Larval parasite gene sequence data reveal cryptic trophic links in life cycles of porbeagle shark tapeworms

Abstract

The lack of information on marine tapeworm life cycles can be addressed with knowl- edge derived from trophic interactions in marine environments. These trophically transmitted para- sites exploit transmission routes involving predator-prey interactions. Porbeagle sharks Lamna nasus are apex predators feeding on a wide range of organisms, including teleosts and cephalopods. Although the biology of this shark species is relatively well studied, there is a surprising lack of infor- mation about the trophic interactions involving this species that lead to the acquisition of tapeworms. Recently, the use of molecular tools, combined with phylogenetics, has proven useful in identifying trophic links involved in the transmission of marine tapeworms. In the present study, we used sequence data from the D2 domain of the large subunit ribosomal DNA to link adult tapeworms of the species Clistobothrium cf. montaukensis and Dinobothrium sp. parasitising porbeagle sharks to lar- vae recovered from the squid Doryteuthis gahi. To the best of our knowledge, it is the first to provide empirical evidence for a trophic link between porbeagle sharks and D. gahi as a definitive route for the successful transmission of these tapeworms. Furthermore, our data suggest an ontogenetic shift in diet away from squid. Parasite abundance data in D. gahi indicate that the abundance of porbea- gle sharks can be significant in some years.