Institute of Natural &Mathematical Sciences, Massey University, Auckland 0745, New Zealand.
Department of Biology, McMaster University, 1280 Main St. West, Hamilton, Ontario L8S 4K1, Canada.
Nature. 2015 Nov 19;527(7578):367-70. doi: 10.1038/nature15509. Epub 2015 Nov 4.
Classical sexual selection theory provides a well-supported conceptual framework for understanding the evolution and signalling function of male ornaments. It predicts that males obtain greater fitness benefits than females through multiple mating because sperm are cheaper to produce than eggs. Sexual selection should therefore lead to the evolution of male-biased secondary sexual characters. However, females of many species are also highly ornamented. The view that this is due to a correlated genetic response to selection on males was widely accepted as an explanation for female ornamentation for over 100 years and current theoretical and empirical evidence suggests that genetic constraints can limit sex-specific trait evolution. Alternatively, female ornamentation can be the outcome of direct selection for signalling needs. Since few studies have explored interspecific patterns of both male and female elaboration, our understanding of the evolution of animal ornamentation remains incomplete, especially over broad taxonomic scales. Here we use a new method to quantify plumage colour of all ~6,000 species of passerine birds to determine the main evolutionary drivers of ornamental colouration in both sexes. We found that conspecific male and female colour elaboration are strongly correlated, suggesting that evolutionary changes in one sex are constrained by changes in the other sex. Both sexes are more ornamented in larger species and in species living in tropical environments. Ornamentation in females (but not males) is increased in cooperative breeders--species in which female-female competition for reproductive opportunities and other resources related to breeding may be high. Finally, strong sexual selection on males has antagonistic effects, causing an increase in male colouration but a considerably more pronounced reduction in female ornamentation. Our results indicate that although there may be genetic constraints to sexually independent colour evolution, both female and male ornamentation are strongly and often differentially related to morphological, social and life-history variables.
经典的性选择理论为理解雄性装饰物的进化和信号功能提供了一个强有力的概念框架。它预测，由于精子的生产成本低于卵子，因此雄性通过多次交配会获得比雌性更大的适应度收益。因此，性选择应该导致雄性偏性的次要性特征的进化。然而，许多物种的雌性也具有高度的装饰性。这种观点认为，这是由于对雄性选择的遗传反应是相关的，这在 100 多年来被广泛接受为雌性装饰物的解释，并且当前的理论和经验证据表明，遗传限制可以限制性别特定特征的进化。或者，雌性装饰可能是信号需求的直接选择的结果。由于很少有研究探索雄性和雌性装饰的种间模式，因此我们对动物装饰的进化的理解仍然不完整，特别是在广泛的分类尺度上。在这里，我们使用一种新的方法来量化所有约 6000 种雀形目鸟类的羽毛颜色，以确定两性装饰物的主要进化驱动因素。我们发现，同种雄性和雌性的颜色装饰性高度相关，这表明一种性别的进化变化受到另一种性别的限制。在较大的物种和生活在热带环境中的物种中，两性的装饰性都更强。在合作繁殖者中，雌性的装饰性（而不是雄性）增加了——在这些物种中，雌性之间为繁殖机会和其他与繁殖有关的资源而竞争可能很高。最后，雄性的强烈性选择具有拮抗作用，导致雄性颜色增加，但雌性装饰性明显减少。我们的研究结果表明，尽管在性独立的颜色进化中可能存在遗传限制，但雌性和雄性的装饰性都与形态、社会和生活史变量强烈相关，而且通常存在差异。
