Butterfly survival on an isolated island by improved grip

On small isolated islands, natural selection is expected to reduce the dispersal capacity of organisms, as short distances do not require a high rate of dispersal, which might lead to accidental emigration from the population. In addition, individuals foregoing the high cost of maintaining flight capacity may instead allocate resources to other functions. However, in butterflies and many other insects, flight is necessary not only for dispersal but also for most other activities. A weakly flying individual would probably do worse and have an elevated rather than reduced probability of accidental emigration. Here, we report results consistent with the hypothesis that a butterfly population on an isolated island, instead of having lost its flight capacity, has evolved better grip to resist the force of wind and to avoid being blown off the island. Our study suggests that local adaptation has occurred in this population in spite of its very small size (Ne ∼ 100), complete isolation, low ge...

在小型离岸孤岛环境中，自然选择通常会降低生物体的扩散能力：由于岛屿与大陆间距较短，无需维持高扩散率，而高扩散率可能导致个体意外脱离种群。此外，放弃维持飞行能力所需的高昂代谢成本的个体，可将资源重新分配至其他生理功能。然而，对于蝴蝶及多数其他昆虫而言，飞行不仅是扩散的必要条件，同时也是绝大多数生命活动的基础。飞行能力较弱的个体往往生存表现更差，且其意外脱离种群的概率反而会升高，而非降低。本研究的结果支持如下假说：孤岛中的蝴蝶种群并未丧失飞行能力，反而演化出了更强的抓附能力，以抵御风力、避免被风吹离岛屿。本研究表明，尽管该种群规模极小（有效种群数量Ne≈100）、完全隔离且遗传多样性较低（原文此处未完整展示），仍发生了局部适应性演化。