Title: PHYLOGENETIC STRUCTURE WITHIN THE OSTERTAGUNAE (NEMATODA: TRICHOSTRONGYLOIDEA) INFERRED FROM MITOCHONDRIAL AND RIBOSOMAL DNA REPEAT SEQUENCES WITH COMPARISONS OF TWO SPECIES PAIRS OF OSTERTAGIA
Submitted to: Journal of Parasitology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: May 1, 1998
Publication Date: N/A
Interpretive Summary: Several Ostertagia parasites that infect cattle always appear in pairs. Scientists have proposed that parasites making up these pairs are, nonetheless, separate species since they can be morphologically distinguished and have maintained these characteristic identities even though they always appear together. We initiated a DNA sequence analysis o these ostertagines as well as other parasite groups exhibiting the same "species pairs" phenomenon to study their level of genetic similarity. Results indicated that the putative "species pairs" are more similar to each other then to other parasites of the same genus and should therefore be grouped together phylogenetically. This data further supports a "dimorphic species" concept within this genus and will greatly assist in the diagnosis of this highly pathogenic group of cattle parasite.
The mitochondrial (mt) DNA derived cytochrome oxidase I gene (COX-1) and the first internal transcribed spacer DNA (ITS-1) along with the 5.8S ribosomal DNA (rDNA) were enzymatically amplified, cloned and sequenced from five nominal species of Ostertagia as well as Teladorsagia circumcincta, Haemonchus contortus and Haemonchus placei. Mitochondrial DNA sequence data and predicted COX-1 protein sequences were 393 base pairs (bp) and 131 amino acids in length, respectively. The substantial numbers of synonymous substitutions occurring within the mtDNA required analysis of this data at the predicted protein level. The ITS-1/5.8S rDNA consensus sequences ranged from 544 bp T. circumcincta) to 556 bp (H. placei). Pairwise analysis of sequence data showed the highest degree of similarity between the proposed dimorphic species of Ostertagia. Analysis by maximum parsimony of both rDNA and COX-1 protein data also recognized O. ostertagi/O. lyrata and O. mossi/ O. dikmansi as pairs of dimorphic species and supported monophyly of these ostertagiines relative to representatives of the haemonchine outgroup. In the single most parsimonious tree from ITS-1/5.8S rDNA data and in the consensus of three trees from COX-1 protein data, a clade of Ostertagia spp. were identified which all possess parallel synlophes, long esophageal valves and which typically occur in cervid hosts.