Amphibian Metamorphosis: An Integrative Approach

Abstract

Metamorphosis: An Integrative Approach(FN1) Amphibian metamorphosis is a complex process regulated by a number of external (environmental) and internal (hormonal) processes. The transformation from larval to adult form in amphibians provides excellent models for developmental biologists examining tissue and cell differentiation and morphogenesis. Metamorphosis is also an excellent model for endocrinologists because most of the changes during larval development and metamorphosis are under the direct influence of hormones. The metamorphic hormones (the thyroid hormones, and steroids) also function by altering gene expression; thus metamorphosis is an excellent tool for examining gene regulation and hormone-regulated gene expression. Because metamorphic rates are determined by various environmental changes that are translated into hormonal changes, with the hormones functioning at the molecular level, metamorphosis is also an excellent model for integrative studies. Some of the ecological factors regulating metamorphic rate include temperature (Bier, 1978; Hayes et al., 1993), food levels (Wilbur and Collins, 1973; Kupferberg et al., 1994), tadpole densities (Wilbur, 1977; Semlitsch and Caldwell, 1982), pond evaporation rates (Newman, 1993), and predator presence (Wassersug and Sperry, 1977; Arnold and Wassersug, 1978; Kupferberg, 1994). Increasing temperature, decreasing food, overcrowding, pond evaporation, and increased predation all accelerate metamorphosis. Studies also have addressed the ecological complexities of variations in morphogenesis (Collins et al., 1993) and evolutionary patterns and