Data from: Ecological and historical determinants of population genetic structure and diversity in the Mediterranean shrub Rosmarinus officinalis (Lamiaceae)

Population genetic studies of widespread Mediterranean shrubs are scarce compared with those of trees and narrow endemics or studies from phylogeographical perspectives, despite the key role these species may play in Mediterranean ecosystems. Knowledge on the effect of ecological factors in shaping their genetic patterns is also limited. In this study we investigate genetic diversity and population structure across 18 populations of Rosmarinus officinalis, a Mediterranean shrubland plant. Populations were sampled along two elevational gradients, one each on calcareous and siliceous soils in a mountain system in the eastern Iberian Peninsula, to decipher the effect of ecological factors on the genetic diversity and structure based on 11 microsatellite loci. We found overall high levels of genetic diversity and weak population structure. Genetic diversity increased with elevation, whereas population differentiation was stronger among populations growing on siliceous soils. The nested analysis of elevational gradients within soil types revealed that these general patterns were mostly driven by siliceous populations, whereas calcareous populations were more homogeneous along elevational belts. Bayesian analysis of population structure revealed genetic membership of lowland and high-elevation populations to different genetic clusters and a higher admixture of intermediate-elevation populations to both clusters. High-elevation populations were less differentiated from a hypothetical ancestral cluster, suggesting the persistence of their gene pool during the Pleistocene glaciations. In contrast, lowland populations resulted from more recent divergence. We propose that life-history and reproductive traits mostly contribute to explain the high levels of genetic diversity and weak population structure, whereas ecological and historical factors mostly contribute to the stronger differentiation of siliceous populations and a rapid expansion of R. officinalis on calcareous soils possibly mediated by human landscape transformations.

相较于针对树木、狭域特有物种的相关研究，或是从系统地理学视角开展的相关研究，针对广布地中海灌木的种群遗传学研究仍较为匮乏，尽管这类物种在地中海生态系统中扮演着关键角色。目前学界对生态因子塑造其遗传格局的机制认知亦十分有限。本研究以地中海灌丛植物迷迭香（Rosmarinus officinalis）为研究对象，对其18个种群的遗传多样性与种群结构展开系统探究。研究团队在伊比利亚半岛东部的山地系统中，沿两条海拔梯度布设采样样线：分别对应石灰质土壤（calcareous soils）与硅质土壤（siliceous soils）生境，旨在基于11个微卫星位点（microsatellite loci）解析生态因子对其遗传多样性与种群结构的影响。研究结果显示，迷迭香整体遗传多样性水平较高，但种群间结构分化较弱。遗传多样性随海拔升高呈上升趋势，而硅质土壤生境中的种群间遗传分化程度更强。针对土壤类型内海拔梯度的嵌套分析表明，上述整体格局主要由硅质土壤种群驱动，而石灰质土壤种群沿海拔带的分化程度更为均一。种群结构的贝叶斯分析结果显示，低海拔与高海拔种群分别归属于不同的遗传聚类群，而中海拔种群同时兼具两个聚类群的遗传混合组分。高海拔种群与假设的祖先聚类群分化程度更低，暗示其基因库在更新世冰期得以存续。与之相反，低海拔种群则是近期分化的产物。本研究认为，物种的生活史与繁殖性状可较好解释其较高的遗传多样性水平与较弱的种群结构，而生态与历史因子则是造成硅质种群分化程度更高、迷迭香在石灰质土壤中可能借助人类景观改造实现快速扩张的主要原因。