a t u s L . ) . B e h a v i o u r 6 7 : 1 7 8 - 2 0 7 . L a v i n , P.A. and J . D . M c P h a i l . 1985. The e v o l u t i o n o f f r e s h w a t e r d i v e r s i t y i n t h e t h r e e s p i n e s t i c k l e b a c k ( G a s t e r o s t e u s  a c u l e a t u s ) : s i t e - s p e c i f i c d i f f e r e n t i a t i o n o f t r o p h i c m o r p h o l o g y . C a n . J . Z o o l . 6 3 : 2 6 3 2 - 2 6 3 8 . L i , S.K. 1976. S e x u a l s e l e c t i o n i n t h e t h r e e - s p i n e d s t i c k l e b a c k . Ph.D. T h e s i s , U n i v . C a l i f . D a v i s . 121 pp. L i l e y , N.R. 1966. E t h o l o g i c a l i s o l a t i n g m e c h a n i s m s i n f o u r s y m p a t r i c s p e c i e s o f p o e c i l i i d f i s h e s . B e h a v i o u r S u p p l . 13:1-197. L o i s e l l e , P.V. 1982. M a l e s p a w n i n g - p a r t n e r p r e f e r e n c e i n an a r e n a - b r e e d i n g t e l e o s t C y p r i n o d o n m a c u l a r i s c a l i f o r n i e n s i s G i r a r d ( A t h e r i n o m o r p h a : C y p r i n o d o n t i d a e ) . Amer. N a t . 120: 721-73 2 . M c P h a i l , J.D. a n d D.E.Hay. 1983. D i f f e r e n c e s i n m a l e c o u r t s h i p i n f r e s h w a t e r a n d m a r i n e s t i c k l e b a c k s ( G a s t e r o s t e u s a c u l e a t u s ) . C an. J . Z o o l . 6 1 : 2 92-297. M a n n i n g , J.T. 1975. M a l e d i s c r i m i n a t i o n a n d i n v e s t m e n t i n A s e l l u s a q u a t i c u s ( L . ) a n d A. m e r i d i a n u s r a c o v i t z a ( C r u s t a c e a : I s o p o d a ) . B e h a v i o u r 55:1-14. M a y r , E. 1963. A n i m a l s p e c i e s a n d e v o l u t i o n , B e l k n a p P r e s s , M a s s . 797 pp. 80 Munzing, J . 1963. The evolution of variation and d i s t r i b u t i o n a l patterns in European populations of the three-spined stickleback, Gasterosteus aculeatus. Evolution 17:320-332. Nisbet, I.C.T. 1973. Courtship feeding, egg-size and breeding success in common terns. Nature 241:141-147. Perrone, M.Jr. 1978. Mate size and breeding size in a monogamous c i c h l i d f i s h . Env. B i o l . F i s h . 3:193-201. Rowland, W.J. 1982. Mate choice by male sticklebacks, Gasterosteus aculeatus. Anim. Behav. 30:1093-1098. Searcy, W.A. 1979. Female choice of mates: a general model for birds and i t s application to red-winged blackbirds ( Agelaius phoeniceus). Amer. Nat. 114:77-100. Searcy, W.A. 1982. The evolutionary effects of mate sel e c t i o n . Ann. Rev. Ecol.Sys. 13:57-85. Smith, R.L. 1979. Paternity assurance and altered roles in the mating behaviour of a giant water bug, Abedus herberti (Heteroptera: Belostomatidae). Anim. Behav. 27:716-725. Sokal, R.R. and F.J.Rohlf. 1981. Biometry, Freeman, San Francisco. 859pp. Taylor, E.B. and J.D.McPhail. 1986. Prolonged and burst swimming in anadromous and freshwater threespine stickleback, Gasterosteus aculeatus. Can. J. Zool. 64:416-420. Th o r n h i l l , R. 1980. Mate choice in Hylobittacus a p i c a l i s (Insecta: Mecoptera) and i t s r e l a t i o n to some models of female choice. Evolution 34:519-538. Southward, G.M. 1962. A method of c a l c u l a t i n g body lengths from o t o l i t h measurements for P a c i f i c halibut. J. F i s h . Res. Bd. Canada 19:339-361. 81 T r i v e r s , R.L. 1972. P a r e n t a l i n v e s t m e n t a n d s e x u a l s e l e c t i o n . I n C a m p b e l l , B . ( e d ) S e x u a l s e l e c t i o n a n d t h e d e s c e n t o f man. A l d i n e , C h i c a g o . 412pp. Van den Assem, J . 1967. T e r r i t o r y i n t h e t h r e e - s p i n e d s t i c k l e b a c k , G a s t e r o s t e u s a c u l e a t u s . An e x p e r i m e n t a l s t u d y i n i n t r a s p e c i f i c c o m p e t i t i o n d u r i n g r e p r o d u c t i o n . B e h a v i o u r S u p p l . 16:1-164. W i l l i a m s , T. a n d B . C . B e d f o r d . 1973. The a g i n g o f f i s h p p 1 1 4 - 1 2 2 , T.B. B a g e n a l ( e d . ) Unwin B r o s . L t d . S u r r e y , E n g l a n d . 234 pp. W i l z , K. J . 1970. C a u s a l and f u n c t i o n a l a n a l y s i s o f d o r s a l p r i c k i n g a n d n e s t a c t i v i t y i n t h e c o u r t s h i p o f t h e t h r e e -s p i n e d s t i c k l e b a c k ( G a s t e r o s t e u s a c u l a e t u s ) . A n i m . Behav. 18:115-124. W o o t t o n , R . J . 