Data from: Evidence for non-allopatric speciation among closely related sympatric Heliotropium species in the Atacama Desert

The genetic structure of populations of closely related, sympatric species may hold the signature of the geographical mode of the speciation process. In fully allopatric speciation, it is expected that genetic differentiation between species is homogeneously distributed across the genome. In non-allopatric speciation, the genomes may remain undifferentiated to a large extent. In this paper, we analysed the genetic structure of five sympatric species from the plant genus Heliotropium in the Atacama Desert. We used Amplified Fragment Length Polymorphisms (AFLPs) to characterise the genetic structure of these species and evaluate their genetic differentiation as well as the number of loci subject to positive selection using Divergence Outlier Analysis (DOA). The five species form distinguishable groups in the genetic space, with zones of overlap, indicating that they are possibly not completely isolated. Among-species differentiation accounts for 35% of the total genetic differentiation (FST=0.35), and FST between species pairs is positively correlated with phylogenetic distance. DOA suggests that few loci are subject to positive selection, which is in line with a scenario of non-allopatric speciation. These results support the idea that sympatric species of Heliotropium sect. Cochranea are under an ongoing speciation process, characterised by a fluctuation of population ranges in response to pulses of arid and humid periods during Quaternary times.

亲缘关系密切且同域分布的物种，其种群遗传结构往往承载着物种形成地理模式的演化印记。在完全异域成种场景下，物种间的遗传分化会在全基因组范围内呈均匀分布特征；而在非异域成种过程中，基因组整体可保持较高程度的未分化状态。本研究针对阿塔卡马沙漠中天芥菜属（Heliotropium）的5个同域物种开展遗传结构分析。我们采用扩增片段长度多态性（Amplified Fragment Length Polymorphisms, AFLPs）技术对这些物种的遗传结构进行表征，并通过分化异常值分析（Divergence Outlier Analysis, DOA）评估其遗传分化水平，以及受正向选择的位点数量。这5个物种在遗传空间中形成可区分的类群，同时存在重叠分布区域，提示它们可能并未完全生殖隔离。物种间的遗传分化占总遗传分化的35%（FST=0.35），且物种对之间的FST值与系统发育距离呈显著正相关。分化异常值分析结果显示，仅少数位点受到正向选择，这与非异域成种的理论情景高度吻合。本研究结果支持如下观点：天芥菜属（Heliotropium）Cochranea组的同域物种正处于持续的物种形成过程中，其核心特征为种群分布范围随第四纪（Quaternary）时期干旱与湿润周期的脉动而发生动态波动。