Due to the ubiquity of parasites in the natural environment, and the fact that they can affect host physiology, behavior, and ultimately ecology, it is of interest to understand how parasites are distributed among host populations, and if a sub-group of a population (i.e., males or females) could potentially be more susceptible to infection than others. There are both ecological and biological reasons behind reports of males being more likely to be parasitized than females. Males and females exhibit differences in the quantity of food consumed, their body size, behaviors (e.g., territoriality, aggression) and hormones. In vertebrates, sex hormones often mediate hierarchal social relationships and those with the highest levels of these sex hormones are usually at the greatest risk of parasite infection. As part of a baseline study, two to three year old Fundulus heteroclitus L. were collected biannually from seven salt marshes, six within New Jersey (Tuckerton, Sandy Hook, Union Beach, Piles Creek, Mill Creek, and Richard W. DeKorte Park) and one in Long Island, New York (Bullhead Bay) over a two year period. Five organ systems (gills, body cavity, digestive tract, swim bladder, and liver) were examined to determine endoparasite prevalence, species richness and abundance.
Results/Conclusions
A total of 280 fish (138 males and 142 females) were collected in Year 1 (67 male and 73 female) and Year 2 (71 male and 69 female). Using a MANOVA, no significant difference (Wilks’ Lambda P > 0.05) in overall parasite abundance between sexes was found. However, a significant difference was found for the digestive tract (p=0.044, F1,138=4.12) between males and females in Year 1. On average, females had more gut parasites (mean=31.3 ±6.9SE) than their male counterparts (mean=11.2 ±7.2SE). This was due to a surge in number of unidentified digenean trematodes in the guts of female Sandy Hook fish. Two possibilities explaining this sex-biased increase in infection include differences in hormonal levels accompanying reproductive status that can increase the susceptibility of females to parasites and pathogens, or sexual size dimorphism since female Fundulus tend to be larger than their male counterparts. Thus, it may be that the larger sex is infected because of its larger body size and not because of sexual differences per se.