Department of Biological Sciences, University of Pittsburgh, 4249 Fifth Avenue, Pittsburgh, PA 15260, USA.
Ann Bot. 2012 Feb;109(3):571-82. doi: 10.1093/aob/mcr237. Epub 2011 Oct 6.
How and why plants evolve to become selfing is a long-standing evolutionary puzzle. The transition from outcrossing to highly selfing is less well understood in self-compatible (SC) mixed-mating (MM) species where potentially subtle interactions between floral phenotypes and the environment are at play. We examined floral morphological and developmental traits across an entire SC MM genus, Collinsia, to determine which, if any, predict potential autonomous selfing ability when pollinators are absent (AS) and actual selfing rates in the wild, s(m), and to best define the selfing syndrome for this clade.
Using polymorphic microsatellite markers, we obtained 30 population-level estimates of s(m) across 19 Collinsia taxa. Species grand means for the timing of herkogamy (stigma-anther contact) and dichogamy (stigmatic receptivity, SR), AS, floral size, longevity and their genetic correlations were quantified for 22 taxa.
Species fell into discrete selfing and outcrossing groups based on floral traits. Loss of dichogamy defines Collinsia's selfing syndrome. Floral size, longevity and herkogamy also differ significantly between these groups. Most taxa have high AS rates (>80 %), but AS is uncorrelated with any measured trait. In contrast, s(m) is significantly correlated only with SR. High variance in s(m) was observed in the two groups.
Collinsia species exhibit clear morphological and developmental traits diagnostic of 'selfing' or 'outcrossing' groups. However, many species in both the 'selfing' and the 'outcrossing' groups were MM, pointing to the critical influence of the pollination environment, the timing of AS and outcross pollen prepotency on s(m). Flower size is a poor predictor of Collinsia species' field selfing rates and this result may apply to many SC species. Assessment of the variation in the pollination environment, which can increase selfing rates in more 'outcrossing' species but can also decrease selfing rates in more 'selfing' species, is critical to understanding mating system evolution of SC MM taxa.
植物如何以及为何进化为自交是一个长期存在的进化谜题。在自交亲和（SC）、混合交配（MM）物种中，从异交向高度自交的转变理解得还不够充分，因为花部表型和环境之间的潜在微妙相互作用在起作用。我们检查了整个 SC-MM 属 Collinsia 的花部形态和发育特征，以确定在没有传粉者时（AS）和实际野外自交率（s(m)）中，哪些特征如果有的话，可以预测潜在的自主自交能力，并为这个分支最好地定义自交综合征。
使用多态性微卫星标记，我们获得了 19 个 Collinsia 分类群的 30 个种群水平的 s(m)估计值。对 22 个分类群的雌雄蕊先熟（柱头-花药接触）和雌雄蕊异熟（柱头可授性，SR）、AS、花部大小、寿命及其遗传相关性的物种总平均值进行了量化。
根据花部特征，物种分为离散的自交和异交组。雌雄蕊异熟的丧失定义了 Collinsia 的自交综合征。花部大小、寿命和雌雄蕊先熟也在这两组之间有显著差异。大多数分类群的 AS 率都很高（>80%），但 AS 与任何测量的特征都没有相关性。相比之下，s(m)仅与 SR 显著相关。在这两个组中观察到 s(m)的方差很高。
Collinsia 物种表现出明显的形态和发育特征，可诊断为“自交”或“异交”组。然而，“自交”和“异交”组中的许多物种都是 MM，这表明授粉环境、AS 时机和异交花粉前优势对 s(m)的重要影响。花部大小是 Collinsia 物种田间自交率的一个很差的预测因子，这一结果可能适用于许多 SC 物种。评估授粉环境的变化对于理解 SC-MM 分类群的交配系统进化至关重要，因为这种变化可以增加更“异交”物种的自交率，但也可以降低更“自交”物种的自交率。
