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Specific and seasonal variation in survival and sodium balance at low pH in five species of waterboatmen… Needham, Karen Merrie 1990

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SPECIFIC AND SEASONAL VARIATION IN SURVIVAL AND SODIUM BALANCE AT LOW pH IN FIVE SPECIES OF WATERBOATMEN (HEMIPTERA: CORIX1DAE)  By  KAREN MERRIE NEEDHAM B.Sc, The University of British Columbia, 1986 A THESIS SUBMITTED IN PARTIAL FULFILLMENT OF THE REQUIREMENTS FOR THE DEGREE OF MASTER OF SCIENCE in THE FACULTY OF GRADUATE STUDIES DEPARTMENT OF ZOOLOGY  We accept this thesis as conforming to the required standard  THE UNIVERSITY OF BRITISH COLUMBIA October 1990 ©  Karen Merrie Needham, 1990  In  presenting  degree freely  at  the  available  copying  of  department publication  this  of  in  partial  fulfilment  University  of  British  Columbia,  for  this or  thesis  reference  thesis by  this  for  his thesis  and  scholarly  or for  her  of  The University of British Columbia Vancouver, Canada  TH  DE-6  (2/88)  I  I further  purposes  gain  the  shall  requirements  agree  that  agree  may  representatives.  financial  permission.  Department  study.  of  be  It not  that  the  Library  by  understood be  an  advanced  shall  permission for  granted  is  for  allowed  the that  without  make  it  extensive  head  of  copying my  my or  written  ABSTRACT  Sodium  balance  species  of adult  neutral  and  reflect  a  naturally  and m o r t a l i t y waterboatmen  low pH  wide  waters.  range  o f pH  Cenocorixa  occur.  rates  were  examined ' i n  (Hemiptera: C o r i x i d a e ) The  five  species  conditions bifida  i n waters  and  atopodonta  can be found most  often  exposed t o chosen where  expleta  C.  h i g h pH waters, whereas C. blaisdelli  inhabit  were  to  they  normally Hesperocorixa  and  at n e u t r a l  five  pH. Sigara  omani  occur i n a c i d i c waters. Haemolymph  [Na], whole-body  [Na], and sodium  were r e c o r d e d d u r i n g exposures o f 6-9 days C. blaisdelli  3.0. year  (spring,  examined  and H. atopodonta  these c o r i x i d s  both  neutral  Additionally, and sodium rarely  expleta  were  and  acidic  differences  of short-term  f o r a l l s p e c i e s remained below 50% pH  levels  i n haemolymph  throughout  t h e year.  [Na], whole-body [Na],  i n f l u x r a t e s from pH 7.0 t o e i t h e r pH 4.5 or 3.0 were  significant.  However, balance notably,  both  inter-  over t h e range C. blaisdelli  concentrations under  and C.  appeared t o be t o l e r a n t  exposure t o low pH. M o r t a l i t y in  were s t u d i e d throughout t h e  w h i l e S. omani were t e s t e d i n t h e s p r i n g .  i n the f a l l ,  Overall,  rates  at pH 7.0, 4.5, and  and f a l l ) . C. bifida  summer,  influx  both  and i n t r a s p e c i f i c o f pH l e v e l s  natural  tested  and H. atopodonta  o f haemolymph conditions  variation  i n sodium  were apparent. Most  exhibited their  and whole-body  Na  highest  i n t h e summer,  and i n t h e l a b o r a t o r y  at a l l pH  levels.  mortality,  blaisdelli,  C.  For  with  mortality  summer was  also  increasing  as  the time pH  was  of h i g h e s t  lowered.  observed c o r r e l a t i o n between h i g h haemolymph/whole-body high mortality  i n the summer appears t o r e s u l t  l a r g e decrease i n haemolymph and whole-body exposed  t o pH  high. F a l l and  3.0,  was  also  of  [Na]  [Na] when bugs were initially  the season o f lowest haemolymph/whole-body mortality,  blaisdelli  C.  f o r both  and  from a r e l a t i v e l y  at a time when these v a l u e s were  lowest  The  [Na], and  H.  atopodonta.  Interspecific variation not  appear  normally  to r e f l e c t  inhabit.  Of  i n the a b i l i t y t o t o l e r a t e  variation  i n the pH  the  species  five  low pH d i d  o f water  these bugs  H.  atopodonta  tested,  appeared best able t o m a i n t a i n i n t e r n a l homeostasis under conditions, [Na],  despite  whole-body  significantly C.  in  low pH  [Na],  and  from pH  7.0  which  was  blaisdelli,  atopodonta,  b e i n g common t o n e u t r a l  seemed t o be waters.  sodium  t o pH  influx  3.0  collected least  i n any from  waters.  rates  the  exposure  values  recorded  difference  in  i n the  approximately  those  size  twice that  individuals  o f these two  exposed species  of C. blaisdelli)  may  pond  internal  t o pH  r e s u l t e d i n decreased haemolymph and whole-body  change  Furthermore,  same  able t o r e g u l a t e  In C. blaisdelli,  Haemolymph  d i d not  season.  acidic  3.0  as  H.  milieu usually  [Na], r e l a t i v e t o to (H.  pH  7.0.  The  atopodonta  is  account  f o r the  observed v a r i a t i o n s i n t h e i r r e s p e c t i v e sodium balance at low pH.  iv T A B L E OF CONTENTS Page Abstract Table of Contents List  of Tables  List  of F i g u r e s  List  of Appendices  i i iv v vi v i i  Acknowledgements  viii  Introduction  1  M a t e r i a l s and Methods  6  Results  15  Discussion  48  Summary  62  References  64  Appendices  70  V L I S T OF TABLES Page Table 1 Table 2  Table 3  Major i o n c o m p o s i t i o n and pH o f w a t e r s from t h e c o l l e c t i o n s i t e s i n B.C  9  Haemolymph [Na], whole-body [Na], and sodium i n f l u x r a t e s o f f i v e s p e c i e s o f c o r i x i d s i n t h e i r n a t u r a l waters  16  Q u a l i t a t i v e summary o f changes i n haemolymph [Na], whole-body [Na], and sodium i n f l u x r a t e s o f f i v e s p e c i e s of c o r i x i d s upon exposure t o low pH  53  vi  LIST OF FIGURES Page Figure 1 Figure 2  Figure 3  Figure 4  Figure 5  Figure 6  Figure 7  Figure 8  Figure 9  F i g u r e 10  F i g u r e 11  F i g u r e 12  Map o f v a r i o u s c o l l e c t i o n B.C  sites i n 7  R e l a t i o n s h i p between haemolymph [Na] and s o d i u m c o n c e n t r a t i o n o r pH o f t h e n a t u r a l waters f o r f i v e species of c o r i x i d s  17  R e l a t i o n s h i p between whole-body [Na] and s o d i u m c o n c e n t r a t i o n o r pH o f t h e n a t u r a l waters f o r f i v e species of c o r i x i d s  19  R e l a t i o n s h i p between s o d i u m i n f l u x r a t e s and s o d i u m c o n c e n t r a t i o n o r pH o f t h e n a t u r a l waters f o r four species of corixids  21  Seasonal v a r i a t i o n i n cumulative m o r t a l i t y f o r C . b l a i s d e l l i and H. a t o p o d o n t a  25  percent  Cumulative percent m o r t a l i t y during the haemolymph/whole-body e x p e r i m e n t s f o r f i v e species of corixids  28  Cumulative percent m o r t a l i t y during the i n f l u x experiments f o r f i v e species o f corixids  30  S e a s o n a l v a r i a t i o n i n haemolymph [ N a ] , whole-body [ N a ] , and sodium i n f l u x rates f o r C . b l a i s d e l l i  33  S e a s o n a l v a r i a t i o n i n haemolymph [ N a ] , whole-body [ N a ] , and s o d i u m i n f l u x r a t e s f o r H.atopodonta  36  Haemolymph [Na] o f f i v e s p e c i e s o f c o r i x i d s a t t h r e e pH l e v e l s i n t h r e e seasons  39  Whole-body [Na] o f f i v e s p e c i e s o f c o r i x i d s a t t h r e e pH l e v e l s i n t h r e e seasons  41  Sodium i n f l u x r a t e s o f f o u r s p e c i e s o f c o r i x i d s a t two pH l e v e l s i n two s e a s o n s . . . . 44  vii L I S T OF APPENDICES Page Appendix Appendix Appendix  A B C  Raw d a t a from t h e haemolymph experiments  [Na]  Raw d a t a from t h e whole-body experiments  [Na]  Raw d a t a from t h e sodium experiments  70 76  influx 81  v i i i  ACKNOWLEDGEMENTS  I  would  for  his  like  like  supervisor,  knowledge  and  thank  my  committee  members,  for  improved  this  you  out  goes  his  my  of  to  my  thank  wealth  Northcote,  in  to  to  insistence  my his upon  ol'  In  pal  expert  and,  for  more  by  contributed  technical  assistance  gratitude a  mere  which  to  the  be.  Edie,  this  into  a  of  and  gang",  second  home  Scudder,  would and  special  subject  and  thank-  area,  and  accuracy.  and  And  interest  camaraderie  humour  T.  greatly  unrelenting the  also  Dr.  which  very  Shona,  project.  "fourth-floor  institution to  of  his  I  Isman  importantly,  provided  stage  a  conciseness,  graciously  experimental  M.  comments,  knowledge  quality,  assistance  Dr.  addition,  Locke  G.G.E.  inspiration.  valuable  manuscript.  project,  Artistic  their  his  Dr.  Lois.  were Rich  throughout  finally,  for  turning  and  a  unending  U.B.C.  pleasant  the  from  place  in  1  INTRODUCTION  Anthropogenic serious of  acidification  of  natural  freshwaters  is  a  problem, i n f l u e n c i n g both the d i s t r i b u t i o n and abundance  many a q u a t i c  Baker et  al.,  life  forms  (Haines,  1981;  1990). A c i d i f i c a t i o n of  aquatic b i o t a either d i r e c t l y ,  surface  1984;  waters can  affect  et  of H t o x i c i t y  (Packer  and Dunson, 1970), or i n d i r e c t l y , v i a r e c r u i t m e n t f a i l u r e  (Fraser  and Harvey, 1984)  tolerance  differences exchange  be  seen  (Pierce,  surfaces  be  often  populations  (Potts et al.,  correlated  are u s u a l l y  (Pierce,  and  and other  1985), w h i l e i n t r a s p e c i f i c  differences  correlate  of  species losses  physiological  species d i s t r i b u t i o n s Rowe  et  s t u d i e s must  more  tolerant  more a c i d i c n a t u r a l  al.,  first  from a c i d i f i e d n a t u r a l waters few s t u d i e s have attempted  constraints  at  (for e x c e p t i o n s , 1989).  Within  low  see  any  pH with  currently  Then, found  other in  this  to  observed  Havas and Hutchinson,  one  taxon  be conducted on s p e c i e s t h a t  i n these waters. not  history;  found l i v i n g i n the  are q u i t e common i n the l i t e r a t u r e ,  are  Interspecific  ecological  habitat  1979)  in  or  with  Fryer,  al.,  1985).  While r e p o r t s  that  1985).  +  can  survival  differences  may be r e l a t e d t o H p e r m e a b i l i t y of g i l l s  (Servos  1983;  ( E r i k s s o n et  both i n t e r - and i n t r a s p e c i f i c  can  strategies  waters  +  or a l t e r a t i o n of a food c h a i n  1980) . W i t h i n t a x a , acid  as a r e s u l t  al.,  Dillon  s p e c i e s of type  of  of  animals,  are adapted the  for  same group  habitat  can  s u b j e c t e d t o a c c l i m a t i o n and experimentation i n low pH water,  be and  2 these two s e t s o f r e s u l t s may be compared Acid  freshwaters  ionoregulatory enter  problems.  through  time  i f animals  are t o i n h a b i t  the e x t e r n a l medium.  H  conditions,  ions  must  the conformation  longer  -  sodium  uptake  completely  in  many  Hutchinson,  1983; McDonald,  Disruption  of  ion  animals  uptake  +  f o r exchange or these  sites  so t h a t  i s prolonged Despite  ions may they  no  exposed  i s u s u a l l y the  inhibited to  low  pH  to  arrested  (Havas  et al.,  1983a; Vangenechten leads  or  decreases  and  1989). in  both  [Na], and f i n a l l y t o death i f exposure  (McDonald, 1983b; Vangenechten et al.,  these  sites  1980; Wood, 1989; Vangenechten  partially  regulation  haemolymph and whole-body  In  +  (Havas,  is  retained.  these e n v i r o n s they must be  et a l . , 1989). Whatever t h e mechanism, the r e s u l t same  may  of a high concentration of H i n  o f sodium  function properly  water  o r through the  be  the e x t e r n a l s u r f a c e s o f a q u a t i c animals,  alter  and  water must be excreted,  can compete w i t h Na  +  1987).  