Department of Biological and Environmental Sciences, School of Natural Sciences, University of Stirling, FK9 4LA, UK
Institute of Evolutionary Biology, School of Biological Sciences, University of Edinburgh, EH9 3FL, UK.
Genetics. 2018 Jan;208(1):349-364. doi: 10.1534/genetics.117.300498. Epub 2017 Nov 10.
How do environmental conditions influence selection and genetic variation in wild populations? There is widespread evidence for selection-by-environment interactions (SE), but we reviewed studies of natural populations estimating the extent of genotype-by-environment interactions (GE) in response to natural variation in environmental conditions and found that evidence for GE appears to be rare within single populations in the wild. Studies estimating the simultaneous impact of environmental variation on both selection and genetic variation are especially scarce. Here, we used 24 years of data collected from a wild Soay sheep population to quantify how an important environmental variable, population density, impacts upon (1) selection through annual contribution to fitness and (2) expression of genetic variation, in six morphological and life history traits: body weight, hind leg length, parasite burden, horn length, horn growth, and testicular circumference. Our results supported the existence of SE: selection was stronger in years of higher population density for all traits apart from horn growth, with directional selection being stronger under more adverse conditions. Quantitative genetic models revealed significant additive genetic variance for body weight, leg length, parasite burden, horn length, and testes size, but not for horn growth or our measure of annual fitness. However, random regression models found variation between individuals in their responses to the environment in only three traits, and did not support the presence of G*E for any trait. Our analyses of St Kilda Soay sheep data thus concurs with our cross-study review that, while natural environmental variation within a population can profoundly alter the strength of selection on phenotypic traits, there is less evidence for its effect on the expression of genetic variance in the wild.
环境条件如何影响野生种群的选择和遗传变异？有广泛的证据表明存在环境选择相互作用（SE），但我们回顾了估计自然种群中基因型-环境互作（GE）程度的研究，以响应环境条件的自然变化，发现 GE 的证据在野外单个种群中似乎很少见。估计环境变化对选择和遗传变异同时影响的研究尤其稀缺。在这里，我们使用从一个野生斯高特羊群中收集的 24 年数据，量化了一个重要的环境变量，即种群密度，如何影响（1）通过对适应性的年度贡献进行选择，以及（2）在六个形态和生活史特征中表达遗传变异：体重、后腿长度、寄生虫负担、角长、角生长和睾丸周长。我们的结果支持 SE 的存在：除了角生长之外，所有特征在种群密度较高的年份中选择更强，而在更不利的条件下，定向选择更强。数量遗传模型显示体重、腿长、寄生虫负担、角长和睾丸大小具有显著的加性遗传方差，但角生长或我们的年度适应性衡量指标没有。然而，随机回归模型仅在三个特征中发现个体对环境的反应存在差异，并且不支持任何特征存在 G*E。因此，我们对圣基尔达斯高特羊数据的分析与我们的跨研究综述一致，即虽然种群内的自然环境变化可以深刻改变对表型特征的选择强度，但在野生环境中对遗传方差表达的影响证据较少。
