Ornament complexity is correlated with sexual selection: (a comment on Raia et al., "Cope's rule and the universal scaling law of ornament complexity")

Raia et al. propose that the evolution of the shape and complexity of animal ornaments (e.g., deer antlers) can be explained by interspecific variation in body size and is not influenced by sexual selection. They claim to show that ornament complexity is related to body size by an 0.25-power law and argue that this finding precludes a role for sexual selection in the evolution of ornament complexity. However, their study does not test alternative hypotheses and mismeasures antler shape allometry by omitting much of the published data. We show that an index of sexual selection (sexual size dimorphism) is positively correlated with size-corrected antler complexity and that the allometric slope of complexity is substantially greater than 0.25, contra Raia et al. We conclude that sexual selection and physical constraints both affect the evolution of antler shape.

Raia等人提出，动物装饰性状（animal ornaments，如鹿角（deer antlers））的形态与复杂度演化可通过物种间的体型变异解释，且不受性选择影响。他们声称已证实装饰性状复杂度与体型间符合0.25次幂律关系，并认为该发现排除了性选择在装饰性状复杂度演化中发挥作用的可能性。然而，其研究未检验其他备选假说，且因遗漏大量已发表数据，错误测算鹿角形态的异速生长（allometry）关系。本研究表明，性选择指标——性大小二态性（sexual size dimorphism）——与体型校正后的鹿角复杂度呈正相关，且复杂度的异速生长斜率显著大于0.25，与Raia等人的结论相悖。我们最终得出结论：性选择与物理约束共同影响鹿角形态的演化。