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Of flies, fitness and fluctuating environments Roff, Derek A. 1976

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OF F L I E S , FITNESS &.N.D FLUCTUATING  ENVIRONMENTS  EY  DEREK A. EOFF B . S c . ( H o n s . ) , Sydney U n i v e r s i t y ,  1971  A THESIS SUBMITTED IN PARTIAL FULFILLMENT O.F THE REQUIREMENTS  FOR THE DEGREE OF  DOCTOR OF PHILOSOPHY in  t h e Department o f Zoology  He a c c e p t t h i s  thesis  reguired  THE  UNIVERSITY  as c o n f o r m i n g standard  OF B R I T I S H C O L U M B I A  NOVEMBER?, „ 19267 (T)  t o the  Derek A. R o f f , 1976  In presenting t h i s thesis in p a r t i a l f u l f i l m e n t of the requirements for an advanced degree at the University of B r i t i s h Columbia, I agree that the Library s h a l l make i t f r e e l y a v a i l a b l e for reference and study. I further agree that permission for extensive copying of t h i s thesis for scholarly purposes may be granted by the Head of my Department or by h i s representatives.  It i s understood that copying or p u b l i c a t i o n  of t h i s thesis f o r f i n a n c i a l gain s h a l l not be allowed without my written permission.  Department of  2 Q OL O  C^W  The University of B r i t i s h Columbia 2075 W e s b r o o k P l a c e V a n c o u v e r , Canada V6T 1W5  Date  \X /l/tyvt^LtW /f7/£  i  ABSTRACT  Environmental determining  heterogeneity  the  amount  population.  Previous  importance  of  genetics  heterogeneity character. size  for The  i n an  the  study  i s concerned  fitness,  organism  and  i t s development  may  be  used  parameters, size.  r , i s determined  as  a  or  not  A model i s p r e s e n t e d  temporal  to  direct  predation  variation effects  o r due  time.  model  not  parameter organism studied.  on  body  values f o r which  To  from  T h i s group i s the  D£Osop_hila melafi03astern  The  two and  size.  life  with  other  life  size  characters  that the  have  The the  history  hence t h e  in  implausible  factors  body  latter history  of  T h i s e f f e c t may  model i s d e v e l o p e d  these  important  the e f f e c t  as  demonstrate  result the  size upon  environmental  a c t s d i r e c t l y upon  that r e l a t e s  body s i z e .  study  the f e c u n d i t y of  changes  selection  to effects  development does  on  by  These  of  the  ecological  present  of  Is  t o body s i z e  measure  whether  and  time.  correlated  for  a  the e v o l u t i o n o f body  poikilotherm.  of  within  ecologically with  in  analysed  The  consequences  particular  measure  are  variablity  a  'r-selected*  characters  have  g e n e r a l framework.  analyse  important  variation  studies  spatio-temporal  to  be  genetic  theoretical  w i t h i n a very  attempts  of  may  body  spatial be  due  selective such  as  b e h a v i o u r .of t h e assumptions  or  with r e f e r e n c e to  been  D r o s o ^ h i l a and  reasonably most  an  well  particularly,  c o n c l u s i o n s drawn from  the  model  ii  are the  that  s p a t i a l and t e m p o r a l  optimum  'rare'  events  evolution conditions.  of  v a r i a b i l i t y can  body  size  and  may  have  significantly  body  size  than  t h e range  t h e most  determine  i n body s i z e more  effect  frequently  both  and  that  on  the  occurring  iii  TABLE OF CONTENTS  LIST OF FIGURES XiIST  iv  OF T A B X E S • • • • • • • * • • • » • • • • • • • * • • • * *••*•• *'••••• • > • • * • • • • v 1  F X R ST T HO UGHTS  •  •  • • • • * • • • • • • • • • • • ••••#"* • •• * * •  1  I NT ROD OCTXO H « • • • • • • •••••• • • • • •«• • * • • • • • • • • • • * • • • # • • • • •  THB LIFB-HISTORY CHAR ACTERISTICS OF DROSOPHXLA . . . . . . . . . . . DEFINING THE ENVIRONMENT- . . . . . .  6  , ......... ... .......... . . .12  CASE 1 : NO EE PRODUCTIVE COST TO DISPERSAL  . . . . . . . . . . . . . . . 1 4  CASE 2 : DISPERSAL REDUCES FECUNDITY . . . . . . . . . . . . . . . . . . . . . 2 7 DISCUSSION . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4 7 FXGURES T A BTi ES  • •  • •'•«•• • *  • * • • «•  REFERENCES  • » " * ' « * ' • ' • " » • • • • » " « . • # • -56 :  •'•'«••• « • •'  • • • • • •• • • •  • - •  ** • • •*  m-  •"  • •'••;•'§ •. * ' * ' • • ' •''••'•/ • •• •• 7 U  » • • * • • • •• • -=• » » • • • • * • • • # •  iv  L I S T OF FIGURES  Figure  Pagje  1. The l a r v a l are  development  idealized  • Drosophila. 2. The  different from  yeasts  of  found  time.  Type S y e a s t s  is  Type  type  site a  of  development  Map :  showing  a l l  and  cactus  the  proabiiity  fruit  . . . . ... .. 7. The f r e q u e n c y  may  time.  The p r o b a b i l i t y o f a  i s f and t h e p r o b a b i l i t y i s 1-f  larvae the  e i t h e r type F yeasts or  as  yeast  a  average  function  species.  of  Data  the from  v»->. 61 p e r c e n t a g e o f Type S y e a s t s p e r  i n the 5 l o c a l i t i e s  sampled  by Wagner  •w-v.vi-vyy .-Vr.!V*  distribution  of 60  •.•••.^.^.^  . . ..  sites  on t h e r a t e o f i n c r e a s e  contain  Type F y e a s t s  and  of  i s 1-p. >--.w.v.Vy>-v^  ?  the  at  p  T y p e ...s y e a s t s  time  type  containing  D^ rauileri  Bagner (1944) . ,•• 6.  Data  The p r o b a b i l i t y o f a l l s i t e s  a t some g i v e n  containing  5. S u r v i v a l  on t h e  p l a n t , Ofiuntiav  t h e same y e a s t  o f changes i n a d u l t s i z e  containing  site  larvae  s i z e on t h e r a t e o f i n c r e a s e  a l l contain  F yeasts  S yeasts  in  58  ., . . < «hen o v i p o s i t i o n s i t e s S  observed  .•yv>VvVVrvv..-.57  lulleri  host  These  (1944).  given  4. The e f f e c t  study.  actually  Drosophila  o f changes i n a d u l t  -,, c o n t a i n i n g  in this  those  in their  when o v i p o s i t i o n s i t e s any  of  used  .-. .... .. .. .. ....,  curves  Wagner  3. The e f f e c t  versions ..  growth  functions  o f Type S y e a s t s  (1944).  .. in  Austin  62 and  Crestonio, 8.  The  effect  Data from of f l i g h t  confidence 9.  limits  Differences flies  considered between drop  and  10.  The  egg  not  11...The e f f e c t  The  effect  of  The  was 1mm  effect  cost* See  days f o r  shows  the  days  3  duration  group than the + 2 standard  text  on  (day and  o f a one  days  production  flight  3)  the  4  is  unflown  errors.,  hour f l i g h t  for  Confidence l i m i t s  method  of  shown a r e  + 1  •/•'••••••'•»v-»: , >; ,  e g g - p r o d u c t i o n on  duration  rate  as  a  and  Gilmour  of  changes  when  flight  a  in  the  day 67  two  c a l c u l a t e d on has  adjacent  :  flight  from Chadwick  increase  after  flown  of the  13..Respiration  14.  -  : 7  on  flight. /  production  Data  64  '»'•• • «'v*^»v/«'-».• •  of f l i g h t  -, p r o c e e d i n g  errors.  axis  shown a r e  cost.  s^cincLciircl ©irjror* .;• •••  x  between  'reproductive  this  63  d i f f e r e n c e i n egg  f o r the  mel anqga s t e r  calculating  The  Note t h a t  Confidence l i m i t s  Drosophila  12.  production  production  estimated  + 2 standard  y a x i s the  greater  .  production  flown.  days.  egg  significantly group.  egg  shown a r e  the  these  in  on  between  f l o w n and  Wagner(1944)  the  on  days proceeding function  in  1940  adult  the  flight.  and  size  d e c r e a s e i n egg  a fly  of  production  of  1947,  the This  rate  of  reduction  thorax 20  68  frequency.  Chadwick  on  egg  ........  of wingbeat  reduces fecundity. basis that  combined  length  eggs per  day  vi  15. The  size  distribution  compared t o a c o n t r o l , the  junction  Ion Qf 16. The  u cLxn&X size  of  sample  non-dispersing  flies  (n=36) .measurements made from  of l o n g i t u d i n a l  veins 1 and 2 t o the end of  i n 2 •. • • * * •.• ••>•••; ••••vvv v>' »-»>••••••: • vvvv>'y''*-'«''»> ,. 7 'I >  -  :  :  distribution  of  sample  non-dispersing (n=44) .  flies  Heed (1971) .) dU  :  : :  D^limica. 73  Data  (n=38)  .•.:\^/,,,r,,«;vvvtv,i.'.,.,72  17. S i z e d i s t r i b u t i o n o f n a t u r a l and 1st g e n e r a t i o n of  :  :  compared t o a c o n t r o l  stocks  (n=17)  from  laboratory  Kambysellis  and  vii  L I S T OF  TABLES  Table  Pag^e  1. P a r a m e t e r e s t i m a t e s f o r D.  melanoqaster .  2.  production  Effect Egg the  3.  o f cage s i z e production  egg  Effect  4.  Effect  o f cage s i z e  9.clu Xi-S• 5. C o m p a r i s o n  •  The  to  raelanoo^ster*.  production  • • •• • • "* • dispersal  clx£•£©ir€H^ cl^sn s x 11 s s • 6.  cage compared  n  on egg  in  i n one  d e n s i t y on t h e s i z e and  the  D.yme 1 anoga:ster.  ........  •••• •• of  74  o f 15 f e m a l e s i n 15 v i a l s .  between egg p r o d u c t i o n  of l a r v a l  in  o f 15 f e m a l e s i n a l a r g e  production  Comparison  on egg  ..  •*  mean number o f males  • • •-•  D.. gallon  containers  number o f e m e r g i n g • * •"•'•*••  r a t e s of f l i e s  reared  • • • > 77 under  ••••«••••«•••*•••••*••«*•• * and  females  75  remaining  after  73 3  IJSST  THODGHTS  'The t h i n g c a n be done,' s a i d t h e B u t c h e r , '.I t h i n k . The t h i n g must be done, I am s u r e . The t h i n g s h a l l be done! B r i n g me p a p e r and i n k , The b e s t t h e r e i s t i m e t o procure.» The B e a v e r b r o u g h t p a p e r , p o r t f c l i o , p e n s . And i n k i n u n f a i l i n g s u p p l i e s : W h i l e s t r a n g e c r e e p y c r e a t u r e s came o u t o f t h e i r And watched them w i t h wondering e y e s . So e n g r o s s e d was As he wrote w i t h And e x p l a i n e d a l Which t h e B e a v e r  dens  the. B u t c h e r , he heeded them not., a pen i n e a c h hand, l the while i n a popular s t y l e could well understand,  ' t a k i n g Three as the s u b j e c t t o r e a s o n aboutA c o n v e n i e n t number t o s t a t e We add Seven, and Ten, and t h e n m u l t i p l y out By One Thousand d i m i n i s h e d by E i g h t . 'The r e s u l t we p r o c e e d t o d i v i d e , as you see, By Nine Hundred and N i n e t y and Two: Then s u b t r a c t S e v e n t e e n , and t h e answer must be E x a c t l y and p e r f e c t l y t r u e . •The method employed I would g l a d l y e x p l a i n , W h i l e I have i t so c l e a r i n my head, I f I had b u t t h e t i m e and you had b u t t h e b r a i n But much y e t r e m a i n s t o be s a i d . M n one moment I ' v e seen what has h i t h e r t o been Enveloped i n a b s o l u t e mystery, And w i t h o u t e x t r a c h a r g e I w i l l g i v e you a t l a r g e A lesson i n Natural History.' from  "The  Beaver's  Lesson"  XlaS. H u n t i n g o f The Sjiark by Lewis  Carroll  2  INTBODUCTION I t i s a c l e a r and obvious f a c t that spatially  and  formulate  mathematical  genetics  temporally  ignored  variable.  models  in  the  Yet  early  ecology  this variability.  unimportant.  Rather  i t was  mathematical model , j u s t l i k e an must  proceed  analysed  and  considered  1973,  our  (Andrewartha  Holliag  each  picture and  spatial  Darwinian  discussed  (1973), den Boer that  investigation  component  may  be  most  has  increasingly  of  how 1954,  the  natural  den Boer  world  1968, May  1973).  and  present a model  temporal  fitness  of  an  s p a t i a l and temporal v a r i a b i l i t y been  ;a  However, the assumption of  Birch  c o n d i t i o n s may be of c o n s i d e r a b l e the  variability  pragmatic n e c e s s i t y  i n time and space  In t h i s t h e s i s I w i l l that  because  a s i m p l i f i c a t i o n that cannot be made without  grossly distorting functions  such  experimental  understood.  environmental homogeneity been  ecological  T h i s was not done  a  both  from the simple t o the complex. I n t h i s way the  importance and s i g n i f i c a n c e of easily  is  attempts t o  and  of o v e r s i g h t or because i t was thought t h a t was  world  in  that  demonstrates  in  environmental  variations importance organism. in  in  The  ecological  determining  importance of genetics  has  a g e n e r a l way by D i c k i n s o n and A n t o n o v i c s  (1968), Levins (1968) and o t h e r s .  The  model  w i l l be presented i n t h i s t h e s i s i s g e n e r a l i n the sense  t h a t i t may apply to a wide range of organisms but s p e c i f i c i n t h a t a l l f u n c t i o n a l r e l a t i o n s h i p s have  a  biological  meaning  3  and  r e f e r to p a r t i c u l a r l i f e The  in  case  to  be  history characteristics.  considered  a colonizing poikilotherm.  analysed  is  'what  increase  over time  cannot  be  freguently will  be  size ?'  determining  only  maximise be  that the  this  to  be  also  or  most  Further,  are  of  question  average  temporal  s i z e but  body s i z e  average rate  conditions.  and  optimum  of  question  the  shown  considering  spatial the  evolution  specific  environmental  that  not  will  by  occurring shown  The  It will  answered  i s the  it  capable  of  range  in  the  sizes. The  reason  colonizing  for  limiting  organisms,  organisms,  i s to  or  avoid  the  the  scope  more very  of  generally  i n t e r a c t i o n s . Such p r o b l e m s a r e  the  treatment  outlined  tackled  computer s i m u l a t i o n .  probably the be  best  number o f very  The offspring between two  parameters i n v o l v e d  great  situations  by  and  with rate  is  reference of  that  i t  increase,  survive  parameters  are  correlated  character  also  as  the  amenable and  with  upon  developmental  by  the  length  be  size;  increases  to are  increase  consider  by  in may  such  studies.  the  It will  Thus s e l e c t i o n a c t i n g  such  The  to  r, i s determined  reproduction.  