Hiroshima Children's Museum

Hynobiid salamanders of the genus Onychodactylus are known to possess palmar and tarsal black tubercles or asperities during the breeding season, which were once considered male-specific characters used for spawning activity. However, such tubercles and asperities have also been observed in females and are not always developed in breeding individuals; thus, their functions remain unclear. In this study, we investigated the developmental process of the tubercles and asperities in two Onychodactylus species in the Chugoku Mountains. We found that these traits appear rapidly immediately before the start of spawning. Tubercles and asperities were also observed in females, in which they showed a similar temporal developmental pattern to that observed in males; thus, they may be adaptive traits for migration to underground spawning sites or for breeding activity at these sites. In the Chugoku Mountains, O. kinneburi and O. japonicus are known to share breeding sites for spawning, but their reproductive isolation mechanism remains unknown. In the course of our survey, we found a temporal gap in breeding season between the two species, which may be involved in premating reproductive isolation.