osmoregulatory  the integument  necessary  able t o d e a l w i t h the presence  on  dilute  o f the medium. Excess  at the same  addition,  some i n t e r e s t i n g  In such  the body p a s s i v e l y  gut v i a i n g e s t i o n while  present  (Scudder,  problems,  some  aquatic  1989).  animals  are a b l e  to  s u r v i v e and breed i n a c i d waters. Examples o f a c i d t o l e r a n c e are taxonomically diverse, 1977;  McWilliams,  (Berrill 1981,  et al.,  including  1982), 1985),  species of f i s h  amphibians  (Pierce,  and i n s e c t s  1985),  (Henrikson  1985). Since the i o n o r e g u l a t o r y processes  are very s i m i l a r  (Dunson et  al.,  crustaceans  and  Oscarson,  o f these  groups  (Motais and Garcia-Romeu, 1972; Komnick, 1977),  t h e r e may be common mechanisms by which these  animals  adapt t o  3 life  at  within  low  pH.  any  studies  one  of  Therefore,  taxa  other  similarities,  explorations  might  taxa.  provide  By  the reasons  of  these  information  understanding  the  f o r the d i f f e r e n c e s  mechanisms  applicable  extent  of  to  these  between taxa i n the  a b i l i t y to s u r v i v e at low pH might become more apparent. Insects  appear  crustaceans, Lechleitner  to  al.,  et  between  and w i t h i n  most  lost  al.,  of  (Bell al.,  acidified (Okland  low  pH than  either  and  Nebeker,  1969;  While some  insect  1989).  waters, and  sensitivity  Okland,  colonization  Scudder,  acidified,  a c i d freshwaters 1987).  fishless because  waters while  lakes  some  others  Often,  (Henrikson  primarily  differences  al.  become  c o r i x i d species  these d i s j u n c t  Vangenechten et  1971), and  appear to be  successful  inhabit  the and  are  top  alkaline  of d i f f e r e n t  may have been r e l a t e d t o d i f f e r e n c e s  show  differences  in  predators  common  in  1981). in  environments,  s p e c i e s of  (1987)  i n c o r i x i d ion regulation a b i l i t i e s  one can hypothesize  1981,  acid we  corixids  distributions.  (1979b) and Scudder  Thus,  in their  Oscarson,  most  the  family  (Henrikson and Oscarson,  they  might expect the a c i d t o l e r a n c e s to r e f l e c t  Diptera  W i t h i n Hemiptera, some s p e c i e s of the  i n p a r t i c u l a r , been extremely  of  varies  1986).  Havas, 1980), T r i c h o p t e r a ( B e l l ,  (Vangenechten and Vanderborght, 1980)  acid-tolerant.  However,  fish  Rowe et  orders  1986;  C o r i x i d a e have,  1985;  from  tolerant  or  1985;  are  Hemiptera  more  amphibians,  species  (Mierle et  be  in habitat  that d i f f e r e n t  survival  and  depending on t h e i r n a t u r a l h a b i t a t .  report  at  species  low pH, which  characteristics.  s p e c i e s of c o r i x i d s w i l l  sodium  balance  Specifically,  it  at  low pH,  is  predicted  4 that to  s p e c i e s taken from h i g h pH waters  should f i n d  it  difficult  s u r v i v e under low pH c o n d i t i o n s f o r any l e n g t h of time,  species better  which occur n a t u r a l l y i n able  to  regulate  their  a c i d i c environments  while  should be  i n t e r n a l m i l i e u under a range  of  a c i d i c c o n d i t i o n s i n the l a b o r a t o r y . Species which are found most often  in  n e u t r a l waters  a b i l i t y that To  test  waters  is  hypothesis, i n pH were  low pH. Cenocorixa  and  waters  w i t h a pH of  naturally  expected  five  bifida  waters  atopodonta  to  species  from  i n the  regulation  pH  omani  different  neutral  from  was taken  C.  4.5.  from  three  were c o l l e c t e d  Sigara  while  came  a  l a b o r a t o r y at n e u t r a l  and C. expleta  of  have  effectiveness.  studied  9.0-10.0,  acidic  Hesperocorixa  be  intermediate i n i t s  this  varying  will  from  blaisdelli waters  and  (pH  7.0).  P h y s i o l o g i c a l parameters measured are l i s t e d below. Seasonal  v a r i a t i o n i n the  regulate  ions et  (Vangenechten al.,  1988a;  have  seasonal  rates  C.  in  al.,  Frisbie  reported  been  differences The  T h e r e f o r e , the  corixids  will  maintain  Stuart  and Dunson,  blaisdelli.  show  internal  a  of  animals  demonstrated  1979b;  t r e a t e d w i t h head e x t r a c t spring.  ability  in  Cooper  Malpighian  lowest  rates  feeding  1974).  very  Consequently,  Rowe  al.  et  tubule  second hypothesis  occurred i n  seasonal  variation under  of  this  in  acidic  study  their  during  this  sodium l e v e l s  time are  (1988)  tubules i n the is  ability  conditions.  (Jansson  et  secretion  d e r i v e d from c o r i x i d s c o l l e c t e d  homeostasis  little  studies  1985;  c o r i x i d s p e c i e s s t u d i e d t o date overwinter as a d u l t s , or  s u r v i v e and  several  and M o r r i s ,  1988c).  in  to  not  that to The  feeding  and Scudder,  c o n s i d e r a b l y d e p l e t e d by  5 the  spring  sodium  (P. Cooper,  balance  pers.  i n acid  comm.).  waters  could  So, i t i s probable be more d i f f i c u l t  that  in  the  s p r i n g than a t o t h e r times o f t h e year. In c o n t r a s t , summer i s a time  of  high  Presumably,  activity,  then,  internal  including sodium  feeding  (pers.  concentrations  obs.).  a r e h i g h and  exposure t o low pH water should be t o l e r a t e d more e a s i l y . In t h e fall,  many i n t e r n a l p r o c e s s e s a r e slowed down i n p r e p a r a t i o n f o r  overwintering modification  (G. Scudder,  pers.  comm.).  of metabolic a c t i v i t i e s  This  such t h a t  results corixids  i n the may not  be r e a d i l y able t o d e a l w i t h unexpected changes i n t h e i r e x t e r n a l environment.  Fall,  then, may again be a season  o f poor  sodium  balance c a p a b i l i t i e s i n low pH water. To t e s t these hypotheses, four parameters were measured i n t h e five  species  [Na], S.  examined.  and sodium  omani,  spring,  influx  i n the f a l l summer,  atopodonta.  Mortality,  haemolymph  r a t e s were q u a n t i f i e d f o r C. bifida  and  fall  A l l species  [Na], whole-body i n the spring f o r  and C. expleta,  f o r both  C.  were not a v a i l a b l e  and i n t h e  blaisdelli fortesting  and H. in  seasons. Exposures were 6-9 days i n d u r a t i o n , and pH l e v e l s in  a l l three  studies  (Vangenechten  Rowe e t a l . , [Na],  seasons  were  e t a l . , 197 9ab;  influx  used  7.0, 4.5, and 3.0. As i n p r e v i o u s Lechleitner  1988a, 1989), changes i n haemolymph  o r sodium  all  upon  exposure  indicators of ion regulation disruption.  et al.,  1985;  [Na], whole-body  t o low pH were  used as  6  MATERIALS AND METHODS  Adult  c o r i x i d s were  British  Columbia  (Figure  Hesperocorixa  and  Jericho  bifida  hungerford!  Becher's  Figure the  atopodonta Vancouver  Prairie,  l a k e LB2,  Scudder  Sigara  1977).  naturally Graham  acidic  Island,  bog  (Hungerford)  were  123°12'W;  collected  from  Figure  1A) .  Plateau  expleta  (52°00'N,  (Uhler)  122°30'W;  were obtained  (50°45'N, 120°25'W; F i g u r e  IC)  omani  collected  (Hungerford) located  Charlotte  along  were the  Islands.  eastern  Most  of  Figure  major  Clements  i o n composition  and  s i t e s are l i s t e d i n Table Insects flasks the  (53°41'N, pH  collection  2-3  site  of the  waters  from the  of  Queen pool  ID) .  2  The  collection  1.  were t r a n s p o r t e d  containing  132°11'W;  from  the  km  Port  &  coast  extensive  of  from  (Topping  C h a r l o t t e I s l a n d specimens came from a shallow, south  around  (Lansbury) were taken from Lake Lye  pools  Queen  localities  blaisdelli  (49°16'N,  Chilcoltin  Kamloops  various  (Hungerford)  Cenocorixa  IB), while  from  Cenocorixa  1).  Pond,  Cenocorixa on  obtained  t o the  litres (Juncus  of  laboratory  in 4 litre  lake water and  spp.),  to  which  vacuum  some weeds  the  insects  from could  c l i n g . Measurements of pH were made i n the f i e l d and again i n the laboratory,  and  did  not  d u r i n g t r a n s p o r t . In the shallow  more  than  (30 x 24 x 10 cm)  some weeds from the c o l l e c t i o n  were maintained  one-tenth  of  a  unit  l a b o r a t o r y , i n s e c t s were t r a n s f e r r e d to  p l e x i g l a s s containers  of o r i g i n and Corixids  change  at  5° C  i n the  c o n t a i n i n g water  site  dark  and  (Juncus without  spp.). food.  7  Figure  1  Map o f v a r i o u s c o l l e c t i o n s i t e s i n B.C. A) J e r i c h o Pond, Vancouver, B) Lake Lye, Becher's P r a i r i e , C h i l c o t i n P l a t e a u , C) lake LB2, Kamloops and D) P o r t Clements, Queen C h a r l o t t e I s l a n d s . I n s e c t : Cenocorixa expleta.  9 Table 1  Major ion composition and pH of waters from the collection sites in B.C.  Water  Location  Species  Jericho Pond  Vancouver  Cenocorixa blaisdelli Hesperocorixa atopodonta  6  1  7  3  7.0  Lake Lye  Riske Creek (Becher's Prairie)  Cenocorixa bifida  50  4  15  29  9.0  LB2  Kamloops  Cenocorixa expleta  230  11  18  105  9.5  Bog Pools  Port Clements (Q.C.I.)  Sigara omani  6  2  4  —  4.5  Na K cr Total CO2 (mM) (mM) (mM) (mM) +  +  PH  10 Individuals collected body  and  therefore  i n the f a l l need  not  have an adequate  be  fed  (Scudder  W i t h h o l d i n g food i n such i n s e c t s assures t h a t a similar physiological receiving  any  sodium v i a  overwintering can l i v e healthy  condition  their of  f o r long p e r i o d s state  always  s t a t e before  used  possibility  (pers. within  of time  obs.). 1-2  in  weeks  of  fat  1972).  a l l animals are  in  and are  not  At 5° C, which mimics  the  the  (2-3  However,  of  al.,  et  experimentation  food.  adults  reserve  field,  months)  adult  i n an apparently  experimental capture,  of p h y s i o l o g i c a l s t r e s s due t o  corixids  to  insects  were  minimize  the  captivity.  Experiments were designed to measure haemolymph and whole-body sodium  concentrations,  corixid.  These  (spring,  measurements  summer  and  P r e l i m i n a r y experiments males were  and females; conducted  and  sodium  for  were- repeated  fall),  to  examine  of  these  species  times  seasonal  a  of year  variation.  differences  sexes were p o o l e d .  5° C . D e t a i l s  each  several  showed no s i g n i f i c a n t  therefore  at  influx  All  between  experiments  experiments  are  given  below.  Haemolymph and Whole-body Sodium Measurements After 1972),  3-day  acclimation  period  of p l a s t i c  filtered  5° C  (Scudder  et  al.,  screen f o r the i n s e c t s to c l i n g to and 800 ml  J e r i c h o Pond water  Treatments were pH l e v e l s two r e p l i c a t e s  7.0,  (0.45 yum M i l l i p o r e 4.5,  4  and 3 . 0 .  HA f i l t e r s ) .  In most  experiments  of each pH were used. pH was e s t a b l i s h e d  M H S0 . Haemolymph and whole-body 2  at  i n s e c t s were t r a n s f e r r e d to 1 L beakers c o n t a i n i n g a 5 x 7  cm p i e c e of  a  sodium v a l u e s  were  using  0.5  determined  11 on t h e day o f t r a n s f e r this,  (Day 0), and on every second day a f t e r  up t o and i n c l u d i n g  Day 8. In every experiment,  pH was  a d j u s t e d d a i l y and m o r t a l i t y noted. F o l l o w i n g t h e methodology samples  were  collected  o f Scudder e t al.  by removing  (1972), haemolymph  the r i g h t  forewing o f each  c o r i x i d w i t h a p a i r o f f o r c e p s a f t e r t h e i n s e c t had been dry  on f i l t e r  would  well  collected  by  never  capillary  removal  action  pooled.  o f haemolymph Haemolymph  (deionized) water  o f t h e forewing,  of the insect, in a  (Microcap). U s u a l l y  1 /al  than  Upon  up on t h e pronotum  micropipette more  paper.  