Characteristics of Complete Mitochondrial Genomes Reveals a Potential Division of Genus Modiolus into Three Genera

Backgrounds Mussels have been one of the most abundant and highly evolved marine biological groups with high level of genetic differentiation between and within species. The yellow-banded horse mussel, Modiolus modulaides (Röding, 1798), is an important economic species in Philippines and an endangered species in Japan, with no whole mitogenome characterized. Methods and Results In this study, we sequenced the whole mitochondrial genome of Modiolus modulaides (Röding, 1798), a medium-sized mussel collected from Guangxi, China. Result shows a 15,422 bp closed-circular DNA molecule, including 12 protein-coding genes, 22 transfer RNA genes and two ribosomal RNA genes. The genome composition is obviously A+T biased (62.5%), with 23.1% A, 39.4% T, 25.4% G and 12.0% C, making AT-skew and GC-skew being -0.26 and 0.36, respectively. Phylogenetic analysis of Modiolus modulaides and other 36 mussel species based on 12 protein-coding genes and two ribosomal RNAs of mitogenomes shows that Modiolus modulaides is most closely related with Modiolus phillippinum (Hanley, 1843).Conclusions A hypothesis that the current genus Modiolus should be separated three distinctive genera was raised based on morphological and phylogenetic characteristics, as well as gene patterns of mitogenomes. These results put forward new insight of phylogenetic relationship of Modiolus species and will help to further study the taxonomy and phylogeny of Mytilidae.