Environmental factors and the incidence of neoteny in Ambystoma gracile (Baird) (Amphibia: Caudata)

Laboratory experiments were conducted to evaluate the effects of temperature, water evaporation rate, and food availability on the incidence of neoteny in Ambystoma gracile and to assess the nature of its genetic control. Larvae hatched from six clutches of eggs from ponds in British Columbia were reared until they were about to metamorphose. Six experiments were then initiated, each involving larvae from a single distinct clutch. Results indicated that at 12 °C larvae metamorphosed later and the incidence of neoteny was higher than at 19 °C; similarly, larvae fed once per week transformed more slowly and were more frequently neotenic than larvae fed three times per week. The rate at which water evaporated, and associated changes in salinity and depth appeared to have no effect. With one exception, under standard conditions there were no differences in the timing of metamorphosis of larvae from different clutches and different populations. It appears that populations of A. gracile are highly polymorphic, comprising some individuals which always metamorphose, some which never do, and others which may or may not transform, depending on the nature of the habitat.