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Adaptive divergence and the evolution of trophic diversity in the threespine stickleback Lavin, Patrick A. 1985-12-31

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ADAPTIVE  DIVERGENCE IN  AND  THE  THE  EVOLUTION  THREESPINE  OF  TROPHIC  DIVERSITY  STICKLEBACK  by PATRICK  B.Sc,  University  A.  Of  LAVIN  British  Columbia  A THESIS THE  1982  SUBMITTED IN P A R T I A L F U L F I L L M E N T R E Q U I R E M E N T S FOR T H E D E G R E E OF MASTER OF S C I E N C E in T H E F A C U L T Y OF GRADUATE S T U D I E S (Department of Zoology)  We  accept  THE  this thesis required  as conforming standard  UNlVESSXT-Y-^OF B R I T I S H October 1985  @  Patrick  A.  Lavin,  to the  COLUMBLX  1985  OF  In  presenting  degree  this  at the  thesis  in  partial  fulfilment  University of  British  Columbia,  freely available for reference and study. copying  of  department  this or  thesis by  for scholarly  his  or  publication of this thesis  her  Z^g>oVc,  The University of British Columbia 1956 Main Mall Vancouver, Canada V6T 1Y3 Date  DE-6(3/81)  C3c3r  to  }  I7K  the  requirements  I agree  purposes  may  representatives.  be  It  is  for  an  advanced  that the Library shall make it  I further agree  for financial gain shall not  permission.  Department of  of  that permission granted  for extensive  by the head  understood  that  be allowed without  of  my  copying  or  my written  i i  ABSTRACT Five  populations  Gasterosteous (Vancouver  of  aculeatus,from  Island,  Phenotypic  the  British  i n t e r p o p u l a t i o n l e v e l s of divergence  the  threespine  upper  Columbia)  variability  is  assumed  stickleback,  Cowichan  River  were surveyed in  trophic  to be a p o s t - g l a c i a l  n i n t h c h a r a c t e r was l a t e r a l p l a t e number.  surveyed  were  Gasterosteus fewer  the  plates  f i s h species.  Three  associated  Populations  plate  trophic  with  populations  i n lakes with  'morphotypes'  one  and  of  of  three  were lake  predatory  identified, environments.  i n h a b i t i n g benthic dominated environments  were  found  to  reduced  gill  raker  length  to  morph').  feeding  A l l populations  however  than p o p u l a t i o n s  morph')  relative  morph;  event.  i n lakes l a c k i n g p i s c i v o r o u s f i s h had s i g n i f i c a n t l y  lateral  each  low  to assess  morphology.  Nine c h a r a c t e r s were scored; e i g h t were r e l a t e d t o the  system  possess  populations  An  but  from  intermediate  reduced  gill  increased lentic  morph  may  ('benthic  raker number and  upper  jaw  length  environments ('limnetic also  exist  and  is  c h a r a c t e r i z e d by a morphology s u i t a b l e t o e i t h e r t r o p h i c regime. Analysis  of  -stomach c o n t e n t s  showed d i e t type  (benthic or  l i m n e t i c ) t o be s i g n i f i c a n t l y dependent on morph. The  functional  significance  of  differences  in  trophic  morphology was i n v e s t i g a t e d i n t h r e e feeding experiments using a r e p r e s e n t a t i v e p o p u l a t i o n from each morphotype. of  the benthic and i n t e r m e d i a t e morphs allowed  larger  benthic  component  to  prey benthic  than  the  limnetic.  f o r a g i n g success  The longer jaw them t o ingest a No  behavioural  between p o p u l a t i o n s  was  i d e n t i f i e d , although  i n c r e a s e d jaw  spent  prey.  manipulating  was  the  benthic.  d e n s i t y and g i l l limnetic  raker  foraging  The  shortened  the  time  Both the intermediate and l i m n e t i c  morphs were b e t t e r f o r a g e r s on than  length  an  experimental  Head l e n g t h , snout number  were  limnetic  prey  length, g i l l  strongly  raker  correlated  with  success.  quantitative  genetics  governing  the  eight  trophic  c h a r a c t e r s were i n v e s t i g a t e d using the same three r e p r e s e n t a t i v e populations.  Broad sense estimates  ranged from 0.132 to Character j rG|  ^  genetic 0.9),  environment  0.677;  a l l estimates  correlations  while  tended  were  character  to  be  of c h a r a c t e r  heritabilities  were  reasonably  correlations  lower.  Cluster  significant. strong  arising  through  analyses  of the  g e n e t i c c o r r e l a t i o n m a t r i c e s d e f i n e d two c h a r a c t e r first  grouped  measures  measures of g i l l correlations  raker  suggest  of  head  structure.  shape, The  d i r e c t i o n a l s e l e c t i o n had operated  snout  length, g i l l hence  raker  selection  r e l a t e d to food s i z e . limnetic  morphs  second  patterns  number, has  head  operated  hardest depth to  The b e n t h i c - l i m n e t i c  were  separated  by  the  the  grouped  of  between morphotype  that  length;  the  suites,  genetic  the three p o p u l a t i o n s are d i s t i n c t  S e l e c t i o n g r a d i e n t s f o r divergence  (0.3 <  races.  indicated  on head l e n g t h , and  modify and  upper  jaw  characters  intermediate-  greatest  selection  d i s t a n c e while the i n t e r m e d i a t e - b e n t h i c morphs were separated by the s h o r t e s t s e l e c t i o n d i s t a n c e . These  results  support  selection,  arising  from  the  trophic  conclusion  that  directional  resource d i f f e r e n c e s between  i v  lakes,  has  organized  Gasterosteus distinction  within of  each  upper  Cowichan  population  coupled  significance  of  that  the b e n t h i c  at  least  'ecotypes'.  some  the  interpopulation  components and  of  variability  drainage. with  trophic  limnetic  morphs  The  the  be  racial  functional  morphology must  for  indicate  considered  V  TABLE OF CONTENTS  ABSTRACT  i i  LIST OF TABLES  -.vii  LIST OF FIGURES  ix  ACKNOWLEDGEMENTS  x  General I n t r o d u c t i o n  1  Chapter  1  4  Introduction  4  M a t e r i a l s and Methods  5  Cowichan Lake  5  S t a t i s t i c a l Methods  10  Results  12  Discussion  28  Chapter 2  34  Introduction  34  M a t e r i a l s and Methods  36  Establishment Estimation  and F o s t e r i n g of Progeny of  Character  Correlations Reconstructing  Heritabilities  the Pattern of Trophic  H e r i t a b i l i t y and Genetic S e l e c t i o n Gradients'  Chapter 3  and  .  Results  Discussion  36  38 Divergence ....  41 42  Correlations  42 59 60 65  vi  Introduction  65  M a t e r i a l s and Methods  67  Trophic Morphology  67  Gape Experiments  68  Amphipod M a n i p u l a t i o n  Experiments  L i m n e t i c Foraging T r i a l s  70 73  Results  75  Trophic Morphology  75  Maximum Gape  76  Amphipod Manipulation  Experiments  L i m n e t i c Foraging T r i a l s Discussion General  Discussion  References  81 86  ,  88 99 102  vii  LIST OF TABLES  Table  1.  Morphometry data f o r l a k e s i n the upper Cowichan  drainage  8  Table 2. Means and standard d e v i a t i o n s on a d j u s t e d data f o r each v a r i a b l e and p o p u l a t i o n  18  Table 3. PCA from a d j u s t e d data  23  Table 4. Component c o r r e l a t i o n s from the c o r r e l a t i o n of  matrix  a d j u s t e d data  24  Table 5. Experimental design of nested ANOVA  on  component  scores  28  Table 6 . Design of f u l l s i b ANOVA f o r the e s t i m a t i o n of Vg. Table  '7. D e s c r i p t i v e  37  s t a t i s t i c s f o r w i l d c o l l e c t i o n s and  l a b o r a t o r y reared progeny Table  8.  Heritabilities  43  f o r the  three  representative 46  t r o p h i c morphs Table  9. G e n e t i c , phenotypic  and environmental  correlation  matrices f o r Bear Lake Table  10. G e n e t i c , phenotypic  49 and environmental  correlation  m a t r i c e s f o r Caycuse Table  11. G e n e t i c , phenotypic  51 and environmental  correlation  matrices f o r Grant Lake Table of  53  12. Spearman rank c o r r e l a t i o n s between the g e n e t i c , environmental  the  and phenotypic  elements  correlation  matrices Table  13. S e l e c t i o n g r a d i e n t s f o r p o p u l a t i o n t r a n s i t i o n s .  57 . 59  viii  Table  14. ANCOVA  results  forgillraker  density  on  standard  length  75  Table  15. G u t c o n t e n t  Table  1 6 . ANCOVA  length Table  benthic Table on Table  results  and upper  17.  Cell  data  for  wild  population  amphipod  foraging  standard 79  and standard  d e v i a t i o n s f o r ANOVA  on  success  84  r e g r e s s i o n summary  of  foraging  success  19.  85  Correlation time  coefficients  f o r average  86  2 0 . Summary o f l i m n e t i c  Table  21. I n t r a p o p u l a t i o n c o r r e l a t i o n s proportion of limnetic 22.  character  successful  on U P J L  Table  Table  on  .. 77  behaviour  manipulation  the  size  samples.  jaw l e n g t h  means  18. M u l t i p l e  from  Interpopulation and l i m n e t i c  feeding  experiments for  character  87 and  foraging correlation  success  87 coefficients  for 88  LIST OF FIGURES  Figure  1 . The Cowichan drainage system and  the  Strait  of  Georgia region Figure  2.  6  Dendrogram  summary  of lake groupings based on  lake chemistry  '.  13  F i g u r e 3. V a r i a b i l i t y p r o f i l e s f o r the nine sampling  sites  in the Cowichan drainage Figure  4.  Dendrogram  15  summary  of lake groupings based on  p o p u l a t i o n morphology Figure  5.  Bivariate  population,  . .. 20  mean  plotted  component on  the  scores, first  two  for  each  principal  components Figure  6.  26  Dendrogram  summary  of  character  genetic  c o r r e l a t i o n matrices  57  F i g u r e 7. P l o t of amphipod s i z e vs UPJL f o r each morph. ... 82 Figure  8.  limnetic  Plots  of b i v a r i a t e means f o r the p r o p o r t i o n of  f o r a g i n g and adjusted c h a r a c t e r  F i g u r e 9. P l o t s of b i v a r i a t e means f o r limnetic  the  f o r a g i n g and GRL, GRN and GRDENS  89 proportion  of 91  X  ACKNOWLEDGMENTS My  initial  interest  problems was s t i m u l a t e d express  my  patient  most  i n the s t i c k l e b a c k and e v o l u t i o n a r y  by  Dr.  sincere  J.D.  thanks  McPhail.  to  support i n a l l a s p e c t s of t h i s p r o j e c t .  kindly  provided  Melanie  of  Madill  through b o r i n g Drs.  their  deserves  time special  recognition  hours of data r e c o r d i n g  Dolph  Schluter,  would  and  for assistance  Jack  and  enlightening  Wehrhan l e d  multivariate  statistics.  o f f the  squash  were always  and t h i s work was improved by them.  clarity  to  criticisms greatly Alistair  analysis.  f o r the many  and arguments with E r i c T a y l o r  Comments from D r s .  biological  suffering  C.  p a r t i c u l a r l y l i k e t o thank Dolph S c h l u t e r  Discussions  Birch  i n the f i e l d .  for  hours he devoted t o d i s c u s s i n g my work, on and court.  Gary  and key punching.  Maize  (dragged) me through the m y s t e r i e s of  added  wish  f o r h i s c r e a t i v e i n s i g h t and  Melanie M a d i l l , Andrew Simons, E r i c T a y l o r  I  I  my  Judy Myers, C.  Wehrhan and Nick  t h i n k i n g and t h i s t h e s i s .  Giles  Bob Carveth's  improved the f i g u r e s .  Blachford,  sciences  Susan  data center  Ertis  and  provided  the  staff  of the  i n v a l u a b l e a i d i n data  1  GENERAL INTRODUCTION The  t h r e e s p i n e d s t i c k l e b a c k (Gasterosteous  polytypic  species  (Bell  1976)  breeding c o l o u r s (e.g. McPhail (e.g. Hay  and McPhail  body morphology Gross  and  McPhail  exhibiting  1969;  variability  Moodie  McLean 1980;  1972);  1984);  and  in  D e s p i t e the range of  characters  in:  1983);  McPhail  biochemistry  a  behaviour  McPhail and Hay  (e.g. Hagen and G i l b e r t s o n 1972;  Anderson  1985).  1975;  aculeatus) i s  1977;  (Withler and  which  show  a  p r o p e n s i t y to vary, the most e x t e n s i v e surveys of v a r i a t i o n have concentrated  on body armature, p a r t i c u l a r l y with respect to the  l a t e r a l p l a t e s or scutes 1969;  Gross  1977).  (e.g. Munzing 1963;  Miller  and  Hubbs  Recent s t u d i e s have a l s o examined the  of s k e l e t a l p a r t s i n c l u d i n g p e l v i c g i r d l e elements ( G i l e s and d o r s a l and p e l v i c Investigations morphs'  (Hagen  hypotheses resident model  spines (Reimchen of  and  concerning  the  three  Gilbertson the  1983)  1980b).  commonly  1972)  origins  have  described  'plate  generated  two  of freshwater d i v e r s i t y i n  ( i . e . nonanadromous) p o p u l a t i o n s of G a s t e r o s t e u s . outlined  by  Miller  and  loss  Hubbs  maintenance of v a r i a b i l i t y by gene flow.  (1969) The  proposes  authors  The the  suggest  that the d i s t r i b u t i o n of p l a t e phenotypes r e s u l t s from c o n t i n u a l introgression  of  freshwater  genomes  by  genetic  input  from  anadromous p o p u l a t i o n s , i n t h i s case most of the v a r i a t i o n would be n e u t r a l .  S t u d i e s at c o n t a c t zones however,  not  introgression  as  (Hagen 1967).  T h i s o b s e r v a t i o n l e d to the a l t e r n a t e  proposed  hybrids  do  support  appear to be s e l e c t i v e l y d i s f a v o u r e d  by Hagen and McPhail  hypothesis  (1970) which d e s c r i b e s s e l e c t i o n ,  2  as the primary empirical  agent  organizing  freshwater  Later  work i l l u s t r a t e d the s e l e c t i v e advantage of d i f f e r e n t  p l a t e phenotypes (Moodie et a l . coastal  diversity.  Atlantic  p o p u l a t i o n s suggest  morph (once thought to be advantage  1973), while recent s t u d i e s  a  hybrid)  i n some s i t u a t i o n s and  (Hagen and Moodie 1982; Although patterns  Wootton  gene flow  of  may  s e l e c t i o n may  still  that the p a r t i a l l y p l a t e d -may  be  at  a  selective  represent d i s t i n c t  populations  1984).  not  interpopulation  of  contribute  variability,  significantly forces  y i e l d detectable variation.  other  to than  Changes in sea-  l e v e l with temperature minima and maxima d u r i n g the P l e i s t o c e n e , a f f o r d e d anadromous p o p u l a t i o n s lakes.  Freshwater  saltwater  populations  are  d e r i v e d from these marine founder the  invasion  subsequently (1984) has  of  previously  stocks  f o r the e v o l u t i o n of the Gasterosteus Vancouver  Island.  These  (Bell  genetic  that such founder  biological  into  generally  uncolonized  organizes the founder  suggested  routes  thought 1976)  species pair species  in Enos Lake,  exhibit  and  type.  browser  One  feeding  extreme  associated  the d i f f e r e n c e s are congruent  s p e c i e s , the so c a l l e d on  McPhail  i n v a s i o n s are r e s p o n s i b l e  with diet  selection  variation.  i n morphology thought to be  ecology,  to be  following  habitat;  i n t e r s p e c i f i c divergence trophic  glacial  'benthic'  macroinvertebrates,  feeds almost e n t i r e l y on p l a n k t o n i c prey.  while  is  a  bottom  the ' l i m n e t i c '  Bentzen  and  McPhail  (1984) have shown d i f f e r e n c e s i n jaw morphology, between the species,  with  two  to be i n part r e s p o n s i b l e f o r the d i e t a r y d i s t i n c t i o n .  T h i s i s one  of the few  s t u d i e s i n v o l v i n g freshwater  populations  3  of  Gasterosteus  in  which  the  significance  v a r i a b i l i t y has been c l e a r l y d e f i n e d , but indicates  a  potential  mechanism  d i f f e r e n t i a t i o n - adaptive divergence Although  of morphological  more  for  importantly  it  evolution  of  the  (Bentzen  1982).  the s p e c i e s p a i r s are of great i n t e r e s t  be e v o l u t i o n a r y anomalies and hence p r o v i d e l i t t l e describing  the  origins  of  racial differences  they  g e n e r a l i t y in  ( i . e . variation  preserved below the l e v e l of b i o l o g i c a l s p e c i e s ) .  Is there  s i g n i f i c a n c e to i n t e r p o p u l a t i o n d i f f e r e n c e s or i s t h i s neutral,  arising  largely  a d a p t i v e divergence  is  stickleback  then  the observed  variation.  divergence The  we  a  from common  the  effects  mode  of  may  of  any  variation  history?  evolution  in  If the  must be a b l e to a s c r i b e a s i g n i f i c a n c e to This thesis investigates  the  adaptive  i n freshwater p o p u l a t i o n s of G a s t e r o s t e u s . study was  designed to address  three q u e s t i o n s r e l e v a n t  to a d a p t i v e divergence. 1.  How  much morphological v a r i a t i o n e x i s t s w i t h i n  and  between  r e s i d e n t p o p u l a t i o n s of l a k e - d w e l l i n g Gasterosteus? 2.  Does the morphological v a r i a t i o n appear to be under g e n e t i c  control? 3.  If  selection  can  be  implicated  in  shifting  morphology, which c h a r a c t e r s have been s e l e c t i v e l y The  three  chapters  questions in turn.  which  follow  population  modified?  focus on each of these  4  CHAPTER 1  Introduction The  extensive  threespine  phenotypic  stickleback  the dichotomy between generated  two  variation  Gasterosteous the  freshwater  hypotheses  to account  and  phenotypic  variation  McPhail local of  selection. empirical  forms,  focus  phenotype.  that  much  the  i n freshwater h a b i t a t s a r i s e s  from  that most freshwater v a r i a t i o n  The  investigations  that  on body armature,  This character populations  obvious.  Thus, much of  Gasterosteous p l a t e count  is  due  to  l a t t e r h y p o t h e s i s i s supported by a number  between  in  is  the  aculeatus  1973).  particularly  easily  plate  have  count  perceived  complex  scored  identified Many  local  of  these  the l a t e r a l and  complexity  plate  differences  frequencies  are  often  within  the  a r i s e s from i n v e s t i g a t i o n s of  f r e q u e n c i e s , or the f r e q u e n c i e s of  different  plate  Although t h i s c o n c e n t r a t i o n on l a t e r a l p l a t e s has been  p r o d u c t i v e , i t has l e d to c o n f u s i o n (see Hagen and for  has  of  a d a p t a t i o n s (e. g. Hagen and G i l b e r t s o n  morphs.  