Submitted to: Journal of Parasitology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: May 27, 1994
Publication Date: N/A
Interpretive Summary: The Trichostrongylidae is one of the most economically important groups of nematodes which parasitize ruminants throughout the world. However, largely unresolved phylogenetic relationships of the Trichostrongylidae have limited our understanding of host associations, modes of pathogenesis, and parasite biology. Additionally, an understanding of this fauna will yield insights into the production, maintenance and distribution of biodiversity. Phylogenetic analyses of the Trichostrongylidae were completed to: 1) define monophyly for the family; 2) examine relationships among the 6 subfamilies; 3) define the relationship of the Ostertagiinae and Graphidiinae; 4) consider the implications of subfamily phylogeny for trends in character evolution; and 5) begin preliminary assessments of host, habitat, and biogeographic associations of parasites. In as much as systematics forms the foundation for prediction, assessment of the relationships of the trichostrongylids based on phylogenetic analysis at the subfamilial level can form the infrastructure for a more refined understanding of nematode behavior, parasite-host coevolution, and biogeography.
Phylogenetic analysis of the Trichostrongylidae was conducted and a single cladogram, CI=76.7%, resulted from analysis of 22 morphological attributes. Monophyly for the family was defined by the structure of the female tail and copulatory bursa. Two major clades are recognized: the Cooperiinae-clade with the basal Cooperiinae and Libyostrongylinae + Trichostrongylinae and the Graphidiinae-clade with the basal Graphidiinae and Ostertagiinae + Haemonchinae. In comparison, dendrograms presented by Durette-Desset (1985) (CI=57.5%) and Lichtenfels (1987) (CI=60.5%) were found to be relatively inefficient in describing character evolution and in supporting putative relationships among the subfamilies and as such contained minimal phylogenetic information. These latter analyses were largely based on interpretations of single characters, overall similarity, combinations of shared primitive characters and orthogenetic concepts in contrast to the present study. Based on putative relationships developed in the current study, we postulate that the intestine constituted the ancestral habitat for the trichostrongylids and that the stomach/abomasum was independently colonized in each clade. An assessment of host-associations suggests extensive colonization, but also a high degree of coevolution with Bovidae and Cervidae for Ostertagiinae + Haemonchinae in the diversification of this fauna. Biogeography is complex, but this analysis is compatible with a Palearctic or Eurasian origin for Cooperiinae, Haemonchinae and Ostertagiinae.