Numerical and functional responses of intestinal helminths in three rajid skates: evidence for competition between parasites?

Abstract

SUMMARYHost-parasite interactions generally involve communities of parasites. Within these communities, species will co-exist and/or interact with one another in a manner either benefiting the species involved or to the detriment of one or more of the species. At the level of helminth infracommunities, evidence for intra- and inter-specific competition includes numerical responses, i.e. those regulating helminth intensity of infection, and functional responses, i.e. where the presence of competitors modifies the realised niche of infrapopulations. The objectives of this study are to assess the numerical and functional responses of helminths in infracommunities from 3 rajid skates using general linear models. Despite a lack of numerical responses, functional responses to intra- and inter-specific interactions were observed. A positive correlation between the number of individuals in an infrapopulation and its niche breadth (functional response) was observed for the tapewormsPseudanthobothriumspp. andEcheneibothriumspp., in all their respective hosts, and for the nematodePseudanisakissp. in the little skate. Evidence for inter-specific competition includes niche shifts inPseudanthobothrium purtoni(exlittle skate) andPseudanisakissp. (exthorny skate) in the presence ofPseudanisakissp. and the tapewormGrillotiasp., respectively. These results are consistent with other studies in providing evidence for competition between helminths of skates.