marine  i n t r o g r e s s i o n from the marine form; whereas, Hagen and  (1970) argue  studies  the  f o r the e v o l u t i o n of t h i s  M i l l e r and Hubbs (1969) suggest  continual  by  a c u l e a t u s , together with  diversity.  found  exhibited  Moodie  1982  a d i s c u s s i o n of t h i s problem) and, more i m p o r t a n t l y , i t has  obscured  the  characters,  extensive  morphological  particularly  those  exploitation.  This v a r i a t i o n  selection  trophic  on  traits  variability  involved  in  trophic  i s probably a d a p t i v e , may  be  a  in  driving  and  other resource if  so  f o r c e behind  5  p o p u l a t i o n divergence. and  evolutionary  morphology in  head  (e.g.  Recent s t u d i e s emphasize the  significance  of  variation  Witte 1984) and i n  morphology  in  ecological t e l e o s t head  Gasterosteus ,  differences  i n the Enos Lake species p a i r appear to be  a p p r o p r i a t e to t h e i r resource use (Bentzen and McPhail T h i s chapter d e s c r i b e s the degree of v a r i a t i o n morphology Cowichan  between drainage,  interpopulation  Vancouver  variation  regimes between lake  populations  from  five  Island,  lakes  British  1984).  in  trophic  within  the  Columbia.  If  i s a response to d i f f e r e n t  selective  lakes, one would p r e d i c t an a s s o c i a t i o n  characters  and  site-specific  Gasterosteus morphologies.  Thus, I have attempted to i d e n t i f y extant characteristics  and  between  differences  in  lake  a s s o c i a t e these with divergence i n t r o p h i c  morphology.  M a t e r i a l s and Methods  Cowichan Lake Cowichan Lake i s central  Vancouver  a  large,  Island,  oligotrophic  British  Columbia.  through the Cowichan River i n t o the S t r a i g h t 1).  lake  on  south-  The lake d r a i n s  of  Georgia  (Fig.  A recent geologic u p l i f t has caused the r i v e r to sink  i t s own  floodplain, confining  channel  containing  a  the  number  river of  falls  to  a  narrow,  (Carl  into steep  1953).  The  anadromous form of Gasterosteus e n t e r s the lower Cowichan system but i s excluded from my drop  over  a  91  metre  study area by Skutz F a l l s , a run.  The  5.5  metre  e n t i r e Cowichan V a l l e y  was  6  Figure  1. The Cowichan drainage system and the S t r a i t of Georgia r e g i o n . (1 = Kwassin Lake, 2 = Grant Lake, 3 = Beaver Lake, 4 = Mesachie Lake, 5 = Bear Lake, 6 = Honeymoon Bay, 7 = Gordon Bay, 8 = Caycuse, 9 = Bay 10; 6,7,8, and 9 a r e a l l s i t e s w i t h i n Cowichan Lake.)  7  8  g l a c i a t e d d u r i n g the l a s t stages of d e g l a c i a t i o n  ( F r a s e r ) g l a c i a t i o n and i n the i n i t i a l  (about  10,000  BP)  the  study  covered by a s i n g l e g l a c i a l lake ( A l l e y and Chatwin  area  1979).  was This  area now c o n t a i n s Cowichan Lake and four smaller l a k e s ( F i g . All  of  the  lakes  1).  are i n t e r c o n n e c t e d and there a r e no obvious  b a r r i e r s t o s t i c k l e b a c k d i s p e r s a l between the l a k e s . flow i s p o s s i b l e between p o p u l a t i o n s i n d i f f e r e n t on lake morphometry are presented  Thus, gene  lakes.  Data  i n Table 1.  1  Table 1.  Morphometry data f o r lakes i n the upper Cowichan drainage system.  Lake  Area (Hectares)  Maximum Depth(m)  Elevat ion (m)  6176.9 28.0 33.0 2.2 1 .4 76.0  45.7 5.5 5.0 2.5 2.5 10.1  1 63 1 63 181 1 75 175 1 68  Cowichan Bear Beaver Grant Kwassin Mesachie  The chemical  lakes,  and  similarity;  population  sites  within  the l a k e s , were grouped by  these  groups  were  made  at  each  sampling  Five  location:  t u r b i d i t y , c o n d u c t i v i t y , pH, and a l k a l i n i t y . was  compared  to  groupings achieved by morphological a n a l y s i s , on the  s t i c k l e b a c k s c o l l e c t e d from each s i t e . were  then  chemical  measures  dissolved Dissolved  oxygen, oxygen  measured i n the f i e l d , and the four remaining measures were  made on water samples returned to the Environmental Laboratory  (U. B. C. ).  Using  Euclidean  Engineering  distance  as the  s i m i l a r i t y c r i t e r i o n the f i v e v a r i a b l e s were then e n t e r e d i n t o a  9  cluster analysis. computing  the  variable  d i s t a n c e matrix.  by changes in standardized  Each  variable  was  , Euclidean  scaling;  by d i v i d i n g the  Ward's  (Everitt  similar  (Fig.  1974)  2).  classification  separate  lakes  was  in  is affected  all  variable  data  were  kth v a r i a b l e  (Everitt  1974).  used to generate a dendrogram  Eilers  et  a l . (1983)  a n a l y s i s using  relative  weight  distance  i t h s i t e datum of the  d e v i a t i o n of the kth  of lake s i t e s  equal  consequently  by the standard method  given  to  employed  a  three v a r i a b l e s to group  their  susceptibility  to  pole-seines  and  acidification. Sticklebacks  were  collected  minnowtraps from the nine  using  l o c a t i o n s during May  1983.  were preserved  i n 10% b u f f e r e d f o r m a l i n f o r one  then  in  stained  p r e s e r v a t i o n was  a  solution  in 37.5%  of  alizarin  red and  isopropyl alcohol.  (+  0.05mm)  and  Nine  length  (HEAL),  eye  length  (UPJL),  (GRL),  gill  number  morphological  40)  (STDLEN),  diameter  (GRN)  and  Except f o r p l a t e number  Lagler  (1958).  and G i l b e r t s o n (1972). are  (SNOL),  raker  Final  with  ,  head  associated  and  lies  1972;  al.  1983)..  with  (EYED), upper  gill  all  raker  P l a t e s were scored a c c o r d i n g except  t r o p h i c e x p l o i t a t i o n (Kliewer a l . 1978;  Hyatt  1979;  jaw  length  measurments  A l l of these v a r i a b l e s ,  Northmore et  dial  length  head depth (HEAD), inner o r b i t a l width (INOW), and  number (PLN). Hubbs  length  KOH.  and  where necessary an o c u l a r micrometer.  These measures i n c l u d e : standard snout  fish  week, washed  measures were made on each i n d i v i d u a l (21 < N < calipers  All  plate follow  to Hagen plates,  1970;  Fryer  Wright  et  10  S t a t i s t i c a l Methods In  animals  with  indeterminate  growth,  growth  related  d i f f e r e n c e s i n body s i z e f r e q u e n t l y account f o r the m a j o r i t y  of  both  To  inter  and i n t r a p o p u l a t i o n v a r i a b i l i t y  remove such standard  size  length  effects of  each  40mm.  variable  This  (Thorpe 1976).  was  adjustment  adjusted uses  the l i n e a r  r e g r e s s i o n of the l o g of each v a r i a b l e on the l o g of length  (Steele  and T o r r i e  1980).  The b a s i c  to a  standard  form  of the  i s the i t h a d j u s t e d case of the j t h v a r i a b l e  i n the  regression i s , Y i j k = Yjk - 0 j k ( L i k where Y i j k  - 40)  kth p o p u l a t i o n , Yjk i s the sample mean of the j t h v a r i a b l e , 40)  i s the standard  length of the i t h i n d i v i d u a l minus the  grand mean, and /3jk i s the c o e f f i c i e n t variable  on  standard  other authors  of a l l o m e t r y f o r the  length w i t h i n each p o p u l a t i o n .  p o p u l a t i o n s c o n t a i n e d many small i n d i v i d u a l s the a d j u s t e d  curves  of  two p o p u l a t i o n s  individuals  sampled  f u n c t i o n than As  a  length  result,  earlier  t o 40mm.  1984), some  a  of the  I f the r e l a t i v e growth  are s i m i l a r , i n development  sample  length  (< 35mm) and thus I  but  curvilinear;  yield  l a r g e r i n d i v i d u a l s whose growth r a t e adjusting  consisting  a steeper  has  slowed.  of many small  i n d i v i d u a l s t o a standard  length beyond  exaggerate  d i f f e r e n c e s between.populations.  morphological  specific  regression  coefficients  character  (Thorpe 1976).  were  jth  Although  have a d j u s t e d t h e i r data s e t s t o a standard  of 50mm (Hagen and G i l b e r t s o n 1973; McPhail  reduced  (Lik  the sample  used  mean,  to adjust  may Site each  11  Using  Sheffe's  t e s t , m u l t i p l e comparisons of sample means  were made f o r each v a r i a b l e . were s i g n i f i c a n t sites  might  (p <  be  Many of these u n i v a r i a t e c o n t r a s t s  0.05),  grouped  by  while  morphological  p o s s i b i l i t y was i n v e s t i g a t e d by The  methods  of  this  c l u s t e r i n g the lake correlation test  others  clustering  analysis  chemistry  suggested  certain  similarity.  This  morphometric  data.  a r e the same as those used f o r data.  An  element  by  element  of the two E u c l i d e a n d i s t a n c e m a t r i c e s , was used to  f o r congruence of the two dendrograms. P a t t e r n s of  principal matrix were  morphological  components  (Pimentel entered  variable  to  derived  1979).  into each  variation from  the  A l l characters,  the  analysis.  component  correlations  (Pimentel  contributions  of  morphological  differentiation,  was  and  component scores from the f i r s t  The  To  The sampling  not  survey  a  of each  by  the  component  the  to  was performed on the  was  The i n t e g r i t y  investigated  groups suggested  program w i t h i n the  relative  variances  three components.  within  ANOVA.  contribution  ANOVA  nesting  correlation number,  interlocality an  by  plate  define  (see r e s u l t s )  populations  character except  of the i n f e r r e d groupings the  summarized  evaluated  1979).  intra  were  Cowichan  by  by t h i s  drainage  was  of p u t a t i v e m i c r o h a b i t a t s ; t h e r e f o r e n e s t i n g the  p o p u l a t i o n s w i t h i n groups does not random  assignment  1981).  Unless  within  otherwise  violate  a subordinate  noted,  the  level  assumption  (Sokal and Rohlf  a l l s t a t i s t i c a l procedures  performed using MIDAS (Fox and G u i r e  1976).  of  were  12  Results The  results  summarized distinct  of the c l u s t e r a n a l y s i s of s i t e chemistry are  i n F i g u r e 2. group  The four Cowichan  as do Grant and Kwassin l a k e s .  that Bear Lake i s more though  the  Lake  closely  related  to  sites One  form  should note  Beaver  Lake  even  former i s a small bay o f f the main body of Cowichan  Lake and so might have been expected to group with the sites.  a  These  Cowichan  r e s u l t s i n d i c a t e the e x i s t e n c e of two lake types  d e f i n e d by c h e m i s t r y , with the Bear-Beaver p a i r p o s s i b l y forming a third  type.  For each variation  character  population  into  the  (Yablokov  nature  of  1974)  which a p a r t i c u l a r Concordance  evolutionary  of  selection  with to  peaks  a  and  common  genome  (Sokal  (b)  two  troughs,  genetic  the  as  important  responding  a  by  constraints.  differences  is  Such  mechanism  architecture.  reorganization  1978).  but  of  responses: (a) an  s p e c i e s i n t e r a c t s with s e l e c t i v e  amplitudes, suggests that the s p e c i e s  contrast  coefficients  provide  i n d i c a t i o n of c h a r a c t e r c o r r e l a t i o n , and  selection  the  on the unadjusted data are p l o t t e d i n F i g u r e 3.  'variability profiles' insights  and  i n peak to  local  This  i s in  response  to  local  These concepts are t r e a t e d i n d e t a i l  below. For each v a r i a b l e and each p o p u l a t i o n and  the  adjusted  standard d e v i a t i o n s are r e p o r t e d i n Table 2.  significant differences Cowichan  Lake;  (p >  however,  significantly different  0.05)  between  all  Cowichan  (p < 0 . 0 5 )  from a l l  There were no  subsamples subsamples other  means  lakes  within were in  at  13  Figure  2. Dendrogram chemistry.  summary  of  lake  groupings  based  on  lake  9 BAY 10 8  CAYCUSE G O R D O N BAY  6 H O N E Y M O O N BAY MESACHIE BEAR BEAVER GRANT-  1  KWASSIN0.0  20  DISTANCE  30  15  -Figure  3. Variability profiles in the Cowichan drainage.  for  the  nine  sampling  sites  lO  Legend O  BAY10  A BEAR O BEAVER V CAYCUSE GORDON O GRANT •  HONEYMOON  •  KWASSIN  © MESACHIE  HEAL  SNOL  EYED  UPJL GRN CHARACTER  GRL  HEDP INOW  17  least  one  Table  variable.  Mean  plate  2 f o r each p o p u l a t i o n .  within  Cowichan  A l l populations,  Lake, are c l e a r l y the "low  and G i l b e r t s o n 1 9 7 2 ) , although between p o p u l a t i o n s Bear  lakes  number i s a l s o presented  mean  numbers  f o r both Grant and  samples  (p < 0.0001).  p l a t e morph" (Hagen  For both  do not d i f f e r  Cowichan Lake s i t e s or from Mesachie means  Lake;  Beaver  from any  however  and  of  the  the  plate  Kwassin lakes are lower than a l l other  Neither Grant nor Kwassin  any  s p e c i e s of p i s c i v o r o u s f i s h although  in  both  variety  of  fish  Lakes  contain  stickleback populations  l a k e s are subject to avian p r e d a t i o n .  lakes c o n t a i n a  sites  there are s i g n i f i c a n t d i f f e r e n c e s  in mean p l a t e number. plate  including  in  species  A l l of the  known  to  other  prey  on  Gasterosteus. These  univariate  comparisons  suggested  that  populations  w i t h i n the smaller lakes (Bear, Beaver, Grant and Kwassin) morphologically  distinct  the Mesachie Lake c h a r a c t e r data Lake lakes  from both the Cowichan Lake s i t e s  sample.  support  The  dendrogram  t h i s c o n c l u s i o n (Figure 4 ) .  s i t e s and Mesachie Lake form one form  preserves  a  derived  second  cluster.  the grouping  Interestingly,  m a t r i c e s were reasonably  least  two  grouping  in  this  the  smaller analysis  instance  the  The  the pair  distance  s t r o n g l y c o r r e l a t e d (r = 0.653).  the  morphologically site-specific  the  and  Cowichan  c l u s t e r while the  c l u s t e r more c l o s e l y with the Kwassin-Grant group.  within  The  of Bear and Beaver lakes produced by  c l u s t e r i n g of s i t e data, although  Clearly,  from  were  upper Cowichan system there e x i s t at distinguishable  groups.  or are the p o p u l a t i o n s simply  Is  this  components  18  Table  2. M e a n s a n d s t a n d a r d d e v i a t i o n s on a d j u s t e d d a t a f o r e a c h v a r i a b l e and p o p u l a t i o n . A l l data adjusted to 40mm s t a n d a r d l e n g t h . Standard d e v i a t i o n s are given in brackets.  19  Table  2.  Population  Populat ion Bay 1 0  N 21  means a n d s t a n d a r d d e v i a t i o n s adjusted variables.  HEAL  SNOL  EYED  1 1 .98  3 .73  3 .94  ( .51 ) Bear  30  1 2.47  Beaver  23  ( 1 .27) 11 .93  Caycuse  30  1 1 .68  Gordon  29  Grant  30  1 1 .84 (. 4 5 ) 1 2 .60  Honeymoon  21  1 1 .25  Kwassin  30  1 2 .24  Mesachie  30  1 2. 12 (. 4 5 )  ( .50) ( .42)  ( .60) ( .56) ( .67)  ( .15) 3 .67 ( .24) 3 .71 (. 2 0 ) 3 .62 ( .25) 3 .75 (.21 ) 3 .62  UPJL  2 .89 ( . 16) ( .25) 3 .81 3 .04 (. 2 1 ) (. 2 0 ) 3 .73  2 .94  ( . 16) ( .19) 3 .95  2 .95 ( . 16) ( . 2 0 ) 3 .97 2 .83  ( .17)  ( .18)  4 .06  3 .39 (. 2 2 ) 2 .80  ( .32)  ( .17)  3 .50 (. 3 3 ) 3 .99 (. 3 3 ) 3 .73  3 .88  ( .15)  ( . 16) ( . 1 1 )  ( .19)  ( .28)  3 .95 (. 2 0 ) 3 .85  3 .33  ( .27) 3 .10  GRN 20 .10 (1 . 3 3 ) 1 7 .86  for a l l  GRL  HEAD  I NOW  0 .84  5 .55  2 . 45  ( .09) 0 .80 ( 1 . 13) ( . 1 1 ) 18 .60 0 .73 (1 . 3 7 ) ( .08) 1 9 .70 0 .85 ( 1 .08) (. 1 0 ) 20 . 1 7 0 .84 ( 1 . 13) ( . 1 0 ) 17 .46 0 .69 ( .86) ( . 1 1 ) 19 . 3 5 0 .83 (1 . 1 1 ) ( .08) 17 .30 0 .71 ( 1 .46) ( . 15) 19 .06 0 .97 ( 1 .25) ( .07)  ( .25)  (. 13)  5 .55  2 . 38  ( .32)  (. 16)  5 .47  2. 16  ( .27)  (. 14)  5 .50  2 . 37  ( .26)  ( .15)  5 .36  2 . 37  ( .27)  (. 14)  5 .70  2 . 21  ( .36)  ( .16)  5 .31  2. 35  ( .31 )  ( .17)  5 .79  2. 35  (. 3 4 ) 5 .75 (. 2 1 )  (. 1 9 ) 2 . 33 (. 2 2 )  20  F i g u r e 4. Dendrogram summary of lake groupings based on p o p u l a t i o n morphology.  BAY10-? 7  GORDON B A Y  J  CAYCUSEHONEYMOON BAY MESACHIE  BEAR  BEAVER GRANT  KWASSIN  6  4  5  3  2  1  I 0.0  .02  DISTANCE  .044  22  of a l i n e a r a r r a y that has Linear  clinal  variation  subpopulations result  of  arisen could  genetic  (of a  This  drift  that  to  similar  frequencies  or founder e f f e c t correlation  certain  (Endler  matrix  as  1977).  contained  characters  correlation  e i g h t , and as many as twenty, pattern  strongly  responding pattern  to of  suggests  ( g e n e t i c , environmental,  or  some  the  site-specific  reduced  of  directional  selection  correlated characters. was  the  i n v e s t i g a t i o n of t h e i r population  of  principal  i n d i v i d u a l populations  Further,  character  the  covariance be  the  a c t i n g on a l i m i t e d s u i t e of next  issue  character  contribution  component'.  components  SNOL,  coefficients.  UPJL  were  and v a r i a b l e l o a d i n g s  The  to  addressed  s u i t e s and an the  observed  and  e x t r a c t e d from the compared  f o r the  f i r s t p r i n c i p a l component accounted f o r  40-70% of the t o t a l v a r i a n c e across the HEAL,  phenomes a r e  i n t h i s system may  phenotypic  relative  This  differentiation.  Initially,  first  influence.  As a r e s u l t , the  identification  at l e a s t  correlations.  population  interpopulation  i n d i c a t e s that p o p u l a t i o n divergence result  contained  significant  suite.  correlations,a l l  matrices  that  only  be  In c o n t r a s t t o the i n t e r p o p u l a t i o n c h a r a c t e r intrapopulation  The  might  both) a c r o s s h a b i t a t s and t h e r e f o r e a c t i n g as a character  the  a  (p < 0.05) c o r r e l a t i o n s .  phenotypic  influences  events?  