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关键创新特征，对于昆虫的扩散、领域防御、求偶与产卵均至关重要。翅形会影响飞行性能，而自然选择大概率会倾向于优化执行关键行为所需的飞行性能，进而推动翅形的演化。由于翅形同样关乎个体适合度，因此可借助空气动力学预测手段，评估对应特定飞行行为的最优翅形，并将其纳入生态形态学研究框架。蛱蝶科（Nymphalidae）Haeterini族蝴蝶是新热带低地森林林下动物区系中的显著类群。野外观察显示，该演化支内的5个属在飞行高度与飞行行为上存在差异：其中4个类群在林地表层开展滑翔飞行，剩余1个类群则在林地上方进行振翅飞行。然而，无论是在该类群还是其他任何蝴蝶类群中，地表滑翔飞行行为与翅形之间的关联均未得到深入研究。本研究采用基于地标点的几何形态测量学（landmark-based geometric morphometrics）方法，检验Haeterini族蝴蝶及其近缘类群的翅形是否与已观测到的飞行行为相匹配。Haeterini族的4个属以及部分亲缘关系较远的眼蝶亚科（Satyrinae）类群，其翅形与飞行性能权衡的理论预期存在显著相关性，我们将此归因于针对地面效应滑翔的自然选择作用。所有类群的前翅形均存在雌雄二态差异，且雄性的翅形在滑翔飞行中的空气动力学效率显著高于雌性个体。这表明自然选择对雌雄翅形的选择压力存在差异，进一步支持了“性别特异性飞行行为推动性二态性演化”这一学术观点。本研究表明，Haeterini族蝴蝶的翅形演化是对栖息地特异性飞行行为的适应——即沿林地表层利用地面效应滑翔，最终导致类群在形态空间中形成生态形态学分区。眼蝶亚科不同族之间存在的飞行行为与翅形趋同现象，表明飞行环境可能抵消系统发育约束的影响。总体而言，本研究为探索其他利用地面效应滑翔的类群中类似的翅形演化模式提供了坚实的研究基础。