Phylogeny, genetics, and the partial life cycle of Oncomegas wageneri in the Gulf of Mexico

Despite the diversity and ecological importance of cestodes, there is a paucity of studies on their life stages (i.e., complete lists of intermediate, paratenic, and definitive hosts) and genetic variation. For example, in the Gulf of Mexico (GoM) 98 species of cestodes have been reported to date; however, data on their intraspecific genetic variation and population genetic studies are lacking. The trypanorhynch cestode, Oncomegas wageneri, is found (among other places) off the American Western Atlantic Coast, including the GoM, and has been reported as an adult from stingrays and from several teleost species in its larval form (as plerocerci). This study represents the first report of 2 previously unregistered definitive hosts for O. wageneri, namely the Atlantic sharpnose shark Rhizoprionodon terraenovae and the southern stingray Hypanus americanus. In this work, partial sequences of the 28S (region D1–D2) ribosomal DNA were analyzed to include O. wageneri within an eutetrarhynchoid phylogenetic framework. All O. wageneri individuals (which included plerocerci and adults) were recovered as monophyletic and Oncomegas celatus was identified as the sister species of O. wageneri. Furthermore, population genetic analyses of O. wageneri from the southern GoM were carried out using DNA sequences of the mitochondrial cytochrome c oxidase subunit 1 (COI) gene, which reflected high genetic variation and a lack of genetic structure among the 9 oceanographic sampling sites. Based on these results, O. wageneri is panmictic in the southern GoM. More extensive sampling along the species entire distribution is necessary to make more accurate inferences of population genetics of O. wageneri.