Bird predation selects for wing shape and coloration in a damselfly

Wing shape is related to flight performance, which is expected to be under selection for improving flight behaviours such as predator avoidance. Moreover, wing conspicuousness, usually involved in sexual selection processes, is also relevant in terms of predation risk. In this study, we examined how predation by a passerine bird, the white wagtail Motacilla alba, selects wing shape and wing colour patch size in males of the banded demoiselle Calopteryx splendens. The wing colour patch is intra- and intersexually selected in the study species. In a field study, we compared wings of live damselflies to wings of predated damselflies which are always discarded after predation. Based on aerodynamic theory and a previous study on wing shape of territorial tactics in damselflies, we predicted an overall short and broad wing, with a concave front margin shape to be selected by predation. This shape would be expected to improve escaping ability. Moreover, we predicted that wing patch size should be negatively selected by predation. We found that selection operated differently on fore- and hindwings. In contrast to our predictions, predation favoured a slender general forewing shape. However, the predicted wing shape was favoured in hindwings. We also found selection favouring a narrower wing colour patch. Our results suggest different roles of fore- and hindwings in flight, as previously suggested for Calopteryx damselflies and shown for butterflies and moths. Forewings would be more involved in sustained flight and hindwings in flight manoeuvrability. Our results differ somehow from a recently published work in the same study system, but using another population, suggesting that selection can fluctuate across space, despite the simplicity of this predator–prey system.

翅形与飞行性能密切相关，而飞行性能往往会经受选择作用，以优化躲避天敌等飞行行为。此外，常参与性选择过程的翅部醒目程度，同样会对捕食风险产生影响。本研究以雀形目鸟类白鹡鸰（white wagtail, Motacilla alba）的捕食行为为研究对象，探究其如何对华美色蟌（banded demoiselle, Calopteryx splendens）雄虫的翅形与翅色斑块大小施加选择压力。该研究物种的翅色斑块同时受到性内选择与性间选择的作用。在野外实验中，我们对比了健康豆娘（damselfly）的翅部与被捕食后遗留的豆娘翅部。基于空气动力学理论及此前关于豆娘领域行为翅形的研究，我们预测捕食选择会青睐整体短宽且前缘呈凹陷状的翅形——该形态可提升个体的逃逸能力。此外，我们还预测捕食压力会对翅色斑块大小产生负向选择。研究结果显示，捕食选择对前翅与后翅的作用模式存在差异。与我们的预测相悖的是，捕食选择青睐整体修长的前翅形态；但在后翅中，我们预测的翅形则受到了选择的青睐。同时我们发现，捕食选择更倾向于翅色斑块更小的个体。本研究结果表明，豆娘的前翅与后翅在飞行中承担着不同的功能——这一结论与此前针对色蟌属（Calopteryx）豆娘的假说相符，也在蝴蝶与蛾类中得到了验证。其中前翅更侧重于参与持续飞行，而后翅则负责调控飞行机动性。尽管本捕食-被捕食系统结构相对简单，但我们的研究结果与近期同研究体系、不同种群的已发表成果存在一定差异，这表明选择压力可能会随空间尺度发生波动。