Adaptable larval life histories in different populations of the salamander, hynobius retardatus, living in various habitats

Abstract

Several variations in larval life histories were described in a salamander Hynobius retardatus living in Hokkaido, Japan, which had been reported to propagate in larval forms in a specific environment of Lake Kuttara like the axolotl. In almost all populations living in lower land Hokkaido, spawning was observed in early spring, and hatched larvae metamorphosed by August or September. In some populations living in the similar ponds but supplied with a mountain stream or spring water, however, larvae could not complete their metamorphosis by late autumn in the first year. All the larvae passed winter season under snow and then metamorphosed between late May and mid June in the second year. In some specific populations in cold, mountainous ponds, larvae could not metamorphose during the first and second years and metamorphosed in the third year. Thus, three age-groups of larvae, which were 2-year-and 1-year-overwintered larvae, and larvae under the age of one, were concurrently observed in one pond. Body size at the completion of the metamorphosis in the 2-year-overwintered larvae was significantly larger than that in the metamorphosing or metamorphosed larvae under the age of one. When hemoglobin (Hb) transition from larval to adult types in each population was examined, adult globin subunits were expressed in the overwintered larvae, even though they had not completed their morphological metamorphosis, suggesting that the expression of some adult phenotypes was independent of morphological metamorphosis.