COS 48-3 - Mysterious microsporidians: Springtime outbreaks of disease in Daphnia communities in shallow pond ecosystems

Tuesday, August 8, 2023

8:30 AM – 8:45 AM PDT

Location: B111

Presenting Author(s)

AS

Alexander T. Strauss

Assistant Professor
Odum School of Ecology, University of Georgia
Athens, Georgia, United States

Slides (PDF)

Coauthor(s)

DS

Daniel Suh

Odum School of Ecology, University of Georgia
Athens, GA, United States
KG

Kate Galbraith

Odum School of Ecology, University of Georgia, United States
SC

Sarah Coker

Southeastern Cooperative Wildlife Disease Study, University of Georgia, United States
KS

Katie Schroeder

PhD Student
Odum School of Ecology, University of Georgia
Athens, Georgia, United States
CB

Christopher Brandon

Odum School of Ecology, University of Georgia, United States
EW

Elizabeth Warburton

Warnell School of Forestry and Natural Resources, University of Georgia, United States
MY

Michael Yabsley

Southeastern Cooperative Wildlife Disease Study, University of Georgia, United States
CC

Christopher Cleveland

Southeastern Cooperative Wildlife Disease Study, University of Georgia, United States

Abstract: Parasites can play key roles in ecosystems, especially when they infect common hosts that play important ecological roles. Daphnia are critical grazers in many lentic freshwater ecosystems, reaching especially high biomass in early spring. Daphnia have also become prominent model organisms for the field of disease ecology, although most well-studied parasites infect them in fall or summer. Here, we report field patterns of virulent microsporidian parasites that consistently infect Daphnia in springtime. We report results of a field survey of seven shallow ponds in Georgia, USA, sampled every 3-4 weeks for 18 months. Our goals have been to: 1) characterize infection dynamics over time, among ponds, and in three separate species of host (Daphnia ambigua, Daphnia laevis, and Daphnia parvula); 2) identify parasite taxa with PCR and amplicon sequencing and characterize any host-parasite associations; and 3) investigate whether host species differ in terms of their spore yield (number of parasites produced per infected host; proxy for parasite fitness) or the virulent effects of infection on host fitness (quantified as the difference in fecundity between healthy versus infected hosts).

We detected two distinct microsporidian parasite taxa that closely matched sequences of Pseudoberwaldia daphniae and Conglomerata obtusa. Both parasites were found infecting all three species of host (D. ambigua, D. laevis, and D. parvula). To our knowledge, this is the first record of either of these parasites in North America and the first record of them infecting any of these host species. Infection prevalence peaked consistently in February-May for all hosts. However, the severity of these outbreaks differed substantially among ponds, with maximum infection prevalence ranging 1.0% - 70.6%. Host species differed markedly in terms of their maximum infection prevalence (5% [D. parvula] to 72% [D. laevis]), mean reduction in fecundity when infected (70.6% [D. ambigua] to 99.8% [D. laevis]), mean spore yield (62,000 [D. parvula] to 377,000 [D. laevis]), and likelihood of being infected by each parasite. D. laevis and D. parvula were equally likely to be infected by both parasites, but D. ambigua was almost exclusively infected by P. daphniae and rarely infected by C. obtusa. The timing and severity of these disease outbreaks suggests that these parasites could be impactful members of shallow pond ecosystems, and that the strength of their effects is likely to hinge on the composition of zooplankton communities.