Predation risk is often invoked to explain variation in stress responses. Yet, the answers to several key questions remain elusive, including the following: (1) how predation risk influences the evolution of stress phenotypes, (2) the relative importance of environmental versus genetic factors in stress reactivity and (3) sexual dimorphism in stress physiology. To address these questions, we explored variation in stress reactivity (ventilation frequency) in a post-Pleistocene radiation of live-bearing fish, where Bahamas mosquitofish (Gambusia hubbsi) inhabit isolated blue holes that differ in predation risk. Individuals of populations coexisting with predators exhibited similar, relatively low stress reactivity as compared to low-predation populations. We suggest that this dampened stress reactivity has evolved to reduce energy expenditure in environments with frequent and intense stressors, such as piscivorous fish. Importantly, the magnitude of stress responses exhibited by fish from high-predation sites in the wild changed very little after two generations of laboratory rearing in the absence of predators. By comparison, low-predation populations exhibited greater among-population variation and larger changes subsequent to laboratory rearing. These low-predation populations appear to have evolved more dampened stress responses in blue holes with lower food availability. Moreover, females showed a lower ventilation frequency, and this sexual dimorphism was stronger in high-predation populations. This may reflect a greater premium placed on energy efficiency in live-bearing females, especially under high-predation risk where females show higher fecundities. Altogether, by demonstrating parallel adaptive divergence in stress reactivity, we highlight how energetic trade-offs may mould the evolution of the vertebrate stress response under varying predation risk and resource availability.

中文翻译：

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捕食风险和脊椎动物应激反应的进化：应激反应和性别二态性的平行进化。

捕食风险通常被用来解释压力反应的变化。然而，几个关键问题的答案仍然难以捉摸，包括以下内容：（1）捕食风险如何影响应激表型的进化，（2）环境因素与遗传因素在应激反应中的相对重要性以及（3）应激中的性别二态性生理。为了解决这些问题，我们探索了活鱼在更新世后辐射中应激反应性（通风频率）的变化，其中巴哈马蚊鱼（Gambusia hubbsi）栖息在孤立的蓝洞中，捕食风险不同。与捕食性低的种群相比，与捕食者共存的种群个体表现出相似的、相对较低的应激反应。我们认为，这种减弱的压力反应已经演变为减少压力源频繁而强烈的环境中的能量消耗，例如食鱼鱼。重要的是，在没有捕食者的情况下经过两代实验室饲养后，来自野外高捕食地点的鱼类所表现出的应激反应的程度几乎没有变化。相比之下，低捕食种群在实验室饲养后表现出更大的种群间变异和更大的变化。这些低捕食性种群似乎在食物供应量较低的蓝洞中进化出更加抑制的应激反应。此外，雌性表现出较低的换气频率，这种性别二态性在高捕食人群中更强。这可能反映了对生育女性的能源效率的更高重视，特别是在高捕食风险下，雌性表现出更高的繁殖力。总之，通过展示压力反应性的平行适应性差异，我们强调了能量权衡如何在不同的捕食风险和资源可用性下塑造脊椎动物压力反应的演变。