Seminar Schedule

ON THE ORIGINS OF DORYLAIMIDA: A TALE WITH TEETH

Mullin, P.G. Department of Plant Pathology, University of Nebraska

In any given terrestrial soil sample, a significant proportion of the nematodes present will be "free living" forms. The majority of these are often representatives of the subclass Dorylaimia, which includes the orders Dorylaimida and Mononchida. Dorylaimida are considered by many workers to be the most diverse order of soil nematodes, and can be found in all habitats worldwide. The origins and deep phylogenetic relationships of this order, however, have not been clearly determined. Some have proposed the evolution of both Dorylaimida (via the Nygolaimina) and Mononchida from a common ancestor resembling modern Bathyodontidae, while others have envisioned a more basal position for the Mononchida, which then gave rise to the bathydontids and subsequently the Dorylaimida (again via the nygolaims). Phylogenetic analyses using 18s SSU rDNA suggest that bathyodontids share common ancestry with a combined clade comprising Mononchida and Mermithida, and that the origins of Dorylaimida predate the divergence of Bathydontidae and the mermithid-mononchid lineage. Since many of the nematodes classified in Dorylaimia are soil predators, discussion of key adaptations will center on modifications of feeding apparatus that facilitate this mode of existence. Subsequent adaptation of these structures in the Dorylaimida has allowed this group to diversify and exploit a wide range of terrestrial ecological niches.