To  determine  diluted  removed from each t e s t recording  balance;  sodium  a wet weight  samples of  + 0.1 mg a c c u r a c y ) ,  distilled  of c o r i x i d s ,  insects  sodium d e t e r m i n a t i o n s were  insect  (Mettler  they were p l a c e d  i n a drying  were  transferred  (540° C) and ashed. Ash was d i s s o l v e d  This  suitable  assured t h a t f o r analysis.  t h e samples Sodium  oven  (80° C; 24 hours) . The d r y weights  first  t o a muffle w i t h 1 ml o f  3  3  paper.  Gram-atic  c o n c e n t r a t e d HN0 , and then made up t o 25 ml w i t h d i l u t e HN0 .  were  content on a Techtron  values  o f each  recorded, and t h e c o r i x i d s  furnace  ml  to collect  s o l u t i o n and b l o t t e d dry on f i l t e r  and d r i e d t o a constant weight were  in 1  glass  (Model 120).  t h a t had not been used f o r haemolymph  After  However,  and a n a l y z e d f o r sodium  whole-body  and c o u l d then be  i t was not p o s s i b l e  Atomic A b s o r p t i o n Spectrophotometer  haemolymph  1 /al disposable  per insect.  was  blotted  were w i t h i n  content  atomic a b s o r p t i o n spectrophotometer.  was  (0.2 M)  a molar  determined  range on the  12 Sodium I n f l u x I n s e c t s h e l d i n t h e i r n a t u r a l pond water i n vacuum f l a s k s were ' a c c l i m a t e d t o 5° C f o r 3 days. They were then t r a n s f e r r e d t o a 1 L beaker c o n t a i n i n g approximately 800 ml o f s a l i n e s o l u t i o n (mM) : Na+ H S0 . 2  6, K+  1, CI- 8, t o t a l  This . s o l u t i o n  4  composition  was  of Jericho  C0  3) s e t at pH  2  intended  Pond water  to  7.0  mimic  (ions  w i t h 0.5  the  M  chemical  (Table 1), w h i l e at the same  time e l i m i n a t i n g the number o f p o s s i b l e unknown substances i n the latter.  Adjustments  t o pH  and  mortality  counts were made  daily  throughout the a c c l i m a t i o n p e r i o d s and d u r i n g the experiments. After saline  a  further  solution,  solutions:  800  3-day a c c l i m a t i o n insects  ml  o f pH  were 7.0,  at 5° C t o t h i s  placed i n t h e i r pH  4.5  or pH  3.0  artificial  respective saline  test  (chemical  composition as above), w i t h a 5 x 7 p i e c e o f p l a s t i c s c r e e n i n g i n each  beaker.  subsequent from  the  On  day  up  beakers  purchased  the  from  day  of  t o and and  Dupont  transfer  including  placed as  22  in 5  NaCl  (Day  Day ml  6,  0),  insects  of  and  on  were removed  radiolabelled  i n water)  saline  ( Na 22  (0.68 /iCi/ml)  i d e n t i c a l i n chemical composition and pH t o the s a l i n e from they  had  removed cold  been from  (5° C)  removed. the  pH  radioactive  saline,  Packard Minaxi adjustments  After  weighed,  3  hours  solution, and  assayed  at  5° C,  rinsed  each  which  corixids  five  were  times  with  for radioactivity  in a  (Auto-Gamma RIA 5000 S e r i e s ) gamma counter. Again, and  mortality  counts  were  made  daily  for  each  experiment. By the  knowing the amount  of  specific  radioactivity  activity i n the  of the  external  whole-body  of  medium  each  and  insect,  13 i n f l u x c o u l d be c a l c u l a t e d u s i n g t h e e q u a t i o n : M = l/s x  x dQ/dt  0  where M i s t h e i n f l u x o f Na (nmoles/mg wet weight»hr); S i s t h e x  0  specific  activity  minute^umole corixid (Havas the  of  Na); Q  the  external  i s t h e amount  solution  (counts  of r a d i o a c t i v i t y  per  i n each  (counts p e r minute/mg wet weight); and t i s t h e time (hr) & Likens,  1985).  Preliminary  departure from l i n e a r i t y  experiments  determined  that  (time v s . i n f l u x ) i n t h e f i r s t t h r e e  hours o f uptake was minimal. Originally, had  e f f l u x measurements were attempted on i n s e c t s t h a t  been used  i n the i n f l u x  experiments  i n f l u x v a l u e s had been determined, ml o f c o l d  described  After  i n s e c t s were t r a n s f e r r e d t o 5  (unlabelled) s a l i n e and h e l d a t 5° C f o r a week. Then,  h o u r l y measurements o f the amount o f r a d i o a c t i v i t y were r e c o r d e d . However, m o r t a l i t y the  above.  efflux  considered  experiments valid.  The  and  was extremely h i g h throughout  results  efflux  i n t h e medium  could  experiments  therefore were  not be  subsequently  discontinued.  Statistical  Analyses  Preliminary differences  statistical between  tests  data  from  showed  collected  a l l days  on  the  data  statistical  a n a l y s e s . When t h r e e or more c a t e g o r i e s  (pH, s p e c i e s ,  analysis  of variance  Tukey's  Test  or  was  t o determine  season) performed.  pooled  were This  between which  for  compared, was  significant  various  Therefore,  variable  were  few  days.  subsequent of any one a  one-way  followed  pH l e v e l s ,  by a  s p e c i e s , or  14 seasons  significant  sodium  concentrations  differences and  in  sodium  1984). When only two c a t e g o r i e s  haemolymph  influxes  and  had  whole-body  occurred  (Zar,  of any one v a r i a b l e were compared  ( u s u a l l y due to h i g h m o r t a l i t y i n pH 3 . 0 ) ,  an independent  Student  T - t e s t was used. In a l l c a s e s ,  means were c o n s i d e r e d s i g n i f i c a n t l y  different  p<.05. Symbols on a l l graphs represent mean v a l u e s , these  symbols  indicate  +  one  standard  error  Sample  *  significantly different  +  significantly  #  significantly different  sizes  varied  from  to  10  from  found  in  the  figure  legends.  mean.  following:  blaisdelli  C.  from s p r i n g . insects  u s u a l l y e i t h e r 5 or 10 i n s e c t s were used. be  the  from pH 7.0  different  2  while bars on of  C h a r a c t e r s b e s i d e these symbols s i g n i f y one of the  if  per  mean  value;  Exact sample s i z e s can  Means,  standard  deviations,  standard e r r o r s , and numbers sampled f o r each experiment can a l s o be  found  (influx) .  in  Appendices  A  (haemolymph),  B  (whole-body),  and C  15  RESULTS  Sodium B a l a n c e : N a t u r a l Waters A  comparison o f c o r i x i d  waters  and  variation  of  species  i n haemolymph  r a t e s both between In  general,  influx  with  from  different  as  highest  [Na],  sodium  (Table  [Na]  2).  bodies  reveals  [Na], and sodium  whole-body  concentration  sodium  expleta,  influx  [Na],  and  sodium  i n the n a t u r a l  waters  which came from the water  concentration  e x h i b i t e d t h e h i g h e s t haemolymph whole-body  water  natural  s p e c i e s and between seasons.  (Figures 2-4a) . C.  the  taken from the same  [Na], whole-body  haemolymph  increased  increased  species  [Na]  (230  mM;  (188.4 mM)  Table  1),  and the h i g h e s t  (0.42/umoles/mg dry weight) o f any s p e c i e s t e s t e d  These  values  higher, r e s p e c t i v e l y ,  were  27%  (p<.005)  and  320%  (p<.05)  than v a l u e s found f o r C. blaisdelli  within  the same season ( f a l l ) . Figures  2-4  (a) a l s o  show t h a t  water sodium c o n c e n t r a t i o n display  marked  exhibited summer. On  their  [Na], and  at the lowest  cover an e x t e n s i v e range, C.  variation.  For  example,  highest  haemolymph  and  whole-body  hand,  same pond as C. blaisdelli,  body  recorded  seasonal  the other  fi. atopodonta  (6 mM)  values  H.  atopodonta,  which  than C. blaisdelli  were s i g n i f i c a n t l y lower i n the s p r i n g  i n the  came from the  reached t h e i r peak i n the  influx  blaisdelli [Na]  a l s o had lower v a l u e s o f haemolymph sodium  and  fall. [Na], whole-  overall.  These  (WB[Na]: 60% lower, p<.05;  INFLUX: 48% lower, p<.005) and i n the summer  (WB[Na]: 53% lower,  Table 2 Haemolymph [Na], whole-body [Na], and sodium influx rates of five species of corixids in their natural waters.  Season  Spring  Summer  Fall  Species  pHof natural water  Haemolymph [Na] (mM)  Whole-body Sodium [Na] Influx (umoles/mg dry (nmoles/mg wet weight) weight • hr.)  Sigaraomani  4.5  171.1 ±10.4 (5)  0.39±0.04 (5)  0.55±0.02* (5)  Hesperocorixa atopodonta  7.0  126.1 ±19.4 (2)  0.10 ± 0 . 0 2 * (2)  0.22 ± 0 . 0 1 * (5)  Cenocorixa blaisdelli  7.0  123.4 ±16.0 (5)  0.25 ±0.03 (5)  0.42 ±0.05 (5)  Hespercorixa atopodonta  7.0  157.6 ±7.0 (5)  0.19 ± 0 . 0 2 * (5)  0.10 ±0.02 (5)  Cenocorixa blaisdelli  7.0  173.2 ±3.4 (5)  0.40 ±0.04 (5)  Hesperocorixa atopodonta  7.0  162.3 ±4.0 (2)  0.22 ±0.00 (2)  0.24 ±0.02 (5)  Cenocorixa blaisdelli  7.0  148.0 ±11.3 (3)  0.10 ± 0.03 (2)  0.51 ± 0.08 (5)  Cenocorixa bifida  9.0  147.3 ±4.5 (5)  0.34 ±0.07 (5)  Cenocorixa expleta  9.5  188.4 ± 1 . 7 * (5)  0.42 ± 0 . 0 2 * (5)  * = significantly different from C. blaisdelli within the same season (p< .05) Numbers in parentheses indicate sample size  0.49 ±0.10 (5)  17  Figure  2  Haemolymph [Na] o f f i v e s p e c i e s o f c o r i x i d s i n three seasons plotted against (a) sodium c o n c e n t r a t i o n o f t h e i r n a t u r a l waters and (b) pH of their natural waters. + = significantly d i f f e r e n t from C . b l a i s d e l l i w i t h i n the same season (p<.05). n = 5, except where noted i n Table 2. | = C . b l a i s d e l l i - spring ± = H.atopodonta - s p r i n g 9 = S.omani - s p r i n g 0 = C . b l a i s d e l l i - summer £ = H.atopodonta - summer • = C.blaisdelli - fall A = H.atopodonta - f a l l O = C.bifida - f a l l V = C.expleta - f a l l  18  a 190-r  180 +  140 +  130-H  120+1  50  100 150 200 [Na] of Natural Waters (mM)  250  b 190 +  180 +  170+  i  160+  4  140 +  130+  120 +  2  H 4  h 6  pH of Natural Waters  6  10  19  Figure  3  Whole-body [Na] o f f i v e s p e c i e s o f c o r i x i d s i n three seasons plotted against (a) sodium c o n c e n t r a t i o n o f t h e i r n a t u r a l waters and (b) pH of their natural waters. + = significantly d i f f e r e n t from C . b l a i s d e l l i w i t h i n t h e same season (p<.05). n = 5, except where noted i n Table 2. • = C . b l a i s d e l l i - spring • = H.atopodonta - s p r i n g # = S.omani - s p r i n g 0 = C . b l a i s d e l l i - summer A. = H.atopodonta - summer • = C.blaisdelli - fall A = H.atopodonta - f a l l 0 = C.bifida - f a l l V = C.expleta - f a l l  20  0.40  ft  0.35 +  0.30+  §  3  0.254*  0.20+,  0.15-  0.10-  0.05 +  50  100  150  200  250  [Na] of Natural Waters (mM)  0.40 +  0.35 +  ? D  0.30 +  |  0.25 +  0.20+  0.15 +  0.10 +  0.05 +  10 pH of Natural Waters  21  Figure 4  Sodium i n f l u x r a t e s o f f o u r s p e c i e s o f c o r i x i d s i n three seasons plotted against (a) sodium c o n c e n t r a t i o n o f t h e i r n a t u r a l waters and (b) pH of their natural waters. + = significantly d i f f e r e n t from C . b l a i s d e l l i w i t h i n the same season (p<.05). n = 5. Note: data not a v a i l a b l e f o r C . b l a i s d e l l i (summer) or f o r C . b i f i d a ( f a l l ) . c . b l a i s d e l l i - spring H .atopodonta - s p r i n g S .omani - s p r i n g H .atopodonta - summer C.blaisdelli - fall H .atopodonta - f a l l V = C.expleta - f a l l  22  a O.6O-1-  0.50  0.40-  0.304  I-  0.204  0.10-k  50  100  1 50  200  250  [Na] of Natural Waters (mM)  b o.60-r  0.504  0.404  0.304  0.204  0.104  4  6  p H of Natural Waters  8  10  23 p<.005).  In c o n t r a s t  S.  to this,  omani,  d i f f e r e n t water body than C. blaisdelli in  which  t h e sodium  extremely influx those  high  rates.  The i n f l u x  o f C. blaisdelli  p<.05).  These  high  was  t h e same  [Na], whole-body rates  were  from  may be r e l a t e d  a  but one  (6 mM) , had  [Na], and  significantly  i n t h e same season values  came  and H. atopodonta  concentration  haemolymph  which  sodium  higher  than  (SPRING: 31% higher, to the fact  that  5.  