reproduction.  best  t o r e p r o d u c e and  but  not  thesis  p a r t i c u l a r case  and  fecundity  this  to  •r-selected'  under such c i r c u m s t a n c e s  birth  increases  in  probably to  study  d i f f i c u l t problems imposed  intra-specific analytic  this  of  of  time  shown t h a t  these  increasing  size  the some  rate  number  age life  will  at  first  history  result in a  4  change  in  body  environmental either  on  size  thesis  may  or  act  I  as  indirectly  a b s t r a c t model w h i l e b e i n g  i n a p p r o p r i a t e t o any  may  this  c h a r a c t e r w h i c h i n f l u e n c e s body  An  the  In  heterogeneity  directly  history  be  size.  will a  biologically  present  the  model  with  To  selection  agent  some  correct  s i t u a t i o n because  are  D£osop.hila  i  reasonably The  values  a v o i d t h i s problem I  reference  well  may  either  parameter  to a particular  known.  will  group  o r g a n i s m s f o r w h i c h t h e r e q u i r e d r e l a t i o n s h i p s and values  life  size.  mathematically  'real world'  unrealistic.  how  through  f u n c t i o n a l forms of the submodels or t h e be  show  of  parameter  T h i s group i s the  genus  genus D r o s o p h i l a i s s u i t a b l e f o r s e v e r a l  ether  reasons, 1)  there  i s considerable inter-specific  s i z e , f o r example, the Hawaiian body  length  (Carson  familiar  species  D..  has  with  Prevosti  1971,1973,  geographic  1955,  David  ( S t a l k e r and  Carson  and 1948)  Heed  location  1962,  ( S t a l k e r and  Sokoloff  1965,  Bocguet 1972,1973,1974,1975), or season  ( S t a l k e r and  stage body  not  a  result  (although size).  of environmental  David altitude  Carson  c o n d i t i o n s i n the  c o n d i t i o n s i n the l a r v a l  stage  do  may  Carson  T a n t a w y 1 9 6 4 ) . T h e s e d i f f e r e n c e s h a v e been shown t o be and  a  melanogaster  body s i z e v a r i e s w i t h i n a s p e c i e s , s u c h v a r i a t i o n  associated  1947,  times  D., c ^ r t o l o m a  et a l 1970).  2) be  five  species  v a r i a t i o n i n body  1949, genetic larval  influence  5  3) lying  the  heritability  between  0.2  and  of  body  0.4,  and  response  to  conditions  produces a s i g n i f i c a n t  3  or  selection  4 generations  Druger  1962,  and  Kojima  the  laboratory  size  1966,  (Anderson Thus  variable,  under  (Robertson  Tantawy e t a l Tantawy  and  Reeve  Tayel  and  a high  the  environmental within  Robertson  Rafcha  Flies  1964,  1960, Frahm  retained  in  a l s o show c h a n g e s i n body Bocguet  Drosojohila  genetic  of  and  1970).  high,  importantly,  1952,  Tantawy  1966,1973, D a v i d in  more  deviation detectable  years  size  i s relatively  variety  f o r a number o f  body has  ,  a  1964,  and  size  1975).  i s a character  component  and  which i s  will  respond  to  different  species  of  selection. The  population  £ £ o s o £ h i l a have not  dynamics  been  available  suggests t h a t ,  not  utilise  fully  selected* 1957,  w e l l s t u d i e d . The in general,  a v a i l a b l e resources  organisms  Tantawy  of  1964,  ( B i r c h and Pipkin  information  Drgsojahila p o p u l a t i o n s and  are  B a t t a g l i a 1957,  1965).  that i s  therefore Da  do 'r-  Cunha e t a l  6  M I I z SIS TORY CH1RACTERS OF DHQSOJiflliA--  2111  In  this  section  characteristics £i  of  fflglgnggaster  In  A  assigning  not  fuctions  attempted  necessary actual  if,  body  example,  in  size  this  in  D  study,  factors  the  characteristics life  simply  influence  of  from  values.  The  features  increase  2)  body  and  there  the  exist  growth the  increase  in  growth  of  at  curve  is  in D,_  of  larvae is  increases more o r  an  is  less  have  would  It  the  is  that  be  not limit  study  is  to has  melanoaaster>  The  data  on  species  body  are  used  concerning size  assumptions  does  or  not  parameter  characteristics of  the  the  model  that  are,  size are sets  markedly  curvilinear with  and  that  this  time two  with  model  the  hypothesis  body  and  organism  history  least  to  /  only  that  factors  development  with  concerned  purpose of  by  the  osop_hila  relationships  accuracy  the  size  development  growth.curve size  the  life  fir  melanoqaster.  unrealistic  initial  of  history  'reasonable'  of  variabilty  the  fecundity  instance  the  that  1)  3) which  of  the  size  |K  body  life  attempting  characteristics  biologically  for  were  :  been  are  degree  exemplified  environmental  necessary  that  describe  limit  demonstrate  result  are  may  history  to  to  species  have  of  melanoaaster  A  what  the  we  growth  show  on  a  the  functional  I  values  achieve  population  intended,  the  values  and  define  typical  defining  to for  shall  a  parameter  obtaining  I  time. linear;  correlated. of  conditions  different. such  In  that  the  the  the  second  rate  of  under  In rate  one of  instance increase  7  in  size  i s independent  4)  the  proportion  decreases with time beyond  which  In  of  such t h a t  no l a r v a e  larvae  Tinkle  et  1 9 3 3 , Green  fecundity general  al  i n body  i n fecundity  pupation  is  time  1966,  generally  and b o e r g e r  by  an  1969,  Salthe  The r e l a t i o n s h i p  1971).  c a n be d e s c r i b e d  size  (Clifford  1 9 5 6 , Bagenal  Hadley  1970,  and s i z e  to  survive.  by an i n c r e a s e  Mackerras  surviving  t h e r e i s some d e v e l o p m e n t a l  p o i k i l o t h e r m s an i n c r e a s e  accompanied 1974,  of time.  equation  between of  form,  (1)  Nocx^  where  N  is  the  number o f young, x i s some body  such  a s body l e n g t h  o r weight  the  organism  the  fecundity that  and  in  egual to 3  B a r k e r and P o d g e r The  daily  McMillan et equation p._  al  to  melano^asterx  egg  body  dimension and  dimension (Robertson  x.  Measurements  describe  on of  Ih £seudoobscura• i n d i c a t e  such  as t h o r a x l e n g t h  m  is  1 9 5 7 , Tantawy and V e t u k h i v  1970).  p r o d u c t i o n h a s been s t u d i e d  (1970  measurement  and m i s a c o n s t a n t d e p e n d i n g  p.. m e l a n o m a s t e r  i f x i s some l i n e a r  approximately 1960,  the  a,b). the  They  developed  daily  egg  i n d e t a i l by  the  following  production  in  N (t)  =  M(1.-e  )e  (2)  where N (t)  : t h e egg  to '.the M  day  : the  €jOL  the  : constants  H  size. case  upon  of  which egg  potential  Equation body  p r o d u c t i o n on  (2)  day  t  production  maximum d a i l y  egg  d e p e n d i n g upon t h e  begins production  strain  does n o t c o n s i d e r t h e e f f e c t  Eguation  (1) may  be  variable  body s i z e .  used  of  to extend  T h i s can  be  changes  equation  done by  in  (2)  to  replacing  by  M = H'X"*  where M'J.S The growth  a constant next  d e p e n d i n g upon t h e  life  f u n c t i o n of  history  the  suppose t h a t the l a r v a l  of  the  animal  kingdom  reproduction takes and  development  several  development time  general,  are r e l a t e d ;  to r e a c h  p a r a m e t e r t h a t we  F e n c h e l {1974)  in  has  body  the l a r g e r  s e x u a l m a t u r i t y . The time  workers.  s p e c i e s and  larvae. Intuitively  to  adult size.  (3)  has  David  will  s i z e and the  r e q u i r e i s the  i t seems  shown  strain.  reasonable  ba a f u n c t i o n  that, t h e age  animal  for at  the first  the l o n g e r  r e l a t i o n s h i p between  size  been measured f o r p.. me l a nog a s t e r and  Bocquet  (1974) measured t h e  i t  b  Y  adult  9  weight  and  duration  P.. I § l § n o g a s t e r  of development  31  x  French  They f o u n d  a significant  and  weight  body  strains  and  in  correlation  or  sex  in either  f o r the  of the French  the r e l a t i o n s h i p  differently  selected  significant  the  correlation  therefore,  there  assumption  that  is  strains  19 t r o p i c a l  females of the  tropical  strains  of p  A  Robertson and  body s i z e  and  but  development  melanogasteri.  evidence  development  to  no  strains  (1960  a,b)  time i n  He  between t h e s e p a r a m e t e r s ,  sufficient  time  Japanese  males o f t h e t r o p i c a l  strains.  of  strains.  between d e v e l o p m e n t  between s i z e  strains  Japanese  and  m a l e s and  i n the females o f correlation  studied  strains  both  significant  o f 47  found  a  over-all  justify  time a r e  ,  the  generally  correlated. The  developmental  phases,  the  growth and pupation  in  the  from  s l o w s and  size  is  can  oviposition  pupal p e r i o d .  be  divided  Prior  Thus  to  the  we  can  pupation, a period  constant or i n c r e a s i n g  of the  (Bakker  1959,  (Chiang  and  described  larvae  Robertson Hodson  may  et a l  1950).  by t h e e g u a t i o n s  These  two  time  of  d e f i n e two  the  the  and  no  periods rate  first  linearly  or  of  a period i n  increase exponentially or  of  where l i t t l e  with time  1968)  three  period  actual  i n which  i t i s d e c r e a s i n g to zero. During the length  into  to hatching, the  there i s a period  occurs.  h a t c h i n g and  increase which  the  growth  increase between  time  period  period  with with  time time  growth f u n c t i o n s can  be  10  T = ae  (4)  T = a + ct  (5)  where T i s the thorax l e n g t h  of  the  adult  (assumed  to  p r o p o r t i o n a l to the l e n g t h at p u p a t i o n ) , t i s the time hatching  and  the  between  moment the growth r a t e slows down, and  and c are constants. I have assumed that the d u r a t i o n second  phase  decreases) pupal  of  growth  of  a,b the  ( that i n which the i n c r e a s e i n s i z e  , the p e r i o d from o v i p o s i t i o n to hatching  period  be  are constant. Although  and  the  not p e r f e c t mathematical  d e s c r i p t i o n s of the growth curves equations  (4)  and  embody  are  sufficiently  the  general  characteristics  a c c u r a t e f o r the present two  study. The  and  general  shapes  (5)  of  do  these  f u n c t i o n s are shown i n f i g 1. The  differences  i n the form of the growth curves may  a t t r i b u t a b l e to d i f f e r e n c e s i n the type of the  yeast  upon  be  which  l a r v a e are f e d . T h i s i s shown by the growth of D.. m u l l e r i  l a r v a e on the nine yeasts found cacti  of  vary  from  the  larval  host  the genus, Ojsuntia (Wagner 1944) . The growth being  curvilinear The  on  more  or  less  linear  to  being  plant, curves highly  ( f i g 2).  final  parameters  s u r v i v a l r a t e s of l a r v a e and  necessary  to c a l c u l a t e r are the  a d u l t s . There i s only  one  study  11  on  the  s u r v i v a l of  and  Hodson  (1950)  proportion the  slope  larvae.  of of  line  Under of  several  cases  on  daily  depending  laboratory  any  resemblance  the  is  I  determined  by  the  that  the  length  of  time  may  wild.  of  larvae  which  growing',  that  (4)  and  (5).  The  proprtion  surviving declines  this  t i m e such  that  ely there  i s a p p r o x i m a t e l y an  survival in  rate  the  of  i s lower  been e x t e n s i v e l y no  reliable  effect small of  of  day  t h a n the  best  low  but  f o r the  studied d a t a on  changes i n the  I  reproduction a constant  under  parameters d e s c r i b e d  determined  of  survival not  adult  survival l a r g e l y by  1965).  For  given  In  this  are  equations  linearly 80  with  percent  rates  the  but  very  r  there  is  early  reason  i n Table  The  The very  period I  values 1.  is has  conditions. on  this  it  adults  conditions  rate  This  observed  that  s u r v i v a l p r o b a b i l i t y . The above a r e  bear  surviving  from  think  in  not,  larvae  s u r v i v a l of  laboratory  the  ' a c t i v e growth'.  s u r v i v a l under n a t u r a l  (Lewontin daily  do  w i l d . The  because r i s determined  assumed the  a  laboratory  unrealistically  is  surviving  time  or  of  much l o w e r .  the  in  time,  although  be  'actively  probabability  i s the  may,  proportion  with  The  laboratory  been f o u n d t o  in  Chiang  density  percent,  conditions  of  larvae.  linearly  the  90  survival rates  have assumed  of  initial  in  about  s u r v i v a l has  s u r v i v a l under  paper  the  conditions  The  to  survival  on  i s generally  the  development, t h a t  surviving declines  optimal  larvae  during  the  larvae  the  survival  larvae  have of  12  Having organism  we  The  the  for  l a r v a e of  been  Drosophila  species  (Carson  and  Carson  1958)  vary.  each s i t e  only  will For  classify  yeasts  F  (or  grow a t  or  the  wild  are  are  In  The  adults  temperate  of D r o s o p h i l a  have  exudates from v a r i o u s  tree  and  thus  describes  the  1951,  Carson  t r o p i c s l a r v a e may  living  sites  scattered  suitably  Drosophila.  Carson  (Birch  within  sites  on  As one  the  the  type  be  Battaglia  plant parts scattered  1952,  found  1957,  in  Heed  ( P i p k i n et  over  larval  flora  yeast  the  occurs.  type  of  present  types,  space  yeasts. constant  patch  al as  will,  in  assume t h a t  at  growth  upon which  d i s c u s s i o n we with  growth r a t e . Those  growth')  The  yeast  defined  i s curvilinear  less  i n each  approximation I s h a l l  upon t h e  i n t o two  a more o r  yeast  of  sake of  in length 'fast  of  a first  depend  feeding.  increase  in  which  growth  upon y e a s t s .  S t a l k e r 1951,  composition  general,  effect  of  in  habitats.  