Molecular investigation of Campula oblonga (Cobbold, 1858) reveals complex evolutionary history of parasites within the family Brachycladiidae (Odhner, 1905), parasites of wild cetaceans.

Abstract

Speciation in parasites of marine mammals represents an important yet relatively understudied facet of marine research.Evolutionary and ecological interactions between the trematode family Brachycladiidae and their cetacean definitive hosts have previously been investigated at family level, but not at genus level.Using the molecular markers NADH dehydrogenase subunit 3 (mtND3) and 28s, the Brachycladiidae family are utilised as a model to study speciation and divergence events that underpin variation within parasites of marine mammals, with issues surrounding accurate taxonomy and the extent to which specific parasite species can utilise multiple definitive hosts.Specifically, Campula oblonga was investigated; a cosmopolitan, globally distributed brachycladiid liver fluke, capable of infecting multiple Phocoenidae species, but also considered to be phylogenetically challenging.Here, it is found that C. oblonga is in fact several cryptic species and that divergence is ultimately linked to the evolutionary histories and ecological traits of the specific host population or species.These findings indicate that parasite speciation occurs across spatial and host species scales, illustrating the importance of not only geographical isolation but also host specialisationwith potential applications for cetacean conservation, utilising patterns of parasite speciation and divergence as evidence of host evolutionary history.This study also highlights issues with the current classification of brachycladiid parasites within the genera Oschmarinella and Orthosplanchnus, proving recommendations for future studies to fully resolve brachycladiid phylogeny.