Data from: Cruising the rain forest floor: butterfly wing shape evolution and gliding in ground effect

Flight is a key innovation in the evolutionary success of insects and essential to dispersal, territoriality, courtship and oviposition. Wing shape influences flight performance and selection likely acts to maximize performance for conducting essential behaviours that in turn results in evolution of wing shape. As wing shape also contributes to fitness, optimal shapes for particular flight behaviours can be assessed with aerodynamic predictions and placed in an ecomorphological context. Butterflies in the tribe Haeterini (Nymphalidae) are conspicuous members of understory faunas in lowland Neotropical forests. Field observations indicate that the five genera in this clade differ in flight height and behaviour: four use gliding flight at the forest floor level, and one utilizes flapping flight above the forest floor. Nonetheless, the association of ground level gliding flight behaviour and wing shape has never been investigated in this or any other butterfly group. We used landmark-based geometric morphometrics to test whether wing shapes in Haeterini and their close relatives reflected observed flight behaviours. Four genera of Haeterini and some distantly related Satyrinae showed significant correspondence between wing shape and theoretical expectations in performance tradeoffs that we attribute to selection for gliding in ground effect. Forewing shape differed between sexes for all taxa, and male wing shapes were aerodynamically more efficient for gliding flight than corresponding females. This suggests selection acts differentially on male and female wing shapes, reinforcing the idea that sex-specific flight behaviours contribute to the evolution of sexual dimorphism. Our study indicates that wing shapes in Haeterini butterflies evolved in response to habitat-specific flight behaviors, namely gliding in ground effect along the forest floor, resulting in ecomorphological partitions of taxa in morphospace. The convergent flight behaviour and wing morphology between tribes of Satyrinae suggests that the flight environment may offset phylogenetic constraints. Overall, this study provides a basis for exploring similar patterns of wing shape evolution in other taxa that glide in ground effect.

飞行是昆虫演化成功的核心创新，对于扩散、领地行为、求偶与产卵均至关重要。翅膀形状影响飞行性能，而自然选择（natural selection）通常会最大化物种开展关键行为所需的飞行表现，进而推动翼形的演化。由于翅膀形状同样影响适合度（fitness），特定飞行行为的最优翼形可通过空气动力学预测，并置于生态形态学（ecomorphology）框架下进行分析。蛱蝶科（Nymphalidae）黑眼蝶族（Haeterini）的蝴蝶，是新热带区低地森林林下动物群中的显眼类群。野外观察显示该演化支（clade）下的5个属在飞行高度与行为上存在差异：4个类群在林地表层开展滑翔飞行，另有1个类群则在林地上方使用振翅飞行。尽管如此，无论是该类群还是其他任何蝴蝶类群，地表滑翔飞行行为与翼形之间的关联此前从未被探究过。本研究采用基于标志点的几何形态测量法（landmark-based geometric morphometrics），检验黑眼蝶族及其近缘类群的翼形是否与其观测到的飞行行为相匹配。4个黑眼蝶属类群与部分亲缘关系较远的眼蝶亚科（Satyrinae）类群，其翼形与性能权衡（performance tradeoffs）的理论预期存在显著对应关系，我们将此归因于针对地表效应（ground effect）滑翔的自然选择。所有类群的雌雄个体前翅形状均存在差异，且雄性翼形在滑翔飞行中的空气动力学效率高于对应雌性个体。这表明自然选择对雌雄翼形的作用存在分化，进一步支撑了“性别特异性飞行行为推动性二态性（sexual dimorphism）演化”这一论点。本研究表明，黑眼蝶蝴蝶的翼形演化是对栖息地专属飞行行为的响应——即沿林地表层利用地表效应滑翔，最终导致类群在形态空间（morphospace）中形成生态形态学分区。眼蝶亚科各族之间趋同的飞行行为与翼形形态表明，飞行环境可能抵消了系统发育约束（phylogenetic constraints）的影响。总体而言，本研究为探索其他利用地表效应滑翔的类群中类似的翼形演化模式提供了研究基础。