Salinity tolerance of eggs of Hynobius retardatus in Hokkaido, Japan

Hynobius retardatus is a salamander distributed in Hokkaido, Japan which is a subarctic region, and populations breed in both urban and coastal areas. To understand why some populations of this species can breed in coastal areas, we tested the salinity tolerance of H. retardatus eggs collected from both coastal and urban areas. At 0 ppt salinity (control), over 95% of eggs hatched normally in both coastal and urban populations. However, survival rate of eggs was significantly different among populations in 4 ppt and 5 ppt salinity. No eggs hatched over 10 ppt salinity in all populations. Deformation rate was also increased with salinity level, and differed among populations. Our results showed that eggs from coastal populations had higher survival in high salinity compared to eggs from urban populations.