Data from: Sexual dichromatism drives diversification within a major radiation of African amphibians

Theory predicts that sexually dimorphic traits under strong sexual selection, particularly those involved with intersexual signaling, can accelerate speciation and produce bursts of diversification. Sexual dichromatism (sexual dimorphism in color) is widely used as a proxy for sexual selection and is associated with rapid diversification in several animal groups, yet studies using phylogenetic comparative methods to explicitly test for an association between sexual dichromatism and diversification have produced conflicting results. Sexual dichromatism is rare in frogs, but it is both striking and prevalent in African reed frogs, a major component of the diverse frog radiation termed Afrobatrachia. In contrast to most other vertebrates, reed frogs display female-biased dichromatism in which females undergo color transformation, often resulting in more ornate coloration in females than in males. We produce a robust phylogeny of Afrobatrachia to investigate the evolutionary origins of sexual dichromatism in this radiation and examine whether the presence of dichromatism is associated with increased rates of net diversification. We find that sexual dichromatism evolved once within hyperoliids and was followed by numerous independent reversals to monochromatism. We detect significant diversification rate heterogeneity in Afrobatrachia and find that sexually dichromatic lineages have double the average net diversification rate of monochromatic lineages. By conducting trait simulations on our empirical phylogeny, we demonstrate our inference of trait-dependent diversification is robust. Although sexual dichromatism in hyperoliid frogs is linked to their rapid diversification and supports macroevolutionary predictions of speciation by sexual selection, the function of dichromatism in reed frogs remains unclear. We propose that reed frogs are a compelling system for studying the roles of natural and sexual selection on the evolution of sexual dichromatism across both micro- and macroevolutionary timescales.

理论预测，处于强烈性选择作用下的性二态性特征，尤其是参与两性间信号交流的特征，能够加速物种形成并引发分化爆发。两性色型差异（sexual dichromatism，即体色维度的性二态性）被广泛用作性选择的替代指标，并与多个动物类群的快速分化相关联；然而，利用系统发育比较方法专门检验两性色型差异与分化之间关联的研究，却得出了相互矛盾的结论。两性色型差异在蛙类中较为罕见，但在作为非洲蛙类支系（Afrobatrachia）多样辐射演化核心类群的非洲苇蛙中，该特征既醒目又普遍。与绝大多数其他脊椎动物不同，苇蛙呈现雌性偏倚的色型二态性：雌性个体可发生体色转变，其体色通常比雄性更为艳丽。我们构建了非洲蛙类支系（Afrobatrachia）的稳健系统发育树，以探究该支系内两性色型差异的演化起源，并检验色型差异的存在是否与净分化速率提升相关联。研究发现，两性色型差异在苇蛙类（hyperoliids）中仅演化一次，随后又多次独立逆转回单色型状态。我们检测到非洲蛙类支系（Afrobatrachia）存在显著的分化速率异质性，并且发现具有性二态色型的支系，其平均净分化速率是单色型支系的两倍。通过在经验系统发育树上开展性状模拟，我们证实了依赖性状的分化这一推论具有稳健性。尽管苇蛙类（hyperoliids）的两性色型差异与其快速分化相关联，并支持性选择驱动物种形成的宏观演化预测，但苇蛙中该色型差异的功能仍不明晰。我们提出，苇蛙是一个极具研究价值的实验体系，可用于在微观和宏观演化时间尺度上，探究自然选择与性选择在两性色型差异演化中的作用。