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The role of vocalizations in spacing out and mate selection in Pacific tree frogs Whitney, Carl Linn 1973

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THE ROLE OF VOCALIZATIONS  IN SPACING OUT  AND  MATE SELECTION IN PACIFIC TREE FROGS  by CARL LINN WHITNEY B.S., Iowa S t a t e U n i v e r s i t y ,  1970  A THESIS SUBMITTED IN PARTIAL FULFILLMENT OF THE REQUIREMENTS FOR THE DEGREE OF MASTER OF SCIENCE  In the Department of Zoology  We accept t h i s t h e s i s as conforming t o the required  The  standard  U n i v e r s i t y of B r i t i s h September, 1973  Columbia  In p r e s e n t i n g  t h i s t h e s i s i n p a r t i a l f u l f i l m e n t of the requirements f o r  an advanced, degree at the U n i v e r s i t y of B r i t i s h Columbia, I agree t h a t the  L i b r a r y s h a l l make i t f r e e l y a v a i l a b l e f o r r e f e r e n c e  and  study.  I f u r t h e r agree t h a t p e r m i s s i o n f o r e x t e n s i v e copying o f t h i s t h e s i s f o r s c h o l a r l y purposes may by h i s r e p r e s e n t a t i v e s .  be granted by  permission.  Department of  Zoology  The U n i v e r s i t y o f B r i t i s h Columbia Vancouver 8, Canada  Date  1t  September  Department or  I t i s understood t h a t copying or  of t h i s t h e s i s f o r f i n a n c i a l g a i n written  the Head of my  1973  s h a l l not be  publication  allowed without  my  ii  ABSTRACT  This in  thesis  two  investigates  aspects  behavior:  Spacing  selection  of  o f mates by  calling  An  randomly  addition  experiment  tend  to c a l l  added  to  an  occupied  by  role  Pacific  of  males  analysis  vocalizations Frog  breeding  of nearest  on  the  space  breeding areas  neighbor out  available  and  calling  (control) frogs,  of equal  enclosure  distances  more  c o r r o b o r a t i v e evidence  too c l o s e t o g e t h e r ;  calling  male  Tree  on  t h a t males  provided  empty  of  females.  f r o g s showed  distributed  not  of out  §£acino^out:  the  than  if  sites.  An  that  males  numbers o f  frogs  and  an  more s u b s e q u e n t l y  enclosure  called  in  the  control. The  species'  "mating"  call  attracting  females,  experiment,  fewer f r o g s c a l l e d  by  spacing than frog  out.  ca. may  50 then  vocalization I f two  i n an  (S c a l l )  calling  cm),  t h a t the  males  the  D  as  both  usually  S call call.  than  i n the  as  addition  occupied  only  control.  seems t o f u n c t i o n o n l y i n  begin  close  together  making  the S c a l l .  physical  combat  may  i s a s t r o n g e r warning A  well  i n an  enclosure  f r o g s come  move away; i f n o t ,  hypothesized than  call),  functions i n spacing out;  p l a y i n g back D c a l l s  loudspeakers Another  (D  playback  experiment  (less One  follow. I to  nearby  partially  iii  supported  this  hypothesis.  I c o n s i d e r p o s s i b l e f u n c t i o n s of spacing out, and that males which maintain spacing than  they  would  otherwise,  may  attract  more  suggest females  perhaps because females  can more  e a s i l y l o c a t e them. Mate s e l e c t i o n : hypotheses: their  body  attempted  F i r s t , females  low-pitched  correlation of  I  select  test  (there  is  an  between c a l l p i t c h and body l e n g t h ) . A  lengths  and c a l l  this  calling  inverse  comparison  p i t c h e s of males found  hypothesis.  two  l a r g e males on the b a s i s of  vocalizations  with a sample of males from the support  to  i n amplexus  population  Second, females  did  choose males which  i n i t i a t e bouts of c a l l i n g  (chorus  field  a l a b o r a t o r y experiment support  observations  and  leaders).  h y p o t h e s i s . Chorus l e a d e r s a l s o end choruses, r a t e during choruses, choruses, may  and c a l l  a l s o use  call  Eoth  systematic  call  at a f a s t e r  louder than other f r o g s . In nature,  calling  a l l of the time, yet f r o g s show freguent  responsive  by  (measured  latency  s h o r t l y a f t e r having stopped  short-term  females  l e a d e r should s e l e c t f o r  experiment showed t h a t f r o g s  I  as  these d i f f e r e n c e s as cues i n mate s e l e c t i o n .  i n c a l l i n g . A playback  period.  this  more during p e r i o d s not d e f i n e d  The advantages of being a chorus frogs  not  hypothesized waning  of  lulls  are  less  to c a l l ) to stimulus  calls  c a l l i n g than l a t e r  in  the  lull  that f a t i g u e i s r e s p o n s i b l e f o r t h i s calling  tendency.  A  respirometry  i v:  experiment  suggested  (but  quite  f a t i g u e hypothesis i s f e a s i b l e .  inconclusively)  that  the  TABLE OE  CONTENTS  Page  TABLE OF CONTENTS  ,.  i-V  ABSTRACT  i i  L I S T OF TABLES  ...vii  L I S T OF FIGURES  I.  ACKNOWLEDGEMENTS  X  INTRODUCTION  1  A.  1  B.  II.  ix  THE PROBLEMS 1.  Spacing  out  2.  Mate s e l e c t i o n  2 6  THE STUDY ANIMAL  10  1.  Natural history  2.  Vocalizations  C.  STUDY  D.  GENERAL METHODS  ..  10 11  AREAS  ....15 16  THE ROLE OF VOCALIZATIONS IN SPACING OUT OF CALLING FROGS  17  A.  SPACING OUT  17  B.  ROLE OF THE D CALL IN SPACING OUT  24  C.  ROLE OF THE S CALL IN SPACING OUT  30  D.  MOVEMENTS OF MALES  36  E.  SUMMARY 1. 2.  AND  ON THE BREEDING GROUNDS  DISCUSSION  38  o r g a n i z a t i o n of spacing behavior i n P a c i f i c Free Frogs 38 D e f i n i t i o n o f t e r r i t o r i a l i t y i n a n u r a n s ... 39  3. III.  The f u n c t i o n of spacing out  THE ROLE OF VOCALIZATIONS  IN HATE SELECTION .'  41 43  A.  CALL PITCH AS A CUE IN HATE SELECTION  B.  CHORUS-LEADING AS A CUE IN MATE SELECTION ...... 51  C.  43  1.  Chorus l e a d e r s  51  2.  F i e l d evidence that females choose chorus l e a d e r s  54  3.  C o r r e l a t e s of c h o r u s - l e a d i n g .............. 57  4.  Use of c h o r u s - l e a d i n g as a cue i n mate selection  5.  Short-term changes i n c a l l i n g tendency .... 66  SUMMARY AND DISCUSSION  61  70  LITERATURE CITED  72  APPENDIX I  77  vii  LIST  OF/ TABLES  Table  Page  1.  Chronology  2.  Numbers o f f r o g s c a l l i n g control enclosures  3.  of the addition  experiment  . . . . . . . . . . . . . . . 20  i n t h e e x p e r i m e n t a l and  Chronology of the a d d i t i o n loudspeakers  22 experiment  using 25  4.  Numbers o f f r o g s c a l l i n g i n t h e e x p e r i m e n t a l ( o c c u p i e d by f o u r l o u d s p e a k e r s ) and c o n t r o l enclosures ..............28  5.  Mean d i s t a n c e (cm) t o n e a r e s t male n e i g h b o r o f S - c a l l i n g f r o g s and D - c a l l i n g f r o g s  ..31  6.  V o c a l r e s p o n s e o f D - c a l l i n g males t o p l a y b a c k o f D c a l l s 40 cm b e h i n d them . . . . . . . . . . . . . . . . . . . . . . . . . . . 32  7.  R a t e s o f D - c a l l i n g and S - c a l l i n g i n t e n s i t i e s of the c a l l s  8.  A g o n i s t i c responses D c a l l s and S c a l l s  and  relative ......34  o f m a l e s t o 1 min p l a y b a c k c f 35  9.  S n o u t - v e n t l e n g t h s (mm) o f males f o u n d i n amplexus compared w i t h c a l l i n g males i n 1972 and 1973 .....46  10.  F u n d a m e n t a l f r e q u e n c y and dominant f r e q u e n c y ( c y c l e s / s e c ) o f a m p l e c t a n t m a l e s and c a l l i n g males ..48  11.  Maximum number o f c h o r u s e s s t a r t e d (of a t o t a l c f f o u r ) by a member o f e a c h o f 19 p a i r s o f f r o g s ......53  12.  S u c c e s s o f c h o r u s l e a d e r s compared w i t h o t h e r f r o g s i n a t t r a c t i n g f e m a l e s : F i e l d o b s e r v a t i o n s .....56  13.  Relationship  14.  Mean c a l l r a t e s ( c a l l s / 3 0 s e c ) d u r i n g c h o r u s e s o f c h o r u s l e a d e r s and n o n - c h o r u s l e a d e r s  of chorus-leading to chorus-ending  .....58 60  viii  15.  Mean number of c a l l s per 15 min during p e r i o d s not d e f i n e d as choruses of chorus l e a d e r s and non-chorus l e a d e r s  60  16.  R e l a t i o n s h i p o f fundamental frequency and dominant frequency (both i n c y c l e s /sec) to c a l l intensity ...........62  17.  Success of chorus l e a d e r s compared with other f r o g s i n a t t r a c t i n g females: Laboratory experiment ,......6<4  18.  Mean l e n g t h of l u l l (sec) i n c a l l i n g when no D c a l l s were played back during the l u l l compared with when D c a l l s were played back (data f o r the two playback c o n d i t i o n s were lumped) .......68  19.  Mean l a t e n c y t o c a l l (sec) when stimulus presented i n the f i r s t p a r t of a l u l l compared with when presented l a t e r i n a l u l l .................68  ix  L I S T OF  FIGURES  Figure  Page  1.  A. Sound s p e c t r o g r a m o f a t y p i c a l d i p h a s i c c a l l (water=14 C; a i r = 8 . 5 C ) . B. S e c t i o n t h r o u g h a p p r o x i m a t e l y the s i x t h p u l s e o f t h e c a l l ...........12  2.  Sound s p e c t r o g r a m a i r = 8 . 5 C)  of  3.  Sound s p e c t r o g r a m C; a i r = 8 . 5 C)  of a monophasic c a l l .  a staccato  call  (water=14 C; ..............13 (water=14 14  4.  O b s e r v e d (shaded) and e x p e c t e d d i s t r i b u t i o n s o f n e a r e s t n e i g h b o r d i s t a n c e s o f c a l l i n g f r o g s .........21  5.  The a r r a n g e m e n t o f l o u d s p e a k e r s i n the e x p e r i m e n t a l e n c l o s u r e f o r the a d d i t i o n experiment.  .27  6.  S p a c i n g o f f r o g s from l o u d s p e a k e r s t a t i o n s when s p e a k e r s a r e p l a y i n g back D c a l l s (shaded) compared w i t h when no s p e a k e r s a r e p r e s e n t ..........29  7.  R e l a t i o n s h i p o f dominant f r e g u e n c y and f u n d a m e n t a l f r e q u e n c y (of a p p r o x i m a t e l y p u l s e o f t h e f i r s t phase) o f D c a l l s t o length  8. 9.  the s i x t h body .............44  R e l a t i o n s h i p o f d o m i n a n t f r e q u e n c y and f u n d a m e n t a l f r e q u e n c y t o water t e m p e r a t u r e  ..........47  R e l a t i o n s h i p of fundamental f r e q u e n c y ( c o r r e c t e d t o 12.5 C) t o body l e n g t h i n c a l l i n g f r o g s compared w i t h s u c c e s s f u l f r o g s ( e x c l u d i n g one f r o g w i t h an aberrant voice)  49  10.  R e l a t i o n s h i p of dominant f r e g u e n c y ( c o r r e c t e d t o 12.5 C) t o body l e n g t h i n c a l l i n g f r o g s compared w i t h s u c c e s s f u l f r o g s ( e x c l u d i n g one f r o g w i t h an aberrant voice) ............................50  11.  R e l a t i o n s h i p o f c a l l i n t e n s i t y t o body l e n g t h i n c h o r u s l e a d e r s compared w i t h o t h e r f r o g s ............59  12.  A t o p view o f t h e a r e n a used i n t h e l a b o r a t o r y e x p e r i m e n t t e s t i n g whether f e m a l e s a r e a t t r a c t e d to chorus leaders ..................63  X  ACKNOWLEDGEMENTS  I am g r a t e f u l allowing and  guidance a t a l l stages with  drafts  of  the f i e l d this  also c r i t i c a l l y short  crucial S.  my  supervisor.  me t o u n d e r t a k e t h i s  aiding  on  to  o f t h e work. I t h a n k D. J . Tapp f o r  work and f o r c r i t i c a l l y  computing.  reading  several  t h e s i s . Dr. C. J . K r e b s and D r . J . D. M c P h a i l read  'experiments. and  for  p r o j e c t , and f o r h i s a s s i s t a n c e  t h e m a n u s c r i p t . R. Corman  n o t i c e , the e l e c t r o n i c devices  Borden,  Dr. J . R. K r e b s ,  Thanks  B. Webb  are  also  f o r assistance  kindly  necessary due with  built,  for several  D. L a u r i e n t e , programming and  1  CHAPTER  I  INTRODUCTION  A.  THE  PROBLEMS  Males  of  vocalizations  most during  anuran the b r e e d i n g  many y e a r s s p e c u l a t e d a b o u t vocalizations,  but  investigations of  most o f  species females of  s t u d i e s has  are a t t r a c t e d sympatric  biological with  thereby  mechanisms.  of  several  attracted  to  presumably  this  breeding  This possible  conspecific is a  some a n s w e r s .  the  The  focus  r o l e of v o c a l i z a t i o n s have  calls,  species  but  shown  not  and  also  (e.g. B l a i r for  of  experimental  in  that  to  calls  Loftus-Hills  s e r v e as pre-mating  calls  mechanism  have f o r  significance  (e.g. L i t t l e J o h n  may  Males  Observers  studies  to conspecific  1968); v o c a l i z a t i o n s  stereotyped  recent  been t h e  Several  species  make  season.  begun t o g e t  identification.  other  the  only  have t h e y  these  species  isolating  seem 1968  aggregating  to  be  p.  297);  males  into  choruses.  thesis  reports  functions  (Hjla r e a i l l a ) .  of  First, spacing  investigations  vocalizations I wanted  in  maintaining  and  second,  call  parameters or c a l l i n g  whether  on  females  use  behavior  two  i n P a c i f i c Tree  to f i n d  between m a l e s on  of  out the  other Frogs  i f calls function breeding  differences  areas,  among males i n  as c u e s i n mate  selection.  2  1.  Spacing out  Spacing  o u t o f males on b r e e d i n g a r e a s has been  reported  /  for  a  number  (Goodman 1973), Hyla  of  1971;  anuran  Crump  Engystomops arborea  species:  1972),  Dendrobates  Dendrobates  H.  l§£i^ionalis  L§£i°^S£iilus  melanonotus  (Brattstrom  Phyllomedusa  hypochondrialis  (Pyburn  £seudaghrjne 1971),  bibroni,  1969),  hammondi  (Whitford  1960).  in  males  space out:  arenicolor, Ralin  Sana  1967),  Pcostherapis In  trinitatis  territoriality  Glidewell  1971),  and P.  dendi  (Pengilley Emleri  1953),  Tomodactylus  aalindoi  that  the  and  H.  boettgeri  and  1968;  Scaphiopus  nitidus  (Duellman  (Bogert  (Rabb  and  Pipa  pipa  (Pierce (Snyder Rabb  (Duellman  and and  1963a),  (Rabb  and  1966),  and  1960).  the authors describe most  usual  Jvia  1966),  versicolor  panamensis  (Sexton  However, of  calls"  ( S e x t o n 1962),  Prostherapis  one  1968),  ( L u t z 1 9 6 0 ) , Hjfla r e q i l l a  a l l of these r e p o r t s ,  regarding  and  Yarnell  they  Hymenochirus  as " t e r r i t o r i a l . "  and  1970),  of s e v e r a l other s p e c i e s suggest that  Leptodactylus insularum 1963b),  1968),  and  chrysoscelis,  1965),  Yarnell  (Paillette  (Martof  and  (Bunnell  chasing  Dendrobates  H.  and  (Durham and B e n n e t t 1963; clamitans  1972), H y l a f a b o r  Jameson  Rabb  corroboree,  Observations of " t e r r i t o r i a l  fighting too  P.  Rana c a t e s b e i a n a  Wiewandt  pumilig  pustologus (Brattstrom  and  qranuliferus  do  not  provisos  the animals  provide in  the animals defend " f i x e d  evidence  definitions areas"  of  (Brown  3  and  Orians  1970)  o r "home a r e a s "  which d i d m o n i t o r arbitrariness  the  of  this  stipulation:  male B u l l f r o g s  same  night after  the defended former  areas  frogs  were l e s s  qualify  as  ambiguity,  the a p p l i c a t i o n  of the  out.  anurans  Although  distances settled  the  Several  (Bunnell 1970; in  1973;  Snyder  most  of  work on 1969):  Jenssen  1965;  workers observed  behavior.  The  of B u n n e l l  fixed.  animal's  most  the  the l a t t e r  not?  i  studies  of  o u t , none o f  be  done s i m p l y  i f  individuals  investigated  the  anuran  territoriality  and  Preston  1968;  Paillette  1969).  The  approach  to that  territory  i n the bulk  (see  whether c o n s p e c i f i c territory,  e.g.  calls,  elicited  pumilio.  