Community interactions and environmental drivers of host-parasite dynamics in an estuarine system
Gehman, Alyssa-Lois Madden
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Not all hosts, communities or environments are equally hospitable for parasites. Direct and indirect interactions between parasites and their predators, competitors and the environment can influence variability in host exposure, susceptibility and subsequent infection, and these influences may vary across spatial scales. I evaluate abiotic and biotic drivers of parasite abundance and host-parasite dynamics utilizing the parasite Loxothylacus panopaei, which infects an oyster reef dwelling mud crab Eurypanopeus depressus. I conducted a survey of host, parasite, and predator abundance, parasite prevalence, and environmental characteristics of oyster reef communities from Florida to North Carolina. I found that water depth, predators and host characteristics were all positively correlated with the probability of infection within a reef. I further investigated whether the predatory crab Callinectes sapidus and other predators preferentially feed on E. depressus infected with L. panopaei and evaluated a mechanism behind prey choice. I evaluated prey choice through mesocoms experiments, field tethering experiments and behavioral trials. I found that C. sapidus preferentially consumed infected E. depressus in the lab and this pattern was confirmed in the field. Contrary to expectations, I found that infected crabs ran faster in behavioral trials than uninfected E. depressus. Finally, I evaluated the influence of temperature on host and parasite survival and parasite reproduction. I quantified thermal response curves encompassing the thermal breadth of both host and parasite, and found a thermal mismatch in survival optima between infected and uninfected hosts. I then parameterized a physiologically based epidemiological model to predict the sensitivity of a host-parasite system to seasonal varying temperature and future climate change scenarios. I found that the model accurately recreates annual cycles and seasonality in this host-parasite system, and that the parasite is locally extirpated from the system under a 3ºC warming scenario. Together, these findings demonstrate the importance of community interactions and environmental drivers in driving the abundance and prevalence of L. panopaei infection in E. depressus at a regional, local scale and under climate warming scenarios.