omani was c o l l e c t e d from waters with t h e lowest pH (4.5). When pH  o f t h e water  haemolymph  i s considered,  [Na], whole-body  the highest  [Na], and sodium  influx  values o f occurred at  the extremes - pH 4.5 and pH 9.5 (Figures 2-4b). Values t h r e e parameters i n C. blaisdelli  f o r these pH  7.0  evident.  varied S.  greatly,  omani  but  again  and H. atopodonta  seasonal  e x h i b i t e d extremely  [Na],  [Na], and sodium  measurements were a l s o high,  high  influx.  values  Summer C.  blaisdelli  and these t h r e e h i g h sodium  relationship  o f i n c r e a s i n g haemolymph  body  [Na] w i t h  i n c r e a s i n g pH. C o n s i d e r i n g only t h e t h r e e  data  points  influx  at pH  o f haemolymph  show a l i n e a r  f o r sodium  produces t h e opposite  records  and wholehighest  a t pH 9.5. F a l l  C. blaisdelli  S.  trend;  omani had t h e h i g h e s t i n f l u x r a t e a t pH 4.5, while C. expleta the lowest  at  d i f f e r e n c e s are  a t pH 4.5 i n t h e s p r i n g and C. expleta  9.5 i n t h e f a l l , whole-body  recorded  had  r a t e s l i e i n between.  S u r v i v o r s h i p : Season Mortality while  H.  varied  atopodonta  survivorship.  greatly  between  e x h i b i t e d only  However,  f o r both  seasons small  species  blaisdelli,  i n C.  seasonal  variation i n  mortality  was  always  24 lowest i n t h e f a l l . During  the haemolymph/whole-body  showed the h i g h e s t (34%,  (7.0),  5a).  m o r t a l i t y was h i g h e s t  only 30%. A t a l l pH l e v e l s , the best fall,  blaisdelli  m o r t a l i t y i n the summer i n both t e s t pH l e v e l s  pH 4.5; 100%, pH 3.0; F i g u r e  water pH  C.  experiments,  In the c o n t r o l or n a t u r a l i n the s p r i n g , but reached  s u r v i v o r s h i p occurred  i n the  w i t h 30% m o r t a l i t y i n pH 3.0, and no m o r t a l i t y i n e i t h e r pH  4.5 or pH 7.0. While blaisdelli 54%)  conducting  the  was highest  was lowest i n the f a l l ; atopodonta  (4.5, 49%; F i g u r e  mortality  5 c ) . Again,  almost  experiments  no  mortality  i n the i n f l u x  mortality  still  mortality  occurred  23%,  pH  mortality  i n any  season.  during Only  s p r i n g , and only i n pH 3.0, d i d a 5% m o r t a l i t y occur Results  f o r C.  no animals d i e d i n e i t h e r pH.  exhibited  haemolymph/whole-body  experiments,  i n the s p r i n g i n both the c o n t r o l pH (7.0,  and i n t h e t e s t pH  H.  influx  experiments  were  more  (Figure 5b).  remained under 35% i n every season. The  4.5), w h i l e  no m o r t a l i t y  occurred  i n the  variable,  i n the summer i n both pH l e v e l s  the  but  highest  (34%, pH 7.0;  i n the f a l l  (Figure  5d) . Mortality  discussed  data  f o r 5.  i n the following  omani,  C.  bifida,  section,  since  was only t e s t e d i n one season and  and  C.  expleta  each o f these  (SPRING: S. omani;  FALL: C.  C. e x p l e t a ) .  Survivorship: Survivorship  Species v a r i e d between s p e c i e s  i n a l l seasons.  are  species bifida  25  Figure 5  Seasonal v a r i a t i o n i n cumulative percent m o r t a l i t y d u r i n g the haemolymph/whole-body experiments f o r (a) C . b l a i s d e l l i and (b) H.atopodonta, and d u r i n g the i n f l u x experiments f o r (c) C . b l a i s d e l l i and (d) H.atopodonta. • = C . b l a i s d e l l i - PH 7 .0 c . b l a i s d e l l i - pH 4 .5 A = c . b l a i s d e l l i " PH 3 .0 • = H .atopodonta " PH 7 .0 O = H .atopodonta " PH 4 .5 A = H .atopodonta - pH 3 .0  •=  Day 8 Cumulative % Mortality (H/WB)  Day 8 Cumulative % Mortality (H/WB)  Ch  27 C. blaisdelli  u s u a l l y e x h i b i t e d the and fl. atopodonta  one season,  Of the t h r e e consistently  higher  mortality  exhibited  f r e q u e n t l y e x h i b i t e d the  s p e c i e s t e s t e d i n the mortality  at  and the  influx  haemolymph/whole-body had  h i g h e s t m o r t a l i t y w i t h i n any  values  ranging  mortalities  pH  levels  experiments.  from  from  C. blaisdelli  spring,  all  5-23%, C.  0-18%,  C. blaisdelli  summer,  fl.  atopodonta  i n the  fl.  atopodonta  exhibited  at  (Figure 6b) . During the  summer i n f l u x  atopodonta  had  mortality  reversal  i n the  in  pH  3.0  higher  Figure  mortality  displayed  by  7b) .  t r e n d of  day  5  of  was  these  two  i n C.  the  8-day  experiments, C.  than  This  than  Although  any pH, m o r t a l i t y  experiment  14-15%;  omani  atopodonta  fl.  experiments.  reached  (23-34% versus  the  had a much h i g h e r m o r t a l i t y  no m o r t a l i t y  slightly  both  6a and 7a) .  blaisdelli  a  had a  While 5.  blaisdelli  haemolymph/whole-body  100%  in  and  m o r t a l i t y v a l u e s r a n g i n g from 10-54% (Figures In the  lowest.  the  fl.  blaisdelli  only  species  time  a  occurred,  though. Four s p e c i e s were t e s t e d i n the  C. expleta  fall.  h i g h e s t m o r t a l i t y d u r i n g the haemolymph/whole-body all  pH l e v e l s  (20-32%;  Figure  m o r t a l i t y by day 2 o f the 7c). sets  experiments  mortality,  while  Although (3.0)  the  C. blaisdelli  mortality  was  C.  and fl. atopodonta  in  the haemolymph/whole-body  but  the  experiments  at  bifida  had  6-day sodium i n f l u x experiment  Values f o r C. blaisdelli of  6c) ,  exhibited  fall;  fl.  100%  (Figure  were low f o r both  atopodonta  showed  no  and only  in  lowest  pH  mortality  for  only d i e d at pH 3.0,  experiment  a  (27% m o r t a l i t y ) .  generally  d u r i n g the haemolymph/whole-body  highest  in  experiments,  the  28  Cumulative percent mortality during the haemolymph/whole-body experiments f o r f i v e s p e c i e s of c o r i x i d s at t h r e e pH l e v e l s i n (a) s p r i n g , (b) summer and (c) f a l l . • = C . b l a i s d e l l i - spring A = H.atopodonta - s p r i n g • = S.omani - s p r i n g E3 = C . b l a i s d e l l i - summer A = H.atopodonta - summer • = C.blaisdelli - fall A = H.atopodonta - f a l l O = C.bifida - f a l l V = C.expleta - f a l l  Day 8 Cumulative % Mortality (H/WB)  Day 8 Cumulative % Mortality (H/WB)  Day 8 Cumulative % Mortality (H/WB)  VO  30  Figure  7  Cumulative percent m o r t a l i t y d u r i n g the i n f l u x experiments f o r f i v e s p e c i e s o f c o r i x i d s at two pH l e v e l s i n (a) s p r i n g , (b) summer and (c) f a l l . • = C . b l a i s d e l l i - spring • = H.atopodonta - s p r i n g • = S.omani - s p r i n g E3 = C . b l a i s d e l l i - summer A = H.atopodonta - summer • = C.blaisdelli - fall A = H.atopodonta - f a l l O = C.bifida - f a l l V = C.expleta - f a l l  32 four  out  of  exception) influx  the  five  was always  species  tested  lower i n pH 4.5  bifida  (C.  being  than i n pH 7.0  the  d u r i n g the  experiments.  H+ T o x i c i t y : Season Haemolymph  [Na],  whole-body  [Na],  and  sodium  v a r i a t i o n w i t h season i n both C. blaisdelli general,  the  highest  o c c u r r e d i n the fall  C.  for  values  summer,  blaisdelli  of  while and  in  Sodium i n f l u x showed a l e s s d e f i n i t e C. blaisdelli,  In [Na]  were  levels with  significantly  (H[Na]:  the  Figure  8a) .  to  the  of  the  Additionally,  spring  than  spring  WB[Na]:  values  fall  (38% lower,  at  fact  that  mortality  haemolymph/whole-body  experiments  haemolymph  the  lowest).  i n the  Sodium i n f l u x lowest  i n the  in  fall  fall  C.  was  the  blaisdelli  were  (21% lower,  i n the [Na])  and pH 4.5  i n the  also so  at  relate  during  highest  was h i g h e s t  i n both pH 7.0  [Na]  T h i s may  (when haemolymph/whole-body  C. blaisdelli  (p>.05;  but only s i g n i f i c a n t l y  in  pH  p<.01),  [Na] was  (corresponding to the h i g h e s t haemolymph/whole-body lowest  all  pH 3.0  p<.001). Whole-body  at a l l pH l e v e l s ,  in  49% h i g h e r ,  [Na] of  whole-body  values  (18% lower than s p r i n g , p<.05; F i g u r e 8b).  the  atopodonta.  haemolymph and  haemolymph fall  H.  for  the  trend. of  p<.001;  [Na]  occurred i n  lower than s p r i n g v a l u e s i n both pH 4.5  and pH 3.0  lowest i n the pH 7.0  higher  22% h i g h e r ,  exception  significantly p<.001)  summer v a l u e s  In  and whole-body  lowest v a l u e s the  showed  and H. atopodonta.  haemolymph  the  influx  the  summer and was  values  were  s p r i n g and  (reliable  summer  33  Figure  8  Seasonal v a r i a t i o n i n (a) haemolymph [Na], (b) whole-body [Na] and (c) sodium i n f l u x r a t e s f o r C . b l a i s d e l l i at t h r e e pH l e v e l s . * = s i g n i f i c a n t l y d i f f e r e n t from pH 7.0 (p<.05); # = s i g n i f i c a n t l y d i f f e r e n t from s p r i n g (p<.05). n = 5 or 10 f o r (a) and (b) ; n = 5 f o r (c) , except where noted i n Appendices A, B, or C. • = pH 7.0 # = pH 4.5 A = PH 3.0  Spring  Summer  Fall  35 values  are  not  significant the  available).  i n pH 4.5  However,  (31% decrease,  this  lowest  to  sodium  mortality  the time influx  whole-body both t e s t the  higher (28%, values found  (4.5  9a) .  these  almost  no  [Na]  [Na] i n  higher  in  and 13% (p<.01),  i n the  (29%, p<.05)  summer  were  and i n pH 4.5  (p>.05; F i g u r e 9 b ) . The lowest [Na] i n H. atopodonta unlike  with  o c c u r r e d i n the f a l l .  C.  were blaisdelli,  R e c a l l that for  no m o r t a l i t y o c c u r r e d i n any season d u r i n g  experiments.  Sodium i n f l u x 7.0,  with  Haemolymph  by 10% (p<.05)  i n a l l cases,  whose lowest c o n c e n t r a t i o n s H. atopodonta,  season  the  summer haemolymph and  Whole-body  but not i n pH 3.0  spring  while  were s i g n i f i c a n t l y  o f haemolymph and whole-body i n the  experiment)  influx,  the  the h i g h e s t .  and 3.0)  i n the s p r i n g ,  (Figure  only  experiment).  than i n the s p r i n g i n pH 7.0 p<.05),  in  (as i n C. blaisdelli),  pH l e v e l s  respectively  sodium  occurred  [Na] were g e n e r a l l y  summer than  (spring-influx  highest  values  (fall-influx  In H. atopodonta  of  was  p=.005; F i g u r e 8 c ) . Again,  season w i t h the h i g h e s t m o r t a l i t y  corresponded  decrease  i n H. atopodonta  was lowest i n the summer i n pH  but lowest i n the s p r i n g i n pH 4.5  highest  i n both  occurred influx  pH l e v e l s  i n the summer  values  seen  i n the  fall.  (Figure 9 c ) . Values were The h i g h e s t  mortality  (which may correspond t o the low sodium  in this  season)  and l i t t l e  o c c u r r e d i n t h e s p r i n g and i n the f a l l .  or no m o r t a l i t y  36  Figure  9  Seasonal v a r i a t i o n i n (a) haemolymph [Na], (b) whole-body [Na] and (c) sodium i n f l u x r a t e s f o r H.atopodonta at t h r e e pH l e v e l s . * = s i g n i f i c a n t l y d i f f e r e n t from pH 7.0 (p<.05); # = s i g n i f i c a n t l y d i f f e r e n t from s p r i n g (p<.05). n = 5 or 10 f o r (a) and (b) ; n = 5 f o r (c) , except where noted i n Appendices A, B, or C. • = pH 7.0 O = PH 4.5 A = pH 3.0  38 H+ T o x i c i t y : Of the  Species  five  s p e c i e s t e s t e d across  three  seasons,  a l l except C.  blaisdelli  were able to m a i n t a i n a remarkably constant  [Na]  decreasing  with  pH. Whole-body C. bifida  most s p e c i e s ; however, that  live  decrease  normally  i n whole-body  i n f l u x was constant In  the  10a) . low  [Na]  This and  mortality  measured [Na]  to  and  a  S p r i n g whole-body a l l pH l e v e l s  [Na]  were  blaisdelli,  approximately and  S.  omani  fall.  lower  constant  omani  having  at pH 3.0  the  spring  (Figure  for  examined;  for  relatively  spring  (10-54%),  [Na]  at  low pH,  haemolymph  [Na]  haemolymph  levels  (22%-28%  haemolymph  [Na]  than  lower,  were  constant  H.  p=.01).  