Post-Metamorphic Carry-Over Effects in a Complex Life History: Behavior and Growth at Two Life Stages in an Amphibian, Anaxyrus fowleri

Carry-over effects, which occur when an animal's early life experience has lasting effects on its later life, may be manifested in an animal's behavior, growth, and fitness, and are often overlooked as contributing factors to such aspects of animal ecology. Metamorphosis is a process that can produce such effects in animals with complex life histories, due to the significant energetic cost and physical changes undergone during this process. We explored the potential impact of tadpole density after metamorphosis in a pond-breeding amphibian, Anaxyrus fowleri. If larval density induces carry-over effects, then there should be a positive correlation in behavior and/or relative growth rate between pre-metamorphic tadpoles and the same animals as post-metamorphic toadlets. We raised tadpoles at six density levels, ranging from 0.08 tadpoles/L to 1.67 tadpoles/L, designed to produce variation in growth rate and toadlet size, and quantified relative activity by monitoring movement per five-second intervals in tadpoles and one-minute intervals in toadlets. Among tadpoles, activity varied with density as a quadratic curve and best predicted growth rate as a negative loge-linear function. For toadlets, their density as tadpoles did not predict relative growth rate. Alternatively, we found a positive relationship between activity level and toadlet body size and, when considered in terms of density treatments as larvae, found evidence for body size predicting opposite trends in activity between the two life stages. Our results show evidence of density-dependent carry-over effects when comparing relative growth rate, and indirectly when comparing size-dependent activity level between life stages, in this pond-breeding amphibian. Further information is needed to determine if carry-over effects impact individual fitness, which can have implications at the population level.