Data from: Rapid, habitat-related evolution of land snail colour morphs on reclaimed land

I made use of the known dates of reclamation (and of afforestations) in the IJsselmeerpolders in The Netherlands to assess evolutionary adaptation in Cepaea nemoralis. At 12 localities (three in each polder), I sampled a total of 4390 adult individuals in paired open and shaded habitats, on average 233 m apart, and scored these for genetic shell colour polymorphisms. The results show (highly) significant differentiation at most localities, although the genes involved differed per locality. Overall, though, populations in shaded habitats had evolved towards darker shells than those in adjacent open habitats, whereas a ‘Cain & Sheppard’ diagram (proportion yellow shells plotted against ‘effectively unbanded’ shells) failed to reveal a clear pattern. This might suggest that thermal selection is more important than visual selection in generating this pattern. Trait differentiation, regardless of whether they were plotted against polder age or habitat age, showed a linear increase of differentiation with time, corresponding to a mean rate of trait evolution of 15–31 kilodarwin. In conclusion, C. nemoralis is capable of rapid and considerable evolutionary differentiation over 1–25 snail generations, though equilibrium may be reached only at longer time scales.

本研究利用荷兰艾瑟尔湖围垦区（IJsselmeerpolders）已知的围垦与造林时间节点，以评估森林葱蜗牛（Cepaea nemoralis）的进化适应性。本研究在12个采样点（每个围垦区设置3个采样点）中，于成对的开阔生境与遮阴生境内共计采集4390头成体个体，两组生境的平均间距为233米，并对这些个体的壳色遗传多态性进行了分型鉴定。结果显示，多数采样点均存在（极）显著的种群分化，尽管所涉及的功能基因存在位点特异性差异。不过整体而言，遮阴生境中的种群其壳色演化得比相邻开阔生境的种群更深；而凯恩-谢泼德图（Cain & Sheppard diagram，以黄色壳个体比例为纵坐标、"有效无纹"壳个体比例为横坐标的作图方式）并未呈现出明确的分布模式。这一结果或表明，在该分化模式的形成过程中，热选择相较于视觉选择发挥了更为关键的作用。无论以围垦区形成时长还是生境形成时长作为横轴，性状分化均随时间呈线性增长，对应的性状演化平均速率为15~31千达尔文（kilodarwin）。综上，森林葱蜗牛（Cepaea nemoralis）可在1~25个蜗牛世代内实现快速且显著的进化分化，不过种群分化的平衡状态仅可能在更长的时间尺度下达成。