and sodium i n f l u x species t e s t e d . same  (Figure  example,  H.  the  11a).  rates  In a d d i t i o n ,  for  H.  whole-body  atopodonta,  However,  H.  sodium  influx  values  C.  atopodonta  e x h i b i t e d a much lower sodium i n f l u x i n the s p r i n g than the species  a  relatively  had a lower pH  a  Sodium  a  the  lowered  species  exhibited  with  haemolymph  three  the  S.  i n the  for  seasons.  (5-23%). However,  overall  (12% lower,  for a l l  in  C. blaisdelli all  [Na]  well  seen  two  maintain  (9%, p<.005)  reduced  significantly  at pH 7.0  the  lakes,  only  C. blaisdelli  the  in  to  with  rates  with  species.  omani  S.  atopodonta  in  for  explain  in this  than  p<.001),  rate  correlating  help  able  corresponds  (0-18%) and S. omani  not  might  were  result  constant  lowered pH i n the  pH decreased,  general  higher m o r t a l i t y while  saline  i n haemolymph [Na]  stable  atopodonta  with  species  as  increase  also  and C. expleta,  alkaline, [Na]  was  for a l l species tested i n a l l  spring,  haemolymph slight  in  [Na]  haemolymph  other  were  7 9%  39  Figure  10  Haemolymph [Na] o f f i v e s p e c i e s o f c o r i x i d s at t h r e e pH l e v e l s i n (a) s p r i n g , (b) summer and (c) fall. * = s i g n i f i c a n t l y d i f f e r e n t from pH 7.0 (p<.05); + = significantly different from C.blaisdelli (p<.05). n = 5 or 10 except where noted i n Appendix A. • = C. b l a i s d e l l i - spring • = H . atopodonta - s p r i n g • = S .omani - s p r i n g 0 = C . b l a i s d e l l i - summer £ = H .atopodonta - summer • = C.blaisdelli - f a l l A = H .atopodonta - f a l l 0 = C.bifida - f a l l V = C.expleta - f a l l  'Haemolymph [Na] (mM)  Haemolymph |Na) (mM)  "Haemolymph [Nal (mM)  41  Figure  11  Whole-body [Na] o f f i v e s p e c i e s o f c o r i x i d s a t t h r e e pH l e v e l s i n (a) s p r i n g , (b) summer and (c) fall. * = significantly different from pH 7.0 (p<.05); + = significantly different from C.blaisdelli (p<.05). n = 5 or 10 except where noted i n Appendix B. • = C . b l a i s d e l l i - spring A = H.atopodonta - s p r i n g 9 = S.omani - s p r i n g E3 = C . b l a i s d e l l i - summer A = H.atopodonta - summer • = C.blaisdelli - fall A = H.atopodonta - f a l l O = C.bifida - f a l l V = C.expleta - f a l l  Whole-Body [Nal (umoles/mgDW)  X  ui  Whole-Body [Na] (umoles/mgDW)  Whole-Body [Na] (umotes/rngDW)  43 lower  H.  in  atopodonta  than  C.  in  blaisdelli  (p<.001;  Figure  12a) . While H. atopodonta [Na]  in  the  decrease at  pH  was a b l e t o m a i n t a i n a constant  summer,  i n haemolymph 4.5  haemolymph (p<.001;  were [Na]  Figure  lowered  9% at  [Na]  pH  3.0  were  blaisdelli  at a l l pH l e v e l s be  noted  blaisdelli, no  that  100% in  only  in the  the  showed  fall,  a  [Na]  p<.001)  slightly  to  i n pH 4.5  f o r C.  summer was  significant  Reliable  an o v e r a l l  the  fall;  lower  haemolymph  v a l u e s measured at pH 4.5  those at pH 3.0 C. bifida  were 45% lower  and C. expleta as  pH was  only  by  It C.  atopodonta influx  summer,  than  C.  so a  blaisdelli  exhibiting  p<.001)  a  lower  and i n pH 3.0  C. bifida but  (38%  d i d have a  this  was  only  C. blaisdelli  all  other  were 30% lower  also  species  (p,.001),  in and  (p<.005).  both experienced  lowered.  a  season.  p<.05).  [Na]  for  sodium  i n the  i n pH 3.0,  (9% i n c r e a s e ,  high  H.  while  tested, pH  with  p<.01; F i g u r e l i b ) .  (Figure 10c). [Na]  control  measured  those  3.0,  (19% lower,  the  for H.  atopodonta  decreased  than  (p<.005);  measured  the  species  than i n pH 7.0  had  [Na]  the  e l e v a t e d haemolymph  marginally  body  all  response  haemolymph lower,  of  7.0  values  summer.  f o r H.  pH  [Na]  constant  than  pH  significant  remained  s p e c i e s comparison cannot be made i n t h i s In  at  (36-46% lower, in  a  pH. Haemolymph  lower  [Na]  lower  mortality  mortality  v a l u e s are a v a i l a b l e  16%  However,  significantly  reaching  exhibited  values  were  species.  atopodonta  should  than  Whole-body  both  exhibited  with decreasing  lower  10b).  pH f o r  blaisdelli  C.  haemolymph  F o r C. bifida,  a decrease i n this  whole-  decrease  was  44  F i g u r e 12  Sodium i n f l u x r a t e s of four s p e c i e s o f c o r i x i d s at two pH l e v e l s i n (a) s p r i n g and (b) f a l l . + = s i g n i f i c a n t l y d i f f e r e n t from C . b l a i s d e l l i (p<.05). n = 5 except where noted i n Appendix C. Note: data not a v a i l a b l e f o r summer or f o r C . b i f i d a ( f a l l ) . • = C . b l a i s d e l l i - spring • = H.atopodonta - s p r i n g # = S.omani - s p r i n g • = C.blaisdelli - fall A = H.atopodonta - f a l l V = C.expleta - f a l l  46 significant  only at pH 3.0  (32% lower,  For C.  p=.001).  expleta,  whole-body . [Na] was s i g n i f i c a n t l y lower than the c o n t r o l value at both pH 4.5 Figure body  (24% lower,  11c). [Na]  values  C. blaisdelli  with  decrease,  p<.001).  C. bifida  significantly atopodonta  exhibited  lower  in  low and f a i r l y highest  the  [Na]  and C. e x p l e t a  fall  stable  mortality  observed  were  in  whole-  pH 3.0  (31%  had  the  37%  lower  (p<.05),  concentrations  but  lowest than  were  not  for  H.  experiments  was  obtained  decrease  haemolymph/whole-body  overall, in  increase  from  C. expleta  for a l l species t e s t e d . which  whole-body  remained below 32%. C. blaisdelli  went  at  p<.005;  (p>.05).  Mortality  drastic  only  consistently  Whole-body  than  (28% lower,  a decrease  pH, s i g n i f i c a n t  blaisdelli  C.  overall.  found i n  and at pH 3.0  also  decreasing  measured  those  p=.01)  might [Na],  be  but  a  result  the  had the of  the  mortality  was the only s p e c i e s t o  rate  show a  i n m o r t a l i t y r a t e w i t h d e c r e a s i n g pH; m o r t a l i t y  0% i n  pH 7.0  and  pH 4.5  to  27%  in  pH 3 . 0 .  This  corresponds w e l l w i t h the drop i n both haemolymph and whole-body [Na]  experienced  C. blaisdelli  by  i n the  fall  at  both  levels,  and may a l s o e x p l a i n the o v e r a l l lower v a l u e s  blaisdelli  compared w i t h other s p e c i e s t e s t e d i n t h i s  Sodium 4.5 but,  influx  than at pH 7.0 as  in  i n f l u x value species rate  values  the  experienced  not  f o r any of the  spring,  (62% lower,  examined  were  H.  C.  found i n C. season.  different  at pH  s p e c i e s measured i n the  atopodonta  had  a  decreased  fall, sodium  p<.001) when compared w i t h the other two  (Figure 12b). by  significantly  t e s t pH  expleta  S u r p r i s i n g l y , the in  these  high m o r t a l i t y  experiments  is  not  reflected bifida  in  mortality  in  the  the  influx  fall  are  (100% i n pH 3.0)  rates not  themselves. available  d u r i n g t h i s set  Influx  owing  to  rates the  f o r C. complete  of experiments.  48  DISCUSSION  Sodium Balance: N a t u r a l Waters Although many s t u d i e s of  have  compared the  chemical  a h a b i t a t w i t h e c o l o g i c a l parameters such as  (Hall  et  al.,  1980;  Bendell,  and  Carrick,  1973),  (Sutcliffe  1986) few  or  have  composition  density/abundance species  attempted  diversity to  explain  s p e c i e s d i s t r i b u t i o n s by c o r r e l a t i n g chemical composition aquatic  environment  animals t h a t In  the  various  live  physiological  physiological  measurements  study,  pH and  habitats  in  characteristics  sodium  B . C . were of the  five  c o u l d be d i s c e r n e d . Most n o t a b l y ,  from the  water w i t h the  expleta)  had the h i g h e s t  highest  normally h i g h whole-body  concentrations  seen  in  waters  conditions. expleta,  C. below  (1988)  collected  This a  pH 9.0  report  that  [Na]  is  (Scudder, a  species  a  attribute  certain  found t h a t ,  and pH (C.  i n amphibians, a  c o r r e l a t e d w i t h a low  which  the  does  1969ab) . of  stream  mayfly,  high not  tolerance  concentrations usually  However,  Hall  inhabit et  Leptophlebia  this  [Na] than the  with  a  much  lower  to  a  permanent  [Na] or  Some  the s p e c i e s which came  and  and pH  same s p e c i e s pH.  long-term  The  al.  cupida,  from a stream w i t h a h i g h sodium c o n c e n t r a t i o n  a c t u a l l y had a lower whole-body from  compared  with  the  of haemolymph and whole-  may e x p l a i n  species  of  sodium c o n c e n t r a t i o n  body sodium. Freda and Dunson (1984)  acidic  the  concentrations  s p e c i e s examined.  patterns  to  of  the  there.  present corixid  with  of  taken  authors  environmental  49 influence since  on  adult  breeding larval  cation corixids  (Jansson stages  tolerances Also  accumulation often  not  the  disperse  and Scudder,  are  in  as  to  play  in  the  present  summer f o r C. blaisdelli  study  was  (1988a)  also  found  that  Na o c c u r r e d i n the  femoratum,  under  of  high  (Jansson elevate other  a  and  that  i n the role  or  egg  in  or  adult  control  activity Scudder,  the  summer f o r  and,  the  Feeding  most  Rowe  concentrations  summer i s  extensive certainly  [Na] i n the b l o o d and body above those v a l u e s  of  Stenonema  mayfly,  For c o r i x i d s ,  consequently,  1974).  natural  s p r i n g or f a l l .  highest  conditions.  under  [Na] were h i g h e r i n the  than i n e i t h e r the  whole-body  time  But,  t o h i g h or low pH waters.  noted  al.  nymphs.  overwintering  adaptations  c o n d i t i o n s haemolymph [Na] and whole-body  et  or  before  1974),  likely  eggs  a  feeding  serves  to  recorded i n  seasons.  S u r v i v o r s h i p : Species/Season All low  corixids pH  the  to  (Vangenechten  Vanderborght, that  tested  1980;  five  date  al.,  et  Scudder,  been  It  is  examined  of i n c r e a s e d  extremely  197 9ab;  1987).  c o r i x i d species  remarkably t o l e r a n t  have  tolerant  Vangenechten  not  and  surprising,  in this  study  then,  were  study  increased  from pH 7.0  to pH 3.0  (at l e a s t i n the haemolymph/whole-body experiments),  remained  below  throughout in  the  mortality  in  both  year.  However,  were  apparent.  also  acidity.  Although m o r t a l i t y i n the present  50%  of  neutral specific In  and  acidic  and seasonal  particular,  C.  pH  it  levels  differences blaisdelli  50 experienced either  the  greater  mortality  than  any  s p r i n g or summer. As w e l l ,  other  this  species  same s p e c i e s  much g r e a t e r m o r t a l i t y i n the summer (100% i n pH 3.0) spring  or  fall  during  Cooper  et  al.  (1987)  blaisdelli fall.  i n the  also  found  increased  (1988a)  report  summer as  Stenonema  m o r t a l i t y f o r the mayfly,  suffered  experiments. in  C.  only 5% i n  the  mortality  versus the  femoratum,  in  than i n the  haemolymph/whole-body  summer - 50% (at pH 7.0)  al.  Rowe et  the  tested  time  of  highest  i n both pH 6.5 and  3.5. High  summer m o r t a l i t y ,  atopodonta,  supports the  different the peak  result  either  the  able  to  readily  Introduction). the present instead  have  been  s p r i n g or deal  the  with  due  to  the  condition.  In  fall,  water  much  is  experimental . temperature  C. blaisdelli al.  (1988a)  that  fall  in  when  the  was the  found  mortality for t h e i r test  fall  (Cooper et  closer  time  in  of  in  summer, al.,  its less (see  in  both  1987), may  were  collected  be  particular,  temperature related,  the  to  then,  lowest m o r t a l i t y  Cooper et al.  species.  