from gene-flow between  p o s s i b l e 28) s i g n i f i c a n t  suggests  responding  result  stochastic  that possess d i f f e r e n t a l l e l e  i n t e r p o p u l a t i o n phenotypic eight  through  HEAD  As a r e s u l t ,  nine  consistantly the  populations  populations having were  with  the h i g h e s t pooled  and  23  components  extracted  from the t o t a l pooled c o r r e l a t i o n  Table 3 summarizes the  results  of  this  principal  matrix.  components  analysis.  Table  3. PCA from a d j u s t e d data ( a l l v a r i a b l e s except p l a t e number). P r i n c i p a l Components Axis 1  Var i a b l e HEAL SNOL EYED UPJL GRN GRL HEAD I NOW Eigenvalue %variance  The  0. 41 699 0. 45125 0. 31298 0. 43590 -o. 1 071 8 0. 16016 0. 45600 0. 29907, 3. 5524 44 .40  first  variance. to of  Axis 2  Axis 3  -0. 18473 0. 1 4857 0. 00425 -0. 29276 0. 60835 0. 55495 -0. 03063 0. 42317 1 .7035 21 .50  0. 10923 0. 1 9395 -0. 83628 0. 05008 -0. 27465 0. 39478 0. 09243 -0. 09353 0. 7939 9. 92  three components account f o r 75.62% of the t o t a l  As a r e s u l t of the i n i t i a l adjustment of the data s e t  a grand mean of 40mm, a l l components must be shape  differences.  c o e f f i c i e n t s between the component.  Table  4  presents  i t h original  Head depth, snout  be  Character  correlation  and  the j t h  l e n g t h , upper jaw length and head component  which  thought of as a summary v a r i a b l e d e s c r i b i n g head shape. c o r r e l a t i o n s tend to decrease  components. the  the  variable  l e n g t h are a l l h i g h l y c o r r e l a t e d with the f i r s t may  representations  The component c o r r e l a t i o n  on  the  as  the  proportion  of  two  i s o f t e n c o n s i d e r e d t o be  i t h v a r i a b l e ' s response to the j t h stimulus  ; consequently  following  variance  (Morrison  1967)  accounted  for  24  Table 4. C o r r e l a t i o n c o e f f i c i e n t s between each c h a r a c t e r and p r i n c i p a l component. Eigenvector Var i a b l e  Axis2  Axis 1  HEAL SNOL EYED UPJL GRN GRL HEAD I NOW  ( i . e. the  0.0973 0.1728 -0.7452 0.0446 -0.2447 0.3518 0.0824 -0.0833  -0.2411 0. 1939 0.0056 -0.3821 0.7940 0.7243 -0.0474 0.5523  0.7859 0.8505 0.5899 0.8215 -0.2020 0.3018 0.8594 0.5636  decreases  Axis3  effect  of the major s t i m u l i are removed)  c o r r e l a t i o n s of any given v a r i a b l e are l i k e l y  to decline.  remain however, three r e l a t i v e l y high c o r r e l a t i o n s on two  axes: g i l l  raker number and g i l l  a x i s and, eye diameter should  not  be  on  the  There  the  next  raker l e n g t h on the second  third  axis.  These  responses  d i s m i s s e d as they may be the f e a t u r e s  producing  the group d i f f e r e n t i a t i o n o u t l i n e d below. The  d i s t r i b u t i o n of v a r i a n c e summarized by the f i r s t  components was examined by ANOVA. total  variation;  21.0% of  PCI accounts  this  proportion  f o r 44.4% of the is a  v a r i a t i o n among p o p u l a t i o n s and the remainder i s due population  variance.  PCII  accounts  three  r e s u l t of to  within  f o r 21.5% of the t o t a l  v a r i a t i o n : 63.9% r e s u l t s from d i f f e r e n c e s among p o p u l a t i o n s suggests  that  gill  raker  number and l e n g t h , may be important  aspects of p o p u l a t i o n divergence. with  gillraker  Populations  number  from the  and  Upper  jaw  length  contrasts  and l e n g t h on t h i s component (Table 3 ) .  small  Grant) tend t o have longer  shallow  lakes  jaws but reduced  (Bear,  Beaver  and  g i l l r a k e r number and  25  length  (Table 2) compared t o p o p u l a t i o n s  from the l a r g e r , deeper  lakes (Cowichan and Mesachie). Finally, 34.7%  of  PCIII  this  proportion  populations. the  first  accounts  In  results  summary,  three  f o r 9.9% of the t o t a l from  variation;  differences  among  26.5% of the v a r i a n c e summarized by  components,  arises  from  differences  among  and standard d e v i a t i o n s of the component  scores  populations. The  means  are p l o t t e d i n F i g u r e 5.  Although  the i n t r a p o p u l a t i o n v a r i a t i o n  reduces group d i s c r i m i n a t i o n on the f i r s t appears  to  yield  the  a x i s , the second  s e p a r a t i o n of at l e a s t two groups.  intermediate p o p u l a t i o n s may, or  may  grouping.  integrity  To  groups, a nesting  investigate  nested  ANOVA  populations  the  was  within  indicated  that  not, represent  performed lake  design of t h i s a n a l y s i s i s given test  of  on  groupings  i n Table  test  Tukey's  was  among  used  sites  to  identify  .05).  nested  as the i n i t i a l  demonstrated  inferred scores,  (UBC:GENLIN).  5.  Since  The  Bartlett's  Tukey's m u l t i p l e  differences  Significant  within  among  groups.  significant  sites.  p  <  0.05).  This  was  also  result  was  w i t h i n group v a r i a n c e on PCI. yielded  significant  among groups (p = 0.000) with much reduced <  variation  s i n g l e c l a s s i f i c a t i o n ANOVA had  ANOVA on the scores from PCII  0.0  third  HSD i d e n t i f i e d two homogeneous subsets among PCI scores  expected  (  these  The  the v a r i a n c e among the lake groupings d i d  - [2,1] and [ 3 ] , (p < found  a  component  not v i o l a t e the assumption of h o m o s c e d a s t i c i t y ; range  axis  In t h i s  already Nested  differences  within site  variation  i n s t a n c e Tukey's t e s t i n d i c a t e d  26  Figure  5. B i v a r i a t e mean c o m p o n e n t s c o r e s , f o r e a c h p o p u l a t i o n , p l o t t e d on t h e f i r s t t w o p r i n c i p a l components. G l y p h s i n d i c a t e mean p o s i t i o n f o r e a c h p o p u l a t i o n ; b l a c k b a r s i n d i c a t e one s t a n d a r d d e v i a t i o n on e i t h e r s i d e o f t h e m e a n .  3.5  C O X  <  LU  1  z o  7 1  9  H  1  1  CL  s  o o Q  z o o LU  CO  -3.5  0  FIRST C O M P O N E N T AXIS  ro  28  Table 5. Design of the nested ANOVA on component scores from the f i r s t three e i g e n v e c t o r s . Lake Group 1  2  Caycuse Bay 10 Gordon Bay Honeymoon Bay Mesachie  3  Beaver Bear  Grant Kwassin  three homogeneous subsets - [ 3 ] , PCI11  produced  [2],  and  [1].  Scores  from  s i g n i f i c a n t d i f f e r e n c e s both between and w i t h i n  lake groups (p = 0.000) and two  subsets were i n d i c a t e d  -  [3,1]  and [ 2 ] .  Discussion Here  I  have  multivariate organizing  attempted  response  of  f o r c e s , and  to  address  Gasterosteus  two  issues:  populations  (a) the  to  some  (b) the c h a r a c t e r i z a t i o n of these f o r c e s  as l o c a l s e l e c t i v e e f f e c t s .  There  is  clearly  a  multivariate,  s i t e - s p e c i f i c , morphological d i f f e r e n t i a t i o n w i t h i n the Cowichan drainage  system  and  the d i s t r i b u t i o n of these morphologies  congruent  with lake d i f f e r e n c e s .  Given  this  result,  subset of lake d i f f e r e n c e s are the phenomes responding? variables teleost  scored, trophic  variables'  ecology.  lateral  what  A l l the  p l a t e s , are a s s o c i a t e d with  Consequently  the  'latent  factor  (Morrison 1967), d e s c r i b e d by the three axes must be  multivariate observed  except  to  is  summaries  population  the phenotypic  of  trophic  morphology.  Hence,  the  divergence i n d i c a t e d by these summaries i s  response of  each  population  to  some  inherent  29  (site-specific) implicated 1970;  stimulus.  Gill  in p l a n k t i v o r y i n  a  Magnuson and H e i t z 1971;  inhabiting  pelagic  regions  numerous rakers, while  raker variety  are  found in  benthic  production  rakers.  T h i s p a t t e r n has been noted  North  America  Anderson and  the  characterized  by  observed  differences,  for  Gasterosteus found  diet  of  cladocerans  and  although  and  dominated and  by  fewer  both  in  Europe (Gross  and  raker  architecture  s i t e type and small  I  suggest  compared  to  v a r i a n c e , are a response to t r o p h i c d i f f e r e n c e s  with  comparatively  in these  l a k e s are  little open  c l o s e to shore except these (Carl  animals 1953).  is  populations  feed  studies  individuals  foragers,  d u r i n g the breeding  dominated  by  lentic  development.  pelagic  season.  copepods  shown  regions,  on m a c r o i n v e r t e b r a t e s that  the  jaw  and  from  Cowichan  Lake  and  these  (Chapter  morphology  from Grant Lake allows them to i n g e s t  l a r g e r prey than those differences  littoral  by  In c o n t r a s t Grant and Kwassin l a k e s  primarily have  dominated  water  are very shallow with no a p p r e c i a b l e l e n t i c  Feeding  long  sites.  environments  The  been  (Kliewer  Gasterosteus  Both Cowichan and Mesachie l a k e s are  rarely  possess  shorter  In the Cowichan system g i l l  intrapopulation between  to  (Hagen and G i l b e r t s o n 1972)  1984).  teleosts  habitats  head morphology are a s s o c i a t e d with  that  of  has  Wright, et a l . 1983); p o p u l a t i o n s  populations  are  architecture  3). of  significantly  (Chapter  3).  The  in t r o p h i c morphology between p o p u l a t i o n s t h e r e f o r e  appear to be e c o t y p i c .  At t h i s p o i n t however, I w i l l  use of the term 'ecotype'  and  instead d e f i n e three  forego  the  morphotypes:  30  a  limnetic,  a benthic and an  intermediate.  Cowichan  Mesachie  the b e n t h i c morph i n c l u d e s both Grant  and  Kwassin  populations The  lakes;  while  from Bear and  the  in  l i m n e t i c morph  i n c l u d e s a l l samples from Lake p o p u l a t i o n ;  Lake  The  intermediate  morph  to  describes  summarized by the  i n t e r e s t i n g as they g i v e a s t a t i s t i c a l  raker  number  and  gill  raker  length  appear  1978).  to form a  c h a r a c t e r s u i t e independent of head shape d e s c r i b e d by the component. patterns  However,  to  of phenotypic  indication  that  variability  the  profiles  extend  evolutionary  covariance, pattern  has  a  ( F i g 3.)  i n t h i s study  genetic  that  populations would  the  require  basis.  suggest that  could find  (Futuyma  number  a  1979).  integrated  component,  Sokal  (1978)  by  It  as  is  this  considers  selection  across  populations,  Populations  are  host If linkage  of the  genetically genotype  disequilbrium  independent  in  a  due  to the to  be  simultaneous characters  given p o p u l a t i o n i s  and/or  of s e l e c t i v e deaths per g e n e r a t i o n  it  characters  thought  s u f f e r the g e n e t i c l o a d a s s o c i a t e d with on  there  p r o f i l e s between  f u n c t i o n a l l y independent  'cost of s e l e c t i o n ' argument.  selection  of  genetic  on a l l p o p u l a t i o n s .  simultaneous  to  a  The  s i m i l a r s e t s of environmental c o n s t r a i n t s a c t i n g  u n l i k e l y that one  unable  concordance  would e x i s t without  simultaneously  under  observed  from  to have some  i s a g e n e t i c component to each of the c h a r a c t e r s s c o r e d . unlikely  first  arguments  i t i s necessary  PCA  measure  of the degree to which the phenotype i s i n t e g r a t e d (Sokal Gill  the  Beaver l a k e s .  p a t t e r n s of c h a r a c t e r c o v a r i a n c e  are p a r t i c u l a r l y  addition  pleiotropy,  the  decreases r e l a t i v e to  31  a p o p u l a t i o n c o n t a i n i n g genotypes c o n t r o l l e d by l a r g e numbers of independent genes. correlation that  P l e i o t r o p y and  (Falconer 1981), hence we  these  trophic  characters  genetically correlated. detail  in Chapter  Although  Correlations  numbers  inadequate  within  the  morphology.  character suites. predatory  fish  have an  vary  Cowichan  This  to  indication  at l e a s t  in part,  in  between  the  lakes,  occur  of  the  drainage.  greater  two  plate  interpopulation  Within  independent  suggests  of  the system,  selection  independently  t h i s r e s u l t may  suite  evolved  be b i a s e d .  is  dependent  of  the  independently  on  the  Beaver  and  Within p o p u l a t i o n s both  of  Bear  1980a).  These  specialist the t o t a l Valen high  populations  (Moodie  distributions  phenotypes  each  linked  scute and  This  may  number  shows  among  Reimchen  selection  be the mechanism p r e s e r v i n g  At a l l s i t e s , with the plate  indicate  1976;  'Niche v a r i a t i o n h y p o t h e s i s ' ,  intrapopulation variation  lateral  may  Larson  spine  for  adapted to a r e s t r i c t e d segment of  lake h a b i t a t ( i . e .  1965).  1972;  the  lakes  phenotypes appear to d i s t r i b u t e themselves d i f f e r e n t i a l l y within  No  questionable  Perhaps p l a t e phenotype i s p l e i o t r o p i c a l l y  t r o p h i c morphology.  sites  on  in e i t h e r Grant or Kwassin lakes and.thus  morphology  populations.  initial  treated  descriptor  Unfortunately  character  intermediate  character  are  the c o n c l u s i o n that p l a t e phenotype evolved trophic  to  are probably  s e l e c t i o n on p l a t e s appears to be trophic  lead  2.  plate  phenotype i s an variation  linkage  i n Gasterosteus  exception a  strong  of  relatively  (Reimchen 1980b).  Grant mode  Van  at  and  Kwassin,  seven.  This  32  arrangement i s a s s o c i a t e d with the presence of p i s c i v o r o u s (Hagen  and  Gilbertson  heritability Kwassin  (Hagen 1973).  however,  invertebrate  both  on  Libellula  sp.)  suggested  Very l i t t l e  of the  investigated  for t h i s s p e c i e s biology  of  suggests  reduced  that  The  If a  of  sp.,  invertebrate  Recently, armature  Reimchen  may  and  evolutionary  be  a  p l a t e frequencies  h y b r i d i z a t i o n and  differences.  and  selective  may  inferences  confuse  the  h i s t o r y on v a r i a t i o n .  habitat  described  interpopulation d i f f e r e n t i a t i o n different  narratives  however, i s such that  morphology  regimes.  above,  i n t h i s system i s Two  predictions  must have a g e n e t i c  component i f  hypothesis.  characters  given  Dytiscus  observed  body  fish  l e s s obvious morphological v a r i a t i o n has  Gasterosteus,  they are to evolve  measured  in response to s e l e c t i o n .  trophic  character(s)  s e l e c t i o n between p o p u l a t i o n s , the  and  of  americanus,  lakes.  in Gasterosteus,  o r i g i n a t e from t h i s  2.  Grant  predation.  selection,  a response to  1.  a modest  densities  u s u a l l y extend from more d i s t i n c t  of  concordance  high  I have  both  based on p l a t e phenotypes and effects  contain  and  in  that  response to i n v e r t e b r a t e  The  p l a t e numbers i n  (Lethocerus  Gasterosteus  (1980b) has  The  low  lakes  predators  Aeshna sp. and  been  The  p l a t e phenotype has  lakes are a s s o c i a t e d with the absence of predatory  species;  attacks  1973), and  fish  one  has  should  been  organized  by  be a b l e to demonstrate  f u n c t i o n a l s i g n i f i c a n c e of that c h a r a c t e r  by c o n t r a s t i n g i t s  performance i n d i f f e r e n t environments. Both  of  these  predictions  are  tested  i n the  following  33  chapters.  34  CHAPTER 2  Introduction Recent c r i t i c i s m s of the to  clearly  (Lewontin  define 1978;  reexamination  the  Gould  of  target and  smaller  'holism'  (Bock 1980;  is  Mayr  demanded i f one  morphological only  evolution. recently  subunits  (Gould  characters defined)  1984).  may  obscure  Hence,  some  described  evolve  for and  such are  an  of of  approach  based  functional  and  on  units  the which  Consequently a l l phenotypic  only  within  the  they  context  are  of  the  1982).  i m p l i c a t i o n s of phenotypic  recognized,  a  the  degree  ( d e s p i t e the o r g a n i z a t i o n a l l e v e l at which necessarily  to  i s to p r o p e r l y d e f i n e processes  and Lewontin 1979).  organism (Cheverud The  led  i n t e r f a c e of phenotype  r e c o g n i t i o n of organisms as i n t e g r a t e d evolve  has  S t u d i e s t h a t atomize the  Methodologies  been  studies  of n a t u r a l s e l e c t i o n  1979),  design.  of s e l e c t i o n a c t i v e at the  environment  have  features  Lewontin  organismal  phenotype i n t o smaller and processes  i n a b i l i t y of e v o l u t i o n a r y  Darwin f i r s t  suspected  integration  are  t h e i r existence  in  not  newly  1859,  "...the whole organism is so tied together... that when s l i g h t v a r i a t i o n s in one part occur, and are accumulated through n a t u r a l s e l e c t i o n , other p a r t s become m o d i f i e d . This is a very important subject, most imperfectly understood." pl82. Morphological  i n t e g r a t i o n i s thought to a r i s e p r i m a r i l y through  the e f f e c t s of p l e i o t r o p y and yield  character  linkage  correlations.  In  (Falconer  1981),  which  most s t u d i e s , workers have  35  sought  to  identify  polygenic  patterns  characters,  important.  Working  of  for with  which  be  polygenic  (Leworitin  correlations  pleiotropy  polygenic  advantages: most e v o l u t i o n a r i l y to  character  may  characters  important  be  most  has  two  c h a r a c t e r s are thought  1974); the g e n e t i c s of p o l y g e n e t i c  systems has been e x t e n s i v e l y t r e a t e d i n the l i t e r a t u r e , based  largely  on  parametric  background has become concerned  with  the  character  statistics.  foundation  for  integration.  This  the  statistical  association  testing  hypotheses  Indeed, Cheverud  1981,  (1982)  measured  of the phenotype, and s e v e r a l  workers (Leamy 1977; A t c h l e y and Rutledge Cheverud  and i s  statistical  f e e l s s t r o n g l y that the 'degree of i n t e g r a t i o n ' may be by  in  1982; Leamy and A t c h l e y  1980;  Atchley  1984) have  1981;  concentrated  e f f o r t s on d e s c r i b i n g these a s s o c i a t i o n s . In t h i s chapter breeding 1.  