Sexually selected ornaments are highly variable and the factors that drive variation in ornament expression are not always clear. Rare instances of female-specific ornament evolution (such as in some dance fly species) are particularly puzzling. While some evidence suggests that such rare instances represent straightforward reversals of sexual selection intensity, the distinct nature of trade-offs between ornaments and offspring pose special constraints in females. To examine whether competition for access to mates generally favours heightened ornament expression, we built a phylogeny and conducted a comparative analysis of Empidinae dance fly taxa that display female-specific ornaments. We show that species with more female-biased operational sex ratios in lek-like mating swarms have greater female ornamentation, and in taxa with more ornate females, male relative testis investment is increased. These findings support the hypothesis that ornament diversity in dance flies depends on female receptivity to mates, which is associated with contests for nutritious nuptial gifts provided by males. Moreover, our results suggest that increases in female receptivity lead to higher levels of sperm competition among males. The incidence of both heightened pre-mating sexual selection on females and post-mating selection on males contradicts assertions that sex-roles are straightforwardly reversed in dance flies. This article is protected by copyright. All rights reserved.

中文翻译：

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获得配偶的竞争预测了女性特有的纹饰和男性对相对睾丸大小的投资

性选择的装饰品变化很大，驱动装饰品表达变化的因素并不总是很清楚。女性特有的装饰品进化的罕见例子（例如在一些舞蝇物种中）特别令人费解。虽然一些证据表明，这种罕见的例子代表了性选择强度的直接逆转，但装饰品和后代之间权衡的独特性质对雌性造成了特殊的限制。为了检查获得配偶的竞争是否通常有利于提高装饰品的表达，我们建立了系统发育，并对展示女性特定装饰品的 Empidinae 舞蝇类群进行了比较分析。我们表明，在类似lek的交配群中，具有更多偏雌性操作性别比的物种具有更多的雌性纹饰，而在雌性较多的分类群中，雄性相对睾丸投入增加。这些发现支持了这样一个假设，即舞蝇的装饰多样性取决于女性对配偶的接受度，这与男性提供的有营养的婚礼礼物的竞争有关。此外，我们的研究结果表明，女性接受度的增加导致男性之间精子竞争水平的提高。雌性的交配前性选择和雄性的交配后性选择都增加的发生率与舞蝇中性别角色直接颠倒的断言相矛盾。本文受版权保护。版权所有。这与男性提供的营养婚礼礼物的竞赛有关。此外，我们的研究结果表明，女性接受度的增加导致男性之间精子竞争水平的提高。雌性的交配前性选择和雄性的交配后性选择都增加的发生率与舞蝇中性别角色直接颠倒的断言相矛盾。本文受版权保护。版权所有。这与男性提供的营养婚礼礼物的竞赛有关。此外，我们的研究结果表明，女性接受度的增加导致男性之间精子竞争水平的提高。雌性的交配前性选择和雄性的交配后性选择都增加的发生率与舞蝇中性别角色直接颠倒的断言相矛盾。本文受版权保护。版权所有。