less  from  of  Falls played  territorial  o f t h e s e s t u d i e s on  or  which  to  (1973) on D e n d r o b a t e s meters  being*  other.  similar  and  1969)  nearest-neighbor  expected  Wiewandt  detailed  p l a y e d back two  of  the  Do  space  experimentally  vocalizations  the t e s t  calls  1968;  Jameson  back w i t h i n  that  have  t h e s e s t u d i e s was  bird The  distribution  study  to a l l anurans  do  the  defended  f o r i t . T h i s can  vocalizations  Emlen  and  the a n i m a l s  w i t h r e s p e c t t o each  of  out  (Wiewandt  but  "territorial"  that  studies  accept, f o r the time  distribution  workers  relationship  geographically  tested  the  a t random  catesbeiana)  but i n another  I will  observed  with  point  i n most o f t h e a b o v e - m e n t i o n e d  i t seems c l e a r  comparing  Those  F o r example, i n one  territorial,  term  the a u t h o r s r i g o r o u s l y by  (Rana  night,  Because of t h i s  space  1971).  movements o f i n d i v i d u a l s  (Emleri 1968) areas  (Krebs  She males  anurans found  is  that  elicited  approach that  behavior;  these r e s u l t s concurred  males s p a c e more t h a n two  usually  r e t r e a t upon a p p r o a c h  caused  changes  in  which  Bunnell  calling, Male  D.  a  b o t h as  1965),  1970), H.  catesbeiana  (Eralen  (Jenssen and  Preston  distinct  from  respective  calls  calls may  their  are  function  T h e r e has the  role  of  Peeke f o u n d  been o n l y  that  only  species;  muted  their  as  equally  Peeke c o u l d  which o f  the  indirect  nine  their  of an  as  not,  of  Jameson  1969), and  R.  vocalizations  territories;  when these  defense. i n any  animal,  territory;  that  (Peeke  increased as  seem  trespassing to  c o u r s e , d e t e r m i n e from territorial  defense,  i t i s the  but  was  1972).  defense" i n  controls  of  controls  Vocalizations  vocalizations that  that  H.  mating c a l l s  territorial  able  and  and  l e s s s u c c e s s f u l than  in t e r r i t o r i a l  evidence  to  species*  territories.  males s u f f e r e d  make i s most i m p o r t a n t from  Wiewandt  change  of  of v o c a l i z a t i o n  (Snyder and  d e t a i l e d study,  line  also  intruders.  arborea  ( J a e l a u i s phoeniceus)  a "first  were  trespassers. results  1968;  1968)  muted m a l e s a r e  maintaining  they  one  warn  Hjla  in territorial  Blackbirds  function  but  only  intruders  i n a t t r a c t i n g females  renilla  back w i t h i n  that  patterning"  kind  v o c a l i z a t i o n s i n maintaining  i n Red-winged  in  played  also one  However,  clamitans  mating  might  observations  Playback  "temporal  have o n l y  call.  (Paillette  Rana  and  suggested  and  residents.  a "mating" c a l l  "territorial"  l§£i^i2Salis  of  rate  £umilio e v i d e n t l y  which s e r v e s as  the  meters a p a r t  with  he  to this  rate, expel these males argued  " a d v e r t i s i n g " song,  a  5  v o c a l i z a t i o n given s i m u l t a n e o u s l y (which  Peeke  territorial  also  maintainance  experimentally  (1970)  suggests  study that  function  in  of  Hyla  and  H.  She r e p o r t e d t h a t males  moved  p l a y i n g back c o n s p e c i f i c mating  calls;  and i f c o n f i n e d near the loudspeaker, She  arborea  vocalizations aid in t e r r i t o r i a l  i n these s p e c i e s .  away from a loudspeaker  altogether.  to  display  defense).  Paillette*s geridionalis  showed  with a wing e p a u l e t  also  found  males would stop c a l l i n g  t h a t the t e r r i t o r i a l  g r e a t e r e f f e c t i n c a u s i n g f r o g s to  retreat  call.  difficult  Unfortunately,  it  is  than to  c a l l had a the  mating  assess  the  s i g n i f i c a n c e of P a i l l e t t e ' s r e s u l t s because she d i d not r e p o r t on important  a s p e c t s of experimental  design, such as  the  use  of  c o n t r o l s , nor d i d she present r e s u l t s i n a manner s u i t a b l e  for  statistical Chapter  of Tree  analysis.  I I d e s c r i b e s my  vocalizations Frogs.  in  s t u d i e s of spacing and  maintaining  the  role  spacing among male P a c i f i c  6  2.  Mate  selection  Evolutionary levels  of  choose the  theory  p r e d i c t s that animals  d i s c r i m i n a t i o n i n mate s e l e c t i o n :  partners  o f t h e same s p e c i e s .  show  two  First,  they  will  they  will  " b e s t " a v a i l a b l e c o n s p e c i f i c mates by r e s p o n d i n g  which a r e c o r r e l a t e d w i t h a  Second,  will  wide v a r i e t y  many o f t h e s e However,  second  indeed,  mate s e l e c t i o n  there  the  has  than  most  Studies  of  the  received  i s no e v i d e n c e  cues  detailed  study  of  t h e c u e s used i n  ( e . g . 1972)  Drosoghila  fiseudoobscura.  Using  inbred  mating  (the  females). allow  was a b l e  females to s e l e c t  exclude as  She  the p o s s i b i l i t y  wing v i b r a t i o n  that  this  populations  In Black  system of  for  selection  to  show  rare-type  Borisov mate  she  rare-type  olfactory  m a l e s by  cues  alone  m a l e s , b u t h e r work d i d n o t  (1970)  selection  cues,  presented also  such  evidence  occurs  i n wild  Drgsgphila.  v e r t e b r a t e s , t h e work o f K r u i j t Grouse  on  frequency-dependent  of  that  work  strains,  t h a t f e m a l e s a l s o use o t h e r  rates. of  two  responsible  preferential  that  random.  i s Ehrman's  mechanisms  little  f o r most s p e c i e s  mate s e l e c t i o n  the  of  used.  very  intraspecific  studied  to t r a i t s  the f i r s t p r e d i c t i o n ;  analyses  prediction  i s other  Perhaps  a s a mate.  o f s p e c i e s have v e r i f i e d  include detailed  the  attention;  desirability  select  (Lyjrurus t e t r i x )  and W i l e y  and  Hogan  (1967)  (1970) on Sage  on  Grouse  7  (Centrocercus urgphasianus) species  display  on  is  leks  noteworthy.  to  Males  which f e m a l e s  territories  mating  a Black Grouse l e k the f o u r  males performed five  more t h a n  or s i x p e r i p h e r a l  males,  totalling  accomplished lek.  central  and  and  as c u e s  85%  of the  than  than  Hogan  10$  75%  i n mate s e l e c t i o n : (females  may  be  activity  (especially  fighting);  males seem t o use  In  Littlejohn  and  males w i l l  breed.  i n dense groups,  brief  breeding  neighboring  males  and  (Licht  the breeding season,  which group.  are f i r s t  a  females,  s p e c i e s shows  calls 1968;  female  (e.g.  Bogert  Schmidt  choice  1969).  determines  f o r example,  d u r i n g the f i r s t  few  frequently  attempt  1969) ; a t l e a s t the  successful  t o r u s h o u t and  However, i n  general  In Rana g r e t i o s a ,  season  number  clasp of  male  "tactics."  Loftus-Hills that  might  smaller  of  courting  to c o n s p e c i f i c  p. 211;  between  females  level  females  are a t t r a c t e d  Grouse  to areas of high  i n a number o f a n u r a n  which  a Sage  males have  higher (3)  population,  differences  more e f f e c t i v e  T h i s a l o n e d o e s not e s t a b l i s h  of  on  the  central  J  Experimental evidence  1960  call  male  attracted  males have a  central  while  the  (1) C e n t r a l  (2) C e n t r a l  mating.  most  t h a n \5%;  three  density);  that  of  both  greatest  less  o f the matings  suggested  the  p e r i p h e r a l B l a c k G r o u s e males t h a t  territories  central  far  copulations,  males p e r f o r m e d  less  more  Kruijt  use  on  by  come f o r  Males h o l d i n g c e n t r a l success:  have  of  days  females  species,  of  the  amplexus  during the males  males  may  with  early be  part those  approaching  the  observations  of  8  females approaching  males and t o u c h i n g  before  move  the  males  from  (Blair  1963 p. 706; Bragg  Brown  and  Pierce  Casual  observations  species  males  which  pitches and to  vary  reveal  that them  in  Rana  and  this  (Bogert  large  1960).  evidence that lacking,  but  the  advantage o f a g r e a t e r females. this with  The  The  work  discussion.  reason,  low-pitched  smaller  of  males  vocalizations  of large very  of  Capranica that  call  Snyder  re ^ i l la,  holds  appealing that  f o r other t o suggest  females  choose  vocalizations.  Direct  select  large  small,  may large  males  non-calling  in  male, this  males  and way  to  male Rana c a t e s b e i a n a to  i s  is male he take  attract  (1965) i s a l s o r e l e v a n t t o  playback  males b u t n o t t o c a l l s briefly,  and  H_y l a  a larger calling  ability  He f o u n d  territorial  mating c a l l s  mates, and  around  among  First,  (1965)  r e l a t i o n s h i p probably  (1959) o b s e r v e d  gathered  that  mate.  and  It i s intuitively  Axtell  species,  pitch i s inversely related  catesbeiana  of their  1952;  variability  Capranica  call  1968;  c h o r u s o f a l m o s t any  vocal  f e m a l e s of any s p e c i e s  Bufo s p e c i o s u s suggested  that  males make b e t t e r  on t h e b a s i s  these  may u s e i n mate s e l e c t i o n .  (1965) f o u n d  size  in  males w i l l  of  Yarnell  1938; L i v e z e y  that,  a breeding  among i n d i v i d u a l s .  respectively, species  of  two k i n d s  females  Jameson body  1958) i n d i c a t e  them  stations to clasp  and  1968; Green  does d e t e r m i n e which  anuran  calling  1959; B r a t t s t r o m  1965; Emlen  M a r t o f and Thompson female choice  their  or almost touching  that  respond  of c o n s p e c i f i c  of the  small  males.  high-pitched  9  v o c a l i z a t i o n s o f the s m a l l males c o n t a i n energy i n a frequency range  which  Capranica  inhibits  the  territorial  calls,  i t seems reasonable t o  males do not respond t e r r i t o r i a l l y not  serious  competitors  of  call  1968;  in  calling  1967;  inconclusive  Brattstrom and Y a r n e l l  F o s t e r 1967; P a i l l e t t e  field  observations  to  be  clearly  1970).  first  Workers  individuals  (Brattstrom  (Insecta),  this  Busnel  found that s t r i d u l a t i o n l e a d e r s are more s u c c e s s f u l at  a t t r a c t i n g females than other males; however, i t i s not what  1962;  1968) have been made which support  In a s i m i l a r system i n T e t t i g o n i i d a e  (1967)  behavior.  when a chorus begins, are favored by f e m a l e s , but only  few  idea.  because  i n i t i a t i o n by i n d i v i d u a l s i n breeding  have s p e c u l a t e d that "chorus l e a d e r s " , the  a  perhaps  (see Bogert 1960 f o r review; Brattstrora and Y a r n e l l  Duellman  to c a l l  if  calls.  choruses of a l a r g e number of s p e c i e s appears non-random  that,  to s m a l l males, s m a l l males  The second kind o f v a r i a b i l i t y i s sequence  suggest  f o r females,  females are not a t t r a c t e d t o t h e i r  The  Although  d i d not study t h e responses of females to l a r g e and  s m a l l males*  are  response.  cues  the  females  use  in  mate  selection  s t r i d u l a t i o n l e a d e r s a l s o behave d i f f e r e n t l y i n s e v e r a l  clear because other  ways from non-leaders. These  two  hypotheses  are not n e c e s s a r i l y  females c o u l d r e j e c t s m a l l males on the b a s i s and  select  of  alternatives; call  chorus l e a d e r s from the remaining males.  pitch Chapter  10  III  describes  B.  THE  1.  Natural  my  Pacific  which  Tree  Hylidae.  Montana, shallow,  for  is  a  member  I t i s a small  frog,  and  and  temporary  east Nevada  ponds,  season  is  from  least  eight  (Stebbins  as w e l l  but d u r i n g  relatively  long  call  during  t h e peak o f t h e the  day.  highly  nearly  variable in to the  I t breeds i n  permanent  water.  f o r temperate  Columbia,  season  zone  males  characteristically breeding  tip  Ocean t o w e s t e r n  1966).  more  Males  the  Columbia  as  weeks.  of  the P a c i f i c  i n t h e Lower M a i n l a n d o f B r i t i s h  at  night, also  Idaho,  breeding  frogs;  Frog  ranges from s o u t h e r n B r i t i s h  Baja C a l i f o r n i a ,  The  hypotheses.  history  cosmopolitan  of  o f both  STODY ANIMAL  The  color,  investigations  call  they  call at may  11  2.  Vocalizations  This that  study  i s concerned  males make.  The s p e c i e s *  diphasic first  vocalization  phase  As  many  can  be s e e n  second  (Fig. 1a).  a v e r a g i n g about  i n F i g . 1).  harmonic  Calls  harmonic;  this  cycles/sec less The  show  (only  i n Marion Lake  frogs.  4  a  pulses.  the lowest  from  is  1790  Marion  five  i n the to  Lake,  peak o f e n e r g y  "fundamental" f r e q u e n c y ranged  is  are pulsed, the  freguency  from  a smaller  call)  the second,  i t ranged  frogs  vocalizations  (D  phases  The " d o m i n a n t "  o f 60  2330  British  i n the f i r s t  from  850 t o 1250  The h i g h e r h a r m o n i c s  contain  energy. second  which  vocalization  males  than c a .  50 cm).  longer  than  D  the  studied  i s a "staccato"  call  make i n r e s p o n s e t o o t h e r s c a l l i n g  (less  (Fig.  call  Both  12 p u l s e s ;  ( F i g . 1b);  in calls  Columbia.  call)  mating  a s seven f r e g u e n c y bands o c c u r  cycles/sec  even  w i t h two d i s t i n c t  This c a l l  call,  and  is  not  divided,  (S  nearby  is  much  h a s a' much s l o w e r p u l s e  rate  2). A third  vocalization  but  i t s significance  in  pulse  rate  These  call  individuals call  i s mentioned  was n o t s t u d i e d .  to the D c a l l ,  seem t o g i v e t h i s non-calling  (M c a l l )  in  The M c a l l  b u t monophasic  response  i n the thesis,  to  i s  similar  (Fig. 3).  movements  of  Males nearby  (males o r f e m a l e s ) .  characteristics  agree  largely  with  those  12  Figure  1.  Air=8.5 call.  a. Sound spectrogram o f a t y p i c a l d i p h a s i c c a l l C).  (Water=14 C  b. S e c t i o n through a p p r o x i m a t e l y the s i x t h p u l s e o f the  13  F i g u r e 2.  Sound spectrogram o f a s t a c c a t o c a l l  (Water=14 C; Air=8.5 C ) .  Cycles —^  O  o o _ l  o o I  Per  Second  GO  O  o o -  I  (Jl  O  1  1_  14  F i g u r e 3.  Sound spectrogram o f a monophasic c a l l  (Water=14 C; Air=8.5  C).  Seconds  15  reported from  C.  for Pacific  whom I b o r r o w e d  T r e e F r o g s by S n y d e r and Jameson  (1965),  t h e d e s c r i p t i v e names f o r t h e c a l l s .  STUDY AREAS  Most p a r t s o f t h e s t u d y were done a t M a r i o n L a k e , a s m a l l (800  m  by  Mountains (1967) from  200 m) l a k e  50 km e a s t  described  emergent  during  April,  Some British  was  the  done i n s m a l l  Endowment L a n d s  u s u a l l y temporary  call  during  differences  around  Columbia.  Pacific  Efford  Tree Frogs  periphery  of  the  call lake  May, and J u n e .  Columbia  but  British  the lake i n d e t a i l .  are  frogs,  a t 300 m e l e v a t i o n i n t h e C o a s t  o f Vancouver,  vegetation  work  March,  Vancouver  lying  April,  drying  ponds on t h e U n i v e r s i t y o f  near Vancouver. up i n l a t e  were  noted.  Here  ponds frogs  and May.  frogs average s l i g h t l y otherwise  summer.  These  no  smaller  morphological  than Marion or  Lake  behavioral  16  D.  GENERAL METHODS  Most captured the  field frogs  light  not  on  vent  was  done  at  with the a i d of a  frogs  further  minutes.  work  usually  disturbed,  Frogs  six-volt  caused most  night.  them  would  I observed  lantern.  