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

Several variations in larval life histories were described in a salamander Hynobius retardatus living in Hokkaido, Japan, which had been reported to p ropagate 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 o r September. In some populations living in the similar ponds but supplied w ith a mountain stream or spring water, however, larvae could not complete t heir metamorphosis by late autumn in the first year. All the larvae passed winter season under snow and then metamorphosed between late May and mid Ju ne in the second year. In some specific populations in cold, mountainous po nds, larvae could not metamorphose during the first and second years and me tamorphosed 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, w ere concurrently observed in one pond. Body size at the completion of the m etamorphosis in the 2-year-overwintered larvae was significantly larger tha n that in the metamorphosing or metamorphosed larvae under the age of one. When hemoglobin (Hb) transition from larval to adult types in each populati on was examined, adult globin subunits were expressed in the overwintered l arvae, even though they had not completed their morphological metamorphosis , suggesting that the expression of some adult phenotypes was independent o f morphological metamorphosis.