Ivey Christopher T, Dudley Leah S, Hove Alisa A, Emms Simon K, Mazer Susan J
California State University, Chico, CA 95929-0515, USA.
University of Wisconsin, Stout, Menomonie, WI 54751, USA.
Ann Bot. 2016 Oct 1;118(5):897-905. doi: 10.1093/aob/mcw134.
Background and Aims Mating systems of plants are diverse and evolutionarily labile. Abiotic environmental factors, such as seasonal drought, may impose selection on physiological traits that could lead to transitions in mating system if physiological traits are genetically correlated with traits that influence mating system. Within Clarkia, self-fertilizing taxa have higher photosynthetic rates, earlier flowering phenology, faster individual floral development and more compressed flowering periods than their outcrossing sister taxa, potentially reducing the selfing taxa's exposure to drought. In theory, this contrast in trait combinations between sister taxa could have arisen via correlated evolution due to pleiotropy or genetic linkage. Alternatively, each trait may evolve independently as part of a life history that is adaptive in seasonally dry environments. Methods To evaluate these hypotheses, we examined relationships between photosynthetic rates (adjusted for plant height and leaf node position) and outcrossing rates (estimated by allozyme variation in progeny arrays) during two consecutive years in multiple wild populations of two mixed-mating Clarkia taxa, each of which is sister to a derived selfing taxon. If the negative association between photosynthetic rate and outcrossing previously observed between sister taxa reflects correlated evolution due to a strong negative genetic correlation between these traits, then a similarly negative relationship would be observed within populations of each taxon. By contrast, if the combination of elevated photosynthetic rates and reduced outcrossing evolved independently within taxa, we predicted no consistent relationship between photosynthetic rate and outcrossing rate. Key Results We found no significant difference in outcrossing rates within populations between groups of plants with high versus low photosynthetic rates. Conclusions Overall, these results provide support for the hypothesis that the joint divergence in photosynthetic rate and mating system observed between Clarkia sister taxa is the result of independent evolutionary transitions.
背景与目的 植物的交配系统多种多样且在进化上不稳定。非生物环境因素，如季节性干旱，可能会对生理性状施加选择，如果生理性状与影响交配系统的性状存在遗传相关性，那么这种选择可能会导致交配系统的转变。在克拉花属植物中，自花受精的类群比其异交的姐妹类群具有更高的光合速率、更早的开花物候、更快的个体花发育速度以及更紧凑的花期，这可能会减少自交类群遭受干旱的风险。理论上，姐妹类群之间这种性状组合的差异可能是由于基因多效性或遗传连锁导致的相关进化产生的。或者，每个性状可能作为适应季节性干旱环境的生活史的一部分独立进化。方法 为了评估这些假设，我们在两个混合交配的克拉花分类群的多个野生种群中连续两年研究了光合速率（根据株高和叶节位置进行调整）与异交率（通过子代阵列中的等位酶变异估计）之间的关系，每个分类群都是一个衍生的自交类群的姐妹分类群。如果之前在姐妹类群之间观察到的光合速率与异交率之间的负相关反映了由于这些性状之间强烈的负遗传相关性导致的相关进化，那么在每个分类群的种群中也会观察到类似的负相关关系。相比之下，如果光合速率升高和异交率降低的组合在分类群内是独立进化的，我们预测光合速率与异交率之间不存在一致的关系。主要结果 我们发现光合速率高的植物组和光合速率低的植物组之间，种群内的异交率没有显著差异。结论 总体而言，这些结果支持了以下假设：在克拉花姐妹分类群之间观察到的光合速率和交配系统的共同差异是独立进化转变的结果。
