Macroevolutionary patterns of sexual size dimorphism in copepods

Major theories compete to explain the macroevolutionary trends observed in sexual size dimorphism (SSD) in animals. Quantitative genetic theory suggests that the sex under historically stronger directional selection will exhibit greater interspecific variance in size, with covariation between allometric slopes (male to female size) and the strength of SSD across clades. Rensch's rule (RR) also suggests a correlation, but one in which males are always the more size variant sex. Examining free-living pelagic and parasitic Copepoda, we test these competing predictions. Females are commonly the larger sex in copepod species. Comparing clades that vary by four orders of magnitude in their degree of dimorphism, we show that isometry is widespread. As such we find no support for either RR or for covariation between allometry and SSD. Our results suggest that selection on both sexes has been equally important. We next test the prediction that variation in the degree of SSD is related to the adu...学界存在多种相互竞争的理论，用以阐释动物性别大小二态性（sexual size dimorphism, SSD）所呈现的宏观演化趋势。数量遗传学理论提出，在历史上经受更强定向选择的性别，其体型的种间变异程度更高，且不同演化支的异速生长斜率（雌雄体型比值）与性别大小二态性强度之间存在共变关系。伦施法则（Rensch's rule, RR）同样认为二者存在相关性，但其主张雄性始终是体型变异更显著的性别。本研究以自由生活的浮游类与寄生类桡足类（Copepoda）为研究对象，对上述相互竞争的预测展开检验。在桡足类物种中，通常雌性为体型更大的性别。我们比对了二态性程度跨越四个数量级的多个演化支，结果显示等速生长现象广泛存在。据此，我们未发现支持伦施法则的证据，亦未发现异速生长与性别大小二态性存在共变关系的证据。本研究结果表明，对雌雄两性的选择压力同等重要。我们随后检验了一项预测：性别大小二态性的程度差异与成体（原文此处截断为adu...）相关。