Effects of temperature on urinary corticosterone metabolite responses to short-term capture and handling stress in the cane toad (Rhinella marina).

Extreme temperature can cause metabolic, immune and behavioural changes in amphibians. Short-term stress hormonal response via increased secretion of corticosterone enables amphibians to make necessary physiological and behavioural adjustments for coping with stressors. The effect of temperature on short-term corticosterone responses has not been studied in amphibians. In this study, this relationship was evaluated in adult male cane toads (Rhinella marina). We acclimated male toads (n=24 toads per group) at low, medium and high temperature (15, 25 or 35°C) under controlled laboratory conditions for a 14 day period. After thermal acclimation, short-term corticosterone responses were evaluated in the toads subjected to a standard capture and handling stress protocol over a 24h period. Corticosterone metabolites in toad urine were measured via enzyme-immunoassay. During acclimation, mean baseline urinary corticosterone level increased after transfer of the toads from wild into captivity and returned to baseline on day 14 of acclimation for each of the three temperatures. At the end of the 14 days of thermal acclimation period, baseline corticosterone level were highest for toad group at 35°C and lowest at 15°C. All toads generated urinary corticosterone responses to the standard capture and handling stressor for each temperature. Both individual and mean short-term corticosterone responses of the toads were highest at 35°C and lowest at 15°C. Furthermore, Q(10) values (the factor by which the reaction rate increases when the temperature is raised by 10°) were calculated for mean corrected integrated corticosterone responses as follows; (15-35°C) Q(10)=1.51, (15-25°C) Q(10)=1.60; (25-35°C) Q(10)=1.43. Both total and corrected integrated corticosterone responses were highest for toads at 35°C followed by 25°C and lowest for the 15°C toad group. Overall, the results have demonstrated the thermodynamic response of corticosterone secretion to short-term capture and handling stress in an amphibian species.