Changes in chiropteran community structure associated with the white-nose syndrome epidemic: evidence for competitive release?

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Date: 2014-05-01

Creator: Adam Eichenwald

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Fitness and sex effects of a novel microsporidian parasite on its Daphnia host

Date: 2025-01-01

Creator: Gracie Scheve

Access: Open access

Parasitism can influence host ecology and evolution in powerful ways, although the specific impacts on host fitness and life history may be context dependent and involve complex trade-offs. In this study, I investigated the effects of a novel microsporidian gut parasite on Daphnia ambigua, a freshwater zooplankton with a cyclical parthenogenetic life cycle. Combining extensive field sampling at Sewall Pond, Maine, with chronic exposure experiments in the lab, I assessed the parasite's impact on Daphnia fitness and propensity to shift from asexual to sexual reproduction. Field observations revealed a correlation between gut parasite prevalence and increased production of males and sexual females, independent of known sex inducers such as crowding, food limitation, and photoperiod. Lab experiments confirmed that chronic spore exposure significantly reduced Daphnia survival and reproductive output, particularly in clones previously naïve to this strain of the parasite. However, no induction of sex or male offspring was observed in response to parasite exposure under laboratory conditions. This suggests that more complex environmental interactions might be triggering sex in Daphnia. While sex provides the benefit of increased genetic diversity for future generations, I hypothesize that while Daphnia undergo sexual reproduction their ability to resist or tolerate parasite infection is diminished. Phylogenetic analyses indicate the parasite is closely related to the less virulent microsporidian Ordospora pajunii but genetically distinct, potentially constituting a new species or genus. These findings provide insight into the ecological and evolutionary tradeoffs involved in host-parasite interactions and introduce a new host-parasite system for this study.

Egg Size, Breeding Phenology, and Parental Investment in Leach’s Storm Petrels

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Date: 2020-01-01

Creator: James L. O'Shea

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