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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