The maintenance of polymorphisms often depends on multiple selective forces, but less is known on the role of stochastic or historical processes in maintaining variation. The common wall lizard (Podarcis muralis) is a colour polymorphic species in which local colour morph frequencies are thought to be modulated by natural and sexual selection. Here, we used genome-wide single-nucleotide polymorphism data to investigate the relationships between morph composition and population biogeography at a regional scale, by comparing morph composition with patterns of genetic variation of 54 populations sampled across the Pyrenees. We found that genetic divergence was explained by geographic distance but not by environmental features. Differences in morph composition were associated with genetic and environmental differentiation, as well as differences in sex ratio. Thus, variation in colour morph frequencies could have arisen via historical events and/or differences in the permeability to gene flow, possibly shaped by the complex topography and environment. In agreement with this hypothesis, colour morph diversity was positively correlated with genetic diversity and rates of gene flow and inversely correlated with the likelihood of the occurrence of bottlenecks. Concurrently, we did not find conclusive evidence for selection in the two colour loci. As an illustration of these effects, we observed that populations with higher proportions of the rarer yellow and yellow-orange morphs had higher genetic diversity. Our results suggest that processes involving a decay in overall genetic diversity, such as reduced gene flow and/or bottleneck events have an important role in shaping population-specific morph composition via non-selective processes.

中文翻译：

---

历史生物地理学在塑造普通壁蜥蜴颜色形态多样性中的作用

多态性的维持通常取决于多种选择力，但人们对随机或历史过程在维持变异中的作用知之甚少。普通壁蜥蜴（Podarcis uralis）是一种颜色多态性物种，其中局部颜色变形频率被认为是通过自然选择和性选择来调节的。在这里，我们使用全基因组单核苷酸多态性数据，通过将比利牛斯山脉采样的 54 个种群的形态组成与遗传变异模式进行比较，研究区域尺度上形态组成与种群生物地理学之间的关系。我们发现遗传差异可以用地理距离来解释，而不是用环境特征来解释。形态组成的差异与遗传和环境分化以及性别比例的差异有关。因此，颜色变形频率的变化可能是由于历史事件和/或基因流渗透性的差异而产生的，可能是由复杂的地形和环境决定的。与这一假设一致，颜色形态多样性与遗传多样性和基因流速率呈正相关，与瓶颈发生的可能性呈负相关。同时，我们没有找到两个颜色基因座选择的决定性证据。为了说明这些影响，我们观察到稀有黄色和黄橙色变体比例较高的种群具有较高的遗传多样性。我们的结果表明，涉及整体遗传多样性衰退的过程，例如基因流减少和/或瓶颈事件，在通过非选择性过程塑造群体特异性形态组成方面具有重要作用。