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 were dete rmined for brackishwater gobiid fishes, genus Tridentiger, collected f rom geographically distant locations in the Japanese Archipelago, and their interspecific and geographic variations were analyzed and compar ed. Contrary to the results of a previous allozyme analysis which reve aled the existence of considerable genetic divergence (Nei's genetic d istance > 0.5) between T. obscurus and T. brevispinis, the mtDNA haplo types (mitotypes) of these two species were very similar and could not be distinguished by any of the neighbor-joining, maximum-likelihood o r parsimony analyses. Hybrid individuals between the two species were also found, with several mitotypes being shared by both species and th eir hybrids. The phylogenetic relationships of mitotypes were divided into three subgroups, the geographical distributions of the latter bei ng allied to geographical features of the Archipelago. These results s uggested the occurrence of multiregional introgression between the two species, with mitotypes transferring from one species to the other.