and  Shining  to stop c a l l i n g , resume c a l l i n g  but i f  in a  few  from  snout  to  toe-clipped  for  individual  Uher  Report-L  were c a p t u r e d by hand, measured  to the nearest m i l l i m e t e r ,  and  identification.  Calls recorders speed  were equipped  was  temperature 1 cm  recorded  always 1 cm  with 9.5  Dher  above t h e water  surface  were t a k e n  A small measure c a l l  and  4000  microphones.  After  below t h e s u r f a c e  model 675  M514  cm/sec.  were a n a l y z e d f o r f u n d a m e n t a l Kay  with  each and  Recording  recording, a i r  water  temperature  t o t h e n e a r e s t 0.5 dominant  tape  C.  frequency  Calls  using  a  used  to  sound s p e c t r o g r a p h .  s o u n d - l e v e l meter intensities.  (Realistic  33-1028)  was  17  CHAPTER THE  A.  ROLE OF  SPACING  VOCALIZATIONS IN SPACING OUT  the  and  Tree  calling  "either  Jameson  Frogs  male  D call  space  is  out  to the S c a l l .  the  study,  (1965) on  approached  CALLING FROGS  Both  reported evidence  the  by  i n v a d i n g male has  accommodates t o t h e my  OF  OUT  Snyder Pacific  II  breeding  another  to t e s t  grounds:  male,  If  i t changes  f r o g s make t h e  S  call  a  from until  r e t r e a t e d o r t h e r e s i d e n t male  invader's presence."  I attempted  t h a t male  the  As a f i r s t  hypothesis  step  t h a t males  in  space  out. A  direct  question: at  "Do  random  question,  test  of  the  hypothesis  c a l l i n g f r o g s space  on I  the made  available a  out  would  more t h a n  calling sites?"  "nearest-neighbor"  of  distribution  o f f r o g s t o a random d i s t r i b u t i o n .  hypothesis  in  which e q u a l  calling if from  the  frogs)  i n d i r e c t l y by  area  and  an  means o f an  unoccupied  unoccupied  area.  the  answer of  the  tested  experiment, occupied  I predicted  area  this  observed  I also  t o an  the  distributed  the  addition  area.  o f c a l l i n g f r o g s i n an  c a l l i n g t h e r e , more o f  To  comparing  numbers o f f r o g s were added  presence  previously  frogs,  if  analysis  dispersion  the  calling  answer  prevents  added f r o g s would c a l l  (by that  others in  the  18  Methods Both  the  nearest-neighbor  analysis  and  experiment were done at Marion Lake i n f i e l d enclosures  measured  approximately  3.2  the  addition  enclosures.  m by 3.2  The  m with  walls  c o n s t r u c t e d of p o l y e t h y l e n e i n a manner such t h a t f r o g s not  could  escape. leasestzliexahbor_ana 1 j s i s :  an e n c l o s u r e , allowed determined, with  I introduced  them approximately  the a i d of a g r i d  the  position  of  each  both  the X and  Y coordinates.  for  five  separate  yielding  a  observed  distribution  compared  with  of  The  sites  the  enclosure, 10 cm f o r  p o s i t i o n s of c a l l i n g  10, 8, 6, and  was  calculated  35  nearest  of  nearest-neighbor  at  random  6.  The  for  neighbor  simulated expected  a l l o w i n g " f r o g s " to s e t t l e calling  placed over  then  frogs  i n t r o d u c t i o n s were determined, the number  to nearest c a l l i n g neighbor  a  24 hr to s e t t l e ,  c a l l i n g f r o g to the nearest  c a l l i n g being, r e s p e c t i v e l y , 5,  total  12 male f r o g s to  each  frog,  distances.  This  distances  was  distribution on  distance  the  56  obtained  different  used during the p e r i o d of o b s e r v a t i o n s .  56 s i t e s i n c l u d e  those  observations  several  of  which of  were  used  during  by  These  subsequent  the f i v e groups of f r o g s  (these  o b s e r v a t i o n s were not i n c l u d e d i n the spacing a n a l y s i s because of p o s s i b l e non-independence from the each group). could  settle  The was  first  observation  for  only other r e s t r i c t i o n placed on where f r o g s that  they  could  not  s e t t l e on any  site  19  a l r e a d y occupied by another f r o g .  The s i m u l a t i o n was done  times,  t a b l e , f o r each of the f i v e  using  observed  a  random  group s i z e s .  nearest neighbor  numbers  The sum of the average  d i s t a n c e s f o r the f i v e  with the observed  Two  ex  enclosure,  f r o g s was  then  enclosures.  to  groups  was  compared  e n c l o s u r e s were used.  established  numbers  of  i n the  experimental  f r o g s were added t o both the chronology  of the  of a n a l y s i s , the  number  of  frogs  already  i n the experimental e n c l o s u r e before a d d i t i o n of f r o g s  both e n c l o s u r e s was d e f i n e d as the maximum number observed  calling after  on n i g h t s two and t h r e e ; t h e number of the a d d i t i o n  calling  frogs  on n i g h t s four and f i v e .  The  The experiment  main reason f o r doing the  t o ensure  frequent  was run t h r e e  experiment  high d e n s i t i e s of c a l l i n g  frogs.  in  time.  enclosures  Because of the  and s u b s t a n t i a l movements of f r o g s , the d e n s i t i e s i n  unenclosed obtain  calling  i n each e n c l o s u r e was the maximum number  times, the r o l e s of the two e n c l o s u r e s a l t e r n a t i n g each  was  A  procedures.  For purposes calling  equal  field  Table 1 d e s c r i b e s i n d e t a i l  experimental  d i s t r i b u t i o n s of  distribution.  j ^ M f e i g " E§Iiinen-t: group of c a l l i n g  10  areas vary widely i n time, making i t  sufficient  and  c o n s i s t e n t experimental r e s u l t s .  a l l three t r i a l s , the a b s o l u t e enclosure  (10, 8, 6/ca.  difficult  density  10 m , 2  g r e a t e r than the maximum observed  i n the  to For  experimental  r e s p e c t i v e l y ) was equal to or outside.  However, I d i d not  20  Table  1,  Chronology o f the a d d i t i o n experiment.  Ma n ipu 1 a t i o n s a nd 0bserya t ign§ Night  Experimental E n c l o s u r e  1  Add 12 f r o g s  2  Count number of c a l l i n g f r o g s  3  Count number of c a l l i n g Add  4  Contro1_Enclosure  frogs  8 frogs  Add 8 f r o g s  Count number of c a l l i n g f r o g s Count number of c a l l i n g f r o g s  5  consider that  that t h i s  Count number of c a l l i n g frogs count number of c a l l i n g frogs  would i n v a l i d a t e the  results;  I  reasoned  i f c a l l i n g f r o g s i n an area i n h i b i t o t h e r s from  there, t h i s e f f e c t different,  w i l l simply  be g r e a t e r ,  not  calling  qualitatively  when the d e n s i t i e s are higher.  Hesults_and^Discussign Nearest neighbor a n a l y s i s :  Figure  males space out more than, i f d i s t r i b u t e d called  closer  together  than  4  shows t h a t randomly;  calling  no  40 cm, and a spacing  frogs  effect i s  n o t i c e a b l e up to 50 cm. A d d i t i o n experiment: Fewer f r o g s c a l l e d to the e n c l o s u r e  a l r e a d y occupied  after  being  by c a l l i n g f r o g s than  added called  21  Figure 4.  Observed (shaded) and expected d i s t r i b u t i o n s of nearest  neighbor distances of c a l l i n g frogs. p<0.01 (Kolmogorov-Smirnov t e s t ) .  The difference i s s i g n i f i c a n t ,  21a  12-  T  20  1  V I 40 60  l l  I  I  80  Distance  I 100 120 I  to  I  I  r i 1 i i I * 140 160 1 8 0 2 0 0 2 2 0 2 4 0 2 6 0 1  Nearest  1  1  1  I  Neighbor  1  (cm)  i  22  after  being  added to the empty e n c l o s u r e  Table 2. Numbers of f r o g s c a l l i n g control enclosures.  in  (Table 2 ) .  the  Most of  experimental  and  Number C a l l i n g Experimental,,Enclosure Trial  Before after Addition Addition  Contrgl_ Enclosure  (AfterBefore) 1  Before After Addition Addition  (AfterBefore) 1  1  10  13  3  0  7  7  2  8  11  3  0  6  6  2  6  7  1  0  5  5  24  31  7  0  18  18  Total  ^ s i g n i f i c a n t l y d i f f e r e n t ^ p<0.001  (t=18.7)  the f r o g s which d i d not c a l l  were  walls  evidently  of  the  enclosures,  These r e s u l t s a r e not simply f r o g s than c a l l i n g one  time,  the  number  a  observed  or  attempting  consequence  of  near  to escape. having  different  sites  used  sites  during  The r e s u l t s of both the nearest-neighbor  together.  experiment The  more  (as judged by the  experimental period) f a r exceeded the number of c a l l i n g  addition  the  s i t e s i n the experimental e n c l o s u r e ; a t any  the number of p o s s i b l e c a l l i n g of  on  show  results  that of  the  entire frogs.  a n a l y s i s and the  f r o g s tend not to c a l l c l o s e addition  experiment  are  23  particularly calling  having  to the area. high  elsewhere  greatly  of  in  that  the  time,  calling  stations  never  areas  a t Marion  small  Lake.  areas  f o r no a p p a r e n t  up." As  fluctuated reason;  this  was l i m i t i n g  the  which a p p e a r e d  t o have  suitable  Therefore, spacing  behavior  i tquite likely  limits  males i n t h e densities  in  areas. The  deduced  role from  of  vocalizations  these r e s u l t s ;  following  sections.  e n c l o s u r e s and a t l a r g e  that  in  Observations  followed soon  "bouncing" toward toward  The r e s i d e n t  immediately  one  behavior  which  each  other  frog.  be t a k e n  a D-calling  frog  would  or at  in  i nthe means  o c c a s i o n s I saw a  begin  begin  S-calling,  I f one o f t h e f r o g s d i d  would  first  another  male, s t o p , t h e n  usually  both  up  o f f r o g s both  On s e v e r a l  by t h e i n t r u d e r .  retreat,  the  o u t c a n n o t be  i n the lake did reveal  male swim n e a r  D-calling.  spacing  subject w i l l  m a i n t a i n i n g s p a c i n g , however.  non-calling  not  frogs  and s e t t l e  the population of c a l l i n g  l a k e a s a whole, a l t h o u g h  of  in  had f r o g s .  p r o b a b l y does not l i m i t  the  t h i s i s t h e case  A l s o , many a r e a s  other  areas are " f i l l e d  n o t have o c c u r r e d i f s p a c i n g b e h a v i o r  population.  in  presence o f  individuals,  calling  times  the  f r o g s presumably a v o i d  densities  many  that  calling  calling  unless a l l possible  mentioned above,  small  showing  In nature,  densities  i s no e v i d e n c e  should  in  f r o g s i n an a r e a c a n i n h i b i t  confined  There  interesting  not  a  distinctive be  oriented  The f r o g s would soon b e g i n  t o bounce  o t h e r , making p h y s i c a l  might  begin  c o n t a c t with bouncing  blows  24  of  vocal  sac  followed  by  while end  against the  front  legs  deflated,  B,  frogs  S - c a l l i n g and  a f t e r one  THE  (Snyder  and  f r o g would  Jameson spacing  long  postulated  results  suggest  serve  both  that  designed  spacing  males.  One spacing  (1970) d i d the  study  this  to observe  speaker.  is  to  a n i m a l has  method,  through  sac),  the  mating  to  In  test  mute  can  D  from  indirect  whether a  the  This  approach  may  A similar  this  of  evidence.  the  has  Hylids  of  of  role  other I  describe  plays  an  a role in  vocalizations a n i m a l s , as  Blackbirds.  kind  in  two  D call  role  females  (1970)  section,  infer  taken  The  function  dual  in  Peeke  However, i f  v o c a l i z a t i o n , using role  of  A more d i r e c t  particular vocalization,  was  the  Paillette's  experimental  a loudspeaker, i n h i b i t s  would  deflating i t .  call  whether t h e  only  fight  attracting  s o n g , and  more t h a n one  one  in  calls  the  a l l the  swim away.  i n h i s s t u d y o f Red-winged  vocalizations is  the  the  be  OUT  bird  method f o r s t u d y i n g out  then  between m a l e s . for  might  (usually a n t e r i o r to  vocal  SPACING  functions.  experiment of  Usually  other  1965),  behavior  to c l a s p each o t h e r ,  t o i t s known f u n c t i o n  maintaining been  the the  D CALL IN  In a d d i t i o n  This  kicking strongly.  around  defeated  sac.  trying  frog clasped and  ROLE OF  vocal  a n i m a l s from  approach  played  calling  t o examine t h e  specific  back  near  r o l e of  the  the  D  25  call  i n spacing  rationale  to  out.  An  addition  D  inhibit  similar  t h e one d e s c r i b e d a b o v e , was d e s i g n e d  two q u e s t i o n s : "Do f r o g s s p a c e back  experiment,  calls?"  and  o u t from  f r o g s c o n f i n e d t o the a r e a  from  t o answer  loudspeakers  "Does t h e p r e s e n c e  of D c a l l s  in  playing  i n an a r e a  calling?"  Methods Experimental as  f o r the f i r s t  the  procedures addition  experimental  loudspeakers  ( T a b l e 3) were b a s i c a l l y  experiment,  enclosure  playing  back D  Chronology Table 3. loudspeakers.  was  except  that  occupied  t h e same  this  time  by  four  only  calls.  of  addition  experiment  using  M a n i p u l a t i o n s and O b s e r v a t i o n s Niqht  Experimental  1  Turn Add  2  of  A  minor  on  Enclosure  loudspeakers Add  12-13 f r o g s  Count number calling frogs  difference  number o f c a l l i n g  Control  Enclosure  of  i n procedure  f r o g s o n l y on  the  C o u n t number calling frogs  was t h a t  first  12-13 f r o g s  I counted  night  after  the the  26 \  addition, calling first  because  I  had  found  no d i f f e r e n c e i n the number  on the f i r s t and second n i g h t s a f t e r a d d i t i o n addition  experiment.  The  ( A l t e c 405A) i n the e n c l o s u r e i s speaker they  originally  air=10 C).  T h i s was  identical  loop tape was  to  a  stepping  accomplished  relay  which  Thus,  in  a  db 50 cm  bouts  minutes  water=15 C;  with a loop tape  containing  speakers  minutes before c a l l i n g  in  of  four  played  back  frogs,  calls of  then  are  real  frequent  The i n t e n s i t y of the  Since f r o g s  the l a k e .  approximately  The  speakers  above the s u r f a c e of the water on remained  on f o r only  calls  w i t h i n the range of typically silent  call  equal  in  for several  a g a i n , a v a r i a b l e on-off timer was  to s e t the amount of c a l l i n g frogs  connected  to the a n t i p h o n a l c a l l i n g  long,  Each  calls/min;  i n f r o n t of the speaker) was intensities.  several  5.  the r a t e a t which  turned each speaker  chorus  natural calling  the  Figure  to play back a t 120 c a l l s / m i n .  the  corresponding  (although  (30  o v e r l a p p i n g of c a l l s would o c c u r ) . (92  in  the  loudspeakers  played on a s i n g l e tape r e c o r d e r ,  every f o u r t h c a l l . seguentially,  recorded  D c a l l s , spaced  The  frogs  shown  played back D c a l l s at approximately  were  nine  arrangement of  in  to  used  that  of  were p l a c e d about 4 cm  wooden stands.  The  stands  i n both e n c l o s u r e s f o r a l l t r i a l s of the experiment,  but I a l t e r n a t e d the speakers  between the e n c l o s u r e s .  For the spacing a n a l y s i s , I computed the d i s t a n c e of each calling  f r o g from the nearest speaker  distribution  stand and  compared  obtained f o r f r o g s i n the experimental  the  (speakers  27  Figure 5.  The arrangement of loudspeakers i n the experimental enclosure  for the addition experiment.  Each speaker faced a corner of the  2  enclosure.  The 1 m  area i n the middle of the enclosure was  fenced to  keep frogs out because, unlike the c a l l s of r e a l fro.gs, the sound from the loudspeakers was  unidirectional.  w  loudspeaker  ~— enclosure  wall  28  playing)  enclosure  with  that  of  frogs  in  the  control  enclosure.  