Predation favours Bicyclus anynana butterflies with fewer forewing eyespots

There are fewer eyespots on the forewings versus hindwings of nymphalids but the reasons for this uneven distribution remain unclear. One possibility is, in many butterflies, the hindwing covers part of the ventral forewing at rest and there are fewer forewing sectors to display eyespots (covered eyespots are not continuously-visible and are less likely to be under positive selection). A second explanation is that having fewer forewing eyespots confers a selective advantage against predators. We analysed wing overlap at rest in 275 nymphalid species with eyespots and found that many have exposed forewing sectors without eyespots: i.e. wing overlap does not constrain the forewing from having more eyespots than the hindwing. We performed two predation experiments with mantids to compare the relative fitness of and attack damage patterns on two forms of Bicyclus anynana butterflies, both with seven hindwing eyespots, but with two (in wildtype) or four (in Spotty) ventral forewing eyespots....蛱蝶科（Nymphalidae）昆虫的前翅（forewings）眼斑（eyespots）数量少于后翅（hindwings），但这种分布不均的成因至今仍不明确。第一种可能的解释是：在多数蝶类中，静止状态下后翅会覆盖部分腹面前翅（ventral forewing），且前翅可展示眼斑的区域更少——被覆盖的眼斑无法持续暴露，因此更难受到正选择（positive selection）作用。第二种解释则认为，前翅眼斑更少可赋予蝶类抵御捕食者的选择优势（selective advantage）。我们对275种带有眼斑的蛱蝶科物种开展了静止翅重叠状态分析，结果发现多数物种的前翅暴露区域并无眼斑：换言之，翅重叠并未限制前翅演化出比后翅更多的眼斑。我们利用螳螂（mantids）开展了两项捕食实验（predation experiments），对比了两种品系的矍眼蝶（Bicyclus anynana）的相对适合度（fitness）与攻击损伤模式（attack damage patterns）：这两种品系的后翅均带有7个眼斑，但腹面前翅的眼斑数量分别为野生型（wildtype）的2个，以及Spotty品系的4个。