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The adaptive value of melanism in alpine Colias butterflies (Lepidoptera:Pieridae) Roland, Jens 1981

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THE ADAPTIVE VALUE OF MELANISM IN ALPINE COLIAS BUTTERFLIES (LEPIDOPTERA:PIERIDAE) by JENS ROLAND B.Sc (Hons.), U n i v e r s i t y of A l b e r t a , 1976 A THESIS SUBMITTED IN PARTIAL FULFILLMENT OF THE REQUIREMENTS FOR THE DEGREE OF MASTER OF SCIENCE i n THE FACULTY OF GRADUATE STUDIES (Department of Zoology) We accept t h i s t h e s i s as c o n f o r m i n g t o the r e q u i r e d s t a n d a r d THE UNIVERSITY OF BRITISH COLUMBIA 2 October 1981 © Jens R o l a n d , 1981 In p r e s e n t i n g t h i s t h e s i s i n p a r t i a l f u l f i l m e n t of the requirements f o r an advanced degree at the U n i v e r s i t y o f B r i t i s h Columbia, I agree t h a t the L i b r a r y s h a l l make i t f r e e l y a v a i l a b l e f o r r e f e r e n c e and study. I f u r t h e r agree t h a t p e r m i s s i o n f o r e x t e n s i v e copying of t h i s t h e s i s f o r s c h o l a r l y purposes may be granted by the head o f my department o r by h i s or her r e p r e s e n t a t i v e s . I t i s understood t h a t copying or p u b l i c a t i o n of t h i s t h e s i s f o r f i n a n c i a l g a i n s h a l l not be allowed without my w r i t t e n p e r m i s s i o n . Department of The U n i v e r s i t ^ o f B r i t i s h Columbia 2075 Wesbrook P l a c e Vancouver, Canada V6T 1W5 DE-6 (2/79) i i ABSTRACT Many i n s e c t p o p u l a t i o n s become d a r k e r a t h i g h e l e v a t i o n s and h i g h l a t i t u d e s . D e s p i t e absence of e m p i r i c a l e v i d e n c e , i t i s commonly b e l i e v e d t h a t melanism a l l o w s more e f f i c i e n t b a s k i n g by i n s e c t s i n s u n l i g h t , t h e r e b y r a i s i n g body tem p e r a t u r e and i n c r e a s i n g a c t i v i t y . V a r i a t i o n i n melanism w i t h i n a s i n g l e p o p u l a t i o n of a l p i n e C o l i a s s u l p h u r b u t t e r f l i e s ( L e p i d o p t e r a : P i e r i d a e ) a l l o w e d d e t e r m i n a t i o n of the advantage, i n c o l d e n v i r o n m e n t s , f o r t h i s c h a r a c t e r i s t i c . A l t e r n a t i v e hypotheses r e l a t i n g the e f f e c t of melanism t o f e c u n d i t y , p r e d a t i o n , d i e l a c t i v i t y , and s e a s o n a l s u r v i v o r s h i p were t e s t e d by f i e l d and l a b o r a t o r y o b s e r v a t i o n and e x p e r i m e n t . At low t e m p e r a t u r e , m e l a n i s t i c females a r e more fe c u n d . A b a l a n c i n g advantage f o r l i g h t c o l o u r e d females does not e x i s t a t h i g h t e m p e r a t u r e s . Dark i n d i v i d u a l s s u f f e r lower p r e d a t i o n r a t e s a t h i g h a l t i t u d e than do l i g h t i n d i v i d u a l s ; the o p p o s i t e i s not t r u e a t low e l e v a t i o n . D u r a t i o n of d i e l a c t i v i t y i s markedly extended f o r d a r k e r b u t t e r f l i e s under c o o l c o n d i t i o n s , but o n l y s l i g h t l y f o r l i g h t i n d i v i d u a l s d u r i n g warm sunny p e r i o d s . M e l a n i s t i c i n d i v i d u a l s a re a b l e t o p r o l o n g the d u r a t i o n of a c t i v i t y f o r f e e d i n g , mate l o c a t i o n , o v i p o s i t i o n and escape from p r e d a t i o n under c o l d c o n d i t i o n s . T h i s appears t o the prime b e n e f i t f o r melanism i n t h i s p o p u l a t i o n . T h i s i s the f i r s t d e m o n s t r a t i o n , i n a n a t u r a l p o p u l a t i o n , of the b e n e f i t of a l p i n e melanism i n i n s e c t s . i i i TABLE OF CONTENTS ABSTRACT i i LIST OF TABLES ... v LIST OF FIGURES v i i ACKNOWLEDGEMENTS i x GENERAL INTRODUCTION 1 MELANISM AND THE DURATION OF DIEL ACTIVITY 8 INTRODUCTION 8 MATERIALS AND METHODS 13 S p e c i e s 13 Study Area 13 F i e l d Methods 14 Body Temperature Measurement 15 I n i t i a t i o n of F l i g h t 16 Maintenance of A c t i v i t y 17 Se a s o n a l A c t i v i t y 18 S u r v i v o r s h i p 18 RESULTS 20 Body Temperature Measurements 23 I n i t i a t i o n of F l i g h t 23 Maintenance of A c t i v i t y 24 Se a s o n a l A c t i v i t y .» 37 S u r v i v o r s h i p 37 DISCUSSION 55 MELANISM AND FECUNDITY 63 i v INTRODUCTION 63 METHODS AND MATERIALS 69 RESULTS 74 N a t u r a l C o l o r a t i o n 74 O v i p o s i t i o n Rate 74 M a t u r a t i o n Rate ... 75 M a n i p u l a t e d C o l o u r 76 O v i p o s i t i o n Rate 76 M a t u r a t i o n Rate 76 M a t i n g Frequency 77 DISCUSSION 80 MELANISM AND PREDATION 87 INTRODUCTION 87 MATERIALS and METHODS 91 Rest S i t e S e l e c t i o n 91 Ground P r e d a t i o n 92 B i r d P r e d a t i o n 92 RESULTS 93 Rest S i t e S e l e c t i o n 93 Ground P r e d a t i o n 93 B i r d P r e d a t i o n 97 DISCUSSION 99 GENERAL CONCLUSION 103 LITERATURE CITED 109 V LIST OF TABLES T a b l e I . M u l t i p l e r e g r e s s i o n of C o l i a s n a s t e s body temp e r a t u r e as a f u n c t i o n of a i r t e m p e r a t u r e , s u n l i g h t , and degree of melanism 24 T a b l e I I . Comparison of r a d i a t i o n - t e m p e r a t u r e o b s e r v a t i o n s f o r a c t i v i t i e s by dark and l i g h t C o l i a s n a s t e s 30 T a b l e I I I . Comparison of t h r e s h o l d s f o r v a r i o u s a c t i v i t i e s , w i t h t h o s e f o r f l i g h t 31 T a b l e IV. P r o p o r t i o n of f l i g h t time a v a i l a b l e t o C o l i a s n a s t e s of d i f f e r i n g melanism v a l u e s 34 T a b l e V. Mean d a i l y d i s t a n c e moved by dark and l i g h t C o l i a s n a s t e s 41 T a b l e V I . Mean d a i l y d i s t a n c e moved by male and female C o l i a s n a s t e s 52 T a b l e V I I . Summary of f e c u n d i t y e x p e r i m e n t s on female C o l i a s b u t t e r f l i e s 70 T a b l e V I I I . C o r r e l a t i o n s between degree of melanism and mean d a i l y o v i p o s i t i o n r a t e of C o l i a s females 75 T a b l e IX. C o r r e l a t i o n s between degree of melanism and mean d a i l y egg m a t u r a t i o n r a t e of C o l i a s females 76 T a b l e X. Mean number of eggs o v i p o s i t e d per day by normal and a r t i f i c i a l l y darkened C o l i a s females 77 T a b l e X I . Mean number of eggs matured per day by normal and a r t i f i c i a l l y darkened C o l i a s females 77 T a b l e X I I . P r e d a t i o n l o s s e s of dark and l i g h t C o l i a s v i n a s t e s a t two e l e v a t i o n s 96 T a b l e X I I I . E l e v a t i o n a l change i n beak mark f r e q u e n c y f o r C o l i a s n a s t e s 98 T a b l e XIV. E l e v a t i o n a l change i n beak mark f r e q u e n c y f o r dark and l i g h t C o l i a s n a s t e s 98 LIST OF FIGURES F i g u r e 1. Photograph of v a r i a t i o n i n melanism i n C o l i a s n a s t e s from Marmot Creek R e s e a r c h B a s i n , A l b e r t a 3 F i g u r e 2. Flow diagram of p o s s i b l e f u n c t i o n s of melanism i n C o l i a s b u t t e r f l i e s 6 F i g u r e 3. Frequency d i s t r i b u t i o n of melanism f o r C o l i a s n a s t e s and C o l i a s meadi i 21 F i g u r e 4. S o l a r r a d i a t i o n and a i r tem p e r a t u r e a t which dark and l i g h t C o l i a s n a s t e s were o b s e r v e d f l y i n g 26 F i g u r e 5. S o l a r r a d i a t i o n and a i r t e m p e r a t u r e a t which dark and l i g h t C o l i a s n a s t e s were f e e d i n g , c o u r t i n g , o v i p o s i t i n g , and v e r t i c a l b a s k i n g . 28 F i g u r e 6. Lower l i m i t l i n e s of f l i g h t f o r f i v e melanism groups of C o l i a s n a s t e s 32 F i g u r e 7. Daytime change i n p r o p o r t i o n of dark i n d i v i d u a l s on " c o o l " and "hot" days 35 F i g u r e 8. S e a s o n a l change i n mean melanism of C o l i a s n a s t e s and daytime t e m p e r a t u r e s f o r each week d u r i n g the f l i g h t season 38 F i g u r e 9. 1980 r e s i d e n c e c u r v e s f o r C o l i a s n a s t e s . ...... 42 F i g u r e 10. 1979 r e s i d e n c e c u r v e s f o r C o l i a s n a s t e s 44 F i g u r e 11. 1979 r e s i d e n c e c u r v e s f o r C o l i a s m e a d i i 46 F i g u r e 12. F l i g h t t h r e s h o l d s f o r male and female C o l i a s n a s t e s 48 F i g u r e 13. 1980 r e s i d e n c e c u r v e s f o r male and female v i i i C o l i a s n a s t e s 50 F i g u r e 14. Residence c u r v e s f o r e n t i r e C o l i a s n a s t e s p o p u l a t i o n i n 1979 and 1980 . 53 F i g u r e 15. F e c u n d i t y of C o l i a s p h i l o d i c e as a f u n c t i o n of body temperature 66 F i g u r e 16. C o l o u r m a n i p u l a t i o n used i n C o l i a s n a s t e s r f e c u n d i t y e x p e r i m e n t s 71 F i g u r e 17. Frequency of mating f o r dark and l i g h t C o l i a s n a s t e s females 78 F i g u r e 18. F e c u n d i t y s i m u l a t i o n r e s u l t s 83 F i g u r e 19. Photograph of wings r e m a i n i n g a f t e r p r e d a t i o n . 94 F i g u r e 20. P h y s i o l o g y and b e h a v i o u r of C o l i a s b u t t e r f l i e s as a f u n c t i o n of body te m p e r a t u r e ....104 i x ACKNOWLEDGEMENTS I would l i k e t o thank the s t a f f of the K a n a n a s k i s E n v i r o n m e n t a l R e s e a r c h C e n t r e ( U n i v e r s i t y of C a l g a r y ) f o r l a b o r a t o r y space and equipment, and f o r t h e i r h e l p i n making each f i e l d season both e n j o y a b l e and p r o d u c t i v e f o r me. I would a l s o l i k e t o thank Mr. R. H. Swanson and Mr. Z. F i s e r a (Environment Canada) f o r t h e i r c o - o p e r a t i o n w i t h my f i e l d s t u d i e s a t Marmot Creek R e s e a r c h B a s i n . A b l e f i e l d and l a b o r a t o r y a s s i s t a n c e was p r o v i d e d by Woody B e n n e t t , C a t h l e e n N i c h o l s , and Don Q u i r i n g , w i t h o u t whose e n t h u s i a s m and s t r o n g l e g s much of the work c o u l d not have been done. I am a l s o i n d e b t e d t o Susan Hannon, P e t e r M o r r i s o n , and Laura R i c h a r d s f o r t h e i r c o n t r i b u t i o n s , comments, and innumerable d i s c u s s i o n s of many of the i d e a s and r e s u l t s c o n t a i n e d h e r e i n . I p a r t i c u l a r l y thank my a d v i s o r , J u d i t h H. Myers, f o r a l l o w i n g me the o p p o r t u n i t y t o pursue a p r o j e c t of s p e c i a l i n t e r e s t t o m y s e l f ; and f o r her c o n t r i b u t i o n of i d e a s , encouragement, and f i n a n c i a l a s s i s t a n c e throughout t h i s s t u d y . Funding f o r t h i s work was p r o v i d e d by a NSERC r e s e a r c h g r a n t t o my a d v i s o r , a U n i v e r s i t y of B r i t i s h Columbia A r c t i c and A l p i n e r e s e a r c h g r a n t (1980), and two A r c t i c I n s t i t u t e of N o r t h America g r a n t s - i n - a i d (1979 and 1980). 1 GENERAL INTRODUCTION A l l p h e n o t y p i c c h a r a c t e r s a r e i n f l u e n c e d by v a r i a t i o n i n t h e g e n e t i c and e n v i r o n m e n t a l background of i n d i v i d u a l s . P h e n o t y p i c v a r i a t i o n f r e q u e n t l y o c c u r s i n a g e o g r a p h i c a l p a t t e r n ( H e s l o p - H a r r i s o n 1964), which c o r r e l a t e s w e l l w i t h an e n v i r o n m e n t a l parameter. In t h i s s i t u a t i o n , i t i s t e m p t i n g t o propose an a d a p t i v e f u n c t i o n t o t h a t c h a r a c t e r , and a s e l e c t i v e mechanism a s s o c i a t e d w i t h the environment. However, the a c t u a l d e m o n s t r a t i o n of a d a p t i v e v a l u e of c h a r a c t e r s i s r a r e a l t h o u g h s p e c u l a t i o n s a r e rampant. Frequent c o r r e l a t i o n of o b s e r v e d p h e n o t y p i c c h a r a c t e r s and e n v i r o n m e n t a l g r a d i e n t s has r e s u l t e d i n the e s t a b l i s h m e n t of a v a r i e t y of g e o g r a p h i c r u l e s ( G l o g e r s R u l e , Bergmans R u l e , A l i e n s R u l e ) . The u s e f u l n e s s of t h e s e r u l e s i s q u e s t i o n a b l e i n l i g h t of the l a c k of e v i d e n c e of any mechanism by which they r e s u l t , and f o r the e x i s t e n c e of numerous e x c e p t i o n s t o each (Mayr 1956). The b e s t d e m o n s t r a t i o n s of the a d a p t i v e v a l u e of p h e n o t y p i c c h a r a c t e r s have come from the s t u d y of polymorphisms (eg. C a i n and Sheppard 1950; K e t t l e w e l l 1955,1956). Less work has been c a r r i e d out on c o n t i n u o u s c h a r a c t e r s (eg. C l a u s e n e t . a l . 1940), and almost none on the a d a p t i v e v a l u e of c h a r a c t e r s which show no v a r i a t i o n ( S i l b e r g l i e d et.aJL. 1 980). To show t h a t a p h e n o t y p i c c h a r a c t e r i s t r u l y a d a p t i v e r e q u i r e s the d e m o n s t r a t i o n t h a t i t i n c r e a s e the " f i t n e s s " of i n d i v i d u a l s which p o s s e s s the c h a r a c t e r r e l a t i v e t o i n d i v i d u a l s which do n o t . F i t n e s s i s o f t e n d e f i n e d as the t o t a l number of o f f s p r i n g s u r v i v i n g t o r e p r o d u c t i v e age ( E h r l i c h e t . a _ l . 1 974). At l e a s t 2 one of the two components of f i t n e s s : s u r v i v o r s h i p and f e c u n d i t y ( r a t e of r e p r o d u c t i o n ) , would t h e r e f o r e have t o be shown t o be a f f e c t e d by v a r i a t i o n i n phenotype. The i n c r e a s e d d a r k e n i n g of a n i m a l s w i t h an i n c r e a s e i n a l t i t u d e and l a t i t u d e has been o b s e r v e d i n many i n v e r t e b r a t e s (Walsingham 1885; L e u s s l e r 1935; Downes 1965; Watt 1968,1969; Douglas and G r u l a 1978). S i n c e t h i s f r e q u e n t l y o c c u r s i n e c t o t h e r m s , workers have proposed t h a t melanism i s an a d a p t a t i o n i n c r e a s i n g the a b s o r p t i o n of s o l a r r a d i a t i o n (Casey 1981). L i t t l e or no e m p i r i c a l e v i d e n c e has been p r o v i d e d t o show t h a t melanism i n c o l d e n v i ronments a f f e c t s the f i t n e s s of the i n d i v i d u a l s c o n c e r ned. My study i s an attempt t o det e r m i n e the e c o l o g i c a l i mportance of melanism i n a r c t i c and a l p i n e s u l p h u r b u t t e r f l i e s of t he genus C o l i a s F a b r i c i u s ( L e p i d o p t e r a : P i e r i d a e ) , s p e c i f i c a l l y C o l i a s n a s t e s B o i s d u v a l ( F i g . 1) and C o l i a s m e a d i i Edwards. Melanism i n t h i s genus i s i n p a r t g e n e t i c a l l y c o n t r o l l e d , and i s modulated by the e f f e c t s of p h o t o p e r i o d and temperature (Hoffman 1978). I f melanism i s a c h a r a c t e r which b e n e f i t s t h e s e i n s e c t s i n c o l d e n v i r o n m e n t s , i t s h o u l d be demonstrated t o a f f e c t some parameter of f i t n e s s . K e t t l e w e l l (1973), s t a t e s f o u r p o s s i b l e f u n c t i o n s of melanism: 1. u l t r a v i o l e t f i l t r a t i o n . 2. aposemasis. 3. c r y p s i s . 4. heat absorbance. 3 F i g u r e 1. C o l i a s n a s t e s specimens showing v a r i a t i o n of melanism a t Marmot Creek R e s e a r c h B a s i n , K a n a n a s k i s , A l b e r t a . 4 5 F a c t o r s a f f e c t i n g t he degree of melanism and the p o s s i b l e e f f e c t s which melanism has on C o l i a s a re shown i n F i g u r e 2. F i t n e s s i s d e t e r m i n e d by b o t h s u r v i v o r s h i p and f e c u n d i t y . Melanism can a f f e c t t h e s e by a v a r i e t y mechanisms. I f melanism i s an a d a p t a t i o n t o i n c r e a s e the degree of c r y p s i s , i t s h o u l d reduce p r e d a t i o n and i n c r e a s e s u r v i v a l . M e lanism, as an a d a p t a t i o n f o r heat absorbance, can a c t t o i n c r e a s e f e c u n d i t y e i t h e r i n d i r e c t l y by i n c r e a s i n g the a c t i v i t y ( f e e d i n g , mate l o c a t i n g , o v i p o s i t i n g ) of the i n s e c t , or d i r e c t l y by i n c r e a s i n g the r a t e a t which b i o c h e m i c a l p r o c e s s e s o c c u r . S i n c e temperature has a s t r o n g impact on i n s e c t l i f e span ( G i l b e r t e t . a l . 1976), melanism c o u l d a l s o have the e f f e c t of r e d u c i n g s u r v i v o r s h i p . Heat absorbance has been the common e x p l a n a t i o n f o r melanism i n a r c t i c and a l p i n e organisms ( L e u s s l e r 1935; Freeman 1958; Downes 1965; Casey 1981). That i t i s such a common b e l i e f , i n l i g h t of almost t o t a l absence of e v i d e n c e of i t s a d a p t i v e v a l u e , made t h i s the p r i m a r y f o c u s of my t h e s i s . I c o n s i d e r e d two components: 1. the e f f e c t of heat absorbance on i n s e c t a c t i v i t y (Chapter One), and 2. the d i r e c t e f f e c t of heat absorbance on r a t e of egg m a t u r a t i o n (Chapter Two). C r y p s i s i s the be s t documented s e l e c t i v e advantage of melanism i n i n s e c t s . The p o s s i b i l i t y of d i f f e r e n t i a l p r e d a t i o n a c t i n g t o cause the ob s e r v e d c l i n e s i n C o l i a s b u t t e r f l i e s i s ad d r e s s e d i n Chapter Three. 6 F i g u r e 2. P o s s i b l e mechanisms by which melanism c o u l d a c t as an advantage f o r a r c t i c and a l p i n e C o l i a s b u t t e r f l i e s . 