R e s u l t s and D i s c u s s i o n Frogs loudspeakers  spaced out more from the speaker s t a t i o n s when the were p l a y i n g back D c a l l s ,  not s i g n i f i c a n t frogs called  (Fig.  but the d i f f e r e n c e was  6 ) . However, i n a l l s i x t r i a l s ,  i n the c o n t r o l e n c l o s u r e  than  more  i n the experimental  (Table 4 ) ; t h i s d i f f e r e n c e was s i g n i f i c a n t .  Table 4, (occupied  Number of f r o g s calling i n the experimental by four loudspeakers) and c o n t r o l e n c l o s u r e s .  Number Trial  Calling  1?P§£imental_ E n c l o s u r e *  Control^Enclosure *  1  8  9  2  6  7  3  3  5  4  7  8  5  8  10  6  9  11  Total  41  ^Significantly  different,  I  50 p<07001  (t=12.5J  29  Figure 6.  Spacing of frogs from loudspeakers when speakers are playing  back D c a l l s (shaded) compared with when no speakers are present.  The  d i s t r i b u t i o n s are not s i g n i f i c a n t l y d i f f e r e n t , 0.20>*p>0.10 (KolmogorovSmimov test) .  29a  20 -  20  40  60  8 0 100 120 140 160  Distance to Nearest Speaker Station (cm)  30  These l a t t e r r e s u l t s maintaining without that  any  other  frogs  from  play  possess  a role  B O L E OF  THE  Snyder  this  to  (less  than  the  which of  50  the  one  when  cm).  leave would  S call  test  the  the  approach  The the  hypothesis of  that other  as  can  The  suggested field  move 5 m male,  I  that  observed  or  the  was  D  that  this  of  males.  the  i s given  i n a random  I  with  in  any  the  The  results  support  5).  the  results  by  no  nearby one  of  fight, the  males:  To  response  to  of  first of  males  examine  systematic  measure  the  S-calling  male  direction,  measure  agree  that  I did a series  male neighbor  is a  males would  section,  to  S call  calling  usually  male neighbor. However,  frogs  D-calling  male began  S call  and  fighting,  females,  observations  methods were  then  area,  inhibit  attracting  In  males,  encountered,  (Table  such  in  OUT  upshot  area  the  nearest  nearest  c a l l s i n an  -  the  D-calling  as  function  distances_gf__S-,.,,and D2calling_  to  nearest  D  spacing,  another  i n spacing  observations.  distance  own  leave.  Mjearest-neighbor  field  (1965) my  do  communication.  Many t i m e s  S-calling ca.  well  SPACING  vocalization;  males would  after role  Jameson  of  mechanisms,  i n male-male  IN  calls  presence  Thus, as  interpretation.  shift  D  for maintaining  S CALL  and  territorial  the  behavioral  c a l l i n g there.  calls  C.  spacing;  show t h a t  select  distance the  the  to i t s  hypothesis  means e x c l u d e  the  31  Table 5. Mean d i s t a n c e (cm) t o nearest male neighbor of S - c a l l i n g f r o g s and D - c a l l i n g f r o g s . Table i n c l u d e s data f o r 10 p a i r s of f r o g s .  S-Ca11in^_Frogs  D-Calling_Frogs  36 Significantly  possibility females; likely  125 d i f f e r e n t , p<0.001  t h a t males a l s o  in  the  S  call  (Hilcoxon  in  test)  response  to  nearby  type of o b s e r v a t i o n s made, one would  not be  to observe t h i s s i n c e , a t any one time on the  breeding  grounds, males g r e a t l y outnumber females. Voca 1_reSJDOnse_to_mgdels: To examine the p o s s i b i l i t y males a l s o s h i f t  to S - c a l l i n g  that  i n response to nearby females, I  made two p l a s t e r - o f - p a r i s models of f r o g s , p a i n t e d t o resemble real  frogs.  One model had an i n f l a t e d  v o c a l sac (to resemble  a male); the o t h e r resembled e i t h e r a female o r (females  major  d i f f e r e n c e being the l i g h t e r c o l o r of females under  of  little  from d e f l a t e d  jaw). Each model, hung from a wire f a s t e n e d  males, the the  to the end  a p o l e , was placed on the water s u r f a c e 30 cm i n f r o n t of a  D-calling responded for  very  "deflatedV  male  lower  differ  a  f r o g , then moved s l o w l y toward the frog,. with  S calls  No  to p r e s e n t a t i o n of e i t h e r model  each model); i n s t e a d , a l l f r o g s responded  .These r e s u l t s agree with f i e l d  observations  frogs (N=10  with the M c a l l . of  frogs  giving  32  the  M call  when e i t h e r d e f l a t e d ,  approached them. inflated the  Thus, v i s u a l d e t e c t i o n  males, does not  possibility  remains  that  y°g, a J:^£g§E9I]§g-  playback playing  to  the  the  disturbance)  D  S-calling,  inflated  although  model  was  Elaybgg]^,, of D , c a l l s : Snyder and  D - c a l l i n g males  calls  40  D-calling  cm  respond  with  S  calls  I repeated t h i s experiment behind  (to  avoid  males at a volume w i t h i n  defined  during  the  1 min  presentation  are s i m i l a r to Snyder and  as one  period.  My  by  the range of  silent.  was  to  visual  For c o n t r o l s , the loudspeakers  response  not  Jameson  natural c a l l i n t e n s i t i e s . A  even  response.  of D c a l l s near them. back  males or females  of nearby f r o g s ,  appear to e l i c i t  r e a l i s t i c enough to e l i c i t  (1965) found t h a t  non-calling  was  or more D c a l l s made results  (Table  6)  Jameson's,  Table 6. Vocal response of D - c a l l i n g males to playback of D c a l l s 40 cm behind them.  Playback  Change t p _ S - C a l l i n g  D calls None Significantly  Hot  Change to  S-Calling  9  1  0  10  d i f f e r e n t , p<0,005 ( F i s h e r ' s  test)  33  These r e s u l t s i n d i c a t e t h a t response  to  the  to argue t h a t function  i t  is  to  that  the  the  D  that  call.  signal  by  one  a  depending  test  than  the  behind  was  upon t h e  was  frogs  show  of  the  as  before the  order  of  avoid  confounding  time  of  night  period. of  by  and  D  the  1  was  and  or  general  D calls  of  40  cm  each f r o g  to  e i t h e r moving calling  S calls,  period.  each  by  the  effect  cm  done to  each  such  30  that  f o r the  was  alternated  to  warning  "bouncing" behavior  p o s s i b l e e f f e c t s of  temperature,  The  or  experiment  and  the  Oxgalls:  -  presentation  ceasing  a  receiver.  i s a stronger  min  The  calls  the  latency  r e t r e a t , as or  case,  retreat  S calls  than  higher-level  experiment.  record  presentation the  S call  suggest  w a r n i n g " as  of ,,S_calls_and  distinctive  fights;  to  call.  males  this  s t a t e of  either  the  In  either  playback  loudspeaker  playbacks The  the  to n e a r b y  its  usually  to f i g h t i n g  imminent  the  playback  presentation  paired frog.  to  that  D  males  more  be  that  the  "stronger  m  I did a  defined  more away from  of  in  reasonable  and  I define  tg playback  or " r e t r e a t " d u r i n g  Attack  out,  warning.  only  I t seems  males or  internal  D - c a l l i n g m a l e s , and  "attack"  i s given  that  warning"  would  hypothesis  D call,  procedure  the  weaker  i  the  with  communicates  Aggnis ti c_resppnses To  of  Operationally,  than  -  males.  spacing  identical  higher-level aggression attack,  in  i s a "stronger  which  aggression  nearby  S call  S - c a l l i n g " b o u t s " between two  retreat S call  of  functions  not  Observations lead  calling  the  or  rest with  different time  variables of  to as  playback  34  on  nearby  frogs  (sometimes  experimental  animals  were  close  together).  To  ensure  that  the c a l l s  were p l a y e d back a t r a t e s and  intensities  similar  t o ' those  of  preliminary  playback  experiment  i n which f i r s t  a frog  real  were r e c o r d e d f o r a p p r o x i m a t e l y  elicited  by  playing  recording  of the frog  Relative c a l l by  playback  D  calls  back  did  a  the D c a l l s  of  tape  frog  recorded  cm away from  the loudspeaker  average  rates  and r e l a t i v e  intensities  1  min.  were measured intensity  as p o s s i b l e  (about a v e r a g e  calls,  for  and S c a l l s  s e t as c l o s e l y  S  r e c o r d e r a 1 min  a tape r e c o r d e r with the average  f o r each  call  were  of D c a l l s  I  15 s e c , t h e n  another  D-calling,  intensities  from  on  frogs,  for  t o 90 db  frogs).  of 50 The  a r e shown i n T a b l e  7.  Table 7. Rates of D-calling i n t e n s i t i e s of the c a l l s .  and  D Rate  (n=8)  Intensity  S-calling  and  Calls  S  41/60 s e c (n=6)  An S c a l l  from  one i n d i v i d u a l  Calls  19/60 s e c  90.3 db  and a D c a l l  relative  88.1  were  db  recorded  35  onto  loop  t a p e s and  played  back a t  these  respective  rates  and  intensities. Most f r o g s or  D  this  calls way  first  by  responded  to  playback  changing to S - c a l l i n g , (92%)  to S c a l l s  more f r o g s a t t a c k e d  or  than to  C  of  with  either S  calls  more r e s p o n d i n g {62%).  calls  r e t r e a t e d i n response  in  Further,  to S c a l l s  (Table  8).  Table 8. A g o n i s t i c r e s p o n s e s of c a l l s and S c a l l s .  Call,Played  Number A t t a c k i n g or R e t r e a t i n g  Back  D call .  Significantly four  Looking  at  significant  but  playback of  attacks  the  and  in  D  Number not A t t a c k i n g or R e t r e a t i n g 13  1  r e t r e a t s and  6  p<0.005  three  (Fisher's test)  attacks  retreats separately,  response  difference  to  in  significantly  playback  number o f  of  S  attacks  calls was  not  (0.20>p>0.10).  These r e s u l t s to S c a l l s  7  different,  more f r o g s r e t r e a t e d (p<0.05),  1 min  0  S call  ^Includes  males t o  and  clearly  D calls.  show t h a t  They s u g g e s t  f r o g s respond that  the  S  differently call  is  a  36  stronger not  warning  to nearby  m a l e s , but  c o n c l u s i v e s i n c e f r o g s d i d not  both  attacking  and  retreating  acceptable alternative more  "submissive"  Paillette arboreal  interpretation  show s i g n i f i c a n t l y in  hupothesis  this  response  i s t h a t the  behavior  than  and  H.  meridionalis.  response  t h a t i f more d a t a  my  original  D.  hypothesis  MOVEMENTS OF  In fixed  areas  MALES ON  for  long  season) .  territories associated  are with  1960), b u t  Frogs,  would be  THE  S  nest s i t e s . in  study  during  moved  very  evaluate  the  mark-recapture  other obvious  Jameson  little,  generality study  of  on  call,  calls  as  of  Hjrla  that several none  were  did  in  collected  time  defend  ( e . g . f o r an  entire  surprising fixed  species,  that  since  including  they  (  Frog  in a  16-day  breeding  individuals Jameson's  birds': are o f t e n  nests  (see  e.g.  Pacific  advantage to defending  of  elicits  individuals  Some f r o g s d e f e n d  Tree  most  D  and  birds,  (1957) f o u n d  the P a c i f i c  calls  not  geographically  t h e r e i s no  Nevertheless,  is  call  BREEDING GROUNDS  periods  It  An  upheld.  many s p e c i e s , most n o t a b l y  breeding  Lutz  suggests  to S c a l l s .  However, t h e f a c t  to  D calls  of  the  f r o g s d i d a t t a c k i n response to  more  S  (1970) r e p o r t e d f o r t h e e q u i v a l e n t  is  fixed  Tree areas.  mark-recapture  season  o n l y a few results,  a s m a l l pond i n V a n c o u v e r .  that  males  inches. I  did  To a  37  I  Methods Males to 26  were captured on 15 d i f f e r e n t n i g h t s from  April  from  approximately  25  a m  roughly and  were c a l l i n g or which captured. the  20 m)  had  area  i n the pond.  their  vocal  (with  10  replaced  cm at  f o r both  sacs  their  the X and  capture  sides  Only males which inflated  The p o s i t i o n of each capture s i t e was  nearest  were  triangular  17 March  determined  Y coordinates.  sites  and  were  any  to  Frogs  movements  o c c u r r i n g during the f o l l o w i n g 60 sec were recorded.  Besults_anfl D i s c u s s i o n The  f r o g s made s u b s t a n t i a l movements: f o r 19  captured a t o t a l successive  of  68  times,  capture s i t e s was  the  4.6  mean  individuals  distance  m (range=0-19.4 m;  between s u c c e s s i v e captures=5.7 days).  Data f o r 8  between mean time  additional  f r o g s captured a t o t a l of 13 times i n d i c a t e that the movements can  not  be  attributed  to my  disturbance.  I observed  f r o g s resume c a l l i n g a t t h e i r capture s i t e s a f t e r yet when next c a p t u r e d , they had (range=0-11.6 days). the by  m;  mean  time  moved an  replacement,  average  of  4.6  m  between s u c c e s s i v e captures=5.5  Nor d i d any obvious change i n the use of any  calling  these  part  of  area occur which" c o u l d account f o r the movements  individuals. On the b a s i s of a s m a l l amount  the movement behavior of Marion  of  mark-recapture  data,  Lake f r o g s seems t o be  similar  38  to  E.  that  o f Vancouver  SUMMARY  Male grounds,  AND  DISCUSSION  Pacific  Tree  The  attracting  females,  presence  given a  of  species'  space  D  there.  calls  stronger and  back n e a r  perhaps  on  call in  (D  maintaining  vocalization,  also  defended  geographically  the  S  the D c a l l ;  nearby,  three  areas  fixed;  of  the  males  from  which may  as  is  males a r e more l i k e l y  to  individual  a mark-recapture  Pacific  to f i t a " t h r e e - l e v e l " by  Peeke  levels  primarily  well  as  t o a t t a c k when t h e S c a l l  spacing behavior of  proposed  as  spacing;  call,  is  frogs  s t u d y showed  played  Tree  system  (1972) f o r Red-winged are  1)  as a l o n g - r a n g e  "advertising warning  system  are that  not frogs  season.  O r g a n i z a t i o n of s p a c i n g b e h a v i o r i n P a c i f i c  general,  maintain  act  make e x t e n s i v e movements d u r i n g t h e b r e e d i n g  The  to  them.  The  1.  breeding  prevent  male b e g i n s c a l l i n g  than  the  call),  a l o n e i n an a r e a c a n  Another  warning  out  p h y s i c a l combat  mating  functions  o n l y when a n o t h e r  retreat  Frogs  u s i n g v o c a l i z a t i o n s and  spacing.  calling  frogs.  Tree  Frogs  Frogs  seems,  of t e r r i t o r i a l Blackbirds.  in  defense Peeke's  song  which  functions  to  repel  potential  39  t r e s p a s s e r s a t a d i s t a n c e " ; 2) at  intermediate  neighboring and the  ranges  The  D call  location  especially locating level  adapted  mates  as  the  f o r these  (Snyder and  of defense  visual  of  in  i s the  "stronger  warning" than  imminent  "third  Definition  level"  must r e m a i n  to  the  animals  i n "home a r e a s . "  definition nest  seems  provides  territory.  by  an  few  be:  long  only  to  second  when  than  another  to  other  be  i t in  rather  seems  warning the  be  a  frog  of  i n anurans  to  be  meaning  "A  attached  fixed  p e r i o d of has  for  in  to  "home  although  never  geographic  area  time."  been  stationary  However, when r e a s o n s  considered  attachment; t h a t i s , they  problems s i n c e ,  obvious  should  frog's  various authors,  territoriality  presents  "chase  physical attack.  The  to  for a relatively which  given  or  species,  i t  A  This c a l l  must show s i t e  explicitly,  in  is  definitions,  stated  group  Indeed,  1965).  D call,  defense  (or i t s e q u i v a l e n t s )  the  (an a c o u s t i c s i g n a l  nearby.  many  3)  f u n c t i o n s s i n c e f e m a l e s use  which  area"  occupied  caller.  of t e r r i t o r i a l i t y  According territorial,  calling  and  advertising  Jameson  Red-wings)  begins  boundaries";  in  S call  individual  actual trespassers  f u n c t i o n s i n a manner a n a l a g o u s  Red-wing's a d v e r t i s i n g c a l l and  d i s p l a y s "which f u n c t i o n  discourage  males at t e r r i t o r i a l  attack."  