Data from: Sexual dichromatism in wing pigmentation of New World dragonflies follows Rensch’s rule

Many animal taxa that display sexual size dimorphism (SSD) exhibit a positive allometric relationship in which the degree of dimorphism increases with body size. This macroevolutionary pattern is known as Rensch's rule. Although sexual selection is hypothesized to be the main mechanism causing this pattern, body size is influenced by several selective forces, including natural and sexual selection. Therefore, by focusing exclusively on SSD one cannot ascertain which of these selective forces drives Rensch's rule. If sexual selection is indeed the main mechanism underlying Rensch's rule, we predict that other sexually selected traits, including colouration-based ornaments will also exhibit interspecific allometric scaling consistent with Rensch's rule. We tested this prediction using wing pigmentation of 89 species of dragonflies. Studies show that male wing pigmentation is generally under strong intra- and intersexual selection, so that sexual dichromatism in this trait should follow Rensch's rule. Conversely, the available evidence suggests that male body size is usually not sexually selected in dragonflies, so we do not expect SSD to follow Rensch's rule. First, we found that sexual dichromatism in wing pigmentation was consistent with Rensch's rule. The phylogenetic major axis regression slope was significantly greater than one. We also showed that the allometric slope for SSD was not different from unity, providing no support for Rensch's rule. Our results provide the first evidence that a trait which appears to be under strong sexual selection, exhibits a pattern consistent with Rensch's rule.

诸多表现出性大小二态性（sexual size dimorphism，SSD）的动物类群，均呈现正异速生长关系——即二态性程度随体型增大而升高。这一大进化模式被称为伦施法则（Rensch's rule）。尽管有假说提出性选择是造就该模式的核心机制，但体型同时受到自然选择、性选择等多种选择压力的调控。因此，若仅关注性大小二态性，便无法确定究竟是哪一类选择压力驱动了伦施法则。
若性选择确为伦施法则的核心驱动机制，则我们可预测：其他受性选择塑造的性状（如基于体色的装饰结构）也应呈现符合伦施法则的种间异速生长缩放关系。
我们以89种蜻蜓的翅色素沉着为研究对象，对该预测进行了验证。已有研究表明，雄性翅色素沉着通常受到强烈的性内选择与性间选择作用，因此该性状的性色二态性（sexual dichromatism）应符合伦施法则。与之相反，现有证据显示蜻蜓雄性体型通常不受性选择作用，因此我们预测其性大小二态性不会符合伦施法则。
首先，我们发现翅色素沉着的性色二态性符合伦施法则：系统发育主轴回归的斜率显著大于1。同时我们还发现，性大小二态性的异速生长斜率与1无显著差异，未为伦施法则提供支持。本研究结果首次证实：一类受到强烈性选择作用的性状，其异速生长模式符合伦施法则。