Data from: Patterns of sexual size dimorphism in Chelonia

Macroevolutionary patterns of sexual size dimorphism (SSD) indicate how sexual selection, natural selection, and genetic and developmental constraints mold sex differences in body size. One putative pattern, known as Rensch’s Rule, posits that among species with female-larger SSD, the relative degree of SSD declines with species’ body size, whereas among male-larger SSD species, relative SSD increases with size. Using a dataset of 196 chelonian species from all fourteen families, we investigated the correlation in body size evolution between male and female Chelonia and the validity of Rensch’s Rule for the taxon and within its major clades. We conclude that male-female correlations in body size evolution are high, but these correlations differ among chelonian families. Overall, SSD scales isometrically with body size; Rensch’s Rule is valid for only one family, Testudinidae (tortoises). Since macroevolutionary patterns of SSD can vary markedly among clades, even in a taxon as morphologically conservative as Testudines, one must guard against inappropriately pooling clades in comparative studies of SSD. Our results also indicate that regression models that assume the x - variable (e.g. male body size) is measured without statistical error, although frequently reported, will result in erroneous conclusions about phylogenetic trends in sexual size dimorphism.性大小二态性（sexual size dimorphism, SSD）的宏观进化模式，阐明了性选择、自然选择以及遗传与发育限制如何塑造生物体体型的性别差异。其中一种被称为伦施法则（Rensch’s Rule）的推测模式提出：在雌性体型更大的SSD物种类群中，相对SSD程度会随物种体型增大而降低；而在雄性体型更大的SSD物种类群中，相对SSD程度则随体型增大而升高。本研究依托涵盖龟鳖目（Chelonia）全部14个科的196个物种数据集，探究了龟类雌雄个体体型进化的相关性，以及伦施法则在该类群及其主要演化支内部的适用性。研究结果显示，龟类雌雄个体体型进化的相关性较强，但该相关性在不同龟鳖科之间存在显著差异。整体而言，SSD随体型呈等比例缩放；伦施法则仅在陆龟科（Testudinidae）这一科中成立。鉴于SSD的宏观进化模式在不同演化支之间可能存在显著差异，即便在龟鳖类（Testudines）这类形态保守的类群中亦是如此，因此在SSD的比较研究中，需警惕不当合并不同演化支的行为。此外，本研究结果还表明，尽管假设自变量（如雄性体型）不存在测量统计误差的回归模型被广泛报道，但使用这类模型会得出关于性大小二态性系统发育趋势的错误结论。