The  larvae  larval  fermenting  plant material  Breeding  'island'  and  our  situation.  i s one  of s e v e r a l s p e c i e s  the  whilst  P i p k i n 1965)  1966).  consider  feed  sites  be  1968,  environmental  of r e s o u r c e s  to  fermenting  the  c h a r a c t e r i s t i c s of  'islands'. This s i t u a t i o n  breeding  found  define  oviposition  space as  zones the  life-history  I wish to  distribution  and  the  must now  situation  suitable through  defined  with  of  they  are  can  respect  yeasts  rate  upon  time I s h a l l  broadly  to  their  which call  the Type  Those y e a s t s  upon w h i c h  larvae  rate  call  S  I shall  Type  (or  13  •slow  growth')  yeasts  i s c a l c u l a t e d from e q u a t i o n  growing In Firstly yeast  yeasts.  The s i z e  on Type S y e a s t s the  next  I shall  o f l a r v a e growing (4) and t h e s i z e  two  sections  consider  the  I shall  energy.  If  energy  come f r o m t h e same s t o r e f l i g h t the  consider  consequences  does n o t r e d u c e f e c u n d i t y . D i s p e r s a l uses  second  conclusions of entails  case the  a reduction  I  of  larvae  two  cases.  by e q u a t i o n ( 5 ) .  of  t y p e s i n t i m e and s p a c e where d i s p e r s a l  which  on Type F  shall  first  involves  for flight  variation between  patches  active  flight  and egg p r o d u c t i o n  may r e d u c e egg p r o d u c t i o n . consider  case  in fecundity.  are  to  in  what  modified  extent i f  In the  dispersal  14  CASE J 2 It energy not  i s assumed f c r egg  The  at  point  simple  can  only  new  to  separate  spatial  The  be  in  energy f o r f l i g h t  so  that  and  yeast.  thorax  lengths  i n c r e a s e . The  does  laying.  temporal d i s t r i b u t i o n  the  same  short  so  of  of  yeast.  patches f o r  that  a t any  'newly a r i s e n ' s i t e s .  time the  of  a r i s e a t time t might  suitablity  very  type  habitat  given  Thus  i s composed  Let  r^(T)  T  on  be  the  r a t e of  Type I y e a s t s  number o f  flies  and  r(T)  flies  although  at  types the  of  same  of f l i e s  the  at time t i s given  contain  time  of both  increase  For  oviposition  patches s u i t a b l e f o r o v i p o s i t i o n a l l c o n t a i n  type of  and  dispersal  eggs a f e m a l e i s c a p a b l e o f  patches that  o v i p o s i t e on  mGment  yeast,  are  DISPEBSAL  i n w h i c h a l l h a b i t a t s t h a t become s u i t a b l e  Type S y e a s t s . assumed  section that  i n time c o n t a i n  all  is  any  number o f  most  example, only  in this  types i s that  any  BEPBODUCTIVE COST TO  production  reduce the  yeast  NO  with  mean r a t e  of  by  ?Lr)t N  where N^(T)  i s the  assume t h a t  t i m e may  the  probability  probability interval a  (T)  number o f f l i e s  of  be  divided  Type  are  of length  t.  Now  into discrete intervals ,  with  S yeasts  duration  laid  T at time  occurring  occurring  of s u f f i c i e n t  eggs  (6)  = N^ (T) e  o f Type F y e a s t s  must be  female's  fc  being  being  p and  1-p.  The  that the  within  this  the time  majoritory  of  interval.  In  15  2i jelSHSa^ster t h i s two.  Equation  length  be o f t h e o r d e r  o f a week o r  (6) c a n now be w r i t t e n a s  V  t  where r ^ (T)  would  i s  the  Combining e g u a t i o n s  (T) = $  rate  of  o  (T) e  (7)  increase  per  txme  increment.  {6} and (7) we o b t a i n  (8)  The are  results  cf  be  achieved  only  cannot  than  Drosophila  10mm,  values  because  Type  S  than  T  so  from low  meet m a i n t e n a n c e  of a l a r v a the that  that  a r e present i s  i s so great  which may  physiological  length  i n f i g 3,  T^ on T y p e S y e a s t s  probability  being  yeasts  of  of p  (p=0) t h e  a length  r a t e o f l a r v a e . The t i m e r e g u i r e d  might a l s o r e s u l t yeasts  for  maximum, l a b e l l e d  survival  negligible  i s greater  However, t h e maximum t h o r a x  when  2.5mm. T h i s  greater  length  possible  constraints.  the  (8) f o r v a r i o u s  shown i n f i g 3. I n t h e a b s e n c e o f Type S y e a s t s  optimum t h o r a x not  s o l v i n g eguation  can  i s less  than  determined to reach  be  by  a size  that there  i sa  s u r v i v i n g . T h i s maximum, T^,  nutritional larvae  quality  of length  c o s t s . In t h e l a t t e r  of  greater  Type  S  than T  case the s u r v i v a l  16  of  larvae If  be a f u n c t i o n o f s i z e  the p r o b a b i l i t y  0  than  would  then  r a t h e r than  o f Type S y e a s t s  t h e maximum  time.  occurring  p o s s i b l e thorax  length  is  greater  is T  because  Cat  any  f l i e s that  available with  exceed t h i s  oviposition sites  thorax  lengths  greater  recombination,  and d u r i n g  selection  favour  will  (provided  that  assumption only  size  Type  S  not  leave  progeny  when  contain  only  Type S y e a s t s .  Flies  t h a n T^may  periods  an i n c r e a s e  other  implicit  will  i n t h e above occur  probability  o f Type F y e a s t s occurring  i s very  Under t h e s e  circumstances  length  fliss  and may  to  very  optimum  a  low t h e n  there  population  will  an  when  is  non  a  zero  the p r o b a b i l i t y  will  dominate t h e  crash  cause  a  i s high.  the  average  oviposition  sites  not s u r v i v e .  due t o m a s s i v e  o f Type S y e a s t s  be n o t o n l y  but a l s o t o  occur  of  e x c e e d T . However,  l a r g e r t h a n T^ w i l l  may  that  c  This  larval  occurring  to g r e a t l y reduce the  large  fluctuatuions  in  numbers.  Although probability  T  length i s  i s a chance t h a t  Thus i f t h e p r o b a b i l i t y  body s i z e  above  thorax  i n Type F y e a s t s  large population  low i t s e f f e c t  Note  when t h e r e  the p o p u l a t i o n  t h e progeny o f f l i e s  mortality. is  in  Type S y e a s t s  lead  length  occur  o c c u r r i n g . I f the p r o b a b i l i t y of  s e r i e s o f time i n t e r v a l s  eventually  i n thorax  (p=1) t h e optimum  f u r t h e r from T^. t h a n  of  genetic  i n which Type F y e a s t s  argument).  considerably  long  by  c o n s t r a i n t s do n o t s e t a l o w e r l i m i t ;  yeasts  Type S y e a s t s  be g e n e r a t e d  in  of only  the  ' r e a l ' world'  one t y p e  o f yeast  there  occuring  may  exist  at a given  a  time  17  the  more u s u a l s i t u a t i o n  is  proportion  of each  oviposition  site  probability  o f Type S y e a s t s  of  Type  F  there  yeasts  discriminate fly  type  varies  exists  T-f.  between s i t e s  of thorax  undoubtably over  time.  in  which  the  Assume t h a t a t e a c h  o n l y one t y p e  of yeast.  Let  the  o c c u r i n g be f and t h e p r o b a b i l i t y  Further  assume  that,  . Then t h e number  l e n g t h T produces per time  e  one  = fe  s  +  J  (1-f) e  flies  of  do n o t  offspring  increment  a  i s g i v e n by  (9)  t  Hence r(T)  Equation  = log^(fe  (10) i s p l o t t e d  +{1-f)e  4  )  (10)  in f i g4 for different  values  of f .  rtt?)  For and  flies  equation  of thorax  (10) r e d u c e s 'r(T)  Even A  a  r (T): by  low  available  If  Type  equals  + r^(T)  o f Type S y e a s t s  o f 10 p e r c e n t S  T^ , e  0  to  = log^d-f)  frequency  a t a frequency  0.105.  l e n g t h g r e a t e r than  yeasts  A.  y e a s t s r ( T ) i s reduced  significantly  reduces /\  Type S y e a s t s r e d u c e  comprise by  (11)  0.51.  40  per c e n t  r (T)  of the  Furthermore,  the  A  presence a  o f Type S y e a s t s  produces a l o c a l  v a l u e below T . The p r e s e n c e o f r e l a t i v e l y  low  maximum o f r ( T ) a t  percentages  of  Type  S  18  yeasts  may  severely retard  length  o f the population  a  high  very  population The the  frequency  presence  frequency The  Type  S  yeasts  when  i s valid  time  yeast  types.  I f t h e p e r s i s t e n c e time  than  one site.  (Roff  from  a  suggest  site  is  that  depend  a  that  patch  the  dispersal upon  is  of the p e r s i s t e n c e time  any D r o s q p h i l a  between  are  correlated  insufficient  many  do  seasons o r there i s a mixing  tendency be  of  for local little  differentiation consequence  data  of suitable  species. I f sites  with  in  the  of s i t e s  containing p a r t i c u l a r yeast  produce  local  differentiation.  distribution between them  of  habitat  patches  r e q u i r e s more s t u d y .  and The  give  sites  seasons to  term. types  any  suitable  between  respect  clustering  The  to  long  size  of a f l y  remain  of f l i e s  of  generations  ovipostion  not  with  greater  probability  for  the  t o remain a t  may t h e r e f o r e be a d e c l i n e i n t h e a v e r a g e s i z e There  by  d i s t r i b u t i o n of  some f l i e s  persists  estimate  may  of  positively  site.  the  o f a random  will  expect  from t h i s  for  largely  spatio-temporal  and t h e s p a t i a l  we miqht  1976). I n a s i t e  there  a patch  Experiments  dispersing  the  i s low.  between q e n e r a t i o n s  generation  reduce  very  the  t o which t h e a s s u m p t i o n  of  will  l e n g t h i s determined  persistence  the  yeasts  of  below T^.  o f Type S y e a s t s even  extent  of f l i e s  of  thorax  of such  thorax  i n c r e a s e s . The o c c a s i o n a l p r e s e n c e  mean t o a v a l u e optimum  t h e r a t e a t which t h e mean  size Local  may a l s o  spatio-temporal  t h e movement o f f l i e s  technical  difficulties  19  involved  i n such  a study  Drcso^hila  species  oviposition  sites  developed  a r e extreme a l t h o u g h  which  might  axe  be  highly  fruitful.  a study  specialized  A test  of the  of  those  in  their  hypothesis  above r e q u i r e s i n f o r m a t i o n on (a) t h e  larval  (b) s u r v i v a l (c)  the  growth f u n c t i o n s  as a f u n c t i o n  of time  spatio-temporal  and  size  distribution  of  the  yeast  types. Such d a t a nutritional close  are.very d i f f i c u l t  requirements  to p r o v i d i n g the Dj. j u l l e r i  High  season the  of Oguntia  major  or  identified growth the  fly  and  sole  be  are  source  of  l a r v a e on  the  necessary  that  very low.  Wagner d i d n o t  development surviving  time  optimum  he  size  survival  did  of  the  comes  to pupate  f o r the  larvae.  and  ( f i g 2 ) . From t h e s e  data  survival  the  S.  o f Type S  Type  i t is  S yeasts i s  of l a r v a e during of  significant  survival  yeasts  ? Firstly,  proportion  i s a highly  (r--0.906,  Wagner the  o f l a r v a e on  measure  are  measured  presence  measure t h e  fruiting  the c a c t u s f r u i t  Dj. m u l l e r i  between t h e p e r c e n t a g e  taken  the  Type F o r Type  the  rate  t o p u p a t i o n . There  correlation the  but  of  genus Q£ujrtia.  with  the c a c t i  each  into  Under what c o n d i t i o n s w i l l influence  of the  that  food  y e a s t s from  classified  the  study  Wagner (1944)  associated  i t i s believed  D ± mulleri  y e a s t s can  by  i t s e g g s on c a c t i  9 different  of  mulleri  A  The  necessary information.  lays  numbers o f t h e  of D  to c o l l e c t .  to  P<.01). T h i s  larvae negative  pupation  and  relationship  20  is  shown i n f i g 5. The s i z e  type  of  yeast  Type S y e a s t s fed  on  fail  t o reach  grew  F  the s i z e  they  probably  do n o t  conclude  that  is  very  Flies their size.  i s  rata  reach  Type  (Austin,  an  o f high The  fruit  guestion  Larvae  that  achieved above  attempt  on Type  we  p o s s i b l e on Type  yeasts  Type  Type  S  may  S yeasts  F  yeasts.  most l i k e l y by  to  F yeasts  argument  increase  increasing  their  by t h e o c c a s i o n a l yeasts  in  their  we must, t h e r e f o r e a s k i s 'do  o c c a s i o n a l l y dominate t h e  collected  Oguntia  f o r the  Cotulla  different  o f Type S y e a s t s  f i g 6. The growth c u r v e s  given  these  yeasts could  of  S yeasts  c a n n o t do s o b e c a u s e  f o r g r o w t h on  such  those  most  the  freguncies next  than  yeasts?  i n c r e a s e would be p r e v e n t e d  Hoore, D i l l e y ,  percentages  the  F  f e d on  oviposition  ?' Wagner  in  From  F  the  The  size  T^, t h e maximum s i z e  Type S y e a s t s , a t l e a s t  the  they  the  survive.  upon  environment.  on Type  inadeguate.  o f i n c r e a s e upon  Such  occurrence  sites  that  c l o s e to t h a t observed grown  on  Why do l a r v a e grown on Type  achieved  are n u t r i t i o n a l l y until  dependant  which t h e l a r v a e a r e f e d . L a r v a e  yeasts.  explanation  yeasts  is  (Y-1, Y-3) p u p a t e a t a s m a l l e r s i z e  Type  likely  upon  at pupation  fruit and  from  Crestonio)  survival  f o r the 5 areas f o r y e a s t s Y-8  I have c l a s s i f i e d  9 a s Type S. I n t h r e e a r e a s  and  species of yeast.  by Wagner: on t h e b a s i s o f t h e t i m e  percentage  5 areas  Type S y e a s t s  i n Texas analysed  The a v e r a g e  sampled a r e g i v e n and  taken  Y-9  are not  t o p u p a t e and  Y-8 a s Type make up o n l y  F and Ya  very  21  small  percentage  of  the t o t a l  C r e s t o n i o and A u s t i n , t h e y yeasts fruit are,  present. f o r these  the  contained cacti  which  to  30%  of the c a c t i  that  yeasts  this  distribution It larger  has upon  selecting  the  fruit  t  been  Type  possible  The f a c t  mulleri  to  select i n the  distribution  o n l y Type S  sizes  Thus t h e  t h a t Dj_ m u l l e r i  from  will  out o f  be  five  suggests hypothesis  spatio-temporal  a p p e a r s t o be a t e n a b l e  one.  larvae could  grow  be t e s t e d  by  upon Type F y e a s t s . I t would a l s o for  large  above  size  model  upon t h e Type S that  o f Type S y e a s t s  was  The  will  not  the  select  such  an  o f t h e l a r v a e t o use c o u l d be  tested  c o r r e c t would i t s t i l l  t o be d e t e r m i n e d ?  