Data from: Evidence for selection-by-environment but not genotype-by-environment interactions for fitness-related traits in a wild mammal population

How do environmental conditions influence selection and genetic variation
in wild populations? There is widespread evidence for
selection-by-environment interactions (S*E), but we reviewed studies of
natural populations estimating the extent of genotype-by-environment
interactions (G*E) in response to natural variation in environmental
conditions, and found that evidence for G*E 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 S*E: selection was stronger in years of higher
population density in 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过程与遗传变异水平？目前已有大量研究证实了环境-选择互作（Selection-by-environment interaction, S*E）的广泛存在，但我们针对旨在估算自然环境变异下基因型-环境互作（Genotype-by-environment interaction, G*E）程度的野生种群相关研究进行系统综述后发现，在野外单一种群内部，G*E的相关证据实则较为稀缺。而同时评估环境变异对选择过程与遗传变异的双重影响的研究则尤为罕见。本研究依托针对野生索艾羊（Soay sheep）种群收集的24年监测数据，量化了关键环境变量——种群密度对以下两类过程的影响：(1) 通过年度适合度贡献实现的选择作用，以及(2) 六种形态与生活史性状的遗传变异表达情况。所涉六种性状分别为：体重、后肢长度、寄生虫负荷、角长、角生长量与睾丸周长。研究结果支持S*E的存在：除角生长量外，其余所有性状的选择强度均在种群密度更高的年份中更强，且定向选择在更为严苛的环境条件下更为显著。数量遗传模型分析显示，体重、后肢长度、寄生虫负荷、角长与睾丸尺寸存在显著的加性遗传方差，但角生长量与年度适合度衡量指标则未检测到该方差。然而，随机回归模型仅在三种性状中发现了个体对环境响应的异质性，且未发现任何性状存在G*E的相关证据。综上，通过对圣基尔达群岛（St Kilda）索艾羊种群数据的分析，本研究结果与此前的跨研究综述结论一致：尽管种群内的自然环境变异可显著改变表型性状所受选择的强度，但目前关于其对野外种群遗传变异表达水平的影响的相关证据仍较为有限。