7 GENETICS ENVIRONMENT Temperature Photoperiod ADULT , MELANISM Crypsis ^ Light Absorbance PREDATION / FLIGHT ACTIVITY F e e d i n g I / Courtship \ Oviposition SURVIVORSHIP ^ — ^ FECUNDITY "FITNESS" 8 MELANISM AND THE DURATION OF DIEL ACTIVITY INTRODUCTION One of the d i f f i c u l t i e s f a c e d by e c t o t h e r m s i n c o l d e n v i r o nments i s the e f f e c t of c o l d t e mperature i n r e d u c i n g l o c o m o t i o n . A r c t i c and a l p i n e i n s e c t s have e v o l v e d c h a r a c t e r i s t i c s which a l l o w s u s t a i n e d a c t i v i t y i n t h e s e t h e r m a l l y r i g o u r o u s h a b i t a t s . A d a p t a t i o n t o c o l d e nvironments can be a c h i e v e d b e h a v i o u r a l l y by b a s k i n g ( C l e n c h 1966; Kevan and Shorthouse 1970; Casey 1981), p h y s i o l o g i c a l l y t h r o u g h s h i v e r i n g ( H e i n r i c h 1971,1975), and m o r p h o l o g i c a l l y t h r o u g h s t r u c t u r a l and m e t a b o l i c adjustment such as melanism (Douglas and G r u l a 1978; Watt 1968, 1969), or pubescence ( S t i l e s 1979), and enzyme a d a p t a t i o n (Hochachka and Somero 1973). Melanism, or the d a r k e n i n g of c o l o r a t i o n , has l o n g been noted as a common c h a r a c t e r i s t i c of many t u n d r a i n s e c t s (Walsingham 1885). S e v e r a l hypotheses have been put f o r w a r d t o e x p l a i n t h e g r e a t e r i n c i d e n c e of melanism among a r c t i c and a l p i n e e c t o t h e r m s (Mani 1968). These i n c l u d e the i n c r e a s e d a b s o r p t i o n of v i s i b l e l i g h t t o r a i s e body t e m p e r a t u r e , i n c r e a s e d s c r e e n i n g of u l t r a v i o l e t r a d i a t i o n a t h i g h e l e v a t i o n , and d e c r e a s e d water l o s s t h r o u g h the c u t i c l e . Of t h e s e h y p o t h e s e s , t h e r m o r e g u l a t i o n i s perhaps the most o f t e n s u g g e s t e d . Dark c o l o u r e d i n s e c t s a r e a b l e t o r a i s e t h e i r body tem p e r a t u r e by a b s o r b i n g more v i s i b l e r a d i a t i o n (Gates 1980). P i e r i d b u t t e r f l i e s of the genus C o l i a s F a b r i c i u s a r e an o f t e n c i t e d example of i n c r e a s e d melanism w i t h h i g h e r a l t i t u d e 9 and l a t i t u d e ( L e u s s l e r 1935; Freeman 1965; Watt 1968,1969; K e t t l e w e l l 1973). T h i s c l i n a l v a r i a t i o n i s e x p r e s s e d b o t h w i t h i n and between s p e c i e s (Watt 1968; Roland 1978). C o n t r o l of the amount of m e l a n i n has b o t h g e n e t i c and e n v i r o n m e n t a l components. Larvae and pupae exposed t o c o o l t e m p e r a t u r e s d u r i n g t h e i r development, r e s u l t i n d a r k e r a d u l t s than t h o s e r e a r e d under warm c o n d i t i o n s . Temperature p l a y s an i m p o r t a n t r o l e i n d e t e r m i n i n g the u l t i m a t e c o l o r a t i o n u n t i l t h r e e weeks p r i o r t o e c l o s i o n of the a d u l t (Hoffman 1978). E x p e r i m e n t s by Ward Watt and R i c h a r d Hoffman (Ward Watt p e r s . comm.) have shown, however, t h a t i n l o w l a n d and a l p i n e C o l i a s , dark and l i g h t s t r a i n s can be s e l e c t e d which r e s i s t the e n v i r o n m e n t a l i n f l u e n c e s d e t e r m i n i n g melanism. To maximize heat g a i n from the sun, C o l i a s p e r f o r m l a t e r a l b a s k i n g ( C l e n c h 1966; Kevan and Shorthouse 1970). The i n s e c t o r i e n t s i t s body p e r p e n d i c u l a r t o the sun and, w i t h the wings f o l d e d over the back, t i l t s t he wings such t h a t incoming s o l a r r a d i a t i o n i s e f f e c t i v e l y p e r p e n d i c u l a r t o the v e n t r a l wing s u r f a c e (Watt 1968). The g r e a t e s t e x p r e s s i o n of melanism i s i n the b a s a l p o r t i o n of the h i n d wing s u r f a c e . D u r i n g b a s k i n g , t h i s p a r t of the wing l i e s d i r e c t l y over the t h o r a x and abdomen of the b u t t e r f l y . Heat g a i n by the m e l a n i z e d integument can then be t r a n s f e r r e d t o the body of the i n s e c t p r i m a r i l y by c o n d u c t i o n , and r e r a d i a t i o n ( W a s s e r t h a l 1975). Dark b u t t e r f l i e s a r e more e f f i c i e n t a t a b s o r b i n g s o l a r r a d i a t i o n t o r a i s e body te m p e r a t u r e above ambient t e m p e r a t u r e . B a s k i n g b e h a v i o u r c o m p r i s e s a l a r g e p o r t i o n of the a c t i v i t y of t h e s e i n s e c t s 10 (Watt 1968; Kevan and Shorthouse 1970). Heat s e e k i n g b e h a v i o u r ( o r i e n t a t i o n p e r p e n d i c u l a r t o the s u n ) , predominates when body temperature i s below 30 t o 35°C. (Watt 1968). Body tem p e r a t u r e must exceed 30°C f o r b u t t e r f l i e s t o i n i t i a t e v o l u n t a r y f l i g h t . Heat a v o i d a n c e b e h a v i o u r ( o r i e n t a t i o n p a r a l l e l t o the s u n l i g h t ) , predominates when body t e m p e r a t u r e s a r e above 38°C. Watt (1968) proposes t h a t dark i n d i v i d u a l s have an advantage i n g a i n i n g heat a t c o l d t e m p e r a t u r e s ; l i g h t i n d i v i d u a l s have an advantage i n a v o i d i n g heat s t r e s s a t h i g h t e m p e r a t u r e , and h i g h r a d i a n t l o a d . T h i s advantage f o r l i g h t e r i n d i v i d u a l s would be p a r t i c u l a r l y i m p o r t a n t i n a l p i n e e nvironments where, owing t o i n t e n s e i n s o l a t i o n , and a l a c k of shade, t e m p e r a t u r e s near the ground can p e r i o d i c a l l y be v e r y h i g h , o f t e n e x c e e d i n g 40°C (Mani 1968). Taken t o g e t h e r , t h e s e i m p l i c a t e ambient temperature and s o l a r r a d i a t i o n as i m p o r t a n t c o n s t r a i n t s on d a i l y and s e a s o n a l a c t i v i t y , and u l t i m a t e s u c c e s s of the i n s e c t . K e t t l e w e l l (1973), i n h i s book The E v o l u t i o n of Melanism , s t a t e s t h a t "Watt has ... f o r t h e f i r s t t i me shown, by a s e r i e s of f i n e l y c o n t r o l l e d e x p e r i m e n t s on d a y - f l y i n g L e p i d o p t e r a , the s e l e c t i v e advantages of p i g m e n t a t i o n i n r e g a r d t o temperature c o n t r o l " . A l t h o u g h Watt demonstrated t h a t p i g m e n t a t i o n a f f e c t s t e m perature c o n t r o l , and t h a t dark and l i g h t b u t t e r f l i e s have the same t h r e s h o l d body te m p e r a t u r e f o r the i n i t i a t i o n of f l i g h t , no d e m o n s t r a t i o n of d i f f e r e n t i a l a c t i v i t y by dark and l i g h t members of a p o p u l a t i o n has been demonstrated i n the f i e l d . G r e a t e r a c t i v i t y of m e l a n i c v e r s u s non-melanic two-spot 11 l a d y b i r d b e e t l e s A d a l i a b i p u n c t a t a ( C o c c i n e l i d a e ) has been demonstrated f o r i n d i v i d u a l s which were c o o l e d and then a l l o w e d to warm up under an a r t i f i c i a l l i g h t s o u r c e (Benham e t . a l . 1974). R e s u l t s o b t a i n e d from f i n e l y c o n t r o l l e d e x p e r i m e n t s on a few i n d i v i d u a l s may have l i t t l e r e l e v e n c e i n a p o p u l a t i o n exposed t o e x t r e m e l y v a r i a b l e weather. In the f i e l d , Heodus  v i r g a u r e a e ( L y c a e n i d a e ) i s o n l y c a p a b l e of f l i g h t above a c e r t a i n t h r e s h o l d c o m b i n a t i o n of s u n l i g h t and ambient t e m p e r a t u r e (Douwes 1976). There i s no i n d i c a t i o n of any c o l o u r v a r i a b i l i t y i n t h i s s p e c i e s which might a f f e c t o b s e r v e d a c t i v i t y . The i m p l i e d i n c r e a s e i n a c t i v i t y of d a r k e r i n d i v i d u a l s i n c o o l c l i m a t e s i s based on l i t t l e or no e m p i r i c a l e v i d e n c e . The i n t e n t of t h i s c h a p t e r , i s t o d e t e r m i n e whether, under f i e l d c o n d i t i o n s , dark C o l i a s a r e c a p a b l e of i n i t i a t i n g f l i g h t e a r l i e r and m a i n t a i n i n g g r e a t e r d i e l or s e a s o n a l a c t i v i t y r e l a t i v e t o l i g h t C o l i a s . F l i g h t i s a n e c e s s a r y p r e r e q u i s i t e t o f e e d i n g , mate l o c a t i o n , o v i p o s i t i o n and escape from p r e d a t o r s . In a p o p u l a t i o n which shows v a r i a b i l i t y i n the degree of melanism of i t s members, a d e t e c t a b l e d i f f e r e n c e i n d u r a t i o n of a c t i v i t y and s u r v i v a l of dark and l i g h t i n d i v i d u a l s s h o u l d be d e m o n s t r a b l e . The f o l l o w i n g h y p otheses were t e s t e d : 1. Dark C o l i a s s h o u l d be o b s e r v e d t o i n i t i a t e f l i g h t e a r l i e r than l i g h t e r c o l o u r e d b u t t e r f l i e s . 2. A t h r e s h o l d c o m b i n a t i o n of t e m p e r a t u r e and s u n l i g h t e x i s t s , below which l i g h t b u t t e r f l i e s cannot remain a c t i v e , and a s i m i l a r but lower t h r e s h o l d o c c u r s f o r d ark b u t t e r f l i e s . 3. Dark i n d i v i d u a l s a r e a b l e t o remain 12 a c t i v e l o n g e r d u r i n g the season, and t h e r e f o r e show l o n g e r r e s i d e n c e than l i g h t i n d i v i d u a l s . 1 3 MATERIALS AND METHODS Spec i e s The major p a r t of t h i s study was c a r r i e d out on the a r c t i c s u l p h u r b u t t e r f l y C o l i a s n a s t e s B o i s d u v a l . A d d i t i o n a l d a t a were c o l l e c t e d on Mead's s u l p h u r b u t t e r f l y C o l i a s meadi i Edwards. C o l i a s n a s t e s , i s a h o l a r c t i c s p e c i e s t y p i c a l of t u n d r a e n v i r o n m e n t s . In N o r t h A m e r i c a , C. n a s t e s ranges from the s o u t h e r n A r c t i c I s l a n d s t o t r e e l i n e . In the Rocky M o u n t a i n s , i t o c c u r s as f a r s o u t h as the Canada-United S t a t e s b o r d e r ( H o v a n i t z 1950). C o l i a s m e a d i i , i s a l s o a t u n d r a i n h a b i t a n t , r e s t r i c t e d t o a l p i n e a r e a s of the Rocky Mountains from C o l o r a d o t o c e n t r a l B r i t i s h Columbia and A l b e r t a . The range of C. m e a d i i o v e r l a p s C. n a s t e s from a p p r o x i m a t e l y the Canada - U.S.A. borde r t o c e n t r a l B r i t i s h Columbia and A l b e r t a ( H o v a n i t z 1950). Where they a r e s y m p a t r i c , C. m e a d i i i s g e n e r a l l y found a t lower e l e v a t i o n s than C. n a s t e s . At a l l l o c a t i o n s , a d u l t s f l y from the b e g i n n i n g of J u l y t o the end of August ( H o v a n i t z 1951). Study Area T h i s s t u d y was co n d u c t e d a t Marmot Creek R e s e a r c h B a s i n , K a n a n a s k i s V a l l e y , A l b e r t a (50° 50' N, 115° 11' W), d u r i n g the summers of 1979 and 1980. At t h i s s i t e , C. n a s t e s spp. s t r e c k e r i Grum-Grshmailo, ranges from 2350 t o 2800 metres e l e v a t i o n , i n d r y a l p i n e meadows and r i d g e s . C. m e a d i i spp. 14 e l i s S t r e c k e r , i s found c l o s e r t o t r e e l i n e , from 2200 t o 2550 metres. The study a r e a c o n s i s t e d of a lower e a s t f a c i n g c i r q u e (2350 t o 2500 metres) and a l o n g f l a t s o u t h f a c i n g r i d g e which ascends from the c i r q u e t o an e l e v a t i o n of 2800 m e t r e s . Large meadows of g r a s s and mountain avens ( Dryas i n t e g r i f o l i a M. V a h l . ) t y p i f y the major p a r t of the study a r e a . L a r v a l host p l a n t s , A s t r a g a l u s a l p i n u s L., O x y t r o p i s podocarpa A. Gray, and Hedysarum s u l p h u r e s c e n s Rydberg abound t h r o u g h o u t t h e s e meadows. T o t a l area of the st u d y s i t e i s a p p r o x i m a t e l y t e n h e c t a r e s . F i e l d Methods D i f f e r e n c e s i n melanism a r e due t o a change i n r e l a t i v e f r e q u e n c y of b l a c k and y e l l o w s c a l e s c o v e r i n g the wing. Dark i n d i v i d u a l s have a g r e a t e r p r o p o r t i o n of b l a c k s c a l e s t o y e l l o w s c a l e . In the f i e l d , the number of b l a c k and y e l l o w s c a l e s i n the b a s a l p o r t i o n of the v e n t r a l h i n d wing s u r f a c e was counted w i t h the a i d of a d i s s e c t i n g m i c r o s c o p e equipped w i t h an o c u l a r s c a l e . To f a c i l i t a t e c o u n t i n g , the l i v e specimen, w i t h wings f o l d e d over i t s back, was p l a c e d i n a g l a s s i n e e n v e l o p e . The i n s e c t was p o s i t i o n e d such t h a t the b a s a l p a r t of the Cu^ c e l l was exposed through a s m a l l h o l e i n one s i d e of the en v e l o p e . The l i n e s on the o c u l a r s c a l e were used as p o i n t e r s . The number of b l a c k s c a l e s i n 200 sample p o i n t s was co u n t e d . 15 Body Temperature Measurement I t was i m p o r t a n t t o d e t e r m i n e whether my method of q u a n t i f y i n g melanism a l l o w e d d i s c r i m i n a t i o n of l a r g e enough c o l o u r d i f f e r e n c e s which c o u l d r e s u l t i n d i f f e r e n c e s i n body t e m p e r a t u r e . D i f f e r e n c e s i n melanism between s p e c i e s c a u s e s a marked d i f f e r e n c e i n heat g a i n when exposed t o s u n l i g h t (Watt 1968). To compare t e m p e r a t u r e s of C o l i a s n a s t e s specimens, a s e r i e s of c o p p e r - c o n s t a n t a n thermocouples (32 guage), and a Doran M i n i Thermocouple P o t e n t i o m e t e r Model E4221 were used. So t h a t a s e r i e s of b u t t e r f l i e s of d i f f e r e n t melanism c o u l d be m o n i t o r e d s i m u l t a n e o u s l y , f i v e specimen-thermocouples and one c a l i b r a t i o n thermocouple were each c o n n e c t e d i n p a r a l l e l t h r o u g h a six-way s i n g l e p o l e s w i t c h b e f o r e c o n n e c t i n g t o the p o t e n t i o m e t e r . Each of the s i x thermocouples was c o n n e c t e d i n s e r i e s w i t h a c o l d - j u n c t i o n r e f e r e n c e thermocouple i n an i c e b a t h . Only dead d r y specimens i n the normal b a s k i n g p o s i t i o n were used. The d i f f e r e n c e i n r e s u l t s which would be o b t a i n e d u s i n g l i v e or f r e s h l y k i l l e d specimens would be due t o the g r e a t e r heat c a p a c i t a n c e of a f l u i d - f i l l e d body as compared t o a d r i e d one. T h i s would a f f e c t the r a t e of heat g a i n , but not the s t a b i l i z e d body t e m p e r a t u r e . P r e v i o u s s t u d i e s have shown t h a t the use of dead or l i v e specimens makes l i t t l e d i f f e r e n c e on heat g a i n (Watt 1968; W a s s e r t h a l 1975). E v a p o r a t i v e c o o l i n g p l a y s a v e r y minor p a r t i n d e t e r m i n i n g body te m p e r a t u r e i n th e s e b u t t e r f l i e s (Watt 1968). The d r i e d abdomen of each specimen was removed, and a f a l s e abdomen was made of Lepage's B o n d f a s t g l u e around the t h e r m o c o u p l e , and a t t a c h e d between the 16 \ wings i n the normal p o s i t i o n of the abdomen. B u t t e r f l i e s were a l l p o s i t i o n e d such t h a t t h e i r v e n t r a l h i n d w i n g s u r f a c e was p e r p e n d i c u l a r t o the s u n l i g h t . Measurements were made on two s e r i e s of f i v e b u t t e r f l i e s on two d i f f e r e n t days. From s u n r i s e u n t i l s o l a r noon, "body" temperature was r e c o r d e d f o r each specimen e v e r y h a l f hour. S i m u l t a n e o u s measurement of ambient t e m p e r a t u r e and s o l a r r a d i a t i o n were a l s o made. Four t e s t s were c a r r i e d out t o dete r m i n e a c t i v i t y of dark and l i g h t i n d i v i d u a l s : (1) . I n i t i a t i o n of d i e l f l i g h t a c t i v i t y . (2) . Maintenance of a c t i v i t y over a range of weather c o n d i t i o n s . (3) . D u r a t i o n of s e a s o n a l a c t i v i t y . (4) . S u r v i v o r s h i p of dark and l i g h t morphs d u r i n g the season. I n i t i a t i o n of F l i g h t S i n c e h e a t i n g r a t e s of dark and l i g h t i n d i v i d u a l s d i f f e r (Watt 1968), the time a t which f l i g h t i s i n i t i a t e d i n the morning might i n p a r t be d e t e r m i n e d by c o l o u r . To t e s t t h i s , specimens were c o l l e c t e d , kept o v e r n i g h t i n g l a s s i n e e n v e l o p e s , and p r i o r t o s u n r i s e , were s e t out i n normal b a s k i n g p o s i t i o n . The degree of d a r k e n i n g of each i n d i v i d u a l was known, and the o r d e r i n which they f l e w o f f was r e c o r d e d . I t was p r e d i c t e d t h a t dark i n d i v i d u a l s s h o u l d f l y o f f e a r l i e r than l i g h t ones. 17 Maintenance of A c t i v i t y B u t t e r f l i e s were sampled from a l l e l e v a t i o n s over which the s p e c i e s ranged. When an i n d i v i d u a l was s i g h t e d , i t s b e h a v i o u r was r e c o r d e d a s : b a s k i n g , f l y i n g , f e e d i n g , c o u r t i n g , or o v i p o s i t i n g . V e r t i c a l b a s k i n g , a heat a v o i d a n c e b e h a v i o u r (Watt 1968),was a l s o r e c o r d e d , but was v e r y r a r e l y o b s e r v e d . I n d i v i d u a l s were then pursued and c a p t u r e d by handnet. I t s h o u l d be noted t h a t C o l i a s b u t t e r f l i e s , e s p e c i a l l y C. n a s t e s a r e e x t r e m e l y c r y p t i c when r e s t i n g on the ground or v e g e t a t i o n , and a r e g e n e r a l l y d e t e c t a b l e o n l y when f l y i n g . A l l b e h a v i o u r s r e c o r d e d t h e r e f o r e , were of i n d i v i d u a l s which were f l y i n g when f i r s t o b s e r v e d . C o n t i n u o u s r e c o r d s were kept of ambient temperature and amount of s o l a r r a d i a t i o n . Two Stevenson Screens were s e t up: one a t t r e e l i n e (2350 m), and a second a t the t o p of the study a r e a (2750 m). Each s c r e e n c o n t a i n e d a r e c o r d i n g hygrothermograph. Daytime t e m p e r a t u r e s c o n s i s t e n t l y d i f f e r e d by two t o f i v e degrees C e n t i g r a d e between the two s i t e s , and so, i n t e r p o l a t i o n between them a l l o w e d d e t e r m i n a t i o n of the ambient temperature a t any e l e v a t i o n f o r any p o i n t i n t i m e . S o l a r r a d i a t i o n was r e c o r d e d a t each s a m p l i n g s u b - s i t e w i t h a Weather Measure Model R401 m e c h a n i c a l p y r a n o g r a p h . S i n c e a c o n s i d e r a b l e l a g ( a p p r o x i m a t e l y f i v e m i n u t e s ) o c c u r s i n t h i s i n s t r u m e n t , those p a r t s of the r e c o r d i n g c h a r t s w i t h l a r g e and r a p i d f l u c t u a t i o n s i n s o l a r r a d i a t i o n were not used. T h i s was done because of the r e s u l t i n g d i f f i c u l t y i n p i n p o i n t i n g the e x a c t v a l u e s of s o l a r r a d i a t i o n a t the time of c a p t u r e of the i n s e c t . 