either  yeasts or t h a t  possibility  I f the former reason  o f Type S y e a s t s  cacti  15% o f t h e  yeasts  by t h e  d e t r a c t from t h e a b i l i t y  f o r the s i z e  cactus  function  t h a t i n one a r e a  t o use t h e s e  F y e a s t s . The l a t t e r  the  y e a s t s . There are  Type F y e a s t s . T h i s a s s u m p t i o n c o u l d  would  per  t h a t Type S y e a s t s  i s limited  assumed  It i s implicit  distribution  S  i s not n e g l i g i b l e .  for increased size  experiment.  Type  the d i s t r i b u t i o n  contained  an i n c r e a s e d a b i l i t y  increase  only  o f Type S y e a s t s  spatio-temporal  of  o f Type S y e a s t s  the p r o b a b i l i t y  present.  of D  interesting  yeasts.  approximately  areas,  s m a l l . I n C r e s t o n i o 30ft o f t h e  to c a l c u l a t e  probability  that the s i z e  I n two  a r e shown i n f i g 7. The s a m p l e  contained  estimate  only  fox  areas  present.  o n l y Type S y e a s t s w h i l s t i n A u s t i n  data  the  be  two  fruit  insufficient  comprise  The d i s t r i b u t i o n s  u n f o r t u n a t e l y , very  fruit  yeasts  by t h e ability  by be  spatio-temporal to  utilize  a  22  particular  variety  adaptations.  The  assimilation may  be  of  rarety  of s u c h  governed  by  the  Selection fires  Type  a r r a y . The  a simple  be  multiple  necessary  utilize  of  significantly  influencing  at  a  that  frequency  individuals The  capable  model  is  in  o n l y one  with equal  increasing reach  type  receptor; fires  the  the  The  limits  flooding.  in  growth r a t e . occurred  receive  close These  to  the  the  of  capable  without  being  select  for  yeasts. section  which  may  there  species  conditions  Some p a t c h e s more  the  are  differences  yeast  at  each  within the  in  that  of  sunlight  and  be  example,  may  yeast or  ground  the the  i n the environment,  t h a t temperatures for either  for  be  Suppose, f o r  a l l available  identical.  and  probability  be  those  receptor  reason  to  in this  environmental  t o be  others  may  a d u l t body s i z e  other than  yeast  this  o f Type S y e a s t s may  analysis outlined  of  lethal  For  and  metamorphosis.  the a b i l i t y  these  larval  likely  increase  the  however,  selection  of b e t t e r u t i l i z i n g  the  than  patches  periodic  and  high  and  facility.  a r e not  exposed  Other  receptor  than  yeasts.  l a r v a e were a b l e t o u t i l i z e  may  prevent  as a s t r e t c h  sufficiently  to s i t u a t i o n s  variations  patch  may  biochemical  at pupation,  the  achieved  different  distribution  is  size  to  spatio-temporal  that  size  leading to pupation  much more e a s i l y  changes  to  extended  yeasts  d e v i c e such  a certain  processes  S  array of  f o r a c h a n g e i n t h e t h r e s h o l d a t which t h e  may  larvae  of  an  when a l a r v a e r e a c h e s initiates  y e a s t s i n v o l v e s an  be  more  thereby patch  the l a r v a e . subject  to  environmental  23  conditions with  may  result  location  hospitable  and  for a  developmental  this  may  be  period  different  In  other  selecting  matter  into  that  and  developmental  t o a p p l y t h e above different  analysis yeast  those  which  those  which  persist  persist  for a  mathematically  situation. optimum be  that  remain  as  governed  v e r y low  important  their  degree  such  sites  forces will  of  which  exposure  may  be a v o i d e d . The  on  'poor  sites.  Certain  indicate  'poor  spatio-temporal  patches.  In s i t u a t i o n s  have a v e r y low  of  body of  patches  patches We  of  the  size,  time. may  might  act  expect,  discrimination cues,  risk'  such  as  patches  and  discrimination  freguency  of  where s i t e s  probability  latter  amount o f  risk'  show a d e g r e e  analysis  i s that  optimum  body s i z e .  degree  period.  this  drawn  f o r growth f o r t h e l e a s t  organisms  the  for  the s p a t i o - t e m p o r a l frequency  selective  may  be  hence the  frequency of these  of  upon  categories sites  by  , and  as  can  can  to patches c o n t a i n i n g  manner  that  c h o i c e of o v i p o s i t i o n  the  depend  time  suitable  therefore, that in  conclusion  development  can  Even a  The  we  we  f o r only  'long'  in  same  to  types  In the s i m p l e s t case  groups,  the  long  for a short  may  done  a  environmental  t h o s e c o n t a i n i n g T y p e F y e a s t s . The  be  remain  permit  T y p e S y e a s t s and now  varies  patches  twc  correspond  rate  c o n d i t i o n s may  time  types of patches.  patches  types  of  Instead of d e f i n i n g  ' s h o r t ' p e r i o d and  These  survival  In some p a t c h e s  rapid  I t i s a simple  classify a  long  situation.  define  time.  period.  deterioration period.  in a larval  will  the v a r i o u s are  of p e r s i s t i n g  scarce, may  be  24  selected very  because the  much  lower.  suitability different or  distribution  site of  Another may  depending  be  which  than  .Dodson  as b e i n g  a fish,  population  important  significantly  o r community  circumstance.  As  directly  In  communities these  change  studies  in  predation  species has  been  in  such  e v o l u t i o n of s i z e  model p r e s e n t e d  f r e q u e n t and  to  size.  only  a  selective i n the  size-  lumholtzi  t h e t h r e e - s p i n e d s t i c k l e b a c k (Moodie  Suppose t h a t t h e  is  size  1974). in  how  severe  effect  the  this  development  zoopla.nk.tcn  Dodson  is  acts  the  in  been i m p l i c a t e d a s a  o r g a n i s m s a s t h e c l a d o c e r a n , Da£hnia  order  with  of  been shown t o r e s u l t Further,  through  p r e d a t i o n has  1965,  there  instance selection  composition  q u e s t i o n f o r which t h e  in  in  indirectly  selective  i n the  i s 'how  accept  spatio-temporal  that  has  and  used  the  is  composition.  The  tendencies to  applied  Size  1967)  upon  component,  model d e v e l o p e d  function.  diverse  genetic  which t h e  rather  suggested  the  to  upon s i z e  predation  t o d i s c r i m i n a t e between a  better  sites.  p r e d a t i o n . In t h i s  and  is  show d i f f e r e n t  selective  (Brooks  site  has  a  situation be  major f a c t o r  finding  sites  p o p u l a t i o n s may a  of  I f the a b i l i t y  of o v i p o s i t i o n  reject  section  probability  in this  must s u c h size  (Green 1972).  section  can  predation  distribution  be  of a  ?'  probability  before,  In t h e f i r s t  we  may  case  weakly i n f l u e n c e d by  of  d e f i n e two  the  size  being  eaten types  probability and  in  the  of  increases of  patch  or  being  eaten  second  this  25  probability  increases  rapidly  corresponds mathematically yeasts  and  Following very  the  the  low  important  in  the  i n the  all  eguations  are  monotonic.  different size  Size  spectrum  is, to  most i n t e n s e  selective  eaten  with  size.  in  general,  survival  changes  in  selective evolutionary  hence  the  yeasts. even may  give  be  a  rise  to  bimodal although  h i s t o r y parameters  unecessary  o r t o assume  is  not  a  Another stage  of  of  to  that an  invoke  result  function  the  selective adult  intermediate  may  life  that must cycle  predation  animals  the  predation  f a c t o r that  in  a  variation  community,  various l i f e  F  population  spatial  and  situations  which s i z e  predation  predation  4),  upon s p e c i e s  being  during  show t h a t  may  of  Type  Type S  of a  case  account f o r b i m o d a l i t i e s w i t h i n  complicated  of  former  predation  therefore,  c o n s i d e r a t i o n i s the  effect, adult  size  can  to note that  (fig  o f a community  monotonically  organism  containing  distribution  selective  curve  It  more  probability  size  The  containing  size-selective  the  size  mechanisms  necessarily  into  of  d e s c r i b i n g the  spectrum  Bather  of  fitness  distribution  patch  patch  It i s interesting  intensity  bimodel  size.  same method o f a n a l y s i s we  i n determining  community.  the  to t h e  incidence  or  a  second  to  with  is  size.  if  the  changes be  taken  of  the  i s happening.  may  have  little  upon t h e  optimum s i z e  because changes i n  have r e l a t i v e l y  minot i m p a c t  upon r compared  immature predation  survival of  or  juveniles  generation may  be  f a c t o r because i f happens b e f o r e  length. a  to  Size  significant  reproduction  and  26  hence b e f o r e animals  have made any c o n t r i b u t i o n  to  the  next  generation. In population occurence  summary,  size  of  or  size-dependent  a population w i l l  the rate  d e v i a t e from  by t h e f r e q u e n c y a t which  recombination.  •large*  indxviduals  may be d e t e r m i n e d  o f a s e t o f c o n d i t i o n s i n which  determined and  average  ,measured o v e r t i m e  time-dependent which  the  w i t h which  the  a  rare  there i s s i g n i f i c a n t  mortality. the  by  of  long  The term  degree to mean  these c o n d i t i o n s  animals are generated  is  occur  by g e n e t i c  27  CASE 2 i DISPERSAL REDUCES FECUNDITY In  the  p r e v i o u s s e c t i o n i t was  stores  for  section  I shall  effected  flight  i f  and  egg  consider  flight  production  how  and  assumed  egg  the  that  the  energy  were s e p a r a t a . I n  results  production  of  share  case  this  1  a common  are  energy  store. Is  this  assumption  Diptarans pupa  and  produce t h e i r  lay  them  Rygg(1966) s t u d i e d dipteran  which  Oscinella  frit  influenced pattern often  the  lays  they l a i d  fewer eggs"  Drosophila pattern and  o f egg  Hardeland  flight  lay laying  1967)  activity  eggs l a i d ) flight.  their  eggs  does show a  egg  egg  test  flies 1966) .  this  be  flight  laid  eggs  adult l i f e , eggs  lived  but  circadian  I  of a l a t e x  glue,  permitted  was  were  as  the more  fewer time,  although  rhythm  the  after  did  not  shorter  the  (Reusing used f o r by  the  number  of  a  the  e x p e r i m e n t : f l i e s ( D.. me/lanoqaster ) were a t t a c h e d means  nor  as i s suggested  decreased  hypothesis  was  reserves are  ( measured  a  frit fly,  there  for a  in  were l a i d  sequentially,  production,  should  of  of  day,  the  sequentially.  the  same e n e r g y  production  i n Drosophila To  second  from  or  batches,  longevity  (Rygg  . I f the  work o f Rygg, t h e n  in  in early  these  and  cost  flight or  emergence,  batches  number  when i n s e c t s f l e w e v e r y As  in  eggs  ?  after  total  laying  eggs i n each b a t c h .  one  reproductive its  : "the  egg  eggs  either  by a s i n g l e  of  a reasonable  period  of  foilowing to  to f l y for a given  pins  by  period  of  28  t i m e and  then  measured  the  days. fly  I had  was  time  up t o t h i s  but  permitted than  fourth  day  production  one  production  with  two  daily  eclosion  in (10 may  egg in be  (22  t h e two  individuals  to  time  stop  and  persuation  by  an  individual  s c o r e d as  p r o d u c t i o n one  another  mins  groups. the  and  have  stuck  i n the 36  been  the  Fig Both  8  pins  'flown'  group  mins).  Except  included  i n the  experimental  i s greater than  'unflown'.  f l y were begun  performed  shows  groups  the  on  the  daily  egg  show a d r o p  that  'flown' group,  the  compared  8 i n the  of  the  between days f o r i n d i v i d u a l s  egg  to the  A  problem variance  sample This  the d i f f e r e n c e (Fig 9). This  the  unflown  w i t h i n group  'unflown').  overcome by c o m p a r i n g  in  m a n i p u l a t i o n but  i s n o t , however, s i g n i f i c a n t . i s that  group  onto  ' f l o w n ' and  experiment  production i s very l a r g e  production  few  p r o d u c t i o n o f each  the  foregoing analysis  partially  and  egg  are thus  egg  and  following  the  then  next  to restart  i t s flight  flies  eclosion.  This difference the  hour  hour  drop o f the flown group group.  over the  If gentle  affected  treatments  after  of  I  a f l y would  t o f l y . Of t h e f l i e s  these  t h e two  after  flight.  t h e p i n and  f o r one  Counts of the day  frequently  pin.  point.  flown  stated  the  in getting  insufficient  was  analysis:  one  was  i f flight  flew l e s s  where  time;  ascertain  not  two  blowing  removed from  flies  tapping  p r o d u c t i o n of t h e s e f l i e s  made t o r e s t a r t  and  To  gently  considerable d i f f i c u l t y  n o t be  tapping  of  egg  by  f o r a predetermined  could  it  removed  sizes problem in  egg  analysis  29  shows  that  there  i s significant  g r o u p and t h e u n f l o w n g r o u p even  with  between  (t= 2.0, P<0.05, o n e - t a i l e d  An e s t i m a t e o f t h e d e c r e a s e flight  the flown  (t=2.72 P<0.01, o n e - t a i l e d  t h e r e m o v a l o f t h e two i n d i v i d u a l s  t h a n one hour  after  difference  in  -  flew  )  less  test). t  days  f o r the i t h f l y t days  after  , C f t ) , c a n be o b t a i n e d  <t) = N;{0)  which  test  egg  production  using the formula  <t) - D (0,t)  where (t)  :  the estimated  cost  flight. N • (t)  : t h e number o f e g g s  c  after  laid  by t h e  ith fly  t  days  laid  by t h e i t h f l y on t h e day  flight. N• (0) : t h e number o f eggs  preceeding the f l i g h t . D(0,t) laid  :  t h e mean d i f f e r e n c e  between  t h e number o f eggs  on day 0 and day t by t h e g r o u p o f f l i e s n o t f l o w n . The  plot  c f C • (t)  on t i s shown i n f i g 10. The two  flies  v  which  did  analysis. 