Retardation of larval development in the salamander Hynobius retardatus in a permanent pond with abundant spring water

Abstract

Plasticity in the larval life history of the Ezo salamander Hynobius retardatus has been reported. In the present study, we monitored larvae of this salamander species in a fragmented forest in the environs of Sapporo, Japan. Overwintering larvae were detected in one of the two ponds examined, i.e., in the pond that was permanent, with water supplied from several spring-fed points. Four seasonal transition phases in water temperature were observed because of the abundant spring-fed groundwater supply and canopy cover from May to October. These phases included a warming period, a constant-high period, a cooling period, and a constant-low period. During the constant-low period, premetamorphic larvae that had already emerged during the cooling period were continuously detected; however, the composition of the developmental stages remained unchanged, with larval growth progressing slowly. There is apparently a critical temperature that represents the threshold for metamorphosis initiation. The critical temperature is expected to be slightly higher than the groundwater temperature at the spring-fed points. Emigration of overwintered larvae resumed during the warming period and continued during the constant-high period in the year following hatching. In the nearby temporary pond, the one-year-old cohort completed metamorphosis during the summer of the hatch year.