1972. The b e h a v i o u r o f t h e m a l e t h r e e - s p i n e d s t i c k l e b a c k i n a n a t u r a l s i t u a t i o n : a q u a n t i t a t i v e d e s c r i p t i o n . B e h a v i o u r 4 1 : 2 3 2 - 2 4 1 . W o o t t o n , R . J . 1973. F e c u n d i t y o f t h e t h r e e - s p i n e d s t i c k l e b a c k , G a s t e r o s t e u s a c u l e a t u s ( L . ) . J . F i s h . B i o l . 5:683-688. Y o s h i h a r u , H. a n d E.Tamura. 1984. A n a t o m i c a l a n d b e h a v i o u r a l d i f f e r e n c e s among t h r e e s p i n e s t i c k l e b a c k s : t h e m a r i n e f o r m , t h e l a n d l o c k e d f o r m a n d t h e i r h y b r i d s . A c t a . Z o o l . ( S t o c k h o l m ) 6 5 : 7 9 - 8 7 . 82 APPENDIX 1 83 THE AGING OF STICKLEBACKS FROM THEIR OTOLITHS I n t r o d u c t i o n I t i s i m p o r t a n t f o r t h e a n a l y s i s o f l i f e h i s t o r y d y n a m i c s i n f i s h p o p u l a t i o n s t h a t t h e r e be a q u i c k a n d r e l i a b l e m ethod o f d e t e r m i n i n g t h e age s t r u c t u r e o f t h e p o p u l a t i o n . O t o l i t h s h a v e been w i d e l y u s e d f o r a g e i n g f i s h a l o n g w i t h o t h e r h a r d t i s s u e s u c h a s s c a l e s a n d v e r t e b r a e w h e r e a s s p i n e s h a v e p r o v e d s a t i s f a c t o r y i n some l a r g e r s p e c i e s ( A s h l e y a n d G a r l i n g 1 9 8 0 ) . E x p e r i m e n t a l work ( J o n e s a n d H y n e s , 1950, Campana a n d N e i l s o n , 1982) i n d i c a t e s t h a t o t o l i t h s a r e t h e most s u i t a b l e f o r a g e i n g s t i c k l e b a c k s , t h e r e f o r e t h a t i s t h e method s e l e c t e d f o r t h i s s t u d y . G r o w t h o f O t o l i t h s The t h r e e o t o l i t h s o f t e l e o s t f i s h a r e p a r t o f t h e l a b r i n t h s y s t e m i n t h e e a r a n d t h e s a g i t t a , f o u n d i n t h e s a c c u l u s , i s most s u i t a b l e f o r use i n age d e t e r m i n a t i o n . The s h a p e o f o t o l i t h s i s c h a r a c t e r i s t i c o f t h e g e n e r a o r s p e c i e s , t h e s a g g i t t a o f t h e t h r e e s p i n e s t i c k l e b a c k b e i n g r o u g h l y r o u n d w i t h t h e i n d e n t a t i o n o f t h e s u l c u s g i v i n g i t a h e a r t - s h a p e d a p p e a r a n c e . 84 O t o l i t h s a r e composed m a i n l y o f c a l c i u m c a r b o n a t e c r y s t a l s r a d i a t i n g o u t w a r d i n t h r e e d i m e n s i o n s f r o m a n u c l e u s t h r o u g h a m a t r i x o f o r g a n i c m a t e r i a l a n d t h e y grow a s more m a t e r i a l i s d e p o s i t e d on t h e o u t e r s u r f a c e s . S i n c e l a r v a l f i s h must be a b l e t o o r i e n t i m m e d i a t e l y upon h a t c h i n g i t i s p r o b a b l e t h a t f u n c t i o n a l o t o l i t h s a r e p r e s e n t a t t h i s t i m e . As d e t e r m i n e d by W i l l i a m s a n d B e d f o r d ( 1 9 7 3) i n f i s h e s o f t h e N o r t h e r n h e m i s p h e r e t h e n u c l e u s i s c o m p o s e d o f opaque m a t e r i a l w h i c h c o n t i n u e s t o be d e p o s i t e d t h r o u g h o u t t h e f i r s t m o nths o f t h e l i f e o f t h e f i s h . I n t h e l a t e autumn o r e a r l y w i n t e r t h e t r a n s p a r e n t z o n e b e g i n s t o f o r m a n d d e p o s i t i o n o f opaque m a t e r i a l b e g i n s a g a i n i n l a t e w i n t e r o r e a r l y s p r i n g . T h i s r o u g h p a t t e r n o f s e a s o n a l i t y c o n t i n u e s e a c h y e a r t h r o u g h o u t t h e l i f e o f t h e f i s h . I n t h e e a r l y y e a r s o f t h e l i f e o f t h e f i s h t h e opaque z o n e , l a i d down d u r i n g t h e p e r i o d o f t h e y e a r when t h e f i s h ' s g r o w t h i s r a p i d , i s u s u a l l y w i d e r t h a n t h e c o r r e s p o n d i n g t r a n s p a r e n t z o n e w h i c h i s l a i d down a t t h e t i m e when t h e r e i s l i t t l e o r no g r o w t h . As t h e f i s h grows o l d e r t h e opaque z o n e becomes p r o g r e s s i v e l y n a r r o w e r b u t t h e t r a n s p a r e n t z o n e s r e m a i n a p p r o x i m a t e l y t h e same w i d t h . T h i s p r o c e s s c o n t i n u e s u n t i l t h e o u t e r m o s t r i n g s become e x t r e m e l y n a r r o w , r e g u l a r a n d o f a b o u t e q u a l w i d t h . T h i s v i e w i s a t v a r i a n c e w i t h t h a t i n t h e summary o f r e c e n t work by R. W. B l a c k e r (1974) w h i c h i n d i c a t e s t h a t t h e t i m e o f l a y i n g down o f t h e v a r i o u s z o n e s c a n d i f f e r f r o m s p e c i e s t o s p e c i e s a n d i n some may be t h e r e v e r s e o f t h e a b o v e . 