Mitochondrial DNA Evidence Supports the Hypothesis that Triodontophorus Species Belong to Cyathostominae

Abstract

Equine strongyles, the significant nematode pathogens of horses, are characterized by high quantities and species abundance, but classification of this group of parasitic nematodes is debated. Mitochondrial (mt) genome DNA data are often used to address classification controversies. Thus, the objectives of this study were to determine the complete mt genomes of three Cyathostominae nematode species (Cyathostomum catinatum, Cylicostephanus minutus, and Poteriostomum imparidentatum) of horses and reconstruct the phylogenetic relationship of Strongylidae with other nematodes in Strongyloidea to test the hypothesis that Triodontophorus spp. belong to Cyathostominae using the mt genomes. The mt genomes of Cy. catinatum, Cs. minutus, and P. imparidentatum were 13,838, 13,826, and 13,817 bp in length, respectively. Complete mt nucleotide sequence comparison of all Strongylidae nematodes revealed that sequence identity ranged from 77.8 to 91.6%. The mt genome sequences of Triodontophorus species had relatively high identity with Cyathostominae nematodes, rather than Strongylus species of the same subfamily (Strongylinae). Comparative analyses of mt genome organization for Strongyloidea nematodes sequenced to date revealed that members of this superfamily possess identical gene arrangements. Phylogenetic analyses using mtDNA data indicated that the Triodontophorus species clustered with Cyathostominae species instead of Strongylus species. The present study first determined the complete mt genome sequences of Cy. catinatum, Cs. minutus, and P. imparidentatum, which will provide novel genetic markers for further studies of Strongylidae taxonomy, population genetics, and systematics. Importantly, sequence comparison and phylogenetic analyses based on mtDNA sequences supported the hypothesis that Triodontophorus belongs to Cyathostominae.

The complete mitochondrial genome of Coronocyclus labratus (Rhabditida: Cyathostominae)

“…Species of genus Triodontophorus (T. brevicauda, T. serratus, and T. nipponicus) clustered together with species in subfamily Cyathostominae, although they belonged to subfamily Strongylinae. The dendrogram topology is highly congruent with previous studies (Gao. et al 2017;Li et al 2019).…”

According to mitochondrial DNA evidence, Parascaris equorum and Parascaris univalens may represent the same species

“…Phylogenetic analyses were conducted using two methods: Bayesian inference (BI) and maximum likelihood (ML) (Guindon & Gascuel, 2003; Ronquist & Huelsenbeck, 2003). Selected models and detailed process were as previously described in Gao et al (2017). Phylograms were drawn using Tree View v. 1.65 (Page, 1996).…”

“…In the early 1980s, cytological techniques distinguished P. equorum and P. univalens by the number of chromosomes, but this was not verified in a veterinary parasitology study (Jabbar et al , 2014). The mitochondrial (mt) genome has been widely used as a genetic marker in the identification and differentiation of closely related species (Lin et al , 2012; Liu et al , 2012; Gao et al , 2017). However, to date, only 14 mt genomes of horse parasitic nematodes have been reported.…”

Comparative analyses of the complete mitochondrial genomes of Cyathostomum pateratum and Cyathostomum catinatum provide new molecular data for the evolution of Cyathostominae nematodes

“…Previous studies on Cyathostominae nematodes have focused mainly on their morphology, life history and epidemiology (Lichtenfels et al ., 2008; Stancampiano et al ., 2017), and thus genetic information is limited. Genetic markers, such as the internal transcribed spacer (ITS) of the nuclear ribosomal DNA region and mitochondrial genome sequences, have been used for the genetic classification and evolutionary analysis of cyathostomins (Hung et al ., 2000; Gao et al ., 2017a, b).…”

“…Cyathostominae nematodes are a complex nematode group, with 51 reported species. The mt genomes of only six Cyathostominae species ( Cylicostephanus goldi , Cylicostephanus minutus , Cylicocyclus nassatus , Cylicocyclus insigne , Cyathostomum catinatum and Poteriostomum imparidentatum ) have been sequenced to date (Gao et al ., 2017a, b). Cyathostomum pateratum is one of the most common cyathostomins in equine species, but there are insufficient mtDNA sequence data available to determine its phylogenetic relationships with other species.…”