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.

中文翻译：

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睡眠和饥饿抵抗的表型耦合在黑腹果蝇中进化。


关于睡眠功能的一个假设是，它是一种保存能量的机制。最近的研究表明，增加睡眠可能是提高果蝇在食物匮乏情况下生存的一种适应性机制。为了检验这一假设的普遍性，我们比较了温带和热带黑腹果蝇种群的睡眠及其对饥饿的可塑性反应。我们发现来自温带地区的苍蝇更能抵抗饥饿，并假设它们会采取被认为节省能量的行为，包括增加睡眠和减少运动。令人惊讶的是，与热带果蝇相比，无论在进食还是饥饿条件下，温带果蝇在清醒时睡眠较少且移动较多，因此睡眠与饥饿抵抗力的种群水平差异无关。相比之下，在热带人群中，饥饿时的总睡眠和睡眠百分比变化与饥饿抵抗力呈强烈正相关，但在温带人群中则不然。因此，我们观察到饥饿和睡眠之间出乎意料的复杂关系，这种关系在人群内部和人群之间都有所不同。这些观察结果证伪了睡眠与能量守恒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测试饥饿与代谢表型相关的假设，并发现储存的代谢物部分有助于变异饥饿抵抗。 我们的研究结果表明，饥饿条件下的睡眠功能可以在短时间内迅速演变，并提出了关于睡眠的生理相关性以及自然选择在多大程度上影响睡眠变化的新问题。