85 M a t e r i a l s a n d M e t h o d s C o l l e c t i o n s The f i s h e x a m i n e d i n t h i s s t u d y were o b t a i n e d f r o m t h e L i t t l e C a m p b e l l R i v e r i n s o u t h w e s t e r n B r i t i s h C o l u m b i a . F o u r g r o u p s o f s e x u a l l y m a t u r e f i s h were i n v e s t i g a t e d : 1. F i e l d - c a u g h t m a l e s a n d f e m a l e s c o l l e c t e d by minnow t r a p s i n t h e s p r i n g o f 1982 a n d t h e s p r i n g t h r o u g h summer o f 1983. 2. Young o f t h e y e a r c o l l e c t e d i n A u g u s t 1982 a n d k e p t i n n e a r n a t u r a l c o n d i t i o n s i n an o u t s i d e p o n d (4mx8mx1m) i n t h e c o u r t y a r d o f t h e Z o o l o g y b u i l d i n g a t U.B.C. u n t i l s a c r i f i c e d i n May 1983. 3. Young o f t h e y e a r c o l l e c t e d i n A u g u s t 1983 a n d o v e r - w i n t e r e d i n an o u t s i d e a q u a r i u m ( 2 0 0 g a l . ) i n N o r t h V a n c o u v e r u n t i l s a c r i f i c e d i n J u l y 1984. 4. S i b l i n g s f r o m a s i n g l e m a t i n g h a t c h e d i n t h e l a b o r a t o r y i n May 1982 a n d o v e r - w i n t e r e d i n a c o n t r o l l e d e n v i r o n m e n t chamber u n d e r a s i m u l a t e d n a t u r a l l i g h t a n d t e m p e r a t u r e r e g i m e u n t i l s a c r i f i c e d i n May 1983. The c a p t i v e f i s h i n t h e c o u r t y a r d were f e d u n t i l a n a t u r a l e c o s y s t e m was e s t a b l i s h e d . The a q u a r i u m f i s h were f e d on a 86 r e g u l a r b a s i s . Measurement of F i s h The f i s h were measured from the t i p of the snout to the f l e x i o n p o i n t at the base of the t a i l and these standard lengths recorded to the nearest one-tenth of a m i l l i m e t r e . Photography Photographs were taken of the o t o l i t h s of f i s h of approximately s i m i l a r s i z e , and presumeably age, r e p r e s e n t a t i v e of three groups: the wild-caught from s p r i n g 1983, the c o u r t y a r d f i s h and the l a b o r a t o r y group. • The equipment used was an MKA-1 35mm s i n g l e l e n s r e f l e x camera f i t t e d to a photography tube and using Kodak T r i - X ISO 400 black-and-white f i l m . I l l u m i n a t i o n was p r o v i d e d by a 3 v o l t transformer and the m a g n i f i c a t i o n p r o v i d e d by the o c u l a r was x8 and that of the o b j e c t i v e x50. Exposure time was 0.5secs. The photographs are presented i n F i g u r e 1 and each one r e p r e s e n t s a set of at l e a s t ten s i m i l a r o t o l i t h s . E x t r a c t ion and Treatment of O t o l i t h s Since o t o l i t h s are best read immediately, they were removed from most f i s h i n f r e s h c o n d i t i o n . When f i s h c o u l d not be 87 d i s s e c t e d i m m e d i a t e l y t h e y were s t o r e d i n a 7 0 % EtOH s o l u t i o n f o r a s h o r t t i m e . No d i f f e r e n c e c o u l d be d e t e c t e d i n t h e r e a d i n g s o b t a i n e d by t h e two m e t h o d s . L o n g - t e r m s t o r a g e i n EtOH, h o w e v e r , c a u s e s a d e t e r i o r a t i o n o f t h e o t o l i t h s m a k i n g them b r i t t l e a n d u n r e a d a b l e . A l l d i s s e c t i o n s were c a r r i e d o u t u n d e r a low power d i s s e c t i n g s c o p e . The o t o l i t h s a r e e a s i l y l o c a t e d by c u t t i n g downward, b e h i n d t h e V - s h a p e d mark on t h e t o p o f t h e f i s h ' s h e a d , a t a 60 d e g r e e a n g l e f r o m t h e h o r i z o n t a l , e x p o s i n g t h e c a v i t i e s i n w h i c h t h e y a r e l o c a t e d . Upon r e m o v a l t h e o t o l i t h s were t r a n s f e r r e d t o a g l a s s s l i d e t h e n c l e a n e d a n d f i x e d t o t h e s l i d e w i t h a s m a l l amount o f g l a s s g l u e . The v i s i b i l i t y o f t h e r i n g s t r u c t u r e , i n a w h o l e o t o l i t h , i s i m p r o v e d by v i e w i n g u n d e r t h e g l u e w i t h l i g h t d i r e c t e d on i