Data from: Linking intra- and interspecific assortative mating: consequences for asymmetric sexual isolation

Assortative mating is of interest because of its role in speciation and the maintenance of species boundaries. However, we know little about how within-species assortment is related to interspecific sexual isolation. Most previous studies of assortative mating have focused on a single trait in males and females, rather than utilizing multivariate trait information. Here we investigate how intraspecific assortative mating relates to sexual isolation in two sympatric and congeneric damselfly species (genus Calopteryx). We connect intraspecific assortment to interspecific sexual isolation by combining field observations, mate preference experiments and enforced copulation experiments. Using canonical correlation analysis, we demonstrate multivariate intraspecific assortment for body size and body shape. Males of the smaller species mate more frequently with heterospecific females than males of the larger species, which showed less attraction to small heterospecific females. Field experiments suggest that sexual isolation asymmetry is caused by male preferences for large heterospecific females, rather than by mechanical isolation due to interspecific size differences or female preferences for large males. Male preferences for large females and male-male competition for high quality females can therefore counteract sexual isolation. This sexual isolation asymmetry therefore indicates that sexual selection currently opposes a species boundary.选型交配（assortative mating）因其在物种形成与物种边界维持中的关键作用而备受关注。然而，目前学界对种内选型交配与种间性隔离之间的关联仍知之甚少。既往多数关于选型交配的研究仅聚焦于雌雄个体的单一性状，而非利用多变量性状信息。本研究以两个同域分布的同属蟌科物种（珈蟌属Calopteryx）为研究对象，探讨种内选型交配与性隔离之间的关联，并通过整合野外观测、配偶偏好实验与强制交配实验，构建二者之间的关联分析框架。通过典型相关分析（canonical correlation analysis），本研究证实了体型与体形性状存在多变量种内选型交配模式。相较于体型较大物种的雄性（该类雄性对小型异种雌性的吸引力更低），体型较小物种的雄性与异种雌性的交配频次显著更高。野外实验表明，性隔离不对称性源于雄性对大型异种雌性的偏好，而非种间体型差异导致的机械隔离，亦非雌性对大型雄性的偏好。因此，雄性对大型雌性的偏好以及雄性间针对优质雌性的竞争，能够抵消性隔离效应。这种性隔离不对称性表明，当前性选择正削弱物种边界的维持。