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
Irina Diekmann, Jürgen Krücken, Тetiana А. Kuzmina, Christina M. Bredtmann, Mariana Louro, Vitaliy A. Kharchenko, Thomas Tzelos, Jacqueline B. Matthews, Luís Madeira de Carvalho, Georg von Samson‐Himmelstjerna
Abstract
Morphologically, 64 strongylid species have been described in equines. Co-infections are common, with up to 29 species reported in a single horse. Morphological identification of these species is time consuming and requires expert knowledge due to their similar appearance. Therefore, non-invasive identification methods are needed. DNA barcoding offers a rapid and reliable tool for species identification and the discovery of cryptic species for these most common parasitic nematodes of equines. In total, 269 cytochrome c oxidase subunit I (COI) gene and 312 internal transcribed spacer 2 (ITS-2) sequences from 27 equine Strongylidae species, including sequences from two uncharacterised species, Coronocyclus sagittatus and Triodontophorus tenuicollis , were generated and combined with COI and ITS-2 sequences data from six Cyathostominae species from previous studies. This study represents a comprehensive DNA barcoding analysis of 22 Cyathostominae and six Strongylinae species using mitochondrial COI gene and ITS-2 sequences. Maximum likelihood phylogenetic trees were constructed and the intra- and interspecific genetic distances for both markers were compared. Analysis revealed complex phylogenetic relationships. Para- and polyphyletic relationships were observed among most genera within Strongylinae and Cyathostominae. This challenges current morphological classifications. Although both markers showed overlapping pairwise identities in intra- and inter-species comparisons, COI had higher discriminatory power than ITS-2. Expanding the COI and ITS-2 reference database, including the first sequences for Coronocyclus sagittatus and Triodontophorus tenuicollis, improve a reliable species identification and advanced studies on Strongylinae and Cyathostominae diversity using barcoding and metabarcoding. • Cytochrome oxidase I (COI) and internal-transcribed spacer 2 (ITS-2) evaluated. • New 269 COI & 312 ITS-2 sequences from 21 Cyathostominae & 6 Strongylidae species. • First molecular data for Coronocyclus sagittatus and Triodontophorus tenuicollis. • Complex, para- and polyphyletic relationships observed among most genera. • COI demonstrated higher discriminatory power than ITS-2 sequences.