Parasite-induced Behavior Modification to the Circatidal Rhythm of the Atlantic Mole Crab, Emerita talpoida

Parasites with complex life cycles require transmission from their intermediate host to their definite host to reach sexual maturity. In some parasite-host systems, parasites manipulate the behavior of their intermediate host to enhance transmission to their definitive host. This mode of transmission is termed parasite increased trophic transmission. While there are many examples of parasites inducing atypical behavior in their hosts, little is known about the ability of parasites to modify host biological rhythms. In this study, I examined the effects of parasite load on the strength of host biological rhythms, using the Atlantic mole crab (Emerita talpoida) as a model. Mole crabs are common inhabitants of the swash zone of sandy beaches along the east coast of the United States. They exhibit activity rhythms that are entrained to the tides and act as intermediate hosts for trematode parasites (Microphallus sp.) and acanthocephalan parasites (Profilicollis sp.). For this study, behavioral assays were performed to quantify the strength of the circatidal rhythms of mole crabs before they were dissected to determine parasite load. On average, rhythmic crabs were found to have significantly greater trematode loads but not acanthocephalan loads compared to arrhythmic crabs. This result is further supported by a logistic regression analysis, which revealed trematode load as the most significant predictor of rhythmicity amongst other demographic variables such as size, sex, ovigerity and month of collection. Overall, results from this experiment support the hypothesis that parasites may influence the biological rhythms of their hosts, presenting an additional mechanism through which parasites may enhance trophic transmission.