sex,  2.  to  visual  In  birds,  most s t u d i e d , most  focal defending  this  cases,  point fixed  the  the  for  the  sites  no  are  obscure,  First,  as  in  as mentioned  of  the  is  long  ( e . g . my  study  remains  at  it  a  has  remaining expending  not?  positive the  (to  distance  that  a  their  original  "The  area  site  The suggest  i t might  have  which  than  some but  that  the  i n others animal  imply  site;  a better  long  places  an  necessarily  for  How  that  instead,  strategy  than  operationally  a s : "The several space  displaced way,  tendency times out)  and  more  greater  therefore,  I  accept  territoriality  as " a l l  to  of experimentally  animals  animals  useful  than  the  to r e t u r n  "home a r e a "  return."  Krebs'  With  (1971  to as:  "home  p.  4)  cases o f s p a c i n g out  of  home a r e a s . "  that  of  the  mark-recapture  V a n c o u v e r and attachment  anecdotal  away from  in  territorial,  s i m p l y be  be  distance  results  n o t show s i t e  requirement  arbitrary.  Frogs  does not  capture s i t e s " ;  of  time  arise:  t o move.  area" defined i n t h i s  individual's  may  individuals  to  definition  site  attachment"  displaced  Tree  "attachment"  the energy  "site  difficulties  Second, the f a c t  a particular  For anurans, define  Pacific  (1957) s t u d y a r e a ) areas)  at  two  makes i t s a p p l i c a t i o n Are  ( e . g . Jameson's  anurans,  i n the i n t r o d u c t i o n , t h e  definition enough?  many  their  expected  evidence  a  Lake P a c i f i c  a c c o r d i n g t o my that  capture s i t e s on  Marion  study  frogs released  basis.  Tree  Frogs  definition.  d i d not r e t u r n  random  indirectly  I  several  any  more  Therefore,  I  do  also meters often would  41  t e n t a t i v e l y argue that P a c i f i c Tree Frogs are not t e r r i t o r i a l . T h e i r spacing behavior can perhaps " i n d i v i d u a l d i s t a n c e " (Condor  be best d e s c r i b e d simply as  1949), with f r o g s using the c a l l  i n t e n s i t y o f neighbors as a cue i n determining d i s t a n c e .  3.  The f u n c t i o n of s p a c i n g out  I f the f u n c t i o n of spacing out i n P a c i f i c Tree  Frogs  is  to  p r o t e c t c e r t a i n r e s o u r c e s , such as food or spawning s i t e s ,  one  would expect i n d i v i d u a l s to show s i t e attachment.  As w e l l  as the above-mentioned evidence that they do not, other of  evidence  argue  a g a i n s t these f u n c t i o n s .  only during the g e n e r a l l y n o c t u r n a l periods they  evidently  feed  mostly  observed a male attempt With  regard  amplectant  to  during  to capture  defense  of  a  Males space out of  prey  do  calling,  day  (I  item  spawning s i t e s ,  p a i r s suggest t h a t females  areas defended  the  lines  yet  only once  at  night).  o b s e r v a t i o n s of  not  spawn  i n the  by t h e i r mates; i n s t e a d , they l a y t h e i r eggs i n  a number o f s m a l l , w e l l - d i s p e r s e d masses. Spacing if  out  i t reduced  might be accounted  an i n d i v i d u a l ' s  predator  of  item  intensively  by  (Tinbergen  of  being  selection  taken  by  a  the type which r e a c t s to the d i s c o v e r y of a prey  et  al.  f r o g s on.my study Striped  chance  f o r by n a t u r a l  Skunks  searching 1967).  areas  the  area  f o r other  prey  P o t e n t i a l n o c t u r n a l predators of  include  Raccoons  (Mephitis m e p h i t i s ) , and owls  (Procvon  lotor),  ( e s p e c i a l l y Otus  42  agio).  Raccoons and skunks, e s p e c i a l l y ,  restricted  searching",  may  practice  but i t seems u n l i k e l y that t h i s would  s e l e c t f o r spacing out i n f r o g s .  The  d i s t u r b a n c e of c a p t u r i n g  a f r o g would cause nearby f r o g s to dive to the bottom pond,  where  overlooked necessary  "area  they would probably  by the predator.  of  the  be e i t h e r i n a c c e s s i b l e to or  Thus,  spacing  out  may  not  as an a n t i - p r e d a t o r mechanism i n something as  be  mobile  as f r o g s . Spacing out i s more e a s i l y e x p l a i n e d by sexual One  obvious  way  that  mating i s by reducing by  neighboring  i t c o u l d i n c r e a s e a male's chances of  the i n t e r f e r e n c e to approaching  males.  Observations  indicate that  I f t h i s i s so, why  to space out 50 cm or more? more e a s i l y  The  answer may  that  l o c a t e males which are spaced-out.  when  with s e v e r a l other s p e c i e s of HyJLa and suggested  hypothesis determining  is  easily  whether  the  function  testable females  Ralin  easiest  own  experience  for  and  In my  were  hypothesis  Pierce  it  females  densities  similar  low;  their  i s i t necessary  be  attempts to l o c a t e i n d i v i d u a l males, I found  for  females  touch or n e a r l y touch males before the males leave  c a l l i n g s t a t i o n s to c l a s p .  can  females  Yet t h i s does not seem to account  the e n t i r e area defended. must  selection.  only  select  (1972) had the same  of spacing out. to males  the which  spaced-out over those which are l e s s spaced-out; to the c a u s a t i o n of the response  This  extent are  a  of more  elucidate  would be much more d i f f i c u l t .  43  CHAPTER I I I THE  This  ROLE OF VOCALIZATIONS IN KATE SELECTION  chapter  r e p o r t s on i n v e s t i g a t i o n s of the method of  mate s e l e c t i o n i n P a c i f i c Tree examined:  First,  females  Frogs.  Two  hypotheses  were  s e l e c t l a r g e males on the b a s i s of  t h e i r ' low-pitched c a l l s , and  second,  females  choose  chorus  l e a d e r s , f r o g s which i n i t i a t e bouts of c a l l i n g .  A.  CALL PITCH AS A CUE  For  females  low-pitched inversely  to  IN HATE SELECTION  select  vocalizations related  to  large  requires  body  size.  males  by  that  call  Snyder and  cueing  i n to  pitch  Jameson  (1965)  found t h i s to be the case with P a c i f i c Tree Frogs, and my data  are  in  accordance  c a l l s of 40 Marion frequency  and  freguency  the  length  (r=-0.61,  fundamental  of one c a l l of each f r o g .  F i g u r e 7 shows that both f r e q u e n c i e s decrease snout-vent  own  with t h e i r r e s u l t s : I recorded the D  Lake males and determined  dominant  be  p<0.001;  with  increasing  r=-0.60,  p<0.001,  respectively). If  the c a l l  p i t c h hypothesis i s v a l i d ,  1) be l a r g e r than average  and  2)  have  mated males should  low-pitched  F i e l d data were c o l l e c t e d to t e s t these two  voices.  predictions.  44  Figure 7.  Relationship of dominant frequency and fundamental  frequency  (of approximately the s i x t h pulse of the f i r s t phase) of D c a l l s to body length.  44a  D O M I N A N T 2400-  F R E Q U E N C Y  Y=-52.11X  + 3913  N = 40 2200-  2000-  C  o o  1800 H  CD  CD  1600-  Q. CO CD  O  *  1400FUNDAMENTAL 1200  F R E Q U E N C Y  Y = - 3 2 . 4 8 X + 2112  i  N=  40  1000-  800-  "~r 31  1  1  33  1  1  1  35 S n o u t - V e n t  1  1  37  1  39 Length  (mm)  41  1  1—  43  45  Methods Sizes ofjiated  males:  The  distributions  of  snout-vent  l e n g t h s of a l l males found i n amplexus at Marion Lake i n and  1973  were  compared  with  the  respective  d i s t r i b u t i o n s of males captured from the c a l l i n g the two y e a r s .  The samples of c a l l i n g  the f r o g s captured  year.  p i t c h e s of mated males:  of  a  Amplectant  The  call  sample  and  Lake  males  recorded  sample of c a l l s from  various  of  from  p i t c h e s of males  were  compared  if  males  they subsequently c a l l e d .  in  the  calling  population  field The was  by r e c o r d i n g c a l l i n g f r o g s before c a p t u r i n g them f o r experiments.  in  1972,  frequency (r=0.14,  are  both  S i n c e , f o r a l l f r o g s recorded at Marion fundamental  positively  0.4>p>0.2;  frequencies  were  correlated  r=0.31,  corrected  frequency  with water  p<0.01, to  and  dominant  frequency  are  standard  also  dominant temperature  respectively), water  a c c o r d i n g to the r e l a t i o n s h i p s shown i n F i g u r e 8 and  with  the c a l l i n g p o p u l a t i o n .  males were separated from females, placed i n  enclosures,  collected  population i n  males r e p r e s e n t a l l of  found i n amplexus at Marion Lake i n 1972 those  length  ( i n d i s c r i m i n a t e l y with r e s p e c t to s i z e ) , a n d  marked on the study area i n each Call  1972  all  temperature (fundamental  correlated  with  air  temperature  (r=0.08, p>0.5; r=0.21, 0.1>p>0.05, r e s p e c t i v e l y ) ,  but  these  since  temperature  is  correlations correlated  with  are  weaker,  water  and  since  temperature  air  (r=0.62.  46  p<0.001),  I corrected  only  f o r water  temperature).  lgsults_and_Discussion  Size§^of_mated_malgs: larger 1973  than (Table  Amplectant  calling  males  9) ;  neither  in  males  were  i n 1972, and s l i g h t l y case  was  slightly smaller i n  the  difference  S n o u t - v e n t l e n g t h s (mm) o f males f o u n d w i t h c a l l i n g m a l e s i n 1972 and 1973.  i n amplexus  significant.  Table 9. compared  Calling  Males  Am£lectant  Year  N  1972  185  37.281  22  1973  132  38.442  9  *Not s i g n i f i c a n t l y Not s i g n i f i c a n t l y  2  Call males  Mean L e n g t h  different, different,  p i t c h e s o f mated  were  not  average s i z e (38.17 mm)  lower  significantly  0.50>p>0.40 0.50>p>0.40  males: C a l l  (Table  Mgan_Length 37.641 37.91  fundamental higher  greater  pitches  10); i n f a c t ,  of  (p<0.01),  higher but not s i g n i f i c a n t l y  amplectant  even t h o u g h t h e were  recorded  than t h a t of t h e c a l l i n g  frequency  of and  amplectant dominant  (0.4>p>0.2).  2  (t=0.70) (t=0.73)  o f t h e a m p l e c t a n t males whose c a l l s  was s l i g h t l y  (37.15 mm),  N  Males  This  males  males  frequency  was was  was p a r t l y t h e  47  Figure 8.  Relationship of dominant frequency and fundamental  to water temperature. 2 Y on X and on X  frequency  These relationships were obtained by regressing  + X and choosing the equation which minimized the  residual sum of squares.  47a  D O M I N A N T Y =  2400 A  •o c o o  7 7 . 1 4 X - 2 . 4 3 X  2  +1415  N = 6 4  2200 H  2000  F R E Q U E N C Y  ©  ©  1  1800  GO CD  1600 H  a co £  F U N D A M E N T A L Y = 4.42X  1400  N=  F R E Q U E N C Y  + 9 0 4  6 4  O  1200© ©  ©  1000H  g © & 0  @ O  ©  0  I »*  ©  ©  ©  1  I  ®  800"I  7  i  1  1  9  1  11 Water  1  1  13  T e m p e r a t u r e  1  15 (C)  I  17  48  Table 10, Fundamental frequency and dominant frequency (cycles/sec) o f amplectant males and c a l l i n g males.  1mplectant_Males  Calling,Males  N= 111  Iz.11  ;40  Frequency  Mean  S.E.  Mean  Fundamental  1019  28. 8  996  18.9  940  9. 1  Dominant  2035  40.7  2007  32.6  1994  13. 9  Mean  *Data for frog with aberrant voice (fundamental frequency=1272; dominant frequency=2339) not i n c l u d e d .  e f f e c t of i n c l u d i n g an amplectant v o i c e i n the a n a l y s i s . fundamental  and  But  dominant  higher than f o r c a l l i n g males  are  larger,  fundamental  frequency present relation  (Fig.  the  an to  frog,  10).  size,  Since  males are amplectant  than c a l l i n g amplectant  both  males, i t males  had  An a n a l y s i s of c o v a r i a n c e confirms t h i s (Fig.  9),  In s e c t i o n B of  explanation body  this  of amplectant  average,  body  frequency 10).  without  freguency  appears t h a t , f o r a given  for  even  males (Table  on  higher-pitched c a l l s .  male with an a b e r r a n t l y high  f o r the  length,  of  but not f o r dominant  this  chapter  higher-pitched  males  which  have  I  calls,  will in  attracted  females. In summary, n e i t h e r a n a l y s i s supports the h y p o t h e s i s that females calls.  choose  l a r g e males on the b a s i s o f t h e i r low-pitched  49  Figure 9.  Relationship of fundamental frequency (corrected to 12.5 C)  to body length i n c a l l i n g frogs compared with successful frogs (excluding one frog with an aberrant v o i c e ) . d i f f e r e n t , p<0.01 (F=14.88).  Lines are s i g n i f i c a n t l y  49a  o  S U C C E S S F U L  1200H  Y = - 7.66X N=  M A L E S +  (•)  1287  11  "O  c o o  o  CD  CO CD Q.  % 1000o > N  o  Y = - 1 2 . 3 7 X  + 13.99  N = 40 800 31  33  35 S n o u t - V e n t  37 Length  39 (mm)  41  -i  r~ 43  50  Figure 10.  Relationship of dominant frequency (corrected to 12.5  to body length i n c a l l i n g frogs compared with successful frogs (excluding one frog with an aberrant v o i c e ) . s i g n i f i c a n t l y d i f f e r e n t , p:>0.50 (F=1.26).  Lines are not  50a  2400 H  S U C C E S S F U L  n -D  c  M A L E S  Y  =-21.18X+2181  N  = 11  (a)  2200  o  o  CD  CO CD  a CD  o >.  O  2000H  C A L L I N G Y=  POPULATION  - 18.38X +  (°)  2677  N = 4 0  1800H —i 31  1  1  33  ~i  1—  ~i  35 Snout-Vent  1  1  37 Length  \  39 (mm)  1  1  41  1  '—  4 3  51  B.  CHORUS-LEADING AS  1.  Chorus  is  by c h a n c e .  for  in Pacific  study, I attempted  In s m a l l only  about  50  several call  Foster  calling size  a period  At  Marion  of  calling  frogs,  track  only  Lake,  first  step  in  my  which  a l l Here,  would  in this  are  individuals  complex  section  upon where he  one  in  to  prime  frogs i n i t i a t e d  for  frog  to  was  Marion  done.  The  i n phase.  The  are  synchronous densities  calling  areas.  can  initiate  a  several  hundred  i s located  data c o l l e c t i o n ,  at  i n a r e a s where  an i n d i v i d u a l  f o r anywhere f r o m  silent  the f i r s t  periods  hundred  calling  be c h o r u s l e a d e r f o r a l l  i s more  calling  therefore,  where a t most  typically, a l l  i n the l a k e i s not u s u a l l y  a few  facilitate  then  again.  situation  to perhaps s e v e r a l  o f which  a  anecdotal evidence  time, the p e r i o d s of  minutes,  of silence The  for  depending  To  a t one  t h e work r e p o r t e d  from  low,  call  before c a l l i n g  of groups  are  (1967) r e p o r t e d  such as those i n Vancouver,  several  of a l l f r o g s  varies  more c h o r u s e s t h a n  synchronous f o r a l l i n d i v i d u a l s ;  minutes  where  start  mate  t o g a t h e r some more c o n c l u s i v e e v i d e n c e .  f r o g s i n t h e pond. Lake,  males  T r e e F r o g s , b u t as  males  for  after  h y p o t h e s i s o f t h e method o f  certain  ponds,  are r e l a t i v e l y frogs c a l l  for this  that  expected this  IN MATE SELECTION  leaders  A prerequisite selection  A CUE  i n the  bout other  lake.  I d i d not attempt t o  keep  c h o r u s e s f o r an e n t i r e g r o u p ;  I  52  observed only two c a l l i n g nearest  neighbors,  choruses  males a t a time, always  reasoning  pair  of  t h a t i f one of these s t a r t e d more  f o r the p a i r than expected by chance, even though i t  was not n e c e s s a r i l y chorus l e a d e r f o r an would  a  strongly  suggest  that  non-randomly d i v i d e d among  entire  chorus  individuals  in  group,  this  initiations  are  the  group  as  a  whole.  Methods Using during  a stop watch, I determined whether each f r o g c a l l e d  15  sec periods.  Choruses were a r b i t r a r i l y defined as  o c c u r r i n g when both f r o g s c a l l e d i n a t l e a s t  consecutive  15  sec  one  or both o f the f r o g s had been s i l e n t f o r a t l e a s t  sec  periods.  