Data from: Temperature fluctuations during development reduce male fitness and may limit adaptive potential in tropical rainforest Drosophila

Understanding the potential for organisms to tolerate thermal stress through physiological or evolutionary responses is crucial given rapid climate change. Although climate models predict increases in both temperature mean and variance, such tolerances are typically assessed under constant conditions. We tested the effects of temperature variability during development on male fitness in the rainforest fly Drosophila birchii, by simulating thermal variation typical of the warm and cool margins of its elevational distribution, and estimated heritabilities and genetic correlations of fitness traits. Reproductive success was reduced for males reared in warm (mean 24°C) fluctuating (± 3°C) versus constant conditions but not in cool fluctuating conditions (mean 17°C), although fluctuations reduced body size at both temperatures. Male reproductive success under warm fluctuating conditions was similar to that at constant 27°C, indicating that briefly exceeding critical thermal limits has similar fitness costs to continuously stressful conditions. There was substantial heritable variation in all traits. However, reproductive success traits showed no genetic correlation between treatments reflecting temperature variation at elevational extremes, which may constrain evolutionary responses at these ecological margins. Our data suggest that even small increases in temperature variability will threaten tropical ectotherms living close to their upper thermal limits, both through direct effects on fitness and by limiting their adaptive potential.

在气候变化速率持续加快的背景下，阐明生物体通过生理或进化响应耐受热胁迫的潜力，具有至关重要的科学意义。尽管气候模型预测气温均值与变异幅度均会上升，但当前对这类耐受能力的评估通常是在恒定温度条件下开展的。本研究以热带雨林果蝇Drosophila birchii为研究对象，通过模拟其海拔分布区间的温、冷边缘典型温度波动特征，探究了发育阶段温度变异对雄性适合度（fitness）的影响，并估算了适合度相关性状的遗传力（heritability）与遗传相关系数。与恒温饲养条件相比，在平均温度24℃、波动幅度±3℃的温暖波动环境中饲养的雄性个体，其繁殖成功率显著下降；而在平均温度17℃的低温波动环境中则未出现该现象——尽管两种温度波动均导致了个体体型的缩小。雄性个体在温暖波动温度环境下的繁殖成功率，与恒温27℃条件下的结果相近，这表明短暂突破临界热极限（critical thermal limits）所带来的适合度代价，与持续处于胁迫温度环境下的代价相当。所有检测性状均存在显著的遗传变异。然而，反映海拔极端温度变异的各处理组之间，繁殖成功率相关性状并未表现出遗传相关，这可能会限制种群在这些生态边缘地带的进化响应能力。本研究结果表明，即便温度变异程度小幅上升，也会通过直接降低适合度以及限制适应潜力这两种途径，对处于自身高温临界阈值附近的热带外温动物构成威胁。