Multiregional introgressions inferred from the mitochondrial DNA phylogeny of a hybridizing species complex of gobiid fishes, genus Tridentiger

Partial sequences of the cytochrome b gene (402 bp) in mtDNA weredetermined for brackishwater gobiid fishes, genus Tridentiger, collectedfrom geographically distant locations in the Japanese Archipelago, andtheir interspecific and geographic variations were analyzed and compared.Contrary to the results of a previous allozyme analysis which revealed theexistence of considerable genetic divergence (Nei's genetic distance >0.5) between T. obscurus and T. brevispinis, the mtDNA haplotypes(mitotypes) of these two species were very similar and could not bedistinguished by any of the neighbor- joining, maximum-likelihood orparsimony analyses. Hybrid individuals between the two species were alsofound, with several mitotypes being shared by both species and theirhybrids. The phylogenetic relationships of mitotypes were divided intothree subgroups, the geographical distributions of the latter being alliedto geographical features of the Archipelago. These results suggested theoccurrence of multiregional introgression between the two species, withmitotypes transferring from one species to the other.