Swiss Federal Research Institute WSL, Birmensdorf, Switzerland.
Genetic Diversity Centre (GDC), ETH Zurich, Zurich, Switzerland.
Mol Ecol. 2020 Jun;29(11):1972-1989. doi: 10.1111/mec.15467. Epub 2020 Jun 14.
It is generally accepted that the spatial distribution of neutral genetic diversity within a species' native range mostly depends on effective population size, demographic history, and geographic position. However, it is unclear how genetic diversity at adaptive loci correlates with geographic peripherality or with habitat suitability within the ecological niche. Using exome-wide genomic data and distribution maps of the Alpine range, we first tested whether geographic peripherality correlates with four measures of population genetic diversity at > 17,000 SNP loci in 24 Alpine populations (480 individuals) of Swiss stone pine (Pinus cembra) from Switzerland. To distinguish between neutral and adaptive SNP sets, we used four approaches (two gene diversity estimates, F outlier test, and environmental association analysis) that search for signatures of selection. Second, we established ecological niche models for P. cembra in the study range and investigated how habitat suitability correlates with genetic diversity at neutral and adaptive loci. All estimates of neutral genetic diversity decreased with geographic peripherality, but were uncorrelated with habitat suitability. However, heterozygosity (H ) at adaptive loci based on Tajima's D declined significantly with increasingly suitable conditions. No other diversity estimates at adaptive loci were correlated with habitat suitability. Our findings suggest that populations at the edge of a species' geographic distribution harbour limited neutral genetic diversity due to demographic properties. Moreover, we argue that populations from suitable habitats went through strong selection processes, are thus well adapted to local conditions, and therefore exhibit reduced genetic diversity at adaptive loci compared to populations at niche margins.
人们普遍认为，物种原生范围内中性遗传多样性的空间分布主要取决于有效种群大小、种群历史和地理位置。然而，适应位点的遗传多样性与地理边缘化或生态位内的生境适宜性之间的相关性尚不清楚。本研究使用外显子组全基因组数据和阿尔卑斯山脉的分布图，首次检验了地理边缘化是否与瑞士石松（Pinus cembra）24 个阿尔卑斯山种群（480 个个体）中 >17000 个 SNP 位点的四个种群遗传多样性指标相关（四个指标分别为：4 种基因多样性估计、F 型突变量检验和环境关联分析），以区分中性和适应性 SNP 集。其次，本研究建立了瑞士石松在研究范围内的生态位模型，并研究了生境适宜性与中性和适应性位点遗传多样性的相关性。所有中性遗传多样性的估计值都随着地理边缘化而降低，但与生境适宜性无关。然而，基于 Tajima's D 的适应性位点杂合度（H）随着适宜条件的增加而显著下降。适应性位点的其他多样性估计值与生境适宜性无关。本研究结果表明，由于人口统计学特性，处于物种地理分布边缘的种群具有有限的中性遗传多样性。此外，我们认为来自适宜生境的种群经历了强烈的选择过程，因此对当地条件适应良好，与处于生态位边缘的种群相比，适应性位点的遗传多样性降低。
