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发展。

关于睡眠功能的一种假设是，它可以作为一种节省能量的机制。最近的研究表明，增加睡眠可以是改善果蝇食物缺乏条件下生存的适应机制。为了检验该假设的普遍性，我们比较了果蝇黑腹温带和热带人群的睡眠及其对饥饿的塑性反应。我们发现，来自温带种群的苍蝇更耐饥饿，并假设它们会从事被认为可以节省能量的行为，包括增加睡眠和减少运动。令人惊讶的是，与热带果蝇相比，在喂食和饥饿的情况下，清醒时温带果蝇的睡眠更少，移动更多，因此，睡眠与饥饿抵抗的人群水平差异无关。相比之下，饥饿时的总睡眠量和睡眠百分率变化与热带人群中的抗饥饿能力呈正相关，而在温带人群中则没有。因此，我们观察到饥饿与睡眠之间出乎意料的复杂关系，这些关系在人群内部和人群之间都不同。这些观察证伪了睡眠与能量节约之间直接关系的简单假设。我们还通过调查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说，并发现储存的代谢物部分导致了抗饥饿性的变化。