Predation, environment and host characteristics influence the probability of infection by an invasive castrating parasite

Background/Question/Methods

Not all hosts, communities or environments are equally habitable 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. To determine the influences of abiotic, biotic or host characteristics on the probability of infection by Loxothylacus panopaei, an invasive castrating rhizocephalan parasite of the oyster reef-dwelling mud crab Eurypanopeus depressus, we surveyed the host and parasite across >900 km of the southeastern USA. In 10 different estuaries we quantified the density of hosts, predators of the parasite and host, the host’s oyster reef habitat, and environmental variables that might affect the parasite either directly or indirectly. 

Results/Conclusions

Our analyses reveal that while L. panopaei are limited by the density of their host, with the upper limit correlated with 40% infection prevalence, several biotic and abiotic factors are positive predictors of the probability of infection. The depth of water inundation over reefs at high tide was a positive predictor of infection, perhaps because it enhances delivery of waterborne infective stages of the parasite. Predators were also a positive predictor of infection, which can arise if sub-lethal interactions between predator and E. depressus increase the crabs’ susceptibility to L. panopaei infection. We demonstrate that biotic and abiotic community-level variables may enhance our understanding of large-scale determinants of parasite dynamics.