Submitted to: Journal of Parasitology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: August 28, 2004
Publication Date: October 13, 2004
Citation: Hoberg, E.P., Abrams, A. 2004. Pseudostertagia bullosa (Nematoda: Trichostrongyloidea) in artiodactyl hosts from North America: Redescription and comments on systematics. Journal of Parasitology. 91:370-381. Interpretive Summary: Abomosal nematodes in sheep, cattle and wild ruminants continue to represent significant pathogens and parasites in both managed and natural ecosystems across North America. Understanding evolutionary relationships and host associations continues as a cornerstone in our progress to document the impacts of these parasites on food animals. We conducted detailed studies of morphology of the nematode Pseudostertagia bullosa from Montana and Wyoming, contributing to a more refined knowledge of distribution and occurrence. Research focused on the cuticular ridge systems that occur on the surface of the body in these nematodes. We found that patterns typical in Pseudostertagia are both unique, and at the same time share similarities with other nematodes that occur in the abomasum. The ridge system, or synlophe in Pseudostertagia is unique and can be important in providing the basis for identification of both male and female specimens. Additionally it is apparent that the restricted geographic range of P. bullosa may be determined by the distribution of its apparently specific host, the Pronghorn. Pseudostertagia bullosa appears to be a species that has survived in the pronghorn, Antilocapra americana, a relictual pecoran artiodactyl that occurs in dry regions of western North America. The parasite may also occur in mixed infections with a number of ostertagiines in the abomasa of mule deer (Odocoileus hemionus) and domestic sheep (Ovis aries) in regions of common rangelands for pronghorn and these artiodactyls hosts. These observations serve to emphasize the mosaic nature of the parasite fauna in pronghorn and other artiodactyls across North America. Additionally, the free-living stages of this species of nematode may be adapted to dry environments in such a way as to prevent the establishment P. bullosa following the translocation of suitable hosts. Such could account for its absence in O. aries from more humid regions to the east and in the Pacific Northwest, and from black-tailed deer on the west coast of North America. In the context of ecological perturbation associated with climate warming, we may anticipate altered host and geographic associations for P. bullosa and an array of other nematodes in artiodactyls.
Technical Abstract: Relationships of the trichostrongyloid, Pseudostertagia bullosa have been enigmatic. Studies of the synlophe in males and females of P. bullosa revealed a tapering system anterior to the cervical papillae, and a pattern of parallel ridges extending to near the caudal extremity in both lateral and ventro-dorsal fields. Structurally the synlophe differs considerably from that seen among the Cooperiinae, and exhibits homoplasy with respect to ridge systems among some Ostertagiinae. Other structural characters due to symplesiomorphy, homoplasy or because they represent autapomorphies do not serve to reveal the putative relationships for P. bullosa among the trichostrongyloids. Although somewhat equivocal, the 2-2-1 pattern of the bursa and position of rays 2 and 3 suggest an association with the Cooperinae as postulated by M.-Cl.Durette-Desset and others. Pseudostertagia bullosa appears to be a species that has survived in the pronghorn, Antilocapra americana, a relictual pecoran artiodactyl that occurs in xeric regions of western North America; pronghorn are the sole remnant of the late Tertiary radiation for Antilocapridae across North America. It may occur in mixed infections with a number of ostertagiines in the abomasa of mule deer (Odocoileus hemionus) and domestic sheep (Ovis aries) in regions of sympatry for pronghorn and these artiodactyls hosts.