Narayan Edward J, Hero Jean-Marc
Environmental Futures Research Institute, School of Environment, Griffith University, Gold Coast Campus, QLD 4222, Australia.
Environmental Futures Research Institute, School of Environment, Griffith University, Gold Coast Campus, QLD 4222, Australia.
J Therm Biol. 2014 Apr;41:72-6. doi: 10.1016/j.jtherbio.2014.02.011. Epub 2014 Feb 18.
Extreme environmental temperature could impact the physiology and ecology of animals. The stress endocrine axis provides necessary physiological stress response to acute (day-day) stressors. Presently, there are no empirical evidences showing that exposure to extreme thermal stressor could cause chronic stress in amphibians. This could also modulate the physiological endocrine sensitivity to acute stressors and have serious implications for stress coping in amphibians, particularly those living in fragmented and disease prone environments. We addressed this important question using the cane toad (Rhinella marina) model from its introduced range in Queensland, Australia. We quantified their physiological endocrine sensitivity to a standard acute (capture and handling) stressor after exposing the cane toads to thermal shock at 35°C for 30min daily for 34 days. Corticosterone (CORT) responses to the capture and handling protocol were measured on three sampling intervals (days 14, 24, and 34) to determine whether the physiological endocrine sensitivity was maintained or modulated over-time. Two control groups (C1 for baseline CORT measurement only and C2 acute handled only) and two temperature treatment groups (T1 received daily thermal shock up to day 14 only and a recovery phase of 20 days and T2 received thermal shock daily for 34 days). Results showed that baseline CORT levels remained high on day 14 (combined effect of capture, captivity and thermal stress) for both T1 and T2. Furthermore, baseline CORT levels decreased for T1 once the thermal shock was removed after day 14 and returned to baseline by day 29. On the contrary, baseline CORT levels kept on increasing for T2 over the 34 days of daily thermal shocks. Furthermore, the magnitudes of the acute CORT responses or physiological endocrine sensitivity were consistently high for both C1 and T1. However, acute CORT responses for T2 toads were dramatically reduced between days 24 and 34. These novel findings suggest that repeated exposure to extreme thermal stressor could cause chronic stress and consequently suppress the physiological endocrine sensitivity to acute stressors (e.g. pathogenic diseases) in amphibians.
极端环境温度会影响动物的生理和生态。应激内分泌轴为应对急性（每日）应激源提供必要的生理应激反应。目前，尚无实证证据表明暴露于极端热应激源会导致两栖动物产生慢性应激。这也可能调节生理内分泌对急性应激源的敏感性，并对两栖动物应对压力产生严重影响，尤其是那些生活在破碎化且易患病环境中的两栖动物。我们使用来自澳大利亚昆士兰引入区域的蔗蟾蜍（海蟾蜍，Rhinella marina）模型来解决这个重要问题。在将蔗蟾蜍每天在35°C下热休克30分钟，持续34天后，我们量化了它们对标准急性（捕捉和处理）应激源的生理内分泌敏感性。在三个采样时间点（第14天、第24天和第34天）测量皮质酮（CORT）对捕捉和处理方案的反应，以确定生理内分泌敏感性是否随时间保持或受到调节。两个对照组（C1仅用于基线CORT测量，C2仅进行急性处理）和两个温度处理组（T1仅在第14天前接受每日热休克，并经历20天的恢复期，T2每天接受34天的热休克）。结果表明，T1和T2在第14天的基线CORT水平都很高（捕捉、圈养和热应激的综合影响）。此外，T1在第14天后去除热休克后，基线CORT水平下降，并在第29天恢复到基线。相反，T2在34天的每日热休克期间，基线CORT水平持续上升。此外，C1和T1的急性CORT反应幅度或生理内分泌敏感性一直很高。然而, T2蟾蜍在第24天至第34天之间的急性CORT反应显著降低。这些新发现表明，反复暴露于极端热应激源会导致慢性应激，并因此抑制两栖动物对急性应激源（如致病疾病）的生理内分泌敏感性。
