Developmental and evolutionary processes underlying phenotypic variation frequently target several traits simultaneously, thereby causing covariation, or integration, among phenotypes. While phenotypic integration can be neutral, correlational selection can drive adaptive covariation. Especially, the evolution and development of exaggerated secondary sexual traits may require the adjustment of other traits that support, compensate for, or otherwise function in a concerted manner. Although phenotypic integration is ubiquitous, the interplay between genetic, developmental, and ecological conditions in shaping integration and its evolution remains poorly understood. Here, we study the evolution and plasticity of trait integration in the bull‐headed dung beetle Onthophagus taurus which is characterized by the polyphenic expression of horned (‘major’) and hornless (‘minor’) male morphs. By comparing populations subject to divergent intensities of mate competition, we tested whether mating system shifts affect integration of traits predicted to function in a morph‐specific manner. We focussed on fore and hind tibia morphology as these appendages are used to stabilize major males during fights, and on wings, as they are thought to contribute to morph‐based differences in dispersal behavior. We found phenotypic integration between fore and hind tibia length and horn length that was stronger in major males, suggesting phenotypic plasticity in integration and potentially secondary sexual trait compensation. Similarly, we observed that fore tibia shape was also integrated with relative horn length. However, although we found population differentiation in wing and tibia shape and allometry, populations did not differ in integration. Lastly, we detected little evidence for morph differences in integration in either tibia or wing shape, although wing allometries differed between morphs. This contrasts with previous studies documenting intraspecific differentiation in morphology, behavior, and allometry as a response to varying levels of mate competition across O. taurus populations. We discuss how sexual selection may shape morph‐specific integration, compensation, and allometry across populations.

中文翻译：

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牛头粪甲虫 Onthophagus taurus 形态特异性整合的进化和可塑性

表型变异背后的发育和进化过程经常同时针对多个性状，从而导致表型之间的共变或整合。虽然表型整合可以是中性的，但相关选择可以驱动适应性共变。特别是，夸张的第二性征的进化和发展可能需要调整其他支持、补偿或以其他方式协同发挥作用的特征。尽管表型整合无处不在，但遗传、发育和生态条件在塑造整合及其进化过程中的相互作用仍然知之甚少。在这里，我们研究了牛头粪甲虫Onthophagus taurus性状整合的进化和可塑性，其特征是有角（“主要”）和无角（“次要”）雄性形态的多型表达。通过比较受不同强度的交配竞争影响的种群，我们测试了交配系统的变化是否会影响预计以形态特异性方式发挥作用的性状的整合。我们专注于前胫骨和后胫骨的形态，因为这些附肢用于在战斗中稳定主要雄性，而翅膀则被认为有助于基于形态的分散行为差异。我们发现，在主要雄性中，前后胫骨长度和角长度之间的表型整合更强，这表明整合的表型可塑性和潜在的第二性征补偿。同样，我们观察到前胫骨形状也与相对角长度相结合。然而，尽管我们发现种群在翅膀和胫骨形状和异速生长方面存在差异，但种群在整合方面没有差异。最后，我们几乎没有发现证据表明形态在胫骨或翅膀形状整合方面存在差异，尽管形态之间的翅膀异速生长不同。这与之前的研究形成鲜明对比，之前的研究记录了金牛座群体中不同程度的配偶竞争对形态、行为和异速生长的种内差异的反应。我们讨论性选择如何影响不同种群的形态特异性整合、补偿和异速生长。