Systematic Implications of Hybridization Experiments with Some Eurasian Treefrogs (Genus Hyla)

Thirteen kinds of interspecific and intraspecific crosses were performed with Eurasian treefrogs of the genus Hyla. Progeny of eight kinds of interspecific crosses (between females of H. japonica and males of H. hallowellii, H. chinensis, H. suweonensis, H. savignyi, H. meridionalis, H. arborea arborea and H. arborea sarda and between a female of H. suweonensis and males of H. japonica and H. hallowellii) metamorphosed into froglets. The results are consistent with other lines of evidence that indicate close phylogenetic relationship among these Eurasian species. At metamorphosis, all of the hybrids had either nearly normal testes or abnormal ovaries. Sex ratio differed significantly from a 1:1 ratio among progeny in five kinds of interspecific crosses; most of the control froglets had normal ovaries or testes in nearly equal proportion. Gonadal structures in hybrids after one year were also abnormal, suggesting that fertility of adults would be very low, if not absent. The presumed low hybrid fertility supports the specific status of H. japonica, which has often been treated as a subspecies of H. arborea. It also supports the specific status of H. suweonensis, which was distinguished originally on the basis of its characteristic vocalization. This study also suggests specific status of H. savignyi and some genetic divergence between H. japonica of Japan and Korea.