Molecular Phylogeny of a Red-snow-crab Species Complex Using Mitochondrial and Nuclear DNA Markers

Nucleotide sequence variation of mitochondrial DNA COI and nuclear rRNA gene regions was used to reconstruct phylogenetic relationships for the red-snow-crab species complex, including the red snow crab, Chionoecetes japonicus, its nominal subspecies, C. japonicus pacificus, and the triangle tanner crab, C. angulatus. The topologies of the Bayesian and neighbor-joining (NJ) trees of the COI and of NJ trees of rRNA sequences placed C. japonicus and C. angulatus in a single clade. The net sequence divergence between these taxa was d(net) = 0.000 in COI, and strongly suggests that these taxa represent a single species. In contrast, haplotypes in C. j. pacificus clustered separately from the C. japonicus - C. angulatus clade. Net sequence divergence from C. japonicus - C. angulatus to C. j. pacificus was d(net) = 0.026 in COI, indicating that C. j. pacificus should be elevated to a separate species, C. pacificus. A 165 bp insert appeared in the rRNA gene of C. j. pacificus, but was absent in the remaining species of Chionoecetes. This autapomorphic condition in C. j. pacificus adds support for an independent evolution of this taxon. Evolutionary divergences between these taxa may reflect contrasting evolutionary process influenced by ocean bathymetry.