SupplementalTree2.txt from Trade-offs direct the evolution of coloration in Galápagos land snails

Increasingly, multiple selective factors are recognized as jointly contributing to the evolution of morphology. What is not clear is how these forces vary across communities to promote morphological diversification among related species. In this study of Galápagos endemic snails (genus Naesiotus), we test several hypotheses of colour evolution. We observe mockingbirds (genus Mimus) predating live snails and find that avian predation selects against conspicuous shells. The evolutionary outcome of this selection is a diversity of shell colours across snails of the archipelago, each closely matching local backgrounds. We also find that snails more regularly exposed to the hot, equatorial sun reflect more light than shells of species from shadier habitats, suggesting a role for thermoregulatory constraints directing colour evolution. The signature of thermoregulatory selection is most clear in comparatively young communities (on the youngest islands), while the signature of selection from predators is most evident in older communities (on the older islands). Together, our findings point to a scenario of shifting selective forces along island ontogeny and community maturity that lead to the distribution of snail coloration we observe in Galápagos. Complex selective regimes such as these may have more responsibility for morphological diversity than is currently recognized.

学界现已逐渐认识到，多重选择因子共同驱动了形态特征的演化。但目前仍不明确的是，这些选择压力在不同类群群落间如何变化，进而推动近缘物种间的形态多样化。本研究以加拉帕戈斯群岛特有蜗牛（奈斯蜗牛属*Naesiotus*）为研究对象，对多项色彩演化假说进行验证。我们观测到嘲鸫属（*Mimus*）鸟类捕食活体蜗牛，结果显示鸟类捕食会对具有醒目外壳的蜗牛产生负向选择。该选择压力带来的演化结果，是该群岛蜗牛的外壳色彩呈现丰富多样性，且每种壳色均与当地生境背景高度匹配。我们还发现，相较于栖息于阴凉生境的蜗牛物种，长期暴露于赤道烈日下的蜗牛外壳反射更多光线，这表明体温调节约束在色彩演化中发挥了导向作用。体温调节选择的信号在相对年轻的群落（即最年轻的岛屿上）最为显著，而捕食者带来的选择信号则在成熟群落（较古老的岛屿上）表现得最为明显。综合来看，我们的研究结果表明，随着岛屿发育进程与群落成熟度的变化，选择压力也会发生动态转变，这正是加拉帕戈斯群岛蜗牛色彩分布格局形成的原因。此类复杂的选择模式，对形态多样性的贡献或许远超当前学界的认知。