Slavenko Alex, Cooper Natalie, Meiri Shai, Murali Gopal, Pincheira-Donoso Daniel, Thomas Gavin H
Cesar Australia, Brunswick, Victoria, Australia.
Natural History Museum London, London, UK.
Nat Ecol Evol. 2025 Mar;9(3):464-473. doi: 10.1038/s41559-024-02600-8. Epub 2024 Dec 23.
Sexual size dimorphism (SSD) is highly prevalent in nature. Several hypotheses aim to explain its evolution including sexual selection, differential equilibrium and ecological niche divergence. Disentangling the causal mechanism behind the evolution of SSD is challenging, as selection arising from multiple pressures on fitness may act simultaneously to generate observed patterns. Here, we use phylogenetic comparative methods to study the evolution of SSD across tetrapods globally. We estimate directional changes in body size evolution, and compare the number, phylogenetic position and magnitude of size changes between sexes. We find evidence that directional changes in size associated with SSD are typically more common in males-even in lineages where females are larger. However, underlying mechanisms differ among lineages-whereas SSD in amphibians becomes more male-biased with greater increases in male size and mammalian SSD becomes more female-biased with greater decreases in male size. Thus, differing mechanisms of directional body size evolution across sexes are essential to explain observed SSD patterns.
两性体型差异（SSD）在自然界中极为普遍。有几种假说旨在解释其进化过程，包括性选择、差异平衡和生态位分化。由于对适应性的多种压力所产生的选择可能同时起作用以产生观察到的模式，因此厘清SSD进化背后的因果机制具有挑战性。在这里，我们使用系统发育比较方法来研究全球四足动物中SSD的进化。我们估计体型进化的方向性变化，并比较两性之间体型变化的数量、系统发育位置和幅度。我们发现有证据表明，与SSD相关的体型方向性变化在雄性中通常更为常见——即使在雌性体型更大的谱系中也是如此。然而，不同谱系的潜在机制有所不同——两栖动物的SSD随着雄性体型的更大增加而变得更加偏向雄性，而哺乳动物的SSD随着雄性体型的更大减小而变得更加偏向雌性。因此，两性之间体型方向性进化的不同机制对于解释观察到的SSD模式至关重要。
