Dancing drives evolution of sexual size dimorphism in manakins

<b>Abstract</b><br/><p><span lang="EN-GB">Body size mediates life history, physiology, and inter- and intra-specific interactions. Within species, sexes frequently differ in size, reflecting divergent selective pressures and/or constraints. Both sexual selection and differences in environmentally-mediated reproductive constraints can drive sexual size dimorphism, but empirically testing causes of dimorphism is challenging. Manakins (Pipridae), a family of Neotropical birds comprising ~50 species, exhibit both male- and female-biased size dimorphism and are distributed across gradients of precipitation and elevation. Males perform courtship displays ranging from simple hops to complex aerobatic manoeuvres. </span><span lang="EN-GB">We tested associations between sexual size dimorphism and (a) agility and (b) environment, analysing morphological, behavioural, and environmental data for 22 manakin species in a phylogenetic framework. </span><span lang="EN-GB">Sexual dimorphism in mass was most strongly related to agility, with males being lighter than females in species performing more aerial display behaviours. However, wing and tarsus length dimorphism were more strongly associated with environmental variables, suggesting that different sources of selection act on different aspects of body size. These results highlight both the strength of sexual selection in shaping morphology—even atypical patterns of dimorphism—while demonstrating the importance of constraints and ecological consequences of body size evolution.</span></p>

<b>摘要</b><br/><p><span lang="EN-GB">体型介导了生活史、生理过程以及种间与种内相互作用。在物种内部，两性的体型往往存在差异，这反映了二者所经历的选择压力和/或限制因素存在分化。性选择以及环境介导的繁殖约束差异，均可能推动性体型二态性的演化，但实证检验该二态性的成因颇具挑战。侏儒鸟（Pipridae）是新热带界鸟类的一科，包含约50个物种，兼具雄性偏大和雌性偏大的体型二态性类群，其分布范围跨越降水与海拔梯度。雄性会展现求偶炫耀行为，从简单的跳跃动作到复杂的特技飞行动作不等。</span><span lang="EN-GB">我们基于系统发育框架，分析了22种侏儒鸟的形态学、行为学与环境数据，检验了性体型二态性与（a）敏捷性、（b）环境之间的关联。</span><span lang="EN-GB">体重维度的性二态性与敏捷性关联最为紧密：在那些展现更多空中炫耀行为的物种中，雄性体重轻于雌性。然而，翅长和跗跖长的二态性则与环境变量关联更强，这表明不同的选择压力作用于体型的不同特征维度。这些研究结果既凸显了性选择在塑造形态特征——即使是非典型的二态性模式——中的强度，同时也证实了体型演化的限制因素与生态后果的重要性。</span></p>