0.390, for  not  f l y for  The r e g r e s s i o n  p<0.05  of  one  hour (t) on  ) and i n d i c a t e s t h a t  3 t o 4 days a f t e r  a one hour  To d e m o n s t r a t e a c o r r e l a t i o n production  more sample  are t  excluded  is  from  significant  egg p r o d u c t i o n  this (r=-  i s reduced  flight. between  p o i n t s a r e needed  flight  time  and  than o b t a i n e d  egg  i n the  30  previous the  experiment.  f l i e s and  use  the  same  experiment in  egg  glueing  pins  was (fig  of the unflown  a s c r i b e d to the I  measured  the experiment  for  about  one  correlation  half  of  the f l i g h t  production  were a n a e t h e t i s e d  in  and  this placed  t o p i n s d i d not f l y and from  11)  indicating  that the o p e r a t i o n  no i l l e f f e c t s .  the  group  not  The d r o p i n  i n the previous  of egg  experiment  can  production and  the  f o r two  days  after  sample.  There  time  egg  and  the  is  a  the  between  significant  production  flight  time  days f a l l o w i n g f l i g h t  first  experiment  on  the  (r=-0.378 P<0.05, f i g 11 ) . T h e r e  correlation  o f t h e two  o f a l l f l i e s on  and  day  i s also the  (r=-0.471,  egg  P<0.05,  12 ) . The  vials  used  i n the p r e v i o u s  enough t o p e r m i t much f l i g h t 10  Therefore,  different  between f l i g h t  a significant  i m p r a c t i c a l to  no  group  t h e egg  after  following  before.  anaethetise  anaesthetic.  day  fig  as  f l i e s t o t h e p i n s has  production be  procedure  Four o f the f l i e s a t t a c h e d  to  t a k e n zo  them o n t o t h e p i n s i t p r o v e d  production  attached  of the time  the n o n - f l i g h t group  vials.  their  glue  Because  cms  in  production activity placed  height). then f l i e s  is  If  32  cms)  i n which  The  egg  production  activity  flight  (4.5 cms  in  significantly  produce  in a single  fewer eggs.  l a r g e cage  were a v a i l a b l e 15 f o o d of this  group  was  large  diameter reduces  i n l a r g e r c a g e s , where i n c r e a s e d  p o s s i b l e , may  15 f e m a l e s  experiments a r e not  To t e s t  (measuring 32  x egg  flight this x 32  I x  caps f o r o v i p o s i t i o n .  compared  with  that  of  a  31  group  of  15  f e m a l e s i n 15  e x p e r i m e n t s . The 2.  On  a l l three  large  c a g e was  ensure  that  r e s u l t s of days the  experiment t h i s containers.  time  The  vials  Flight lay. in  The the  female  fly  of  of  follows  single the  obtained  in  because  females  in  before;  the  vials.  l a r g e cage I r e p e a t e d  same as  reduces the to  be  eggs  from cost  i s increased a  one  To of the  gallon in  the  flies  in  number o f eggs a f e m a l e  can  f e w e r eggs  flies  than  considered  laid  i s Ms  the  d e p e n d e n t upon the  reduction s i z e of  simple of  ( D.  size  functions  flight  cost'  of  To  and  r a t e of size.  of  obtain  d e c r e a s e as  the  the  the  calories  and  From t h e s e two  distance  as  The  rate  of consumption  r e s p i r a t i o n . The  cost' the  of  calories  rate  speed  of  as  that  the i t  egg  then  the  size  relationship  we  require  the  of  flight  as  can  obtain  the  proportional  to  e q u a t i o n s we  a function of  decrease  functional  that  s i z e of  comm.). Thus g i v e n  'reproductive  unit  of  considerations  dispersal will  c o s t per  rate  will  Ludwig p e r s .  f l y increases.  consumption  aerodynamic  c e r t a i n number o f c a l o r i e s t o p r o d u c e an  'reproductive  between  the  not  significantly  guesticn  energetic  the  flies  Table  ?'  reguires the  of the  in  3) .  number  It the  was  previous  given  l e s s than those i n the  placing  activity  next  used i n t h e  experiment are  production  r e s u l t s are  (Table  vials  females i n the  l a r g e cages produced the  egg  result  between  the  this  significantly  this  interaction  of  size. is  r e s p i r a t i o n during  flight  32  d e p e n d s upon t h e w i n g b e a t of  the  size  respiration wingbeat  frequency  which i s i t s e l f  a function  o f t h e f l y . From t h e o r e t i c a l c o n s i d e r a t i o n s t h e  r a t e o f a f l y of thorax  frequency  according  length i s related  to  t o the equation,  B(T)oc (W (T) j *  where R(T) i s t h e r e s p i r a t i o n and  W(T) t h e w i n g b e a t  than  or egual  Drosophila^ (1940)  and  Williams  to 3  freguency.  using  Chadwick  and Chadwick  (1947),  from  Chadwick  i s . 2.4  (see  measured t h e  body d i m e n s i o n s o f v a r i o u s D r o s o p h i l a  data  t h e r e l a t i o n s h i p between i s found  (12)  consumption during  know  and  (13)  flight  the time taken  information In  and  Gilmour  f i g 1 3 ) . Heed,  wingbeat  frequency  species. Using  frequency  and  this thorax  = 9.4 - 0.431og^T  specify  the  (13)  rate  as a f u n c t i o n o f s i z e .  amount o f e n e r g y consumed to  wingbeat  of x f o r  t o be,  log^W (T)  Equations  be l e s s  1947). The a c t u a l v a l u e  and  length  length T  The e x p o n e n t x s h o u l d  data  (1942)  (12)  r a t e o f a f l y of thorax  (Chadwick  obtained  the  in flying  t h e sheep b l o w f l y ,  find  some u n i t d i s t a n c e  to f l y that  on t h e speed o f f l i g h t  To  o f energy  distance,  ae t h u s  we need require  a s a f u n c t i o n o f body  Phaenicia  sericata,  flight  the  size. speed  33  and  wingbeat  frequency  (Yurkicwicz therefore,  and we  Smyth  can  increase  fraguency.  The  energetic  cost  linearly  1966a,b).  assume t h a t  wingbeat  computed. The  both  of  flight  flying  As  with  an  temperature  approximation,  speed i s p r o p o r t i o n a l  some d i s t a n c e  r e l a t i o n s h i p between t h i s  cost  d,  and  may  size  now is  to  be  given  by  x\j (T) oc d/T  where n^(T)  As  the  i s the  thorax  cost  length  (14)  i n c a l o r i e s or  increases  the  eggs.  reproductive  cost  of  flight  decreases. The  wingbeat frequency  decrease also  experimental  respiration weight  verification.  It i s well  per  incur  The to  established  r a t e , measured unit  time,  respiration but  flight  than f l i g h t  a lower  rate speed  first  (14)  assumption  p r o d u c e an that  egg  is  as  hence  require  i s that  body  the  independent  i n animals i n general  as c a l o r i e s consumed  increases  speed;  more  cost.  made i n d e r i v i n g e q u a t i o n  of c a l o r i e s r e q u i r e d  size.  the  r e s p i r a t i o n rate diminishes  thorax length  larger flies  asssumptions  hence  in thorax length  . However, t h e  result that  number  increase  with i n c r e a s i n g  Two  of  an  decreases  rapidly the  with  and  par  weight  unit  the body  decreases  34  1974).  (Fenchel  relationship weight JQi  oxygen  either  male  , or i n  significant Di  between  in  viracochi  However,  male  correlation  to  the  scale  animals  D\  melanogaster.  range  in  without  weight  that  production  encompassed  by  between c o n s u m p t i o n sample  increase  suggests  may  in  the  may  o f p r o d u c t i o n may,  size.  The  of  to  reduction  i n egg  The is  the  wingbeat quoted  (14)  produce  may  sizes  an  a  may  be  single  due  between  that  across  species  no  i s detectable  with  decreased  consumed  upon t h e s i z e  in  of the  increase with  size the  f l y . The  decreasing  amounts o f c a l o r i e s i n f l i g h t may  not be e q u i v a l e n t  fly  egg  production  will  where  than  in  be l e s s .  more the  by  t o t h e same  calories larger  are  f l y the  Thus t h e e x p o n e n t  in  be an o v e r e s t i m a t e .  second assumption assumption  that  f r e q u e n c y . The above,  a  reported  variation  be so g r e a t  rate  therefore,  number o f e g g s . In t h e s m a l l e r reguired  find  parameters i n female  calories  depend  use o f e q u i v a l e n t  f l i e s of d i f f e r e n t  did  or  sizes.  number  •cost'  equation  She  r a t e and w e i g h t  respiration  o f an egg  and  fi'seudoobscura  i n particular  rates  no  weight  between t h e r e s u l t s  Drosophila  consumption  very l a r g e  An  these  found  wet  D._  female  o f c h a n g e i n body w e i g h t . The  in their  relationship  two  or  g e l a n g g a s t e r T h e discrepency a n i m a l s i n g e n e r a l and  the  consumption/mg  between  for  ( 1 9 6 4 , 1965)  Hunter  that flight  requires  further  examination  speed i n c r e a s e s l i n e a r l y  observations  by Y u r k i e w i c z and  suggest t h i s r e l a t i o n s h i p .  More d i r e c t  with  Smyth, evidence  35  is  really  and  necessary.  weight  of  Hocking  10  (1953) measured t h e  D ± melanggaster.  These  significant  correlation  between f l i g h t  The  sample  and  small  (tethered  flight)  correlation.  size  might be  If  the  reasonable relation assumed one  present  size.  To  hour per  following  day  and  flight.  this  u n d e r e s t i m a t e s i n c e egg days  following  flights  does  a f l y of  may  be  one  flight  fig  14.  (eguation body s i z e  constant  and,  the  the  (5))  cost  assumed and  to  were d e t e c t a b l e (10%).  thorax  A  length  flight  the  for  the  day  is  an  least  Knowing  The  3  that  capable  of  the  cost  other  size  result  of  i n t o the c a l c u l a t i o n s of a  linear  ensure  that  I s e t the o f one  larval any  larval  hour per  f o r which r i s g r e a t e r  t o a much l e s s e r e x t e n t ,  average  I f u r t h e r assumed  survival.  in r I  cost  are  a  on  i s reduced f o r a t  algebra.  r  increases  of  c o s t f o r a f l y o f any  simple  fliq'ht  eggs on  s i z e the  reproductive  a  on  a given  this  at  flies  more e g g s t h a n t h e y  I  a the  is  of f l i g h t  their  i s shown i n  of  size  cost' of  c o s t s i t 20  flight.  incorporating  optimal  of  decrease  by  specimens  equation  effect  1.0mm  estimate  hour  no  weight.  lack  not  calculated  function  the  production  which c o s t f l i e s  producing for  a  the  the  that  'reproductive  length  This  indicate  body  independent  assume  estimate  that a f l y of thorax  for  speed  underestimate.  us  d e s c r i p t i o n of t h e to  is  i s an  let  and  method o f f l y i n g  speed  (14)  data  speed  responsible  flight  exponent i n e q u a t i o n For  the  flight  optimum t h o r a x  growth  shifts  in  mortality day  greatly  than length.  zero This  36  result (14).  does not Compare  reduce  depend  greatly  , f o r example,  fecundity  upon t h e e x a c t f o r m . o f  the case  with t h a t  i n which f l i g h t  but  this  r e d u c t i o n i s independent  in  the  latter  Flies  which  case  in  unrelated  but t h e y  reduces  excess  fecundity  genotypes  will  be  eggs of  or  zero  cannot by  of  less when egg  2 0 eggs.  maintained  have  i n the  a  numbers  In the l a t t e r  fecundity that  i s 2 0 eggs.  number and  maintain t h e i r  not  Suppose  to f l i g h t may  does  reduces  body s i z e .  t h e r e d u c t i o n due  l a y twenty  increase  i n which f l i g h t  equation  rate  of  flight  are  when  flight  circumstance  these  p o p u l a t i o n o n l y by g e n e t i c  recombination. The be  thorax  l e n g t h f o r which r i s g r e a t e r t h a n  i n c r e a s e d even  The  importance  i f the cost of  production  ,flight,  curvature  of  with s i z e  that  decreasing The  As  the  and  causes  very  i t  size.  between  egg  determines  the  I t i s the d e c r e a s i n g c o s t  steep  dispersal  t i m e o f a p a t c h and  patches  with  relationship  i s that  function.  the  of  become more and  their  p e r s i s t e n c e time  over  a  decrease  body s i z e  increased  will  decline  ia  r  with  shown i n f i g 14.  frequency  persistence  the mathematical  the f i t n e s s  size  of f l i g h t  zero  of  the  will  because  the  dispersing  between s i t e s .  upon  both  the  patches.  more u n s t a b l e w i t h r e s p e c t t o of  spreading  increase.  of patches  dispersal  depend  d i s t a n c e between  the advantaqes  number o f p a t c h e s i n the density  will  will  increasing  Because of  On  offspring  t h e o t h e r hand, a  favour a reduction  in  'reproductive cost'  of  the  size-dependence  of  37  this  'reproductive  cost'  the  trade-off  number o f  p a t c h e s i n which e g g s a r e  decrease  in  fecundity  will  example,  if  dispersal  between  zero there  i s no  production  to  however,  be  advantageous  and  will  Increasing The  above  according  genetic  not  fly  of  a  not  be  reduced  of  further  the  p  f l y . The and  suggest  problems; resulted  It  may,  to  to  zero  possibly  for  tunnels  of  results  cast  example, animals  the  rate  (1969)  upon t h e  successful,  because  of d i p s e r s a l  they  that  the  low  were u n w i l l i n g  used  to  that  the  is  under  different activity. level  to  (Ewing  results similar  of  of  f l y . attempts  p r i m a r i l y because o f  upon t h e  and  i n Droe,l a n og a s t e r  for  of  adjusted  suggests  showed t h a t  rates  experimental apparatus  some d o u b t  be  habitat  g e n o t y p e of t h e  selection  that  probability  show d i f f e r e n t l e v e l s o f  Narise  dependent  in  activity.  