two  period  A chorus i n i t i a t i o n c o u l d occur  ( i f one of the f r o g s c a l l e d  during  only a f t e r one  t h i s period, i t  was the l e a d e r f o r the next c h o r u s ) .  I l i s t e n e d to  of  chorus i n i t i a t i o n s .  frogs,  each f o r f o u r c o n s e c u t i v e  d i s t r i b u t i o n o f four could  be  that  chorus  initiations  expected  equals  pairs  two  The frogs  four.  According  to  d i s t r i b u t i o n , the p r o b a b i l i t y of each of these  events o c c u r r i n g i s r e s p e c t i v e l y , The  between  19  both s t a r t two choruses; one s t a r t s three and  the other, one; o r , one s t a r t s a l l binomial  15  number  the r e s p e c t i v e  of  each  0.364,  occurring  probability  d i s t r i b u t i o n was compared with  0.545,  times  and  i n 19 19.  t h i s expected  the three  0.091.  observations  The  observed  distribution.  53  Results_and_Discussion Table 11 shows t h a t , f a r more times than expected, one of the f r o g s s t a r t e d a l l four  choruses.  Thus,  for  pairs  of  Table 11. Maximum number o f choruses s t a r t e d (of a t o t a l of four) by a member of each of 19 p a i r s of males.  Number of Choruses  Expected/19 Observed/19 Difference  10.36  6.91  1.73  males  equalled  chorus l e a d e r . suggests  Four  5  i s significant,  from s t a r t of f i r s t pairs  Three  1  nearest-neighbor  19  Two  p<0.01  13  (Kolmogorov-Smirnov  over s h o r t p e r i o d s of time  chorus to s t a r t of f o u r t h chorus 11.0  test)  (mean time f o r the  min), one of the f r o g s i s u s u a l l y a  T h i s , as w e l l as abundant a n e c d o t a l  evidence,  t h a t , i n l a r g e r groups of f r o g s , c e r t a i n i n d i v i d u a l s  s t a r t most of the choruses.  54  2.  Field  Two  evidence  females  choose  separate investigations  evaluate chorus  that  the  hypothesis  that  females  Lake  selectively  to  mate  with  can  be  leaders.  tested  directly of frogs  would  i s t h e most s u c c e s s f u l  expect  females  chorus  The  by o b s e r v i n g w h e t h e r  Field_ experiment:  the  leaders  w e r e made a t M a r i o n  Systematicf igld_observations:  group  chorus  that  I f females  males found  hypothesis  the chorus  leader f o r a  at attracting  choose  chorus  i n amplexus,  females.  leaders,  one  i f separated  from  and r e p l a c e d on t h e b r e e d i n g g r o u n d s ,  would  become  leaders.  Methods ?Y5tematic _figld,_observations: a  female  c a n b e r e c o g n i z e d by c h a n g e s  It  changes from  the  female's  D-calling approach,  clasps  the female.  group  of  first  five  either  by  to fast then  The f i e l d  a  female,  visual  the chorus  M-calling  procedure frogs  always  inspection.  which  when  a s t w o o r more f r o g s  was  to  chorus  ended  when  a l l or  behavior:  i t detects  confirming  f o r at least  when i t  listen  and determine  The s u c c e s s f u l  calling  attracted  stops calling  leader f o r the previous chorus  defined  has  in i t scalling  abruptly  o r more c a l l i n g  attracted  evidence  A frog  to  which  a  frog  the  auditory  frog  could  (a c h o r u s 30  a l l b u t one o f t h e f r o g s  be was  sec;  a  stopped  55  c a l l i n g f o r a t l e a s t 15 sec) or another  frog.  I i 5 1 d _ e x p e r i f e n t : Amplectant p a i r s  were  encountered  on the breeding grounds, and  male  for  first  c a l l i n g male encountered  capture  each  site  in a f i e l d which pair  s u c c e s s f u l male was  frog  first  On  started  A control  obtained by c a p t u r i n g the  pair.  night,  I  determined  three c o n s e c u t i v e choruses  f o r the  p. 52),  as  and  defined  it  Systematic  field  Discussion  observations:  The  r e s u l t s obtained were  very scanty owing to the slow r a t e at which females  Field_gxEgriment:  s e l e c t chorus The  usable t r i a l s  (others f a i l e d  both of  frogs  the  in  the  amplectant  male c a l l e d and  trial,  the  onto  enclosure). In  two  12).  only  three  the  the c o n t r o l d i d not; i n  male  amplectant  All  trials,  was  the  r e s u l t s , however, are not u n e q u i v o c a l ; previously  yielded  the  three  because I c o u l d not l o c a t e one  hypothesis:  successful  l e a d e r s (Table  experiment  the  supported  of  come  breeding grounds; however, a l l o b s e r v a t i o n s supported  h y p o t h e s i s t h a t females  the  the  leader.  R e s u l t s and  the  the  Both males were placed  the f o l l o w i n g  (chorus d e f i n e d as on  chorus  separated.  when  i n a random d i r e c t i o n from  of the amplectant  enclosure.  collected  chorus one  males c a l l e d  could  or  trials  previously the  other  leader.  The  argue  that  more a c t i v e l y because  some e f f e c t o f having been i n amplexus or  of  having  been  56  Table 1 2 , Success o f chorus l e a d e r s compared with other f r o g s i n a t t r a c t i n g females: F i e l d o b s e r v a t i o n s , «  Minimum Number o f Frogs i n Chorus  Observation  Successful Frog  1  Chorus l e a d e r  1  2  20  Chorus l e a d e r  1  3  5  Chorus l e a d e r  1  p=0.002 (Binomial t e s t ) Was"chorus leader f o r " at preceding amplexus, 1  -  separated The  from t h e i r results  leaders  are  establish  that  -  two  choruses  immediately  mates.  of  more  least  both  likely  i n v e s t i g a t i o n s suggest to  mate;  however,  that chorus  they  do  not  females use c h o r u s - l e a d i n g jper se as a cue i n  mate s e l e c t i o n , f o r chorus l e a d e r s a l s o show other d i f f e r e n c e s in  calling  chorus  behavior.  leaders  are  Casual more  are  more  c a l l i n g , and c a l l  likely  louder.  suggested  that  a c t i v e v o c a l l y than other f r o g s i n  s e v e r a l ways: They end choruses, choruses,  observations  to  c a l l at a faster rate call  during  during general l u l l s i n  57  3.  C o r r e l a t e s of c h o r u s - l e a d i n g  Systematic determine  field  whether  observations  other  were  made  to  rigorously  d i f f e r e n c e s i n c a l l i n g behavior are  c o r r e l a t e d with c h o r u s - l e a d i n g .  Methods To determine whether chorus a f a s t e r r a t e during choruses,  l e a d e r s end choruses,  and are  more  c a l l at  likely  to  call  during g e n e r a l l u l l s i n c a l l i n g than other f r o g s , I made f i e l d observations  similar  f r o g s a r e chorus chorus  The than  those  leaders.  leaders  consecutive  to  as  made to determine i f c e r t a i n  For  frogs  which  I  three  defined or  more  leaders  call  louder  other f r o g s was done a f t e r I had a l r e a d y determined  than  other  frogs.  nearest-neighbor  called  at  a  chorus l e a d e r . measured  by  faster  Therefore,  males,  rate  30  the  either sec  both  Then the c a l l placing  leaders c a l l I  at  a  adopted  from faster  a  less  I simply measured the c a l l r a t e s  s e q u e n t i a l l y , each f o r two  frog.  started  i n v e s t i g a t i o n of whether chorus  time-consuming procedure: two  analyses,  choruses.  the above o b s e r v a t i o n s t h a t chorus rate  these  simultaneously  periods.  If  one  of or  frogs  times, i t was d e f i n e d as the  intensity  of  each  frog  was  sound l e v e l meter 50 cm behind the  The maximum r e a d i n g i n d e c i b e l s f o r a 15 sec r e c o r d i n g  58  of for  each  f r o g was  all  (r=0.56,  frogs  used i n the a n a l y s i s .  recorded  p<0.01),  to  was  Since c a l l  correlated  with  intensity  body  length  avoid confounding by t h i s v a r i a b l e , an  a n a l y s i s of c o v a r i a n c e  of c a l l  done f o r chorus l e a d e r s versus  i n t e n s i t y on  body  length  was  non-chorus l e a d e r s .  Table 13. R e l a t i o n s h i p of c h o r u s - l e a d i n g Table i n c l u d e s data f o r the f i r s t chorus p a i r s of f r o g s .  t o chorus-ending. recorded for 26  Frog Ending Chorus Chorus_Leader  Non-chorus Leader  Expected/26  13  13  Observed/26  21  5  S i g n i f i c a n t l y d i f f e r e n t , p<0.01  The  results  choruses  show  that  (Table 13), c a l l at a  chorus faster  (Chi Square=9.98)  leaders rate  do tend during  to  end  choruses  (Table  14),  call  more during p e r i o d s not d e f i n e d as choruses  (Table  15),  and  call  Again, were  louder  than other f r o g s  (Fig.  the f r o g s d e f i n e d as chorus l e a d e r s f o r these not  necessarily  (or l i k e l y )  11).  analyses  the chorus l e a d e r s f o r the  59  Figure 11.  Relationship of c a l l i n t e n s i t y to body length i n chorus  leaders compared with other frogs. d i f f e r e n t , p"<0.025 (F=6.87).  Lines are s i g n i f i c a n t l y  59a  Snout-Vent  Length  (mm)  60 Table 14. Mean c a l l r a t e s ( c a l l s / 3 0 sec) during choruses of chorus l e a d e r s and non-chorus l e a d e r s . Table i n c l u d e s data f o r 23 p a i r s of frogs (for three other p a i r s of frogs observed, no c a l l r a t e data were c o l l e c t e d ) .  C ho rus Leaders w  ff°l££hg.¥Sf  .,iig 3ers a  22.96  21.05  S i g n i f i c a n t l y d i f f e r e n t p<0.01  (Hilcoxon  test)  Table 15. Mean number of c a l l s per 15 min during p e r i o d s not defined as choruses of chorus l e a d e r s and non-chorus leaders. Table i n c l u d e s data f o r 26 p a i r s of f r o g s .  £horus_Leaders  Non-Chorus Leaders  1.56  0.36  S i g n i f i c a n t l y d i f f e r e n t , p<0.01 (Wilcoxon t e s t )  groups i n which they were c a l l i n g , "real"  chorus  leaders,  but  I  compared to the other  groups^ show s i m i l a r d i f f e r e n c e s i n c a l l i n g An e x p l a n a t i o n to  body  size,  males (see p. 46) presented chorus captured  argue  now  be  attempted:  that  frogs i n t h e i r  behavior. calls, in  relation  males found i n amplexus compared t o  can  show that  leaders  f o r the h i g h e r - p i t c h e d  of  would  Results  other  thus  far  1) s u c c e s s f u l males are chorus l e a d e r s ,  call  louder  i n amplexus tend  than  other f r o g s , and  to be chorus l e a d e r s  when  3)  2)  males  replaced  61  on the breeding  grounds.  of males captured to  body  size  an  if  call  individual  sometimes  of  these r e l a t i o n s h i p s , the c a l l s  i n amplexus w i l l be h i g h - p i t c h e d i n r e l a t i o n  i n t e n s i t y , as suggested calls  Given  pitch by f i e l d  makes  relatively  i s p o s i t i v e l y r e l a t e d to c a l l observations  after  low  than  louder c a l l s ) .  by  the  fundamental  frequencies  of two  db,  from each of f i v e  recorded  fundamental call  4.  and  The  used  mate  few  calling  are  these  calls  frequencies  males.  dominant frequency the  In  was  and  all  seem tested  dominant  by at l e a s t 2 cases,  were higher f o r the  both louder  hypothesis.  of c h o r u s - l e a d i n g as a cue i n mate s e l e c t i o n  vocal  by  chorus-leading of  first  T h i s hypothesis  behavior  of chorus l e a d e r s d i f f e r s i n s e v e r a l  ways from t h a t of other f r o g s ; any be  in  c a l l s , d i f f e r i n g i n loudness  (Table 16) , thus upholding  Use  lull  intensity;  lower-pitched comparing  a  (the  females was  in  mate  of these d i f f e r e n c e s  selection.  However, because  the v a r i a b l e measured i n f i e l d  selection,  a  laboratory  r i g o r o u s l y examine the use of t h i s  experiment cue.  might  observations was  done  to  62  Table 16. R e l a t i o n s h i p of fundamental frequency and frequency (both i n c y c l e s / s e c ) t o c a l l i n t e n s i t y .  Fundamental.Frequency Quieter  Frog  Call  dominant  DominantFrequency  Louder_Ca11  0.uieter_Call  Louder_Call  910  1000  1930  1990  1020  1030  2080  2180  3  880  910  1910  1940  4  900  930  1930  1990  5  870  890  1910  1940  1 2  ,  Methods The  experiment  was  done i n a c i r c u l a r arena  (Fig.  having four loudspeakers on the circumference p l a y i n g c a l l s v i a a system experiment  (see  s i m i l a r to t h a t used i n the second p.  26).  A randomly chosen  chorus l e a d e r f o r each t r i a l ;  number of times f o r a chorus l e a d e r t o c a l l join).  Choruses  between. water female  filled  (the same temperature collected  Marion Lake was  the  the  three  (not an unusual  before other f r o g s  l o n g , with one  to,a depth of 10 cm  as the D c a l l  D  addition  speaker was  was  minute with  lulls 15  C  recorded a t ) .  A  on breeding areas e i t h e r i n Vancouver or at  held i n a c i r c u l a r cage i n the c e n t e r  arena u n t i l about Then,  were two minutes  The arena was  back  f o r each chorus i t c a l l e d  times before the other speakers were turned on  12)  of  the  15 sec a f t e r the s t a r t of the f o u r t h chorus.  hidden observer removed the cage top by r a i s i n g i t  63  Figure 12.  A top view of the arena used i n the laboratory experiment  testing whether females are attracted to chorus leaders.  Females  were placed i n the c i r c u l a r cage (with i t s f l o o r s l i g h t l y submerged) i n the center of the arena.  The wooden platforms i n front of each  speaker were s l i g h t l y submerged; females frequently rested on their edges during experiments.  1 meter ^  loudspeaker wooden cage arena  platform  for  female  wall  64  with an a t t a c h e d s t r i n g . came  within  2  cm  A "choice" occurred  horizontal  distance  when  a  female  of a speaker.  If a  female d i d not make a c h o i c e w i t h i n 60 min a f t e r r e l e a s e , experiment  was  terminated;  female began to climb Non-responding  females  the  l i k e w i s e , i t was terminated i f a  screen  (most  fence  around  the  1969)  arena.  f r e q u e n t l y ones which were not  captured i n amplexus) were g i v e n 1000 I.U. of human gonadotrophin  the  intraperitoneally  chorionic  to induce o v u l a t i o n  (Schmidt  and r e t e s t e d the next day.  R e s u l t s and _ D i s c u s s i o n The r e s u l t s confirm that females are a t t r a c t e d leaders  (Table  17).  The  mean  time  to  chorus  f o r females to make a  /  Table 17. Success o f chorus l e a d e r s compared with other f r o g s i n a t t r a c t i n g females: l a b o r a t o r y experiment.  Number_of_Females_Attracted Chorus Leader  Others  Expected/11  2.75  8.25  Observed/11  9  2  S i g n i f i c a n t l y d i f f e r e n t , p<0.001 (Binomial t e s t )  c h o i c e a f t e r r e l e a s e from the c e n t r a l cage was 18 min  (range:  65  1-r43  min) ,  only  but  four chorus  "interested" 45  degrees  even a t t h e moment o f r e l e a s e initiations),  i n the chorus  females  chorus-leading during and by  calling  not  may  Ralin  cinerea  X H.  cinerea  very  reversed t h e i r  few  calls  frogs,  it  individual  except  at  initiating  very  at  least  locating  males.  at  within  in  correlates  of  a  faster  Gerhardt  voices;  in  calling,  (1968)  (cited  female  when he  male t o 5 db  g r e a t e r than t h a t of a  natural  would  differences  or ending  hybrid  experiment,  involving  difficult in  distances.  choruses  and  On  H. H.  conspecific  more  for  loudness  H.  female  p r e f e r e n c e f o r the  seem  short  a  Hyla  increased  call  choice  from  rate  of a mating  p e r i o d s are g i v e n a t times of minimal and,  the  calling  However, i n t h e d i n o f a c h o r u s  distinguish rate,  gratigsa  more  that  reported evidence that  male i n a l a b o r a t o r y  cinerea  possibility  to  males w i t h l o u d  be  were f a c i n g  more d u r i n g g e n e r a l l u l l s  1972)  prefer  to  (p<0.01).  