Department of Evolution and Ecology, University of California Davis, Davis, California, USA.
Department of Molecular and Cellular Biology, University of California Davis, Davis, California, USA.
BMC Evol Biol. 2020 Sep 22;20(1):126. doi: 10.1186/s12862-020-01691-8.
One hypothesis for the function of sleep is that it serves as a mechanism to conserve energy. Recent studies have suggested that increased sleep can be an adaptive mechanism to improve survival under food deprivation in Drosophila melanogaster. To test the generality of this hypothesis, we compared sleep and its plastic response to starvation in a temperate and tropical population of Drosophila melanogaster.
We found that flies from the temperate population were more starvation resistant, and hypothesized that they would engage in behaviors that are considered to conserve energy, including increased sleep and reduced movement. Surprisingly, temperate flies slept less and moved more when they were awake compared to tropical flies, both under fed and starved conditions, therefore sleep did not correlate with population-level differences in starvation resistance. In contrast, total sleep and percent change in sleep when starved were strongly positively correlated with starvation resistance within the tropical population, but not within the temperate population. Thus, we observe unexpectedly complex relationships between starvation and sleep that vary both within and across populations. These observations falsify the simple hypothesis of a straightforward relationship between sleep and energy conservation. We also tested the hypothesis that starvation is correlated with metabolic phenotypes by investigating stored lipid and carbohydrate levels, and found that stored metabolites partially contributed towards variation starvation resistance.
Our findings demonstrate that the function of sleep under starvation can rapidly evolve on short timescales and raise new questions about the physiological correlates of sleep and the extent to which variation in sleep is shaped by natural selection.
睡眠的功能之一是作为一种节能机制。最近的研究表明，在果蝇中，增加睡眠可以作为一种适应机制，以提高在食物剥夺下的生存能力。为了检验这一假设的普遍性，我们比较了温带和热带果蝇种群的睡眠及其对饥饿的可塑性反应。
我们发现，温带种群的果蝇对饥饿的抵抗力更强，我们假设它们会采取被认为是节能的行为，包括增加睡眠和减少运动。令人惊讶的是，与热带果蝇相比，无论是在喂食还是饥饿条件下，温带果蝇在清醒时的睡眠更少，运动更多，因此睡眠与饥饿抵抗的种群水平差异无关。相比之下，热带种群的总睡眠时间和饥饿时睡眠时间的变化百分比与饥饿抵抗能力呈强烈正相关，但温带种群则没有。因此，我们观察到饥饿和睡眠之间的关系非常复杂，这种关系在不同种群之间存在差异。这些观察结果否定了睡眠和能量节约之间存在直接关系的简单假设。我们还通过研究储存的脂质和碳水化合物水平来检验饥饿与代谢表型相关的假设，发现储存的代谢物部分解释了饥饿抵抗能力的变异。
我们的研究结果表明，在短期时间内，饥饿条件下的睡眠功能可以迅速进化，并对睡眠的生理相关性以及睡眠变异在多大程度上受到自然选择的影响提出了新的问题。
