Nematodes are one of the most diverse groups of organisms, but much of their evolutionary history remains unresolved. Genetic tools have greatly advanced this field, especially in cases of cryptic diversity. Here, we reconstructed the mitogenomes of four parasitic nematodes, each from a different genus of the family Pharyngodonidae (Nematoda: Oxyuroidea): Spauligodon, Pharyngodon, Parapharyngodon, and Thelandros. For each species, whole genome sequencing was performed, using an Illumina HiSeq 2500 platform. Mitochondrial genomes were reconstructed using both reference-based mapping and bait-based iterative assembly approaches. The resulting mitogenomes were 13,692 to 16,700 bp long, included 12 protein-coding genes, 22 tRNAs and the 12S and 16S rRNA regions and all lacked the ATP8 gene. All genes were on the same strand and in the same orientation, which is congruent with the composition and organization observed in other oxyurid nematodes. Also as observed in other nematode groups, the four mitogenomes exhibited major differences in gene order. It is still unknown what promotes such extensive gene order rearrangements within nematodes, even amongst related groups, but it is expected to influence the rates of evolution, especially for parasitic species, and help to explain their impressive diversity.
Tomé et al. (Thu,) studied this question.