t a t an a n g l e f r o m a b o v e . T h i s m e t h o d of p r e s e r v a t i o n u n d e r g l a s s g l u e p r o v e d s a t i s f a c t o r y a n d no d e t e r i o r a t i o n o r c h a n g e was o b s e r v e d i n t h e o t o l i t h s when r e -s c o r e d one y e a r a f t e r t h i s t r e a t m e n t . S c o r i n g o f O t o l i t h s The o t o l i t h s were s c o r e d f o r a g e i n g u n d e r a d i s s e c t i n g m i c r o s c o p e u s i n g r e f l e c t e d l i g h t a n d a d a r k b a c k g r o u n d . The opaque z o n e s a p p e a r l i g h t and t h e c l e a r z o n e s d a r k when an o t o l i t h i s v i e w e d a g a i n s t a b l a c k b a c k g r o u n d by r e f l e c t e d l i g h t . The s c o r i n g method a d o p t e d f o l l o w s t h a t o f J o n e s a n d Hynes (1950) on s t i c k l e b a c k o t o l i t h s : 88 S = o t o l i t h w i t h c e n t r e ( n u c l e u s ) a n d o n e t r a n s p a r e n t r i n g . S+ = o t o l i t h w i t h c e n t r e , o n e t r a n s p a r e n t r i n g a n d a n o p a q u e z o n e a t t h e e d g e . 2 S = o t o l i t h w i t h c e n t r e a n d t w o t r a n s p a r e n t r i n g s , o n e f o r m i n g t h e e d g e . 3 S = o t o l i t h w i t h c e n t r e a n d t h r e e t r a n s p a r e n t r i n g s , o n e f o r m i n g t h e e d g e . S i n c e o n l y m a t u r e f i s h w e r e e x a m i n e d t h e S - c a t e g o r y f o r y o u n g o f t h e y e a r w a s o m i t t e d . T h e f i n e r g r a d a t i o n s o f 2S+ a n d 3S+ w e r e a l s o o m i t t e d a s t h e y a r e t o o o p e n t o s u b j e c t i v e i n t e r p r e t a t i o n . 89 I n t e r p r e t a t i o n o f O t o l i t h s W i t h p r a c t i c e most o t o l i t h s , o r one o f a p a i r , c o u l d be c l a s s i f i e d w i t h r e s p e c t t o t h e m a i n r i n g s . T h i r t e e n o f t h e 429 s e t s o f o t o l i t h s e x a m i n e d ( 3 . 0 3 % ) were c l a s s i f i e d a s u n r e a d a b l e . S i x t e e n o f t h e 416 u s a b l e s e t s were r e a d f r o m a s i n g l e o t o l i t h ( 3 . 8 5 % ) and i n 27 c a s e s o v e r a l l t h e r e was some d o u b t i n t h e i n t e r p r e t a t i o n ( 6 . 2 9 % ) . T a b l e 1 shows t h e p e r c e n t a g e of f i s h p l a c e d i n e a c h o t o l i t h c a t e g o r y a n d T a b l e 2 t h e s i z e c l a s s i f i c a t i o n o f t h e g r o u p s e x a m i n e d . I n May 1982 t h e m a j o r i t y o f t h e b r e e d i n g f e m a l e s c a p t u r e d on t h e b r e e d i n g g r o u n d s were c a t e g o r i z e d a s 2S ( 5 9 % ) b u t t h e r e was a c o m p a r a t i v e l y h i g h p r o p o r t i o n o f S f e m a l e s p r e s e n t ( 3 7 % ) . T h e s e S f e m a l e s t e n d e d t o f a l l i n t h e s m a l l e r age c l a s s e s b u t t h i s r e l a t i o n s h i p i s n o t a l w a y s r e l i a b l e . The m a l e s were f a i r l y e v e n l y s p r e a d o v e r t h e f i r s t t h r e e o t o l i t h c a t e g o r i e s . I n May 1983, f o l l o w i n g a s e v e r e w i n t e r i n w h i c h t h e c o l l e c t i n g s i t e was f r o z e n o v e r f o r a number o f w e e k s , f e w e r f e m a l e f i s h a r r i v i n g on t h e s p a w n i n g g r o u n d s f e l l i n t o t h e 2S c a t e g o r y t h a n i n t h e p r e v i o u s y e a r a n d many more were i n t h e i n t e r m e d i a t e S+ c a t e g o r y . On t h e o t h e r h a n d , many more o f t h e b r e e d i n g m a l e s were 2S t h a n i n 1982. I n J u n e 1983, a f t e r a m i l d s p e l l o f w e a t h e r , many more of t h e f e m a l e s c a p t u r e d were i n t h e 2S c a t e g o r y . Few m a l e s were t a k e n a t t h i s t i m e a s most h a d a l r e a d y e s t a b l i s h e d t e r r i t o r i e s . By J u l y 1983 t h e r e were few b r e e d i n g f e m a l e s p r e s e n t b u t a l l were i n t h e 2S c a t e g o r y . The s i z e s o f f i s h c a p t u r e d i n 1983 90 were s m a l l e r t h a n i n t h e p r e v i o u s y e a r , none b e i n g f o u n d i n t h e l a r g e s t s i z e c l a s s . M o s t 2S f i s h , b o t h m a l e a n d f e m a l e , f e l l i n t h e s m a l l e s t s i z e c l a s s . The m a l e s and f e m a l e s w h i c h were t h e y o u n g o f t h e 1982 y e a r a n d o v e r - w i n t e r e d i n t h e z o o l o g y c o u