Comparative study on morphological traits and mitogenomes of the genus Echinolaelaps

The genus Echinolaelaps is a group of large gamasid mites. Although only three species are currently known, its taxonomic status is controversial because the species within this genus have strikingly morphological similar characters except for the distance between genito-ventral plate and anal plate. The mitogenomes of the three known Echinolaelaps species range from 14,402 to 15,736 bp in size and share the common feature that the D-arm of trnS₁ and trnC is lacking. Notably, the lack of the D-arm in trnS₁ is common across metazoans, whereas its absence in trnC appears to be a unique, shared derived feature that unites the three Echinolaelaps species into a distinct clade, suggesting it may be a generic characteristic. Such mitogenomic data are valuable for phylogenetic estimation and molecular evolution. In particular, mitochondrial gene rearrangement pattern has been the hot topic in understanding evolutionary processes. Interestingly, the mitogenomes of all three Echinolaelaps species exhibit extensive gene rearrangements and two novel gene arrangement pattern. We found that three Echinolaelaps species share a comparable number of breakpoints with species in Laelapidae and Varroidae. Selection pressure analysis showed differences in rapidly evolving protein-coding genes of three Echinolaelaps species. Although no palindromic repeats directly associated with these rearrangements were detected, other repeat sequences were present. The phylogenetic analysis strongly supports the monophyly of the genus Echinolaelaps. However, the current data remain insufficient to conclusively resolve its precise taxonomic position within the family Laelapidae.