Lima Alan Siqueira, de Figueredo Aymam Cobo, Floreste Felipe Rangel, Garcia Neto Patrício Getúlio, Gomes Fernando Ribeiro, Titon Stefanny Christie Monteiro
Departamento de Fisiologia, Instituto de Biociências, Universidade de São Paulo, Rua do Matão, trav. 14, 101, São Paulo, SP 05508-090, Brazil.
Integr Comp Biol. 2022 Dec 30;62(6):1671-1682. doi: 10.1093/icb/icac105.
Currently, effects of increased atmospheric temperature, in the context of ongoing climate change, have been investigated in multiple organisms and levels of biological organization. While there has been a focus on the impacts of increased mean temperature, an emergent and equally important point is the consequences of recurrent exposure to extreme temperature events, simulating heat waves. This study investigated the effects of serial exposure to high temperatures on immune and endocrine variables before and after exposure to an acute secondary stressor in bullfrogs (Lithobates catesbeianus). Adult males were divided into three groups and subjected to three thermal regimes: control (c; constant 22°C); experimental 1 (E1; kept at 22°C and exposed to 4 days of 30°C every 16 days); and experimental 2 (E2; kept at 22°C and exposed to 4 days of 30°C every 6 days). Blood samples were collected on the last day of key extreme heat events. Two weeks after the last extreme heat event, animals were subjected to restraint stress (1 h) and sampled again. Blood samples were used to determine neutrophil: lymphocyte ratio, plasma bacterial killing ability, as well as, corticosterone and plasma testosterone levels. Overall, we found exposure to extreme heat events did not affect immune and endocrine variables over time. Meanwhile, the previous exposure to extreme heat events modulated the responsiveness to restraint. The amplitude of increased corticosterone plasma levels and neutrophil: lymphocyte ratio in response to restraint decreased with the number of previous exposures to extreme heat events. These results suggest that exposure to extreme climatic events has hidden effects on bullfrog's stress response, expressed as diminished reactive scope to a novel stressor. This represents a highly deleterious facet of climate change since diminished responsiveness prevents proper coping with wildlife challenges.
当前，在持续的气候变化背景下，大气温度升高对多种生物及生物组织水平的影响已得到研究。尽管研究重点一直是平均温度升高的影响，但一个新出现且同样重要的问题是反复暴露于极端温度事件（模拟热浪）的后果。本研究调查了牛蛙（美国牛蛙）在暴露于急性二次应激源之前和之后，连续暴露于高温对免疫和内分泌变量的影响。成年雄性牛蛙被分为三组，并接受三种热环境处理：对照组（c；恒定22°C）；实验组1（E1；保持在22°C，每16天暴露于30°C环境4天）；实验组2（E2；保持在22°C，每6天暴露于30°C环境4天）。在关键极端高温事件的最后一天采集血样。在最后一次极端高温事件两周后，对动物施加束缚应激（1小时）并再次采样。血样用于测定中性粒细胞与淋巴细胞比例、血浆细菌杀伤能力以及皮质酮和血浆睾酮水平。总体而言，我们发现随着时间推移，暴露于极端高温事件并未影响免疫和内分泌变量。同时，先前暴露于极端高温事件调节了对束缚的反应性。随着先前暴露于极端高温事件次数的增加，束缚应激导致的皮质酮血浆水平升高幅度以及中性粒细胞与淋巴细胞比例降低。这些结果表明，暴露于极端气候事件对牛蛙的应激反应有潜在影响，表现为对新应激源的反应范围减小。这代表了气候变化的一个极具危害性的方面，因为反应性降低会妨碍野生动物应对挑战。
