Data from: Positive correlations between pre- and post-copulatory sexual traits in warblers

Theoretical models predict that investment in pre-copulatory and post-copulatory sexually selected traits should trade-off. At the macroevolutionary scale, the majority of studies to date have focused on male weaponry as the target of pre-copulatory sexual selection, but the trade-off should equally apply to traits used to attract females, such as bird song and plumage. We studied the Old World leaf warblers (Phylloscopidae), a group of socially monogamous songbirds that experience relatively high levels of sperm competition. We examined the relationships between song duration and number of elements in the song with sperm length across 21 species, and between the same song variables and combined testes mass in a subset of these species (n=10). Across species, these song variables and testes mass/sperm length were generally positively correlated, albeit not statistically significantly so or with borderline significance. In contrast to theory, we found no evidence for negative associations between pre- and post-copulatory traits. We argue that this is a consequence of males of some species investing more into overall fertilization success (i.e. the sum of pre- and post-copulatory sexual selection) than males of other species, and high fertilization success is achieved through investment into both mate attraction and sperm competition.

理论模型预测，针对交配前与交配后性选择性状的资源投入应存在权衡关系。在宏观进化尺度下，迄今为止的多数研究均以雄性武器作为交配前性选择的研究对象，但该权衡关系同样应适用于用于吸引雌性的性状，如鸟鸣与羽色。本研究以旧大陆柳莺科（Phylloscopidae）为研究对象，该类群为社会单配制鸣禽，且经历较高程度的精子竞争。我们分析了21个物种的鸣唱时长、鸣唱元素数量与精子长度之间的关联，并在其中10个物种子集中探究了上述鸣唱变量与睾丸总质量之间的关系。跨物种分析显示，上述鸣唱变量与睾丸质量、精子长度总体呈正相关趋势，但未达到统计学显著性水平，或仅处于临界显著性水平。与理论预测相悖的是，本研究未发现交配前与交配后性状间存在负相关关联的证据。我们认为，这一结果源于部分物种的雄性相较于其他物种，会在整体受精成功率（即交配前与交配后性选择的总和）上投入更多资源；而通过同时对配偶吸引与精子竞争相关性状进行投入，可实现较高的受精成功率。