Subterranean temnocephalid flatworms of the Dinaric Karst are not picky about the hosts but compete for them: an analysis of literature data

Epizoic-host species interactions in subterranean environments are rare and poorly understood. A little-known case of epizoic-host interaction involves flatworms (Temnocephalidae) and large subterranean crustaceans (cave shrimps of the family Atyidae and amphipods of the genus Niphargus ) living along the Dinaric Karst. The taxonomy and distribution of Dinaric temnocephalids were thoroughly studied in the previous century. There are 15 subterranean temnocephalid species living on different crustacean species in the area. However, analyses of associations between epizoic and host species, as well as co-occurrence of epizoic species, are lacking. In this study, we extracted literature data and analysed epizoic-host interactions using network analysis, complemented by co-occurrence patterns among temnocephalid species. The network analysis indicates low host specificity between temnocephalids and crustaceans; one species is specialized on Niphargus , whereas the others attach to different cave shrimp species. Of these, only one species seems to be specialized to a specific host body part, while the rest can attach to different body parts of cave shrimps. The analysis of co-occurrence patterns implies that many temnocephalid species pairs generally compete for their hosts. We conclude that epizoic-host specificity in subterranean temnocephalids, detectable at the order level, evolved long ago, and that most species cannot be highly specialized due to oligotrophic conditions in caves. As a result, there is substantial competition among them for a host. We discuss potential caveats of the study based solely on the literature and provide a roadmap for future research.