r t y a r d showed s i m i l a r o t o l i t h b a n d i n g p a t t e r n s i n two d i s t i n c t c a t e g o r i e s w i t h no i n t e r m e d i a t e S+ g r o u p . H owever, t h e m a j o r i t y o f t h e m a l e s f e l l i n t o t h e 2S g r o u p i n g w h i l e most o f t h e f e m a l e s showed o n l y S. The f i s h o f a p p r o x i m a t e l y t h e same s i z e a n d , p r e s u m e a b l y , age c l a s s i n 1983, w h i c h were o v e r - w i n t e r e d i n N o r t h V a n c o u v e r i n i d e n t i c a l c o n d i t i o n s showed c o n s i d e r a b l e d i f f e r e n c e s i n t h e i r r i n g s t r u c t u r e i n t h e f e m a l e s b u t l e s s i n t h e m a l e s . M ost o f t h e f i s h f e l l i n t h e i n t e r m e d i a t e s i z e c l a s s a t m a t u r i t y b u t , l i k e a l l o t h e r g r o u p s t h e r e were a few e x t r a - l a r g e f e m a l e s . The s i b l i n g f i s h w h i c h were k e p t i n c o n t r o l l e d c o n d i t i o n s i n t h e l a b o r a t o r y h a d o t o l i t h s c o n s i s t e n t t h r o u g h o u t t h e g r o u p , a s w o u l d be e x p e c t e d , a l l s h o w i n g a s e c o n d S r i n g , b u t w i t h s e c o n d a r y c l e a r i n g i n t h e n u c l e u s . The c o n t r o l l e d e n v i r o n m e n t f i s h , b o t h m a l e and f e m a l e , f e l l i n t o a s i n g l e s i z e c l a s s , w i t h t h e e x c e p t i o n o f a s i n g l e l a r g e f e m a l e . I n a l l c o l l e c t i o n s more f e m a l e s t h a n m a l e s were p r e s e n t i n e a c h g r o u p and i n t h e c a p t i v e s i t u a t i o n s t h e s u r v i v a l r a t e was much h i g h e r f o r f e m a l e s t h a n f o r m a l e s . D i s c u s s i o n J o n e s a n d Hynes (1950) s t a t e d t h a t t h e c o r e o f s t i c k l e b a c k 91 o t o l i t h s c a n be e i t h e r t r a n s p a r e n t o r o p a q u e . I n t h e f i s h o f t h e L i t t l e C a m p b e l l R i v e r t h e c o r e i s a l m o s t i n v a r i a b l y o p a q u e . I f any s e c o n d a r y c l e a r i n g o f t h e c e n t r e i s o b s e r v e d i t c a n u s u a l l y be p i n - p o i n t e d a s s u c h a n d d o e s n o t a f f e c t t h e i d e n t i f i c a t i o n o f t h e n u c l e u s . C o n s i s t e n t w i t h W i l l i a m s a n d B e d f o r d ( 1 9 7 3 ) t h e f o l l o w i n g i n t e r p r e t a t i o n o f t h e d a t a f r o m t h e w i l d - c a u g h t f i s h was made. When t h e y o u n g s t i c k l e b a c k i s h a t c h e d t h e c e n t r e opaque n u c l e u s f i l l s t h e w h o l e o t o l i t h . The f i r s t t r a n s p a r e n t z o n e i s l a i d down i n t h e w i n t e r a f t e r h a t c h i n g a n d t h e f i r s t opaque r i n g s t a r t s t o f o r m i n s p r i n g when t h e p e r i o d o f r a p i d g r o w t h b e g i n s . T h us an o t o l i t h w i t h an opaque n u c l e u s a n d two t r a n s p a r e n t r i n g s , one f o r m i n g t h e edge ( 2 S ) , s h o u l d i d e n t i f y a f i s h w h i c h h a s s u r v i v e d i t s s e c o n d w i n t e r ( F i g u r e 1 b ) . O n l y one f e m a l e w i t h t h r e e t r a n s p a r e n t r i n g s was c a p t u r e d so i t i s s a f e t o s a y t h a t few o f t h i s p o p u l a t i o n o f s t i c k l e b a c k s ( m a l e o r f e m a l e ) s u r v i v e s t h r o u g h t h e i r t h i r d w i n t e r . The f e m a l e s w h i c h move t o t h e s p a w n i n g a r e a i n t h e L i t t l e C a m p b e l l R i v e r a r e p r e d o m i n a t e l y i n t h e i r s e c o n d y e a r a n d a r e t h e r e f o r e somewhat l a r g e r t h a n t h e r e s t . However, c o n s i d e r a t i o n o f t h e s i z e o f a f i s h when c a l c u l a t i n g age f r o m o t o l i t h s s h o u l d be u s e d w i t h c a u t i o n b e c a u s e t h e r e i s g r e a t v a r i a t i o n i n g r o w t h r a t e s . L e n g t h may be a u s e f u l i n d i c a t o r a s t o t h e l i k e l y age o f a f i s h b u t i t i s n o t n e c e s s a r i l y a f u n c t i o n o f a g e . S p a w n i n g i n t h e L i t t l e C a m p b e l l R i v e r i s u s u a l l y a t i t s peak i n May b u t t h i s may v a r y f r o m y e a r t o y e a r d e p e n d i n g on 92 c l i m a t i c c o n d i t i o n s . I n 1983 t h e s p a w n i n g peak s h i f t e d t o J u n e