Characterization of the complete mitochondrial genome of Marshallagia marshalli and phylogenetic implications for the superfamily Trichostrongyloidea

Abstract

Marshallagia marshalli (Nematoda: Trichostrongylidae) infection can lead to serious parasitic gastroenteritis in sheep, goat, and wild ruminant, causing significant socioeconomic losses worldwide. Up to now, the study concerning the molecular biology of M. marshalli is limited. Herein, we sequenced the complete mitochondrial (mt) genome of M. marshalli and examined its phylogenetic relationship with selected members of the superfamily Trichostrongyloidea using Bayesian inference (BI) based on concatenated mt amino acid sequence datasets. The complete mt genome sequence of M. marshalli is 13,891 bp, including 12 protein-coding genes, 22 transfer RNA genes, and 2 ribosomal RNA genes. All protein-coding genes are transcribed in the same direction. Phylogenetic analyses based on concatenated amino acid sequences of the 12 protein-coding genes supported the monophylies of the families Haemonchidae, Molineidae, and Dictyocaulidae with strong statistical support, but rejected the monophyly of the family Trichostrongylidae. The determination of the complete mt genome sequence of M. marshalli provides novel genetic markers for studying the systematics, population genetics, and molecular epidemiology of M. marshalli and its congeners.

Molecular analysis of polymorphic species of the genus Marshallagia (Nematoda: Ostertagiinae)

“…However, in the ITS2 phylogenetic analysis presented in Additional file 2: Figure S1, these two sequences are (i) not grouped closely together and (ii) also virtually identical to ITS2 sequences deposited in GenBank for other Marshallagia species. Based on the present findings it can be assumed that the complete mitochondrial genome reported by Sun et al [45] does not represent a M. marshalli but instead a M. mongolica sequence.…”

“…All available Marshallagia sequences come from only three studies. One from China [44] reporting 36 cox1 sequences, another Chinese study reporting a complete mitochondrial genome annotated as M. marshalli [45] and 13 sequences from the present study. [45].…”

“…One from China [44] reporting 36 cox1 sequences, another Chinese study reporting a complete mitochondrial genome annotated as M. marshalli [45] and 13 sequences from the present study. [45]. The fact that two species sequences (M. marshalli and M. occidentalis) both occur in two different clusters clearly indicates that at least some of the published specimens were morphologically misidentified.…”

“…All available Marshallagia sequences come from only three studies. One from China [ 44 ] reporting 36 cox 1 sequences, another Chinese study reporting a complete mitochondrial genome annotated as M. marshalli [ 45 ] and 13 sequences from the present study. The clusters I ( Ostertagia lanceata erroneously assigned to the genus Marshallagia by Lv et al [ 44 ] as indicated by Hoberg et al [ 2 ], IV ( M. occidentalis ) and V ( M. hsui ) contained only sequences reported by Lv et al [ 44 ].…”

“…The fact that two species sequences (M. marshalli and M. occidentalis) both occur in two different clusters clearly indicates that at least some of the published specimens were morphologically misidentified. Neither Lv et al [44] nor Sun et al [45] provided any morphological data for the specimens used to obtain their DNA sequences. Lv et al [44] not even mentioned the criteria used for identification or any species identification key while Sun et al [45] explicitly stated that morphological identification was difficult, and that molecular identification was used.…”