Data from: Genetic diversity and gene flow decline with elevation in montane mayflies

Montane environments around the globe are biodiversity ‘hotspots’ and important reservoirs of genetic diversity. Montane species are also typically more vulnerable to environmental change than their low-elevation counterparts due to restricted ranges and dispersal limitations. Here we focus on two abundant congeneric mayflies (Baetis bicaudatus and B. tricaudatus) from montane streams over an elevation gradient spanning 1400 m. Using single-nucleotide polymorphism genotypes, we measured population diversity and vulnerability in these two species by: (i) describing genetic diversity and population structure across elevation gradients to identify mechanisms underlying diversification; (ii) performing spatially explicit landscape analyses to identify environmental drivers of differentiation; and (iii) identifying outlier loci hypothesized to underlie adaptive divergence. Differences in the extent of population structure in these species were evident depending upon their position along the elevation gradient. Heterozygosity, effective population sizes and gene flow all declined with increasing elevation, resulting in substantial population structure in the higher elevation species (B. bicaudatus). At lower elevations, populations of both species are more genetically similar, indicating ongoing gene flow. Isolation by distance was detected at lower elevations only, whereas landscape barriers better predicted genetic distance at higher elevations. At higher elevations, dispersal was restricted due to landscape effects, resulting in greater population isolation. Our results demonstrate differentiation over small spatial scales along an elevation gradient, and highlight the importance of preserving genetic diversity in more isolated high-elevation populations.

全球山地生境均为生物多样性热点区域，亦是遗传多样性的重要储库。相较于低海拔同类物种，山地物种因分布范围受限、扩散能力不足，通常更易受环境变化影响。
本研究聚焦于一条海拔跨度达1400米的山地溪流中的两种优势同属蜉蝣（Baetis bicaudatus与B. tricaudatus）。研究采用单核苷酸多态性（single-nucleotide polymorphism, SNP）基因型数据，通过以下三方面手段评估这两个物种的种群多样性与脆弱性：（1）解析沿海拔梯度的遗传多样性与种群结构，以明确物种分化的潜在机制；（2）开展空间显式景观分析，识别种群分化的环境驱动因子；（3）筛选被认为与适应性分化相关的离群位点。
研究发现，两个物种种群结构的差异程度与其在海拔梯度上的位置密切相关。随着海拔升高，杂合性、有效种群大小与基因流均呈下降趋势，导致高海拔物种（B. bicaudatus）形成了显著的种群结构。
在低海拔区域，两个物种的种群遗传相似度均更高，提示存在持续的基因流。仅在低海拔区域检测到距离隔离效应，而高海拔区域的遗传距离则更易被景观屏障所解释。
在高海拔区域，景观效应限制了物种扩散，进而加剧了种群隔离。
本研究结果表明，沿海拔梯度在微小空间尺度上即可发生种群分化；同时凸显了保护更为孤立的高海拔种群遗传多样性的重要性。