PREMISE The timing of self-fertilization has potentially important consequences for the trajectory of mating system evolution, the opportunity for outcrossing, and the maintenance of genetic variation in populations. For primarily selfing taxa, it remains poorly understood as to how floral variation influences the opportunity for outcrossing and whether those attributes vary among populations across geographic ranges. METHODS We examined variation in floral traits (herkogamy, protandry, flower size, stigma stage at anthesis, timing of stigma receptivity) in seven populations of Clarkia xantiana ssp. parviflora, a primarily selfing taxon, spanning from the western to eastern margins of its distribution. We also performed experimental emasculations and pollinations (followed by stigma severing) to quantify the extent of opportunities for outcrossing across flower development. RESULTS There was marked among-population variation in all floral traits, particularly between far eastern and western populations. Emasculation experiments showed that the eastern populations had minimal autonomous selfing, but western populations had high rates of selfing within 24 h after anthesis. Population variation in autofertility was significantly predicted by floral trait variation, especially protandry and petal size. CONCLUSIONS Greater protandry both extended the time over which outcrossing could potentially occur and reduced the probability of autonomous selfing, suggesting that there may be a tradeoff that results in fitness loss when pollinator visits are not common. The east-west pattern of differentiation in some floral traits parallels that of postglacial range expansion, suggesting that selection on the mating system may have been strong in the process of range expansion.

中文翻译：

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异交的机会在主要自交的 Clarkia xantiana ssp 的地理范围内有所不同。小花

前提自我受精的时机对交配系统进化的轨迹、异交的机会以及种群遗传变异的维持具有潜在的重要影响。对于主要自交的分类群，人们对花卉变异如何影响异交机会以及这些属性在不同地理范围内的种群之间是否存在差异仍知之甚少。方法我们检查了 7 个 Clarkia xantiana ssp 种群的花卉性状（雌雄同体、前体、花大小、花期柱头阶段、柱头接受时间）的变异。parviflora，一种主要的自交类群，从其分布的西部到东部边缘跨越。我们还进行了实验去雄和授粉（随后进行柱头切断）以量化跨花发育的异交机会的程度。结果所有花卉性状在种群间存在显着差异，尤其是远东和西方种群之间。去雄实验表明，东部种群在花后24小时内自交率最低，而西部种群自交率高。自体受精的种群变异可以通过花卉性状变异显着预测，尤其是前突和花瓣大小。结论 更大的前突既延长了异交可能发生的时间，又降低了自主自交的可能性，表明当传粉者访问不常见时，可能存在导致适应度损失的权衡。一些花卉性状的东西向分化模式与冰后范围扩大的模式相似，表明在范围扩大的过程中对交配系统的选择可能很强。