18 Graph v a l u e s of i n s t a n t a n e o u s s o l a r r a d i a t i o n i n t e n s i t y were c o n v e r t e d t o gm.cal/cm 2/minute. A d d i t i o n a l d a t a f o r each specimen i n c l u d e d : time of day, e l e v a t i o n , and sex. For each c a p t u r e of an i n d i v i d u a l , t h e r e f o r e , i t s sex, degree of melanism, ambient t e m p e r a t u r e , amount of s o l a r r a d i a t i o n , and b e h a v i o u r were known. S e a s o n a l A c t i v i t y S i n c e temperature and the amount of s u n l i g h t d e c r e a s e over the a d u l t f l i g h t season, I p r e d i c t e d t h a t a g r e a t e r p r o p o r t i o n of the p o p u l a t i o n would be dark l a t e r i n t h e summer. A s i m p l e t e s t of the s e a s o n a l d u r a t i o n of a c t i v i t y was t o compare the degree of melanism of c a p t u r e d i n d i v i d u a l s t o the date on which they were c a p t u r e d . F i e l d work spanned the e n t i r e f l i g h t season of the b u t t e r f l i e s ( e a r l y J u l y t o the end of A u g u s t ) . S u r v i v o r s h i p C a p t u r e d i n d i v i d u a l s were permanently marked w i t h an i d e n t i f y i n g number on the v e n t r a l s u r f a c e of the f o r e wing w i t h a f i n e p o i n t permanent marker. The h i n d wing c o v e r e d the number when the b u t t e r f l y was a t r e s t , so i t would not be o b v i o u s t o p r e d a t o r s when the i n s e c t was on the ground. In f l i g h t , the v e n t r a l wing s u r f a c e would not be e a s i l y seen by a e r i a l p r e d a t o r s . Q u a n t i f i c a t i o n of melanism was done a t a c e n t r a l s i t e on the s t u d y a r e a from which a l l specimens were r e l e a s e d a t f i r s t c a p t u r e . T h i s a l l o w e d e a s i e r c a l c u l a t i o n of d i s t a n c e s 19 moved between the i n i t i a l and subsequent c a p t u r e . R e c a p t u r e d b u t t e r f l i e s were r e l e a s e d from the p o i n t of c a p t u r e . 20 RESULTS In 1979, 272 c a p t u r e s of 229 C o l i a s n a s t e s and 146 c a p t u r e s of 125 C o l i a s m e a d i i were made over the seven week f l i g h t p e r i o d ( J u l y 11 t o August 2 8 ) . Recapture r a t e s f o r the s p e c i e s were: 18.8% f o r C. n a s t e s , and 16.8% f o r C. m e a d i i . In 1980, the f l i g h t season was s l i g h t l y l o n g e r ( J u l y 5 t o August 2 6 ) , and weather was g e n e r a l l y c o o l e r . Only C. n a s t e s was s t u d i e d i n t h i s y e a r . A t o t a l of 566 c a p t u r e s of 433 i n d i v i d u a l s was made. Rec a p t u r e r a t e was 30.7%, w i t h some i n d i v i d u a l s r e c a p t u r e d up t o s i x t i m e s . The g r e a t e r number of r e c a p t u r e s was p r i m a r i l y due t o a more i n t e n s e s a m p l i n g program. C o l i a s n a s t e s i s d a r k e r i n c o l o u r ( h i g h e r b l a c k s c a l e count) than C. m e a d i i ( F i g . 3 ) . In 1 980, the p o p u l a t i o n of C. n a s t e s was d a r k e r than the 1979 p o p u l a t i o n ( F i g . 3a and b ) . The p r i m a r y d i f f e r e n c e i n melanism between the two y e a r s was a dec r e a s e i n the number of l i g h t e r c o l o u r e d i n d i v i d u a l s ( C h i -square goodness of f i t , p<.001). L i t t l e d i f f e r e n c e i n the p r o p o r t i o n s of d a r k e r i n d i v i d u a l s o c c u r r e d between y e a r s . In both y e a r s , a wide range of melanism was e x h i b i t e d by t h i s p o p u l a t i o n . D u r i n g l a r v a l development, c o o l t e m p e r a t u r e s cause d a r k e r c o l o r a t i o n i n the r e s u l t a n t a d u l t s (Hoffman 1978); t h i s c o u l d e x p l a i n t h e d e c r e a s e d number of l i g h t i n d i v i d u a l s o b s e r v e d i n 1980. S i n c e i t was s u s p e c t e d t h a t c o o l t e m p e r a t u r e s might a l s o a f f e c t t h e a b i l i t y of l i g h t e r b u t t e r f l i e s t o f l y , t he ob s e r v e d i n c r e a s e d melanism i n 1980 might s i m p l y r e f l e c t a reduced 21 F i g u r e 3. Frequency d i s t r i b u t i o n of b l a c k s c a l e c o u n t s from the q u a n t i f i c a t i o n of melanism of wing c o l o u r . H i g h c o u n t s r e p r e s e n t dark i n d i v i d u a l s , low c o u n t s r e p r e s e n t l i g h t i n d i v i d u a l s . Median s c a l e c o u n t s a r e i n d i c a t e d by a r r o w s . ( a ) . C. n a s t e s 1980; ( b ) . C. n a s t e s 1979; ( c ) . C. meadii 1979. 50 100 C. nastes 1980 N=383 C. nastes 1979 N = 277 200 C. meadii 1979 N=II3 50 100 150 200 # Black Scales 23 c a p t u r e of l i g h t a d u l t s . To t e s t t h i s , h i s t o g r a m s of b l a c k s c a l e c o u n t s f o r 1979 and 1980 were r e c a l c u l a t e d from i n d i v i d u a l s caught on warm sunny days when a l l b u t t e r f l i e s s h o u l d be a b l e t o f l y . L i g h t e r b u t t e r f l i e s were s t i l l u n d e r r e p r e s e n t e d (p<.005). , T h e r e f o r e , a r e a l d i f f e r e n c e i n c o l o r a t i o n does occur between y e a r s , i n d i c a t i n g a s t r o n g e n v i r o n m e n t a l component a f f e c t i n g o b s e r v e d melanism of the p o p u l a t i o n . Body Temperature Measurements I f we assume t h a t body t e m p e r a t u r e i s a f u n c t i o n of ambient t e m p e r a t u r e , s o l a r r a d i a t i o n and degree of melanism, then m u l t i p l e r e g r e s s i o n a n a l y s i s s h o u l d p r o v i d e a measure of the c o n t r i b u t i o n each makes. Ambient t e m p e r a t u r e , s o l a r r a d i a t i o n and melanism a l l a f f e c t body t e m p e r a t u r e s i g n i f i c a n t l y ( T a b l e I ) . An i n c r e a s e i n the number of b l a c k s c a l e s , r e s u l t s i n an i n c r e a s e i n body t e m p e r a t u r e . T h e r e f o r e , s c a l e c o u n t s o b t a i n e d from my q u a n t i f i c a t i o n t e c h n i q u e have a r e a l meaning as a d e s c r i p t i o n of the degree of melanism w i t h i n the s p e c i e s , and i t s e f f e c t on body t e m p e r a t u r e . I n i t i a t i o n of F l i g h t S i n c e the rank o r d e r of melanism i s known f o r specimens s e t out i n the morning, a Spearman's Rank c o r r e l a t i o n can be made w i t h th e o r d e r i n which i n d i v i d u a l s f l e w o f f . No 24 Tab l e I . M u l t i p l e r e g r e s s i o n of body tem p e r a t u r e as a f u n c t i o n of ambient t e m p e r a t u r e (°C), s o l a r r a d i a t i o n (gm.cal/cm 2/min), and degree of melanism ( b l a c k s c a l e c o u nt) f o r C o l i a s n a s t e s . var i a b l e pa r t i a 1 c o r r e l a t i o n r e g r e s s i o n c oef f i c i e n t s i g n i f i c a n c e a i r temp. .395 .625 P<.Q01 s o l a r r a d i a t i o n .508 .025 P<.001 degree of me l a n i sm .362 .047 P<.001 t o t a l r 2 = .798, N=156 c o r r e l a t i o n between the two v a r i a b l e s was found. There i s no tendency f o r dark C. n a s t e s t o i n i t i a t e f l i g h t e a r l i e r than l i g h t ones. Maintenance of A c t i v i t y M elanism i n the s e s p e c i e s i s not p o l y m o r p h i c but i s e x p r e s s e d as a continuum w i t h normal d i s t r i b u t i o n ( F i g . 3 ) . I n i t i a l l y , the median count of b l a c k s c a l e s was used t o a r b i t r a r i l y d i v i d e t h e p o p u l a t i o n i n t o a dark h a l f ( l e s s than the median number of b l a c k s c a l e s ) , and a l i g h t h a l f ( g r e a t e r than o r e q u a l t o the median number of b l a c k s c a l e s ) . By p l o t t i n g c a p t u r e s of f l y i n g i n d i v i d u a l s from the two c o l o u r groups on axes of a i r tem p e r a t u r e and s o l a r r a d i a t i o n , lower l i m i t s of ob s e r v e d f l i g h t can be d e t e r m i n e d . Data f o r C. n a s t e s were combined f o r bo t h y e a r s f o r the comparison of lower t h r e s h o l d a c t i v i t y c u r v e s f o r dark and l i g h t b u t t e r f l i e s . When combined, the median count was 125.5 b l a c k s c a l e s . The 25 sample was t h e r e f o r e d i v i d e d i n t o a dark h a l f (126 or more, N=283), and a l i g h t h a l f (125 or fewer, N=253). These c a p t u r e s were then p l o t t e d on axes of s o l a r r a d i a t i o n and t e m p e r a t u r e ( F i g . 4 ) . The lower l i m i t of t e m p e r a t u r e and s o l a r r a d i a t i o n a t which each group was a b l e t o f l y was d e t e r m i n e d by e x c l u d i n g the extreme 2.5% of the p o i n t s . In t h i s way, some of the v a r i a n c e i n e s t i m a t e s of c o l o u r and measurement of weather i s e l i m i n a t e d . R e s u l t a n t l i m i t l i n e s were t h e r e f o r e d e f i n e d as the t h r e s h o l d c o m b i n a t i o n of s o l a r r a d i a t i o n and t e m p e r a t u r e below which members of t h a t group were not o b s e r v e d t o be a c t i v e . A l a r g e d i f f e r e n t i a l between the l i m i t s of f l i g h t f o r dark and l i g h t C o l i a s e x i s t s ( F i g . 4 ) . To t e s t whether the t h r e s h o l d l i n e s a r e s i g n i f i c a n t l y d i f f e r e n t f o r the dark and l i g h t i n d i v i d u a l s , the number of c a p t u r e s above and below the h i g h e r t h r e s h o l d were cou n t e d f o r the dark and l i g h t h a l f of the sample, and a 2 X 2 c o n t i n g e n c y t a b l e was made ( T a b l e I I ) . P l o t s of r a d i a t i o n - t e m p e r a t u r e f o r o t h e r b e h a v i o u r s were s i m i l a r l y made ( F i g . 5) and t h r e s h o l d d i f f e r e n c e s between dark and l i g h t groups compared f o r each ( T a b l e I I ) . Melanism a p p a r e n t l y a f f e c t s the a b i l i t y of the i n s e c t s t o f l y and t o f e e d . Once the b u t t e r f l i e s a r e f l y i n g , the degree of melanism may not a f f e c t t h e i r a b i l i t y t o c a r r y out o t h e r a c t i v i t i e s , a l t h o u g h sample s i z e s f o r o v i p o s i t i o n and c o u r t i n g a r e s m a l l . Each b e h a v i o u r appears t o have a d i s t i n c t t h r e s h o l d below which i t cannot be u n d e r t a k e n ( F i g s . 5a-d). T h i s d i f f e r e n c e among b e h a v i o u r s however, c o u l d s i m p l y r e f l e c t s m a l l e r sample 26 F i g u r e 4. S o l a r r a d i a t i o n and a i r temperature at which dark (•) and l i g h t ( O ) C. nastes were observed f l y i n g . Lower l i m i t l i n e s f o r f l i g h t by the two groups are i n d i c a t e d . Dark and l i g h t groups are d e f i n e d i n the t e x t . o CD 3 •o CD cn CD o po O o cn Solar Radiation (gm-cal/cmV'mih.) ho ^ fr> bo 5 bo I l H I • I I 28 F i g u r e 5. S o l a r r a d i a t i o n and a i r t e m p e r a t u r e a t time of o b s e r v a t i o n of v a r i o u s b e h a v i o u r s f o r dark (•) and l i g h t ( O ) C. n a s t e s . Lower l i m i t l i n e s f o r each group are i n d i c a t e d . 29 CM -E I2( £ £ -8I o \ o 4f o £ c n ol Feeding L & ° N = I0 N = I3 Courting c|.2| o "5 I T * o co .4 0 Ovipositing vo _ Vertical Basking 10 15 20 0 5 Temperature 10 15 20 25 (°C) 30 Ta b l e I I . Comparison of d i s t r i b u t i o n s of r a d i a t i o n -t e m perature o b s e r v a t i o n s f o r v a r i o u s a c t i v i t i e s by dark and l i g h t C o l i a s n a s t e s . A c t i v i t y F l y i n g F e e d i n g C o u r t i n g O v i p o s i t i n g V e r t i c a l b a s k i n g Melanism* dark l i g h t dark l i g h t dark l i g h t dark l i g h t dark l i g h t # O b s e r v a t i o n s Above L i g h t T h r e s h o l d 263 247 59 69 7 12 1 1 5 0 1 Below L i g h t T h r e s h o l d 20 6 8 2 3 1 0 3 1 0 p** .0088 .0394 .1999 .0578 .5000 * d i v i s i o n i n t o dark and l i g h t based on p o p u l a t i o n median b l a c k s c a l e c o u n t . ** F i s h e r s E x a c t P r o b a b i l i t y T e s t , o n e - t a i l e d . s i z e r e s u l t i n g i n a h i g h e r t h r e s h o l d . D i s t r i b u t i o n of r a d i a t i o n - t e m p e r a t u r e o b s e r v a t i o n s d u r i n g f l i g h t were t h e r e f o r e compared t o the d i s t r i b u t i o n s f o r o t h e r b e h a v i o u r s t o d e t e r m i n e whether apparent d i f f e r e n c e s i n the r e s p e c t i v e t h r e s h o l d s a r e an a r t i f a c t of sample s i z e . Ambient c o n d i t i o n s f o r f l i g h t d i d not d i f f e r s i g n i f i c a n t l y from t h o s e f o r f e e d i n g , a l t h o u g h they d i d d i f f e r s i g n i f i c a n t l y from t h o s e f o r o t h e r a c t i v i t i e s ( T a b l e I I I ) . The advantage of melanism i n c o l d e n v i r o n m e n t s , i n terms of i t s e f f e c t on a c t i v i t y , i s o n l y on the d u r a t i o n of f l i g h t . To d e t e r m i n e whether f l i g h t d i f f e r e n c e s h o l d t r u e on a f i n e r s c a l e , the t o t a l sample was d i v i d e d i n t o f i v e melanism 31 T a b l e I I I . Comparison of d i s t r i b u t i o n s of r a d i a t i o n - t e m p e r a t u r e o b s e r v a t i o n s f o r f l i g h t and o t h e r b e h a v i o u r s . # O b s e r v a t i o n s Above Below Act i v i t y T h r e s h o l d * T h r e s h o l d p** F e e d i n g 1 35 3 .12 F l y i n g 510 26 C o u r t i n g 23 0 .0087 F l y i n g 434 1 02 O v i p o s i t i n g 18 1 .0053 F l y i n g 357 179 V e r t i c a l b a s k i n g 2 0 .013 F l y i n g 61 475 * t h r e s h o l d f o r each p a i r , i s t h a t f o r the f i r s t a c t i v i t y ** F i s h e r s E x a c t P r o b a b i l i t y T e s t , O n e - t a i l e d . groups w i t h e q u a l range of b l a c k s c a l e c o u n t s w i t h i n each. Groups were p l o t t e d on axes of r a d i a t i o n and a i r tem p e r a t u r e and t h e i r f l i g h t t h r e s h o l d l i n e s drawn as d e s c r i b e d p r e v i o u s l y . I f the t o t a l s a m p l i n g t i m e i s used t o measure the " t y p i c a l " weather f o r the study a r e a , then an e s t i m a t e of the p r o p o r t i o n of the f l i g h t season which has c o m b i n a t i o n s of r a d i a t i o n and ambient temperature l y i n g above the f i v e l i m i t l i n e s can be made. V a l u e s of temperature and s o l a r r a d i a t i o n f o r each of the two y e a r s , were taken from the r e c o r d i n g c h a r t s f o r e v e r y t e n -minute p e r i o d and p l o t t e d ( F i g s . 6a and b ) . The number of these o b s e r v a t i o n s l y i n g above t h e r e s p e c t i v e l i m i t l i n e s was t o t a l l e d . T h i s sum was used t o c a l c u l a t e the p r o p o r t i o n of the t o t a l number of ten-minute o b s e r v a t i o n s which were s u i t a b l e f o r f l i g h t . F o r t h i s p o p u l a t i o n , I e s t i m a t e d t h e amount of time 32 F i g u r e 6. Lower l i m i t l i n e s of f l i g h t by f i v e melanism groups of C. n a s t e s . L i n e s a r e drawn over a s c a t t e r g r a m of s o l a r r a d i a t i o n and a i r temperature f o r the e n t i r e f l i g h t p e r i o d i n (a) 1979, (b) 1980. (melanism groups d e f i n e d i n t e x t . ) o 1 o ' —I C D 3 TD C D —s Q o i o • C D O l • O o ' O l ' Solar Radiation (gmcal cm min) oo o ro 34 t h a t groups of i n c r e a s i n g amounts of melanism would be a b l e t o f l y . In b o t h 1979 and 1980, the amount of time d u r i n g which a c t i v i t y i s i m p o s s i b l e i s s u b s t a n t i a l ( T a ble I V ) . T a b l e IV. P r o p o r t i o n of t o t a l s a m p l i n g time d u r i n g which groups of d i f f e r i n g melanism v a l u e s would be a b l e t o f l y . Groups as d e f i n e d i n t e x t . # of B l a c k S c a l e s 1 979 1 980 146-165 87.9 87.0 126-145 81.8 80.3 106-125 76.9 76.4 86-105 70.5 69.2 66- 85 64.3 57. 1 Those b u t t e r f l i e s most a f f e c t e d i n a c o l d y e a r (1980), a r e l i g h t e s t i n c o l o u r ( T a b l e I V ) . Only two i n s t a n c e s of v e r t i c a l b a s k i n g (heat a v o i d a n c e ) were o b s e r v e d . There was no way t h e r e f o r e , t o t e s t whether a d i f f e r e n t i a l t h r e s h o l d f o r t h i s b e h a v i o u r e x i s t e d between dark and l i g h t b u t t e r f l i e s . F l i g h t by dark b u t t e r f l i e s may be reduced or cease when t e m p e r a t u r e s and i n t e n s i t y of s o l a r r a d i a t i o n a r e h i g h because t h e y must a v o i d over h e a t i n g by shade s e e k i n g and v e r t i c a l b a s k i n g (Watt 1968). L i g h t i n d i v i d u a l s would be a b l e t o p r o l o n g f l i g h t d u r i n g t h e s e hot p e r i o d s . No d e c r e a s e i n the p r o p o r t i o n of dark i n d i v i d u a l s o c c u r s a t noon on " c o o l " days (ambient t e m p e r a t u r e l e s s than 12°C a t 1.5 m above ground s u r f a c e ) ( F i g . 