Mable Barbara K, Adam A
Department of Botany, University of Guelph, Guelph, Ontario, Canada N1G 2W1.
Mol Ecol. 2007 Sep;16(17):3565-80. doi: 10.1111/j.1365-294X.2007.03416.x.
Arabidopsis lyrata is normally considered an obligately outcrossing species with a strong self-incompatibility system, but a shift in mating system towards inbreeding has been found in some North American populations (subspecies A. lyrata ssp. lyrata). This study provides a survey of the Great Lakes region of Canada to determine the extent of this mating system variation and how outcrossing rates are related to current population density, geographical distribution, and genetic diversity. Based on variation at microsatellite markers (progeny arrays to estimate multilocus outcrossing rates and population samples to estimate diversity measures) and controlled greenhouse pollinations, populations can be divided into two groups: (i) group A, consisting of individuals capable of setting selfed seed (including autogamous fruit set in the absence of pollinators), showing depressed outcrossing rates (T(m) = 0.2-0.6), heterozygosity (H(O) = 0.02-0.06) and genetic diversity (H(E) = 0.08-0.10); and (ii) group B, consisting of individuals that are predominantly self-incompatible (T(m) > 0.8), require pollinators for seeds set, and showing higher levels of heterozygosity (H(O) = 0.13-0.31) and diversity (H(E) = 0.19-0.410). Current population density is not related to the shift in mating system but does vary with latitude. Restricted gene flow among populations was evident among all but two populations (F(ST) = 0.11-0.8). Group A populations were more differentiated from one another (F(ST) = 0.78) than they were from group B populations (F(ST) = 0.59), with 41% of the variation partitioned within populations, 47% between populations, and 12% between groups. No significant relationship was found between genetic and geographical distance. Results are discussed in the context of possible postglacial expansion scenarios in relation to loss of self-incompatibility.
琴叶拟南芥通常被认为是一种具有强大自交不亲和系统的专性异交物种，但在一些北美种群（琴叶拟南芥亚种琴叶拟南芥）中发现了交配系统向近交的转变。本研究对加拿大五大湖地区进行了调查，以确定这种交配系统变异的程度，以及异交率与当前种群密度、地理分布和遗传多样性之间的关系。基于微卫星标记的变异（用于估计多位点异交率的子代阵列和用于估计多样性指标的种群样本）以及受控的温室授粉，种群可分为两组：（i）A组，由能够产生自交种子的个体组成（包括在没有传粉者的情况下的自花受精结实），异交率较低（T(m)=0.2-0.6），杂合度（H(O)=0.02-0.06）和遗传多样性（H(E)=0.08-0.10）；（ii）B组，由主要自交不亲和的个体组成（T(m)>0.8），需要传粉者才能结实，并且表现出较高水平的杂合度（H(O)=0.13-0.31）和多样性（H(E)=0.19-0.410）。当前种群密度与交配系统的转变无关，但随纬度变化。除两个种群外，所有种群之间的基因流动都受到限制（F(ST)=0.11-0.8）。A组种群之间的分化程度（F(ST)=0.78）高于它们与B组种群之间的分化程度（F(ST)=0.59），41%的变异存在于种群内部，47%存在于种群之间，12%存在于组间。未发现遗传距离与地理距离之间存在显著关系。我们在与自交不亲和丧失相关的可能的冰期后扩张情景的背景下讨论了结果。