the  in  chorus-ending,  playback i n t e n s i t y  call.  cue  8 o f 11  speaker  exclude  also  appeared  louder than other f r o g s .  P i e r c e and  the  do  choruses, c a l l i n g  cinerea  leader;  of the chorus l e a d e r  These r e s u l t s nature  females  (after hearing  than  a  females  to  or  in  call  t h e o t h e r hand*  calls  acoustical  during  lull  interference,  f o r t h e human o b s e r v e r , a r e e f f e c t i v e  aids i n  66  5.  Short-term changes i n c a l l i n g  Since  females  choruses, call  and  are  also  tendency  attracted  perhaps  to  males  do  males  not  p e r i o d s o f breeding attempting  to  call  the q u e s t i o n  continuously  activity  call  during  start  to males which end choruses and  more than other f r o g s d u r i n g l u l l s ,  "Why  which  as  the  arises,  during the n o c t u r n a l  result  of  each  male  these times when no or few other  f r o g s are c a l l i n g ? " The l u l l s i n c a l l i n g by i n d i v i d u a l f r o g s seem to result  of  a  short-term  waning  s t i m u l u s of other f r o g s c a l l i n g . comes from attempts purpose  of  in  the  the  to  the  Anecdotal evidence f o r  this  (for the  t h e i r v o c a l i z a t i o n s ) by p l a y i n g back D  I soon l e a r n e d t h a t playback s h o r t l y a f t e r the  beginning of a l u l l later  responsiveness  I made to s t i m u l a t e f r o g s to c a l l  recording  c a l l s t o them.  of  be  p e r i o d was l e s s  lull.  effective  A c o n t r o l l e d experiment  more r i g o r o u s l y t e s t t h i s  idea.  /  than  playback  was designed to  67  Methods D e f i n i n g a l u l l as a p e r i o d 15 sec or longer between 30  two  sec or longer bouts of c a l l i n g , I measured the l e n g t h of a  lull  (length=X sec) f o r an i n d i v i d u a l f r o g , then measured  lengths  of  i t s following  three l u l l s under three  different  s t i m u l u s c o n d i t i o n s : no s t i m u l u s , s t i m u l u s presented after  the beginning  60% of X. 200  the  second  first  D call  X  after  lull  was  c o n d i t i o n the s t i m u l u s would be  40 s e c a f t e r the beginning  of the  lull;  - t h i r d c o n d i t i o n , 120 s e c . The order of the three conditions  20% of  and stimulus presented  F o r example, i f the l e n g t h of the  s e c , under  presented  o f the l u l l ,  the  was randomized f o r each t r i a l .  under  the  experimental  The stimulus was a  played back a t normal r a t e and volume approximately  4 m  away from the f r o g .  Results  and_Discussion  a p r e l i m i n a r y a n a l y s i s of the r e s u l t s calls  stimulate  frogs  the l a t e n c y of response the  beginning  of  to c a l l  s t i m u l u s was presented  (Table 18); and, as  (defined as the length  playback  longer bout o f c a l l i n g  confirmed  by  to the  earlier  the beginning frog)  was  i n the l u l l  of  that  D  expected, time  from  of a 30 sec or  longer period  when  the  (Table 19).  These r e s u l t s are i n t e r p r e t e d as showing an i n c r e a s i n g c a l l i n g tendency during  l u l l p e r i o d s ; a compensating waning of c a l l i n g  tendency preseumably occurs  during  choruses.  according  to  68  Table 18. Mean length o f l u l l ( s e c ) i n c a l l i n g when no D c a l l s were p l a y e d back d u r i n g t h e l u l l compared w i t h when D c a l l s were p l a y e d back ( d a t a f o r t h e two p l a y b a c k c o n d i t i o n s were lumped):. T a b l e i n c l u d e s d a t a f o r 12 f r o g s .  No D C a l l s  Played  Back  D_Callg„Played,..Back  202 Significantly  107 different,  p<0.01  (Wilcoxon  test)  T a b l e 19. Mean l a t e n c y t o c a l l ( s e c ) when s t i m u l u s p r e s e n t e d in the f i r s t part o f a l u l l compared w i t h when p r e s e n t e d later i n a l u l l . T a b l e i n c l u d e s d a t a f o r 12 f r o g s .  D C a l l s P l a y e d Back Early_in_a_lull  -  D C a l l s P l a y e d Back Later i n a _ l u l l  60  22  Significantly  this  model,  threshhold phase; a  they  chorus  frogs  chorus  the l a s t  they  (Wilcoxon  test  )  during  the  to stop c a l l i n g  reguire  less  suggest  that  reach a  incremental  a t t h e end o f  s t i m u l a t i o n than  other  calling.  i s appealing  responsible  "spontaneously"  are usually because  p<0.005  l e a d e r s a r e t h e f r o g s which f i r s t  for calling  t o keep  It  different,  for  the  to  recurrent  waning  muscular  fatigue  of c a l l i n g  is  tendency.  69  Other mechanisms such as h a b i t u a t i o n which  or  sensory  adaptation,  are mechanisms f o r adaptive r e d u c t i o n of response,  u n l i k e l y to apply i n t h i s case, s i n c e adaptive  for  requirements The  but  calling  uptake  as  played back through stimulate  a  was  calling.  0.101  0.040 ml. amounts  instead until  energy  difficult  to  would be enhanced by amount  of  test finding  energy.  A  attempted to determine i f t h i s i s to compare  the  rate  of  oxygen  carbon  using  5  dioxide  a loudspeaker  ml  of  25%  absorbant. near  Unfortunately, This frog  the  however, called  potassium D c a l l s were  respirometer only for  one 150  to frog sec,  ml of oxygen; i n the c o n t r o l p e r i o d , i t used only These r e s u l t s suggest  of energy, and  that c a l l i n g  requires  thus provide t e n t a t i v e support  large f o r the  f a t i g u e h y p o t h e s i s ; f i r m e r c o n c l u s i o n s w i l l r e q u i r e much data.  be  f r o g s with t h a t of n o n - c a l l i n g f r o g s i n a  c a l l e d i n the r e s p i r o m e t e r . using  calling  be  significant  respirometer, the  would  credibility  procedure  calling  differential hydroxide  its  experiment was  The  of  continue  hypothesis  takes  respirometry the case.  to  should  force a halt.  fatigue  directly, that  frogs  it  seem  more  70  C.  SUMMARY  The  DISCUSSION  results  f e m a l e s use behavior, Females  AND  presented  individual but  not  choose  choruses,  calling  louder  out  may  than  as  If  so,  one  other  leaders  louder  from  have  them.. T h i s It  call If  the  and  calling  tendency  fatigue,  the  the  location  least  theory  of  at  of  II  for  easily.  system  "robust"  one  in  (p. 42),  and  the  males  by  to h o l d  an  chorus  space out  farther  tested. individual than  male  other  recurrent  mate s e l e c t i o n males,  the  to  frogs.  waning  I have a r g u e d ,  as  males spacing  also: Since  louder  Intuitively,  natural selection,  rate  lulls,  chorus leaders  i s , as of  of  faster  individual  frogs should  in individuals  most  a  general  males i n t h i s r e s p e c t  responsible  using  correlates  i n Chapter  p r e d i c t i o n r e m a i n s t o be  the  selection.  enhance mating s u c c e s s  voices,  calling  cues.  would e x p e c t  proposed  females choosing fatigue  as  a l s o perhaps to c a l l  mechanism  in  leaders,  the  i s t h e r e f o r e a d v a n t a g e o u s f o r an  more  males  chorus  during  frogs  i n d i c a t e that  a s c u e s i n mate  calling  discussed the  advantage over  among  are  more  which may  out;  chapter  perhaps  other  facilitate  females.  which  calling  Another t r a i t spacing  pitch,  chorus-ending,  during  is  in call  and  chorus-leading  this  differences  males  chorus-leading  in  of  muscular  would  males  have which  w e l l as a c c o r d i n g  would p r e d i c t t h a t  to  these  males  make t h e b e s t  mates.  72  LITERATURE  CITED  Axtell; R. W. 1959. Female reaction to male c a l l a n u r a n s ( A m p h i b i a ) . S o u t h w e s t . N a t u r . 3:70-76.  in  two  B l a i r , W. F. 1963. A c o u s t i c b e h a v i o r o f a m p h i b i a , p. 694-708. In R. G. Busnel (ed.) Acoustic behavior of animals. E l s e v i e r P u b l . Co., Amsterdam, L o n d o n , New York. B l a i r , W. F. 1968. A m p h i b i a n s and r e p t i l e s , p. A. Sebeok (ed.) Animal communication. Press, Bloomington.  289-310. In T. Indiana Univ.  B o g e r t j C. M. 1960. The i n f l u e n c e o f sound on t h e b e h a v i o r of amphibians and r e p t i l e s , p. 137-320. In W. E. Lanyon and W. N. T a v o l g a (eds.) Animal sounds and communication. Amer. I n s t . B i o l . S c i . , P u b l . 7, W a s h i n g t o n , D.C. Borisov, A. I. 1970. Disturbances of panmixia i n n a t u r a l p o p u l a t i o n s of D r o s o p h i l a f u n e b r i s , polymorphous by the i n v e r s i o n I I - 1 . G e n e t i k a 6:61-67. Bragg, A. N. triseriata  1959. Response o f a female P s e u d a c r i s n i j j r i t a t o the c a l l o f a male. C o p e i a 1959:341.  B r a t t s t r o m , B. H. 1962. C a l l o r d e r and s o c i a l b e h a v i o r i n the foam-building frog, Engystomops p u s t u l o s e s . Amer. Z o o l . 2:394. ( A b s t r . ) B r a t t s t r o m , B. H. and i n two species 24:222-228. Brown, J. mobile  R. M. Y a r n e l l . 1968. A g g r e s s i v e b e h a v i o r of Leptodactylid frogs. Herpetologica  L. and G. H. Orians. a n i m a l s . Ann. Rev. E c o l .  Brown, L . E. and J . R. breeding behavior S c i . 26:313-317.  1970. S p a c i n g p a t t e r n s i n S y s t . 1:239-262.  Pierce. 1965. Observations on the of c e r t a i n anuran amphibians. Texas J .  B u n n e l l , P. 1973. V o c a l i z a t i o n s i n t h e t e r r i t o r i a l b e h a v i o r t h e f r o g D e n d r o b a t e s j D u m i l i o . C o p e i a 1973:277-284.  of  73  B u s n e l , M. C. 1967. R i v a l i t e acoustigue et hierarchie chez l'ephippiger (Insecte, Orthoptere, Tettigoniidae). Z. V e r g l . P h y s i o l . 54:232-243. C a p r a n i c a , R. R. 1965. The evoked vocal response of B u l l f r o g . R e s . Monogr. 33, M.I.T. P r e s s , C a m b r i d g e . C o n d o r , P. J . 1949. I n d i v i d u a l  distance.  Ibis  the  91:649-655.  Crump, M. L. 1972. Territoriality and mating b e h a v i o r i n Dendrobates granuliferus (Anura: Dendrobatidae). Herpetologica 28:195-198. Duellman, w. E. 1966. frogs. Herpetologica  Aggressive behavior 22:217-221.  D u e l l m a n , W. E . 1967. S o c i a l o r g a n i z a t i o n of some neotropical amphibians. 77:156-163.  i n Dendrobatid  i n t h e mating Amer. Midi.  calls Natur.  Durham, L . and G. W. B e n n e t t . 1963. Age, g r o w t h , and homing i n t h e B u l l f r o g . J . W i l d l . Mgmt. 27:107-123. E f f o r d , I . E. 1967. Temporal and spatial differences in phytoplankton productivity i n Marion Lake, British C o l u m b i a . J . F i s h . Res. Bd. Canada 24:2283-2307. Ehrman, L . 1972. A f a c t o r i n f l u e n c i n g the a d v a n t a g e i n D r o s o p h i l a . Behav. G e n e t . Emlen, S. T. 1968. Territoriality in c a t e s b e i a n a . C o p e i a 1968:240-243.  rare male 2:69-78. the  mating  B u l l f r o g , Rana  F a l l s , J . B. 1969. Functions of territorial song i n the White-throated S p a r r o w , p. 237-262. I n R. fi. H i n d e (ed.) B i r d v o c a l i s a t i o n s . - Cambridge u n i v e r s i t y p r e s s . F o s t e r , W. A. 1967. C h o r u s s t r u c t u r e Pacific Tree Frog, Hy.la 23:100-104.  and v o c a l regilla,  response i n the Herpetologica  Gerhardt, H. C. 1968. Evolutionary aspects of vocal communication and reproductive behavior i n the Hyla cinerea group. Unpublished M.A. Thesis, U n i v e r s i t y of Texas. Goodman, D. 1971. T e r r i t o r i a l b e h a v i o r i n a n e o t r o p i c a l fiendrobates g r a n u l i f g r u s . C o p e i a 1971:365-370.  frog,  74  Green, N. B. 1938. The breeding habits 5£§S^ZEJ12S§ (Cope) w i t h a d e s c r i p t i o n of t a d p o l e . C o p e i a 1938:79-82.  of the  Jameson, D. L. 1957. P o p u l a t i o n s t r u c t u r e and homing i n t h e P a c i f i c T r e e F r o g . C o p e i a 1957:221-228.  Pseudacris eggs and responses  J e n s e n , T. A. and W. B. P r e s t o n . 1968. B e h a v i o r a l r e s p o n s e s o f the male Green F r o g t o i t s r e c o r d e d c a l l . H e r p e t o l o g i c a 24:181-182. K r e b s , J . B. 1971. T e r r i t o r y and T i t , P a r u s major L. E c o l o g y  b r e e d i n g d e n s i t y i n the 52:2-22.  K r u i j t , J . P. and j . A. Hogan. 1967. S o c i a l lek in Black G r o u s e , L_yrurus t e t r i x 55:203-240.  Great  behavior on the t e t r i x (L.) . A r d e a  L i c h t , L. E. 1969. Comparative breeding behavior of the Bed-legged Frog (Rana aurora aurora) and t h e W e s t e r n S p o t t e d F r o g (Rana pretiosa _pretiosa) in southwestern B r i t i s h C o l u m b i a ? Can. J . Z o o l . 47:"l287-1299. Littlejohn, M. J . and J. J. Loftus-Hills. 1968. An experimental e v a l u a t i o n of premating isolation in the Hj^la gwinga complex (Anura: Hylidae). Evolution 227659-663. L i v e z e y , R. L. 1952. Some o b s e r v a t i o n s on Pseudacris triseriata (Wied) in Texas. Amer. Midi. 47:572-587. Lutz,  B. 1960. F i g h t i n g and an i n c i p i e n t n o t i o n i n male t r e e f r o g s . C o p e i a 1960:61-63.  Martof, B. S. clamitans.  1953. Ecology  Territoriality 34:165-176.  i n the  of  njgrita Natur.  territory  Green F r o g ,  Rana  M a r t o f , B. S. and E. F. Thompson, Jr. 1958. Reproductive behavior of the Chorus Frog, P s e u d a c r i s n i g r i t a . Behavior 13:243-258. Paillette, M. 1970. La notion de territoire chez les a m p h i b i e n s a n o u r e s , e t p l u s p a r t i c u l i e r e m e n t l a v a l e u r de e m i s s i o n s s o n o r e s dans l e comportement territorial des hylides: H y l a a r b o r e a e t H y l a m e r i d i o n a 1 i s , p. 35-48. In G. R i c h a r d (ed.) T e r r i t o i r e e t Domaine V i t a l .  75  Peeke, F. W. 1972. An e x p e r i m e n t a l s t u d y of the territorial function of vocal and visual display i n t h e male Red-winged B l a c k b i r d ( A g e l a i u s p h o e n i c e u s ) . Anim. Behav. 20:112-118. Pengilley, R. K. 1971. C a l l i n g and a s s o c i a t e d b e h a v i o u r o f some s p e c i e s o f Pseudophrjrne (Anura: L e p t o d a c t y l i d a e ) . J . Z o o l . L o n d . 163:73-927 Pierce, J . R. and D. B. Ralin. 1972. V o c a l i z a t i o n s and behavior o f t h e males o f three species i n t h e Hjrla v e r s i c o l o r c o m p l e x . H e r p e t o l o g i c a 28:329-337. P y b u r n , W. F. and J . R. G l i d e w e l l . 1971. Nests and breeding behavior of Phyllomedusa h i j a o c h o n d r i a l i s i n Columbia. J . H e r p e t . 5:49-52. Rabb, G. B. and M. S. Rabb. 1963a. A d d i t i o n a l o b s e r v a t i o n s on breeding b e h a v i o r o f the Surinam Toad, P i p a p i p a . Copeia 1963:636-642. Rabb, G. B. and M. S. Rabb. 1963b. On the behavior and breeding biology o f the A f r i c a n p i p i d f r o g Hymenochirus b o e t t g e r i . , Z . T i e r p s y c h o l . 20:215-241. S c h m i d t , R. S. orientation  1969. Preoptic activation i n female anurans. Behaviour  of mating 35:114-127.  call  Sexton, o. J . 1960. Some a s p e c t s o f t h e b e h a v i o r and o f t h e t e r r i t o r y of a dendrobatid frog. Prostherapis t r i n i t a t u s . E c o l o g y 41:107-115. S e x t o n , 0. J . 1962. A p p a r e n t t e r r i t o r i a l i s m i n leptodactylus i n s u l a r u m B a r b o u r . H e r p e t o l o g i c a 18:212-214. S n y d e r , W. F. and D. L. Jameson. 