Desiccation stress response of Bombina variegata tadpoles

Abstract

Many amphibian species inhabit temporary aquatic habitats for reproduction to maximize larval growth under favorable conditions but accelerate developmental rate to rapidly undergo metamorphosis under stress conditions when high desiccation risk exists. Corticosterone, one of the most important vertebrate stress hormone controls development, metabolism, and skeletal growth and together with thyroid hormone have a critical role in anuran metamorphosis under stress conditions. Here we compare the hormonal variation of corticosterone (CORT) in the yellow-bellied toad Bombina variegata tadpoles in response to different water levels (constant highcontrol, constant low, constant high+exogenous CORT) and the corticosterone inhibitor- metyrapone (MET) (treatment constant low water level+MET). Also, we investigated the effects of CORT and MET on life-history and morphological traits at metamorphosis. We found that B. variegata tadpoles cannot accelerate the developmental rate in response to pond drying. The constant low water level did not alter whole-body content of CORT and it did not significantly differ from high water level treatment with exogenous CORT. However, individuals from high water level with exogenous CORT have prolonged development, the highest mortality rate, the smallest body size and mass, and the widest but the shortest tails at metamorphosis. Constant low water level with MET decreased the whole-body content of CORT and it was significantly different between all groups, but it did not affect the developmental rate and tail shape although these tadpoles have intermediate size and mass between high water levels with exogenous CORT and control. We show that responsiveness to pond drying of Bombina variegata and its short larval period is probably associated with modified endocrine signaling pathway that control tadpole metamorphosis. Constitutively high whole-body content of CORT which was unaltered by pond drying leads us to conclusion that Bombina variegata development may be canalized but more research is needed.