Molecular phylogeny of the Pseudaliidae (Nematoda) and the origin of associations between lungworms and marine mammals.

Metastrongyloid lungworms from the family Pseudaliidae infect the lungs and cranial sinuses of cetaceans worldwide, except , which exhibits a striking terrestrial association with the Egyptian mongoose, . Previous phylogenies of the Metastrongyloidea that included some (2-7) marine species of the Pseudaliidae confirmed that these species are closely related, but also grouped species of (family Filaroididae) between the members of the Pseudaliidae. In this study we extracted DNA from representatives of all six genera of the Pseudaliidae and amplified the second internal transcribed spacer (ITS2) and cytochrome oxidase subunit I () genes in order to investigate the concept of the Pseudaliidae as a monophyletic unit. Three species of were also included in the analysis. Maximum Likelihood and Bayesian Inference analyses of the concatenated genes resulted in a well-supported clade including the marine pseudaliids, and spp. These findings validate the status of as a pseudaliid species and support the inclusion of in the Pseudaliidae. Although males of spp. lack a copulatory bursa, this trait itself is highly variable in the Pseudaliidae, which include abursate species. Furthermore, life cycles seem to be closely similar between both taxa. When all the available phylogenetic data on the Metastrongyloidea were mapped of onto a phylogeny of the Laurasiatheria, there was a strong suggestion that the Pseudaliidae may have descended from ancestors infecting terrestrial carnivores, with odontocetes being colonized in the marine realm as a result of a host-switching event from pinnipeds through shared fish prey. The origin of the association between and mongooses remains uncertain.