1965. M u l t i v a r i a t e g e o g r a p h i c variation o f mating c a l l i n populations of the P a c i f i c T r e e F r o g (H£la r e g i l l a ) . C o p e i a 1965:129-142. S t e b b i n s , R. C. 1966. A f i e l d g u i d e t o a m p h i b i a n s . Houghton M i f f l i n Co.,  western Boston.  Tinbergen, N., M. Impekoven, and D. e x p e r i m e n t on s p a c i n g o u t as a d e f e n s e B e h a v i o u r 28:307-321.  reptiles  and  Franck. 1967. An against predation.  W h i t f o r d , W. G. 1967. Observations on territoriality and aggressive behavior i n t h e Western S p a d e f c c t Toad, S e a p h i o p u s hammondii. H e r p e t o l o g i c a 23:318.  76  Wiewandt, T. A. 1969. V o c a l i z a t i o n s , a g g r e s s i v e b e h a v i o r , and territoriality i n t h e B u l l f r o g , Rana c a t e s b e i a n a . C o p e i a 1969:276-285. W i l e y , R. H. 1970. T e r r i t o r i a l i t y and non-random breeding in the Sage G r o u s e ( C e n t r p c e r c u s u r o p h a s i a n u s ) . U n p u b l i s h e d Ph. D. T h e s i s , The R o c k e f e l l e r U n i v e r s i t y .  77  APPENDIX I DIFFERENTIAL SELECTION FOR COLOR BETWEEN THE SEXES IN PACIFIC TREE FROGS  Pacific Individuals,  Tree although  cannot  change  Resnick  and Jameson  major  their  species  1  range.  considerably spring,  California.  considerably,  and Warren 1955; of the  have b e e n d e v e l o p e d by  (1971)  1968.  studied studied only  observations,  the  green  Jameson and  i s s t a b l e because  is  m a l e s , Jameson the breeding not  change  proportions  changed  increased  i n the  males  increased  the  population  o f t h e morphs d i d  However,  males  that  through out the  i n samples taken d u r i n g  each y e a r ;  non-green  reported  Here, sampling  proportions  during  and  that  the polymorphism  i n the f a l l . Peguegnat  On t h e  suggested  the " o v e r a l l  selective  average o u t . "  In least  brown, and r e d  The most i n t e n s i v e l y  to  b a s i s of these  forces  (Brattstrom  color.  Models o f the i n h e r i t a n c e  Peguegnat  season t h e r e l a t i v e  that  basic color  Peguegnat found  1966  for  t o l i g h t e n and d a r k e n  i s stable i n populations  at Julian,  from  polymorphic  (1963).  and  polymorphism  are  1963).  and Jameson  Jameson  and  able  colors-—green,  Resnick  one  Frogs  this  paper,  i n my s t u d y  polymorphism  I  areas,  present the  evidence  factors  c a n n o t be u n d e r s t o o d  indicating  maintaining  without  studying  that, at  the both  color male  78  and  female  frogs.  nearly Lake  are  divided (or  a l l Pacific either  into  two  sometimes  does not have are  A.  form  of  distinct  Each  Vancouver  and  However, s i n c e  has  a  the  broad  and  of a d u l t  forms  with  the  color.  made i n March and  ponds i n V a n c o u v e r s u g g e s t e d  common i n f e m a l e s ,  red  FEMALES  frogs  between  be  the o t h e r  striped  f o r a n a l y s e s I have lumped e a c h  ADULT MALES AND  Marion  o f t h e s e morphs can  mid-dorsal s t r i p e ,  o f t h e same g e n e r a l  t h e morphs d i f f e r  more  in  "sub-morphs": one  brown)  rare,  Collections various  o r brown.  the s t r i p e .  COLORS OF  at  green  dark  relatively  unstriped  Tree Frogs  the s e x e s ,  that  1972  the p r o p o r t i o n s  the g r e e n  T h i s h y p o t h e s i s was  April  morph  tested  being  at  Marion  breeding  area  Lake.  Methods Frogs  were  (approximately in  1972  procedures  and  captured 100  1973.  m by  40  from m)  a  on  Capturing,  were as d e s c r i b e d on  p.  major  the east s i d e marking, 16.  of Marion and  Lake  measuring  79  R e s u l t s and In  both  individuals and  1972  was  and  Discussion  1973,  the  f a r higher i n females  proportion  of  t h a n i n males  green  (Tables  1  2 ) , thus c o n f i r m i n g the h y p o t h e s i s .  Table 1. captured  Numbers o f brown and g r e e n a t M a r i o n L a k e i n 1972.  adult  males and  females  Color sex  Brown  Green  Males  68  107  Females  24  7  Significantly  Two between  possible  the  produced.  These  two  operate  sexes;  (1) The more  (2) D i f f e r e n t i a l  having  p<0.001  explanations  the sexes a r e :  between  morph  different,  greater  green  females  selection  e x p l a n a t i o n s a r e not  the  inheritance  ••fitness"  t o g e t h e r to produce  for  ( C h i Sguare=15.83)  in  color of than  differences  color green  o c c u r s , with females  the o b s e r v e d  males a r e the  green  in  males.  they  could  than  mutually e x c l u s i v e ;  differs  differences  in color.  80 Table 2. Numbers of brown and green a d u l t males and captured at Marion Lake i n 1973.  Sex  females  Green  Brown  Males  45  87  Females  13  1  Significantly  different,  p<0.001  (Chi Square =18.03)  81  B.  COLORS OF JUVENILE MALES AND  - If females  the  differences  occurs e n t i r e l y  probably  the o n l y time  therefore  would  sub-adult  and  between  animals.  one  expect  most brown s u b - a d u l t s  (which i s  selective  be f o u n d  i n both  i f the genetic  most g r e e n  that  behave d i f f e r e n t l y , and  different  should  Conversely,  would  assuming  during the adult stage  to  of the sexes  a d u l t males and  selection,  t h a t the sexes  be s u b j e c t  numbers  valid,  color  a r e due o n l y t c d i f f e r e n t i a l  the s e l e c t i o n  equal  in  FEMALES  forces), morphs i n  hypothesis  sub-adults  t c be  is  females  t o be m a l e s .  Methods Recently collected They  on  metamorphosed the shores  were r a i s e d  snout-vent  i n the  l e n g t h , then  froglets  of Marion  of  both  Lake i n e a r l y  laboratory  to  d i s s e c t e d and  morphs  were  August 1972.  approximately  15  mm  sexed.  R e s u l t s and D i s c u s s i o n I  was  structure  able  t o sex a l l i n d i v i d u a l s  o f t h e gonads.  proportions  of  the  No  significant  morphs o c c u r r e d  u n e g u i v o c a l l y by t h e difference  i n the  between t h e s e x e s  (Table  3). These r e s u l t s differences  a r e c o n s i s t e n t with  i n color  the hypothesis  between a d u l t males and f e m a l e s  that the are  due  82  T a b l e 3. Marion  C o l o r s of j u v e n i l e Lake.  male and  female  f r o g s captured  at  Color Sex  Green  Brown  Males  19  9  Females  19  12  Hot  significantly  only  to  different,  differential  operate  directly  remainder  C.  selection.  on  straight-forward  color,  that  Tree  the  Frogs  all  stage  at  relatively from  the  of  the  ( i . e . that  of  both  of  the  Marion stable  tadpole  will  from stage  at  MORPHS AT  this  need  is  accept  be  two  assuming (Tables  1972  to  to the  brown.  not  the  i t  most  for  the  TADPOLE STAGE  tadpole  are  the  and  egual  2 suggest  in  the  effect  in  the  (determined  is  that i t i s viabilities  o f m a l e s and  comparing stage  until  polymorphism  the r e l a t i v e  a d u l t stage by  color  pleiotrophic  that 1  for  Assuming, t h e r e f o r e ,  morphs  1973),  estimated the  THE  polymorphic  t h e r e i s no  Lake  morphs can morphs  THE  are not  t a d p o l e s t a g e ) , and  stable  selection  since  I  tadpoles are  the v i a b i l i t i e s  tadpole  ( C h i Square=0.30)  paper.  RELATIVE ABUHBANCE OF  metamorphosis;  The  but  hypothesis,  of t h i s  Pacific  0.70>p>0.50  females  proportions by  raising  83  tadpoles  to  proportions  metamorphosis  in  the  laboratory)  with  the  for adults.  Methods Tadpoles same a r e a  were  collected  i n Marion Lake t h a t  They were r a i s e d i n scored  the  study  the  97  metamorphosis,  92  proportions  of  comparison  with  and  (Tables  females  against  green  and  to  was  the  done i n .  metamorphosis,  the  represent  only  morphs a t  the  the  males  and  only  then  2)  the  indicates  females)  occur  appears  were c a p t u r e d  study  area  t h e r e f o r e may  to  estimate  stage.  that  of  Even  morphs i n a d u l t heavy  on  the  more  (presumably  shortly after  the so,  males  selection  both  males  metamorphosis.  s h o r e o f M a r i o n Lake a d j a c e n t  i n e a r l y September  appeared  to  occurs.  green f r o g s  Froglets  rough  tadpole of  raised  5 were brown.  a very  proportions  1 and  successfully  Some s e l e c t i o n a g a i n s t  actual  of a d u l t s  from  Discussion  individuals  were g r e e n  These r e s u l t s  frogs  1972  for color.  Of  the  the  e a r l y August  laboratory  Results  and  in  1972,  conspicuous  have been c a p t u r e d  out  abundance), a s i g n i f i c a n t l y  and  to both of  even t h o u g h  higher  green  investigators  proportion proportion  to of  to  (and their  brown  84  individuals tadpoles  was taken i n t h i s sample than  in  the  sample  of  (Table 4 ) .  Table 4. Numbers of green and brown i n d i v i d u a l s i n f r o g l e t s r a i s e d i n the l a b o r a t o r y from tadpoles and in froglets captured on the lake shore.  Sajti£le  Green  Brown  Captured  as t a d p o l e s  92  5  Captured  as f r o g l e t s  47  17  S i g n i f i c a n t l y d i f f e r e n t , p<0.001  The remainder  selective  pressures  o f the j u v e n i l e  on  (Chi Square=15.17)  the  two  morphs  for  stage are not known; however,  the  since  the behavior of males and females i s not known to be d i f f e r e n t at  this  stage,  and  females.  s e l e c t i o n should occur e q u a l l y on both males  85  D.  SELECTION  Since  IN  ADULT HALES  the  relative  s u b - a d u l t s about presumed can are  at  a  An of  selective  two  with that  age  of  the  same f o r b o t h  adults  morphs.  is  in the  the  one  adult stage, females  individuals  or  both  of the  other  morphs, i f one adult  be  larger  stage, than  relative  to  of  viabilities  compare  Assuming t h a t s i z e f r o g s marked  t h a t the r e l a t i o n s h i p  the  average,  in  ( r e c a p t u r e s i n 1973  i t i s ) and  during  advantage over  morphs  known, r e g a r d i n g  brown m a l e s o r g r e e n  method f o r a s s e s s i n g t h e  morphs  distributions  during  the  r e s p e c t i v e sexes.  indirect  the  selection  that either  morph i n t h e i r  of  t o become a d u l t s a r e n o t  differential  o n l y say  proportions  of s i z e  the  i s correlated  i n 1972 to  those  of the other  indicate  age  morph i s a t a s e l e c t i v e f r o g s of that c o l o r  size  is  the  advantage  should,  on  the  morph.  Methods  For t h i s adult 1972  analysis,  males c a p t u r e d and  analysis.  1973;  on  data  I used  the  size  the b r e e d i n g for  females  and  color  grounds a t were  data  Marion  for  Lake i n  insufficient  for  86  Results  and_Discussion  F o r b o t h 1972 and 1973, green  males  brown  males  ( T a b l e s 5 and 6 ) , s u g g e s t i n g  at a s e l e c t i v e  that  larger  than  brown males a r e  advantage as a d u l t s .  T a b l e 5. Mean s n o u t - v e n t l e n g t h s brown m a l e s , M a r i o n L a k e , 1972.  Green_Males  (n=68)  (mm)  green  males  and  (n= 107)  37.97  Significantly  different,  Table 6. Mean snout-vent lengths brown m a l e s , M a r i o n L a k e , 1973.  Green_Kaj.es  of  Brown M a l e s  35.25  (n=45)  p<0.01  (mm)  o f g r e e n males and  Brown, M a l e s  37.15  When d o e s  were  (n=87)  38.31  Significantly  different,  the s e l e c t i o n  against  p<0.01  green a d u l t  males  occur?  87  The  most  season.  obvious answer, i n t u i t i v e l y , i s during the breeding I n d i v i d u a l males may  breeding the  grounds.  breeding  breeding  At  Marion  grounds  season  spend  is  before  several  should  be  on  the  Lake the g e n e r a l c o l o r a t i o n of  brown, plants  especially  early  in  begin to produce new  T h e r e f o r e , i f i t i s of s u r v i v a l value males  months  a t an advantage.  high p r o p o r t i o n of green females  to  be  the  growth.  cryptic,  brown  By the same argument, the  might be accounted  f o r by the  f a c t that they come onto the breeding grounds f o r only one two  days  each,  and  then  presumably  b o r d e r i n g t h e , l a k e where i t may  not  be  return  or  to the f o r e s t  advantageous  to  be  brown. To  test  the  hypothesis  that  brown  males  s e l e c t i v e advantage during the breeding season, data f o r males captured i n 1972 proportion  of  season.  such  No  brown  males  trend was  and  increased  found  r e s u l t s c o n t r a d i c t the hypothesis is  possible  l a t e r than individuals cryptic). be masked.  that  brown on  green males  the  1973  (Tables  are  I examined  to determine during 7  at  and  the  if  a the the  breeding  8).  These  but not u n e q u i v o c a l l y .  It  males come onto the breeding grounds (this  strategy  would  place  green  breeding grounds when they would be more  I f so, the net s e l e c t i o n a g a i n s t green  males  might  88  Table 7. Numbers of green and brown a d u l t males c a u g h t d u r i n g one-week p e r i o d s a t M a r i o n Lake i n 1972. Data f o r e a c h week i n c l u d e r e c a p t u r e s .  Number Week  Green  Brown  8  27  18  27  16-22 May  28  39  23-29 May  13  14  30 May-6 June  3  12  7-14 J u n e  2  9  1-8 May 9-15  May  1  Not  1  E.  8-day  s i g n i f i c a n t l y d i f f e r e n t , 0.20>p>0.10 ( C h i - S g u a r e = 8 . 8 9 ; df=5)  period  SUMMARY  AND  Pacific  DISCUSSION  Tree  brown.  In a d u l t s ,  females  than  differential  this  selection,  green  Marion Lake a r e e i t h e r  morph  is  much  more  seems t o be e n t i r e l y  which  green or  common  in  the r e s u l t of  probably occurs during the adult  cycle.  morph a p p e a r s  during  the f r o g l e t  froglet  stage to the adult  viabilities  at  the green  i n males;  stage of the l i f e The  Frogs  t o be a t a s e l e c t i v e  s t a g e i n both  disadvantage  f e m a l e s and m a l e s ,  s t a g e , green  females  appear  From t h e t o have  e g u a l t o o r g r e a t e r t h a n brown f e m a l e s , but d u r i n g  89  t h e same p e r i o d ,  the  green  morph  declines  dramatically  in  males. These selective  results  indicate  that  g r e e n ' males  d i s a d v a n t a g e b o t h as j u v e n i l e  Therefore,  the  overall  selective  forces  "average  o u t " as Jameson and P e q u e g n a t  Julian,  California  population.  persist  in  Lake  proportion  Marion of green  males  f r o g s and  The only  on  are as  at  adults.  males  do  (1971) c l a i m e d f o r green because  morph a  females o c c u r s i n the breeding  a  not the  seems t o very  high  population.  Table 8. Numbers of green and brown a d u l t males c a u g h t d u r i n g one-week p e r i o d s a t M a r i o n L a k e i n 1973. Data for e a c h week i n c l u d e r e c a p t u r e s .  Number Week  Green  Brown  11-17  April  4  9  18-24  April  10  14  12  38  9  14  11  24  11  9  25  April-1  2-8  May  May  9-15 16-22  May May Not  s i g n i f i c a n t l y d i f f e r e n t , 0.30>p>0.20 ( C h i - S g u a r e = 7 . 2 1 ; df=5)  90  LITERATURE CITED  Brattstrom, B. H. and J . W. Warren. 1955. Observations on the ecology and behavior of the P a c i f i c Tree Frog, Hjrla r e g i l l a . Copeia 1955:181-191. Jameson, D. L. and S. Peguegnat. 1971. E s t i m a t i o n of r e l a t i v e viability and f e c u n d i t y of c o l o r polymorphisms in anurans. E v o l u t i o n 25:180-194. Resnick, L. E. and D. L. Jameson. 1963. Color polymorphism i n P a c i f i c Tree Frogs. Science 142:1081-1083.  

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