I  present  the  program which was designed  How  much  genetic  results  of  a  laboratory  to address three  variation  i s present  questions: within  each  morphotype; 2.  How are the c h a r a c t e r s organized  to  respond  to  selective  c o n s t r a i n t s ; and, 3.  How have c h a r a c t e r s responded t o s e l e c t i o n d u r i n g the course  of the p o p u l a t i o n ' s  evolution?  36  M a t e r i a l s and Methods  Establishment  and F o s t e r i n g of Progeny  Logistics therefore  chose  populations; limnetic  prevented r a i s i n g progeny from a l l f i v e l a k e s , I to  one  limit  from  the  each  breeding  study  to  of the proposed morphotypes.  the benthic  form was taken from the small  o f f the main body of Cowichan  (Bear Lake).  Mature  adults  were c o l l e c t e d  (1984) using minnow t r a p s without  some e f f o r t  bias  and  pole-sienes.  lengths  Bell  (1984),  i n the  breeding  but  using  on development,  I  water  water.  This  to reduce p o s s i b l e e f f e c t s of lake  p a r t i c u l a r l y those e f f e c t s r e s u l t i n g  d i f f e r e n c e s i n temperature and/or the p o s s i b l e  families  were  population.  dechlorinated  from the l a b o r a t o r y , rather than lake  p r e c a u t i o n was taken i n order  population;  Adults  of eggs was done on s i t e f o l l o w i n g the methodology  by  transported  fungus.  i n June and  was made to choose i n d i v i d u a l s which represented the  Fertilization  water  from three s i t e s  bay  from the f i s h c o l l e c t e d at each s i t e , but  observed range of standard  outlined  Lake  form was from one of the small bog lakes  (Grant), and the intermediate  chosen  The  r e p r e s e n t a t i v e was from the north end of Cowichan  (Caycuse),  July  three  introduction  from of  attempted t o make a minimum of 12 c r o s s e s from each 14  families  were  obtained  from  Grant  from Bear Lake and 12 f a m i l i e s from Caycuse.  l a b o r a t o r y m o r t a l i t y was g e n e r a l l y low, fungus k i l l e d from Caycuse l e a v i n g only t h i s s i t e precluded  10.  The p a u c i t y of breeding  Lake,  12  Although 2 families a d u l t s at  the replacement of these two f a m i l i e s .  37  Fertilized laboratory. 17.5°C  eggs  Egg  until  and  parents  batches hatch  fertilization).  Newly  were  were  returned  incubated  (approximately hatched  in  for  swimup.  litre eight hours  A f t e r swimup, i n d i v i d u a l  aquaria.  8  hours  l i f e t i m e of the progeny. approximately  one  dark)  was  week,  or u n t i l  standard  length,  the  light  f a m i l i e s were p l a c e d i n 20  their  maintained  cycle  for  (16  the e n t i r e  diet  approximately  was  for  the f r y c o u l d i n g e s t Artemia  switched  T u b i f e x , chopped l i v e r , and f r o z e n Artemia.  20 to  millimetres a  Large  mixture of  families  (  >  i n d i v i d u a l s ) were s p l i t i n t o s u b f a m i l i e s by removing f i s h at  random and provided  placing the  them  advantage  in of  environment on the estimate families  were  same  Standard  set  of  other  tanks.  reducing of  maintained  s a c r i f i c e d and preserved. the  into  F r y were fed an i n f u s o r i a c u l t u r e  Once the f r y a t t a i n e d  All  i n the incubator  A constant l i g h t - d a r k  nauplii.  40  after  I l l u m i n a t i o n was by f l u o r e s c e n t l i g h t s mounted  inches above the tanks. light:  days  f r y were l e f t  three days f o l l o w i n g hatch, and then moved  the  a water bath at  seven  for  to  This  the . e f f e c t s  heritability until  subdivision of  common  (Falconer  1981).  February  (1985) and then  Progeny and parents were  characters  as  those  l e n g t h s of progeny v a r i e d widely,  populations,  hence  a l l measures  millimetres.  A l l a d j u s t e d data were l o g  b e f o r e proceeding with any a n a l y s i s .  were  given  scored  in  within  for  Chapter  and  again  adjusted  (base  e)  1.  between t o 40  transformed  38  E s t i m a t i o n of Character The  H e r i t a b i l i t i e s and C o r r e l a t i o n s  heritability  of any p o l y g e n i c c h a r a c t e r i s d e f i n e d as  the r a t i o of a d d i t i v e g e n e t i c v a r i a n c e phenotypic  variance  (Vp).  Heritability  given as Va/Vp and may be estimated designs  (Falconer  1981).  narrow sense h e r i t a b i l i t y offspring  regression  be  low  i n the 'narrow sense' i s  f o r each  character  using  1981).  ( d e s c r i b e d below)  characters  and  regression.  as  Table mean  Table  6  outlines  single  pair  was  the found  a consequence 10-14 estimate  H e r i t a b i l i t y was t h e r e f o r e estimated  u s i n g the progeny of the  midparent-  Unfortunately  f a m i l i e s were not enough t o o b t a i n a reasonable by  character's  I had hoped t o determine a  (Falconer  f o r most  the  by a v a r i e t y of experimental  Initially  intraclass correlation coefficient to  (Va) t o  matings  of Va  from ANOVA  (Becker  1975).  the design of the a n a l y s i s and the expected  squares.  6 Design  of f u l l s i b ANOVA f o r the e s t i m a t i o n of Vg.  Source of V a r i a t i o n  Expected  c5w + No(ct a)  Among F a m i l i e s Within F a m i l i e s ( e r r o r : among i n d i v i d u a l s )  2  * No i s the weighted average f a m i l y  In  this  correlation estimates  design  H  coefficient  2  given as : H  size.  ( t ) where:  2  2  2  i s estimated  a a while S w estimates 2  Mean Square  < 2t (Falconer  t = S  a w.  1981).  2  from 2  the / S  2  intraclass  + S w, and S 2  In t h i s instance  H  2  2  is  The i n e q u a l i t y r e s u l t s from  39  the  estimate  a  of  2  a .  S a estimates  1/2 the a d d i t i v e genetic  2  v a r i a n c e but a l s o 1/4 of the dominance v a r i a n c e The  measure  of  heritability  is  therefore  is a  effects  measure  (Hartl  H (obtained)  of  a l l variance  1979).  As  a  s e t s only an upper l i m i t  2  dominance d e v i a t i o n s are zero then measure  provides  Nevertheless,  the  basis  from  of  except  broad  f o r , the  + Vi.  non-additive  this  estimate, I f the.  2  the estimate  the  l/4(Vd)  to H (population) .  of narrow-sense h e r i t a b i l i t y ,  interactions.  +  arising  consequence  1975).  d e f i n e d as 'broad  sense' and given as Vg/Vp, where Vg = l/2(Va) Vi  (Becker  approximates the  f o r the a d d i t i o n a l  sense  estimate  construction  of  of  H  2  evolutionary  inference. The  estimation  of  additive  proceeds  in  the  characters  genetic v a r i a n c e , but products  are  Becker's  in  computational  partitioning  the  were estimated  same  this  partitioned  genetic  instance  rather  of  f o r each  between  manner as the e s t i m a t i o n of  than  formulae  sums  covariance  the the  (1975)  pair  sums  of  cross-  of squares.  were  cross-products.  character  sums  used  for  Three c o r r e l a t i o n s (x,y),  within  each  population: 1.  Genetic:  r(G) = 2cov(a) (2a a(x) * 2 a a ( y ) ) ' , 2  2.  Phenotypic : R a M x )  3.  Environmental:  2  5  r ( P ) = cov(w) + cov(a) + r j a ( x ) ) * (o w(y) + a a ( y ) ) ] ' , 2  2  2  5  r ( E ) = cov(w) - cov(a)  [(a w(x) - a a ( x ) ) * U w ( y ) + a a ( y ) ) ] 2  where  cov(a)  2  estimates  2  the c o v a r i a n c e  f a m i l i e s and cov(w) estimates within  families.  The  2  terms  ,  between c h a r a c t e r s among  the c o v a r i a n c e  variance  - 5  between  are  characters  the same as those  40  estimated  i n the previous  H , the numerator i n 2  epistatic effects, Interpreting of c h a r a c t e r s  ANOVA.  these  Again, as i n the e s t i m a t i o n of  equations  et  al.  patterns  i s hindered  effects  of s i n g l e c o r r e l a t i o n s between p a i r s  by two f a c t o r s .  (in this  summary technique  case  28  (1983)  as genetic  has  genetic  extracted  correlations,  and  'complete Boag  correlation  gave r e s u l t s very data.  The  linkage'  (1983) data,  from the  from  multiple  c o r r e l a t i o n s , w i t h i n each to  apply  some  kind  of  p r i n c i p a l components d i r e c t l y  are  often  has but  illsuited  similarity  is  less  patterns  matrices,  rigid  the nature of the input matrix.  t h e r e f o r e used to summarize  1977).  r e s u l t s simply  f o r PCA  In c o n t r a s t to PCA, c l u s t e r a n a l y s i s  may be used with many kinds of  using  that  however t h i s method i s not favoured  c o r r e l a t i o n matrices  1977 ; Boag 1983).  concerning  is  (Oxnard 1978).'  from the c o r r e l a t i o n matrix,  genetic  first  due to d i f f e r e n c e s i n gene  The second d i f f i c u l t y  p o p u l a t i o n ) ; hence i t i s p r e f e r a b l e  (Leamy  The  to d e f i n e and d e s c r i b e p a t t e r n s a r i s i n g  Boag  and  s e l e c t i v e regimes and e v o l u t i o n a r y h i s t o r y (Atchley  1981).  inability  dominance  in addition to additive e f f e c t s .  s i n g l e g e n e t i c c o r r e l a t i o n s w i l l vary frequencies,  contains  of  including  i n i t s assumptions C l u s t e r a n a l y s i s was  genetic  correlations  as the c l u s t e r i n g a l g o r i t h m used  'average  linkage'  to  (Everitt cluster  both average linkage and s i n g l e l i n k a g e  s i m i l a r t o those of complete l i n k a g e using  statistical  my  package 'S' (Becker and Chambers 1984)  was used t o compute the c h a r a c t e r  linkages.  41  Reconstructing In  the P a t t e r n of Trophic  the  past  the  process  p a t t e r n s of morphological observation  that  consequently,  1983).  divergence  continuously  i t is difficult  might be c o n s i d e r e d  reconstructing  has been complicated  varying  of  by the  t r a i t s tend to covary;  t o i d e n t i f y those  the t a r g e t s  historical  natural  c h a r a c t e r s which  selection  (Arnold  I f the t a r g e t s of s e l e c t i o n can not be e l u c i d a t e d , then  the processes  of  morphological  obscure (Gould and Lewontin Lande (1979) has p r o v i d e d the  of  Divergence  evolution  1979 ; Bock 1980).  remain  Recently  Russell  a multivariate solution for describing  e v o l u t i o n of c o r r e l a t e d c h a r a c t e r s .  gradient  necessarily  He.defines a s e l e c t i o n  f o r the e v o l u t i o n of mean phenotype a s : /3 = G " [ z ( 0 ) - z ( t ) ] , 1  where G"  i s the i n v e r s e of the symmetric  1  variances  and  covariances;  matrix  z(0) and  of  z ( t ) are  character  vectors  c h a r a c t e r means f o r the p o p u l a t i o n at times '0' and ' t ' . s t r u c t u r e of the c h a r a c t e r complex, constant  as  by  of  selection  '0'  to  't  -  I f the  'G',  over e v o l u t i o n , then the net s e l e c t i o n g r a d i e n t  sum of /3 = G~ 'Az over the generations measure  described  of  is  i s the  1'.  This  i s independent of the path taken between  z(0) and z ( t ) and i s t h e r e f o r e robust  t o changes i n the r a t e and  d i r e c t i o n of e v o l u t i o n (Lande 1979).  Given  the  constancy  of  between p o p u l a t i o n s  'G',  we  may  (or s p e c i e s ) .  c h a r a c t e r means f o r p o p u l a t i o n ' s z(0)  and  transformed  z(t).  If  such t h a t :  the  the  assumption  of  c a l c u l a t e selection gradients In t h i s instance  vectors  of  'a' and 'b' are s u b s t i t u t e d f o r  i n d i v i d u a l v e c t o r s z ( a ) and z ( b ) a r e  42  z* = G" 0 The  =  z*(a)  1  then,  -  z*(b)  (Schluter  1984).  elements /3i of the s e l e c t i o n gradient are the net f o r c e s of  n a t u r a l s e l e c t i o n which have acted on each c h a r a c t e r  independent  of the c o r r e l a t e d responses to s e l e c t i o n on the other  characters  measured.  Recently  length  the v e c t o r  0 as the E u c l i d e a n  Schluter  (1984) has d e f i n e d  the  of  distance  B = [Z(z'i(a) - z ' i ( b ) ) ] . 2  B then,  i s the net f o r c e of d i r e c t i o n a l s e l e c t i o n which would be  required  to s h i f t mean morphology from z(a) t o z ( b ) .  I f 'G' i s  known, s e l e c t i o n g r a d i e n t s between p a i r s of p o p u l a t i o n s calculated  under  the  assumptions that  without  e r r o r , and that i t has remained  (Price  et  a l . 1984).  from and  the  pooled  covariances  be  'G' has been determined constant  Given the preceding  c a l c u l a t e d net s e l e c t i o n g r a d i e n t s  may  time  assumptions, I have  for population  w i t h i n p o p u l a t i o n s matrix  through  transitions  of genetic  variances  ( S c h l u t e r 1984).  Results  Heritability The  and Genetic  Correlations the  adjusted  progeny values and the w i l d p o p u l a t i o n values are given  i n Table  7.  means and standard  For  deviations  of  the progeny data, there are four more s i g n i f i c a n t  0.05) c h a r a c t e r c o n t r a s t s between p o p u l a t i o n s data.  both  This  suggests  than f o r the  (p < wild  that s e l e c t i o n and/or environment may be  masking some i n t e r p o p u l a t i o n d i f f e r e n c e s  in  gene  frequencies.  43  Table 7. Descriptive s t a t i s t i c s for wild c o l l e c t i o n s l a b o r a t o r y r e a r e d progeny.  and  i  i  Table  I.  7. M e a n s  Wild  and standard d e v i a t i o n s of a d j u s t e d each c h a r a c t e r and p o p u l a t i o n . *  data f o r  Populations Populat ion  Character  Bear N  HEAL SNOL EYED UPJL GRL GRN HEAD I NOW  2.52(0.092) 1 .29(0.065) 1 .34(0.058) 1.11 ( 0 . 0 6 5 ) -0.23(0.131) 17.86(1.130) 0.86(0.071) 2.88(0.063)  II.  (ac)b# (abc) a be (ab)c (ab) c (ac) b (ab)c (ab)c Laboratory  Lake(a) = 30  Caycuse(b) N = 30  Grant Lake(c) N = 30  2.46(0.036) 1 .29(0.068) 1.37(0.042) 1.07(0.071 ) -0.16(0.126) 19.17(1.080) 0.86(0.067) 2.98(0.055)  2.53(0.053) 1 .28(0.090) 1.40(0.043) 1.22(0.066) -0.37(0.167) 17.46(0.860) 0.79(0.076) 2.86(0.049)  Progeny Population Bear  Character HEAL abc SNOL abc E Y E D (ab)c UPJL ( a b ) c GRL (ac)b GRN abc HEAD abc INOW abc  N  Lake(a) = 357  2.54(0.038) 1.45(0.061 ) 1.39(0.053) 1.13(0.072) -0.06(0.115) 19.25(1.070) 0.89(0.068) 2.96(0.055)  Caycuse(b) N = 179 2.56(0.034) 1.49(0.067) 1 .39(0.063) 1.13(0.083) -0.01(0.120) 20.34(1.370) 0.95(0.060) 3.01(0.077)  Grant Lake(c) N = 292 2.56(0.049) 1.42(0.062) 1.41(0.052) 1.17(0.079) -0.07(0.104) 18.14(1.170) 0.93(0.061) 2.89(0.065)  * A l ld a t a l o g ( b a s e e) t r a n s f o r m e d . # L e t t e r s i n b r a c k e t s i n d i c a t e no d i f f e r e n c e s a d j u s t e d means.  between  45  Three of  points  data,  c a n be e m p h a s i z e d  that  significantly  a r e of i n t e r e s t different  significantly  greater  Caycuse  has s i g n i f i c a n t l y  8.  results  A l l  each  longer  was  of H  i s now  UPJL  i s  population,  but does not  Bear  or  rakers  Lake  than  Caycuse;  either  Bear  populations  which  in general  influenced between forces  by gene  (Falconer  environmental progeny  raised  heritability).  o f common  families  reared  and  than  or  in  turn  2  under  reared  H  The  elsewhere  different  (h  2  across  conditions,  i s specific  to  A l l genetic  components a r e  addition  we  constant  the  under  tends to  H . 2  value  of  increase  reduce  Progeny  inflates H  2  of  which the  to  environment,  which  vary  component  seek  i n estimating  to  and s t o c h a s t i c  the  environment  reason  population  are likely  on t h e c o n d i t i o n s  inflates  moderate  values  2  of s e l e c t i o n  apart,  a  for  population.  reported  under  significant  i s only  of  i n Table  heritability  each  and t h e r e f o r e  (a c o n s t a n t  environment  those  as h  In  depends  together,  that  result  It i s for this  effects  S a,  a  1981).  variance  were  similar  as  than  1981).  frequencies  populations  within  reared  value,  (Falconer  there  Comparisons  been  of l i t t l e  environment  variance  1973).  had  the average  suggesting  i s lower  have  a n a l y s i s are given  a l l populations,  low,  f o r GRN  2  0 . 5 8 , 21 ° C , H a g e n  2  in  of a d d i t i v e genetic  estimate  of  either  ( p < 0.05) a l t h o u g h  population  amount  more  Lake  of the h e r i t a b i l i t y  characters,  heritabilities  and  d i s c u s s i o n : SNOL  sets  lakes. The  are  between  o f t h e two  a l l populations;  i n the Grant  significantly  =  to later  between  differ  Grant  i n the comparison  tend  the  within t o be  estimates obtained.  46  Table 8. H e r i t a b i l i t i e s f o r the three r e p r e s e n t a t i v e morphotypes. The standard e r r o r of the estimate i s give in brackets.  Table  8. H e r i t a b i l i t i e s f o r t h e t h r e e r e p r e s e n t a t i v e m o r p h o t y p e s . E s t i m a t e s a r e b a s e d on f a m i l y s i z e weighted i n t r a c l a s s c o r r e l a t i o n s among f u l l sibs.  Population Character  Bear  HEAL  .2173*** (.1243) .1624*** ( .0896) .3229*** ( .1381 ) .1489** ( .0859) . 1824*** ( .0926) .1263** (.0798) .4570*** ( .1705) .1438** (.0833) .22 12,357  SNOL EYED UPJL GRL HEAD I NOW GRN X N Note:  ***  (p <  Lake  .0001),  **  Caycuse .2155** 0.1375) .2614** (.1534) .2377** ( . 1460) .2170** (.1393) .6777*** (.2420) .1922** (.1310) .4122*** (.1946) .2210** (.1406) .30 10, 176 (p <  .001),  Grant  Lake  . 1436** ( . 1197) . 1676** (.1006) .7957*** (.2112) .3822*** (.1554) .1320* (.0898) .2566*** (.1254) . 4 5 4 4 * * *  (.1699) .3577*** (.1500) .34 14,292 *(p <  .01)  48  Estimates  of  heritability  environments  even  constant  (Hartl  lateral  plates  0.83  to  0.5  in with  Nevertheless,  within  drastically  phenotypic  Hagen (1973) found  across  v a r i a n c e remains  the  heritability  the t h r e e s p i n e s t i c k l e b a c k t o decrease an  depend the  significant  change  i f the expressed  1979).  