Data from: An experimental evolution study confirms that discontinuous gas exchange does not contribute to body water conservation in locusts

The adaptive nature of discontinuous gas exchange (DGE) in insects is contentious. The classic “hygric hypothesis”, which posits that DGE serves to reduce respiratory water loss (RWL), is still the best supported. We thus focused on the hygric hypothesis in this first ever experimental evolution study of any of the competing adaptive hypotheses. We compared populations of the migratory locust (Locusta migratoria) that underwent ten consecutive generations of selection for desiccation-resistance with control populations. Selected locusts survived 36% longer under desiccation stress but DGE prevalence did not differ between these and control populations (~75%). Evolved changes in DGE properties in the selected locusts included longer cycle and interburst durations. However, in contrast to predictions of the hygric hypothesis, these changes were not associated with reduced RWL rates. Other responses observed in the selected locusts were higher body water content when hydrated and lower evaporative water loss rates. Hence, our data suggest that DGE cycle properties in selected locusts are a consequence of an evolved increased ability to store water, and thus an improved capacity to buffer accumulated CO2, rather than an adaptive response to desiccation. We conclude that DGE is unlikely to be an evolutionary response to dehydration challenge in locusts.昆虫不连续气体交换（discontinuous gas exchange, DGE）的适应性本质迄今仍存在广泛争议。经典的湿度适应假说（hygric hypothesis）提出，DGE的核心功能为减少呼吸失水（respiratory water loss, RWL），该假说仍是目前实证支持度最高的理论。本研究作为首个针对各类竞争性适应性假说开展的实验进化研究，便聚焦于这一湿度适应假说。我们以飞蝗（Locusta migratoria）为研究对象，设置了连续十代抗干旱选育的实验组与对照组。结果显示，经选育的蝗虫在干旱胁迫下的存活时长较对照组提升36%，但两组的DGE发生率并无显著差异（均约75%）。选育组蝗虫的DGE特性出现了演化性改变，具体表现为循环周期与爆发间期延长。然而，这一结果与湿度适应假说的预测相悖：上述DGE特性的改变并未伴随呼吸失水速率的降低。此外，选育组蝗虫还表现出其他适应性响应：水合状态下的体含水量更高，而蒸发失水速率更低。据此，我们的研究数据表明，选育组蝗虫的DGE循环特性并非针对干旱的适应性进化响应，而是演化增强的储水能力带来的附带结果——该变化提升了蝗虫缓冲体内二氧化碳积累的能力。综上，我们得出结论：在飞蝗中，DGE不太可能是应对脱水胁迫的进化响应。