Does host diet govern the structure and diversity of tapeworm assemblages in sharks? Insights from the literature and a model shark species; Cephaloscyllium isabellum

Abstract

Previous research has shed some light on what phylogenetic and ecological factors may be important determinants of tapeworm parasite diversity in elasmobranchs (sharks, skates and rays). However, several potentially key factors for tapeworm transmission, including the breadth and composition of host’s diets, have been recognised as crucial gaps in our understanding.

The main objective of this research was to investigate the relative importance of sharks’ diets for the structure and diversity of their tapeworm assemblages. First, the literature was searched for information on tapeworms and host features for a large subset of different shark species, and aspects of shark’s diets (including their diet breadth, diet composition and trophic level) were assessed for their relative importance as predictors of tapeworm diversity. Second, literature records were used to conduct a comprehensive analysis of the relationship between shark’s diet compositions and tapeworm compositions. Finally, the importance of host diet was examined as a potential encounter filter for restricting tapeworm diversity in a model shark species, Cephaloscyllium isabellum.

The results of this study revealed diet breadth to be a key predictor of tapeworm richness in sharks, indicating that sharks with broader diets generally harbour more tapeworm species. The composition of tapeworms infecting a shark species was found to be related to its diet composition, and moreover, certain tapeworm taxa were found to be useful indicators of the host species' ecology and evolutionary history. The research on C. isabellum here offered only limited insights into the potential importance of diet as an encounter filter for the shark, but provided some new important data on both the diet and parasites of this species.

Ultimately, the observational studies carried out within this research emphasise that aspects of sharks’ diets can have important implications for their tapeworm parasite assemblages. Further exploration of these patterns with experimental research may be able to validate the influence of these patterns in nature.