Rohner Patrick T, Macagno Anna L M, Moczek Armin P
Department of Biology Indiana University Bloomington IN USA.
Ecol Evol. 2020 Sep 2;10(19):10558-10570. doi: 10.1002/ece3.6711. eCollection 2020 Oct.
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 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 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 populations. We discuss how sexual selection may shape morph-specific integration, compensation, and allometry across populations.
表型变异背后的发育和进化过程常常同时作用于多个性状，从而导致表型之间的协变或整合。虽然表型整合可能是中性的，但相关选择可以驱动适应性协变。特别是，夸张的第二性征的进化和发育可能需要调整其他以协同方式支持、补偿或发挥其他功能的性状。尽管表型整合无处不在，但在塑造整合及其进化过程中，遗传、发育和生态条件之间的相互作用仍知之甚少。在这里，我们研究了牛头蜣螂性状整合的进化和可塑性，该物种以有角（“大型”）和无角（“小型”）雄性形态的多型表达为特征。通过比较经历不同强度配偶竞争的种群，我们测试了交配系统的转变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。我们重点关注前足胫节和后足胫节的形态，因为这些附肢在战斗中用于稳定大型雄性，还关注翅膀，因为它们被认为导致基于形态的扩散行为差异。我们发现前足胫节和后足胫节长度与角长度之间存在表型整合，在大型雄性中更强，这表明整合中存在表型可塑性以及潜在的第二性征补偿。同样，我们观察到前足胫节也与相对角长度整合。然而，尽管我们发现翅膀和胫节形状及异速生长存在种群分化，但种群在整合方面没有差异。最后，我们几乎没有发现胫节或翅膀形状在整合方面存在形态差异的证据，尽管不同形态之间翅膀的异速生长有所不同。这与之前的研究形成对比，之前的研究记录了种内形态、行为和异速生长的分化，作为对不同种群间配偶竞争水平变化的反应。我们讨论了性选择如何塑造不同种群间形态特异性的整合、补偿和异速生长。
