Data from: Hybridisation and genetic diversity in introduced Mimulus (Phrymaceae)

Hybridisation among taxa with different ploidy levels is often associated with hybrid sterility. Clonal reproduction can stabilise these hybrids, but pervasive clonality may have a profound impact on the distribution of genetic diversity in natural populations. Here we investigate a widespread triploid taxon resulting from hybridisation between diploid Mimulus guttatus and tetraploid Mimulus luteus, two species that were introduced into the United Kingdom (UK) in the nineteenth century. This hybrid, Mimulus x robertsii, is largely sterile but capable of prolific vegetative propagation and has been recorded in the wild since 1872. We surveyed 40 Mimulus populations from localities across the UK to examine the current incidence of hybrids, and selected seventeen populations for genetic analysis using codominant markers. Cluster analyses revealed two main groups of genetically distinct individuals, corresponding to either diploid (M. guttatus) or polyploid (M. luteus and M. x robertsii) samples. Triploid hybrids were found in around 50% of sampled sites, sometimes coexisting with one of the parental species (M. guttatus). The other parent, M. luteus, was restricted to a single locality. Individual populations of M. x robertsii were genetically variable, containing multiple, highly heterozygous clones, with the majority of genetic variation distributed among- rather than within populations. Our findings demonstrate that this largely sterile, clonal taxon can preserve non-negligible amounts of genetic variation. The presence of genetically variable hybrid populations may provide the material for the continued success of asexual taxa in diverse environments.不同倍性类群间的杂交往往伴随杂种不育。克隆繁殖可使这类杂种得以稳定存续，但广泛存在的克隆性可能对自然种群的遗传多样性分布产生深远影响。本研究针对一个由二倍体沟酸浆（Mimulus guttatus）与四倍体黄花沟酸浆（Mimulus luteus）杂交形成的广布三倍体类群展开调查，这两个物种均于19世纪被引入英国（UK）。该杂交种——罗伯茨沟酸浆（Mimulus x robertsii）——基本不育，但可通过营养繁殖实现大量增殖，且自1872年起便有野外记录。我们对英国境内多个产地的40个沟酸浆种群开展了调查，以评估当前杂交种的发生情况，并选取其中17个种群，利用共显性分子标记开展遗传分析。聚类分析结果显示存在两个遗传分化显著的主要类群，分别对应二倍体样本（M. guttatus）与多倍体样本类群（包括M. luteus与M. x robertsii）。约50%的采样位点中均发现了三倍体杂种，部分位点中该杂种会与其中一个亲本物种（M. guttatus）共存；另一亲本M. luteus则仅在单个产地有分布记录。罗伯茨沟酸浆的单个种群存在遗传异质性，包含多个高度杂合的克隆株系，且其绝大多数遗传变异分布于种群间而非种群内部。本研究结果表明，这一基本不育的克隆类群可保留相当可观的遗传变异。具有遗传异质性的杂交种群或许可为无性类群在多样环境中持续存续提供遗传基础。