Abstract
BackgroundOne 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.ResultsWe 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.ConclusionsOur 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.
Highlights
One hypothesis for the function of sleep is that it serves as a mechanism to conserve energy
To test whether starvation resistance evolves through changes in sleep, we quantified behavioral traits in 10 isofemale lines each from two populations sampled from endpoints of the well-studied North American cline, Maine (ME) and Panama City (PC)
Based on previous work [19, 28, 29], we hypothesized that they would be more starvation resistant, and behavioral patterns that conserve energy, such as increased sleep and reduced locomotion under starvation, would contribute to their increased starvation resistance compared to the PC population
Summary
One hypothesis for the function of sleep is that it serves as a mechanism to conserve energy. Drastic reductions in sleep have been observed during mating season [12], under increased predation risk [13] and Sarikaya et al BMC Evolutionary Biology (2020) 20:126 during migration [14]. These studies did not note a reduction in performance for animals sleeping less, suggesting that animals can, at least in some cases, attenuate sleep without incurring negative fitness effects. Food deprivation commonly reduces sleep across animals [15,16,17], and multiple studies have found a trade-off between energy expending behavior (wakefulness and foraging) and length of survival under food deprivation [18, 19]. There are multiple instances where suppression of sleep has no obvious fitness effect, and other instances where it does
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