a s shown by t h e i n c r e a s e i n s e c o n d y e a r f i s h p r e s e n t i n J u n e a s c o m p a r e d w i t h May 1983. I n a l l o t o l i t h c a t e g o r i e s t h e f i s h f e l l i n t o s m a l l e r s i z e c a t e g o r i e s i n t h a t y e a r . When t h e o t o l i t h s o f t h e y o u n g o f t h e 1982 y e a r , w h i c h o v e r - w i n t e r e d i n t h e c o u r t y a r d , were e x a m i n e d t h e y f i t t e d t h e p a t t e r n o f f i s h w h i c h had been b o r n i n one y e a r , s u r v i v e d t h e i r f i r s t w i n t e r a n d were s t a r t i n g t h e i r f i r s t b r e e d i n g s e a s o n ( F i g u r e l a ) . Two o f them e x h i b i t e d a 2S p a t t e r n i n s p i t e o f b e i n g , a p p a r e n t l y , o f t h e same s i z e c l a s s i n t h e p r e v i o u s f a l l a s t h e S f i s h . The o t o l i t h s o f t h e l a b o r a t o r y f i s h f e l l w i t h i n a s i n g l e s i z e c l a s s a n d o t o l i t h c a t e g o r y c o n f i r m i n g t h a t f i s h w i t h t h e same l i f e h i s t o r i e s e x h i b i t i d e n t i c a l o t o l i t h p a t t e r n s . As a g e n e r a l o b s e r v a t i o n i t c a n be s t a t e d t h a t f i s h o f t h e 2S g r o u p p r e d o m i n a t e on t h e u p p e r C a m p b e l l R i v e r s p a w n i n g g r o u n d s t h o u g h t h e r e i s a l w a y s a s m a l l e r g r o u p o f S a n d S+ f i s h p r e s e n t . T h i s s t r a t e g y w o u l d be e x p e c t e d i f t h e m a l e s p r e f e r t o mate w i t h l a r g e r f e m a l e s . U n l e s s a f e m a l e r e a c h e s a c e r t a i n s i z e a t m a t u r i t y i t w o u l d n o t be p r o f i t a b l e f o r h e r t o i n v e s t i n t h e p r o d u c t i o n o f eggs a t t h e e x p e n s e o f g r o w t h . A f t e r m a t u r i t y t h e s i z e o f t h e o t o l i t h s d o e s n o t c h a n g e a p p r e c i a b l y i n s t i c k l e b a c k s and t h i s f a c t , a l o n g w i t h t h e g r e a t d i f f e r e n c e s i n s i z e a t m a t u r i t y w i t h i n a n d b e t w e e n p o p u l a t i o n s , makes t h e a p p l i c a t i o n o f an o t o l i t h s i z e / s t a n d a r d l e n g t h r e l a t i o n s h i p i n a p p l i c a b l e f o r t h e s p e c i e s . T h i s t y p e o f r e l a t i o n s h i p h a s p r o v e d s u c c e s s f u l i n h e l p i n g age s p e c i e s w h i c h 93 a r e l o n g - l i v e d a nd grow t o c o n s i d e r a b l e s i z e s u c h a s t h e P a c i f i c h a k e ( S o u t h w a r d , 1 9 6 2 ) . As b e f i t s a s m a l l f i s h , s t i c k l e b a c k o t o l i t h s a r e s m a l l and e v e n when t h e y a r e e x a m i n e d u n d e r t h e d i s s e c t i n g m i c r o s c o p e v a r i a t i o n s i n t h e s i z e o f o t o l i t h s a n d t h e w i d t h s o f t h e bands i s n o t r e a d i l y a p p a r e n t t o an o b s e r v e r . F o r t h i s r e a s o n t h e s e r i e s o f p h o t o g r a p h s was t a k e n o f t h e o t o l i t h s f r o m t h e t h r e e d i f f e r e n t g r o u p s . The s i z e s o f t h e f i s h s e l e c t e d d i f f e r e d o n l y s l i g h t l y ( w i t h i n 5mm) a n d t h e m a g n i f i c a t i o n was i d e n t i c a l i n e a c h c a s e ( x 4 0 0 ) . The s i m i l a r s i z e o f t h e o t o l i t h s i s a p p a r e n t i n t h e p h o t o g r a p h s b u t what i s s t r i k i n g i s t h e d i f f e r e n c e i n t h e b a n d i n g p a t t e r n s . I n e a c h c a s e t h e s i z e o f t h e n u c l e u s i s s i g n i f i c a n t l y d i f f e r e n t . T h e s e d i f f e r e n c e s s u g g e s t t h a t a t m a t u r i t y a r e o r g a n i z a t i o n o f t h e m a t e r i a l i n t h e o t o l i t h s t a k e s p l a c e r a t h e r t h a n an a c c r e t i o n o f m a t e r i a l f r o m y e a r t o y e a r a f t e r m a t u r i t y . The o t o l i t h o f t h e l a b o r a t o r y - r e a r e d f i s h w o u l d s u g g e s t t o t h e c a s u a l o b s e r v e r t h a t t h i s was a f i s h w h i c h h a d j u s t s u r v i v e d i t s t h i r d w i n t e r a n d h a d e n c o u n t e r e d a summer i n i t s s e c o n d y e a r o f e x t r a o r d i n a r y b o u n t y a f t e r a s h o r t a n d m i l d f i r s t w i n t e r ( F i g u r e 1 c ) . I t i s g e n e r a l l y a g r e e d ( r e v i e w by B