Shift in ecological strategy helps marginal populations of shepherd's purse (Capsella bursa-pastoris) to overcome a high genetic load

The outcome of species range expansion depends on the interplay of demographic, environmental and genetic factors. Self-fertilizing species usually show a higher invasive ability than outcrossers but selfing and bottlenecks during colonization also lead to an increased genetic load. The relationship between genomic and phenotypic characteristics of expanding populations has, hitherto, rarely been tested experimentally. We analyzed how accessions of the shepherd’s purse, C. bursa-pastoris, from the colonization front or from the core of the natural range performed under increasing density of competitors. First, accessions from the front showed a reduced fitness than those from the core. Second, for all accessions, competitor density impacted negatively both vegetative growth and fruit production. However, despite their higher genetic load and lower absolute performances, accessions from the front were less affected by competition than accessions from the core. This seems to be due to phe...物种分布范围扩张的结局，取决于种群动态、环境与遗传三类因素的交互作用。自交物种通常比异交（outcrosser）物种表现出更强的入侵能力，但在定居过程中发生的自交与种群瓶颈效应，也会导致遗传负荷（genetic load）升高。迄今为止，扩张种群的基因组与表型特征之间的关联，极少得到实验验证。我们以荠菜（Capsella bursa-pastoris，C. bursa-pastoris）为研究对象，分析了来自自然分布范围核心区与扩张前沿的种质材料（accession）在竞争者密度递增环境下的生长表现。其一，来自扩张前沿的种质材料，其适合度（fitness）低于核心区材料。其二，对于所有种质材料而言，竞争者密度均对营养生长与结实量产生了显著的负向影响。尽管前沿种质材料的遗传负荷更高、绝对表现更差，但相较于核心区材料，其受竞争抑制的程度更低。这一现象似乎源于表型（phenotypic）...