Data from: Neutral and adaptive genomic signatures of rapid poleward range expansion

Many species are expanding their range polewards and this has been associated with rapid phenotypic change. Yet, it is unclear to what extent this reflects rapid genetic adaptation or neutral processes associated with range expansion, or selection linked to the new thermal conditions encountered. To disentangle these alternatives, we studied the genomic signature of range expansion in the damselfly Coenagrion scitulum using 4950 newly developed genomic SNPs and linked this to the rapidly evolved phenotypic differences between core and (newly established) edge populations. Most edge populations were genetically clearly differentiated from the core populations and all were differentiated from each other indicating independent range expansion events. In addition, evidence for genetic drift in the edge populations, and strong evidence for adaptive genetic variation in association with the range expansion was detected. We identified one SNP under consistent selection in four of the five edge populations and showed that the allele increasing in frequency is associated with increased flight performance. This indicates collateral, non-neutral evolutionary changes in independent edge populations driven by the range expansion process. We also detected a genomic signature of adaptation to the newly encountered thermal regimes, reflecting a pattern of countergradient variation. The latter signature was identified at a single SNP as well as in a set of covarying SNPs using a polygenic multilocus approach to detect selection. Overall, this study highlights how a strategic geographic sampling design and the integration of genomic, phenotypic and environmental data can identify and disentangle the neutral and adaptive processes that are simultaneously operating during range expansions.

诸多物种正向极地扩张其分布范围，这一现象与快速的表型（phenotypic）变化密切相关。然而目前尚不明确，这类变化在多大程度上源于快速的遗传适应、与分布范围扩张相关的中性过程，或是与新遭遇的热环境相关的选择作用。为厘清这些可能性，我们以蟌（Coenagrion scitulum）为研究对象，利用4950个新开发的基因组单核苷酸多态性（SNPs）标记分析其分布范围扩张的基因组特征，并将其与核心种群与（新建立的）边缘种群间快速演化的表型差异进行关联。多数边缘种群在遗传层面与核心种群存在显著分化，且各边缘种群间也彼此分化，这表明存在多次独立的分布范围扩张事件。此外，本研究检测到边缘种群存在遗传漂变的相关证据，同时也找到了与分布范围扩张相关的适应性遗传变异的有力佐证。我们在5个边缘种群中的4个里，找到了一处受持续选择作用的SNP位点，并证实频率升高的等位基因与飞行能力提升存在关联。这表明在由分布范围扩张过程驱动的独立边缘种群中，存在附带发生的非中性演化变化。本研究还检测到针对新遭遇热环境的适应性基因组特征，这一特征反映出逆梯度变异（countergradient variation）的分布模式。借助多基因多位点选择检测方法，我们既在单个SNP位点处，也在一组协同变异的SNPs中识别出了上述适应性特征。综上，本研究阐明了如何通过科学的地理采样设计，整合基因组、表型与环境数据，来识别并厘清分布范围扩张过程中同时发生的中性与适应性演化过程。