l a c k e r , 1974) t h a t t h e t r a n s p a r e n c y o f t h e c l e a r b a n d s i s due t o a l e s s e r amount o f c a l c i u m c a r b o n a t e b e i n g p r e s e n t i n t h i s a r e a . T h e r e i s a p o s s i b i l i t y t h a t t h e o n s e t o f m a t u r i t y c a u s e s a r e s o r p t i o n o f c a l c i u m f r o m t h e opaque a r e a s o f t h e o t o l i t h . T h u s , d e p e n d i n g on t h e r e q u i r e m e n t s o f t h e d e v e l o p i n g c l u t c h , more o r l e s s 94 c a l c i u m may be w i t h d r a w n f r o m t h e o t o l i t h . T h i s m i g h t a c c o u n t f o r t h e c o n f u s i o n a b o u t w h e t h e r t h e n u c l e u s i s opaque o r t r a n s p a r e n t . A h i g h r e q u i r e m e n t f o r c a l c i u m m i g h t e v e n i n v o l v e i t s b e i n g w i t h d r a w n f r o m t h e c e n t r e o f t h e n u c l e u s , a phenomenon w h i c h was o b s e r v e d i n 10% o f t h e o t o l i t h s e x a m i n e d . I f t h i s i s t h e c a s e f e m a l e f i s h o f e q u a l age w o u l d have d i f f e r e n t b a n d i n g p a t t e r n s d e p e n d i n g upon w h e t h e r o r n o t t h e y h a d grown l a r g e e n ough t o move t o t h e s p a w n i n g g r o u n d s a f t e r t h e f i r s t w i n t e r . R e a d i n g o f t h e o t o l i t h s o f t h e L i t t l e C a m p b e l l R i v e r f i s h was n o t d i f f i c u l t a s t h i s p o p u l a t i o n d i d n o t s u f f e r f r o m t h e a c e n t r i c n u c l e i a n d d i s c o n t i n u o u s b a n d i n g p r o b l e m s e n c o u n t e r e d by B l o u w a n d Hagen ( 1 9 8 1 ) . The w o r s t c a s e e r r o r component o f 6.29% was c o n s i d e r e d a c c e p t a b l e . S i m i l a r l y I d i d n o t e n c o u n t e r t h e i r p r o b l e m s w i t h t h e i r l a b o r a t o r y s t o c k . The o t o l i t h s i n t h i s p a r t o f t h e s t u d y were e x t r e m e l y r e g u l a r l y s h a p e d a n d t h e b a n d i n g p a t t e r n s d i d n o t v a r y b e t w e e n a n d w i t h i n p a i r s o f o t o l i t h s . I t s h o u l d be p o i n t e d o u t t h a t t h e s e l a b - r e a r e d f i s h were s i b l i n g s f r o m a s i n g l e h a t c h w h e r e a s t h o s e o f Bl o u w a n d Hagen ( 1 9 8 1 ) were f r o m v a r i o u s l a b o r a t o r y c r o s s e s a n d 12 d i f f e r e n t b r o o d s . T h i s e a s e o f r e a d i n g i s n o t n e c e s s a r i l y t h e c a s e i n a l l l o c a l p o p u l a t i o n s a s p r e l i m i n a r y e x a m i n a t i o n o f o t o l i t h s f r o m f i s h o f t h e S a l m o n R i v e r a n d T i n Can C r e e k r e v e a l e d many w h i c h were c r y s t a l l i n e a n d u n r e a d a b l e . L i k e t h e a b o v e i n v e s t i g a t o r s I a l s o f o u n d t h a t a g e i n g s t i c k l e b a c k s f r o m p e l v i c s p i n e s was i m p o s s i b l e a s no c l e a r a n n u l i were v i s i b l e . I s t r o n g l y recommend p h o t o g r a p h i n g t h e o t o l i t h s f o r an o b j e c t i v e e v a l u a t i o n o f t h e d i f f e r e n t z o n e s . M e a surement a nd 95 e v a l u a t i o n o f t h e v a r i o u s bands i s much e a s i e r f r o m p h o t o g r a p h s . A p a r t f r o m a few p a p e r s w h i c h i n c l u d e e l e c t r o n m i c r o g r a p h s , t h e r e i s a d e f i n i t e l a c k o f p h o t o g r a p h s o f w h o l e o t o l i t h s i n p u b l i s h e d p a p e r s , an o v e r s i g h t w h i c h makes t h e i r e v a l u a t i o n d i f f i c u l t a n d c o m p a r i s o n i m p o s s i b l e . A n o t h e r r e c o m m e n d a t i o n I w o u l d make i s t h a t m a l e s and f e m a l e s s h o u l d be s c o r e d s e p a r a t e l y a s t h e o t o l i t h p a t t e r n i n f e m a l e s may be a f f e c t e d by t h e age a t f i r s t s p a w n i n g . As a f i n a l r e c o m m e n d a t i o n I s u g g e s t a t h o r o u g h t i m e s t u d y o f t h e o t o l i t h c h a r a c t e r i s t i c s p e c u l i a r t o t h e p o p u l a t i o n u n d e r s t u d y a s t h e r e a r e d i f f e r e n c e s b e t w e e n p o p u l a t i o n s w h i c h may o r may n o t be i n v a r i a n t . C o n c l u s i o n T h e r e i s a s y e t no q u i c k a n d r e l i a b l e way o f a g e i n g t h e s h o r t - l i v e d s t i c k l e