Heterogeneous evolution of sex chromosomes in torrent frog genus Amolops

The sex-chromosome homomorphy has been suggested to result from high turnovers that are observed across deeply diverged clades, yet little is known about the tempo and mode of sex chromosome evolution among most closely related species. Here, we examine patterns of sex chromosome evolution among nine species of the torrent frog genus Amolops. We find that the sex chromosome homomorphy results from both turnover and XY recombination in the Amolops species, simultaneously exhibiting heterogeneous evolution on homologous and non-homologous sex chromosomes. The lower turnover rate of non-homologous sex chromosomes exists in these torrent frogs, whereas the ongoing XY recombination in homologous sex chromosomes would act as an indispensable force to prevent the sex chromosomes from differentiations.