Abstract
Cyathostomins are important intestinal nematode parasites of equines and include 50 accepted species. Their taxonomy has been frequently revised and the presence of cryptic species suggested. Furthermore, usually molecular- and morphology-based phylogenetic analyses give divergent results. In this study, the nucleotide sequences of the nuclear second internal transcribed spacer (ITS-2) and the mitochondrial partial cytochrome c oxidase subunit I (COI) were determined for adults of six cyathostomin species (Coronocyclus coronatus, Coronocyclus labiatus, Cylicocyclus nassatus, Cylicostephanus calicatus, Cylicostephanus longibursatus, Cylicostephanus minutus) collected from different equine species within two geographic regions. Maximum likelihood trees were calculated for ITS-2, COI, and concatenated data. No obvious differentiation was observed between geographic regions or equine host species. As previously reported, Coronocyclus coronatus and Cylicostephanus calicatus revealed a close relationship. Cryptic species were detected in Cylicostephanus minutus and Cylicostephanus calicatus. Cylicocyclus nassatus and Coronocyclus labiatus showed diverse mitochondrial and nuclear haplotypes occurring in different combinations, while Cylicostephanus longibursatus was comparatively homogenous. In conclusion, a combined analysis of nuclear and mitochondrial haplotypes improved resolution of the phylogeny and should be applied to the remaining cyathostomin species and across additional equine host species and geographic regions.
Highlights
Cyathostomins are important intestinal nematode parasites of equines and include 50 accepted species
Due to several problems in identification of cyathostomins to the species level summarized by Bredtmann et al.[11], little is known about the biology and ecology of individual species or how species interact with one another in the host or in the external environment
This study applies molecular methods to assess the utility of two different genes—the nuclear second internal transcribed spacer (ITS-2) and the mitochondrial partial cytochrome c oxidase subunit I (COI)—as barcode regions and the phylogenetic relationships of six common species of cyathostomins (Cor. coronatus, Cor. labiatus, Cyc. nassatus, Cys. calicatus, Cys. longibursatus, Cys. minutus)
Summary
Cyathostomins are important intestinal nematode parasites of equines and include 50 accepted species. The nucleotide sequences of the nuclear second internal transcribed spacer (ITS-2) and the mitochondrial partial cytochrome c oxidase subunit I (COI) were determined for adults of six cyathostomin species (Coronocyclus coronatus, Coronocyclus labiatus, Cylicocyclus nassatus, Cylicostephanus calicatus, Cylicostephanus longibursatus, Cylicostephanus minutus) collected from different equine species within two geographic regions. This study applies molecular methods to assess the utility of two different genes—the nuclear second internal transcribed spacer (ITS-2) and the mitochondrial partial cytochrome c oxidase subunit I (COI)—as barcode regions and the phylogenetic relationships of six common species of cyathostomins (Cor. coronatus, Cor. labiatus, Cyc. nassatus, Cys. calicatus, Cys. longibursatus, Cys. minutus). While for two pairs of species, previous publications have presented partial data sets[24], the present study includes two additional species, adds data derived from additional specimens for the previously studied species, and, most importantly, provides a complete analysis of intra- and interspecies variability over these six recognized species
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