Larval plastic responses to warming and desiccation delay gonadal maturation in post-metamorphic spadefoot toads.

Developmental plasticity allows organisms to adjust life-history traits to varying environmental conditions, which can have concomitant effects across life stages. Many amphibians are suitable model systems to study plasticity because their larvae can adjust growth and differentiation under fluctuating environments. It is unknown, however, whether somatic and gonadal differentiation are equally affected by environmentally-induced plasticity, or whether their decoupling alters gonadal maturation post-metamorphosis, which may affect fitness. We tested if developmental acceleration in response to warming and desiccation risk results in shifts in gonadal maturation during metamorphosis and post-metamorphic growth in western spadefoot toads (Pelobates cultripes). We found additive effects of increased temperature and desiccation risk on development and growth at metamorphosis, which largely constrained gonadal maturation in metamorphic and post-metamorphic individuals of both sexes. Furthermore, the conditions experienced as larvae incurred sex-specific carry-over effects on the gonadal maturation of juveniles five months after metamorphosis. In females, high temperature delayed ovarian maturation regardless of the water level. In males, exposure to high temperature and high water levels slightly delayed testes' maturation. These results highlight the relevance of larval plasticity in the gonadal maturation of species undergoing metamorphosis, which may have implications for population demographics and the evolution of life histories.