are  change  insects  and,  Possibly  to  reach  and then a c c l i m a t e d to the 5°C  spring  used.  to  However,  corixids  i n the  that  not  seasons.  environmental  fact  and H. atopodonta. also  survivorship differs  increased mortality  experimental  observation  H.  for mortality  study and an e a r l i e r one been  in  fall,  from pond water t h a t was 20°C-25°C,  pond  that  but  and i n d i f f e r e n t  would have  Thus,  C . blaisdelli  in  hypothesis  s p e c i e s of c o r i x i d s  expected in  seen  the the  is  the  for  both  (1987) and Rowe et  season  with  the  least  51 One  other  possibility  noted by Rowe e t al. whole-body exhibit [Na]  to explain  summer  mortality,  as  (1988a), i s t h a t t h i s i s t h e time o f highest  [Na]. Indeed,  their  high  highest  C.  blaisdelli  and H.  l e v e l s o f haemolymph  i n t h e summer.  Because  summer, t h e whole-body  these  levels  [Na] (haemolymph  atopodonta  did  [Na] and whole-body are so high  i n the  [Na]) l o s s e s which occur  when animals are exposed t o low pH are g r e a t e r ,  relatively,  than  at other times o f t h e year. I t i s t h i s g r e a t e r r e l a t i v e l o s s t h a t is  associated  1988a),  with  and which may a l s o  seen i n t h e c o r i x i d ,  i n S.  mortality  explain  C. blaisdelli,  femoratum  (Rowe  the higher  summer  et  al.,  mortality  s t u d i e d here.  H+ T o x i c i t y : Season/Species A  further  i n d i c a t i o n that  i n t h e present pH  was  [Na],  ability  and sodium  those  t o maintain  influx  Differences  recorded  significant. physiological differences  corixid  species  examined  study were extremely t o l e r a n t o f exposure t o low  their  decreased.  a l l five  at  rates  between  either  However,  pH  season  parameters  haemolymph  within  tight  values  recorded  4.5  or  did affect  measured,  i n o v e r a l l values  [Na], whole-body  pH  boundaries  3.0  levels  and t h e r e  between  at pH  species  were of  were  as pH 7.0 and rarely  a l l three significant  within  any one  season. Both levels all  C.  blaisdelli  o f haemolymph  three  and H.  atopodonta  exhibited  [Na] and whole-body  their  [Na] i n t h e summer at  pH l e v e l s t e s t e d . As mentioned p r e v i o u s l y ,  time o f profuse  feeding  f o r these s p e c i e s ,  highest  summer i s a  and d i e t i s known t o  52 be  an  extremely  insects 1989).  important  (Frisbie  source  and Dunson,  U n l i k e haemolymph  o f sodium  1988abc;  f o r many  Sutcliffe  [Na] and whole-body  aquatic  and Hildrew,  [Na], sodium  influx  d i d not appear t o be a f f e c t e d by season. No other seasonal study of sodium i n f l u x i n i n s e c t s has been r e p o r t e d t o date. Although,  i n general,  a l lcorixids  tested  were  tolerant  of  exposure t o low pH, s p e c i e s d i f f e r e n c e s d i d occur. I t i s apparent that  the c o r i x i d s  examined d i f f e r  i n i o n i c balance under  c o n d i t i o n s . Table 3 summarizes t h e changes, data  f o r t h e t h r e e parameters  measured  versus  pH 3.0  (haemolymph/whole-body  versus  pH 4.5  (influx  when p o s s i b l e Scudder  (1987)  species  differences  or l a c k t h e r e o f , when  are compared  experiments)  experiments). E f f l u x  from the p a t t e r n s seen and Vangenechten in  the  e t al.  at pH 7.0  or a t pH 7.0  trends  are i n f e r r e d  i n t h e measured  sodium  acidic  (1979ab)  regulating  variables.  also  report  abilities  of  corixids. Overall,  H.  atopodonta  internal milieu whole-body  seem  (Table 3) . In every  [Na] remained  ability  tested.  In c o n t r a s t ,  C. blaisdelli,  atopodonta,  exhibited  H.  haemolymph summer  atopodonta.  maintain  were  to  balance  haemolymph  much  under  their  [Na] and  indicating a  all  conditions  o b t a i n e d from t h e same pond significant  decreases  in  both  [Na] from pH 7.0 t o pH 3.0 i n the  Additionally, overall  season,  homeostasis  [Na] and whole-body  and f a l l .  blaisdelli  to  able  constant as pH decreased,  strong  as  best  f o r C.  c o n c e n t r a t i o n s recorded  lower  than  those  recorded  f o r H.  T h i s v a r i a t i o n i n t o l e r a n c e t o a c i d i c c o n d i t i o n s may  be due t o t h e s i z e d i f f e r e n c e i n these two s p e c i e s . H.  atopodonta  53  Table 3  Qualitative summary of changes in haemolymph [Na], whole-body [Na], and sodium influx rates of five species of corixids upon exposure to low pH.  Season  Species  Spring  Sigara omani  Increased  Hesperocorixa atopodonta  Summer  Fall  Sodium Influx (pH 7.0 vs. pH 4.5)  Sodium Efflux (Inferred)  No change  No change  Decreased  No change  No change  No change  No change  Cenocorixa blaisdelli  No change  No change  No change  No change  Hespercorixa atopodonta  No change  No change  Increased  Increased  Cenocorixa blaisdelli  Decreased  No change  Hesperocorixa atopodonta  No change  No change  No change  No change  Cenocorixa blaisdelli  Decreased  Decreased  No change  Increased  Cenocorixa bifida  Increased  Decreased  Cenocorixa expleta  No change  Decreased  Haemolymph Whole-body [Na] [Na] (pH 7.0 vs (pH 7.0 vs. pH 3.0) pH 3.0)  For actual values, see graphs in Results section or Appendices A.B, and C.  —  —  No change  —  —  No change or Increased  54 is  approximately twice  weights: have  a  the  45 mg and 20 mg, greater  surface  passive  l o s s e s of  animals  than  larger  to  H  +  C. blaisdelli  of  respectively).  to  volume  sodium at  in  susceptibility  size  ratio  (average  Since  smaller  than  larger  low pH should be g r e a t e r  ones  (Rowe,  toxicity  is  1986).  reflected  d i s t r i b u t i o n p a t t e r n s ; while H. atopodonta  The  often  occur  in  ponds  with  a  animals animals,  in smaller  difference  by  these  in  species'  can be found n a t u r a l l y  o c c u r r i n g i n waters of e i t h e r n e u t r a l or a c i d i c pH, C. most  wet  blaisdelli  c i r c u m n e u t r a l pH  (Scudder,  1987). C. bifida in  high  and C. expleta,  pH waters  which are  (Scudder,  1969ab),  whole-body  [Na] i n pH 4.5  al.  found t h a t whole-body  the  (1989)  mayflies  days  of  Stenonema  exposure  to  L e c h l e i t n e r et al. 3.0  versus  pH  Interestingly, sodium  loss  cells)  of  similar Schmitz, (1969),  these  the  cells  femoratum  (1985) 8.0  to  1977),  their  a  of  gill.  Rowe et  [Na] decreased s i g n i f i c a n t l y and Leptophlebia  to  stonefly  authors the  decreased  after  In  addition,  pH 6.5.  osmoregulatory Corixids  integument on  are  (Komnick, their  labia  proteus.  the  whole-body  cells known  1977;  (chloride to  possess  Komnick  (Jarial  use these c h l o r i d e c e l l s  8  [Na] i n pH  Pteronarcys  attribute  in  cupida  (1977) has suggested t h a t waterbugs,  as other a q u a t i c i n s e c t s , absorption.  the  particularly  and Komnick  showed  r e l a t i v e t o pH 7 . 0 .  relative  latter  stonefly  also  exclusively  found a decreased whole-body  for  damage  in  and pH 3.0  pH 3.5  found almost  et  and al.  as w e l l  f o r Na and CI  55 S. omani,  the  only s p e c i e s t e s t e d which normally i n h a b i t s  waters of pH 4 . 5 ,  were a c t u a l l y able to i n c r e a s e t h e i r haemolymph  [Na]  when exposed  this  was  to  pH 3.0  accomplished v i a  whole-body  experimental  a decreased  is  ionic  low pH water  deal  stress  supported  Presumably  sodium e f f l u x ,  in  often  as  neither  an i n d i c a t i o n o f animals s u f f e r i n g  these by  stressful  the  al.,  (McDonald et  1985), perhaps a decreased e f f l u x  with  conditions.  [Na] nor sodium i n f l u x changed with v a r y i n g pH. Since  increased efflux  Likens,  acid  conditions  observation  that  1983;  from  Havas and  suggests an a b i l i t y successfully. S.  overall  omani  to  This  is  had  the  h i g h e s t l e v e l s of haemolymph [Na] of any s p e c i e s t e s t e d i n a l l pH levels,  even though they  sodium c o n c e n t r a t i o n measured i n t h i s concentrations respect  to  Corixidae Scudder,  the  waters  study.  a  days  efflux  low  c o u l d not  be  characteristic  1972;  Vangenechten  gradient  with  of many of et  al.,  the  197 9b;  1987). and Vanderborght  punctata, (pH 3 . 5 ) .  of  f i n d that  (1980)  the  These  authors  found no s i g n i f i c a n t  corixids,  waterboatman  though,  loss  of Na  as compared to pH 6.0.  After  Vangenechten  haemolymph [Na] was e l e v a t e d ,  flux  s t u d i e d the  a s p e c i e s which a l s o occurs n a t u r a l l y i n low pH  starvation,  t o have no a f f e c t In  an extremely  concentration  medium i s  al.,  et  steep  and CI from the haemolymph at pH 3.0 7  with  The a b i l i t y to m a i n t a i n haemolymph i o n i c  external  (Frick  from water  (6 mM) . U n f o r t u n a t e l y ,  against  Vangenechten Corixa  came  on t h i s studies  the g e n e r a l  et  al.  (197 9b)  did  but e x t e r n a l pH appeared  increase. that  have  been  conducted  c o n c l u s i o n has been t h a t  to  date  on  these i n s e c t s  are  56 capable  of  internal  utilizing sodium  Vangenechten Chloride active  (Komnick via  an  and  uptake  in  the  head  and Schmitz,  influenced  by the  1979a).  pH of  The  concentrations  Vangenechten,  the  also  Vangenechten  at a c i d pH and a low ambient  [Na]  h i g h e r at pH 3.0 versus pH 6.0 As water  perhaps i t  is  used  in  the  seasons, One  influx  the  site  al.  is  (Vangenechten of  chloride  et  cell  1969).  (1979a)  study that  had a  found  was  that  depressed actually  [Na]  of  6 mM,  i n f l u x at pH 4.5  was  f o r any s p e c i e s t e s t e d i n any  like  C . punctata  present  dentipes,  and C.  from pH 7.0  to pH 4.5  in  so i n the summer. study  has  recorded f o r a l l B . C . s p e c i e s t e s t e d ,  w i t h those r a t e s  which  i n water w i t h a [Na] g r e a t e r than  i n sodium i n f l u x  throughout  and  mM), i n f l u x was  although only s i g n i f i c a n t l y  dilemma rates  et  (<1.4  present  H. atopodonta,  Indeed,  which  ( J a r i a l et al.,  not so s u r p r i s i n g , t h e n ,  e x h i b i t e d an i n c r e a s e all  a  dentipes  exchanger,  and C. dentipes  seldom lower than i n f l u x at pH 7.0 season.  +  this  occurs  solution  be  for  Influx  kinetics  external  i n both C. punctata  sodium i n f l u x  +  saturation  labium may  while  Na /H  1984).  Corixa  1983).  for  197 9a;  al.,  et  and  a  al.,  et  responsible  punctata  i n some c o r i x i d s p e c i e s  Interestingly,  this.  are  possibly  Michaelis-Menten  environment  Witters  and l e g s  1977;  mechanism,  external  1980;  Corixa  both  the  (Vangenechten  Vanderborght,  on  uptake  from  regulation  cells  displays  al.,  sodium  the  low  i n comparison coworkers  for  c o r i x i d s p e c i e s i n Belgium (nmoles/hour versus /amoles/hour -  see  references values  r e p o r t e d by Vangenechten and h i s  been  above).  However,  Cooper  et  al.  (1987)  did  report  i n the nmole range f o r c a l c u l a t e d sodium i n f l u x r a t e s  via  57 d r i n k i n g i n C. blaisdelli.  In a d d i t i o n ,  these authors  found t h a t  d r i n k i n g r a t e s were approximately twice as h i g h i n freshwater in  salt  water  suggest  that  specific,  et  drinking  essential  Corisella The  (Cooper  al.,  may  solutes  1987).  