Spatial Variation in Egg Sac Transparency of the Japanese Black Salamander, Hynobius nigrescens, Related to Environmental Gradients in the Ryohaku Mountains, Ishikawa Prefecture

Abstract: The Japanese black salamander, Hynobius nigrescens, is endemic to Japan and breeds in still water. Egg sacs of three colors (white, intermediate, and transparent) have been identified to date. However, the cause of this variation is not well understood. Therefore, we conducted a survey within the Ryohaku Mountains, where genetic differences are assumed to be small, and investigated egg sac color type in 10 spawning ponds. Our results confirmed that the ratio of the intermediate and transparent types increases with altitude. Regarding egg sac color type at each altitude, all egg sacs found above 740 m asl were white, whereas the transparent and intermediate types began to appear from at or above 740 m. As altitude increased, the incidence of the white type decreased and that of the transparent and intermediate types increased. In addition, a redundancy analysis was performed to determine the relationship between egg sac color and the topographical and meteorological conditions and to clarify the results for each pond. The analysis revealed that maximum snow depth was strongly correlated with an increase in the number of egg sacs of intermediate and transparent types.