SupplementalTable5.csv 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 <i>Naesiotus</i>), we test several hypotheses of colour evolution. We observe mockingbirds (genus <i>Mimus</i>) 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.

越来越多的研究证实，多重选择因子共同推动了形态性状的演化。但目前学界尚未明确的是，这些选择压力在不同生物群落间如何变化，进而推动近缘物种间的形态多样性分化。本研究以加拉帕戈斯群岛（Galápagos）特有的螺类——纳瑟螺属（*Naesiotus*）为研究对象，对多项壳色演化假说进行了验证。我们观测到嘲鸫属（*Mimus*）的鸟类捕食活螺，并发现鸟类捕食会对壳色显眼的螺类产生负选择压力。该负选择带来的演化结果，使得该群岛内的螺类壳色呈现丰富多样性，且每种壳色均与当地生境背景高度契合。我们同时发现，相较于栖息于阴凉生境的螺类，长期暴露于赤道强光下的螺类壳体色反射更多光线，这表明体温调节约束在螺类壳色演化中起到了导向作用。体温调节选择的信号特征在相对年轻的群落（即最年轻的加拉帕戈斯岛屿上的群落）中最为显著，而捕食者带来的选择信号则在成熟群落（较古老岛屿上的群落）中更为突出。综上，本研究结果表明，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移，这正是我们在加拉帕戈斯群岛观测到的螺类壳色分布格局的形成原因。此类复杂的选择机制，或许比当前学界认知的更能推动形态多样性的产生。