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Two subspecies of the tiger salamander, Ambystoma tigrinum, have a distinctive polymorphic life history that can include four adult morphs as well as typical and cannibalistic larval morphs. We evaluated the effect of environment on development of larval morphology in two laboratory experiments. In Experiment I, 180 larvae were raised in individual 3-liter containers and fed one of three food levels. Larvae in Experiment II received one of two levels of food, and were raised at three densities: one larva per 3 liters of water (50 containers), three larvae per 22 liters of water (18 containers), or seven larvae per 22 liters of water (18 containers). Cannibalistic morphs developed only in nine containers at the highest density, and their occurrence was independent of the two food levels. Our results suggest the typical and cannibalistic larvae which occur in some populations of Ambystoma tigrinum nebulosum is an environmentally induced developmental polymorphism that results from some individuals responding to the environment differently than others. This difference in response may or may not be associated with genetic differences between these morphs. Based on our results we cannot discriminate between two models that differ in their assumptions about the genetic background of individual larvae.
Collins et al. (Tue,) studied this question.