Data from: Independent evolution of the sexes promotes amphibian diversification

Classic ecological theory predicts that the evolution of sexual dimorphism constrains diversification by limiting morphospace available for speciation. Alternatively, sexual selection may lead to the evolution of reproductive isolation and increased diversification. We test contrasting predictions of these hypotheses by examining the relationship between sexual dimorphism and diversification in amphibians. Our analysis shows that the evolution of sexual size dimorphism (SSD) is associated with increased diversification and speciation, contrary to the ecological theory. Further, this result is unlikely to be explained by traditional sexual selection models because variation in amphibian SSD is unlikely to be driven entirely by sexual selection. We suggest that relaxing a central assumption of classic ecological models—that the sexes share a common adaptive landscape—leads to the alternative hypothesis that independent evolution of the sexes may promote diversification. Once the constraints of sexual conflict are relaxed, the sexes can explore morphospace that would otherwise be inaccessible. Consistent with this novel hypothesis, the evolution of SSD in amphibians is associated with reduced current extinction threat status, and an historical reduction in extinction rate. Our work reconciles conflicting predictions from ecological and evolutionary theory and illustrates that the ability of the sexes to evolve independently is associated with a spectacular vertebrate radiation.经典生态学理论预测，性二型（sexual dimorphism）的演化会通过限制物种形成可利用的形态空间（morphospace），进而制约物种多样化（diversification）。与之相对，性选择（sexual selection）可能推动生殖隔离（reproductive isolation）的演化，并提升物种多样化速率。本研究以两栖类为研究对象，通过检验性二型与物种多样化之间的关联，验证这两种假说的对立预测。分析结果显示，体型性二型（sexual size dimorphism, SSD）的演化与更高的物种多样化和物种形成速率相关，这与经典生态学理论的预测相悖。进一步而言，该结果无法通过传统性选择模型得到充分解释，因为两栖类体型性二型的变异不太可能完全由性选择驱动。本研究提出，若放宽经典生态学模型的核心假设——即两性共享同一适应性景观（adaptive landscape），则可得到另一替代假说：两性的独立演化可促进物种多样化。当性冲突（sexual conflict）的限制被解除后，两性便可探索原本无法触及的形态空间。与这一新假说相符的是，两栖类体型性二型的演化与当前更低的灭绝威胁等级，以及历史上更低的灭绝速率相关联。本研究调和了生态学与演化理论间的对立预测，并表明两性独立演化的能力与脊椎动物的壮观演化辐射密切相关。