heritabilities  may  increase  4°C.  from  Obviously  then,  s t r o n g l y on p o p u l a t i o n and circumstance.  results  proportion  populations,  of  of  presented  of  the  arises  here  indicate  phenotypic  as  a  result  variance of  that  a  expressed  variance  among  genotypes. Tables  9,  environmental  term  strong  with  the  between  g e n e t i c , phenotypic and characters  for  are  suggesting  characters. greater  than  In  populations  covariance  a l l i n s t a n c e s the  the  environmental  the l a t t e r are l a r g e l y r e s i d u a l  I f the genetic c o r r e l a t i o n s a r e moderate  the phenotypic  to  In  the  case  supported  (Table of  by the Spearman rank-order  12) between elements of the three both  Caycuse  The  exception  i s found  This  correlation matrices.  and Grant Lake, the rank-order  c o r r e l a t i o n s between r(G) and r(P) exceed r(P).  and  c o r r e l a t i o n s a r e moderate, r(G) may be c o n s i d e r e d  is  coefficients  (Leamy  high,  to c o n t r i b u t e more to r(P) than does r(E) ( P i r c h n e r 1969). conclusion  each  (0.3 ^ |rG| ^ 0.9), however the average  other  correlations  correlations, 1977).  give  i s much lower as a r e s u l t of the reduced  f o r GRN  genetic  11  Many of the g e n e t i c c o r r e l a t i o n s w i t h i n  reasonably  correlation  and  correlations  population. are  10  those  f o r r ( E ) , and  f o r Spearman c o e f f i c i e n t s w i t h i n  Bear Lake, i n which the c o r r e l a t i o n between elements of r ( P ) and  49  Table  9. G e n e t i c , p h e n o t y p i c and e n v i r o n m e n t a l correlation m a t r i c e s f o r Bear Lake. I = Genetic correlation matrix, II = Phenotypic (above the d i a g o n a l ) and environmental (below the d i a g o n a l ) c o r r e l a t i o n m a t r i c e s . A l l v a r i a n c e s and c o v a r i a n c e s were c a l c u l a t e d f r o m l o g ( b a s e e) t r a n s f o r m e d d a t a .  Table  9.  Genetic, matrices contains  HEAL (I) HEAL SNOL EYED UPJL GRL HEAD INOW GRN  .3306 .915 . 227 •- . 2 3 5 •- . 1 4 2 6 •- . 0 9 0 7 •- . 1 1 1 5 .3963E-3  (ID HEAL . 598 SNOL EYED . 2658 UPJL .622 . 2458 GRL HEAD . 2807 INOW -- . 0 4 4 0 GRN -- . 0 0 5 9  p h e n o t y p i c and environmental correlation f o r Bear L a k e . D i a g o n a l of rG m a t r i x g e n e t i c v a r i a n c e (*E-3) for each c h a r a c t e r .  SNOL  .6036 . 3036 . 159 .6170 .3151 . 2558 .855E-2  . 6350 .0923 . 3888 . 4054 . 2274 .3856 .0037  EYED  .9170 . 7646 - .4304 . 2726 . 5535 -- . 1 2 9 E - 1  . 2536 .1391 . 3438 . 1644 . 2939 . 1 192 .0583  UPJL  GRL  . 7754 . 359E- 1 2.418 .6046 -.3264 -.4282 . 7490 .185E-1 .120E-1  .4658 . 3035 .4287 .4754 -.4321 .2266 -- . 0 0 5 1  . 1684 . 2294 . 1223 .4015 .3917 .2877 -.0063  HEAD  .4346 . 8753 -.472E-1  .2171 . 2396 . 281 1 .4556 .2815 .1521 -.0021  INOW  2 . 122 -.23E-1  .623E-2 .3300 .2816 .3493 .0687 .3148 .0049  GRN  1 6 6 .. 4 6  - .. 2 0 , 44E-2 42E-2 , 26E-2 , 23E-2 45E-2 26E-2  51  Table  10. G e n e t i c , p h e n o t y p i c and e n v i r o n m e n t a l correlation matrices for Caycuse. I = Genetic correlation matrix, II = P h e n o t y p i c (above the d i a g o n a l ) and environmental (below the d i a g o n a l ) c o r r e l a t i o n m a t r i c e s . A l l v a r i a n c e s and c o v a r i a n c e s were c a l c u l a t e d from l o g (base e) t r a n s f o r m e d data.  Table  10.  Genetic, Diagonal for each  HEAL (I) HEAL SNOL EYED UPJL GRL HEAD INOW GRN  . 2834 . 7899 . 4823 . 7243 -• . 3 0 7 0 . 7396 . 5258 .0455  (ID HEAL SNOL EYED UPJL GRL HEAD I NOW GRN  . 5980 . 2658 .6220 . 2458 . 2807 - .0440 - .0059  p h e n o t y p i c and of rG c o n t a i n s character.  SNOL  1 . 2860 . 48 1 1 . 3724 - . 1912 . 9849 -.3455 .0569  . 6350 .0923 . 3888 . 4054 . 2274 . 3856 -.0036  EYED  . 9870 . 1256 . 6499 1.0357 -.2732 . 0246  . 2536 .1391 . 3438 . 1644 . 2939 . 1 192 .0583  environmental correlations for Caycuse. the g e n e t i c variance (*E - 3 )  UPJL  1 . 5280 -.5158 .0769 . 2983 .0228  . 4658 . 3035 . 4287 .4754 .4321 . 2266 -.0051  GRL  9 .6420 .9761 -.3649 -.0107  . 1684 . 2294 . 1223 .4015 .3917 . 2877 -.0063  HEAD  INOW  .4696 -.0417 -.0181  1.6940 -.0095  .2171 . 2396 . 28 1 1 . 4556 .2815 . 1521 .0021  .62E- 2 . 3300 .2816 . 3493 .0687 .3148 .0049  GRN  430.6  -.48E-2 - . 44E-2 . 0 4 16 -.26E-2 -.23E-2 -.45E-2 -.26E-2  53  Table  11. G e n e t i c , p h e n o t y p i c and e n v i r o n m e n t a l correlation matrices f o r Grant Lake. I = Genetic correlation matrix, II = Phenotypic (above the d i a g o n a l ) and environmental (below the d i a g o n a l ) c o r r e l a t i o n m a t r i c e s . A l l v a r i a n c e s and c o v a r i a n c e s were c a l c u l a t e d from l o g ( b a s e e) t r a n s f o r m e d data.  Table  11. G e n e t i c , p h e n o t y p i c , a n d e n v i r o n m e n t a l G r a n t L a k e . T h e d i g o n a l o f rG c o n t a i n s f o r each c h a r a c t e r .  HEAL (I) HEAL SNOL EYED UPJL GRL HEAD INOW GRN,  . 3942 .8137 .6965 . 8409 .2106 . 2323 -.0343 .0283  (II) HEAL SNOL EYED UPJL GRL HEAD INOW GRN  .4576 . 2794 . 3806 . 3829 . 2657 . 2475 -.0031  SNOL  . 6534 . 2621 . 4626 - . 2 101 . 3049 -.08678 .022 1  . 5 153 . 3552 . 5221 . 5068 . 1934 . 2476 -.0130  EYED  2 . 208 . 8446 -.1007 . 4836 .6279 .01326  . 3535 . 2421 . 1952 . 5699 .0797 -.0547 -.0255  UPJL  2.474 -.3129 .3907 .5797 .0278  .4748 .4915 . 5352 .6241 . 1654 . 1262 -.0210  GRL  1 .425 -.8535 - .6632 .0325  . 3590 . 3995 . 2073 .3867 . 2830 . 2247 -.0205  correlations for genetic variances  HEAD  INOW  1 .695 . 7499 -.0252  1 . 735 -.0111  . 2566 .2245 . 2495 . 2344 .0702 -.0398 .0014  . 1620 . 1908 . 3595 .3148 -.0081 .2308 .0008  GRN  500.4  .41E-2 -.41E-2 - .47E-2 -.29E-2 -.82E-2 -.67E-2 - . 4 1E-2  55  r(E) exceeds that  f o r r ( P ) and r ( G ) .  The l a t t e r  r e s u l t may be a  consequence of Bear Lake having the lowest estimates  of H  2  .  If  the phenotypic c o r r e l a t i o n i s expressed a s : = r(G) * H x * H y + r ( E ) * [(1 - H 2 X ) ( 1  r(P)  2  2  H x  where  - H y)]' 2  5  and H y are the h e r i t a b i l i t i e s of  (Pirchner  1969),  characters  'x' and 'y' r e s p e c t i v e l y , the compound nature of r ( P )  becomes e v i d e n t .  Table  In a d d i t i o n i t  is  1 .0 0.8236  0 .3048  0.2331  r(G) 1 .0 r(E) -0.2184 0.6021 r(P)  Caycuse  x Grant  1 .0 0.5362  0 .3749  0.2191  r(G) 1 .0 r(E) -0.1598 r(P) 0.5742 x  depends  r(E)  r(G) 1 .0 0.0071 0.4347  r(G) r(E) r(P) x  on  contributes  1 .0 0.5529  0 .3544  0.2245  the h e r i t a b i l i t i e s  heritabilities  are  more  imprecise,  remain  2  apparent  that  r(P)  also  12. Spearman rank c o r r e l a t i o n s between the elements of the g e n e t i c , environmental and phenotypic c o r r e l a t i o n matrices.  Bear Lake  are  2  the  to  small,  1.0 0.2156  1 .0 0.1777  1 .0 0.2249  of the two c h a r a c t e r s . the  This  have e f f e c t e d the o v e r a l l  contributions result  When the  environmental  r ( P ) , but i f the estimates  relative  questionable.  r(P)  of  component  of H x and H y 2  r(G)  2  and r ( E )  however does not appear t o  s t r u c t u r e of the c o r r e l a t i o n  matrices  56  described  below, and  I have proceeded under the assumption that  r(G) c o n t r i b u t e s s i g n i f i c a n t l y to r(P) w i t h i n Bear Lake. F i g u r e 6 shows the three dendrogram summaries of clustering  implied  by  r(G)  for each p o p u l a t i o n .  c h a r a c t e r c l u s t e r s are very s i m i l a r At  the  level  evident. hence  The  of  about  first  been  implicated  in  The  second  1981).  r(G) = 0.2,  c o n t a i n s two  groups the two  grouping  the  same  distinct  supports  largely The progeny  contains  remaining  a  the head  the  suggesting (i.e.  is  The  anamolous.  most it not  distant is  GRN  grouping  indeed  groups d e f i n e d  data  two  principal  (Chapter  covariance  1).  results  for  the  Caycuse  a  the of  previous GRL  distinctly  clusters  has been  GRL  organized  and GRL existence  integrated character.  a  has been separated result  which  are both c h a r a c t e r s  from  appears  and is  preserved, character  s t r o n g l y i n t e g r a t e d by p l e i o t r o p y , with the  dendrogram,  planktivorous an  cluster.  covariance.  only s i m i l a r i t y to  c h a r a c t e r s measured). present  six  q u i t e d i f f e r e n t than those d e s c r i b e d f o r Grant  Bear l a k e s . that  and  Lindsey  shape  given by the f i r s t  c h a r a c t e r c l u s t e r s d e r i v e d from r(G) are  GRL,  1970;  the c o n c l u s i o n that phenotypic  from genotypic  c l u s t e r s are  and  s t r u c t u r e of the two  that  lakes.  s t r u c t u r e which have  components d e r i v e d from the w i l d p o p u l a t i o n This  Bear  (e.g. Kliewer  i n t e r p r e t e d as  as  P a t t e r n s of  and  c h a r a c t e r s , GRN  planktivory  I n t e r e s t i n g l y , the c h a r a c t e r is  two  f e a t u r e s of g i l l r a k e r  c h a r a c t e r s and might be  here,  f o r Grant  character  GRN  other  in  the  intuitively  associated  with  a  and one might w e l l expect them to form I t i s p o s s i b l e that the  structure  of  57  F i g u r e 6. Dendrogram summary of c h a r a c t e r genetic correlation matrices. (A = Bear Lake, B = Caycuse, C = Grant Lake)  58  (A)  -.2 i  .2 1  .6  1  1  1.0  1  1  1  8 5  3  fl  4  I  6  I  z 1 2  (B) -.2  1.0  _4  J. _§ _2  _a 6  (C) -.2  1.0 — i 8  5 6 1 HEAL  2  3 4 5 6  7  8  SNOL EYED UPJL GRL HEAD INOW GRN  2 _1 _3 4  59  the  dendrogram  derived  from  the  Caycuse c o r r e l a t i o n  r e s u l t s from low genetic variances and r(G). for for  Bear  former  than does Caycuse, yet the s t r u c t u r e of population  i s nearly i d e n t i c a l  g e o g r a p h i c a l l y d i s p a r a t e population unlikely  that  considering structure  the  the  latter  number  of  -  of  result  Lake.  could  arise  correlations  of r(G) f o r Caycuse i s r e a l ,  r(G)  to that of the  Grant  It  seems  by  involved.  chance If  reorganized.  Gradients  Selection morphologies  gradients are given  for transitions 13.  i n Table  of each g r a d i e n t are dimensionless magnitudes  of  each  between  population  The i n d i v i d u a l elements 0 i  t h e r e f o r e only  /3i are of i n t e r e s t .  the  relative  In the c a l c u l a t i o n of  each g r a d i e n t , z* f o r the second p o p u l a t i o n was s u b t r a c t e d z*  f o r the f i r s t  i n d i c a t i o n of divergence  has  selection to  these  on  HEAL  and  averaged  strongest  first  five  B,  not  an  SNOL,  characters,  followed  INOW,  suggests  EYED  that  much and the  a c r o s s a l l three  directional  i n t e n s i t i e s f o r HEAD and UPJL are  s e l e c t i o n have acted on distance,  character  i n d i c a t e t h a t the  operated  and  on that c h a r a c t e r .  /3i's f o r each  populations  from  p o p u l a t i o n , as a consequence, the sign of each  /3i i s a r e s u l t of the magnitude of the second term  The  the  i t may i n d i c a t e t h a t the  genome i n t h i s p o p u l a t i o n has been i n part  Selection  estimates  Lake however, has lower average a d d i t i v e v a r i a n c e s  each c h a r a c t e r the  imprecise  matrix,  by  GRN.  similar.  weaker GRL.  selection Average Relative  net f o r c e s of Net  selection  Limnetic-Benthic  and  60  Table  13. S e l e c t i o n g r a d i e n t s f o r the three r e p r e s e n t a t i v e morphotypes based on the p o o l e d - w i t h i n v a r i a n c e - c o v a r i a n c e matrix. Population T r a n s i t i o n s Bear/Caycuse  HEAL SNOL EYED UPJL GRL HEAD INOW GRN  Bear/Grant  Caycuse/Grant  2174.64 -1494.97 - 190.66 - 771.12 18.50 902.33 367.93 1015.56  -219.67 188.09 - 15.64 64.02 42.67 - 76.24 - 7.28 -141 .03  -2394.30 1682.07 175.02 835.15 61.18 - 978.50 - 375.22 -1156.59  3093.90  259.40  3424.80  B  Intermediate-Limnetic  p o p u l a t i o n s are separated  selection  while the Intermediate-Benthic  distance,  are separated  by the  greatest  populations  by the s h o r t e s t s e l e c t i o n d i s t a n c e .  Discussion The  relatively  characters  low  scored,  suggests  with which e c o l o g i c a l l y selection.  This  and has  in  adaptive  significance.  heritabilities,  the  i s no longer  for  the  there i s l i t t l e a d d i t i v e v a r i a n c e  i s not past  uncommon  l e d to  may in  tenuous  respond  to  evolutionary inference  of  I t i s o f t e n assumed that c h a r a c t e r s with but which are d i r e c t l y  l i e a t e q u i l i b r i u m (an fitness  observed  s i g n i f i c a n t characters  paradox  ecology,  low  heritabilities  adaptive  peak),  r e l a t e d to f i t n e s s ,  and  that  i n c r e a s i n g (Futuyma 1979).  their  mean  However i t i s  e q u a l l y l i k e l y that a d d i t i v e v a r i a n c e was.reduced by  a  event  population  ( i . e . i s the  historical  consequence  of  a  founder  61  bottleneck).  If  freshwater  post-glacial  derivatives  g e n e r a l l y assumed ( B e l l potential error.  exists  an  the  1970).  have  in  turn  freshwater  provided  these  is  thought  to  to  the  sampling  modify  the  by these i n v a s i o n s (Hagen electrophoretic  studies  forms of G a s t e r o s t e u s , i n B r i t i s h  empirical  support  for  this  model  1984).  estimates are reasonable r e f l e c t i o n s of Va,  freshwater p o p u l a t i o n s may  not be capable of response  selective  regime  it  variation  may  variance.  Large amounts of  variance'  are  Wootton 1984), then c e r t a i n l y  Recently data from  (Withler and McPhail If  Gasterosteus  f o r the r e d u c t i o n of v a r i a n c e due  marine and  Columbia,  of  anadromous marine form, as i s  of extant v a r i a t i o n produced  and McPhail of  of  1976;  Natural selection  patterns  populations  should  not  in  arise,  represent  negative  T h e o r e t i c a l models suggest  Va  the  however  to a novel  the  expressed  scope of a v a i l a b l e  may  be  genetic  preserved  correlations  that s t a b i l i z i n g  then  additive  as  'hidden  (Lande  1975).  selection w i l l  lead  to  the f i x a t i o n of p o s i t i v e l y c o r r e l a t e d t r a i t s , but that under  a  constant  regime  correlations  will  of  evolve  stabilizing  selection,  negative  p r e s e r v i n g v a r i a n c e (Lewontin  1964).  T h e i r e f f e c t s on the phenotype c a n c e l producing small d e v i a t i o n s from the mean. the  P e r t u r b a t i o n s of these complexes  expression  possible  that  populations and may  still  of the  that  variance of  1982).  lead  Thus  to  i t is  freshwater  Gasterosteus  have p r e s e r v e d v a r i a n c e i n coadapted  gene complexes  respond  genepools  (Rose  will  to s e l e c t i o n  P o p u l a t i o n founder  events  (the  f o l l o w i n g a founder establishment  of  event. daughter  62  populations  from  followed  incipient  by  daughter all  founder  population  individuals),  isolation  (which  or  is  are thought  Carson  (1984) d i s t i n g u i s h  speciating  lineages  derived  speciating  lineages  may  between  speciating  arise  species'.  from  the  Non-  dispersal  (or  t o c o l o n i z e - so  rapid  expansion  into  environments but whose a r c h i t e c t u r e i s r e s i s t a n t to change  founder  effects  mutable genomes are haploid  species,  (Carson thought  yet  1984). tightly  Speciating  Templeton  belong  peak.  non-mutable  lineages  highly  inbred  are  (Carson  thought  to  and  or  coadapted Templeton  a r i s e from l e s s  under s e l e c t i o n , r e s u l t i n g i n a s h i f t  populations?  to  a  new  I n c i p i e n t " i s o l a t i o n may r e s u l t as a consequence  architecture  morphological  has  divergence  1981).  facilitated between  I b e l i e v e the e s t i m a t i o n  between c h a r a c t e r s In  These non-  o l d s p e c i e s with t i g h t l y  of the movement between peaks (Templeton genetic  to  1984).  i n t e g r a t e d complexes which are broken by a founder event  reorganized  adaptive  and to  very  gene complexes may a l s o be  and  non-  Such an organism probably possesses a  g e n e r a l i s t genome (Baker 1965), a l l o w i n g  by  and  from a n c e s t r a l p o p u l a t i o n s .  s u b d i v i s i o n ) of species which show a p r o p e n s i t y  novel  Not  f o r the e v o l u t i o n of i s o l a t i o n .  and  'weed  i f the  species).  possess  be  genomic  required  called  not  the  architecture  to  may  required  i s to emerge as a b i o l o g i c a l  ancestral populations  Templeton  may  the  What  type  of  evolution  of  freshwater  stickleback  of the g e n e t i c  covariance  suggests two a l t e r n a t i v e s .  reconstructing  the  pattern  of  interpopulation  m o r p h o l o g i c a l divergence, I have assumed constancy of the pooled  63  variance/covariance made  without  matrix.  e r r o r i t may  The  between c h a r a c t e r s ,  operates  to  correlated characters this  definition  which may  directional  traits;  the  negatively other  second  characters  (e.g. GRN) allowing Could  in  Shape  with s h i f t s  a more r a p i d response  to  a  the  By  includes from  on  weaker  novel  extensive  two  two  selection  one  of  two  i n t r o p h i c resource  these  that  of  change and/or change in  by  be  This  positively correlated  selection  promoted  it  be  weak  correlation.  arising two  be  s h i f t s in  phenotype  selection  of  from  traits.  associated  will  mean  first  one  arising  correlated  the  antagonistic  change  been  by  facilitate  the s i g n of the  subsets of s e l e c t i v e f o r c e s : the for  has  s e l e c t i o n (Lande 1979).  