Talal Stav, Ayali Amir, Gefen Eran
Department of Zoology, Tel Aviv University, Tel Aviv, Israel
Department of Zoology, Tel Aviv University, Tel Aviv, Israel.
Biol Lett. 2016 Dec;12(12). doi: 10.1098/rsbl.2016.0807.
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 10 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 (approx. 75%). Evolved changes in DGE properties in the selected locusts included longer cycle and interburst durations. However, in contrast with 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 total 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 CO, rather than an adaptive response to desiccation. We conclude that DGE is unlikely to be an evolutionary response to dehydration challenge in locusts.
昆虫间断性气体交换（DGE）的适应性本质存在争议。经典的“湿度假说”认为DGE有助于减少呼吸水分损失（RWL），该假说仍是得到最多支持的。因此，在针对任何一种竞争性适应性假说的首次实验进化研究中，我们聚焦于湿度假说。我们将连续经过10代抗干燥选择的飞蝗（Locusta migratoria）种群与对照种群进行了比较。经过选择的蝗虫在干燥胁迫下的存活时间延长了36%，但这些种群与对照种群之间的DGE发生率并无差异（约75%）。经过选择的蝗虫DGE特性的进化变化包括周期和爆发间期延长。然而，与湿度假说的预测相反，这些变化与RWL速率降低并无关联。在经过选择的蝗虫中观察到的其他反应包括水化时更高的体内含水量和更低的总蒸发失水率。因此，我们的数据表明，经过选择的蝗虫的DGE周期特性是进化而来的储水能力增强的结果，从而也是缓冲积累的二氧化碳能力提高的结果，而非对干燥的适应性反应。我们得出结论，DGE不太可能是蝗虫对脱水挑战的进化反应。
