Data from: The evolution of fecundity is associated with female body size but not female-biased sexual size dimorphism among frogs

Sexual size dimorphism (SSD) is one of the most common ways in which males and females differ. Male-biased SSD (when males are larger) is often attributed to sexual selection favouring large males. When females are larger (female-biased SSD), it is often argued that natural selection favouring increased fecundity (i.e. larger clutches or eggs) has co-evolved with larger female body size. Using comparative phylogenetic and multi-species regression model selection approaches, we test the hypothesis that among-species variation in female fecundity is associated with the evolution of female-biased SSD. We also ask whether the hypothesized relationship between SSD and fecundity is relaxed upon the evolution of parental care. Our results suggest a strong relationship between the evolution of fecundity and body size, but we find no significant relationship between fecundity and SSD. Similarly, there does not appear to be a relationship between fecundity and the presence or absence of parental care among species. Thus, although female body size and fecundity coevolve, selection for increased fecundity as an explanation for female-biased SSD is inconsistent with our analyses. We caution that a relationship between female body size and fecundity is insufficient evidence for fecundity selection driving the evolution of female-biased SSD.

性大小二态性（Sexual size dimorphism, SSD）是雌雄个体间最为普遍的差异形式之一。雄性偏向型性大小二态性（即雄性体型大于雌性）通常被归因于性选择对大体型雄性的青睐。当雌性体型更大时（雌性偏向型性大小二态性），学界普遍认为自然选择倾向于提升雌性繁殖力（即更大的窝卵数或卵粒尺寸），该过程与雌性体型增大存在共同演化关系。

本研究采用比较系统发育分析与多物种回归模型选择方法，检验“物种间雌性繁殖力的差异与雌性偏向型性大小二态性的演化相关”这一假说。我们同时探究双亲抚育的演化是否会削弱性大小二态性与繁殖力之间的假定关联。

研究结果显示，繁殖力与体型演化间存在显著关联，但未发现繁殖力与性大小二态性间存在显著相关性。类似地，物种间的繁殖力与双亲抚育的存在与否亦无明显关联。

因此，尽管雌性体型与繁殖力存在共同演化关系，但以繁殖力提升作为雌性偏向型性大小二态性演化的解释，与本研究的分析结果并不一致。我们特此提醒，仅凭雌性体型与繁殖力间的关联，不足以证明繁殖力选择驱动了雌性偏向型性大小二态性的演化。