7 a ) . On "hot" d a y s , the p r o p o r t i o n of dark b u t t e r f l i e s i n our samples d e c r e a s e d markedly d u r i n g the warmest p a r t of the day ( F i g . 7 b ) . 35 F i g u r e 7. Daytime change i n the p r o p o r t i o n of dark i n d i v i d u a l s on ( a ) , " c o o l " days ( l e s s than 12°C), and (b) . "hot" days (g r e a t e r than 12 ° C ) . 36 1.0 0.8| 0.6 O 0.4 : o <-> 0.2 a Q Q.01 1.01 ~ 0.81 O g- 0.61 n 0.4 0.2 0.01 08=00 93 l i Cool" days 71 69 78 39 1200 M i • .11 I&00 Hot days 94 94 r 155 25 08=00 12=00 16=00 Mountain Standard Time 37 S e a s o n a l A c t i v i t y Throughout the f l i g h t season, t h e r e i s h i g h v a r i a b i l i t y , i n melanism f o r the p o p u l a t i o n . There i s l i t t l e tendency f o r i n d i v i d u a l s c a p t u r e d l a t e i n the season t o be d a r k e r i n c o l o u r ( F i g . 8 ) . In 1979, t h e r e was a s i g n i f i c a n t i n c r e a s e i n melanism t h r o u g h the season, but t h i s does not c o r r e l a t e w i t h a c o o l i n g i n t e m perature ( F i g . 8 ) . A g e n e r a l c o o l i n g d u r i n g the l a t e r p a r t of 1980 ( F i g . 8) i s not r e f l e c t e d i n an i n c r e a s e i n d a r k e n i n g of these b u t t e r f l i e s . T h e r e f o r e , I f e e l t h a t melanism p l a y s l i t t l e i mportance i n p r o l o n g i n g f l i g h t l a t e i n the season by compensating f o r a r e d u c t i o n i n ambient t e m p e r a t u r e . S u r v i v o r s h i p Comparison of s u r v i v a l i n each year between dark and l i g h t b u t t e r f l i e s , r e q u i r e d t h a t the p o p u l a t i o n be a r b i t r a r i l y d i v i d e d i n t o two groups u s i n g the median b l a c k s c a l e count as d e s c r i b e d p r e v i o u s l y . Rather than u s i n g the median b l a c k s c a l e count f o r C. n a s t e s from both y e a r s as i n c a l c u l a t i n g t h r e s h o l d s , the median count f o r each year was used t o s p l i t t he r e s p e c t i v e samples (1979: 120 b l a c k s c a l e s , 1980: 128 b l a c k s c a l e s ) . S u r v i v o r s h i p e s t i m a t e s were t h e r e f o r e c a l c u l a t e d f o r each h a l f of the p o p u l a t i o n f o r each y e a r . The number of days between the f i r s t and l a s t c a p t u r e of a b u t t e r f l y i s a c o n s e r v a t i v e e s t i m a t e of the s u r v i v o r s h i p of t h a t a n i m a l . I t must have been a l i v e and r e s i d e n t p r i o r t o f i r s t c a p t u r e , and was s t i l l a l i v e and r e s i d e n t a f t e r the l a s t 38 F i g u r e 8. S e a s o n a l change i n mean melanism (number of b l a c k s c a l e s ) and weekly mean daytime temperature i n 1979 and 1 980. Temp Black (°C) Scales _ _ r o r o ^ o o r o o> o o o o 1 I I I ' I t i l l ! 6£ 40 c a p t u r e . When the number of a n i m a l s s u r v i v i n g a g i v e n number of days a r e t o t a l l e d and p l o t t e d , an e s t i m a t e of the l o s s r a t e of a n i m a l s can be made. What i s o f t e n termed a s u r v i v o r s h i p c u r v e i s i n f a c t a r e s i d e n c e c u r v e ( E h r l i c h 1961) s i n c e l o s s of a n i m a l s from the p o p u l a t i o n can be due t o bo t h m o r t a l i t y and e m i g r a t i o n . R e s i d e n c e c u r v e s , a l t h o u g h a f f e c t e d by both p a r a m e t e r s , cannot s e p a r a t e them. A n e g a t i v e e x p o n e n t i a l l o s s r a t e has been suggested t o d e s c r i b e the shape of the r e s i d e n c e c u r v e s ( A n d r z e j e w s k i and Wierzbowska 1961). T h i s t e c h n i q u e r e q u i r e s the c a l c u l a t i o n of a mean r e s i d e n c e time ( t ) f o r the p o p u l a t i o n by summing the number of b u t t e r f l y - d a y s and d i v i d i n g by the t o t a l number of i n d i v i d u a l s . The i n v e r s e of t h i s v a l u e (P. ) i s the number of o i n d i v i d u a l s l o s t from the p o p u l a t i o n per u n i t time (per d a y ) . G i v e n the number of i n d i v i d u a l s i n i t i a l l y caught ( N # ) , the ex p e c t e d number s u r v i v i n g (N) a t any time t would be d e s c r i b e d by the e q u a t i o n : N t = N e. e • P l o t t e d on a l o g s c a l e , N t w i l l t h e r e f o r e have a l i n e a r r e l a t i o n t o t . The e x p e c t e d s t r a i g h t l i n e s h o u l d d e s c r i b e the observ e d d a t a . In 1980, the ob s e r v e d d i s t r i b u t i o n of l o s s of b u t t e r f l i e s from the p o p u l a t i o n f i t s the e x p e c t e d e x p o n e n t i a l decay i f the group of i n d i v i d u a l s caught o n l y once i s e l i m i n a t e d . I n c l u s i o n of t h i s group r e s u l t s i n a poor f i t of obs e r v e d t o e x p e c t e d . A n i m a l s which a r e caught o n l y once may be i n d i v i d u a l s moving t h r o u g h the p o p u l a t i o n ( A n d r z e j e w s k i and Wierzbowska 1961), and t h e r e f o r e can be used as an i n d i c a t i o n 41 of the d i s p e r s a l component of the p o p u l a t i o n . In 1980, C. n a s t e s had a h i g h e r i n i t i a l l o s s of dark i n d i v i d u a l s than l i g h t e r ones ( F i g . 9 ) , and s t e e p e r e x p o n e n t i a l decay (Kolmogorov-Smirnov Two-Sample T e s t , p<.05). Dark i n d i v i d u a l s a r e t h e r e f o r e l o s t from the p o p u l a t i o n a t a f a s t e r r a t e than l i g h t e r c o n s p e c i f i c s . A s i m i l a r d i f f e r e n c e o c c u r r e d i n the 1979 C. n a s t e s p o p u l a t i o n ( F i g . 10,p<.10) and C o l i a s  meadi i p o p u l a t i o n ( F i g . 11, p<.05). Dark i n d i v i d u a l s a r e t h e r e f o r e s u b j e c t t o g r e a t e r m o r t a l i t y or have a h i g h e r r a t e of e m i g r a t i o n . From the comparison of the d u r a t i o n of f l i g h t a c t i v i t y of C o l i a s b u t t e r f l i e s ( F i g . 4 ) , we know t h a t dark i n d i v i d u a l s a r e a c t i v e a s u b s t a n t i a l l y g r e a t e r amount of time than l i g h t i n d i v i d u a l s . Mean d a i l y d i s t a n c e t r a v e l l e d between s e q u e n t i a l c a p t u r e s was a l s o g r e a t e r f o r d a r k e r i n d i v i d u a l s (Table V ) . T a b l e V. Mean d a i l y d i s t a n c e moved between s e q u e n t i a l c a p t u r e s of dark and l i g h t C o l i a s n a s t e s b u t t e r f l i e s . C o l o u r N Mean d i s t a n c e (m/day) dark 61 147.2 l i g h t 89 109.3 p<.037, Mann-Whitney U o n e - t a i l e d t e s t A l l of t h e s e o b s e r v a t i o n s suggest t h a t dark i n d i v i d u a l s f l y more f r e q u e n t l y and f o r a l o n g e r d u r a t i o n , r e s u l t i n g i n h i g h e r e m i g r a t i o n from the p o p u l a t i o n . Observed d i f f e r e n c e s a r e not sex b i a s e d . F l i g h t t h r e s h o l d s 42 F i g u r e 9. 1980 r e s i d e n c e c u r v e s f o r dark (#) and l i g h t ( O ) C. n a s t e s . L i n e s a r e the n e g a t i v e e x p o n e n t i a l l o s s r a t e as c a l c u l a t e d w i t h the e x c l u s i o n of those a n i m a l s caught o n l y once ( A n d r z e j e w s k i and Wiersbowska 1960). « Colias nastes #"Days in Residence 44 F i g u r e 10. 1979 r e s i d e n c e c u r v e s f o r dark (#) and l i g h t ( O ) C. n a s t e s . L i n e s as i n F i g u r e 9. 500 Colias nastes 1979 0 5 10 15 20 25 #Days in Residence 4 6 F i g u r e 11. 1979 r e s i d e n c e c u r v e s f o r dark (#) and l i g h t (O ) C. m e a d i i . L i n e s as i n F i g u r e 9. 500 0 Col ias meadi i 1 9 7 9 10 15 20 25 #Days in Residence 48 F i g u r e 12. F l i g h t t h r e s h o l d s f o r male and female C o l i a s  n a s t e s as a f u n c t i o n of s o l a r r a d i a t i o n and a i r t e m p e r a t u r e . 49 1.2-c o 1.0' dia /mi .8 o CM cr E .6 o a a £ .4 o .2 Female N=270 Male N=275 5 10 15 20 25 Temperature (°C) 50 F i g u r e 13. 1980 r e s i d e n c e c u r v e s f o r male (•) and female (•) C. n a s t e s . L i n e s as i n F i g u r e 9. # Individuals — ai cn o o 52 a r e s i m i l a r ( F i g . 12); r e s i d e n c e c u r v e s a r e not s i g n i f i c a n t l y d i f f e r e n t ( F i g . . 1 3 ) ; and mean d i s p e r s a l d i s t a n c e s do not d i f f e r between sexes (Table V I ) . T a b l e V I . Mean d a i l y d i s t a n c e moved between s e q u e n t i a l c a p t u r e s of male and female C o l i a s n a s t e s . Sex N Mean d i s t a n c e (m/day) Male 72 130.6 Female 78 118.0 p<.764, Mann-Whitney U t w o - t a i l e d t e s t A l t h o u g h not s t a t i s t i c a l l y d i f f e r e n t , i t i s of note t h a t female r e s i d e n c e time was l e s s than t h a t f o r males ( F i g . 13), but d i s p e r s a l d i s t a n c e was s h o r t e r ( T a b l e V I ) . T h i s s u p p o r t s s i m i l a r d a t a f o r C o l i a s a l e x a n d r a Edwards i n C o l o r a d o (Watt e t a l . 1977). G r e a t e r l o s s of females w i t h l e s s movement i m p l i c a t e s h i g h e r m o r t a l i t y among females than among males. I f dark b u t t e r f l i e s a r e l e a v i n g the p o p u l a t i o n more r a p i d l y because of h i g h e r body t e m p e r a t u r e s , i t would be ex p e c t e d t h a t g r e a t e r l o s s of a l l i n d i v i d u a l s would o c c u r a t h i g h e r ambient t e m p e r a t u r e s by v i r t u e of the r e l a t i o n s h i p betweeen a i r and body tem p e r a t u r e ( T a b l e I ) . For the e n t i r e C. n a s t e s p o p u l a t i o n , a s t e e p e r r e s i d e n c e c u r v e o c c u r r e d i n 1979 ( F i g . 14, p>.05 ), which was the warmer of the two y e a r s ( F i g s . 6 and 8 ) . E x p e r i m e n t s and o b s e r v a t i o n s c a r r i e d out t o t e s t the p o s s i b i l i t y of c r y p s i s and d i f f e r e n t i a l p r e d a t i o n of dark and l i g h t C. n a s t e s a r e d i s c u s s e d i n Chapter t h r e e . 53 F i g u r e 14. R e sidence c u r v e s f o r e n t i r e C o l i a s n a s t e s p o p u l a t i o n i n 1979 (•) and 1980 (#). L i n e s as i n F i g u r e 9. Colias nastes 0 5 10 15 20 25 # D a y s in Residence 55 DISCUSSION That dark i n s e c t s i n s u n l i g h t heat up more q u i c k l y than l i g h t i n s e c t s seems t r i v i a l s i n c e any dark o b j e c t w i l l do so ' r e l a t i v e t o one l i g h t e r i n c o l o u r . The p r i m a r y s h o r t c o m i n g of p r e v i o u s s t u d i e s on the a d a p t i v e v a l u e of melanism f o r a r c t i c and a l p i n e i n s e c t s , has been the f a i l u r e t o e x t r a p o l a t e the c a r e f u l l y measured body t e m p e r a t u r e d i f f e r e n c e s t o the a c t i v i t y and u l t i m a t e s u c c e s s of the i n s e c t i n the n a t u r a l environment. Extreme s p a t i a l and t e m p o r a l v a r i a b i l i t y i n both t e m p e r a t u r e and s u n l i g h t i n t u n d r a e n v i r o n m e n t s (Mani 1968) c o u l d w e l l r e s u l t i n no e f f e c t i v e d i f f e r e n c e among i n d i v i d u a l s i n the supposed advantages which h i g h e r body t e m p e r a t u r e s convey t o C o l i a s b u t t e r f l i e s . D i f f e r e n c e s may be so s u b t l e as t o not be measurable i n a h i g h l y v a r i a b l e environment. I f , however, a c l e a r and s u b s t a n t i a l advantage r e l a t i n g v a r i a t i o n i n a c h a r a c t e r t o the s u r v i v o r s h i p and/or f e c u n d i t y of the organism can be demonstrated ( d e s p i t e l a r g e e n v i r o n m e n t a l v a r i a b i l i t y ) , a s t r o n g c o n c l u s i o n r e g a r d i n g the a d a p t i v e v a l u e of t h a t c h a r a c t e r can be made. Thermocouple e x p e r i m e n t s have shown t h a t the degree of melanism w i t h i n t h i s s p e c i e s has a h i g h l y s i g n i f i c a n t e f f e c t i n d e t e r m i n i n g s t a b l i z e d body t e m p e r a t u r e (Table I ) . Melanism a l s o a f f e c t s the r a t e of heat g a i n (Watt 1968), but the advantage of b e i n g m e l a n i s t i c i s not due t o the i n c r e a s e i n t h e r a t e of h e a t i n g of the i n s e c t s i n c e t h e r e was no i n d i c a t i o n t h a t m e l a n i s t i c C. n a s t e s v o l u n t a r i l y f l e w e a r l i e r i n t h e morning than d i d l i g h t e r i n d i v i d u a l s . 56 A body temperature i n e x c e s s of 30°C i s r e q u i r e d by C o l i a s b u t t e r f l i e s b e f o r e f l i g h t i s i n i t i a t e d . From Watt's (1968, 1969) d a t a , the time d i f f e r e n c e between a dark and l i g h t b u t t e r f l y r e a c h i n g t h i s c r i t i c a l t e m p e r a t u r e , i s o n l y 10 t o 30 seconds. The o n l y way t h e r e f o r e , t h a t a s i g n i f i c a n t c o r r e l a t i o n would be e x p e c t e d when comparing the d a r k n e s s of c o l o u r t o t h e o r d e r i n which they f l e w o f f , i s i f they f l e w the i n s t a n t t h e y were c a p a b l e of d o i n g so. Even i f t h i s d i d o c c u r , the i m p l i e d advantages of l o n g e r f l i g h t ( i n c r e a s e d f e e d i n g , mate l o c a t i o n , o v i p o s i t i o n and escape from p r e d a t i o n ) would be n e g l i g a b l e . F or many f l y i n g i n s e c t s , the t e m p e r a t u r e t h r e s h o l d between non-f l i g h t and f l i g h t f o r a p o p u l a t i o n i s u s u a l l y v e r y narrow ( T a y l o r 1963). D i f f e r e n t i a l h e a t i n g r a t e s r e s u l t i n g from v a r i a b i l i t y i n melanism appear t o have l i t t l e e f f e c t i n b r o a d e n i n g the time d i f f e r e n t i a l f o r i n s e c t s t o r e a c h t h i s t h r e s h o l d . In s u n l i g h t , dark i n d i v i d u a l s not o n l y heat up more q u i c k l y , but s t a b i l i z e a t a h i g h e r body t e m p e r a t u r e . The s t a b i l i z e d t emperature d i f f e r e n c e between dark and l i g h t i n d i v i d u a l s can be as much as f o u r degrees C e n t i g r a d e (Watt 1968,1969; Douglas and G r u l a 1978). A l t h o u g h a b s o l u t e body t e m p e r a t u r e s v a r y w i t h d i f f e r e n t ambient t e m p e r a t u r e s , a d i f f e r e n c e between morphs always o c c u r s p r o v i d e d the b u t t e r f l i e s a r e exposed t o s u n l i g h t . Under c e r t a i n c o m b i n a t i o n s of ambient temperature and s u n l i g h t , the s t a b i l i z e d t e m p e r a t u r e of dark b u t t e r f l i e s would l i e above the n e c e s s a r y f l i g h t t h r e s h o l d , l i g h t e r ones would l i e below i t . I n such s i t u a t i o n s , 57 o n l y the d a r k e r members of a p o p u l a t i o n would be ob s e r v e d f l y i n g . Under these c o n d i t i o n s , l a r g e segments of the p o p u l a t i o n a r e i n c a p a b l e of f e e d i n g , l o c a t i n g mates, o v i p o s i t i n g , or e s c a p i n g from p r e d a t o r s . We know t h a t a l t h o u g h o t h e r a c t i v i t i e s have d i f f e r e n t t e m p e r a t u r e - r a d i a t i o n t h r e s h o l d s , melanism o n l y a f f e c t s the i n s e c t s ' a b i l i t y t o f l y . T h e r e f o r e , when c o n s i d e r i n g the advantage of melanism f o r d i e l a c t i v i t y , i t i s o n l y of consequence t o c o n s i d e r i t s e f f e c t on f l i g h t . I f f l i g h t i s not p o s s i b l e d u r i n g a s u b s t a n t i a l p a r t of the s h o r t a d u l t season, m e l a n i s t i c i n d i v i d u a l s p o s s e s s a c l e a r advantage. D u r i n g the f l i g h t season of C. n a s t e s ( J u l y and A u g u s t ) , mean d a i l y s o l a r r a d i a t i o n a t Marmot Creek i s .74 gm.cal/cm 2/min, a l e v e l a t which a l l b u t t e r f l i e s s h o u l d be a b l e t o f l y . At the a r c t i c IBP s i t e , Devon I s l a n d N. W. T. (75° 30' N, 84° 40'W), which l i e s i m m e d i a t e l y n o r t h of t h e extreme range of C. n a s t e s ( H o v a n i t z 1950), mean s o l a r r a d i a t i o n d u r i n g the f l i g h t season i s always below .4 t o .5 gm.cal/cm 2/min ( C o u r t i n and L a b i n e 1977). Under the s e c o n d i t i o n s , F i g u r e 6 would p r e d i c t t h a t o n l y b u t t e r f l i e s w i t h b l a c k s c a l e c o u n t s g r e a t e r than 125 would be a b l e t o f l y . A s m a l l sample (7) of C. n a s t e s from the B o o t h i a P e n n i n s u l a (70° N, 94° W), r e v e a l e d a mean b l a c k s c a l e count of 153, w i t h a range of 124-176. T h i s begs the q u e s t i o n of why a l l C o l i a s a r e not d a r k ; why t h e r e s h o u l d be such a wide range i n o b s e r v e d melanism e s p e c i a l l y a t low l a t i t u d e s . Watt (1968) s u g g e s t e d t h a t l i g h t C o l i a s a r e a b l e t o a v o i d heat s t r e s s s i n c e heat a v o i d a n c e 58 b e h a v i o u r predominated a t body t e m p e r a t u r e s i n e x c e s s of 38°C. At h i g h a l t i t u d e s , i n low l a t i t u d e s , i n t e n s e i n s o l a t i o n and l i t t l e shade c e r t a i n l y r e s u l t i n v e r y h i g h t e m p e r a t u r e s near the ground, o f t e n e x c e e d i n g 40°C (Mani 1968). Watt (1968) a n e c d o t i c a l l y o b s e r v e d t h a t on calm sunny days i n the a l p i n e near J a s p e r , A l b e r t a , C. n a s t e s showed d e c r e a s e d a c t i v i t y d u r i n g midday. T h i s he a t t r i b u t e d t o i n c r e a s e d heat a v o i d a n c e b e h a v i o u r such as shade s e e k i n g and v e r t i c a l b a s k i n g . K e t t l e w e l l (1973) noted t h a t d u r i n g "heat waves" i n B r i t a i n , samples of B i s t o n b e t u l a r i a c o n t a i n e d h i g h e r p r o p o r t i o n s of the l i g h t t y p i c a morph, and d e c r e a s e i n the p r o p o r t i o n of the dark c a r b o n a r i a morph. C o l i a