ZEFI-PTR-G-ThermalChallenge

In a rapidly warming world, exposure to high temperatures may impact fitness, but the gene regulatory mechanisms that link sublethal heat to sexually selected traits are not well understood, particularly in endothermic animals. Our experiment used zebra finches (Taeniopygia guttata), songbirds that experience extreme temperature fluctuations in their native Australia. We exposed captive males to an acute thermal challenge (43°C) compared with thermoneutral (35°C) and lower (27°C) temperatures. We found significantly more heat dissipation behaviors at 43°C, a temperature previously shown to reduce song production and fertility, and more heat retention behaviors at 27°C. Next, we characterized transcriptomic responses in tissues important for mating effort – the posterior telencephalon, for its role in song production, and the testis, for its role in fertility and hormone production. Differential expression of hundreds of genes in the testes, but few in the brain, suggest the brain is less responsive to extreme temperatures. Nevertheless, gene network analyses revealed that expression related to dopaminergic signaling in the brain co-varied with heat dissipation behaviors, providing a mechanism by which temporary thermal challenges may alter motivational circuits for song production. In both brain and testis, we also observed correlations between thermally sensitive gene networks and individual differences in thermoregulatory behavior. Although we cannot directly relate these gene regulatory changes to mating success, our results suggest that individual variation in response to thermal challenges could impact sexually selected traits in a warming world.在快速变暖的全球背景下，高温暴露可能影响个体生存适合度（fitness），但将亚致死高温与性选择性状相关联的基因调控机制仍未得到充分阐释，尤其在恒温动物（endothermic animals）中。本研究以斑胸草雀（Taeniopygia guttata）为实验对象——该鸣禽的原生栖息地澳大利亚存在极端温度波动。我们将圈养雄性斑胸草雀分别暴露于43℃急性热应激（acute thermal challenge）、35℃热中性（thermoneutral）与27℃低温环境开展对照实验。结果显示，在43℃环境下（该温度此前被证实会降低鸣唱产出与繁殖能力），个体的热消散行为显著增多；而在27℃环境下，热保留行为则更为频繁。随后，我们对与繁殖投入密切相关的组织开展转录组响应分析：包括参与鸣唱调控的端脑后部（posterior telencephalon），以及负责繁殖与激素合成的睾丸（testis）。睾丸组织中存在数百个差异表达基因，而脑组织中的差异表达基因却寥寥无几，这表明脑组织对极端温度的响应程度较低。不过，基因共表达网络分析显示，脑组织中与多巴胺能信号通路（dopaminergic signaling）相关的基因表达水平与热消散行为呈共变异关系，这为暂时性热应激如何改变鸣唱调控的动机环路提供了潜在机制。此外，我们在脑组织与睾丸组织中均观察到，热敏感基因网络与个体间体温调节行为的差异存在相关性。尽管我们无法直接将这些基因调控变化与繁殖成功率建立关联，但本研究结果表明，在全球变暖的背景下，个体对热应激的响应差异可能会影响性选择性状的表达。