Investigating the Temporal Effects of Thermal Stress on Corticosterone Release and Growth in Toad Tadpoles

Corticosterone (CORT) is a key glucocorticoid hormone that regulates energy balance and physiological responses to environmental stressors, making it a valuable biomarker for assessing how organisms cope with changing conditions. Understanding how amphibians respond to chronic thermal stress is critical in the context of climate change and urbanization. We investigated the effects of a week-long exposure to elevated water temperatures on CORT release rates and growth in Gulf Coast toad (Incilius nebulifer) tadpoles, a species adapted to variable thermal environments. Using a non-invasive water-borne hormone method, we measured CORT at multiple time points (1 h, 2 h, 6 h, 24 h, 48 h, and 5 days) post-treatment to assess how CORT varied with time after exposure to elevated heat vs. the control temperature. We found a significant time-by-treatment response in tadpoles after a week of exposure to 32 °C versus 23 °C (control) temperatures. Both control and treatment individuals showed a marked decrease in CORT release rates 6 h post-return to room temperature, but by 24 h post-experiment, CORT release rates were higher in the tadpoles exposed to 32 °C. Heat-exposed tadpoles also showed significantly faster growth during and after treatment, but a lower survival to 12 days, indicating a potential trade-off between survival and accelerated growth. Overall, our study highlights a trade-off for populations of I. nebulifer when exposed to thermal stress and suggests that amphibian responses to chronic environmental stressors are shaped by adaptive physiological strategies, with implications for understanding and conserving amphibian populations in a rapidly changing world.