Natural hybridization and gene flow between two Tridentiger gobies in LakeHinuma (Ibaraki Prefecture, Japan)

Of 851 specimens of Trinentiger obscurus and T. brevispinis collected from Lake Hinuma (Ibaraki Prefecture, Japan) from July 1996 to February 1998, 49 (5.8%) comprised F-1 hybrids and backcross progeny of the two species. Sin ce the mitochondrial DNA haplotypes of the F-1 hybrids reflected those of T . brevispinis, most instances of hybridization are thought to have occurred between male T. obscurus and female T. brevispinis. Although both allozyme and mitochondrial DNA analyses indicated backcrossing and introgression of mitochondrial DNA, the frequency of backcross progeny was relatively low, suggesting the existence of a natural selection to backcrossing.