change  against  then,  'G'  matrix i s c h a r a c t e r i z e d  mean phenotype under a n t a g o n i s t i c selection  of  i n d i c a t e that G a s t e r o s t e u s should  viewed as a weed s p e c i e s . correlations  If t h i s measure  correlations,  selective  freshwater  use  regime.  diversity  of  G a s t e r o s t e u s r e s u l t s from a g e n e r a l i s t genome, c h a r a c t e r i z e d  by  ' l o o s e l y ' c o r r e l a t e d complexes of coadapted genes? The  similarity  in  structure  of  the Bear and  Grant Lake  dendrograms would seem to support the hypothesis of a g e n e r a l i s t genome.  These p o p u l a t i o n s  environmental  appear to be  constraints  with the  responding to  different  same a r c h i t e c t u r e .  However  t h e i r o r g a n i z a t i o n c o n t r a s t s with that of Caycuse which shows much  different  pattern  structure i s  real  measurements  of  considered  of c h a r a c t e r  ( i . e . does Va)  genetically  then  not the  distinct  clusters.  arise Caycuse from  from  If the Caycuse error  population Bear  a  Lake  in must  the be (the  64  geographically comparison t o reorganized  proximate i t and  with  selection.  Grant  respect  imply a more t i g h t l y broken d u r i n g  p o p u l a t i o n ) and may be r e o r g a n i z e d i n  the  Lake  to  (or  Caycuse).  conversely,  they  Reorganization  are would  i n t e g r a t e d a n c e s t r a l a r c h i t e c t u r e which was founder  Unfortunately,  episode,  or  we  little  know  possibly  altered  by  about the types or  i n t e n s i t y of s e l e c t i v e pressures that would be r e q u i r e d to a l t e r character c o r r e l a t i o n s . experiments  have  Short  demonstrated  v a r i a n c e / c o v a r i a n c e matrix Leamy and A t c h l e y In  the  term  and  long  considerable  term constancy  over time (Cheung and Parker  of the 1974  ;  1984).  face  of the r e s u l t s , the second s t r a t e g y (genomic  r e o r g a n i z a t i o n ) seems somewhat u n l i k e l y compared (colonizer  selection  genome).  to  the  first  I f g e n e t i c r e o r g a n i z a t i o n of the a n c e s t r a l  p o p u l a t i o n has o c c u r r e d  it  is  unlikely  that  the  pattern  of  character  correlations  w i t h i n Grant and Bear l a k e s would be so  similar.  Rather,  results  responding  to  a  the  variety  correlations f a c i l i t a t i n g significance chapter.  of  these  of shifts  shifts  suggest selective in is  a  generalist regimes,  trophic  examined  genome  with  weak  phenotype.  The  in  the f o l l o w i n g  65  CHAPTER 3  Introduction Reproductive i s o l a t i o n a r i s i n g through adaptive of  subpopulations,  is still  speciation  (review  focus  the h i s t o r i c a l  on  typically  and  i n Templeton  attempt  variability  thought  to  correlate  of  histories  inference  (Mayr 1983).  criticized  fortheir  of  (Clarke  erroneous power  are  population  by  1978)  and  an some  and  Lewontin  histories from  1979)  (Chapter  direct  inferential  and  c o r r e l a t i o n with studies  However  studies  may  knowledge  of  a  measurement (Boag  be  ecology  particular  trait's  t h i s approach has  natural  and  the  Grant  selection in 1981).  This  (e.g. M i l e s and R i c k l e f s 1984; M i t t l e b a c h 1984;  Grant  in  to the  i n v e s t i g a t i o n of the organism's  of Darwin's f i n c h e s  study and others  leading  2).  of  the  from  to p r o p e r l y d e f i n e the t a r g e t s of  allowed  In  genetic  1  Recently  divergence  or  primarily  f u n c t i o n a l s i g n i f i c a n c e (Bock 1980).  Schluter  divergence  Such a d a p t a t i o n i s t programs' have been  derived  both  populations  which  1983; F e l l e y 1984); that i s ,  reconstructed  inability  n a t u r a l s e l e c t i o n (Gould  increased  studies  with one or more s e l e c t i v e c o n s t r a i n t s (e.g. M i t t e r  evolutionary  explanatory  Those  morphological  Futuyma 1979; F i n d l e y and Black  erection  to be a primary mode of  1981).  patterns  divergence  1984) have  trophic  morphology  concentrated (e.g. beak  on s e l e c t i o n f o r size)  and i t s  food type and a v a i l a b i l i t y . of t e l e o s t e v o l u t i o n , m o d i f i c a t i o n s of t r o p h i c  morphology are thought t o be a common mechanism  promoting  such  66  e v o l u t i o n a r y phenomena as the e x p l o s i v e r a d i a t i o n of the A f r i c a n Great  Lakes  cichlids  (Greenwood 1984).  Almost a l l occurrences  of these " s p e c i e s f l o c k s " i n v o l v e some a l t e r a t i o n of the feeding apparatus  (review i n E s h e l l e and K o r n f i e l d  t e l e o s t t r o p h i c morphology i s not multiple  radiations.  species p a i r , appear  to  Lindsey  In  limited  systems  correlated  with  to  in  resource  Divergence i n  cases  containing  interspecific differences be  1984).  only  trophic  involving a  single  morphology  partitioning  (e.g.  1981).  In  the  threespine  interpopulation characters Island,  stickleback  morphological  (review i n B e l l  biological  variability  1984).  speciation  In  Enos  (Mayr  species  complex,,  i s evidenced Lake  on  i n many  Vancouver  1963) i s a s s o c i a t e d with  extreme divergence  i n t r o p h i c morphology and t h i s divergence has  r e s u l t e d i n almost  complete s e p a r a t i o n of food type e x p l o i t e d by  the two s p e c i e s (Bentzen and McPhail wish  to  trophic  examine  the  morphology  1984).  In t h i s  between  lake-dwelling  populations  Having  site-specific  of  intent  I  f u n c t i o n a l s i g n i f i c a n c e of divergence i n  G a s t e r o s t e u s w i t h i n the Cowichan drainage. morphological  w i t h i n each l a k e , and  chapter  proposed  variability three  of  d e s c r i b e d the  each  population  morphotypes,  i t i s my  to demonstrate that each morphotype i s indeed an ecotype  (sensu Turesson  1922).  67  M a t e r i a l s and  Trophic  Methods  Morphology  In a l l the feeding experiments d e s c r i b e d below I have again used animals r e p r e s e n t i n g each of the proposed morphotypes. representative populations the g e n e t i c from  study  Grant  Hereafter 'limnetic', trophic  three  variables  (UPJL),  gill jaw  and  the  and  were  upper  intermediate  populations  'benthic'  significance:  Upper  ( i . e . the l i m n e t i c from Caycuse,  Lake,  the  chosen were the same as those  be  'intermediate'  chosen  jaw  will  for  length  raker number(GRN)  and  Bear  Lake). to  respectively.  length gill  benthic  referred  studies  -  used in  the  from  of of  raker  length i s thought to be a surrogate  head to  shape have  (Aleev  strongly  phenotypes.  Gill  c h a r a c t e r c l u s t e r d e f i n e d and been  strongly  altered  by  on  it,  in  the  premaxilla  length  (GRL).  measure of mouth  l i k e UPJL, selection.  GRN  al.  1983).  Gill  raker  spacing  and  however  to due  identify to  the  the second  appears  to  have  V a r i a t i o n in g i l l r a k e r  Heitz  been shown to be 1971;  Wright  et  i s thought to be the mechanism  a f f e c t i n g p a r t i c l e retention in planktivores. sought  the  between  raker a r c h i t e c t u r e , was  (Magnuson  gape-  s e l e c t i o n appears  transitions  morphology has been s t u d i e d e x t e n s i v e l y and has r e l a t e d to p l a n k t i v o r y  Three  UPJL i s a r e p r e s e n t a t i v e of  c l u s t e r d e f i n e d i n Chapter 2, and  operated  population  1969).  as  functional  gape and hence should be c o r r e l a t e d with p a r t i c l e s i z e i n l i m i t e d predators  The  interpopulation  For t h i s reason I  differences  small s i z e of these animals,  in  spacing;  differential  68  spacing raker Gill  i s confounded by measurement e r r o r . density  was estimated  were  determined  each " p o p u l a t i o n from r a k e r s on the f i r s t  and L a g l e r  1958).  gill  as a surrogate measure of spacing.  raker number and l e n g t h  from  Consequently  for  individuals  gill  arch  The arch was then e x c i s e d from the  (Hubbs  opercular  c a v i t y and an enlarged t r a c i n g made of the o u t l i n e using a WildM5  dissecting  gill  scope  and  camera l u c i d a .  rakers was determined by d i g i t i z i n g the t r a c i n g s .  t e s t was used to compare d i f f e r e n c e s raker one  Area occupied  density  was  expressed  square m i l l i m e t e r .  standard  contents  of  were  different  morphs.  Gill  occupying  plotted  against  by ANCOVA.  as  benthic  or  (1970) and a c h i - s q u a r e contingency  accentuate  Feeding  lake  areas  spring.  limnetic following  test  performed f o r  p a t t e r n s may change with  d i e t a r y d i f f e r e n c e s between the l i m n e t i c and  benthic  taken  from  breeding  Cowichan  but  dispersal should  Sticklebacks  after  Prey  this  t r a w l s d u r i n g winter (Carl  then  from each lake i n l a t e  classified  d i e t and p o p u l a t i o n . to  area.  p o p u l a t i o n was broadly c h a r a c t e r i z e d by gut  of samples taken  organisms Kliewer  each  relative  Sheffe's  as the number of rakers  The r e s u l t s were  length and analyzed  Diet  in  by the  Lake  seem t o be e n t i r e l y dependent  i n midwater on  plankton  1953).  Gape Experiments The maximum amphipods  functional gape,  was  relationship determined  (Eogammarus  by  between upper jaw l e n g t h and presenting  confervicolus)  to  each  brackishwater of  the  three  69  populations.  Several  determinations  of maximum  Larson  1976, Bentzen  experiments  are  workers  have  gape  amphipods  f o r Gasterosteus  1982) thus  readily  used  results  comparable  from  (Burko 1973, the present  to previous  I n d i v i d u a l f i s h were h e l d i n 20 l i t r e aquaria f o r 3 to each t e s t and fed amphipods. painted  a  uniform  brown  coloured p a r t i t i o n s . each t e s t longer  behaviour  24  have  i n Gasterosteus  Amphipods were measured  been  based  as  base of  the uropods  on  the d i s t a n c e  divisions  preceding  to i n f l u e n c e feeding  with  body  carbonated  water  and  Each amphipod was assigned length.  Body  length  was  from the base of the antennae t o the  with  the body  flexed  S i x t e e n s i z e c l a s s e s were t e s t e d ranging from size-class  hours  (Beukema 1968).  anaesthetized  defined  prior  P e r i o d s of s t a r v a t i o n  shown  with an o c u l a r micrometer.  to a s i z e category  days  and a q u a r i a were separated by beige-  F i s h were s t a r v e d f o r 24  hours  studies.  The bottom of each aquarium was  i n order to s t a n d a r d i z e hunger.  than  in  were  0.77mm.  (Bentzen  1982).  1.55mm t o 13.17mm;  Amphipods were allowed t o  recover f u l l y before i n t r o d u c t i o n t o the a q u a r i a . Three amphipods, one from each of three s i z e - c l a s s e s , presented  t o .each f i s h .  Pilot  were  s t u d i e s r e v e a l e d an a p p r o p r i a t e  amphipod s i z e range with which t o begin each t r i a l .  Fish  were  allowed one hour i n which to i n g e s t the prey; a f t e r one hour the amphipods  were  removed,  were fed t o s a t i a t i o n Following rerun  a  r e a n e a s t h e t i z e d and remeasured.  with  chopped  liver  after  each  Fish trial.  f u r t h e r 24 hour p e r i o d of s t a r v a t i o n , the t e s t was  and each  size-class  presented  was  increased  by one  70  division. longer  This  sequence was continued  until  ingest the maximum c l a s s presented  days.  Data  standard  were analyzed  by ANCOVA.  f o r three  of  relative  upper  jaw  >  T h i s a n a l y s i s was repeated  length  the  covariate.  In  t o determine the  length  populations. as  consecutive  In the i n i t i a l a n a l y s i s ,  length was t r e a t e d as the c o v a r i a t e  effects  the f i s h could no  on  gape,  across  s u b s t i t u t i n g upper  this  instance  jaw  significant  i n t e r p o p u l a t i o n d i f f e r e n c e s i n mean amphipod s i z e a t t a i n e d indicate  the c o n t r i b u t i o n  of some e f f e c t other  must  than upper jaw  length.  Amphipod Manipulation  Experiments  Since w i l d f i s h had been used i n the gape experiment I was interested  i n examining  the c o n t r i b u t i o n  d i f f e r e n c e s i n f o r a g i n g success. amphipods fish  The  litre  scored  aquarium  behaviour  In t h i s s e r i e s of  from a s i n g l e s i z e - c l a s s were presented  i n a 218  observer  of  f o r twenty  behaviour through a hole  prey s i z e - c l a s s chosen was 4.65mm.  experiments  to individual  minutes  while  i n a black  T h i s s i z e - c l a s s had been  prey were presented  t o each f i s h , as some i n d i v i d u a l s  observed  as  minute feeding bout. aquaria  and s t a r v e d  the experimental  many  as  Fifteen had been  ten prey items d u r i n g a twenty  F i s h were h e l d i n d i v i d u a l l y f o r 24 hours.  i n 20  litre  I n d i v i d u a l s were placed i n  tank f o r 15 minutes preceding  time f o r a c c l i m a t i o n .  the  partition.  ingested by f i s h as small as 30mm from a l l p o p u l a t i o n s .  t o take  to  each run t o allow  A f t e r 15 minutes the prey were  from the top of the tank and r e c o r d i n g of the t r i a l  introduced  began  after  71  the f i r s t  orientation.  F i v e behaviours were scored:  1.  O r i e n t a t i o n t o a prey  2.  S t r i k e on a prey  3.  End of a s u c c e s s f u l m a n i p u l a t i o n  4.  End of an u n s u c c e s s f u l m a n i p u l a t i o n  5.  A break i n o r i e n t a t i o n with no s t r i k e a t the prey.  Each t r i a l prey.  item  item  l a s t e d twenty minutes and f i s h never consumed a l l the  A l l data  were  collected  u s i n g an OS-3 event  recorder  ( O b s e r v a t i o n a l Systems I n c . ) . A  two  proportion success  way of  was  fixed  effects  foraging  defined  success.  as  Probability  performed  p r o p o r t i o n of f o r a g i n g  of  successful  (cumulative  were  transformed  (Sokal and Rohlf  1981).  population  and  upper  experiment  were  strikes  percent  of the  i n d i c a t e d that these p r o p o r t i o n a l data  had a s i g n i f i c a n t l y non-normal d i s t r i b u t i o n . data  on the  i n g e s t i o n ) d i v i d e d by the number of  plots  d i s t r i b u t i o n vs raw data)  was  The  the number  ( i . e . those f o l l o w e d by prey strikes.  ANOVA  Consequently  using the a r c s i n e square-root The jaw  capable  two  factors  length.  of  As  taking  the  in  the  transform  the ANOVA  a l l the f i s h size-class  were  in this of  prey  presented, I p r e d i c t e d no d i f f e r e n c e i n f o r a g i n g success between populations,  given  success were  approximately  significant  effect  that the b e h a v i o u r a l components t o f o r a g i n g  of  constant  between  populations.  p o p u l a t i o n or a s i g n i f i c a n t  term would i m p l i c a t e some  effect,  apart  from  A  interaction  morphology,  in  b e n t h i c f o r a g i n g success. Initially  upper  jaw  l e n g t h was d i v i d e d  i n t o three  levels  72  based on the f o l l o w i n g standard 50-60mm.  Regression  lengths:  equations  30-40mm,  obtained  40-50mm  from  and  previously  c o l l e c t e d samples were used to determine upper jaw l e n g t h . fish  were  to  be  unable t o a t t a i n resulted  run i n each c e l l  complete  cells  upper jaw l e n g t h .  f o r two  behavioural  relatively  independent  manipulation  time and s t r i k e time  prey, which were  weighted design;  which  therefore  as a two way but with only two l e v e l s  examined f o r two b e h a v i o u r a l  manipulation  size-classes  of  The ANOVA was performed using UBC:GENLIN.  Interpopulation  number  of the ANOVA, however I was  i n an unbalanced, and badly  the data were analyzed  Ten  differences  i n f o r a g i n g were  v a r i a b l e s which were thought to be  of  morphology: probability.  average  successful  Average  successful  was d e f i n e d as the t o t a l time spent eventually  of prey i n g e s t e d .  ingested,  divided  by  handling  the  total  S t r i k e p r o b a b i l i t y was expressed as a  proportion  of the number of o r i e n t a t i o n s which were followed  a strike.  A K r u s k a l l - W a l l i s one way ANOVA was performed on each  variable as  across populations.  i t i s less  sensitive  by  T h i s non-parametric t e s t was used to  outliers  than  i t s parametric'  equivalents. To  investigate  the  relative  behaviours t o f o r a g i n g success,  contributions  in addition  upper jaw l e n g t h , each behaviour was entered a  multiple  regression.  to  these  the e f f e c t  simultaneously  of into  The p r o p o r t i o n of f o r a g i n g success was  the dependent v a r i a b l e i n the model; upper jaw successful  manipulation  treated  the p r e d i c t o r  as  of  time,  and  variables.  strike The  length,  average  probability  were  d i s t r i b u t i o n s of  73  foraging normal;  success and s t r i k e p r o b a b i l i t y were s i g n i f i c a n t l y consequently these data were again  transformed.  T h i s t r a n s f o r m a t i o n was  arcsine  successful  non-  square-root  in normalizing  the data f o r m u l t i p l e r e g r e s s i o n .  Limnetic Foraging T r i a l s Foraging laboratory  ability  using  1979).  is  a  of  salini i  teleosts  significant  Size-selective  significance  limnetic  Artemia  P a r t i c u l a t e feeding behaviour  on  prey  was  as  the  to  be  tend  tend  s t a n d a r d i z e any  colour  (review i n Hyatt,  1979).  responses Lab-reared  i n an attempt  to  l e a r n e d component of i n t e r p o p u l a t i o n b e h a v i o u r a l feeding.  