s p h i l o d i c e eurytheme i n C a l i f o r n i a , show peaks i n d a i l y a c t i v i t y a t s o l a r noon d u r i n g the f a l l , but marked s u p p r e s s i o n of a c t i v i t y from 12:00 t o 16:00 d u r i n g the summer ( L e i g h and Smith 1959). T h i s was a t t r i b u t e d t o the need to a v o i d heat s t r e s s . Under hot c o n d i t i o n s , d i f f e r e n t i a l s u r v i v a l or f e c u n d i t y as a r e s u l t of d i f f e r e n t i a l f l i g h t time would t h e r e f o r e convey an advantage t o l i g h t i n d i v i d u a l s . To m a i n t a i n the c r y p t i c green c o l o u r of the b u t t e r f l y , a c e r t a i n p r o p o r t i o n of y e l l o w s c a l e s t o b l a c k s c a l e s must be m a i n t a i n e d . I f the i n s e c t were e n t i r e l y b l a c k , they would be more h i g h l y v i s i b l e w h i l e f l y i n g ( K e t t l e w e l l 1973). Melanism p r o v i d e s l i t t l e or no b e n e f i t i n p r o l o n g i n g s e a s o n a l a c t i v i t y . C o l i a s n a s t e s and C o l i a s m e a d i i o v e r - w i n t e r as t h i r d i n s t a r l a r v a e (Ae 1958). C o l i a s meadi i has a d e v e l o p m e n t a l t h r e s h o l d of 5°C, and a t 27°C, t a k e s 12 days t o r e a c h t h i r d i n s t a r (Ae 1958). A mean August temperature a t 59 Marmot Creek of 8.8C would r e s u l t i n l a r v a e r e q u i r i n g a t l e a s t f i v e t i m e s as l o n g ( n i n e weeks) t o r e a c h the o v e r - w i n t e r i n g s t a g e . Whether or not a m e l a n i s t i c b u t t e r f l y can remain a c t i v e an e x t r a week i n the autumn seems i r r e l e v a n t i f i t s o f f s p r i n g a r e not a b l e t o r e a c h t h i r d i n s t a r by the m i d d l e of October when te m p e r a t u r e s never r i s e above the d e v e l o p m e n t a l t h r e s h o l d of 5°C (Water Surveys of Canada 1977). I i n i t i a l l y h y p o t h e s i z e d t h a t dark C o l i a s might p e r s i s t l o n g e r d u r i n g the f l i g h t season and t h e r e f o r e show a lower r a t e of l o s s of i n d i v i d u a l s from the p o p u l a t i o n . R e s i d e n c e c u r v e s i n d i c a t e t h a t d a r k e r i n d i v i d u a l s are i n f a c t l o s t from th e p o p u l a t i o n a t a g r e a t e r r a t e . T h i s i s the case f o r C. n a s t e s i n b o th y e a r s , and f o r the congener C. meadi i , s u g g e s t i n g i t t o be a g e n e r a l phenomenon. D i f f e r e n t i a l l o s s by e m i g r a t i o n or p r e d a t i o n c o u l d r e s u l t from the g r e a t e r f l i g h t a c t i v i t y of d a r k e r b u t t e r f l i e s f o r two r e a s o n s : (1) g r e a t e r f l i g h t a c t i v i t y would i n c r e a s e d i s t a n c e s moved by i n d i v i d u a l s , and t h e r e f o r e i n c r e a s e the l i k e l i h o o d of e m i g r a t i o n from the s a m p l i n g a r e a ; (2) g r e a t e r f l i g h t a c t i v i t y would i n c r e a s e the l i k e l i h o o d of p r e d a t i o n on the wing by a v i a n p r e d a t o r s (see Chapter 3 ) . Data show t h a t dark i n d i v i d u a l s a r e moving s i g n i f i c a n t l y f u r t h e r per day (Table V ) , i m p l i c a t i n g d i f f e r e n t i a l e m i g r a t i o n as c a u s i n g the g r e a t e r l o s s of dark b u t t e r f l i e s . T h i s does n o t , however, r u l e out the p o s s i b i l i t y of d i f f e r e n t i a l m o r t a l i t y a c t i n g t o i n c r e a s e or d e c rease s u r v i v a l of dark i n d i v i d u a l s r e l a t i v e t o l i g h t ones. L i f e span of i n d i v i d u a l s w i t h h i g h body te m p e r a t u r e ( d a r k e r i n c o l o u r ) would be e x p e c t e d t o be s h o r t e r than t h o s e 60 w i t h lower body t e m p e r a t u r e s ( G i l b e r t e t . a l . 1976). The g r e a t e r l o s s of dark i n d i v i d u a l s from the p o p u l a t i o n might be the r e s u l t of both h i g h e r e m i g r a t i o n r a t e and s h o r t e r l i f e span r e l a t i v e t o l i g h t i n d i v i d u a l s . S t r o n g e v i d e n c e has been p r e s e n t e d here t o support the h y p o t h e s i s t h a t melanism a l l o w s the i n c r e a s e d a c t i v i t y of i n s e c t s i n c o l d e n v i r o n m e n t s . F l i g h t appears t o be the o n l y a c t i v i t y which i s i n f l u e n c e d by the degree of melanism of the b u t t e r f l y . I n c r e a s e d melanism of b u t t e r f l i e s a t t h i s s i t e , can r e s u l t i n an i n c r e a s e i n f l i g h t a c t i v i t y of up t o 55%. The assumption remains however, t h a t i n c r e a s e d f l y i n g time r e s u l t s i n i n c r e a s e d s u c c e s s by the i n d i v i d u a l . C e r t a i n l y complete i n a b i l i t y t o f l y would r e s u l t i n no o f f s p r i n g . Mate l o c a t i o n by male C o l i a s r e q u i r e c o n t i n u a l p a t r o l l i n g of open a r e a s ( S c o t t 1975). The importance of f l i g h t i s t h e r e f o r e paramount i n d e t e r m i n i n g the a b i l i t y of males t o l o c a t e mates. From the time of emergence, C o l i a s females a r e c o n t i n u o u s l y m a t u r i n g eggs ( S t e r n and Smith 1960). Eggs a r e o v i p o s i t e d s i n g l y , and f l i g h t i s n e c e s s a r y f o r females t o move from p l a n t t o p l a n t . Females p r o b a b l y never o v i p o s i t a l l t h e i r eggs d u r i n g t h e i r l i f e s p a n ( S t e r n and Smith 1960), and so, any g a i n i n f l i g h t time would r e s u l t i n i n c r e a s e d f e c u n d i t y . N e c t a r f e e d i n g by t h e s e b u t t e r f l i e s r e q u i r e s f l i g h t between f l o w e r s ( u s u a l l y s i n g l e -headed Composites: Haplopappus l y a l l i i A. Gray and E r i g e r o n  aureus G r e e n e ) . Reduced f e e d i n g by a d u l t females d e c r e a s e s egg output ( S t e r n and Smith 1960). I f the amount of c o u r t i n g and c o p u l a t i o n , o v i p o s i t i o n , and egg m a t u r a t i o n a r e p r o p o r t i o n a l t o 61 the amount of time f l i g h t i s p o s s i b l e , then a marked d i f f e r e n c e i n f e c u n d i t y of dark and l i g h t C o l i a s c o u l d be e n v i s a g e d . The d i r e c t e f f e c t of a r a i s e d .body temperature on f e c u n d i t y i s a d d r e s s e d i n Chapter 3. The g r e a t e r v a r i a b i l i t y i n m i c r o c l i m a t e of s o u t h e r n a l p i n e a r e a s as compared t o a r c t i c s i t e s (Remmert and W u n d e r l i n g 1969), might account f o r the a b i l i t y of l i g h t e r c o l o u r e d C o l i a s t o be s u c c e s s f u l members of t h e s e s o u t h e r n p o p u l a t i o n s . D i f f e r e n c e s i n melanism between y e a r s a r e p a r t l y d e t e r m i n e d by the e f f e c t of temp e r a t u r e on l a r v a l development. S i n c e 1979 was warm r e l a t i v e t o 1980, two p r e d i c t i o n s can be made r e g a r d i n g the r e l a t i v e importance of the g e n e t i c and e n v i r o n m e n t a l e f f e c t s d e t e r m i n i n g the degree of melanism: ( 1 ) . I f melanism i s p r i m a r i l y g e n e t i c a l l y d e t e r m i n e d , a warm year (1979) s h o u l d p r o v i d e an advantage t o l i g h t e r i n d i v i d u a l s , and t h e i r l i g h t c o l o u r e d o f f s p r i n g would t h e r e f o r e c o n s t i t u t e a l a r g e r p r o p o r t i o n of the p o p u l a t i o n the f o l l o w i n g y e a r (1980). ( 2 ) . I f melanism i s p r i m a r i l y e n v i r o n m e n t a l l y c o n t r o l l e d , an advantage g a i n e d by l i g h t b u t t e r f l i e s i n a warm year (1979) would be masked by a d a r k e n i n g of t h e i r o f f s p r i n g i n the f o l l o w i n g c o l d e r year (1980). G r e a t e r r e p r e s e n t a t i o n of dark i n d i v i d u a l s o c c u r r e d i n 1980 i n d i c a t i n g a s t r o n g e n v i r o n m e n t a l component. U n f o r t u n a t e l y , no u n e q u i v o c a l statement r e g a r d i n g t h e r e l a t i v e importance of the two d e t e r m i n a n t s of melanism can be made s i n c e t h e r e i s no " c o n t r o l " by which t o compare t h e s e r e s u l t s . For example, i f t h e r e was no g e n e t i c e f f e c t t o i n c r e a s e r e p r e s e n t a t i o n of " l i g h t " genes, the melanism i n the 62 1980 p o p u l a t i o n melanism might have been even d a r k e r than o b s e r v e d . S i n c e the r e l a t i v e importance of the g e n e t i c i n f l u e n c e on melanism i s not known, advantages demonstrated by l i g h t e r or d a r k e r i n d i v i d u a l s can o n l y be a c c u r a t e l y termed "advantages", not s e l e c t i v e a d v a n t a g e s . T h i s i s the f i r s t f i e l d d e m o n s t r a t i o n of an advantage f o r i n s e c t s t o be m e l a n i s t i c i n c o l d e n v i r o n m e n t s . C a r e f u l l y c o n t r o l l e d thermocouple e x p e r i m e n t s have shown melanism t o i n c r e a s e i n s e c t body t e m p e r a t u r e . These d i f f e r e n c e s have not u n t i l now been e x t r a p o l a t e d t o the n a t u r a l environment which shows l a r g e s p a t i a l and t e m p o r a l v a r i a t i o n i n temperature and s o l a r r a d i a t i o n . Melanism p r o v i d e s an o b v i o u s b e n e f i t t o t h e i n s e c t by i n c r e a s i n g i t s a b i l i t y t o m a i n t a i n f l i g h t a c t i v i t y under c o l d c o n d i t i o n s . F e c u n d i t y i s h i g h l y dependent on f l i g h t , and the s u b s t a n t i a l i n c r e a s e i n f l i g h t time d u r i n g the s h o r t season would r e s u l t i n an i n c r e a s e d p o t e n t i a l number of o f f s p r i n g . Those b u t t e r f l i e s whose f l i g h t time i s c u r t a i l e d most by c o l d weather are l i g h t e s t i n c o l o u r . I n c r e a s e i n l a t i t u d e and a l t i t u d e would cause more of t h e l i g h t e r i n d i v i d u a l s t o be i n c a p a b l e of normal a c t i v i t y . F e c u n d i t y would be reduced most i n the l i g h t e s t members of the p o p u l a t i o n . The a d a p t i v e v a l u e of melanism i n c o l d e nvironments f o r t h e s e b u t t e r f l i e s p r o b a b l y r e s u l t s from an i n c r e a s e d f e c u n d i t y m a n i f e s t t h r o u g h s u b s t a n t i a l d i f f e r e n c e s i n f l i g h t a c t i v i t y . 63 MELANISM AND FECUNDITY INTRODUCTION F i t n e s s , or the r e l a t i v e s u c c e s s of an organi s m t o produce o f f s p r i n g , i s g e n e r a l l y measured as the t o t a l number of o f f s p r i n g of t h a t i n d i v i d u a l , s u r v i v i n g t o r e p r o d u c t i v e age. The t o t a l number of progeny produced i s d e t e r m i n e d by both the r a t e of p r o d u c t i o n of young and the d u r a t i o n of the r e p r o d u c t i v e stage of the l i f e c y c l e (Futuyma 1979). F e c u n d i t y of female i n s e c t s can be a f f e c t e d d i r e c t l y by b i o t i c f a c t o r s such as amount of food ( D e t h i e r 1959), q u a l i t y of foo d ( G i l b e r t 1972), and number of matings (Benz 1970), and by a b i o t i c f a c t o r s such as temperature ( G r e e n f i e l d and K a r a n d i n o s 1976), and h u m i d i t y ( S t e r n and Smith 1960). B e h a v i o u r , p h y s i o l o g y , morphology, or phenology of i n s e c t s i n d i r e c t l y a f f e c t f e c u n d i t y by m o d u l a t i n g the e f f e c t of t h e s e f a c t o r s . I t i s t h e s e p h e n o t y p i c c h a r a c t e r s upon which s e l e c t i o n a c t s . Body temperature of a female i n s e c t s t r o n g l y a f f e c t s the r a t e a t which she i s a b l e t o produce eggs (Uvarov 1931). Rate of p r o d u c t i o n has a tem p e r a t u r e t h r e s h o l d below which no eggs mature. I n c r e a s e d body t e m p e r a t u r e r e s u l t s i n i n c r e a s e d r a t e of egg o u t p u t t o some maximum. At even h i g h e r t e m p e r a t u r e s , f e c u n d i t y d e c r e a s e s . A r c t i c and a l p i n e i n s e c t s a r e s t r o n g l y a f f e c t e d by c o l d t e m p e r a t u r e and s h o r t season of t h e environment i n which they l i v e . By d e f i n i t i o n , a r c t i c and a l p i n e h a b i t a t s have a mean d a i l y maximum temperature which never exceeds 10°C i n any 64 month. A v a r i e t y of mechanisms a r e used by i n s e c t s t o i n c r e a s e body temperature a t low ambient t e m p e r a t u r e . These i n c l u d e b a s k i n g b e h a v i o u r ( C l e n c h 1966, Kevan and Shorthouse 1970), and m o r p h o l o g i c a l a d a p t a t i o n such as pubescence ( S t i l e s 1979) and melanism (Watt 1968; K e t t l e w e l l 1973; Douglas and G r u l a 1978). Among the s u l p h u r b u t t e r f l i e s of the genus C o l i a s F a b r i c i u s , the t u n d r a s u l p h u r b u t t e r f l y C o l i a s n a s t e s B o i s d u v a l , shows marked i n c r e a s e i n d a r k e n i n g of i t s wing c o l o r a t i o n w i t h i n c r e a s e i n both a l t i t u d e and l a t i t u d e . T h i s v a r i a t i o n i s e q u a l l y e x p r e s s e d i n both s e x e s . In a s s o c i a t i o n w i t h o b v i o u s p r o l o n g e d b a s k i n g b e h a v i o u r (Kevan and Shorthouse 1970), i t i s thought t h a t melanism i n these b u t t e r f l i e s i s an a d a p t a t i o n a c t i n g t o r a i s e the i n s e c t s body tem p e r a t u r e (Watt 1968, 1969). The e f f e c t which melanism has on f e c u n d i t y , by v i r t u e of i t s e f f e c t on body t e m p e r a t u r e , has not been t e s t e d . M e l anism does a f f e c t the d u r a t i o n of f l i g h t a c t i v i t y and f e e d i n g by C o l i a s b u t t e r f l i e s (Chapter One). Melanism t h e r e f o r e , does i n d i r e c t l y a f f e c t f e c u n d i t y by i n c r e a s i n g i m a g i n a l f e e d i n g r a t e which r a i s e s f e c u n d i t y ( S t e r n and Smith 1960). I n c r e a s e d body temperature r e s u l t i n g from melanism c o u l d , however, be a c t i n g d i r e c t l y on the r a t e of egg m a t u r a t i o n by g e n e r a l l y i n c r e a s i n g the r a t e of b i o c h e m i c a l p r o c e s s e s . I n t e n s i t y of s u n l i g h t a f f e c t s body t e m p e r a t u r e , and the magnitude of t h i s e f f e c t i s p r o p o r t i o n a l t o the degree of melanism of the i n s e c t (Chapter One). I f melanism i s an a d a p t a t i o n which i n c r e a s e s f e c u n d i t y i n c o l d c l i m a t e s , a d i f f e r e n c e i n f e c u n d i t y r e l a t e d t o d i f f e r e n c e 65 i n degree of melanism s h o u l d be d e m o n s t r a b l e . Body temperature g r e a t l y d e t e r m i n e s f e c u n d i t y of C o l i a s  p h i l o d i c e L a t r e i l l e ( S t e r n and Smith 1960) ( F i g . 15a). T h i s r e l a t i o n s h i p would be s i m i l a r f o r a l l i n d i v i d u a l s . The c u r v e of egg p r o d u c t i o n a g a i n s t ambient temperature would i n t h e o r y be s h i f t e d t o the l e f t f o r dark i n d i v i d u a l s , and t o the r i g h t f o r l i g h t e r b u t t e r f l i e s ( F i g . 15b). T h e r e f o r e , i t would be p r e d i c t e d t h a t a t low ambient t e m p e r a t u r e s , dark females w i l l produce more eggs than l i g h t f e m a l e s ; the o p p o s i t e would occur a t h i g h e r ambient t e m p e r a t u r e . D i f f e r e n c e s i n f l i g h t a c t i v i t y may a f f e c t the l i k e l i h o o d of females b e i n g mated. C o l o u r of female C o l i a s can a l s o a f f e c t a t t r a c t i v e n e s s t o males (Graham e _ t . a l . 1980). T h e r e f o r e , f e c u n d i t y d i f f e r e n c e s r e s u l t i n g from a d i f f e r e n c e i n mating f r e q u e n c y c o u l d o c c u r . I f melanism i n c r e a s e s the l i k e l i h o o d of mating i n c o l d h a b i t a t s , i t would be p r e d i c t e d t h a t dark females s h o u l d mate more f r e q u e n t l y by b e i n g more a c t i v e . A f t e r a s h o r t one t o two day p r e - o v i p o s i t i o n p e r i o d , female C o l i a s p h i l o d i c e mature eggs thr o u g h o u t t h e i r l i f e s p a n and o v i p o s i t these eggs s i n g l y ( S t e r n and Smith 1960). C. n a s t e s appear t o mature and o v i p o s i t eggs s i m i l a r l y . L i f e s p a n can be as l o n g as 25 days, but avera g e s 6.8 days f o r females i n the p o p u l a t i o n I s t u d i e d (Chapter One). I f body temperature i s c o n s i s t e n t l y h i g h e r d u r i n g t h e day i n dark f e m a l e s , a marked d i f f e r e n c e i n egg m a t u r a t i o n r a t e s h o u l d r e s u l t . The i n t e n t of t h i s c h a p t e r i s t o compare the r a t e s of egg p r o d u c t i o n of dark and l i g h t C o l i a s females under the same 66 F i g u r e 15. (a) F e c u n d i t y of C o l i a s p h i l o d i c e as a f u n c t i o n of body t e m p e r a t u r e . O v i p o s i t i o n r a t i n g i s the p e r c e n t a g e of the maximum r a t e . Adapted from S t e r n and Smith 1960. (b) T h e o r e t i c a l f e c u n d i t y c u r v e f o r dark and l i g h t C o l i a s as a f u n c t i o n of ambient t e m p e r a t u r e . 15 20 25 30 35 40 45 Body Temperature (°C) D a r k / ' / ^ Light 1 N N / ' N \ / ; \ * Ambient Temperature t e m p e r a t u r e and l i g h t i n t e n s i t y . My wo r k i n g h ypo the se s were : 1 . Dark f ema le s under c o l d c o n d i t i o n s mature and o v i p o s i t eggs more r a p i d l y than l i g h t e r f e m a l e s . 2 . T h i s d i f f e r e n c e d e c r e a s e s as amb ient t e m p e r a t u r e i n c r e a s e s . 3. Dark f ema le s mate more f r e q u e n t l y t han l i g h t e r conspec i f i e s . 