The complete mitochondrial genome of the Mexican-endemic cavefish Ophisternon infernale (Synbranchiformes, Synbranchidae): insights on patterns of selection and implications for synbranchiform phylogenetics

" Ophisternon infernale is one of the 200+ troglobitic fish species worldwide, and one of the two cave-dwelling fishes endemic to the karstic aquifer of the Yucatán Peninsula, Mexico. Because of its elusive nature and the relative inaccessibility of its habitat, there is virtually no genetic information on this enigmatic fish. Herein we report the complete mitochondrial genome of O. infernale, which overall exhibits a configuration comparable to that of other synbranchiforms as well as of more distantly related teleosts. The KA/KS ratio indicates that most mtDNA PCGs in synbranchiforms have evolved under strong purifying selection, preventing major structural and functional protein changes. The few instances of PCGs under positive selection might be related to adaptation to decreased oxygen availability. Phylogenetic analysis of mtDNA comparative data from synbranchiforms and closely related taxa (including the indostomid Indostomus paradoxus) corroborate the notion that indostomids are more closely related to synbranchiforms than to gasterosteoids, but without rendering the former paraphyletic. Our phylogenetic results also suggest that New World species of Ophisternon might be more closely related to Synbranchus than to the remaining Ophisternon species. This novel phylogenetic hypothesis, however, should be further tested in the context of a comprehensive systematic study of the group "