A l l f i s h were i n i t i a l l y  on l i v e Artemia n a u p l i i before s w i t c h i n g to a mixture f r o z e n Artemia  ; consequently  reared  of  liver  i n d i v i d u a l r e p r e s e n t a t i v e s of  the three morphotypes were exposed to l i v e lengths of time.  appears  D i f f e r e n c e s i n prey  i n t h i s s e r i e s of experiments  differences in limnetic  and  (O'Brien  size  In a d d i t i o n n a u p l i i  to  and  morphology, f o r t h i s reason o n l y a s i n g l e  for a v a r i e t y of t e l e o s t s used  prey.  size-selective  have been shown to mediate d i f f e r e n t i a l a t t a c k  were  the  the  used.  would  to be approximately constant at t h i s stage.  fish  experimental  component of s e l e c t i v i t y  predation  in  obscure  c l a s s of Artemia was  colour  tested  Test f i s h were chosen  shrimp  for  similar  at random from the tanks  in which they had been r a i s e d . Each  test  was  run in the same 20 l i t r e a q u a r i a as used i n  the maximum gape experiments. with  dechlorinated  water  Tanks were scrubbed and between  each  trial  to  refilled minimize  74  suspended p a r t i c u l a t e s which might a l t e r were h e l d i n d i v i d u a l l y live  Artemia  to  f o r a g i n g success.  f o r two days p r i o r to each t e s t  satiation.  Tank temperature  At t h i s temperature  t o t a l gut evacuation time  hours  1960).  (Tugendhat  Immediately  was is  Fish  and  fed  10 + 1.0  more  preceding  °C.  than  each  16  test,  i n d i v i d u a l s were s t a r v e d f o r 24 hours to s t a n d a r d i z e hunger. the b e g i n n i n g of each t r i a l to each i n d i v i d u a l . after in  100 Artemia  F i s h were allowed  which they were removed and  10%  buffered  approximately  formalin.  one  upper and  lower  contents  flushed  out  fish:  GRL.  the  (Wootton  with  water,  per stomach was  d i s s e c t i n g microscope. each  to  feed  for  one  hour  Preservation  fish  had  fixed  for  1976),  opened,  and  the  using a m i c r o p i p e t t e .  scored  with  the  aid  The of  a  Nine m o r p h o l o g i c a l measures were made on  STDLEN, HEAL, SNOL, EYED, UPJL, HEAD, INOW, GRN  Gillraker  was  week t h e i r stomachs were e x c i s e d between the  sphincters  number of Artemia  ( 5 / l i t r e ) were presented  sacrificed.  After  At  density  was  determined  from  and  regression  of  expressed as a p r o p o r t i o n of the  100  g i l l r a k e r area on standard l e n g t h . Foraging  success  was  prey taken by each f i s h .  P r o b a b i l i t y p l o t s i n d i c a t e d these data  had a non-normal d i s t r i b u t i o n data  were  1980).  arcsine  success  square-root  T h i s transform was  Interpopulation were  correlations  examined made  each  population,  transformed  hence  (Sokal  and  successful in normalizing  differences  were  for  in  using within  a  the  proportion  one-way  ANOVA.  the of  the Rohlf data.  foraging  Univariate  and among p o p u l a t i o n s f o r each  m o r p h o l o g i c a l v a r i a b l e scored, a g a i n s t  foraging  success.  All  75  morphological  variables  were  l o g (base e) transformed  for a l l  analyses.  Results  Trophic  Morphology  S h e f f e ' s t e s t on differences  in  the  gill  adjusted raker  mean  area,  areas  thus  the  i n t e r m e d i a t e p o p u l a t i o n s appear to be packing the  same  r e l a t i v e space as the l i m n e t i c  raker d e n s i t y on standard case.  Table  Slopes  length suggests  indicated benthic  fewer rakers  fish. this  ANCOVA f o r is  probably  of p o p u l a t i o n r e g r e s s i o n s were not  and into gill the  significantly  14. Summary of ANCOVA r e s u l t s f o r g i l l r a k e r on standard  no  density  length.  Population Bear 13.49  Mean raker density A d j u s t e d mean raker d e n s i t y (Std.  Error)  Grant  Caycuse 11.26  14.16  12.03  0.42  0.48  1 1 .02 9.42 0.49  Note: p r o b a b i l i t y of equal a d j u s t e d means = 0.000. d i f f e r e n t ; however there were adjusted standard more  mean  gill  l e n g t h , the  closely  However, the  raker  significant density  intermediate and  spaced rakers then intermediate sample  differences  (Table 14). limnetic  For any  given  individuals  have  the benthic type also  had  between  (p < 0.0001).  significantly  more  76  rakers than the l i m n e t i c morph (p < 0.001). the g u t content data Diets  of  in  f o r samples recovered by p o l e - s e i n e i n May.  and o s t r a c o d s . the  stomachs  A of  small the  p l a n k t o n i c C r u s t a c e a were found form.  Diet  of  copepods morph,  i n the stomachs of  were  but  the  no  benthic  of the l i m n e t i c morph was n u m e r i c a l l y dominated by  contributed  contingency  number  intermediate  l i m n e t i c and s u r f a c e prey, although again  15 summarizes  the intermediate and benthic morphs were dominated by  chironomids found  Table  test  to  showed  depend s i g n i f i c a n t l y  diet diet  chironomids  and  composition. type  (limnetic  The or  ostracods chi-square  benthic)  to  on morph (p < 0.001).  Maximum Gape The r e s u l t s of the gape experiments are summarized 16.  For both c o v a r i a t e s , standard l e n g t h and upper jaw l e n g t h ,  the r e l a t i o n s h i p with maximum amphipod  length  was  t h e r e f o r e a l l data were l o g (base e) transformed. all  r e g r e s s i o n s of amphipod  be s i g n i f i c a n t l y d i f f e r e n t did  i n Table  amphipods  were  The s l o p e s of  l e n g t h on standard l e n g t h proved to  from zero (p < 0.05), but the  not d i f f e r among p o p u l a t i o n s .  ingested  curvilinear  slopes  The adjusted mean l e n g t h s of  significantly  heterogeneous  between  p o p u l a t i o n s , a f t e r the e f f e c t of the c o v a r i a t e had been  removed.  P a i r - w i s e t - t e s t s i n d i c a t e d no d i f f e r e n c e between the l e n g t h s of amphipods  ingested by the intermediate and l i m n e t i c morphs (p >  0.05); however, both of these mean less linear  than  that  relation  achieved between  by  lengths  were  the benthic morph.  amphipod  size  and  significantly The s t r o n g l y  standard  length  77  Table  15.  Gut  content data from w i l d p o p u l a t i o n samples.  78  Table 15. Summary of gut content data from samples recovered with p o l e - s e i n e s i n May 1983. Tabulated v a l u e s are the pooled number of prey items/stomach f o r each sample Population I tern Chi ronomids Chaoborus Megaloptera(larvae) Megaloptera(adult) Ephemeroptera Simulidae(adult) Tipulidae(adult) Unidentified insect (adult) Unidentified insect (larvae) Gasterosteus eggs U n i d e n t i f i e d eggs Ostracods Hydracarina Nematodes Gammaridae Cladocera C y c l o p o i d copepods C a l a n o i d copepods  Bear (N = 30) 103  4 2 1 2  Caycuse (N = 20) 12  — " ~'  6  6  28  312  20  2 2  1 28 1 1 1 5 8 3 4  4  1 2  Grant (N = 30)  26 68  99 10 433 1 5'  79  Table 16. ANCOVA r e s u l t s l e n g t h and upper jaw  f o r amphipod s i z e on length.  standard  Table (A)  16. Summary of ANCOVA r e s u l t s f o r amphipod s i z e on: (a) standard l e n g t h (b) upper jaw l e n g t h . Standard l e n g t h . Populat ion  Mean amphipod size Adjusted mean amphipod s i z e (Std.Error)  Bear 1.6527  Caycuse 1.6205  Grant 1.8745  1.6292  1.5577  1.9437  0.0575  0.0694  0.0596  Note: p r o b a b i l i t y of equal a d j u s t e d means = 0.0007 (B)  Upper jaw l e n g t h . Populat ion  Mean amphipod size Adjusted mean amphipod s i z e (Std.Error)  Bear 0.7177  Caycuse 0.7037  Grant 0.8140  0.7278  0.7081  0.8008  0.0243  0.0285  0.0244  Note: p r o b a b i l i t y of equal a d j u s t e d means = 0.04  81  suggests that the d i f f e r e n c e i n mean s i z e - c l a s s a t t a i n e d , a r i s e s through  increases  i n c r e a s e d standard upper  in  mouth  length.  gape  This  (upper  jaw  length)  conclusion  was  tested  jaw l e n g t h as the c o v a r i a t e i n the ANCOVA.  is p l o t t e d against  upper  jaw  length  in  with using  Amphipod  Figure  7.  size  Clearly  i n c r e a s e d upper jaw l e n g t h c o n f e r s an increased maximum gape f o r a l l populations. population another  ANCOVA i n d i c a t e d that the slopes of i n d i v i d u a l  r e g r e s s i o n s were not s i g n i f i c a n t l y d i f f e r e n t  (p  >  0.05)  but  the  adjusted  s i g n i f i c a n t l y heterogeneous (p < 0.05).  from one  p o p u l a t i o n means were Benthic  i n d i v i d u a l s are  able to ingest l a r g e r prey  items than i n d i v i d u a l s of e i t h e r  limnetic  or  morphs.  although  there  jaw  length  intermediate  length.  success;  size  and  there are d i f f e r e n c e s between p o p u l a t i o n s  For  populations,  One should note however that  i s a c l e a r r e l a t i o n between prey  a r i s e by some mechanism other wild-caught  than  differences  I  in  sought  to  upper  of v a r i a b l e  address  general  upper  that must  f i s h , behavioural v a r i a b i l i t y  seems the most obvious source  therefore  the  jaw  between foraging  behavioural  m o d i f i c a t i o n s between p o p u l a t i o n s .  Amphipod M a n i p u l a t i o n  Experiments  The ANOVA i n d i c a t e d no h e t e r o g e n e i t y among  populations  (p  >  0.05)  in  foraging  however there were  success  significant  d i f f e r e n c e s i n v a r i a n c e among the two l e v e l s of upper jaw length (p = 0.0005).  The i n t e r a c t i o n  length) was not s i g n i f i c a n t . . cell  variances  were  term  (population  B a r t l e t t ' s test  homogeneous.  This  *  upper  jaw  i n d i c a t e d that a l l  result  confirms the  82  F i g u r e 7.  Plot  of amphipod s i z e vs UPJL f o r each morph.  Legend BEAR  —  0.8  0.9  1.1  1.2  1.3  1.4  UPPER JAW LENGTH (In mm)  1.5  1.6  i 1.7  O  CAYCUSE  •  GRANT  84  e f f e c t of upper jaw length on f o r a g i n g success experiments.  It  remains  demonstrated  the  gape  Table  17. C e l l means and standard d e v i a t i o n s f o r ANOVA on the p r o p o r t i o n of benthic  UPJL  possible  foraging  however  Bear 0.2099(0.2819) 0.4824(0.2672)  i n d i v i d u a l variance differences  success.  in  between  Caycuse 0.1344(0.2328) 0.5360(0.3191)  foraging  morph  success  types  in  Grant 0.2591(0.3127) 0.5372(0.2199) obscures  any  outliers.  Standard  high  17) suggesting  (Table indeed  deviations  individual  more  The  inflated  mean f o r a g i n g success variation  i n f l u e n c e f o r a g i n g success.  v a r i a t i o n there may be behaviour  of  extant  f o r a g i n g behaviour.  w i t h i n p o p u l a t i o n component of v a r i a n c e i s probably  jaw  that  Population  Level 1 Level 2  does  in  general  in  by were  behaviour  Aside from t h i s random  differences  in  foraging  between p o p u l a t i o n s which enhance the e f f e c t of upper  l e n g t h i n the gape experiments.  identify  patterns  of  behaviour  I  therefore  which  might  attempted  to  contribute  to  interpopulation foraging success. The K r u s k a l l - W a l l i s ANOVA i n d i c a t e d populations heterogeneity manipulation  were  differences  i n p r o b a b i l i t y of s t r i k e , but there was among  populations  time.  time manipulating morphs.  no  The  benthic  the prey before  for  average  among  significant successful  morph appeared to spend l e s s i n g e s t i o n than  the  other  two  Both of the b e h a v i o u r a l v a r i a b l e s and upper jaw l e n g t h  entered  into  a  multiple  regression.  The  independent  85  variables  in  the  regression  data were s t a n d a r d i z e d  and the c o e f f i c i e n t s of r e g r e s s i o n become  Beta weights which are 1981). The  directly  comparable  (Sokal  and  Rohlf  The r e s u l t s of t h i s a n a l y s i s are summarized i n Table  overall  however  regression  only  upper  manipulation  time  was  jaw had  highly length  partial  contributed s i g n i f i c a n t l y  Table  are of mixed mode, t h e r e f o r e the  significant and  (p = 0.0000);  average  regression  18.  successful  coefficients  to the model (p = 0.0001).  that  The  Beta  Summary of 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 using a r c s i n e transformed p r o p o r t i o n s of f o r a g i n g success as the dependent v a r i a b l e .  18.  Beta-weight  Var i a b l e Strike probability Upper jaw l e n g t h Average s u c c e s s f u l manipulation time  Significance  Std.Error  0.0829 0.3939  0.0986 0.0986  0.4008 0.0001  0.4106  0.0980  0.0002  Note: m u l t i p l e R = 0.6117 weights  for  these  I  suspected  Therefore successful certainly result  variables that  manipulation  time  some p r o p o r t i o n  are  upper  very  jaw  might  be  of manipulation  nearly  length strongly time  is  identical.  and  average  correlated; expected  to  from morphology.  This  prediction  was  tested  by c o r r e l a t i o n f o r upper jaw  l e n g t h and average s u c c e s s f u l manipulation  time, both w i t h i n and  between p o p u l a t i o n s .  the  negative  (Table  populations  was  19).  In  a l l instances  Pearson's  significant  correlation  ' r ' f o r data pooled  within  populations  only,  was  across the  86  coefficient  attained  significant.  Table  for  the l i m n e t i c morph was  These r e s u l t s suggest  that  the  statistically  contribution  of  19. C o r r e l a t i o n c o e f f i c i e n t s f o r average s u c c e s s f u l manipulation time and upper jaw l e n g t h .  Treatment Pooled P o p u l a t i o n s  N 70  Coefficient -0.2981*  Within Populations Bear Caycuse Grant  31 21 18  -0.4556 -0.5234* -0.4227  * S i g n i f i c a n t at p < 0.05. manipulation jaw  time to f o r a g i n g success  morphology.  Thus  behavioural processes,  I  was  i s largely attributable  unable  independent  of  morphology,  have produced the d i f f e r e n c e s observed  Limnetic Foraging  to i d e n t i f y any  to  general  that  might  in the gape experiments.  Trials  A summary of l i m n e t i c f o r a g i n g i s given f o r each p o p u l a t i o n in  Table 20.  I n d i v i d u a l s from the benthic p o p u l a t i o n were poor  limnetic  f o r a g e r s compared to both the intermediate and l i m n e t i c  morphs.  Sample means were s i g n i f i c a n t l y heterogeneous by  (p  <  0.05).  differences however,  Sheffe's  between  both  the  populations  contrasts limnetic had  success compared to the benthic  with  morphology  or  no  significant  intermediate  significantly  higher  morphs; foraging  population.  C o e f f i c i e n t s for a l l u n i v a r i a t e success  indicated  ANOVA  are given  correlations in Table 21.  of  foraging  None of  these  87  Table 20. Summary of l i m n e t i c  feeding  Population  N  Mean Number of Artemia Taken  Bear Caycuse Grant  30 31 33  30.56(21.16) 31.93(22.15) 18.03(18.45)  experiments. Mean P r o p o r t i o n s of Limnetic Foraging 0.55(0.26) 0.56(0.27) 0.36(0.28)  Note: p r o b a b i l i t y of equal means = 0.005. intrapopulation  correlations  were  significant  (p  >  0.05).  Table 21. I n t r a p o p u l a t i o n c o r r e l a t i o n s f o r c h a r a c t e r and l i m n e t i c f o r a g i n g s u c c e s s . Character  Bear -0.1271 -0.1710 -0.1313 -0.0286 -0.0887 -0.2641 -0.2345 -0.1229 0.0563  HEAL SNOL EYED UPJL GRL HEAD INOW GRN GRDENS Within by  Caycuse  Grant  -0.1034 -0. 1826 0.1362 -0.0010 -0.1921 -0.0268 -0.1277 -0.0005 0.1441  -0.0292 -0.1445 -0.1980 -0.0918 0.1336 0.1100 0.2757 -0.2251 -0.1004  each p o p u l a t i o n f u n c t i o n a l  two f a c t o r s :  population  and  (a) the (b)  limited  r e l a t i o n s h i p s may be obscured size  range  tested  for  individual behavioural variation.  p o p u l a t i o n a small number of f i s h appear to do extremely or  extremely well on Artemia.  I was h e s i t a n t  22.  0.05).  analysis  two  poorly  relationships.  c o r r e l a t i o n c o e f f i c i e n t s are given i n Table  Despite the f a c t there i s only one  this  In each  t o l a b e l these as  o u t l i e r s as they may be extensions of l e g i t i m a t e Interpopulation  each  of  the  degree  correlations  A chi-square t e s t i n d i c a t e d  of  freedom  in  are s i g n i f i c a n t (p <  the p r o b a b i l i t y  of  finding  88  Table 22. Interpopulation correlation coefficients for transformed c h a r a c t e r and limnet i c f o r a g i n g s u c c e s s . Character HEAL SNOL EYED UPJL GRL HEAD INOW GRN GRDENS  0.999* 0.999* 0.318 -0.454 0.356 -0.033 -0.069 0.716 0.865  * S i g n i f i c a n t at p < 0.05. only two s i g n i f i c a n t c o r r e l a t i o n s , low  (0.05  foraging  <  <  success  addition  to  positively  0.1). and  HEAL  for  and  GRL  SNOL, with  is  B i v a r i a t e means  proportion  of l i m n e t i c  The b i v a r i a t e means are p l o t t e d f o r  adjusted  correlated  correlation weaker.  p  i f these a r i s e by chance, was  character GRN  and  limnetic  in for  foraging  the  in  GRDENS  foraging  predicted  GRL,  Figure  GRN  and  are plotted  8.  are  In  strongly  success;  the  d i r e c t i o n but much GRDENS  with  the  i n F i g u r e 9.  Discussion Previous  investigations  have  examined  between UPJL and maximum s i z e of p a r t i c l e s Larson  1976;  Bentzen  1982),  in  was a d i r e c t consequence of  (1976)  and  differences  in  maximum  and gape  eaten  a l l cases  ingested  Bentzen  the  between  (Burko  1975;  the maximum s i z e  individual  McPhaiK1984)  relationship  also  limnetic  gape.  Larson  demonstrated and  benthic  89  F i g u r e 8.. P l o t s of b i v a r i a t e means f o r the p r o p o r t i o n of l i m n e t i c f o r a g i n g and a d j u s t e d c h a r a c t e r . Glyphs i n d i c a t e mean p o s i t i o n f o r each p o p u l a t i o n ; black bars i n d i c a t e one standard e r r o r on e i t h e r side of the mean.  • LIMNETIC • INTERMEDIATE • BENTHIC  f  SNOL  8_ CD  H E A D  S  CD  § I  CD CD  S-  4.10  CD  i  4.15  i  1—  4.20  4.25  1  4.30  5J  6  l  1  5.7  5.8  1  1  6  6.1  —|  5.9  INOW  E Y E D CD  +  §-1 CD  o CD  o I i 3: 9 0 3.92 3.94 3.96  1  3.98  CD ~ l  2.3  r~ 2.4  4.  2.5  1  1  2.6  2.7  91  F i g u r e 9. P l o t s of b i v a r i a t e means f o r the p r o p o r t i o n of l i m n e t i c f o r a g i n g and GRL, GRN and GRDENS. Glyphs i n d i c a t e mean p o s i t i o n f o r each p o p u l a t i o n ; black bars i n d i c a t e one standard e r r o r on e i t h e r side of the mean.  • •  LIMNETIC INTERMEDIATE  •  BENTHIC  0 (0-  0 ti  8-. 0 LO ti  0  10  CO  RAKER NUMBER  0500.92 054 056 0.98 1 102  RAKER LBCIHN  9 10 H 12 13 14 15  RAKER DENSflY (numbers/sqmm)  93  Gasterosteus  species  particle  is a significant  size  populations benthic  and  with  pairs.  The  present  s e l e c t i v e force operating  hence r e s p o n s i b l e  for ecotypic  l e n g t h r e s u l t s in  energetic  advantage  (Schoener The  decreased and  should  itself  access  time,  which  be s e l e c t i v e l y  lack of an  interpopulation  foraging  is  somewhat  behavioural  differences  in  other  surprising  as  in  Enos  Lake,  compared to the benthic at  sorting  that  morphological Northcote  i s a poor forager on benthic  substrate  species.  prey  Lab-reared male l i m n e t i c s  from the benthic divergence  substrate.  was  far  found in the Cowichan drainage,  forms behave as b i o l o g i c a l s p e c i e s  1984).  The  a  to  limnetic  benthic  of  favoured  (1984) have shown that the  study however, morphological than  an  behavioural  groups of t e l e o s t s ( S c h u l t z and  Bentzen and McPhail  poorly  is  component  m o d i f i c a t i o n has been shown to be a s s o c i a t e d with  species  increased  1971).  benthic  1972).  The  to a wider  In a d d i t i o n  handling  between  variation.  i t s i n c r e a s e d gape i s permitted  range of prey s i z e s than i s the l i m n e t i c . jaw  study suggests that  and  In  more  did their  extreme,  the l i m n e t i c  and  (Ridgeway and  McPhail  Enos Lake s p e c i e s p a i r i s presumed to be the  result  double (or m u l t i p l e )  such b e h a v i o u r a l  invasion(s)  d i f f e r e n c e s may  result  (McPhail from  1984)  therefore  historical  rather  than s e l e c t i v e i n f l u e n c e s . If be  behaviour  unreasonable  and to  morphology are t i g h t l y c o r r e l a t e d i t may  attempt  c o n t r i b u t i o n s to f o r a g i n g . morphology  and  to  separate  their  individual  Indeed a g e n e t i c c o r r e l a t i o n between  behaviour would r e s u l t  i n a c o r r e l a t e d response  94  to  selection  character', The  and  a  'trophic  comprising aspects of both morphology and  behaviour.  existence  handling  of  possible  such  a b i l i t y of  benthics, McPhail  the  F1  evolution  a character hybrids  of  i s supported by the  of  Enos  Lake  compared to e i t h e r of the p a r e n t a l  limnetics  limnetic foraging,  certainly  Forward  behaviour and  tightly correlated.  contribute  to  behavioural  forms (Bentzen  Arctic Grayling  variation  apparent  linkage,  contributions component  it  of  in  O'Brien  may  prove  individual  plankton  to  eye  1982). difficult  was  interpopulation  behavioural  however, i t would  suggest  genetic  s i n c e the  control, regimes.  limnetic  lab-reared  In t h i s i n s t a n c e ,  t a r g e t of s e l e c t i o n and  again the  the p r e d i c t e d d i r e c t i o n .  The  No  is  case under  behaviour alone would be  interpopulation  responses  the are  r e s u l t s however, i n d i c a t e that gillraker  morphology  probably  intermediate  and  Artemia.  G i l l r a k e r morphology may which  from  f i s h experienced s i m i l a r  performance of the  l i m n e t i c morphs on  entirely  behaviour  contribute  superior  behavioural  I f t h i s i s the  in  the  in  to d i s t i n g u i s h the  interpopulation differences to  prey  examined i n t h i s study and i t  differences. that  diameter have  As a r e s u l t of t h i s  characters.  of l i m n e t i c feeding  almost  feeders.  limnetic  i s p o s s i b l e that the observed d i f f e r e n c e s r e s u l t  particle  and  of head morphology  increased  reactive distance  (Schmidt and  morphology are  Many f e a t u r e s  p o s i t i o n i n g of the eyes and  been shown to increase  in  and  1984).  For  feeding  poorer  i s retained  set a lower l i m i t (Hyatt  1979).  The  on the  size  of  p r o b a b i l i t y that  95  an  i n d i v i d u a l plankter  buccal  cavity,  retention thought  (Drenner to  (e.g.  Seghers 1975; is  the  Typically minimum  particle  may  spacing  The  and  f o r aspects  mechanism of  of  retained. exceeds  Some the  Intrapopulation  point  s p e c i e s of  gillrakers  is  (Wright  many  must  exist  at  variation  may  would account f o r the l a c k of Interpopulation  greater  density  By  should c o n t r o l  fewer  'step'  plankton minimum  of  the  are  spacing nauplii.  c o n t a i n such a step, which  correlation  within  the benthic p o p u l a t i o n with  i s a s i g n i f i c a n t l y poorer  than e i t h e r the intermediate  than  1983); here  populations.  c o n t r a s t s however do c o n t a i n s i g n i f i c a n t  i n raker morphology and gillraker  complex.  constraints.  which  and  particulte  more  et a l .  dimension not  these  be able to i d e n t i f y a  which  size  In  spacing  somewhat  at  maximum  gillraker  (e.g.Polyodon  s i z e c l a s s of Artemia n a u p l i i one  composition  1971;  feeders'  other  is  and  some t e l e o s t s ,  and  retained  is  In  between  of s i z e - s e l e c t i v i t y and  in g i l l r a k e r  gillraker  Heitz  relation  might have allowed  only one  the  numerous s t u d i e s  a g a i n , behaviour seems to modify morphological using  of  act p a s s i v e l y as a s i e v e .  role  size  Magnuson  'filter  be a d i r e c t  the  into  architecture  understood.  For Gasterosteus  however,  function  gillraker  1983).  so-called  gillrakers  particle size.  a  1970;  imperfectly  i n s t a n c e s there may  feeders  between  Wright et a l .  particularly  be  passing  a p l a n k t o n i c e x i s t e n c e , and  Kliewer  still  spathula),  to  after  Hence i n c r e a s e d g i l l r a k e r d e n s i t y  correlation  planktivory  escape,  thought 1977).  permit  have drawn a  action  is  will  breaks  its  reduced  planktonic  forager  or l i m n e t i c p o p u l a t i o n s .  96  I  was  unable  morphology  of  intermediate the  fish  determine  from  Bear  characters  tested.  limnetic  sample. is  limnetic  associated  T h i s may  not  with  intermediate and  the  out  may  of  be  a  The  littoral  regions  littoral  1983).  Although  to  population  spends  environment. pelagic benthic The  zone  a  Artemia  was  of  the  morphology  of  the  within of  generation Gasterosteus  which i s o f t e n  prey  contains  (Gross an  and  extensive  pelagic  region  In Bear Lake the  in  breeding  majority  of  In c o n t r a s t , Grant Lake the  its  life  contains  in  a  no  pelagic  appreciable  p o p u l a t i o n i s c o n s i s t e n t l y s u b j e c t to a  environment. results  differences  in  of  this  study  indicate  that  type.  The  marginal  p o p u l a t i o n t r o p h i c morphology are s u f f i c i e n t  produce d e t e c t a b l e d i f f e r e n c e s i n f o r a g i n g success prey  the  densities  of  large  of  for more than a month and a h a l f , hence the the  and  on  limnetic Lake  from  This i s also true  a f t e r breeding,  which f i s h no doubt contact plankton. last  total linked  success  Populations  zone, i t i s dominated by  season does not  the  gillraker  Bear  from  of  i s more c l o s e l y  gillraker  consequence  accompanied by a d i e t a r y switch Anderson  terms  Efficiency  f l u c t u a t i n g s e l e c t i v e pressures. move  in p a r t r e s u l t  in  then,  success.  limnetic.  i n t o an  significantly different  UPJL  higher  intermediate  translated  i n the p r e d i c t e d d i r e c t i o n .  foraging  intermediate  For  the  was  d i s t a n c e , the i n t e r m e d i a t e  intermediate for  Lake  Although,  the benthic morph, UPJL was  the  whether  foraging e f f i c i e n c y .  morphological to  to  implications  of  this  result  on are  a  to  given  two-fold.  97  Firstly,  the r e s u l t  supports  the hypothesis  that d i f f e r e n c e s  p o p u l a t i o n t r o p h i c morphology, w i t h i n the Cowichan drainage, adaptive  responses  to  the  primary  small l i m n e t i c prey or a l a r g e such  variation  genetically race  to  be  adaptive variation  is  clearly  distance  alone  may  population however  to  racial  be  the  proximity  degree  (Turesson for  be  considered  a  independence and  an  benthic  1922). the  and  i s o l a t i n g mechanism.  Geographic  maintenance limnetic  of the intermediate and  of  morphs;  l i m n e t i c morphs  In t h i s  Once two is  seasons of the two  forms e s t a b l i s h d i v e r g e n t  established  for  incipient  Hagen (1967) has demonstrated that  anadromous  must  instance  of h a b i t a t s e l e c t i o n must be o p e r a t i n g to maintain  framework  1963).  be  for  differences, interpopulation  r a c i a l d i s t i n c t i o n , as the breeding  the  Secondly,  population  genetic  responsible  i d e n t i t y between the  concurrent.  prey).  each  Given  ecotypic  p r e c l u d e s d i s t a n c e as an some  benthic  independent; each p o p u l a t i o n must  significance  are  resource consumed ( i . e . a  maintained  (sensu Dobzhansky 1951).  in  forms  of  Gasterosteus  h a b i t a t c h o i c e , and Hay  and McPhail  the  forms are  habitat  choice  isolation  (Mayr  freshwater  and  separate d u r i n g breeding (1975) have shown that  by  these  forms e x h i b i t p o s i t i v e a s s o r t a t i v e mating, based in part on male choice  (McPhail and Hay  As yet there are no ecotypes  1983). data  on  assortative  between  i n the Cowichan drainage, however the i n v e s t i g a t i o n of  t h i s p o s s i b i l i t y would be p a r t i c u l a r l y provide  mating  insight  into  between the sympatric  the species  origin pairs.  of  interesting  as  reproductive It  would  be  it  may  isolation of  great  98  interest  to know whether s e l e c t i o n maintains r a c i a l  distinction  a f t e r secondary c o n t a c t , or whether h a b i t a t s e l e c t i o n has l e d t o isolating  mechanisms  as  Certainly  many l a b o r a t o r y  a  byproduct  however,  Sage and Selander may  speciation. Grosse  need not r e s u l t  achieved  through  A similar conclusion  (1980)  to  that  morphological  Gross  changes  radiation  polymorphism  was  reached  by  of  trophic  rather  than  Turner  f o r the d i f f e r e n t i a t i o n of I l y o d o n .  and  C l e a r l y the  next stage of the c u r r e n t r e s e a r c h must be the i n v e s t i g a t i o n assortative  mating  between  c o n t a c t , i n an attempt racial  integrity  trophic  to i d e n t i f y  in  in reproductive i s o l a t i o n .  (1975) have shown that  be  change.  (e.g. Dobzhansky and  1967; D i j k e n and Scharloo 1979 ).  morphology  morphs  response  under c o n t r a s t i n g s e l e c t i v e regimes  Pavlovsky  genetic  i n v e s t i g a t i o n s have demonstrated  i s o l a t i o n may a r i s e as a p l e i o t r o p i c shifts  of  morphs  the  at  some  mechanism(s)  i n Gasterosteus i s maintained.  of  zone of by  which  99  GENERAL DISCUSSION Heuts  (1947)  recognized t h a t n a t u r a l s e l e c t i o n appears t o  favour d i s t i n c t complexes of genes c o n t r o l l i n g p l a t e morphs, different  ecological  niches,  and that t h i s s e l e c t i o n would by  d e f i n i t i o n g i v e r i s e to adaptive study  in  divergence.  In  the  present  I have attempted t o demonstrate that s e l e c t i o n on t r o p h i c  morphology  may  Unfortunately,  also  lead  to  population  with no knowledge of the founder  term 'divergence'  in  this  instance  must  divergence. p o p u l a t i o n , the  describe  only  the  r e l a t i v e d i f f e r e n c e between p o p u l a t i o n phenotypes (although each population  has  ancestor).  The response of t r o p h i c phenotype t o d i f f e r e n c e s i n  primary  most  1984;  comparisons Schluter  a d a p t i v e divergence demonstrated,  and  from  a  common  marine  (e.g. L i s t e r  1976;  Grant  The s i g n i f i c a n c e of  1984).  t o s p e c i a t i o n i n Gasterosteus  certainly  establishment  conditions  of r e p r o d u c t i v e i s o l a t i o n  seem to be present  i n t h i s system.  whether  reproductive  although  the  latter  isolation are  selection  systems  identified  f o r Gasterosteus  1984).  diverged  resource type consumed has been demonstrated p r e v i o u s l y  in i n t e r s p e c i f i c McPhail  likely  remains t o  appropriate (e.g. r a c i a l  to  and  be the  integrity)  One can only s p e c u l a t e as t o would l e a d to mating  thought  (Templeton  Bentzen  to  1981),  be some  (Hagen 1967;  fostered  barriers, by  sexual  of which have been  Ridgeway  and  McPhail  I n t e r e s t i n g l y , sexual s e l e c t i o n may be based on t r o p h i c  f e a t u r e s alone  ( R a t c l i f f e and Grant  There a r e s e v e r a l q u e s t i o n s variability  described  in  1983).  that remain with r e s p e c t t o the  Chapter  1.  For  example,  how  100  generalized  i s the i n t e r p o p u l a t i o n response  to  resource?  primary  show  .multiple  (Schluter river  system,  different.  Within some s p e c i e s p o p u l a t i o n s appear to  solutions  and  Grant the  In  of t r o p h i c phenotype  to  similar  1984),  response  addition  selective  constraints  i t i s p o s s i b l e that  i n a separate  to  selection  the  phenotypic  by  selection  morphology may be m o d i f i e d  might  be  response on  entirely  of t r o p h i c  linked  character  suites. The  extensive intrapopulation v a r i a t i o n  study a l s o deserves i n v e s t i g a t i o n . recombination maintained  of  by  suggested  the  some  Is  identified  i t due  simply  in this to the  d i p l o i d genome each g e n e r a t i o n , or i s i t  selective  force?  Reimchen  (1980b)  has  that l a k e - d w e l l i n g p o p u l a t i o n s of G a s t e r o s t e u s may be  s u b j e c t to c r y p t i c  intralacustrine  environmental  differences,  which p r e s e r v e polymorphisms w i t h i n each p o p u l a t i o n . Given apparent  the  divergence  of  these  populations  the  cichlids  suggested may  be  their  i n d i v i d u a l g e n e t i c i d e n t i t y , why has there not been the  e x p l o s i v e r a d i a t i o n of freshwater b i o l o g i c a l in  and  (review  s p e c i e s as  i n Greenwood 1974).  that the g e n e t i c i d e n t i t y l a r g e l y independent  of  Bell  freshwater  of adaptive morphology.  evident  (1976) has populations If this i s  the case, there must be c o n s t r a i n t s a c t i n g on freshwater systems of G a s t e r o s t e u s .  One p o s s i b l e source of c o n s t r a i n t  is  history.  C i c h l i d s a r e a very o l d group (Greenwood 1984) and a r e l i k e l y to have been s u b j e c t to many more t r a n s i e n t course  of  their  evolution,  changes i n lake l e v e l .  primarily  Although  i s o l a t i o n events i n the those  Gasterosteus  a s s o c i a t e d with has  experienced  101  geomorphological  events,  preserved i n r e f u g i a and  cichlid  have undergone m u l t i p l e  i s u n l i k e l y that there were any populations  of  pleistocene. therefore followed The Wootton  (1984)  British  evolution  to be c h a r a c t e r i z e d  rederivation  second  in  freshwater  appears by  g l a c i a l refugia  Gasterosteus The  populations  for  that  on the  during  the  may  extinction  1976). be  internal.  range of v a r i a t i o n e x h i b i t e d  G a s t e r o s t e u s ( i n c l u d i n g such anomalies as the  loss  elements)  plasticity'  represents  an  'evolutionary  constraint.  There are a v a r i e t y of p o s s i b l e  mechanisms:  genetic  1980);  stochastic  (Cheverud  1984);  (Mayr 1983); and  gene  complexes  underlying  have been r e o r g a n i z e d is  constrained  systems may rather  be  by forced  to  than s p e c i a t i o n .  speciation  remains  system t r o p h i c speciation.  The  unclear  speciation  mechanism promoting the 1984)?  constraints  through  under  As  (Alberch  1976).  The  only.  The  trophic  complexes.  respond  r a d i a t i o n may If  (Bell  t r o p h i c morphology do not  extant  skeletal  developmental  (Chapter 2), t h e r e f o r e the  of  appear to expression  a result,  trophic  be  1982),  the c o n s t r a i n e d  is  evolution  so  species  and  however in t h i s alternative  constrained, of  the  polytypism  r e l a t i o n s h i p between a d a p t a t i o n (Gottlieb  by  internal constraint  ecological  present r e s u l t s allow comment on genetic  the  stickleback  by p e r i o d s of  speciation  It  freshwater  Columbia of  probably  recontacts.  from the marine form ( B e l l  constraint feels  were  what  pairs  to  i s the (McPhail  102  REFERENCES  Alberch,P. 1980. Ontogenesis and morphological Amer. Z o o l . 20:653-667. Aleev,Y.G. 1969. Prog. Sc i .  diversification.  F u n c t i o n and gross morphology i n f i s h . I s r a e l Trans. Nat. Tech. I n f . Serv. S p r i n g f i e l d , VA.  A l l e y , N . 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