Phylogenetic relationships of species within the tribe Labiostrongylinea (Nematoda: Cloacinidae) from Australian marsupials based on ribosomal DNA spacer sequence data

Abstract

Parasitic nematodes of the tribe Labiostrongylinea (Family Cloacinidae) occur in the stomachs of a wide variety of potoroid and macropodid marsupials in Australia, Papua Indonesia and Papua New Guinea. The aim of the present study was to infer the evolutionary relationships of the five genera of labiostrongyline nematodes that occur in Australian potoroids and macropodids using sequence data of the nuclear first and second internal transcribed spacers of ribosomal DNA. The phylogenetic analyses resulted in the separation of the Labiostrongylinea into two major groups reflecting coevolution between hosts and parasites. Two nematode species belonging to the genus Potorostrongylus formed a sister group to the remaining species of the Labiostrongylinea. This genus occurs exclusively in potoroid marsupials, which are considered to be basal to the macropodid marsupials. The second major group included species of Labiostrongylus, Labiosimplex, Labiomultiplex and Parazoniolaimus, all of which occur in macropodids. These species formed two distinct clades, one predominating in the host genera Thylogale and Onychogalea, and the second in the genus Macropus, which includes the more recent macropodids. However, there is also evidence of colonisation by both nematode clades of relatively unrelated hosts. In addition, genetic differences among individuals of Lm. eugenii from geographically isolated populations of M. eugenii, and among Ls. longispicularis from different subspecies of M. robustus suggest the existence of sibling species that may have arisen by allopatric speciation. The broad coevolutionary relationship between the labiostrongyline nematodes and their marsupial hosts therefore represents a mixture of potential cospeciation and colonisation events.