be  Frick  important  from a d i l u t e  and  for  Sauer  the  (1974)  uptake  media i n the  as  of  corixid,  edulis. above  study,  results,  in  conjunction with  those  of  the  present  seem to i n d i c a t e t h a t the major route of sodium entry  corixids  in  drinking,  r a t h e r than v i a an e x t e r n a l uptake mechanism such as a  chloride  cell.  cuticular  the  In  waters.  (in  support  permeability  salinity via  freshwater  This  was  the  of  absence  this,  low  the  bifida  Scudder  (1965)  found t h a t  may  (1981)  via  that  from  low  sodium e n t r y  cuticle  under  drinking  was  and v a r i e d w i t h environmental c o n d i t i o n s  be  found  collected  importance of  mouth r a t h e r than through the  conditions.  food)  Cannings  i n C.  emphasizes  of  into  freshwater significant  i n both C. bifida  and C.  expleta.  S u r v i v a l a t Low pH While loss  of  acidification species,  almost  of  surface  every  group of  which have managed to make the success  of  these  behaviourial  species  is  waters  generally  animals has  transition due  in  part  results  in a  some members  into  a c i d waters.  to  physiological  compensatory mechanisms which a l l o w  The or  for survival in  a low pH environment. Molluscs organisms  are one of the most (Okland  and Okland,  acid-sensitive 1986).  In  soft  groups of water,  aquatic  decreased  58 growth,  decreasing  species  often  1984; few  Servos  occur  with  al.,  et  species  densities,  of  increasing  1985;  molluscs  and a r e d u c t i o n acidity  in  (Rooke  Okland and Okland,  appear to  be  the  of  and Mackie,  1986).  largely  number  However,  unaffected  by  a  low  pH. Pisldium lakes  equilaterale P.  and  fecundity  in  ferrugineum  exhibit  (Servos  only  al.,  et  f o r by the d i f f e r e n t  larvae  1985; There  is  of  these  clams  Okland and Okland, a  wide  variety  crustaceans.  appears  to  failure  (Wood and Rogano,  result  from  0.  exhibited  elevated  levels  following  Cambarus  robustus  (Morgan and McMahon, 1982; 1986) .  This increase  dissolution  of  buffer against  the  from  tolerance of  the  In  of these which  is  1985). As  low  pH,  since  (Servos  et  of  to  [Ca]  species  ionoregulatory  where  [Ca]  tolerances  and  low pH, while  sensitive corkii  decreased  i n the  more  i n i o n l e v e l s were d e t e c t e d  H o l l e t t et al.,  i n blood  sensitive  Procambarus  and  to  no change  low pH  1987), the  haemolymph  exposure  to  crayfish,  propinquus,  blood acidosis  habits  shell  and/or  et al.,  (Berrill  carapace  tolerance  responses  more  acidosis  1986).  rusticus,  [Na]  of  blood  Orconectes.  This  (Servos et al.,  protected  acid  1986).  Mortality  vary widely between s p e c i e s  haemolymph  are  in  reduced  sediment,  occurs w i t h i n the mother's  amongst  tolerant  1985).  P i s i d i i d clams u s u a l l y burrow i n the  embryonic development al.,  slightly  ecological  l e s s a c i d i c than the surrounding waters well,  reduced growth  exhibited  a c i d waters  may be accounted species.  d i d not  1986;  appears  to  o b t a i n CaC0 , 3  Wood and Rogano, be the  result  which can act  (Wood and Rogano,  1986).  as  of a  59 Delayed moulting  as  a result  of  decreased  c a l c i u m uptake  a c i d waters has a l s o been noted i n crustaceans Orconectes  virilis,  c a l c i u m uptake  was  (Havas,  reduced  i n h i b i t e d below pH 4.0  (Malley, 1980). Post-moult  more  pH than  sensitive  individuals As  to  insect  mentioned,  groups  does occur, (Havas,  either  3.5  pH 5.75  it  of  aquatic  or  inter-moult  insects  are  organisms.  one  of  the  most  When m o r t a l i t y  at  s p e c i e s use  (1977)  chloride  has suggested t h a t  and 4 . 5 .  cells  for Na/Cl  uptake. cupida  F o l l o w i n g m o u l t i n g , whole-body  al.  Rowe et  spp.  Rowe  was  egg  at  shell  embryo a g a i n s t Like  amphibians  s t u d i e d the  hatching  they  pH < 6.5.  egg  vibrans,  at pH l e v e l s  [Na] and [CI] were  stage of  Stenonema  available  femoratum,  mortality  and Baetis  The authors  spp.)  have  most of  (Rowe et al., species  of  in  the  before  the  did more  hatching  suggested t h a t  the  for  the  to  be  1988b). amphibians  low pH ( P i e r c e ,  terrestrial,  and  rates  i n some s p e c i e s may p r o v i d e p r o t e c t i o n +  cupida,  L.  and development  observed  (S. femoratum  tolerant are  but  ambient H  insects,  relatively  also  Habrophlebia  pH,  species  complete  mayfly  (1986)  1986).  They found t h a t  with  sensitive  (Rowe,  (1988b)  a l o n g w i t h t h a t of  vary  aquatic  T h e r e f o r e , i n c r e a s e d m o u l t i n g i n a c i d waters c o u l d be  ion absorption  not  low pH  several  a mechanism f o r i n c r e a s i n g the number of c h l o r i d e c e l l s  Baetis  acid-  i s u s u a l l y the r e s u l t o f i o n o r e g u l a t o r y d i s r u p t i o n  1980). Komnick  stabilized.  for  and  i n d i v i d u a l s are  pre-moult  found t h a t moulting i n c r e a s e d i n Leptophlebia of  1980) . In  (Malley, 1980) .  previously  tolerant  low  at  in  1985).  effects  of  appear Since acid  many water  adult are  60 g e n e r a l l y r e s t r i c t e d to the egg and l a r v a l stages 1986). These e f f e c t s  include mortality  1985;  reduced h a t c h i n g  Freda,  1986),  the  " c u r l i n g defect",  the  vitelline  balance  membrane  tolerance  in  h a b i t a t pH ( P i e r c e , from  acidic  bogs  (Clark  al.,  Dale et  al.,  1976;  and L a Z e r t e ,  1985),  c h a r a c t e r i z e d by the embryo c u r l i n g w i t h i n (Freda,  1986),  (Freda and Dunson, 1984,  Acid  (Pough,  (Mierle et  and d i s r u p t i o n  1985;  amphibians  Freda,  can  in  New  Jersey  be  correlated  several  were  Na/Cl  1986).  often  1985). F o r example,  of  found  with  s p e c i e s of  to  resist  frogs  acidity  better  than these same s p e c i e s b r e e d i n g i n nearby h a b i t a t s  of a  higher  pH ( P i e r c e ,  wood  frog,  Rana  sylvatica,  populations levels  were  (Pierce,  tolerant  1985) .  varying  correlated  it  larvae  1984).  their  has been  acidification  of  temporary f o r e s t tolerance  of  maintenance  amphibian b r e e d i n g ponds)  acid  the  physiological  (Schofield,  seems  that  habitat  reported that  the  species  possibly  via  less  (Freda  vulnerability  habitats  (typically  pH  acid-  [Na] and l o s e  has over time c o n f e r r e d t h i s  conditions,  several  to  small,  group w i t h a  selection  for  the  of low whole-body sodium l e v e l s .  are  decreased  it  the  of  different  low pH than a c i d - s e n s i t i v e  Thus,  of  tolerances  s p e c i e s have lower i n i t i a l whole-body  Dunson,  Fish  i n the  acid  with  1985) . As w e l l ,  sodium when exposed to and  Similarly,  or  most  thoroughly  distress are  in  seriously  1976). In f i s h ,  low  studied pH  threatened  taxa  water. in  with  Populations  many  a c i d water i n f l u e n c e s  secretion  of  mucous,  respect  and  acidified  to have  lakes  ionoregulation,  acid/base  balance,  gill  (McDonald,  1983a). Opinions v a r y as to the r e l a t i v e  structure  importance of  61 each  of  these  serious acid  problems,  a  (pH 4.0-5.0)  Upon exposure of  changes  (Wood,  few  species  ionic  coating  on the  disturbances;  gills this  i n c r e a s e d mucous r e s u l t e d normally d i s p l a c e  +  increased effect  Ca  [H]  species.  has  of  the  been  surface  1977). did  not  change  [Ca]  found  McWilliams,  increase  at  these  1982).  the  release  1983a). The  for  the  in  correcting useful  gill  if  surface.  i n a c i d waters.  Therefore,  c o u l d have a l a r g e  mitigating  in  a  (Chelrodon  mechanism  few  fluviatilis,  fish  pH 4.0  al.,  (Dunson et  even i n pH 4.0  was  those which  sodium i n f l u x  from c o n t r o l v a l u e s  resist  a pH of 3.0  comparable to  s p e c i e s at  to  acid-tolerant  axelrodi),  sodium l o s s e s  In the p e r c h , Perca  be  particularly  ionoregulatory  o c c u r r e d i n an a c i d - s e n s i t i v e  with  1983a).  demonstrated  produce net  be  from the g i l l  gill  still  a mechanism  i n a higher  In c a r d i n a l t e t r a s  r e q u i r e d to  1977; will  may be  (McDonald,  +  ability  ++  can  even  and s k i n (McDonald,  would  at the g i l l  on H t o x i c i t y  The high  {Ca]  fish  low pH, many f i s h  mucous from c e l l s i n the g i l l s  thicker  H  of  However,  (Dunson et al.,  waters to  1989) .  and  efflux  (McWilliams,  1982). Both  the  physiological  basis  for  behaviourial modification u t i l i z e d to conditions  require  further  through t h i s  type  compensatory  mechanisms  study  in  acid  and  the  a l l o w f o r s u r v i v a l i n such all  taxonomic  of experimentation w i l l the in different  tolerance  groups.  similarities  t a x a be e l u c i d a t e d  Only among  and the  s p e c i e s l o s s e s i n a c i d i f i e d s u r f a c e waters f u l l y understood.  62  SUMMARY  The H.  five  corixid  atopodonta,  general, and  C.  species  tested i n this  bifida,  C.  expleta,  t o l e r a n t of exposure t o  low  The  pH.  of  important  greatest  highest  seasonal  mortality  (summer)  at  five  low pH.  in  low  pH  whole-body their  C.  waters, [Na]  as pH  i n low bifida  conditions,  pH  poorly  levels  waters. As  and  C.  w h i l e S.  expleta  time  time  of  Fall  was  concentrations.  from an  and  and  regulate  conditions, [Na]  life  [Na]  seemed t o  acidic  better  adapted f o r  haemolymph  haemolymph  did  the  i n C. b l a i s d e l l i .  constant  species  the  s t r a t e g i e s of sodium balance  under  of  seasonal  parameters  that  to  i n t e r n a l sodium  a  in  sodium i n f l u x ) .  observed was  decreased. C. b l a i s d e l l i  milieu  decreased  and  appeared t o be the best  maintaining  were,  However, both  [Na],  [Na]  varied in their  H. atopodonta  internal  exhibiting [Na]  species  low  omani)  corresponded  haemolymph and whole-body  a time of low m o r t a l i t y and All  trend  S.  blaisdelli,  i n each of the  (haemolymph [Na], whole-body  most  (C.  and  s p e c i f i c d i f f e r e n c e s were detected  measured  study  often  whole-body  a l k a l i n e environment,  than  omani performed as had  expected  in  acid  been p r e d i c t e d  for a  s p e c i e s n a t u r a l l y o c c u r r i n g i n a c i d waters. Finally, sodium  in  drinking the  five  may  be  species  an of  i n f l u x r a t e s were extremely low used, the  and  are  therefore  specialized  external  important corixids i n the  probably  not  structures  route  of  examined  dilute,  entry  here.  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The e f f e c t s o f season and exposure to reduced pH (abrupt and gradual) on some p h y s i o l o g i c a l parameters i n brown t r o u t (Salmo t r u t t a ) . Can. J . Z o o l . 63: 1078-1083. Sutcliffe, in the  D. and C a r r i c k , T . 1973. E n g l i s h Lake D i s t r i c t .  Studies on mountain streams I. pH, calcium and the  69 d i s t r i b u t i o n of i n v e r t e b r a t e s B i o l . 3: 437-462.  in  the  R i v e r Duddon.  Freshwat.  Sutcliffe, D. and H i l d r e w , A . 1989. I n v e r t e b r a t e communities a c i d streams. In: A c i d t o x i c i t y and a q u a t i c animals, M o r r i s , E . T a y l o r , D. Brown and J . Brown ( e d s . ) , 13-29.  in R.  Vangenechten, J . 1983. A c i d i f i c a t i o n i n West-European Lakes and p h y s i o l o g i c a l a d a p t a t i o n to a c i d s t r e s s i n n a t u r a l i n h a b i t a n t s of a c i d l a k e s . Wat. Q u a l . B u l l . 