egg  larger size  control, will  e t a l ( 1 9 5 8 ) have shown  melanogaster  very  the  nature of the  the  select for different activity been  that  a v a i l a b l e evidence  therefore  experiments is  coworkers  dispersing.  l o c a t i o n s , thereby  i s under g e n e t i c  c o n t r o l . Sakai  activity to  a  spatio-temporal  activity  strains In  it  to the  of  For  reduces a f l y ' s  in  p r o g e n y i n two  arguments  if  s i z e of  level  conseguent  size-dependent.  patches  will  the  i t s fitness.  dispersal,  the  leave  be  v e r s u s the  point  for  because i t ' s f e c u n d i t y  it  laid  also  disperse  between i n c r e a s i n g  have  experimental  activity  rate  move t h r o u g h 1963,1967). Narise  apparatus  and to  the  These his  measure  38  T h e r e i s no  information  spatio-temporal species for  of  distribution  Drosophila.  insects  correlated  in  capable  problem the  general,  pond  of f l i g h t  The  the  will,  of  a  fly  by  may  the  be  obtained  flies..  vials to  To  disperse  generate 12  level  any  that, is  ,however,  by  the that  insects  wings.  to solve  much  this  two  easier  problem  more To  emerging f l i e s  rapidly control within  the  than for  these  Thus  the  in  degree  different  larvae  at  flies,  the  produced  density  those  vials  and  than  for I  I 24  placed  open a t  the  h y p o t h e s i s above i s c o r r e c t  low  the  stakes  by  flies  vial  resulting flies on  sized  less active  oviposit in a  of  different  s i z e d i s t r i b u t i o n s of  females to  frcm  upon  d e n s i t i e s , are  i n boxes s u p p o r t e d  emerging  containing;  evidence  colonized  small  permit d i s p e r s a l . I f the  conditions.  be  rearing  p r i o r t o emergence o f  outside  flies  this  larvae.  than optimal  e i t h e r 2 or Just  for  dispersal activity  dependent  Reed (1938) showed t h a t  at higher  allowed  the  f o r example, i t i s o b v i o u s  is  flies  raising  sites  o f s i z e upon d i s p e r s a l r a t e i s a  a  bottom  At  and  manner.  size  densities.  of  those without  c r o w d i n g i t e x p e r i e n c e s as  the  level  i n general than  activity  (1962) g i v e s  to i n v e s t i g a t e . I attempted  The  hours.  r a t e s of  oviposition  stability.  rather  effect  following  large  cf  i s almost t r i v i a l :  a newly formed  the  Southwood  with h a b i t a t  observation  on  from effect I  put  conditions the of out  high the  should density  density  three  of  boxes  39  Each  1)  15  vials  of l a r v a e  at the  low  density  2)  30  vials  of  larvae  a t the  low  density,  3)  15  vials  of  larvae  at the  high  density  of  f r e s h food  box  also  b a n a n a . To vials  contained  estimate  20  vials  numbers e m e r g i n g I p l a c e d  a t each d e n s i t y .  I collected  the  out  remaining  and  mashed  10  sealed  flies  after  4  days. The (Table the  number o f 4)  flies  purpose are  4).  which  not on  low  the  were  they  side two  a  Thus  sexes:  be  density  at  conditions  reared  increases  density  of  from  the  I t can the  boxes  be  pooled  at the  within  within  Table  the  6  for  density  lower  density  vials  of  from  with  an  conclusion  is  the  other  vials  the  means  gives  hence  no  seen t h a t i n both  probability  the  higher  s e x e s were n o t and  density  containing  the  5). This  vials be  with  two  at the  flies  5).  differ  significantly  (Table  unfortunately  separated standard  sexes  dispersal  there  with  a  size.  rate  which t h e y  are  can  remaining  (see T a b l e  in  possibility  f o r the  than these r e a r e d  given.  i n body the  flies  inclusion  walls  reduction  reduction  The  larval the  does n o t  densities  reared  were removed can  counts  number o f f l i e s  i n the  the  errors  the  The  a f f e c t e d by  for  is  at  analysis.  they  increase  as  reared of  emerging  hence the  ,however, s m a l l e r  (Table  or  and  flies  of  dispersal  are  reared  that  starved  flies  of f l i e s  d e c r e a s e s as  i s increased. reared  under  upon emergence f r o m t h e  the  There  remains  high  density  pupa  and  this  40  factor,  not  size,  determines  h y p o t h e s i s c a n be t e s t e d well  fed  flies  different  of  v  by c o m p a r i n g  different  used  i n experiments  t e m p e r a t u r e on d i s p e r s a l r a t e could  are  t h u s be used  correlated.  placed  outside.  distribution of  a  control  designed t o study (Roff  to determine  These  flies  The a n a l y s i s  sample.  1976)  In  excessively  which  were a l l w e l l  control are  The are  that  Without  The  sample  size  test this  been  retained  comparing flies  of  flies  only  the  size  with  that  than  i t is  dispersing  the  is  detectable; flies  estimates of  these  one e x p e r i m e n t ,  that  r e m a i n e d . No m a l e s were  of  these  flies  and t h e  i n f i g 15. The n o n - d i s p e r s i n g  smaller  rate being  s u i t a b l e samples  any a p r i o r i  distributions  a r e shown  the e f f e c t of  t h e sample o f r e m a i n i n g  selected  control  females  sample  (t=2.25  test). r e s u l t further I released  t h e same manner a s b e f o r e  three  of  by r e a r i n g a t  make a d i f f e r e n c e i n s i z e  I conservatively  P<0.025, o n e - t a i l e d  in  to  small.  significantly  To  rates  fed before  (non-dispersing)  17 o f t h e 50 f e m a l e s r e l e a s e d  measured.  This  i f s i z e and d i s p e r s a l  selecting  i t must n o t be so l a r g e  conditions in  large  had  c o n s i s t s of  o f the remaining  sufficiently  is  rate.  the d i s p e r s a l  s i z e s , produced  n e c e s s a r y t o e n s u r e t h a t t h e number  but  dispersal  densities.  Flies  and  the  days a f t e r t h e r e l e a s e .  about  220  females  and c o l l e c t e d t h e r e m a i n i n g Approximately  s i z e d i s t r i b u t i o n s of these  flies  70 f l i e s  and t h e  shown i n f i g 16. T h e r e i s a h i g h l y  remained.  control  significant  flies  sample  difference  41  in  the  variances,  group of  very  This  ( F=3.14, P<0.001) due  small  flies  experiment  i n the  was  non  repeated  repeating  experiments).  inconclusive. flies  of  conditions  although  More e x p e r i m e n t s  (such  i s the  highly  are  required  not  a  both  error  of  is  only  using  different  larval  sizes  resulting  from  but  using  flies  genetically  of  in  suggestive,  different also  of  sample.  2 more t i m e s and  r e s u l t s were n o n - s i g n i f i c a n t  evidence,  presence  dispersing  c a s e s the  The  t o the  different  sizes. The  transient  essential given  for Drosophila  above  sites  may  the  an  This  will  size I  suggest  be  dispersal. extent  assumptions  will  have  assumption  that  of the  the be  made. The  not  not  avoid  fluxes containing  so  that  there  species  is  larvae that  is  dependent.  i s that for  unrealistic  o r pupae  little  To  of s i t e s  are  of  Two  of  what effect  simplifiing which  oviposition.  This  because  (Cole e t evenly  variation  temporal  p a t c h e s upon  t h a t o v i p o s i t e on  sites  rate  of  ?  sites.  suitable  altogether  Drosophila  assumption  first  arguments  the  consequences of  it  distribution  distribution  the  density  are  size  population  first  that  space  be  makes  general  spatio-temporal  spatio-temporal  found  second  the  The  also  fed is  disperse.  sites  r a t e may  consider in  to  oviposition  parameter i n determining  distribution  variability  of  important  the  shall  larvae  nature  in  i t has  slime  been  fluxes  a l 1970).  The  distributed in the  distance  42  between  adjacent  accept  sites  the average  approximation degree  of  p  distance  contagion). (8).  c f thorax  cost  i s c (T)  of  be  Let' r ^ ( T )  a  of a density  = p r (T)  +  5  this  instance  upon  size  a t which t h e c o s t density  a reduction  during  (1-p) t h e  (1-p)rp(T)  t h e optimum  length  the r e p r o d u c t i v e  thorax  (15)  thorax  length  density  (8) .  w i l l not of  below  will  cost  o f d i s p e r s a l (see f i g  be d e t e r m i n e d  (hereafter c a l l e d  zero  D ). Flies c  t h e p e r i o d when s i t e s  be e l i m i n a t e d  14).  size  by t h e d e n s i t y o f that  is,  the  t h a t a r e so s m a l l  eggs p e r day r e d u c e s  will  sites  d o e s n o t depend t o any g r e a t  of d i s p e r s a l i s h i g h e s t ,  o f c (T)  of  i s D^. . L e t  be e f f e c t e d , however, i s t h e minimum t h o r a x  minimum  increase  increase  T, and  g r e a t l y by c h a n g e s i n t h e  extent  that  of  (15) has e x a c t l y t h e same form a s e q u a t i o n  t h e optimum t h o r a x  lowest  and i g n o r e t h e  a t which the d i s p e r s a l c o s t i s  ^(T)  because  sites  reasonable  , a t which t h e d i s p e r s a l  by,  e f f e c t e d very  The  a  T when t h e d e n s i t y o f s i t e s  density  choose t o  r ( T ) can be c a l c u l a t e d by  be t h e r a t e  i s given  in  What w i l l  d i s p e r s a l distance  Then r ( T )  Equation However,  as  eggs p e r day f o r a f l y o f s i z e  probability negligible.  we might  sites  In t h i s case  lengths  be t h e p r o b a b i l i t y  alternatively between  of t h e average  means o f e q u a t i o n flies  (  their  from  rate  of  the p o p u l a t i o n  are sparsely d i s t r i b u t e d  (density  D ). c  The  probability  of finding  flies  i n the  population  that  43  are  smaller  probability  than o f such  contagion of If  densities  s m a l l e r than  sites  approaches  produced  depend and  low  densities  g r e a t e r than those that  D  may  will  in r(T)  occur  can  very c l o s e  size  spatial  e v e n a s assumed distributed  so  densely  packed  areas  sites  possible  limit  is  between  /  so f a r . S i t e s that and  the optimum  and  T.  whilst  A  a very  there  the c o s t be  of s i t e s  D,  of  could will  body  size  and  c  the  very  steep  will  favour  slow  decline  of  far  small  flies  i s unlikely  probably  will  be  apart  and in  is the  which  flies  c o n c e n t r a t i o n s of patches  term  survival  but t h e i r  for a  cost  density  may period  probability  be  negligible  because  patches  in  this  will  consequent  other  dispersal the  will  its  in  are  of  which a r e s m a l l e r t h a n  persist  area  as  contagiously  low;  dispersal distance may  t o be  be a r e a s i n which s i t e s  dispersal  h i g h e r than average,  with  frequency  when t h e d e n s i t y  below i t s optimum  will  local  reproduction  of  a l o n e . These numbers  r (T)  distribution  s e t by t h e a v e r a g e  of  the d e g r e e  range.  may  Genotypicaily  density  the  at the d e n s i t y  consequently higher. Within areas  the  and  upon  with a high  persist  to t h e optimum  f a v o u r a wider  patches  depend  i n numbers g r e a t e r t h a n  as T decreases  y  The  occurring  D  be f o u n d  functional relationship  animals  will  upon t h e d i s t a n c e between  smallest  decrease  s e t by D  by g e n e t i c r e c o m b i n a t i o n  i n part  the  limit  patches.  flies  be  the  persist. in of  long  eventually  decrease.  such  the  Sexual  genetic recombination  may  44  continually  produce  a small  minimum s i z e d e t e r m i n e d density  may  tend  distributions season  to  but  counterbalance between  If a  fly  i n the  do  prevent  pupate  is  at  of  upon which i t has  oviposition.  If sites  are  distribution to  see  of  an  are  sites  not  in  at  the  range of  'small'  of  a natural  generation for  Robertson  population laboratory  a Hawaiian  mixing  by  may  c  species,  stock. D_j_  of  size  assuming for  that  further  subobscura  have  an  we  or  at  As  a  the  expect  organism  it  not  chance  should  to  metamorphoses  a population are  a  area  an  observed  (1963) measured D_j.  to  average  density.  which  phenotypes t h a t  of  due  lowest  the  still  lowest  at  been  flies  d i s t r i b u t e d a f l y which  Thus w i t h i n  has  of  will  patches.  unsuitable  D  breeding  differentiation  ability  conditions.  M c F a r g u h a r and  The  d i s t r i b u t e d the  this  optimal  This  one  between s e a s o n s  becomes more c o n t a g i o u s  increase  genotypes.  from  i f i t i s within  under  'small'  flies  by  a s i z e below t h a t  a  size  between s i t e s ,  set  metamorphose a t  find  in  contagiously  successfully  t i m e i n which s i t e s  differences  grown i s  p u p a t e s a t a s i z e below t h a t reproducing  local  determined  dispersing  the site  times of  should  below in  local  evenly  are  differences  differentiation. also  that  Local  mixing of  persistence  cost  flies  persist  patches are  patch  of  not  habitat  re p r o d u c t i v e the  the  such  D^.  generate  i f sites  s e a s o n s may  variation  by  to  another  number o f  we  should  represented in  by  Prosophila^  the  size distribution  and  that  of  the  first  S i m i l a r measurements were made  mimica  x  by  Kambysellis  and  Heed  45  (1971) of  ( f i g 17  ).  