Data from: Causes and consequences of large clonal assemblies in a poplar hybrid zone

Asexual reproduction is a common and fundamental mode of reproduction in plants. Although persistence in adverse conditions underlies most known cases of clonal dominance, proximal genetic drivers remain unclear, in particular for populations dominated by a few large clones. In this study, we studied a clonal population of the riparian tree Populus alba in the Douro river basin (northwestern Iberian Peninsula) where it hybridizes with Populus tremula, a species that grows in highly contrasted ecological conditions. We used 73 nuclear microsatellites to test whether genomic background (species ancestry) is a relevant cause of clonal success, and to assess the evolutionary consequences of clonal dominance by a few genets. Additional genotyping-by-sequencing data were produced to estimate the age of the largest clones. We found that a few ancient (over a few thousand years old) and widespread genets dominate the population, both in terms of clone size and number of sexual offspring produced. Interestingly, large clones possessed two genomic regions introgressed from P. tremula, which may have favoured their spread under stressful environmental conditions. At the population level, the spread of large genets was accompanied by an overall ancient (>0.1 Myr) but soft decline of effective population size. Despite this decrease, and the high clonality and dominance of sexual reproduction by large clones, the Douro hybrid zone still displays considerable genetic diversity and low inbreeding. This suggests that even in extreme cases as in the Douro, asexual and sexual dominance of a few large, geographically extended individuals does not threaten population survival.无性繁殖是植物常见且基础的繁殖方式。尽管多数已报道的克隆优势案例均以逆境耐受为核心基础，但近端遗传驱动机制仍未明确，尤其在少数大型克隆主导的种群中更是如此。本研究以伊比利亚半岛西北部杜罗河流域的河岸树种银白杨（Populus alba）克隆种群为研究对象，该种群与生长在生态条件差异极大的欧洲山杨（Populus tremula）存在自然杂交。我们利用73对核微卫星（nuclear microsatellites）标记，验证基因组背景（即物种祖先组分）是否为克隆成功的关键诱因，并评估少数基株克隆优势所带来的进化后果。我们额外生成了基于测序的基因分型（genotyping-by-sequencing）数据，以估算最大克隆的形成年代。研究发现，少数古老（距今数千年）且分布广泛的基株在种群中占据主导地位，无论是克隆规模还是有性后代产量均如此。值得注意的是，大型克隆携带了两个来自欧洲山杨的渐渗基因组区域，这或许助力其在胁迫环境中成功扩散。在种群水平上，大型基株的扩散伴随有效种群规模经历了一场持续超过10万年的平缓下降过程。尽管存在上述有效种群规模下降，且种群兼具高克隆性与大型基株主导有性繁殖的特征，杜罗河杂交带仍保留了较高的遗传多样性与较低的近交水平。这表明，即便在杜罗河种群这类极端案例中，少数体型庞大、地理分布广泛的个体的无性与有性繁殖优势，并不会对种群存续构成威胁。