8: 150-155, 169. Vangenechten, J . and Vanderborght, 0. 1980. E f f e c t of a c i d pH on sodium and chloride balance in an inhabitant of acid freshwaters: the waterbug Corixa punctata (Insecta, Hemiptera). I n : E c o l o g i c a l Impact of A c i d P r e c i p i t a t i o n , D. Drablos and A . T o l l a n ( e d s . ) , 342-343. Vangenechten, J . , Van Puymbroeck, S. and Vanderborght, 0. 1979a. E f f e c t of pH on the uptake of sodium i n the waterbugs Corixa dentipes and Corixa punctata (Hemiptera, H e t e r o p t e r a ) . Comp. Biochem. P h y s i o l . 64A: 509-521. Vangenechten, J . , Van Puymbroeck, S. B a s i c p h y s i o l o g i c a l data r e l a t i v e waterbugs:  Corixa  Heteroptera).  dentipes  and  and Vanderborght, 0. to i o n i c regulation Corixa  Comp. Biochem. P h y s i o l .  punctata  64A: 523-529.  197 9b. i n two  (Hemiptera,  Vangenechten, J., Witters, H. and Vanderborght, 0. 1989. Laboratory s t u d i e s on i n v e r t e b r a t e s u r v i v a l and p h y s i o l o g y i n a c i d w a t e r s . I n : A c i d t o x i c i t y and a q u a t i c animals, R. M o r r i s , E . T a y l o r , D. Brown and J . Brown ( e d s . ) , 153-169. Witters, H., Vangenechten, J., Van Puymbroeck, S. and Vanderborght, 0. 1984. I n t e r f e r e n c e of aluminum and pH on the N a - i n f l u x i n an a q u a t i c i n s e c t Corixa punctata. Bull. Envir. Contam. T o x i c o l . 32: 575-579. Wood, C . 1989. The p h y s i o l o g i c a l problems of f i s h i n a c i d waters. In: A c i d t o x i c i t y and a q u a t i c animals, R. M o r r i s , E . T a y l o r , D. Brown and J . Brown ( e d s . ) , 124-152. Wood, C . and Rogano, M. 1986. P h y s i o l o g i c a l responses to a c i d stress in crayfish (Orconectes): Haemolymph i o n s , acid-base status, and exchanges with the environment. Can. J . F i s h . Aquat. S c i . 43: 1017-1026. Zar, J . 1984. B i o s t a t i s t i c a l H a l l , I n c . New J e r s e y .  Analysis  (second e d i t i o n ) .  Prentice-  70  APPENDIX A  Raw d a t a from t h e haemolympyh  [Na] e x p e r i m e n t s  71 HAEMOLYMPH [Na] (mM) Season  Species  PH  Day  Mean  Standard Deviation  Standard Error  Number Sampled  Spring  Sigara omani  7.0  2  172.5  17.4  5.5  10  -  4  163.8  15.1  4.8  10  6  169.1  14.4  4.6  10  8  168.0  9.3  2.9  10  2  172.2  13.6  4.3  10  4  166.1  50.8  16.1  10  6  176.6  19.0  6.0  10  8  175.8  10.8  3.4  10  2  186.9  12.4  3.9  10  4  193.6  15.6  4.9  10  6  174.2  33.9  10.7  10  8  185.6  16.2  5.1  10  4  158.3  17.0  7.6  5  8  146.7  4.5  2.0  5  4  155.3  19.6  8.8  5  8  151.4  5.3  2.4  5  4  151.4  6.7  3.0  5  8  135.0  3.2  1.4  5  4  132.1  15.1  6.8  5  8  137.5  14.9  6.7  5  4.5  3.0  Hesperocorixa atopodonta  7.0  4.5  3.0  Cenocorixa blaisdelli  7.0  cont...  72 HAEMOLYMPH [Na] (mM) cont.. Season  Species  pH  Day  Mean  Standard Deviation  Standard Error  Number Sampled  Spring  Cenocorixa blaisdelli  4.5  4  141.6  14.2  6.3  5  8  134.7  6.4  2.9  5  4  136.8  18.6  8.3  5  8  136.0  15.6  7.8  4  2  158.9  19.8  8.9  5  4  161.3  26.1  11.7  5  6  152.4  24.1  10.8  5  8  156.1  12.2  5.5  5  2  164.5  7.4  3.3  5  4  169.0  7.2  3.2  5  6  164.9  7.5  3.3  5  8  160.9  17.3  7.8  5  2  153.6  9.9  4.4  5  4  168.5  3.2  1.4  5  6  162.5  4.9  2.2  5  8  152.8  29.8  13.3  5  2  175.9  13.7  4.3  10  4  177.3  12.5  4.0  10  6  180.4  19.9  6.3  10  8  174.4  26.5  8.4  10  3.0  Summer  Hesperocorixa atopodonta  7.0  4.5  3.0  Cenocorixa blaisdelli  7.0  cont..,  73 HAEMOLYMPH [Na] (mM) cont... Season  Species  pH  Day  Mean  Standard Deviation  Standard Error  Number Sampled  Summer  Cenocorixa blaisdelli  4.5  2  157.0  12.6  4.0  10  4  157.1  17.2  5.4  10  6  161.9  11.8  3.7  10  B  155.1  7.1  2.9  6  2  134.7  20.9  6.6  10  4  147.0  4  159.8  8  3.0  Fall  Hesperocorixa atopodonta  7.0  4.5  3.0  Cenocorixa blaisdelli  7.0  4.5  —  1  13.5  6.8  4  146.9  19.4  9.7  4  4  157.9  8.9  4.5  4  8  153.9  8.3  4.1  4  4  152.4  6.3  3.1  4  8  153.9  8.5  4.2  4  2  143.1  6.2  2.0  10  4  131.2  12.4  3.9  10  6  123.5  7.1  2.2  10  8  119.5  8.7  2.8  10  2  115.6  5.0  1.6  10  4  112.3  10.2  3.2  10  6  98.3  11.4  3.6  10  8  81.7  14.9  4.7  10  —  cont...  74 HAEMOLYMPH [Na] (mM) cont.. Season  Species  Fall  Cenocorixa  Cenocorixa  blaisdelli  bifida  pH  Day  Mean  Standard Deviation  Standard Error  Number Sampled  3.0  2  53.8  23.2  8.2  8  4  91.2  35.2  11.1  10  6  73.4  26.1  8.3  10  6  83.1  28.8  14.4  4  2  135.9  36.1  11.4  10  4  155.1  20.5  6.5  10  6  158.5  10.8  3.4  10  8  151.8  30.1  9.5  10  2  149.7  57.4  19.1  9  4  158.9  29.0  9.2  10  6  145.0  26.9  8.5  10  8  163.9  5.3  1.7  10  2  170.1  18.2  5.7  10  4  158.7  29.0  9.2  10  6  173.4  9.4  3.0  10  8  161.0  31.0  9.8  10  2  121.4  11.9  3.8  10  4  125.5  8.7  2.7  10  6  133.8  18.7  5.9  10  8  126.0  14.4  5.5  7  7.0  4.5  3.0  Cenocorixa  expleta  7.0  cont...  75 HAEMOLYMPH [Na] (mM) cont... Season  Species  Fall  Cenocorixa expleta  pH  4.5  3.0  Day  Mean  Standard Deviation  Standard Error  Number Sampled  2  131.6  21.8  6.9  10  4  134.3  15.6  4.9  10  6  128.2  21.5  6.8  10  8  136.9  14.7  6.6  5  2  114.9  34.0  10.8  10  4  107.1  40.2  12.7  10  6  116.6  53.2  16.8  10  8  119.5  31.9  16.0  4 end  76  APPENDIX B  Raw d a t a from t h e whole-body  [Na]  experiments  77 WHOLE-BODY [Na] (ujnoles/mg dry weight) Season  Species  Spring  Sigara omani  pH  Day  Mean  Standard Deviation  Standard Error  Number Sampled  7.0  2  0.19  0.06  0.02  10  4  0.19  0.05  0.02  10  6  0.12  0.04  0.01  9  8  0.20  0.08  0.03  6  2  0.19  0.06  0.02  10  4  0.18  0.04  0.01  10  6  0.14  0.07  0.02  10  8  0.13  0.06  0.03  5  2  0.22  0.05  0.02  10  4  0.22  0.06  0.02  10  6  0.17  0.07  0.02  10  8  0.15  0.05  0.02  5  0.16  0.02  0.01  5  8  0.15  0.03  0.01  5  4  0.16  0.02  0.01  5  8  0.17  0.04  0.02  5  4  0.18  0.08  0.03  5  8  0.15  0.02  0.01  4  0.24  0.11  0.05  5  0.35  —  4.5  3.0  Hesperocorixa atopodonta  7.0  4.5  3.0  Cenocorixa blaisdelli  7.0  4  4  8  —  1 cont,  78 WHOLE-BODY [Na] (umoles/mg dry weight) cont... Season  Species  Spring  Cenocorixa blaisdelli  pH  Hesperocorixa atopodonta  Standard Deviation  Standard Error  Number Sampled  4  0.14  0.08  0.04  5  8  0.13  0.02  0.01  3  4  0.15  0.05  0.02  5  0.17  0.03  0.01  5  4  0.21  0.05  0.02  5  6  0.19  0.02  0.01  5  2  0.21  0.01  0.01  5  4  0.19  0.04  0.02  5  6  0.18  0.02  0.01  5  2  0.20  0.04  0.02  5  4  0.19  0.02  0.01  5  6  0.15  0.01  0.00  5  0.36  0.08  0.03  10  4  0.39  0.09  0.03  10  6  0.29  0.06  0.02  10  8  0.33  0.07  0.03  4  2  0.28  0.11  0.03  10  4  0.26  0.09  0.03  10  6  0.32  0.08  0.02  10  8  0.36  0.06  0.05  2  7.0  4.5  3.0  Cenocorixa blaisdelli  Mean  4.5  3.0 Summer  Day  7.0  4.5  2  2  cont...  79 WHOLE-BODY [Na] (umoles/mg dry weight) cont... Season  Species  Summer  Cenocorixa blaisdelli  Fall  Hesperocorixa atopodonta  pH  Day  Mean  Standard Deviation  Standard Error  Number Sampled  3.0  2  0.23  0.11  0.04  8  7.0  4  0.16  0.02  0.01  4  8  0.20  0.06  0.03  3  4  0.16  0.03  0.01  4  8  0.21  0.01  0.01  3  4  0.17  0.02  0.01  4  8  0.21  0.01  0.00  3  0.26  0.05  0.02  10  4  0.22  0.06  0.02  10  6  0.15  0.06  0.02  9  8  0.23  0.06  0.02  10  2  0.19  0.05  0.02  10  4  0.18  0.05  0.02  10  6  0.18  0.04  0.01  10  8  0.21  0.05  0.02  10  2  0.13  0.07  0.02  10  4  0.15  0.06  0.02  10  6  0.16  0.05  0.02  10  0.32  0.16  0.05  10  0.38  0.19  0.06  10  4.5  3.0  Cenocorixa blaisdelli  7.0  4.5  3.0  Cenocorixa bifida  7.0  2  2  4  cont..  80 WHOLE-BODY [Na] (umoles/mg dry weight) cont... Season  Species  PH  Day  Mean  Standard Deviation  Standard Error  Number Sampled  Fall  Cenocorixa bifida  7.0  6  0.32  0.14  0.04  10  8  0.44  0.25  0.09  7  2  0.31  0.18  0.06  10  4  0.28  0.18  0.06  10  6  0.18  0.09  0.03  9  8  0.41  0.13  0.05  7  2  0.25  0.14  0.05  10  4  0.20  0.05  0.02  10  6  0.19  0.07  0.02  10  8  0.29  0.08  0.03  9  2  0.30  0.09  0.03  10  4  0.28  0.09  0.03  10  6  0.34  0.13  0.04  10  2  0.22  0.07  0.02  10  4  0.24  0.12  0.04  10  6  0.16  0.04  0.02  7  2  0.23  0.08  0.03  10  4  0.20  0.07  0.02  10  6  0.18  0.06  0.02  10  4.5  3.0  Cenocorixa expleta  7.0  4.5  3.0  end  APPENDIX C  Raw  d a t a from t h e sodium i n f l u x  experiments  3  82 SODIUM INFLUX (nmoles/mg wet welghMiour) Season  Species  pH  Day  Mean  Standard Deviation  Standard Error  Number Sampled  Spring  Sigara omani  7.0  3  0.73  0.19  0.09  5  7  0.73  0.09  0.04  5  9  0.35  0.02  0.01  5  3  0.48  0.15  0.07  5  7  0.74  0.16  0.07  5  9  0.43  0.08  0.04  4  1  0.20  0.07  0.03  5  2  0.15  0.04  0.02  5  3  0.09  0.03  0.01  5  4  0.12  0.05  0.02  5  5  0.06  0.03  0.01  5  6  0.09  0.03  0.02  5  1  0.18  6.06  0.04  5  2  0.21  0.08  0.03  5  3  0.13  0.07  0.03  5  4  0.12  0.05  0.02  5  5  0.08  0.04  0.02  5  6  0.06  0.03  0.01  5  1  0.52  0.20  0.09  5  2  0.85  0.41  0.18  5  4.5  Hesperocorixa atopodonta  7.0  4.5  Cenocorixa blaisdelli  7.0  cont...  83  SODIUM INFLUX (nmoles/mg wet weight-hour) cont... Season  Species  Spring  Cenocorixa blaisdelli  pH  Day  7 . 0  4.5  Summer  Hesperocorixa atopodonta  7.0  4.5  (not used)  Standard Standard Number Deviation Error Sampled  0.56  0.22  0.11  4  5  0.58  0.32  0.19  3  1  0.56  0.05  0.02  5  2  0.86  0.26  0.12  5  3  0.88  0.39  0.17  5  5  0.70  0.41  0.19  5  0.13  0.03  0.02  5  2  0.07  0.02  0.01  5  3  0.07  0.01  0.01  5  4  0.08  0.01  0.00  5  5  0.14  0.04  0.02  4  6  0.10  0.02  0.01  4  0.24  0.10  0.04  5  2  0.22  0.09  0.04  5  3  0.15  0.06  0.02  5  4  0.13  0.05  0.02  5  5  0.21  0.05  0.02  5  6  0.13  0.04  0.02  5  12.30  7.41  3.31  5  14.04  3.84  1.72  5  3  1  1  -  Cenocorixa blaisdelli  Mean  7.0  2 3  cont..  84 SODIUM INFLUX (nmoles/mg wet weight>hour)  Season  Species  Summer  Cenocorixa blaisdelli (not used)  pH  Day  Fall  Hesperocorixa atopodonta  Cenocorixa blaisdelli  Standard Deviation  9.55  3.18  1.42  5  5  10.56  2.50  1.12  5  6  13.87  1.64  0.74  5  2  2.01  1.14  0.51  5  3  0.05  0.07  0.03  5  4  10.78  2.61  1.17  5  5  9.94  3.52  1.57  5  6  14.59  4.05  1.81  5  0.10  0.03  0.02  5  2  0.10  0.02  0.01  5  3  0.10  0.01  0.01  5  4  0.21  0.03  0.01  5  6  0.17  0.02  0.01  5  1  0.22  0.01  0.00  5  2  0.17  0.05  0.02  5  3  0.19  0.03  0.01  5  4  0.13  0.02  0.01  5  6  0.09  0.02  0.01  5  1  10.75  3.64  1.63  5  2  7.00  2.06  0.92  5  4  7.0  4.5  (1988-not used)  Mean  7.0  4.5  7.0  cont..  1  Standard Error  Number Sampled  cont...  85 SODIUM INFLUX (nmoles/mg wet weight-hour) cont.. Season  Fall  Species  Cenocorixa blaisdelli  -(1988-not used)  pH  Mean  Standard Deviation  3  1.43  0.50  0.22  5  4  16.40  7.08  3.17  5  5  15.58  5.79  2.59  5  6  1.87  0.90  0.40  5  11.52  3.12  1.39  5  2  11.78  2.51  1.12  5  3  10.24  5.77  2.58  5  4  17.12  9.78  4.37  5  5  4.65  1.03  0.46  5  6  2.66  0.96  0.43  5  1  0.66  0.10  0.04  5  2  0.54  0.08  0.04  5  3  0.45 •  0.03  0.01  5  4  0.50  0.12  0.05  5  6  0.46  0.23  0.10  5  0.39  0.12  0.05  5  2  0.49  0.08  0.04  5  3  0.41  0.15  0.07  5  4  0.55  0.08  0.03  5  6  0.40  0.06  0.03  5  7.0  4.5  Cenocorixa blaisdelli(1989)  Day  7.0  4.5  1  1  Standard Error  Number Sampled  cont..,  86 SODIUM INFLUX (nmoles/mg wet weight-hour) cont...  Season  Species  Fall  Cenocorixa bifida  (not used)  Cenocorixa expleta  pH  Day  Mean  Standard Deviation  Standard Error  Number Sampled  7.0  3  36.65  6.49  2.90  5  3.0  3  27.43  17.78  8.89  4  7.0  3  0.39  0.12  0.06  4  6  0.44  0.10  0.06  3  3  0.27  0.05  0.03  4  6  0.47  0.09  0.04  4  4.5  end  

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