b a c k s f r o m t h e i r o t o l i t h s . The r e s u l t s i n t h i s s t u d y show some o f t h e r e a s o n s t h a t t h e r e a r e w i d e d i s a g r e e m e n t s i n t h e l i t e r a t u r e on a g e i n g s m a l l f i s h f r o m t h e i r o t o l i t h s . I n t h e o p i n i o n o f W i l l i a m s a n d B e d f o r d (1973) t h e a c c u r a c y o f a g e - d e t e r m i n a t i o n d e p e n d s f i n a l l y upon t h e t r a i n i n g a n d s k i l l o f t h e r e a d e r . They s u g g e s t , a f t e r a t r a i n i n g p e r i o d o f s i x months f o l l o w e d by two y e a r s e x p e r i e n c e and t h e e x a m i n a t i o n o f up t o 10,000 o t o l i t h s , a r e a d e r s h o u l d become r e a s o n a b l y p r o f i c i e n t p r o v i d e d he h a s a n a t u r a l a p t i t u d e f o r t h e wor k. S i n c e few f i s h r e s e a r c h e r s h a v e t h e t i m e o r i n c l i n a t i o n t o 96 devote the n s e l v e s i n t h i s way to the sometimes minor c o n s i d e r a t i o n of the age s t r u c t u r e of t h e i r study p o p u l a t i o n the development of the s k i l l of ageing from o t o l i t h s w i l l have to remain i n the hands of the e x p e r t s . 97 Figure 1. Photographs of prepared o t o l i t h s . a) U.B.C. courtyard. b) Wild-caught. c) Laboratory-bred. 39 Fig. l a . courtyard. Fig. lb. wiId-caught. Fig. Ic. laboratory. Table l Percentage of each o t o l i t h group in samples Wild-caught 4 of f i s h S S* 25 3S Unreadable Doubt Only one May 19B2 Females 90 37 3 59 1 6.7 2.2 Males 55 37 25 38 1.8 Hay 1983 Females 73 22 37 40 Hales 20 15 15 70 1.4 4.2 8.3 5.0 Jun 1983 Females 93 16 13 71 Hales 4 50 50 4. 1 16.1 7.53 J u l 19B3 Females 100 Courtyard Hay 1983 Females IB 89 Hales 10 30 11 70 11.0 20.0 N.Vanc. Jul 19B« Females 28 Hales 4 22 39 39 50 50 3.6 3.6 Laboratory Hay 1983 Females 13 Males 3 - 100 - 100 7.1 7.7 6fc.O T a b l e 2 S i z e d i s t r i b u t i o n of groups examined (can) L i t t l e C a m p b e l l 30-99.5 40 - 4 9.5 50-59.5 T o t a l Doubt O n l y May 1962 r e s a l e s S 16 10 7 33 - -3 3 2S B 12 33 5 3 2 -3S 1 i Unr e a d a b l e - 1 5 6 T o t a l 26 23 4 5 96 2 0 M a l e s S 11 9 20 S* 7 7 - 14 2S 2 11 6 21 3S - -U n r e a d a b l e l - - 1 T o t a l 21 27 8 56 0 0 Kay 1963 Females S 12 4 - 16 1 2 S* 25 2 27 - 3 2S 27 2 - 29 2 1 3S - -U n r e a d a b l e 1 - - -T o t a l 65 8 0 7 3 3 6 Ma l e s S 2 1 - 3 1 -S- 3 - - 3 - -2S* 13 1 - 14 3S - -U n r e a d a b l e - - - -T o t a l IB 2 0 20 1 0 101 June 1983 Females s 2 9 4 15 2 s * 2 7 3 12 3 2 S « 28 34 66 10 3S - -Unreadable - 4 - 4 Total 6 46 4 1 97 15 Males S - 2 - 2 S* - . - . . . 2S 2 2 -3S - - -Unreadable - 1 1 Total 0 5 0 5 0 J u l y 1983 Females 2S 0 5 0 5 Table 2 (cent.) Toung of 1962 i n courtyard u n t i l Kay 1963 Females S S* 2S 3S Unreadable T o t a l Males S s* 2S 3S Unreadable T o t a l Toung of 1963 i n N.Vanc. u n t i l J u l y 1964 Females S s* 2S 3S Unreadable Total Kales 5 S* 2S 3S Unreadable Total 30-39.5 40-49.5 50-59.5 Tot a l Doubt One on 9 7 16 2 - - 2 2 -II 7 0 IB 2 0 3 - 3 5 2 7 2 8 2 10 2 3 2 1 6 1 1 4 7 11 - -2 7 2 11 9 16 3 28 1 i 2 2 2 2 0 4 0 4 0 0 Lab h a t c h i n l a b u n t i l May 1983 Females S s» 2S 3S U n r e a d a b l e T o t a l M a l e s S s* 2S 35 U n r e a d a b l e T o t a l 

Cite

Citation Scheme:

        

Citations by CSL (citeproc-js)

Usage Statistics

Share

Embed

Customize your widget with the following options, then copy and paste the code below into the HTML of your page to embed this item in your website.
                        
                            <div id="ubcOpenCollectionsWidgetDisplay">
                            <script id="ubcOpenCollectionsWidget"
                            src="{[{embed.src}]}"
                            data-item="{[{embed.item}]}"
                            data-collection="{[{embed.collection}]}"
                            data-metadata="{[{embed.showMetadata}]}"
                            data-width="{[{embed.width}]}"
                            async >
                            </script>
                            </div>
                        
                    
IIIF logo Our image viewer uses the IIIF 2.0 standard. To load this item in other compatible viewers, use this url:
http://iiif.library.ubc.ca/presentation/dsp.831.1-0096679/manifest

Comment

Related Items