phenotypically  •small'  both s p e c i e s  small  g e n o t y p e s . The  that although period  In  of  'small'  time  in  flies  there  which a r e  absence of  phenotypes the  long  i s a large not  percentage  represented  'small' genotypes may  persist  term  any  indicates  over  genetically  by  a  short  'small*  flies  cannot p e r s i s t . It  would  stability reduced  of  i n t e r e s t i n g to  sites  size.  moth, l i r i a and  be  Myers  (1976) has  jacobaeae  successful  between  in relation  pupation  years within  were r e a r e d  under  relationship  , the  to the  ability  differs  identical  In  and  summarize t h e  r e s u l t s of t h i s  1)  In D r o s o p h i l a  flight  3) part  for Drosophila  Because of upon  distribution 4) to  The  of  1)  its  There i s l i t t l e  nature to  and size  of  disperse  2)  the  in  be  a  cinnabar weight and  larvae  that  . the  i s , in  part  acted  upon  section, fecundity.  oviposition sites between  makes i t  habitats.  f i t n e s s of a f l y w i l l  relation  to the  depend  spatio-temporal  patches.  e f f e c t on  increase  reduces  pupation  hence c a n  To  essential  the  suggesting  successful  natural selection.  transient  in  and  pupate a t  these experiments  conditions  between s i z e and  The  to  b o t h between p o p u l a t i o n s  a population.  by  2)  that  distribution  r e l a t i o n s h i p between l a r v a l  l e a s t , g e n e t i c a l l y determined  is  the  shown  at  in  study  the  r (T)  of  s i z e at  c h a n g e s i n the which r (T)  e f f e c t upon t h e  optimum  density  i s greater size.  of  sites  than  zero.  46  5)  The  greatly  6)  density  The  probability  of  7) in  the  the  lowest  does n o t  persistence of  the  by  i s greater density  than  zero  of s i t e s  have a s i g n i f i c a n t  may  that  be  occurs  e f f e c t upon  the  size.  contagion  in  which r{T)  influenced  (D ) . T h i s optimum  s i z e at  patches flies  time of  a  are  smaller  patch factors  than  and  the  that  determined  by  amount  influence D  of the  persisting  population. The  two  evolution  much below  that  f a c t o r s m e n t i o n e d i n 6) of the at  ability  may  a l s o be  o f a f l y t o p u p a t e at  which i t p u p a t e s under o p t i m a l  important a  size  conditions.  47  DISCUSSION The  general  distribution the  message  of a c o l o n i z i n g  spatio-temporal  Furthermore, estimated  the  from  when  effect  'good'  Consider  upper  size  fitness  they  limit  dependent  or  foregoing  analysis  (larval  size. will  this  a size  conditions.  instance  upper  i t s  by  environment.  genotype  cannot  conditions;  or  be  'poor' larger  important  to  make  determinant  o f the  poikilotherm.  It is  i s s u b j e c t e d t o one o r more mortality  and  a  functions.  single  with  selection  In  time will  mortality  timethe  function  to pupation). Given a  f a v o u r some  particular  more growth r a t e s a r e p o s s i b l e which  o b t a i n e d under  closer  necessary  i s the average the d i f f e r e n t  t o t h a t o b t a i n e d under  of  selection  the  constant  possible  conditions  the l e a s t f a v o u r a b l e  I f a t any i n s t a n c e i n t i m e t h e whole p o p u l a t i o n i s to  the  the same  same food  environmental substate,  limit.  conditions,  then  changes i n the e n v i r o n m e n t a l c o n d i t i o n s the  the size  proportionately  •r-selected'  decreases  growth r a t e ,  sizes  that  c o n d i t i o n i s o b t a i n e d by t h e p r e s e n c e  rates  favour not a s i z e  subjected  an  an  size-dependent  two  a  conditions  organism  growth  When  optimum but  the  an  survival  particular  of  have  is  c a n be d e t e r m i n e d  environmental  occur  of  that  different  poikilotherm  of a p a r t i c u l a r  conditions  reguired  of  paper  conditions.  first  environmnental  this  variability  the average  conditions than  of  in  this  i t i s the temporal  that  will  determine  Under t h e s e c i r c u m s t a n c e s i t i s n o t n e c e s s a r y  48  that  the  habitat  p r o b a b l y few or  other  be  d i s t r i b u t e d p a t c h i l y i n space.  circumstances  relevent  population's  environmental  of  host  plants  in  a  Drosophila of  often  are  d i s t r i b u t i o n of  an  example,, a s  many l e p i d o t e r a n  frequency  of  unfavourable  are  species.  resources.  conditions  The  source  same o v e r  a  habitat  will  a  food  oviposition  and  the The  be  d i s t r i b u t i o n of upper s i z e  important  occur over  are  a large  limit  temporal  and  factor i s  how  part  part  of  environment. It  should  conditions rates  pertain  adult  with a d u l t  value  age  replace In  Thus g i v e n  deaths, raise  the  to of  larval  state.  adult  early  1965). T h i s  is  upon  the  Varying  mortality  little  influence  size  because  r  is  offspring production,  individual  declining may  not,  very  the  rapidly  however, be  true  size. a p a r t i c u l a r g e n o t y p e must  particular  that  emphasis  have r e l a t i v e l y  the  themselves  some  the  optimum  poikilotherras  size any  will  o f an  lower l i m i t  persist.  by  that  to the  or  (Lewontin  Individuals  minimum  stage  largely  reproductive  least  noted  upper l i m i t  determined  the  be  that  i n the  upon t h e  of  The  the  food  i s the  'mosaic e n v i r o n m e n t ' depends upon b o t h t h e  spatial  the  factor  domain. More g e n e r a l l y  mosaic of c o n d i t i o n s . sites  ,however, i n which t h e  There  is  in  order  fecundity  that  rate  reduces  I t has  to  genotype  at to  of  size.  is  some  births  egual  fecundity  will  there  necessary t o ensure t h a t  to s i z e .  able  i s a function  mortality  environmental f a c t o r that lower l i m i t  for  ba  been shown t h a t  energy  49  in  Drosqphila  flight  i s not separately  and  stores  number o f eggs t h a t are be the  distributed seguestered size  i n space,  which  sites.  will  absolute  The  be t h e l o w e r  reproductive  spatial  limit  cost  to  even f u r t h e r . As n o t e d  not  t h e optimum  The  generality  production  as a r e s u l t  experimental migrations In  such  flight  ni.grofaciatus  support  begins.  (Dingle sites  are all  for  and  Arora  indeed example,  offspring  productive of  the  the  constraints  do  degree.  of reduction  i n egg  be a s c e r t a i n e d by  they  make  long  t h e pupa.  seam  to  make f l i g h t s  i f  In this in  the  female  species space  In  after when  m u s c l e s and  and s t a b l e t h a t female.  be.  muscles  of the f l i g h t  not occur  1973).  the  t h a t egg p r o d u c t i o n and  are patchily distributed  sufficiently the  will  of  that  upon emergence from  Histolysis  o f egg p r o d u c t i o n  oviposition patches  ,  fact  poikilotherms  to find  t o meet  decreases r a i s e s  t o any g r e a t  phenomenum  that  a r e apart the  t h e pupa b u t h i s t o l y s e t h e f l i g h t  production  starved  The  above, t h e s e  a r e p a r t i t i o n e d i n time as  onset  patches  must  means  sufficient  of d i s p e r s a l can only  groups we might e x p e c t  reduces the  distribution  size.  analysis. Certain flying  emergence f r o m  the  the  or d i s p e r s a l f l i g h t s  Dysdercus  egg  body s i z e of  This  i n c r e a s e s as s i z e  this limit affect  patches.  the  for  energy r e s e r v e s  i s at least  further  stores  the o v i p o s i t i o n s i t e s  part of a f l y ' s  fecundity  into  Thus f l i g h t  a f l y can l a y . Since  i s a function of the  oviposition higher  f o r reproduction.  f o r d i s p e r s a l between  at  mortality  partitioned  is  suitable but  the  they can  Br-osophila,.  50  oviposition  patches are  probably  high  p r o b a b i l i t y that  a patch  the  larvae  to  for  are  a female to  would  be  habitat flight  her  interesting  to  dispersion  and  unless account.  examine  Intra-specific  even i n t h e s e c a s e s one  in  habitat  effect  of  model t h a t  involve the  can  present  is  the  species  of  strong  lack  sedentary in  complication  that  the  stumbling  are  cannot  are  be  taken  much e a s i e r  b e a r i n mind  that  c f more g e n e r a l  ending  i s that  block  to  size made into  t o make changes  changes i n  simulation dynamics  any  mobile i s where t h e  activity the  animal,  the  Even  presence  more l i k e l y  c o n t r o l of population  of  1962).  dispersed  Under  to  extremely,  (Southwood  less  of  predictions  of case h i s t o r i e s .  a colonizing species.  density-dependent  in a  population  or h i g h l y  high  l e s s mobile the i s not  the  dipterans  i n c o r r e c t l y suggest  the  density  hopefully  simple  particularly  and  of  life-  at  habitat  effect  the  greatest  A further  It  a reasonably thorough study of  The  wings may  the  d i f f e r e n c e s i n body  proper  successfully predict  as  patches.  this  organism,  a species  advantageous  of  species.  difficult,  should  A  before  investigation  the  classify  and  characteristics  symptomatic  conditions.  should  history  are  unsuitable  is a  species.  comparisons  but  there  r e l a t i o n s h i p between  stability  dipteran  life-history  environmental  the  t o changes i n h a b i t a t  density  and  a number o f  about i n t e r - s p e c i f i c  relate other  become  eggs o v e r  habitat  i n a v a r i e t y of  they  will  unstable  pupate. I t i s , t h e r e f o r e  spread  Predictions as  able  very  the i t is  conditions  numbers  the  51  quality  of  offspring  rather  than  the  number  may  be- o f  overriding significance. The  e f f e c t of s p a t i a l  and  maximum  the  effect  important  body s i z e a r e l i k e l y of  dispersal  consideration  function  vary  on is  o f s i z e and t h i s  Even i n v e r t e b r a t e example,  and t e m p o r a l  from  pond  the that  pond  minimum the  body  than  size.  survival  rate  The is  a  i s v a r i a b l e i n s p a c e and t i m e .  poikilotherms  to  optimum  t o have w i d e r g e n e r a l i t y  rate  the time-dependent  e v e n t s on t h e  this condition  mortality  may h o l d .  of l a r v a l  and y e a r t o y e a r  For  amphibians  may  (Savage 1 9 * * , B e l l  1974) . Other f a c t o r s such as c o m p e t i t i o n upper  limit  below  the  environmental conditions. limits. Below  limit  this  limits.  limit,  sets  predominating  significance.  size-dependent  mating  success In very  in  by  are  a  food  the  and the In  success,  hierarchy  behavioural  lowest  limit  some i n s t a n c e s  i n others  crowded c o n d i t i o n s  the  individual  will  environmental  that  depend  factors  the upon  ether  Such o r g a n i s m s a r e n o t l i k e l y  of  and i n o t h e r s  success how  than  well  upper  to size.  factors will this  an in  set  be  of  could  probability i tcould  an ' r - s e l e c t e d ' o r g a n i s m , by d e f i n i t i o n , chance  set  variability  i n s u r v i v i n g a v a r i e t y of environmental  great  may  are p h y s i o l o g i c a l l i m i t s  ecological  The f a c t o r t h a t  survival  set  There  At t h e e x t r e m e t h e r e  for  be of  be t h e  conditions. there  is  a  of a p a r t i c u l a r s i z e d i t can  cope  members o f i t s own  to reach large  population  with  species. sizes  52  in  relation  to  their  resources  population  dynamics i s r a t h e r  selected'  organism. Despite  in  the  laboratory there  its  o v i p o s i t i o n s i t e s or  of  a  particular  approach  The  more d i f f i c u l t the  in  the  lepidopterans  are  effects  on of  these  larval  intra-specific this  'scramble'  or  depend  more o r l e s s e q u a l l y  growth  rate:  of p^  of t h i s that and  type  the hence  a result  numbers. thinly  density  distributed  intensity  reduce  that  numbers of  the  in this  respect.  of  larval  l a r v a e i s of is  to of  the  severely  competition  may  stabilize  the  probability  of  reached  in  resources  rate  are  increase  with  size.  between  different  t h i s f o r m . The  high  is  same  the  fluctuations  be  of  the  population  survival  effect  competition  decrease  the  the  having  competition  becomes v e r y the  such  former case the  may  decrease  fruitful  'k-selected'  conclusions  mortality w i l l  body s i z e  will  I f the  a  a study  between l a r v a e  that  melanoqaster  average  population  hence  shown  of competition  i t  dynamics  most  r e w a r d i n g . The  whether  In t h e  divided  strains  of  'k-  locating  population  attractive  be  upon  upon  'contest'.  B a c k e r (1951) has  study  a  Drosophila  in  The  their  plants i n c o r p o r a t i n g c o n s i d e r a t i o n s of  competition  as  success  p l a n t s and  c r o w d i n g would  thesis will  of r e a r i n g  the  of  than with  field.  involve a  Many s p e c i e s have m u l t i p l e h o s t survival  success  understanding  to  hence a s t u d y  been l i t t l e  species  i s most l i k e l y  organism.  has  and  probability  will in  exceed  may  very  reduced. population extinction  T  population  resources is  effect  be  so  low  and  a  low  numbers  and  Thus  but  a  high  53  intensity  of competition  extinction latter  because  probability  the c o m p e t i t i o n 'contest'  will  few  increase  larvae  would  obtain  be d e c r e a s e d  changed  from  the  some a n i m a l s o b t a i n e d more t h a n  is  some  indication  size  density and  at  pupation  definition, i t s rate  an  In  even  some  ensures next This  that  a female  strategy  'fair  initially  type  to  the  between  larvae  share'.  There  with  :  increasing  at very high d e n s i t i e s  not  (Chiang  an  appropriate  time  descendants.  