Predicting Probability of Infection of an Estuarine Crab by a Castrating Isopod Parasite

Abstract

Entoniscid (Entoniscidae) are endoparasitic isopods that infect both male and female white-tipped mud crabs (Rhithropanopeus harrisii) along the Atlantic and Gulf of Mexico coasts. When these parasites infect a host, they effectively castrate the host so that it can no longer reproduce. Once infected, the host’s energy is utilized by the parasite, allowing the entoniscid eggs to mature inside the host. 105 R. harrisii were collected from three sites throughout the Chesapeake Bay via crab condos and hand collection. All crabs were dissected and the presence or absence of entoniscid infection was noted. The response variable of entoniscid infection presence (n = 287) was analyzed via Generalized Linear Mixed Models (GLMMs). Four GLMMs were ran with site as the random variable and different combinations of fixed variables (carapace width (CW) and sex). The full model (CW * Sex) was selected as the best model as it had the lowest AICc value and explained 33% of the data. This model states that the interaction between CW and sex plays a significant role in determining the probability that R. harrisii will be infected by an entoniscid in the Chesapeake Bay. Where larger females R. harrisii are more likely to be parasitized than smaller females and that males have a significantly lower probability of being parasitized regardless of size.