Data from: Gynodioecy in structured populations: understanding fine-scale sex ratio variation in Beta vulgaris ssp. maritima

Natural selection, random processes, and gene flow are known to generate sex ratio variations among sexually polymorphic plant populations. In gynodioecious species, in which hermaphrodites and females coexist, the relative effect of these processes on the maintenance of sex polymorphism is still up for debate. The aim of this study was to document sex ratio and cytonuclear genetic variation at a very local scale in wind-pollinated gynodioecious Beta vulgaris ssp. maritima, and attempt to elucidate which processes explained the observed variation. The study sites were characterized by geographically distinct patches of individuals and appeared to be dynamic entities, with recurrent establishment of distinct haplotypes through independent founder events. Along with substantial variation in sex ratio and unexpectedly low gene flow within study sites, our results showed a high genetic differentiation among a mosaic of genetically distinct demes, with isolation by distance or abrupt genetic discontinuities taking place within a few tens of meters. Overall, random founder events with restricted gene flow could be primary determinants of sex structure, by promoting the clumping of sex-determining genes. Such high levels of sex structure provide a landscape for differential selection acting on sex-determining genes, which could modify the conditions of maintenance of gynodioecy in structured populations.众所周知，自然选择、随机过程与基因流可导致性多态性植物种群间出现性比变异。在雌株与雌雄同株个体共存的雌全异株（gynodioecious）物种中，上述过程对性多态性维持的相对效应仍存在争议。本研究以风媒传粉的雌全异株物种海甜菜（Beta vulgaris ssp. maritima）为对象，旨在极局域尺度下记录其性比与核质遗传变异（cytonuclear genetic variation），并尝试阐明何种过程能够解释观测到的变异。研究样地以地理上相互分隔的植株斑块为特征，且属于动态系统，可通过独立的奠基者事件（founder events）反复形成不同的单倍型。除研究样地内存在显著的性比变异与出乎意料的低水平基因流外，我们的结果还显示，由遗传背景各异的居群（deme）构成的镶嵌结构中存在高度遗传分化，数十米范围内即可出现距离隔离（isolation by distance）现象或显著的遗传不连续性。总体而言，受限于基因流的随机奠基者事件，可通过促进性决定基因的聚集，成为种群性结构形成的主要驱动因素。这种高度显著的性结构为作用于性决定基因的差异化选择提供了演化场景，进而可改变结构化种群中维持雌全异株现象（gynodioecy）的条件。