69 METHODS AND MATERIALS Female C o l i a s n a s t e s were c o l l e c t e d i n the f i e l d by handnet. Two c o l l e c t i o n s were made each season: one a t the s t a r t of the six-week f l i g h t season, and a second two t o t h r e e weeks l a t e r . At the time of c a p t u r e i t was p o s s i b l e , i n most c a s e s , t o de t e r m i n e whether females had mated. T h i s was done by l i g h t l y s q u e e z i n g the abdomen t o f e e l the h a r d round spermatophore ( S t e r n and Smith 1960). The degree of melanism of each female was q u a n t i f i e d as d e s c r i b e d i n Chapter One. One c o l l e c t i o n of C o l i a s m e a d i i females was made i n 1979. A l l o v i p o s i t i o n e x p e r i m e n t s were c a r r i e d out i n c o n t r o l l e d environment chambers. Each female was p l a c e d i n a c l e a r p l a s t i c cage (25cm X 20cm X 15cm) s c r e e n e d on one s i d e . The legume, A s t r a g a l u s a l p i n u s , i s known t o be a p r i m a r y h o s t p l a n t f o r C o l i a s n a s t e s ( E h r l i c h and E h r l i c h 1961), and each female was p r o v i d e d w i t h s e v e r a l upon which t o o v i p o s i t . S i n c e i t was h y p o t h e s i z e d t h a t dark females were c a p a b l e of m a t u r i n g more eggs than l i g h t females under c o l d e r c o n d i t i o n s , comparison of egg output was made under a range of t e m p e r a t u r e s (12-34°C). Maximum l i g h t i n t e n s i t y p o s s i b l e i n t h e s e chambers was o n l y .4 gm.cal/cm 2/min (one t h i r d the v a l u e of s u n l i g h t a t s o l a r noon). L i g h t i n t e n s i t y was t h e r e f o r e not v a r i e d among e x p e r i m e n t s . Growth chambers were c y c l e d on a 14:10 hour c y c l e f o r both l i g h t and t e m p e r a t u r e . " N i g h t " t e m p e r a t u r e was 5°C f o r a l l t r e a t m e n t s r e g a r d l e s s of "daytime" t e m p e r a t u r e . Comparison of f e c u n d i t y was made u t i l i z i n g b o t h n a t u r a l c o l o u r v a r i a t i o n and by m a n i p u l a t i n g the degree of d a r k n e s s . 70 M a n i p u l a t i o n was done by s l i g h t l y d a r k e n i n g the b a s a l p o r t i o n of the v e n t r a l h i n d w i n g s u r f a c e s , on h a l f of each group of b u t t e r f l i e s , w i t h a f i n e - p o i n t b l a c k permanent marker ( F i g . 16). The undarkened h a l f of each r e p l i c a t e was t o r e c e i v e a " c o n t r o l " t r e a t m e n t by a p p l i c a t i o n of y e l l o w permanent marker. T h i s was, however, not done s i n c e i t produced a dark brown c o l o u r which would a c t s i m i l a r t o the b l a c k t r e a t m e n t i n terms of i t s e f f e c t on r a i s i n g body t e m p e r a t u r e . Both e x p e r i m e n t a l and c o n t r o l groups had the same range of n a t u r a l c o l o u r v a r i a t i o n . C o l o u r m a n i p u l a t i o n t r i a l s were run a t 22°C o n l y . Summary of e x p e r i m e n t s i s p r e s e n t e d i n T a b l e V I I . Table V I I . Summary of e x p e r i m e n t a l c o n d i t i o n s f o r r a t e of o v i p o s i t i o n e x p e r i m e n t s on dark and l i g h t C o l i a s b u t t e r f l i e s . S p e c i e s # Females Temp (°C) C o l o u r C. n a s t e s C. n a s t e s C. m e a d i i C. n a s t e s C. n a s t e s C. n a s t e s C. n a s t e s C. n a s t e s 1 2 12 12 20 21 20 20 20 1 2 22 22 22 22 22 22 34 n a t u r a l n a t u r a l n a t u r a l n a t u r a l m a n i p u l a t e d m a n i p u l a t e d m a n i p u l a t e d n a t u r a l E very one t o two day s , the t o t a l number of eggs each female had o v i p o s i t e d was co u n t e d . In most c a s e s , e x p e r i m e n t s were run f o r a 14 day p e r i o d . P l a n t s were o n l y r e p l a c e d i f they 71 F i g u r e 16. C o l o u r m a n i p u l a t e d and normal C o l i a s n a s t e s females used i n f e c u n d i t y e x p e r i m e n t s . 7 3 showed s i g n s of d e t e r i o r a t i o n . At the c o m p l e t i o n of each e x p e r i m e n t , females were d i s s e c t e d . The p r e s e n c e and number of spermatophores i n each female was r e c o r d e d t o c o n f i r m t h a t mating had o c c u r r e d . The number of c h o r i p n a t e d eggs r e m a i n i n g i n the female ( u n o v i p o s i t e d e g g s ) , was a l s o r e c o r d e d . T h i s was added t o the number of o v i p o s i t e d eggs t o p r o v i d e the a c t u a l number of eggs matured. In t h i s way, d i f f e r e n c e s which were due t o d i f f i c u l t y i n a c t u a l o v i p o s i t i o n c o u l d be d e t e r m i n e d , and any e f f e c t which p l a n t s i z e or q u a l i t y might have on o v i p o s i t i o n b e h a v i o u r was reduced. 7 4 RESULTS A g r e a t d e a l of v a r i a t i o n i n the d a i l y o v i p o s i t i o n r a t e o c c u r r e d among females ( c o e f f i c i e n t of v a r i a t i o n e q u a l l e d 156% i n the l a r g e s t g r o u p ) . In subsequent a n a l y s i s , a t t e m p t s were made t o account f o r and reduce v a r i a t i o n . S i n c e age i s a im p o r t a n t d e t e r m i n a n t of r a t e of egg output ( S t e r n and Smith 1960), I used o n l y d a t a from females c o l l e c t e d a t the s t a r t of the f l i g h t p e r i o d . Thereby,the p o s s i b l e range i n age was reduced from a maximum of 25 days (Chapter One) t o two t o t h r e e days. D a i l y o v i p o s i t i o n r a t e , and d a i l y egg m a t u r a t i o n r a t e were compared t o both n a t u r a l c o l o u r and c o l o u r which was a r t i f i c i a l l y a l t e r e d . N a t u r a l C o l o r a t i o n O v i p o s i t i o n Rate Because of the v e r y h i g h v a r i a n c e of t h e s e d a t a , n a t u r a l melanism was t r e a t e d as a c o n t i n u o u s c h a r a c t e r (number of b l a c k s c a l e s ) , r a t h e r than a b i n a r y c h a r a c t e r (dark h a l f , l i g h t h a l f of each sample). O v i p o s i t i o n r a t e was c o r r e l a t e d w i t h the degree of melanism ( T a b l e V I I I ) . A l l subsequent a n a l y s e s i n v o l v i n g n a t u r a l c o l o r a t i o n were t r e a t e d s i m i l a r l y . P r e d i c t e d r e s u l t s a r e s u p p o r t e d l a r g e l y as t r e n d s . At low tem p e r a t u r e s (12°C), i n c r e a s e i n melanism i n c r e a s e s the r a t e of egg o v i p o s i t i o n ( p o s i t i v e c o r r e l a t i o n ) . At h i g h e r t e m p e r a t u r e s 75 T a b l e V I I I . C o r r e l a t i o n between the degree of melanism (number of b l a c k s c a l e s ) , and mean d a i l y number of eggs o v i p o s i t e d by C o l i a s females under v a r i o u s t e m p e r a t u r e regimes. Temp # # C o r r e l a t i o n S p e c i e s (°C) Days Females C o e f f i c i e n t * S i g n i f i c a n c e C. n a s t e s 12 14 12 .6416 p<.05 C. n a s t e s 22 14 39 - . 2 4 3 5 .I0<p<.20 C. n a s t e s 34 6 20 - . 0 5 5 3 p>.90 C. m e a d i i 22 11 12 .4668 . I0<p<.20 * Spearman's Rank C o r r e l a t i o n ( 22°C), the r e l a t i o n s h i p i s r e v e r s e d . At the h i g h e s t e x p e r i m e n t a l temperature ( 3 4°C), s u r v i v o r s h i p of females was v e r y low, and no apparent d i f f e r e n c e i n o v i p o s i t i o n r a t e o c c u r r e d ( t h e r e was a l s o no d i f f e r e n c e i n s u r v i v a l between dark and l i g h t f e m a l e s ) . C o l i a s m e a d i i were kept a t o n l y one temperature (22°C) where dark females tended t o produce more eggs than l i g h t e r f e m a l e s . M a t u r a t i o n Rate When the number of matured but u n o v i p o s i t e d eggs i s i n c l u d e d i n the c a l c u l a t i o n of f e c u n d i t y , r e s u l t s do not d i f f e r markedly ( T a b l e I X ) . T h i s would i n d i c a t e t h a t d i f f e r e n c e s i n egg output a r e due t o a c t u a l m a t u r a t i o n r a t e d i f f e r e n c e s and not t o d i f f i c u l t i e s i n o v i p o s i t i o n . Under c o l d t e m p e r t u r e s dark females mature s l i g h t l y more eggs than l i g h t e r f e m a l e s . H i g h e r t e m p e r a t u r e s r e s u l t i n g r e a t e r r a t e of m a t u r a t i o n by l i g h t e r c o l o u r e d f e m a l e s . The tendency f o r h i g h e r r e p r o d u c t i o n i n l i g h t f e m ales d e c r e a s e s somewhat a t 76 T a b l e IX. C o r r e l a t i o n between degree of melanism (number of b l a c k s c a l e s ) and mean number of eggs matured by C o l i a s f e m a l e s . Temp # # C o r r e l a t i o n S p e c i e s (°C) Days Females C o e f f i c i e n t * S i g n i f i c a n c e C. n a s t e s 12 14 12 .3846 .I0<p<.20 C. n a s t e s 22 14 39 -.4455 P<.01 C. n a s t e s 34 6 20 -.3583 .I0<p<.20 C. m e a d i i 22 11 12 .6416 p<.05 *Spearman's Rank C o r r e l a t i o n 34°C. M a n i p u l a t e d C o l o u r O v i p o s i t i o n Rate No s i g n i f i c a n t d i f f e r e n c e i n the mean d a i l y number of eggs o v i p o s i t e d o c c u r r e d between a r t i f i c i a l l y darkened and undarkened i n d i v i d u a l s ( T a ble X ) . O v i p o s i t i o n r a t e was not d i f f e r e n t f o r n a t u r a l and m a n i p u l a t e d groups ( T a b l e X ) . From t h e s e r e s u l t s , I c o n c l u d e t h a t i n c r e a s i n g the darkness of female c o l o r a t i o n does not i n c r e a s e her r a t e of o v i p o s i t i o n . M a t u r a t i o n Rate The i n c l u s i o n of n o n - o v i p o s i t e d but mature eggs i n the measure of f e c u n d i t y does not r e s u l t i n s i g n i f i c a n t d i f f e r e n c e between darkened and undarkened females ( T a b l e X I ) . A r t i f i c i a l l y d a r k e n i n g females does not g r e a t l y i n c r e a s e the 77 T a b l e X. Mean number of eggs o v i p o s i t e d per day f o r m a n i p u l a t e d and n a t u r a l l y dark and l i g h t groups of C o l i a s f e m a l e s . Mean # Eggs Temp C o l o u r (°C) N Dark L i g h t S i g n i f i c a n c e * * m a n i p u l a t e d 22 20 2.96 2.02 ns n a t u r a l * 22 39 2.75 1 .70 ns *dark and l i g h t groups based on median b l a c k s c a l e c o u n t . ** S t u d e n t ' s t - t e s t . r a t e of egg m a t u r a t i o n . T a b l e X I . Mean number of eggs matured per day f o r m a n i p u l a t e d and n a t u r a l l y l i g h t and dark groups of C o l i a s f e m a l e s . Mean # Eggs Temp C o l o u r (°C) N Dark L i g h t S i g n i f i c a n c e * * m a n i p u l a t e d 22 20 5. 2 3.0 ns n a t u r a l * 22 39 3. 1 6.8 ns *dark and l i ght groups based on median b l a c k s c a l e c o u n t . * * S t u d e n t ' s t - t e s t . M a t i n g Frequency Females which c o n t a i n e d no spermatophores were i n c l u d e d i n the a n a l y s i s of mating f r e q u e n c y . Dark females c o n t a i n e d on average fewer spermatophores than d i d l i g h t females ( F i g . 17), i n d i c a t i n g t h a t t hey a r e l e s s l i k e l y t o mate. Mean spermatophore count f o r dark and l i g h t groups were 1.14 and 1.37 r e s p e c t i v e l y (p<.05, S t u d e n t ' s t - t e s t ) . 78 F i g u r e 17. Frequency d i s t r i b u t i o n of spermatophore c o u n t s f o r dark and l i g h t C o l i a s n a s t e s f e m a l e s . # Spermatophores 80 DISCUSSION In t h e o r y , a dark female b u t t e r f l y s h o u l d be a b l e t o produce eggs a t a r a t e more r a p i d than l i g h t e r females under c o o l c o n d i t i o n s . I have shown t h a t under r e l a t i v e l y c o o l c o n d i t i o n s (12°C), t h i s does i n f a c t happen. C l e a r c u t r e s u l t s a t warmer t e m p e r a t u r e s were not o b t a i n e d , but the advantage f o r dark females does d e c r e a s e . At warm t e m p e r a t u r e s , t h e r e i s a t l e a s t an i n d i c a t i o n t h a t l i g h t females w i l l have some advantage i n egg p r o d u c t i o n . A m b i g u i t y might r e s u l t from one of a number of r e a s o n s : 1. The v e r y h i g h v a r i a n c e i n m a t u r a t i o n r a t e among females would make the d e t e c t i o n of any d i f f e r e n c e i n f e c u n d i t y d i f f i c u l t . Very l a r g e sample s i z e s would be r e q u i r e d t o d e t e c t t h i s d i f f e r e n c e . 2. Thermocouple measurements of body tem p e r a t u r e of dark and l i g h t i n d i v i d u a l s i n s u n l i g h t (Chapter One), show a maximum temperature d i f f e r e n c e of f o u r °C. Because of the r e l a t i v e l y low r a d i a t i o n l e v e l i n the growth chamber, and the l i k e l i h o o d of a warm boundary l a y e r i n the cages from h e a t i n g of the s o i l and p l a n t s , t emperature d i f f e r e n c e among c o l o u r t y p e s i n t h e s e e x p e r i m e n t s a r e l i k e l y much l e s s . 3. Egg p r o d u c t i o n r a t e i s p r e d i c t a b l e from body temp e r a t u r e ( S t e r n and Smith 1960), but t h e s e were not measured f o r i n d i v i d u a l s i n growth chambers. Body temperature can be p r e d i c t e d i f i t s r e l a t i o n s h i p t o ambient t e m p e r a t u r e , s o l a r r a d i a t i o n , and degree of melanism i s known. Without t h i s r e l a t i o n s h i p , i t i s not p o s s i b l e t o d e t e r m i n e whether the 81 c o n d i t i o n s used i n the growth chambers were such t h a t a d i f f e r e n c e i n f e c u n d i t y c o u l d o c c u r . Three p o s s i b l e ambient temperature regimes e x i s t which might r e s u l t i n no e f f e c t i v e d i f f e r e n c e i n f e c u n d i t y : a. ambient temperature t o o low, such t h a t body te m p e r a t u r e s l i e t o the l e f t of the c u r v e i n F i g u r e One b. ambient temperature t o o h i g h , such t h a t body te m p e r a t u r e s l i e t o t h e r i g h t of t h e c u r v e i n F i g u r e One c. ambient temperature i s a t the p o i n t where the two c u r v e s f o r dark and l i g h t i n d i v i d u a l s ( F i g . 2) i n t e r s e c t , r e s u l t i n g i n the same f e c u n d i t y . A s i m u l a t i o n model was used t o det e r m i n e whether the ambient t e m p e r a t u r e s I used c o u l d r e s u l t i n any of the above t h r e e c o n d i t i o n s . The r e l a t i o n s h i p between body tem p e r a t u r e and f e c u n d i t y f o r C o l i a s was d e r i v e d from d a t a of S t e r n and Smi t h ( i 9 6 0 ) and s c a l e d t o the maximum o u t p u t of my f e m a l e s . E=.00002Tb 5-.0044Tb"+.33Tb 3-12.3Tb 2+224.7Tb-1602 where: E = the number of eggs produced per day Tb = body temperature (°C) Body t e m p e r a t u r e , as a f u n c t i o n of ambient t e m p e r a t u r e , l i g h t i n t e n s i t y , and degree of melanism, was o b t a i n e d from m u l t i p l e r e g r e s s i o n a n a l y s i s i n Chapter One. Tb=.625Ta+.025R+.047B+6 where: Tb = body temperature (°C) 82 Ta = ambient temperature (°C) R = s o l a r r a d i a t i o n (gm.cal/cm 2/min) B = melanism e x p r e s s e d as number of b l a c k s c a l e s T h e r e f o r e , f e c u n d i t y can be c a l c u l a t e d f o r any b u t t e r f l y i n the chamber p r o v i d e d melanism i s known. Comparison was made between the p r e d i c t e d f e c u n d i t y of the l i g h t h a l f of the t o t a l sample (mean b l a c k s c a l e count=113) and f e c u n d i t y of the dark h a l f of the t o t a l sample (mean b l a c k s c a l e count=140). L i g h t i n t e n s i t y i n the chamber (.4 gm.cal/cm 2/min) was used i n the model, and s i m u l a t i o n was run f o r ambient t e m p e r a t u r e s from 0 t h r o u g h 50°C. Output c o n s i s t e d of f e c u n d i t y of dark i n d i v i d u a l s minus t h a t of l i g h t i n d i v i d u a l s . T h i s v a l u e e q u a l s z e r o a t chamber te m p e r a t u r e s a t which no d i f f e r e n c e i n f e c u n d i t y would o c c u r . S i m u l a t i o n r e s u l t s a r e p r e s e n t e d i n F i g u r e 18. Assuming t h a t the model i s c o r r e c t , ambient t e m p e r a t u r e s which would not be p r e d i c t e d t o r e s u l t i n no d i f f e r e n c e i n f e c u n d i t y a r e : 1) l e s s than 12°C, and 2) a p p r o x i m a t e l y 24-25°C. From my h i g h t e m p e r a t u r e e x p e r i m e n t , i t i s o b v i o u s t h a t a t 34°C and h i g h e r , s u r v i v o r h i p i s so low as t o make f e c u n d i t y e s t i m a t e s i m p o s s i b l e . In r e t r o s p e c t , t h e r e f o r e , the t e m p e r a t u r e s used i n t h i s experiment (12°C, 22°C, and 34°C) a r e not i d e a l . B e t t e r r e s u l t s would be p r e d i c t e d i f t e m p e r a t u r e s of 17-19°C had been used as a " c o l d " t r e a t m e n t , and 28-29°C used as a "hot" t r e a t m e n t . In summary, e x p e r i m e n t s would have been g r e a t l y improved i f : 1. o n l y females of known age were used. 2. h i g h e r l i g h t i n t e n s i t y was used. 83 F i g u r e 18. S i m u l a t i o n r e s u l t s of f e c u n d i t y d i f f e r e n c e between dark and l i g h t females as a f u n c t i o n of ambient t e m p e r a t u r e . Arrows i n d i c a t e t e m p e r a t u r e s used i n e x p e r i m e n t s . 84 0 10 20 30 40 50 Ambient Temperature (°C) 85 3. t h e r e was no s o i l i n the cage bottom. 