many  Thus o v e r  r . Two e x a m p l e s  that  measure  may f a v o u r a l i f e - h i s t o r y two  offspring  'bet-hedging'  of  that  in  the  ( S t e a r n s 1976). I n  on  r,  but  h o r i z o n . By a d o p t i n g t h e ' b e t - h e d g i n g ' that  which  a male mates w i t h o n l y one f e m a l e ) .  has been c a l l e d  ensures  one  processes a r e unimportant.  leaves at least  (assuming  is  r . I t has been s u g g e s t e d  be  selection  organism  however, i t i s an argument b a s e d  organism  quite  declines  when d e n s i t y - d e p e n d e n t  generation  highest  their  crowding  d o e s o c c u r i n D.. m e l a n o g a s t e r  of increase,  instances  essence, long  this  f o o d . The  i f under s e v e r e 'scramble'  •r-selected'  some i n s t a n c e s r may  fitness  sufficient  of  1950).  maximizes in  that  but i n c r e a s e s s l i g h t l y  fiodscn By  probability  t y p e i n which t h e r e was i n t e r f e r e n c e  and  the  the  generations  t h e l o n g term  hence  i t  with  a  strategy  an  will  s u c h an o r g a n i s m  from t h i s t h e s i s  illustrate  have  has the  this  point  clearly. First,  body s i z e  l e t us c o n s i d e r c a s e  i s actually  1 of this thesis.  t h e one t h a t  maximizes r over  The optimum the  long  54  term. the  Flies  short  when  o f t h i s s i z e can  term  the  probability  environment long  period  The  size  We  unless  we  is  of  very  Suppose  small  will  depend  cannot  speak  that  the  the  developmental  of  time  of  i t s eggs i n t h e  distributes  we  expected is  number  (F-nc)g. will  c.  which  disperse.  Thus no  argument  is  of  on  offspring  disperse  ignores  i s 1-q  distributes  eggs  the  whilst amongst  size  g  the  •cost  leave  n  i t will  moving  from  disperse!  The  the  'what  is  that  probability patches  leave  one  of  that  leaves  no  a  The not  that  does  in  this  an  will  ?'  does  organism  hence. I f it  lays  expected  fallacy  probability  generation  but  suppose  f l y that  than t h e  the the  the Now  for Let  disperse  i s Fg.  that  probability the  of  1  i t grew  average, the  the  thesis.  (0<g<1) .  is  offspring  animal should  this  amongst n p a t c h e s ,  d e s c e n d e n t s more t h a n one  not  a  observe  development time or  i n which  offspring  more  it  we  a patch p e r s i s t i n g  F and  i t will  Clearly,  that  a  yeasts.  might f i n d i n s u c h  I f a f l y does not  of  leave  F  of  horizon.  a f l y larva  that  the  probability Type  In  because  dominating  i s a high  period over  i t s eggs e g u a l l y  disperse  does  yeasts  'best*  same p a t c h  of o f f s p r i n g  leaving  a  a f l y be  all  answer  body s i z e  a l l s i t e s contain  probability  p a t c h t o a n o t h e r be  the  S  there  upon t h e  one  fly  a larger  of f l i e s that  period of  fecundity  number  Type  i n which a l m o s t  define  favour  s e c o n d example i s drawn from c a s e 2 o f  The  total  may  distribution  population it.  selection  always complete development.  a  fly  leave fly  no  that  offspring  is  55  rv (1-q)  . The n c n - d i s p e r s e r  production higher  an  assexually  the longest  eventually  prevail. of  strategy  gives  may  that  might  time  genotypes  will  be  the  alter  persistence very  large  the  simulation  therefore, strategy different.  as  in  whilst the  case  1  we m i g h t  one  The  of Roff  that  we  relationship can only  some  histories  patterns.  case  of  be a b l e  •complex' r e a l i t y good  (1975) o r t o this to  with  i t s and  a  another but sizes  may r e s u l t i n  as demonstrated i n large  study. predict  actually  observe  between  'simple'  be u l t i m a t e l y  will  population  towards such a s t r a t e g y  that  that  result  time t h a n  premature e x t i n c t i o n of t h e p o p u l a t i o n ,  fluctuations  one  this  the  studies  much  the s t r a t e g y  reproduction,  may  a lower  The t r e n d  a l s o has a v e r y  organism  Sexual  produce t e m p o r a r i l y  prevail.  expected  no o f f s p r i n g .  reproducing  persistence  recombination  which  i t has a h i g h e r  o f progeny than t h e d i s p e r s e r  probabilty of leaving  In has  although  population  In  practise,  the  'optimal'  resolved  t o compare p r e d i c t e d  may be  rather  theory  and  whan we  have  and o b s e r v e d  56  FIGOJES  57  Fig  1 : Tha  These  ar?  larval  development  idealized  f u n c t i o n s , used  v=rsions  of those  Drospphila.  TIME -t  in  this  study.  a c t u a l l y ooserved  in  58  Fiq  2 : The  different Wagner  yeasts  curves  found  of  Droso£hi2a  in their  host  mulleri  l a r v x e on  the  p l a n t , Opu^tia.. Data  from  (1944).  i  X r-  growth  i  i  i  i  i  i  <  i  i  i  o z  LU  Y-7  0  30  66  i  i  i  102.  i  i  i  138  •  •  174  i  i  30  TIME-HOURS  i  i  i  66  i  I  I  102  I  138  174-  59  Fiq  3  :  increase type  The  effect  of changes i n a d u l t s i z e  when o v i p o s i t i o n  at  containing  any  given  s i t e s a l l contain  time.  Type S y e a s t s  The  on -cue r a t e o f  t i e same  probability  i s p and t h e p r o b a b i l i t y  of  containing  Type  F yeasts  a l l sites  of a l l  A  i s 1-p.  THORAX LENGTH  yeast  sites  60  Pig  4  :  increase yeasts of a  effect  of changes i n a d u l t  when o v i p o s i t i o n or  a site site  The  Type  S yeasts  containing  containing  sites  may  size  contain  a t some g i v e n  time.  on u e either The  rate  of  type  F  probability  Type S y e a s t s i s f and t h e p r o b a b i l i t y o f  Type  F yeasts  i s 1-f.  THORAX LENGTH  61  Fig  5 : S u r v i v a l o f p.. m u l l e r i l a r v a e  development  time  and  the  as  yeast  a  function  species.  of  Data  the from  Wagner(1944).  Y= 144 - -61X r--«91  100 80  Y-4  © " ©Y-5 Y  6  ©Y-2  60  ®Y-8 ©Y-7  < ^ cr  <Y-1  40-  Y-3  © Y-9  0  100  140 LARVAL  PERIOD  180 (HOURS)  220  62  Fig  6 : Map  per  cactus  showing fruit  the  i n the  average  percentage  5 localities  60  miles  of  sampled  Type by  S  yeasts  Wagner  (1944).  63  Fig and  7  : The  frequency  C r e s t o n i o . Data *  distribution  frcm  o f Type  S yeasts i n Austin  Wagner (1944)  In a l l cases Type S yeasts c o m p r i s e 1 0 0 % of the yeasts present  Crestonia N=9  5 4 3 2 1 CO DC 111 CQ Z)  z  T  8  r  1  1—"—r  Austin N=20  6  2 0  5 T  25 1—"—r  PERCENT  T  45  161 5 1——i——r 85  TYPE S  YEASTS  64  Fig  8 : The e f f e c t  1  of  flight  cn egg  •  net  O  flown  2  production  flown  3 DAY  4  5  6  7  65  Fig for  9 : Differences flies  flown  considered between egg for  between eqg p r o d u c t i o n and  not  and t h e y a x i s  these  days.  production the flown  flown.  the  Note t h a t  The x a x i s  difference after  on  flight  in  adjacent shows <=gg  than  shewn a r e + 2 s t a n d a r d •  NOT  0  FLOWN  t h e unflown  group.  errors.  the days  production  (day 3) t n e d r o p i n  between d a y s 3 and 4 i s s i g n i f i c a n t l y  group  days  Confidence  greater limits \  FLOWN  T,T+1  66  Fig  10  flight  :  The  estimated  'reproductive  i n D r o s g p h i l a melanocjaster  calculating  this  cost.  Sae  A  Confidence  c o s t * of a one hour text  limits  ror  method  shown  are  of +  standard e r r o r . Y - 21.0 - 5.7X  •  1  2  DAY A F T E R  3 FLIGHT  4  I •. . # ."'«  1  67  Fig  11  the  day  : Th* e f f e c t  of  flight  proceeding  flight.  ••-flies  s t u c k on  p i n s which  Y  -  =  55.6  duration  on  egg  production  d i d not f l y .  0.43X  9'  876-  o  ©  °  •  ©  o  «  'o  T—  X  _r  4  20  1 0  0  1  3  4  5  6 - I  FLIGHT TIME-MINSx10  on  Fig  12  :  production Y =  The  effect  o f t h e two  127. 9 - 0. 74X  of f l i g h t  days  d u r a t i o n on  proceeding  flight.  the  combined  69  Fig Data  13 : R e s p i r a t i o n from  Chadwick  rate  as a f u n c t i o n  and G i l r a o u r  SYMBOL  o f wingbeat.  frequency,  1940 and C h a d w i c * 1947.  SPECIES  SEX  t  D. AMERICANA  MALE  0  D. V I R I L I S  MALE  X  C. REPLETA  FEMALE  D. 5 EPLETA  MALE  Y = -22.8+2.4X r =. 0. 89  •5i  •25  £ £ £  0-  -•25-  x •  O  CD  X  - 5  -(—•  Q. U  —75-I  d* o  ••  -1-0  o  -1-25  -1-5  8-7  8-9  —i 9-1  r  9-3  Log (Wingbeat Frequency) e  9-5  70  Fig  14  : The e f f e c t  increase  when  calculated decrease  of changes i n a d u l t  flight  on t h e b a s i s in  eqg  reduces that  production  size  on  fecundity.  rate  of  This reduction  was  a f l y of thorax of  20  tae  leagth  eggs  per  1mm  day  has due  dispersal.  MAXIMA  *  0  i  1  i  1  1  2  1  1  3  THORAX LENGTH  1  1  4  a to  71  Fig  15  : Th-5 s i z e  compared junction  d i s t r i b u t i o n of n o n - d i s p e r s i n g  to a control of  longitudinal  8-j  sample  longitudinal vein  (n=36).measurements veins  1  and  2  to  flies  (n=17)  made from t h e the  end  2.  control  64-  CO DC LU CD  z:  2 0 non  6  dispersers  4-  °  68  70 72  74  76  78  80  82  WING LENGTH-MICROMETER UNITS  84  of  Fig  16 : t h e s i z e  compared  distribution  to a control  sample  of non-dispersing  files  (n  (n=44).  CONTROL 12 8  CO  I  DC  LU CQ  1  i  i  I  I  1  r-"—j——I  I  1  I  i  l  1  I  > '  NON DISPERSERS 12! 8 i  A-  / 64 66  rn.  68 70  72 74  76  78 80 82  WING LENGTH-MICROMETER UNITS  73  Fig  17  :  laboratory  Size  distribution  stocks of  of  p.. s i l i c a .  natural Data  and  from  Kdmbysellis  Heed (1971).  LAB.F1 N = 347 504  40 3020UJ  10  < z  111  WILD  o . cc 2 2  N = 325  111  18 14  6  •  1-3  1-5  •__ i _  1-7  1-9  2-1  2-3  THORAX L E N G T H - M M .  1st g e n e r a t i o n and  TABLE 1 Parameter values used i n c a l c u l a t i n g r . Values based on data f o r Drosophila melanogaster  from a number of sources.  EQUATION  PARAMETER  VALUE  EGG PRODUCTION At  At ( i - -t  y-e  55-  2. O-IX  LARVAL GROWTH EQUATIONS  44. a +• ct  c  LARVAL SURVIVAL (%)• ±Cro  -  st  21.C  ADULT SURVIVAL (% DAILY SURVIVAL)  * t : time i n days # t : hatching time + pupation time + time i n l a s t phase of growth MAJOR REFERENCES i. Alpatov 1929, Bakker 1959, Chiang and Hodson 1950, David et a l 1974, David and C l a v e l 1967, M M i l l a n et a l 1970 a,b, Prowsner 1935.  75  Effect  o f cage  size  on egg p r o d u c t i o n  i n D.. meianoaa-ster. Egg  production  o f 15 f e m a l e s  i n a l a r g e cage  production  o f 15 f e m a l e s  i n 15  DAY  VIALS SD  the  vials.  LARGE CAGE X  compared t o  X  T SD  1  4.20  3.74  9. 93  9.29  2. 21*  2  23.73  13.04  38.00  19. 82  2. 32*  3  31.60  18.92  46.06  25.03  1.78+  * P<0.025 ONE-TAILED + P<0.05 ONE-TAILED  TEST TEST  egg  76  TABLE 3 Effect  of  Comparison  cage  size  on  egg p r o d u c t i o n  between egg p r o d u c t i o n  one  i n EL. m e l a n o g a s t e r i .  gallon  containers  vials.  »  14  LARGE CAGES  VIALS  X  SD  X  37.07  14.20  49.15  t=2.48, P<0.025 o n e - t a i l e d t e s t  SD 10.62  and  77  TAELj! 4  effect  of  larval  density  on t h e s i z e  and number o f e m e r g i n g  adults.  DENSITY  NOS  EMERGING/VIAL  X  SD  WING LEMGTH X  SD  * HIGH LOW  * Total  •  only;  +  24.9  12.66  78.33  2.66  28  19.1  10.03  79.90  2.01  21  numbers e m e r g i n g  + Females  N  (n=10 v i a l s / d e n s i t y ) ;  t=2.25, P<0.025, o n e - t a i l e d  no s i g . D i f f .  test.  78  TABLE 5  Comparison different  of  the  dispersal  rates  of  flies  densities.  DENSITY  A X  HIGH  SD  12.,80  B  C  X  TOTAL  11. 54  2.00  45  LOW  *  6., 85  4. 68  0.25  16  LOW  +  6..20  6. 27  0.50  25  A : Numbers i n v i a l s  from  which f l i e s  B : Numbers i n v i a l s  containing  C  : Numbers on s i d e s o f box  *  15 v i a l s  placed  i n box  + 30 v i a l s  placed  i n box  fresh  emerged medium.  reared  under  79  TAELE 6 the  mean number  DENSITY  o f males and f e m a l e s r e m a i n i n g a f t e r  A  B  10.2  7.87  3 days.  C  MALES HIGH LOR  *  LOW  +  8.9  0.5  3.87  0.0  4.00  0.15  FEMALES HIGH  A  11.9  LOW  *  LOW  +  3.33  8.7  : Numbers e m e r g i n g  from  0.5  2.07  0.25  2.00  0.35  plugged  B : Numbers r e m a i n i n g i n u n p l u g g e d C : Numbers :  + 30  in vials  vials/box  containing  vials vials  f r e s h medium. } * 15 v i a l s / b o x  80  Alpatov, S.w. , fi£2§2il&JLlil  1929. Growth and v a r i a t i o n of t h e l a r v a e nielanogaster., J . E x p . Z o o l . 52; 407-4 32.  A n d r e w a r t h a H. G. Abundance of  a n d L. C . B i r c h . 1 9 5 4 . The D i s t r i b u t i o n A n i m a l s . U n i v . C h i c a g o P r e s s . 782 pps.  of  and  Anderson W . , 1966. Genetic divergence in M. Vetukhiv's experimental p o p u l a t i o n s of D r o s o p h i l a p s e u d o o b s c u r a . 3. D i v e r g e n c e i n body s i z e . G e n e t . R e s . 7 ; 2 5 5 - 2 66  A n d e r s o n W. M . , 197 3 . 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L., 1952 c o n t r a s t i n g t y p e s o f population i n Droso£hila_j. Amer. Nat. 86; 239-248.  Carson H. L., 1958 the population i S M s t a j j . A d v a n c e s G e n e t . , 9; 1-40.  genetics  of  structure  Droso^hila ~ ~  C a r s o n H. L., D. E. Hardy, H. T. S p e i t h and w. S. S t o n e , 1970. The e v o l u t i o n a r y b i o l o g y o f the Hawaiian Prosgfihilidae.. In Hecht, M. K. and ¥. C. Steere, eds. Essays i n Evolution and Genetics in Honor of Theodosius Dobzhansky , pp 437-543 New York, Appleton CenturyCrofts. 1  C a r s o n H. L., f o r some States. Drcsgphila i n  and H. D. S t a l k e r , 1951. N a t u r a l b r e e d i n g sites wild s p e c i e s of D r g s p p h i l a i n the e a s t e r n United C h a d w i c k , I . e . 1947. The r e s p i r a t o r y q u o t i e n t o f f l i g h t . B i o l . B u l l . , woods H o l e 93 :229-239.  Chadwick, I. E. and D. Gilmour. 1940. 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