PHYLOGENETIC SYSTEMATIC ANALYSIS OF THE TRICHOSTRONGYLIDAE (NEMATODA), WITH AN INITIAL ASSESSMENT OF COEVOLUTION AND BIOGEOGRAPHY

Phylogenetic analysis of the subfamilies of the Trichostrongylidae bas ed on 22 morphological transformation series produced a single cladogr am with a consistency index (CI) = 74.2%. Monophyly for the family was supported by the structure of the female tail and copulatory bursa. T wo major clades are recognized: the Cooperiinae clade with the basal C ooperiinae and Libyostrongylinae + Trichostrongylinae, and the Graphid iinae clade with the basal Graphidiinae and Ostertagiinae + Haemonchin ae. Dendrograms presented by Durette-Desset (1985) (CI = 56.1%) and Li chtenfels (1987), based on the key to the Trichostrongylidae by Gibbon s and Khalil (1982) (CI = 59.0%), were found to be relatively ineffici ent in describing character evolution and in supporting putative relat ionships among the subfamilies. Based on the current analysis, the int estine appears to have constituted the ancestral habitat for the trich ostrongylids with the stomach/abomasum having been independently colon ized in each clade. Assessment of host associations suggests extensive colonization but also a high degree of coevolution with Bovidae and C ervidae for Ostertagiinae i Haemonchinae. Biogeography for this assemb lage is complex, but this analysis is compatible with a Palearctic or Eurasian origin for Cooperiinae, Haemonchinae, and Ostertagiinae.