Influence  of  Calcium  depletion  on  susceptibility  of  Daphnia  magna  to  disease    Roisin  Donohoe,  Clayton  Cressler,  William  Nelson  

   

3  Treatments:  

1) 2.5  mg  Ca/L  

2)  5  mg  Ca/L  

3)  10  mg  Ca/L  

20  controls  

40  exposed  20  controls  

20  controls  40  exposed  

40  exposed   Measuring  daphnia    body  size    

Department  of  Biology,  Queen’s  University    

     

Ca  <1.5  mg/L  

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Pasteuria  spores  

•  host-­‐parasite  system:  Daphnia  magna  (daphnia)  and  Pasteuria  ramosa  (Pasteuria)  

•  Pasteuria   infections,   passed   from   host   to   host   via   transmission   spores,   cause  

gigantism  and  castration  in  daphnia  

•  prior  research:  looked  at  the  effects  of  food  and  temperature  on  daphnia  growth/

reproduction  in  conjunction  with  a  Pasteuria  infection  

•  daphnia  are  dependent  on  calcium  (used  to  rebuild  carapace  following  molting)  

•  in   nature,   daphnia   are   increasingly   exposed   to   calcium-­‐depleted   environments  

(concentrations  <  1.5  mg/L)  due  to  previous  displacement  of  calcium  from  soils  via  

acidic  deposition  (acid  rain)3    

•  for  this  reason,  there  is  interest  in  looking  at  the  effect  calcium  deficiency  has  on  

the  susceptibility  of  daphnia  to  infections  like  that  caused  by  Pasteuria    

 

Introduction  

Methods    •  Day  0:  all  daphnia  placed  into  assigned  Ca  treatment4  

•  Day  10:  daphnia  in  “exposed”  conditions  exposed  to  Pasteuria  spores  

•  Day  18:  Pasteuria  spores  removed  

•  Day  36:  experiment  terminated,  all  remaining  exposed  daphnia    

           frozen  pending  further  analysis  (spore  counting)    

•  Daphnia  were  measured/neonates  were  counted  every  other  day    

         Hypotheses  Inducing  calcium  deficiencies  will  have  an  effect  on  Pasteuria-­‐exposed  daphnia  by:  

1)  increasing  the  overall  growth  and  decreasing  the  number  of  neonates  produced  

2)  increasing  the  infection  success  of  Pasteuria  (more  infected  daphnia,  more  spores)  

Further  Reading  1)  Cressler,  C.,  Nelson,  W.A.,    Day,  T.  and  E.  McCauley.  Starvation  reveals  the  cause  of  infection-­‐induced  castration  and  gigantism,  Proceedings  of  the  Royal  Society  B  2014.  

2)  Ebert,  D.,  Rainey,  P.,  Embley,  T.M.  and  D.  Scholz.  Development,  life  cycle,  ultrastructure  and  phylogenetic  position  of  Pasteuria  ramosa  Metchnikoff  1888:  rediscovery    

                 of  an  obligate  endoparasite  of  Daphnia  magna  straus,  Proceedings  of  the  Royal  Society  B  1996.  

3)          Smol,  J.P.  The  power  of  the  past:  using  sediments  to  track  the  effects  of  multiple  stressors  on  lake  ecosystems.  Freshwater  Biology  2010.  

4)          Tan,  Q.  and  W.  Wang.  The  regulation  of  calcium  in  Daphnia  magna  reared  in  different  calcium  environments,  Limnology  and  Oceanography  2009.  

Total    Growth  (mg)  

Calcium  Concentration  (mg/L)    

Combined  Effect  of  Calcium  Concentration  and    Pasteuria  Infection  on  Average  Growth  

Figure  1:  

•  Infected   daphnia   did   reach   a   statistically   larger   size  

(0.42   ±   0.007   mg)   than   uninfected   daphnia   (0.36   ±  

0.003   mg),   without   taking   calcium   into   account  

(F(2,131)=  53.207,  p=0.000)    

•  addition   of   calcium   concentration   as   a   second  

independent   variable   showed   that   the   combination  

of   calcium   concentration   and   infection   did   not  

significantly  affect  the  total  growth  of  the  daphnia    

Results    

Calcium  Concentration  (mg/L)  

Figure  2:  

•  infected   daphnia   did   not   have   statistically   fewer  

neonates  over   their   lifetime     (23.40±  5.418  neonates)  

compared   to   uninfected   daphnia   (26.65±   7.278),  

without  the  effects  of  calcium  

•  addition   of   calcium   concentration   as   a   second  

independent   variable   saw   no   significant   interactions  

between   the   calcium   concentration/Infection   success  

and  total  reproduction  

 

Total    Reproduction  

Combined  Effect  of  Calcium  Concentration  and    Pasteuria  Infection  on  Average  Reproduction  

 

Figure  3:  

•  significant  difference   in   the  number  of  spores   found  

in   daphnia   living   at   different   calcium   concentrations  

(p=0.004);  difference   lies  between  daphnia   found  at  

2.5  vs.  10  mg  Ca/L  

•  high   degree   of   correlation   between   spore   density  

and  calcium  concentration  (R=0.676,  R  square=0.457)  

250000  

450000  

650000  

850000  

1050000  

1250000  

1450000  

1650000  

1850000  

0   2.5   5   7.5   10   12.5  

Spore  Density  (per  daphnia)  

Spore  Densities  at  Various  Calcium  Concentrations    

Calcium  Concentration  (mg/L)  

Average  Spore  Density  

Conclusions  -­‐  inducing   calcium   deficiencies   does   affect   the  

infection   success   of   Pasteuria   à   increases  

vulnerability   of   daphnia   at   low   calcium,  

increases  spore  density  at  high  calcium  

-­‐  fewer   daphnia   were   infected   than   expected  

based  on  previous  experiments1  à  likely  due  to  

later  exposure  to  spores  

-­‐  Pasteuria   also   appears   to   be   calcium  

dependent  à   lower  numbers  of  spores  at   low  

calcium  concentrations