Data from: Survival by genotype: patterns at Mc1r are not black and white at the White Sands ecotone

Measuring links among genotype, phenotype and survival in the wild has long been a focus of studies of adaptation. We conducted a 4-year capture–recapture study to measure survival by genotype and phenotype in the Southwestern Fence Lizard (Sceloporus cowlesi) at the White Sands ecotone (transition area between white sands and dark soil habitats). We report several unanticipated findings. First, in contrast with previous work showing that cryptic blanched coloration in S. cowlesi from the heart of the dunes is associated with mutations in the melanocortin-1 receptor gene (Mc1r), ecotonal S. cowlesi showed minimal association between colour phenotype and Mc1r genotype. Second, the frequency of the derived Mc1r allele in ecotonal S. cowlesi appeared to decrease over time. Third, our capture–recapture data revealed a lower survival rate for S. cowlesi individuals with the derived Mc1r allele. Thus, our results suggest that selection at the ecotone may have favoured the wild-type allele in recent years. Even in a system where a genotype–phenotype association appeared to be black and white, our study suggests that additional factors – including phenotypic plasticity, epistasis, pleiotropy and gene flow – may play important roles at the White Sands ecotone. Our study highlights the importance of linking molecular, genomic and organismal approaches for understanding adaptation in the wild. Furthermore, our findings indicate that dynamics of natural selection can be particularly complex in transitional habitats like ecotones and emphasize the need for future research that examines the patterns of ongoing selection in other ecological ‘grey’ zones.

长期以来，解析野生环境中基因型、表型与存活之间的关联，始终是适应性研究的核心方向。我们针对白沙生态交错带（ecotone，即白沙滩与黑土生境的过渡区域）中的柯氏棘蜥（*Sceloporus cowlesi*，西部栅栏蜥蜴）开展了一项为期4年的标记重捕研究（capture-recapture study），以量化不同基因型与表型个体的存活情况。本研究获得了多项意料之外的发现：其一，此前研究表明，沙丘核心区域的柯氏棘蜥其隐蔽性发白体色与黑皮质素1受体基因（melanocortin-1 receptor gene，Mc1r）的突变存在关联；而本研究中的生态交错带柯氏棘蜥，其体色表型与Mc1r基因型之间仅存在极微弱的关联。其二，生态交错带柯氏棘蜥群体中，衍生型Mc1r等位基因的频率随时间推移呈现下降趋势。其三，标记重捕数据显示，携带衍生型Mc1r等位基因的柯氏棘蜥个体，其存活概率更低。据此，本研究结果表明，近年来生态交错带的自然选择更倾向于保留野生型Mc1r等位基因。即便在基因型与表型关联看似泾渭分明的研究体系中，本研究仍表明，表型可塑性（phenotypic plasticity）、上位性（epistasis）、多效性（pleiotropy）与基因流（gene flow）等额外因素，在白沙生态交错带中可能发挥着重要作用。本研究凸显了整合分子、基因组与个体水平研究方法，以解析野外适应性演化的重要性。此外，本研究结果显示，自然选择的动态过程在生态交错带这类过渡生境中往往尤为复杂；同时，本研究强调，未来需开展更多针对其他生态‘灰色地带’中持续选择模式的相关研究。