Comparative phylogenetic and sequence identity analysis of internal transcribed spacer 2 and cytochrome C oxidase subunit I as DNA barcode markers for the most common equine Strongylidae species.

The research focuses on the application of a DNA barcoding technique to identify and classify multiple species of parasitic nematodes (Strongylidae species) commonly found in horses. The study applies this method to two genetic markers, the mitochondrial cytochrome c oxidase subunit I (COI) and the internal transcribed spacer 2 (ITS-2), comparing their usefulness for such analysis.

Introduction of DNA Barcoding

• The researchers note that traditional identification and classification of the Strongylidae species, a common parasite found in horses, is complex and time-consuming due to their similar appearance.
• To overcome these challenges, the study utilises DNA barcoding, a molecular technique that allows for speedier and more reliable identification of species, and even the discovery of previously unknown species.

Data Collection

• A total of 269 COI and 312 ITS-2 sequences from 27 equine Strongylidae species were generated, including sequences from two previously uncharacterised species, Coronocyclus sagittatus and Triodontophorus tenuicollis.
• The newly generated sequence data was combined with existing COI and ITS-2 sequence data from an additional six Cyathostominae species for analysis.

Analysis of Results

• Analysis was conducted by constructing maximum likelihood phylogenetic trees (a method used to infer evolutionary relationships), and compared the intra-and interspecific genetic distances for both markers, COI and ITS-2.
• The analysis led to interesting revelations about the phylogenetic relationships of these species, including the discovery of para- and polyphyletic relationships amongst most genera within Strongylinae and Cyathostominae.
• Such results suggest that the current morphological classifications of these species may need re-evaluation.

Findings

• Both COI and ITS-2 showed overlapping pairwise identities in intra- and inter-species comparisons. However, COI demonstrated higher discriminatory power than ITS-2.
• The contribution of new sequence data, especially for the two previously uncharacterised species, expanded the COI and ITS-2 reference database.
• The findings of the study indicated that DNA barcoding, especially with the COI gene, can improve species identification and lead to advanced studies on Strongylinae and Cyathostominae diversity using barcoding and metabarcoding.