Temperature varies on multiple timescales and ectotherms must adjust to these changes to survive. These adjustments may lead to energetic trade-offs between self-maintenance and reproductive investment. However, we know little about how diurnal and seasonal temperature changes impact energy allocation. Here we used a combination of empirical data and modeling of both thermoregulatory behaviors and body temperature to examine potential energetic trade-offs in the dung beetle Onthophagus taurus. Beginning in March 2020, universities and laboratories were officially closed due to the COVID-19 pandemic. We thus performed experiments at a private residence near Knoxville, Tennessee, USA, leveraging the heating, ventilation and air conditioning of the home to manipulate temperature and compare beetle responses to stable indoor temperatures versus variable outdoor temperatures. We collected O. taurus beetles in the early-, mid-, and late-breeding seasons to examine energetics and reproductive output in relation to diurnal and seasonal temperature fluctuations. We recorded the mass of field fresh beetles before and after a 24-h fast and used the resulting change in mass as a proxy for energetic costs of self-maintenance across seasons. To understand the impacts of diurnal fluctuations on energy allocation, we held beetles either indoors or outdoors for 14-day acclimation trials, fed them cow dung, and recorded mass change and reproductive output. Utilizing biophysical models, we integrated individual-level biophysical characteristics, microhabitat-specific performance, respirometry data, and thermoregulatory behaviors to predict temperature-induced changes to the allocation of energy toward survival and reproduction. During 24 h of outdoor fasting, we found that beetles experiencing reduced temperature variation lost more mass than those experiencing greater temperature variation, and this was not affected by season. By contrast, during the 14-day acclimation trials, we found that beetles experiencing reduced temperature variation (i.e., indoors) gained more mass than those experiencing greater temperature variation (i.e., outdoors). This effect may have been driven by shifts in the metabolism of the beetles during acclimation to increased temperature variation. Despite the negative relationship between temperature variation and energetic reserves, the only significant predictor of reproductive output was mean temperature. Taken together, we find that diurnal temperature fluctuations are important for driving energetics, but not reproductive output.

中文翻译：

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昼夜温度变化影响能量，但不影响温带粪甲虫跨季节的繁殖努力

温度在多个时间尺度上变化，变温动物必须适应这些变化才能生存。这些调整可能会导致自我维持和生殖投资之间的积极权衡。然而，我们对每日和季节性温度变化如何影响能源分配知之甚少。在这里，我们结合了经验数据和温度调节行为和体温的模型来研究粪甲虫Onthophagus taurus中潜在的能量权衡。从 2020 年 3 月开始，由于 COVID-19 大流行，大学和实验室正式关闭。因此，我们在美国田纳西州诺克斯维尔附近的一处私人住宅进行了实验，利用家中的供暖、通风和空调来控制温度，并比较甲虫对稳定室内温度与可变室外温度的反应。我们在繁殖季节的早期、中期和晚期收集了金牛座甲虫，以检查与昼夜和季节性温度波动相关的能量和繁殖输出。我们记录了 24 小时禁食前后田间新鲜甲虫的质量，并使用由此产生的质量变化作为跨季节自我维持能量成本的代理。为了了解昼夜波动对能量分配的影响，我们在室内或室外饲养甲虫进行了 14 天的适应试验，给它们喂牛粪，并记录了质量变化和生殖输出。利用生物物理模型，我们整合了个体水平的生物物理特征、微生境特定性能、呼吸测量数据和体温调节行为，以预测温度引起的生存和繁殖能量分配的变化。在 24 小时的户外禁食期间，我们发现温度变化较小的甲虫比温度变化较大的甲虫损失了更多的质量，而且这不受季节的影响。相比之下，在为期 14 天的适应试验中，我们发现经历较小温度变化（即室内）的甲虫比经历较大温度变化（即室外）的甲虫获得更多的质量。这种效应可能是由甲虫在适应温度变化过程中新陈代谢的变化所驱动的。尽管温度变化与能量储备之间存在负相关关系，但生殖输出的唯一重要预测因素是平均温度。综上所述，我们发现昼夜温度波动对于驱动能量很重要，但对生殖输出却不是。