4. t e m p e r a t u r e s of a p p r o x i m a t e l y 17-19°C and 28-29°C were used. From t h e s e d a t a I c o n c l u d e t h a t any e f f e c t which melanism has on f e c u n d i t y i s m i n i m a l . T h i s i s p a r t i c u l a r l y so c o n s i d e r i n g the g r e a t m i c r o c l i m a t o l o g i c a l v a r i a n c e i n h e r e n t i n t u n d r a h a b i t a t s (Mani 1968). O v i p o s i t i o n e x p e r i m e n t s by S t e r n and Smith (1960), have shown t h a t r a i s i n g ambient t e m p e r a t u r e i n c r e a s e s egg p r o d u c t i o n by i t s e f f e c t on body t e m p e r a t u r e . I t i s i n t e r e s t i n g , however, t h a t s i m i l a r e x p e r i m e n t s by them, u s i n g i n c r e a s i n g l e v e l s of l i g h t i n t e n s i t y , d i d not i n c r e a s e f e c u n d i t y d e s p i t e an i n c r e a s e i n body t e m p e r a t u r e . T h i s apparent d i s c r e p a n c y i s not a d d r e s s e d by the a u t h o r s . The range of body t e m p e r a t u r e s which r e s u l t e d from the l i g h t i n t e n s i t i e s used was 26-32°C, which i s the r e g i o n of maximal egg o u t p u t . W i t h i n t h i s range body tem p e r a t u r e has no e f f e c t on f e c u n d i t y ( F i g . 15a). That males e x p r e s s the same amount of m e l a n i n v a r i a t i o n as females would imply a more g e n e r a l e x p l a n a t i o n f o r the . b e n e f i t of melanism i n c o l d c l i m a t e s . A 10% i n c r e a s e i n sperm by males would not convey the same s e l e c t i v e advantage as would a 10% i n c r e a s e i n egg p r o d u c t i o n by f e m a l e s . Melanism would be of g r e a t e r s e l e c t i v e advantage t o f e m a l e s , but they a r e no d a r k e r than males. The apparent body t e m p e r a t u r e t h r e s h o l d f o r egg m a t u r a t i o n of 20-22°C ( F i g . 15a) would not be as g r e a t a l i m i t i n g f a c t o r t o t h e s e i n s e c t s as the t h r e s h o l d body tem p e r a t u r e f o r f l i g h t 86 of 30°C (Watt 1968). The range of ambient t e m p e r a t u r e s a t which melanism i s an advantage f o r f e c u n d i t y a re w e l l below t h o s e f o r which i t i s an advantage f o r f l i g h t . The r e l a t i v e r a t e s of egg m a t u r a t i o n a r e i r r e l e v a n t i f t h e s e eggs cannot be o v i p o s i t e d , a b e h a v i o u r f o r which f l i g h t i s n o r m a l l y a r e q u i r e m e n t . In c o l d a l p i n e and a r c t i c h a b i t a t s the p r o b a b i l i t y of body t e m p e r a t u r e s r e a c h i n g c r i t i c a l f e c u n d i t y t e m p e r a t u r e s a r e much h i g h e r than f o r r e a c h i n g c r i t i c a l f l i g h t t e m p e r a t u r e s . I c o n c l u d e t h e r e f o r e , t h a t a l t h o u g h melanism may have some e f f e c t on C o l i a s f e c u n d i t y a t c o l d t e m p e r a t u r e s , i t i s not the major b e n e f i t f o r which i t has been s e l e c t e d , and o c c u r s o n l y as an added bonus t o the g r e a t e r e f f e c t which melanism has on i n c r e a s i n g a c t i v i t y under c o l d c o n d i t i o n s . 87 MELANISM AND PREDATION INTRODUCTION Melanism i n many i n s e c t s has been demonstrated t o o c c u r i n response t o the need f o r c r y p s i s t o a v o i d d e t e c t i o n by v i s u a l p r e d a t o r s ( I s l e y 1938, K e t t l e w e l l 1955, 1956). W i t h i n a s p e c i e s v a r i a t i o n i n melanism f o r c r y p s i s i s a t t r i b u t a b l e t o v a r i a t i o n i n c o l o u r of the backgrounds upon which t h e s e i n s e c t s r e s t . The a b i l i t y t o s e l e c t "optimum" c o l o u r e d r e s t i n g s i t e s has been demonstrated f o r many l e p i d o p t e r a (Boardman e t . a l . 1974). C l i n e s i n melanism, i f t hey a r e the r e s u l t of d i f f e r e n t i a l p r e d a t i o n , i n f e r a c l i n a l change i n d a r k e n i n g of r e s t i n g s i t e s . The b e s t documented case of c l i n e s of melanism o c c u r r i n g i n response t o d i f f e r e n t i a l p r e d a t i o n i s the peppermoth B i s t o n  b e t u l a r i a i n B r i t a i n ( K e t t l e w e l l 1955, 1956). I f i n c r e a s e d melanism of i n v e r t e b r a t e s , w i t h i n c r e a s e i n a l t i t u d e and l a t i t u d e , o c c u r s i n response t o p r e d a t i o n and the c o n c o m i t t a n t "need" t o be c r y p t i c , backgrounds on which t h e s e a n i m a l s occur must a l s o be d a r k e r a t h i g h a l t i t u d e s and l a t i t u d e s . T h i s c o u l d r e s u l t f o r one of two r e a s o n s : 1. The c o l o u r of a l l s u b s t r a t e s become d a r k e r a t h i g h e r e l e v a t i o n s and f u r t h e r n o r t h , t h e r e f o r e , r e g a r d l e s s of where the a n i m a l r e s t s , dark i n d i v i d u a l s would be l e s s v i s i b l e . 2. s e l e c t i o n of an " o p t i m a l " r e s t i n g s i t e by t h e s e a n i m a l s changes over a l t i t u d i n a l and l a t i t u d i n a l g r a d i e n t s . Dark c o l o u r e d r e s t i n g s i t e s (which a b s o r b more s o l a r r a d i a t i o n ) would be warmer and might be p r e f e r e n t i a l l y s e l e c t e d by b u t t e r f l i e s a t c o l d t e m p e r a t u r e s . 88 S i n c e t e m p e r a t u r e s d e c r e a s e w i t h i n c r e a s e i n a l t i t u d e and l a t i t u d e , d a r k e r r e s t i n g . s i t e s s h o u l d be s e l e c t e d a t h i g h a l t i t u d e and l a t i t u d e , and would r e s u l t i n reduced p r e d a t i o n on d a r k e r i n d i v i d u a l s . S u l p h u r b u t t e r f l i e s of t h e genus C o l i a s F a b r i c i u s ( P i e r i d a e ) , a r e f r e q u e n t l y c i t e d as examples of i n s e c t s showing l a t i t u d i n a l and a l t i t u d i n a l c l i n e s of melanism ( L e u s s l e r 1935; Freeman 1958; Watt 1968; K e t t l e w e l l 1973; Roland 1978). C o l o u r v a r i a t i o n w i t h i n t h i s group i s not p o l y m o r p h i c , but i s e x p r e s s e d as a continuum, and o c c u r s both w i t h i n and between s p e c i e s . Melanism i n t h e s e b u t t e r f l i e s i s g e n e r a l l y b e l i e v e d t o occur i n response t o a need f o r t h e r m o r e g u l a t i o n (Chapter One). The m a j o r i t y of work on a d a p t i v e c o l o r a t i o n i n i n s e c t s , however, has shown p r e d a t i o n t o be a v e r y s t r o n g s e l e c t i v e f o r c e (Sheppard 1975). C o l o u r p a t t e r n s which a r e c r y p t i c (eg. K e t t l e w e l l 1955), aposematic (eg. B l e s t 1957), or mimetic (eg. Brower 1958), a c t t o d e c r e a s e r a t e s of p r e d a t i o n on i n d i v i d u a l s which bear them. C o l i a s n a s t e s i s a h o l a r c t i c s p e c i e s t y p i c a l o f , and abundant i n t u n d r a environments (see Chapter One f o r s p e c i e s d e s c r i p t i o n ) . The wings of t h i s i n s e c t a r e c o v e r e d by y e l l o w s c a l e s and b l a c k s c a l e s which t o g e t h e r cause an o v e r a l l green c o l o u r . T h i s c o l o r a t i o n makes them e x t r e m e l y c r y p t i c on the t u n d r a v e g e t a t i o n . D u r a t i o n of f l i g h t a c t i v i t y i s v e r y much r e s t r i c t e d i n t h e s e i n s e c t s due t o the c o l d t e m p e r a t u r e s of t h e i r h a b i t a t (Chapter One). Even under f a v o u r a b l e c o n d i t i o n s , a l a r g e amount of time i s spent b a s k i n g on the ground i n an 89 e f f o r t t o r a i s e body temperature (Watt 1968,1969; Kevan and Shorthouse 1970). Normal b a s k i n g p o s i t i o n i s w i t h the wings f o l d e d over the back, w i t h the m e l a n i s e d v e n t r a l h i n d wing exposed. W h i l e on the ground, th e s e i n s e c t s would be h i g h l y v u l n e r a b l e t o p r e d a t i o n . I f ground p r e d a t i o n were common, any a d a p t a t i o n a c t i n g t o reduce i t s i n t e n s i t y s h o u l d be s e l e c t e d f o r . P r e d a t i o n by b i r d s on C o l i a s b u t t e r f l i e s can a l s o be s i g n i f i c a n t w h i l e the i n s e c t i s i n f l i g h t and e s p e c i a l l y when at r e s t ( S h a p i r o 1974). I n c r e a s e d melanism can i n c r e a s e d e t e c t i o n by a p r e d a t o r s i n c e a moving dark o b j e c t i s h i g h l y v i s i b l e t o any p r e d a t o r , whether i t has c o l o u r v i s i o n or not ( K e t t l e w e l l 1973). For n o n - p a l a t a b l e s p e c i e s , melanism c o u l d serve an aposematic f u n c t i o n . The i n t e n t of t h i s c h a p t e r i s t o d e t e r m i n e whether p r e d a t i o n on C o l i a s n a s t e s a c t s d i f f e r e n t i a l l y on dark and l i g h t i n d i v i d u a l s i n a manner which c o u l d e x p l a i n o b s e r v e d g e o g r a p h i c c l i n e s of melanism. Three hypotheses were t e s t e d : 1. Because of a s t r o n g t h e r m o r e g u l a t o r y r e q u i r e m e n t , C o l i a s  n a s t e s s e l e c t r e s t i n g s i t e s w hich a r e an "optimum" t e m p e r a t u r e . When ambient tem p e r a t u r e s d e c r e a s e , the chosen r e s t i n g s i t e s must be d a r k e r i n c o l o u r f o r i t t o be w i t h i n the optimum temp e r a t u r e range. Under c o l d c o n d i t i o n s t h e r e f o r e , dark i n d i v i d u a l s would be more c r y p t i c . 2. Ground p r e d a t i o n on C o l i a s n a s t e s i s most i n t e n s e on l i g h t i n d i v i d u a l s a t h i g h e l e v a t i o n , and most i n t e n s e on dark i n d i v i d u a l s a t low e l e v a t i o n . T h i s would i m p l y d i f f e r e n t i a l d e t e c t i o n by a v i s u a l 90 p r e d a t o r d u r i n g p e r i o d s when b u t t e r f l i e s a r e unable t o f l y . 3 . D i f f e r e n t i a l b i r d p r e d a t i o n on dark and l i g h t C o l i a s a l o n g the e l e v a t i o n g r a d i e n t a c t t o c r e a t e the o b s e r v e d a l t i t u d i n a l c l i n e of melanism. 91 MATERIALS and METHODS Much of t h i s study was c a r r i e d out i n c o n j u n c t i o n w i t h the f i e l d s t udy of the e f f e c t of melanism on C o l i a s a c t i v i t y d e s c r i b e d i n Chapter One. Study s i t e , weather r e c o r d s , c a p t u r e methods, and q u a n t i f i c a t i o n of melanism a r e t h e r e f o r e the same as p r e v i o u s l y d e s c r i b e d . Rest S i t e S e l e c t i o n B e f o r e an attempt was made t o c a p t u r e a s p e c i f i c b u t t e r f l y , i t was a l l o w e d t o l a n d and t a k e up a normal r e s t i n g or b a s k i n g p o s i t i o n . The e x a c t p o s i t i o n was noted and the i n s e c t c a p t u r e d w h i l e s t i l l on the ground. To o b t a i n a measure of d a r k n e s s of c o l o u r of the r e s t i n g s i t e , a S o l i g o r Spot Sensor spotmeter was used. The amount of l i g h t r e f l e c t e d , from a c i r c u l a r a r e a a p p r o x i m a t e l y t h r e e cm i n d i a m e t e r around the r e s t i n g s i t e used by the b u t t e r f l y , was measured. Changes i n s o l a r a n g l e and c l o u d c o v e r r e q u i r e d s t a n d a r d i z a t i o n of these measurements. A Kodak White S t a n d a r d (90% r e f l e c t i v e ) was p l a c e d i m m e d i a t e l y a d j a c e n t t o the r e s t i n g s i t e a t the same a n g l e as the s i t e s u r f a c e . L i g h t r e f l e c t e d from t h i s s t a n d a r d was measured w i t h the s p o t m e t e r . P e r c e n t r e f l e c t a n c e was c a l c u l a t e d by comparing r e s t i n g s i t e r e f l e c t a n c e t o s t a n d a r d " w h i t e c a r d " r e f l e c t a n c e . R e f l e c t a n c e of chosen r e s t i n g s i t e s was then c o r r e l a t e d w i t h a i r t e m p e r a t u r e measured 1.5 metres above ground l e v e l . 92 Ground P r e d a t i o n D u r i n g the day, a s e r i e s of b u t t e r f l i e s was c o l l e c t e d and t h e i r degree of melanism q u a n t i f i e d . T h i s s e r i e s was then d i v i d e d i n t o a "dark" h a l f and a " l i g h t " h a l f . A l l i n d i v i d u a l s were marked w i t h an i d e n t i f y i n g number on t h e v e n t r a l s u r f a c e of the f o r e w i n g . The number was t o t a l l y o c c l u d e d by the h i n g w i n g when the i n s e c t was a t r e s t , t h e r e b y not a f f e c t i n g v i s u a l d e t e c t i o n . In the e v e n i n g , ( a f t e r 20:00 MST), l o n g a f t e r a l l b u t t e r f l y f l i g h t a c t i v i t y had c eased (Chapter One, F i g . 7 ) , c o l l e c t e d specimens were s e t out i n the f o l l o w i n g manner: 1. One h a l f of the dark sample and one h a l f of the l i g h t sample were s e t out on the ground or v e g e t a t i o n i n a p r e s c r i b e d one-metre square a r e a a t 2480 m e l e v a t i o n . 2. The o t h e r h a l f of each group was s i m i l a r l y s e t out a t 2750 m e l e v a t i o n . At about 06:00 the f o l l o w i n g morning, l o n g b e f o r e b u t t e r f l y f l i g h t a c t i v i t y had begun, p l o t s were t h o u r o u g h l y s e a r c h e d f o r i n d i v i d u a l s which had not been preyed upon. B i r d P r e d a t i o n P r e d a t i o n by b i r d s was measured by r e c o r d i n g t h e p r e s ence of beak marks ( S h a p i r o 1974) on the wing margins of a l l C o l i a s c a p t u r e d . Because b u t t e r f l y wings f r a y w i t h age, c a r e was t a k e n t o o n l y count marks which were symmetric on b o t h l e f t and r i g h t wings. T h i s type of mark would r e f l e c t p r e d a t i o n a t t e m p t s on i n d i v i d u a l s a t r e s t w i t h wings f o l d e d over the back. Beak mark f r e q u e n c i e s were compared between dark and l i g h t morphs a t d i f f e r e n t e l e v a t i o n i n t e r v a l s . 93 RESULTS Rest S i t e S e l e c t i o n P e r c e n t r e f l e c t a n c e of 95 daytime r e s t i n g s i t e s were measured. There was no tendency f o r C o l i a s b u t t e r f l i e s t o choose d a r k e r c o l o u r e d r e s t i n g s i t e s under c o l d e r ambient c o n d i t i o n s ( r 2 = . 0 3 8 , N=95, p>.05). Darkness of r e s t i n g s i t e s was not c o r r e l a t e d w i t h the degree of melanism of e i t h e r C. n a s t e s ( r 2 = . 0 0 4 , N=76, p>.05), or C. meadi i ( r 2 = .237, N=16, p>.05). No tendency f o r s e l e c t i o n of " c o r r e c t " backgrounds was ap p a r e n t . In o r d e r f o r c l i n a l melanism t o p r o v i d e i n c r e a s e d p r o t e c t i o n a g a i n s t daytime v i s u a l p r e d a t o r s , t h e r e would have t o be some c o r r e l a t i o n between the a l t i t u d i n a l or l a t i t u d i n a l g r a d i e n t , and the backgrounds on which the i n s e c t s r e s t . H i g h e r e l e v a t i o n s do not p r o v i d e d a r k e r c o l o u r e d r e s t i n g s i t e s ( r 2 = . 0 0 2 , N=95, p>.05). T h e r e f o r e , i f melanism were an a d a p t a t i o n t o reduce p r e d a t i o n , i t i s not i n response t o c o l o r a t i o n of s e l e c t e d daytime r e s t i n g s i t e s . Ground P r e d a t i o n In some c a s e s ( 1 5 ) , the i n d i v i d u a l specimen was c o m p l e t e l y m i s s i n g a t the morning o b s e r v a t i o n . The remainder of the specimens r e c o r d e d as m i s s i n g (13) had t h e i r wings n e a t l y c u t o f f by the p r e d a t o r p r i o r t o the body b e i n g c a r r i e d away ( F i g . 19). These wings were s t i l l l o c a t e d w i t h i n the e x p e r i m e n t a l p l o t a t the morning c e n s u s . S i n c e wings had been 94 F i g u r e 19. Photograph of wings found r e m a i n i n g a f t e r p r e d a t i o n e x p e r i m e n t . 96 marked, p o s i t i v e i d e n t i f i c a t i o n of th e s e i n d i v i d u a l s were made. Those specimens s t i l l p r e s e n t and a l i v e had moved v e r y l i t t l e or not a t a l l d u r i n g the ten-hour p e r i o d . A l a r g e d i f f e r e n c e i n p r e d a t i o n i n t e n s i t y o c c u r r e d over the a l t i t u d i n a l range which t h e s e e x p e r i m e n t s were c a r r i e d out (Chisquare=7.667, df = 1, N=78). E s s e n t i a l l y no l o s s of b u t t e r f l i e s o c c u r r e d a t the lower e x p e r i m e n t a l p l o t (Table X I I ) . T a b l e X I I . Number of b u t t e r f l i e s of d i f f e r i n g d a r k n e s s p r e s e n t or absent a t each of two e l e v a t i o n s f o l l o w i n g one n i g h t of exposure t o ground p r e d a t i o n . Number of B u t t e r f l i e s 2480 m 2750 m Dark L i g h t Dark L i g h t P r e s e n t 9 13 17 11 Absent 1 2 9 16 p>.75* p<.07 • F i s h e r ' s E x a c t P r o b a b i l i t y T e s t . At the upper s i t e , however, almost 50% of the b u t t e r f l i e s s e t out a t 2 0 : 0 0 i n the e v e n i n g were gone by 0 6 : 0 0 the f o l l o w i n g morning, w i t h the g r e a t e s t l o s s o c c u r r i n g among l i g h t e r i n d i v i d u a l s ( T able X I I ) . U n f o r t u n a t e l y , the i d e n t i t y of the p r e d a t o r i s as y e t s p e c u l a t i v e . C h a r a c t e r i s t i c s of t h e p r e d a t o r a r e : 1. v i s u a l p r e d a t o r 2. c a p a b l e of n e a t l y c u t t i n g wings o f f b u t t e r f l i e s 97 3. c a p a b l e of p r e y i n g upon t h r e e t o f o u r b u t t e r f l i e s per n i g h t . S i n c e t h e s e e x p e r i m e n t s were c a r r i e d out between 20:00 and 06:00, the p r e d a t o r would have t o be a c t i v e d u r i n g t h i s p e r i o d , but not n e c e s s a r i l y r e s t r i c t e d t o i t . B i r d P r e d a t i o n B i r d s were never censused f o r abundance nor d i s t r i b u t i o n . I t was o b s e r v e d , however, t h a t t o t a l number of i n d i v i d u a l s were g r e a t e s t a t t r e e l i n e , d e c r e a s i n g w i t h i n c r e a s e i n a l t i t u d e . P r i m a r y s p e c i e s , i n approximate o r d e r of r e l a t i v e abundance, were: r o b i n ( Turdus m i g r a t o r i u s ), white-crowned sparrow ( Z o n o t r i c h i a l e u c o p h r y s ), h e r m i t t h r u s h ( H y l o c i c h l a g u t a t a ), v a r i e d t h r u s h ( I x o r e u s n a e v i u s ), horned l a r k ( E r e m o p h i l a  a l p e s t r i s ), water p i p i t ( Anthus s p i n o l e t t a ), w h i t e - t a i l e d p t a r m i g a n ( Lagopus l e u c u r u s ), and mountain b l u e b i r d ( S i u l i a  c u r r u c o i d e s ). Of t h e s e , a l l but the white-crowned sparrow would be p o t e n t i a l p r e d a t o r s on b u t t e r f l i e s . For the e n t i r e sample, t h e r e i s no d i f f e r e n c e i n beakmark fre q u e n c y between dark and l i g h t groups (Chisquare=.386, df=1, N=791). When the a l t i t u d i n a l g r a d i e n t i s d i v i d e d i n t o f o u r sub-p l o t s , e q u a l i n c i d e n c e of beak marks was r e c o r d e d from each (T a b l e X I I I ) . I f b i r d p r e d a t i o n i s g r e a t e s t near t r e e l i n e , and beak marks a r e an a c c u r a t e measure of r e l a t i v e p r e d a t i o n i n t e n s i t y , movement of b u t t e r f l i e s a l o n g the a l t i t u d i n a l g r a d i e n t i s s u f f i c i e n t t o mask any r e a l p r e d a t i o n g r a d i e n t . 98 T a b l e X I I I . Frequency of beak marks on C o l i a s n a s t e s wings over the e l e v a t i o n g r a d i e n t of the s t u d y a r e a . E l e v a t i o n (m) Number of B u t t e r f l i e s w i t h beak marks w i t h o u t beak marks p r o p o r t i o n 2400-2500 2500-2600 2600-2700 2700-2800 8 13 86 9 44 86 487 42 .154 .131 .150 .176 C h i - s q u a r e = 0.558, df=3,p> .90 Beak marks a r e i n f a c t a measure of s u c c e s s f u l escape, a f a c t which confounds t h e i r u s e f u l n e s s as a measure of p r e d a t i o n i n t e n s i t y ( S h a p i r o 1974). At most e l e v a t i o n s , d i f f e r e n t i a l p r e d a t i o n on dark or l i g h t morphs i s not ap p a r e n t ( T a b l e X I V ) . T a b l e XIV. E l e v a t i o n a l change i n beak mark fr e q u e n c y f o r dark and l i g h t C o l i a s n a s t e s . P r o p o r t i o n w i t h beak marks E l e v a t i o n (m) L i g h t Dark S i g n i f i c a n c e * 2400-2500 .140 .222 p=1.00 2500-2600 .110 .167 p=0.35 2600-2700 .169 . 1 34 p=0.28 2700-2800 .042 .296 p=0.03 * F i s h e r ' s E x a c t P r o b a b i l i t y T e s t . At the h i g h e s t a l t i t u d e i n t e r v a l , however, beak mark freq u e n c y i s s i g n i f i c a n t l y h i g h e r on d a r k e r c o l o u r e d C. n a s t e s . 99 DISCUSSION Darkness i n c o l o u r of daytime r e s t s i t e s shows no r e l a t i o n s h i p w i t h the degree of melanism of C o l i a s n a s t e s nor w i t h the e l e v a t i o n a l g r a d i e n t . I n t e n s i t y of ground p r e d a t i o n , however, has a v e r y s t r o n g e l e v a t i o n a l component. The h i g h e r r a t e of l o s s of i n d i v i d u a l s a t h i g h a l t i t u d e i s most i n t e n s e on l i g h t e r c o l o u r e d i n d i v i d u a l s . Escape f l i g h t by b u t t e r f l i e s i s i m p o s s i b l e a t low t e m p e r a t u r e s and/or low s o l a r r a d i a t i o n . Ground p r e d a t i o n would t h e r e f o r e not o n l y be i m p o r t a n t a t n i g h t , but anytime weather i s c o o l or c l o u d y . S h a p i r o (1974), found t h a t the g r e a t e s t i n c i d e n c e of observed p r e d a t i o n by b i r d s on p i e r i d s ( i n c l u d i n g C o l i a s eurytheme ), was w h i l e i n s e c t s were a t r e s t on v e g e t a t i o n . Any mechanism which might reduce t h i s p r e d a t i o n i n t e n s i t y , s h o u l d be s t r o n g l y s e l e c t e d f o r . Dark i n d i v i d u a l s , i n my e x p e r i m e n t s s u f f e r e d the l o w e s t p r e d a t i o n a t h i g h a l t i t u d e , but had the h i g h e s t beak-mark f r e q u e n c y a t h i g h e l e v a t i o n . These f a c t s c o u l d be r e l a t e d i f the p r e d a t o r i s a b i r d , a c t i v e i n the morning and e v e n i n g , and i f beak marks a r e c o n s i d e r e d a measure of s u c c e s s f u l escape not p r e d a t i o n . S i n c e t o t a l beak mark fr e q u e n c y i s even a l o n g the a l t i t u d i n a l g r a d i e n t , an even d i s t r i b u t i o n of a v i a n p r e d a t o r s i s i m p l i c a t e d . Absence of c r e p u s c u l a r or n i g h t p r e d a t i o n a t low e l e v a t i o n i n the p r e d a t i o n e x p e r i m e n t s i m p l i e s t h a t , i f the p r e d a t o r i s a b i r d , i t i s not the o n l y s p e c i e s t a k i n g b u t t e r f l i e s d u r i n g the day. D i f f e r e n t p r e d a t o r s might w e l l be i n v o l v e d i n t h e two measures of p r e d a t i o n . 100 C r y p s i s R e s t i n g s i t e s a r e not d a r k e r a t h i g h a l t i t u d e . However, s i n c e p r e d a t i o n o c c u r s d u r i n g p e r i o d s when the d a r k n e s s o r l e n g t h of shadows a r e g r e a t e s t , r e f u g e s f o r d a r k e r C o l i a s might e x i s t . C e r t a i n l y shadows would be j u s t as dark or l o n g a t low e l e v a t i o n , but the apparent a l t i t u d i n a l d i s t r i b u t i o n of the p r e d a t o r i n v o l v e d , r e n d e r s t h i s i m m a t e r i a l . Aposemasis There i s some i n d i c a t i o n t h a t p i e r i d s ( i n c l u d i n g C o l i a s  eurytheme ) might be n o n - p a l a t a b l e ( S h a p i r o 1974). L a r v a l f o o d p l a n t s i n c l u d e locoweed ( O x y t r o p i s spp.) which may p r o v i d e a c h e m i c a l d e f ense f o r the a d u l t s . The u s e f u l n e s s of melanism as a means of i n c r e a s i n g v i s i b i l i t y of the i n s e c t w h i l e a t r e s t i s u n l i k e l y , e s p e c i a l l y i n view of the i n s e c t ' s extreme c r y p t i c i t y . I suggest t h a t the p r e d a t o r might be a s m a l l mammal, a c a r a b i d b e e t l e , or a c r e p u s c u l a r b i r d . E x a c t d e t e r m i n a t i o n of the p r e d a t o r would r e q u i r e a t r a p p i n g program or d i r e c t o b s e r v a t i o n of p r e d a t i o n . Of the b i r d s p e c i e s noted i n the a r e a , w h i t e - t a i l e d p t a r m i g a n i s the o n l y one c o n s i s t e n t l y o b s e r v e d a t the h i g h e s t e l e v a t i o n . I n bo t h y e a r s a t l e a s t one hen w i t h brood was seen i n the v i c i n i t y of the upper sample-s i t e . I have o b s e r v e d p t a r m i g a n t a k i n g i n s e c t s w h i l e f e e d i n g . L e a s t Chipmunk ( Eutamias minimus ) i s the o n l y s m a l l mammal noted a t the upper s i t e , but ranges down t o t r e e l i n e . I t i s not l i k e l y , t h e r e f o r e , t o be i n v o l v e d i n the d i f f e r e n t i a l p r e d a t i o n o b s e r v e d a l o n g the a l t i t u d i n a l g r a d i e n t . C a r a b i d b e e t l e s a r e 101 a c t i v e a t n i g h t , and would t a k e i n s e c t s on the ground. I f the p r e d a t o r i n v o l v e d i s a c a r a b i d b e e t l e , i t s d i s t r i b u t i o n would be r e s t r i c t e d t o h i g h e r e l e v a t i o n s . For the obser v e d l a t i t u d i n a l c l i n e of melanism t o be t h e r e s u l t of d i f f e r e n t i a l p r e d a t i o n would r e q u i r e t h a t the d i s t r i b u t i o n of the same or s i m i l a r p r e d a t o r s be a r r a n g e d a l o n g t h e l a t i t u d i n a l g r a d i e n t i n the same way as the a l t i t u d i n a l g r a d i e n t . In t h i s s t u d y , the degree of melanism does appear t o have a marked, a l t h o u g h s t a t i s t i c a l l y n o n - s i g n i f i c a n t e f f e c t on the r a t e of ground p r e d a t i o n i n the e v e n i n g , and a t n i g h t . The g r a d i e n t of p r e d a t i o n i s v e r y s t e e p , but the o b s e r v e d c l i n e of melanism w i t h i n the s i t e i s v e r y weak. Movement of b u t t e r f l i e s i s g r e a t enough t o swamp the e f f e c t of p r e d a t i o n . From my e x p e r i m e n t s and o b s e r v a t i o n s , t h e r e i s no apparent b a l a n c i n g p r e d a t i o n on dark i n d i v i d u a l s a t low e l e v a t i o n . P r e d a t i o n e x p e r i m e n t s a l o n g a l a t i t u d i n a l g r a d i e n t would be v e r y u s e f u l t o d e t e r m i n e i t s importance as a g e n e r a l s e l e c t i v e f o r c e f o r melanism i n these i n s e c t s . U n t i l f u r t h e r e x p e r i m e n t s a r e c a r r i e d out t o c o n f i r m the d i f f e r e n t i a l p r e d a t i o n i n d i c a t e d , and t o i d e n t i f y the p r e d a t o r i n v o l v e d , i t i s not p o s s i b l e t o c o n c l u d e t h a t p r e d a t i o n a c c o u n t s f o r the broad g e o g r a p h i c a l c l i n e s of melanism w i t h i n c r e a s e d a l t i t u d e and e l e v a t i o n , o b s e r v e d both w i t h i n and between s p e c i e s . L i g h t C o l i a s do not p o s s e s s an advantage i n r e d u c i n g p r e d a t i o n a t low e l e v a t i o n . F o r l i g h t i n d i v i d u a l s t o be p r e s e n t a t a l l , would r e q u i r e the d e m o n s t r a t i o n of some o t h e r advantage f o r l i g h t c o l o r a t i o n , or a " c o s t " of b e i n g m e l a n i s t i c . 102 P r e d a t i o n has been demonstrated t o be a v e r y i m p o r t a n t f a c t o r i n d e t e r m i n i n g a d a p t i v e c o l o r a t i o n of i n s e c t s . My r e s u l t s i n d i c a t e t h a t p r e d a t i o n may be i m p o r t a n t i n c a u s i n g the o b s e r v e d a l t i t u d i n a l c l i n e of melanism, and s h o u l d be pursued f u r t h e r . 103 GENERAL CONCLUSION U s i n g c o l o u r v a r i a t i o n among i n d i v i d u a l s from a s i n g l e p o p u l a t i o n of C o l i a s n a s t e s b u t t e r f l i e s , I have t e s t e d t h r e e a l t e r n a t i v e hypotheses r e g a r d i n g the importance of melanism i n th e s e t u n d r a i n s e c t s . I have a t t e m p t e d t o p r o v i d e e m p i r i c a l e v i d e n c e , from l a b o r a t o r y and f i e l d o b s e r v a t i o n and e x p e r i m e n t , t o demonstrate the mechanism by which melanism i s a d a p t i v e . Melanism does convey some advantage by r e d u c i n g the i n c i d e n c e of n o c t u r n a l ground p r e d a t i o n a t h i g h e l e v a t i o n s . A b a l a n c i n g advantage does n o t , however, e x i s t f o r l i g h t c o l o u r e d b u t t e r f l i e s a t low e l e v a t i o n . That d i f f e r e n t i a l p r e d a t i o n i s a c t i n g t o cause the a l t i t u d i n a l and l a t i t u d i n a l c l i n e s of melanism b o t h w i t h i n and between s e v e r a l s p e c i e s would r e q u i r e t h a t the d i s t r i b u t i o n of the p r e d a t o r (or p r e d a t o r s ) be c o n s i s t e n t l y o r g a n i s e d p a r a l l e l t o the c l i n e s of melanism. The v e r y s h a r p g r a d i e n t of p r e d a t i o n p r e s s u r e and almost non-e x i s t e n t g r a d i e n t of melanism a t t h i s s i t e would i n d i c a t e melanism t o be s e r v i n g some o t h e r f u n c t i o n . U n t i l i d e n t i f i c a t i o n of t h e p r e d a t o r i s d e t e r m i n e d and i t s d i s t r i b u t i o n a s c e r t a i n e d , i t i s not p o s s i b l e t o c o n c l u d e t h a t c r y p s i s i s a g e n e r a l e x p l a n a t i o n f o r a r c t i c and a l p i n e melanism. Body temperature i s s i g n i f i c a n t l y a f f e c t e d by the da r k n e s s of C o l i a s b u t t e r f l i e s . P h y s i o l o g i c a l p r o c e s s e s and b e h a v i o u r can be o r d e r e d w i t h r e s p e c t t o i n c r e a s i n g body temperature ( F i g . 2 0 ) . F e c u n d i t y i s i n c r e a s e d by melanism, but o n l y a t low t e m p e r a t u r e s . There i s some i n d i c a t i o n t h a t a t h i g h ambient 104 F i g u r e 20. P h y s i o l o g y and b e h a v i o u r of C o l i a s b u t t e r f l i e s as a f u n c t i o n of body t e m p e r a t u r e . (Developmental t h r e s h o l d from Ae 1958, egg m a t u r a t i o n from S t e r n and Smith 1960, f l i g h t t h r e s h o l d s from Watt 1968). 105 50 h 40 o o <D k _ 30 Z3 "5 CD CL Tern 20 o DO 10 0 L Egg production upper limit Flight upper threshold Flight lower threshold ^ Flight lower threshold d1 Egg production peak Egg production lower limit Developmental threshold 106 t e m p e r a t u r e s l i g h t females have a h i g h e r f e c u n d i t y . A l t h o u g h f e c u n d i t y d i f f e r e n c e s a r e s m a l l , t h e r e appears t o be a b a l a n c e d advantage f o r both dark and l i g h t i n d i v i d u a l s w i t h r e s p e c t t o f e c u n d i t y over a temperature range. Great d i f f e r e n c e s occur i n d u r a t i o n of a c t i v i t y among C o l i a s b u t t e r f l e s w i t h d i f f e r i n g degrees of melanism. The d a r k e s t i n d i v i d u a l s of t h i s p o p u l a t i o n are a c t i v e up t o 55% l o n g e r than the l i g h t e s t i n d i v i d u a l s . T h i s r e s u l t s i n a much g r e a t e r amount of time a v a i l a b l e f o r f e e d i n g , mate l o c a t i n g , and o v i p o s i t i n g ; a l l of which a r e d e t e r m i n a n t s of f e c u n d i t y . There i s some i n d i c a t i o n t h a t l i g h t b u t t e r f l i e s a r e a b l e t o remain a c t i v e ( f l y i n g ) under the h o t t e s t sunny c o n d i t i o n s , d u r i n g which dark i n d i v i d u a l s must remain i n a c t i v e . In terms of d u r a t i o n of a c t i v i t y , t h e r e f o r e , t h e r e appears t o be a b a l a n c e d advantage f o r both dark and l i g h t b u t t e r f l i e s . A l p i n e and a r c t i c t u n d r a a r e t y p i c a l l y c o l d (monthly mean d a i l y temperature never exceeds 10°C) and have a s h o r t growing season. Time i s t h e r e f o r e a major c o n s t r a i n t on any e c t o t h e r m i n t h e s e h a b i t a t s . Body temperature t h r e s h o l d f o r egg p r o d u c t i o n ( F i g . 20) of 20°C, would be e a s i l y a t t a i n e d compared t o t h a t f o r f l i g h t (30-35°C). Any d i f f e r e n c e s i n f e c u n d i t y caused by melanism would be overshadowed by the u l t i m a t e r e q u i r e m e n t of r e a c h i n g the t e m p e r a t u r e s n e c e s s a r y t o s u c c e s s f u l l y f l y ( f e e d , m a t e , o v i p o s i t ) . T h i s i s e s p e c i a l l y t r u e c o n s i d e r i n g Watt's (1968) f i n d i n g t h a t females r e q u i r e a body temp e r a t u r e of 35°C t o f l y , compared t o the male r e q u i r e m e n t of 30°C. A l t h o u g h s l i g h t l y i n c r e a s e d f e c u n d i t y may r e s u l t from 107 d a r k e n i n g i n c o l o u r , the u l t i m a t e advantage of melanism i s the i n c r e a s e d a b s o r p t i o n of v i s i b l e r a d i a t i o n t o r a i s e body temperature t o the c r i t i c a l f l i g h t t h r e s h o l d . A l t h o u g h t h i s has been s u s p e c t e d i n the p a s t , t h i s i s the f i r s t e m p i r i c a l d e m o n s t r a t i o n t h a t i t i s so. I f , t h roughout the g e o g r a p h i c a l range of C o l i a s n a s t e s , the mean d a i l y temperature never exceeds 10°C, why a r e a l l p o p u l a t i o n s not e q u a l l y dark a l o n g the l a t i t u d i n a l g r a d i e n t ? The r e a s o n , I t h i n k , i s t h a t a l t h o u g h mean t e m p e r a t u r e s a r e s i m i l a r , d i u r n a l temperature f l u c t u a t i o n i n a l p i n e a r e a s i s f a r g r e a t e r (Remmert and W u n d e r l i n g 1969, LeDrew and W e l l e r 1978). T h i s r e s u l t s i n f r e q u e n t , but s h o r t , p e r i o d s of v e r y h i g h temperature i n a l p i n e meadows (Mani 1968). Under th e s e c o n d i t i o n s , a v e r y d e f i n i t e advantage f o r l i g h t i n d i v i d u a l s would be e n v i s a g e d . C o l d t e m p e r a t u r e s tend t o mer e l y slow a c t i v i t y and metabolism down, and can be endured by i n s e c t s f o r l o n g p e r i o d s . High t e m p e r a t u r e s can be endured f o r o n l y r e l a t i v e l y s h o r t p e r i o d s , and the upper l e t h a l t h r e s h o l d i s u s u a l l y v e r y s h a r p ( H e i n r i c h 1981). I t i s p o s s i b l y f o r these reasons t h a t the mechanisms f o r the advantages of b e i n g l i g h t (heat t o l e r a n c e ) a r e so d i f f i c u l t t o observe as compared t o thos e f o r b e i n g dark ( c o l d t o l e r a n c e ) . On a g l o b a l s c a l e , C o l i a s b u t t e r f l i e s a r e p r i m a r i l y i n h a b i t a n t s of a r c t i c and a l p i n e h a b i t a t s ( H o v a n i t z 1950). T h e i r a s s o c i a t i o n w i t h t h e s e h a b i t a t s has p r o b a b l y been v e r y l o n g , and t h e y have c e r t a i n l y e v o l v e d w i t h i t . There i s no a p r i o r i r e a son t o c o n s i d e r t h e s e a n i m a l s o f f s h o o t s of temperate 1 0 8 groups, l i v i n g a t the extreme l i m i t s of t h e i r t o l e r a n c e s by the e v o l u t i o n of s p e c i a l a d a p t a t i o n s such as melanism. A more p l a u s i b l e d e s c r i p t i o n of t h e i r b i o g e o g r a p h y , might be t h a t melanism i s the norm f o r t h e s e and many o t h e r a r c t i c i n v e r t e b r a t e s ; the c l i n a l change i s s i m p l y an i n c r e a s e i n l i g h t e r pigments w i t h d e c r e a s e i n a l t i t u d e and l a t i t u d e . T h i s i m p l i e s t h a t the e n v i r o n m e n t a l p r e s s u r e t o be m e l a n i s t i c i s r e l a x e d i n s o u t h e r n l a t i t u d e s or a t lower e l e v a t i o n s , or t h a t a s p e c i f i c advantage f o r l i g h t c o l o u r e x i s t s i n t h e s e r e g i o n s . I t h e r e f o r e f e e l t h a t f u t u r e work might b e s t be spent on d e t e r m i n i n g the advantage of l i g h t c o l o u r i n s o u t h e r n a r e a s and a t low e l e v a t i o n . 109 LITERATURE CITED Ae, S.A. 1958. 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