Glover Deborah E, Barrett Spencer C H
Department of Botany, University of Toronto, Toronto, Ontario, M5S 1A1, Canada.
Evolution. 1986 Nov;40(6):1122-1131. doi: 10.1111/j.1558-5646.1986.tb05738.x.
A multilocus procedure was used to estimate outcrossing rates from allozyme data in nine populations of Eichhornia paniculata from NE Brazil and Jamaica. The populations were chosen to represent stages in a proposed model of the evolutionary breakdown of tristyly to semi-homostyly; they differed in morph structure (trimorphic, dimorphic, or monomorphic) and floral traits likely to influence the mating system. The interpopulation range in outcrossing rate, t, was 0.96-0.29. Two additional populations from Jamaica, composed exclusively of self-pollinating, semi-homostylous, mid-styled plants, were invariant at 21 isozyme loci, precluding estimates of outcrossing frequency. Trimorphic populations from Brazil had uniformly high outcrossing rates of 0.96-0.88. Values for the floral morphs within populations were not significantly different. A controlled pollination experiment, comparing the competitive ability of self and cross pollen using the Got-3 marker locus, provided evidence that the maintenance of high outcrossing rates in trimorphic populations results from the prepotency of cross pollen and/or the selective abortion of selfed zygotes. Morph-dependent variation in t was detected within a dimorphic population with the L morph outcrossing with a frequency of 0.76 in comparison with 0.36 in the M morph. The difference in the mating system of floral morphs results from modifications in position of short-level stamens in flowers of the M morph resulting in automatic self-pollination. The occurrence of E. paniculata populations composed exclusively of self-pollinating, mid-styled variants is thought to be associated with the spread of genes modifying stamen position. The high level of self-fertilization demonstrated in the M morph would allow automatic selection of these genes, augmented by fertility assurance in the absence of specialized pollinators.
采用多位点程序，根据巴西东北部和牙买加的九个穗花狐尾藻种群的等位酶数据估算异交率。选择这些种群以代表一个从三型花柱进化到半同型花柱的拟议模型中的各个阶段；它们在形态结构（三型、二型或单型）以及可能影响交配系统的花部特征方面存在差异。异交率t的种群间范围为0.96 - 0.29。来自牙买加的另外两个种群，仅由自花授粉的半同型花柱、中型花柱植物组成，在21个同工酶位点上没有变异，无法估算异交频率。来自巴西的三型种群异交率一致较高，为0.96 - 0.88。种群内花部形态的值没有显著差异。一项控制授粉实验，使用Got - 3标记位点比较自花和异花花粉的竞争能力，提供了证据表明三型种群中高异交率的维持是由于异花花粉的优先性和/或自交合子的选择性败育。在一个二型种群中检测到了依赖形态的t变异，L型形态的异交频率为0.76，而M型形态为0.36。花部形态交配系统的差异是由于M型形态花朵中短水平雄蕊位置的改变导致自动自花授粉。仅由自花授粉的中型花柱变体组成的穗花狐尾藻种群的出现被认为与修饰雄蕊位置的基因传播有关。M型形态中表现出的高自交水平将允许对这些基因进行自动选择，在缺乏专门传粉者的情况下，育性保证会增强这种选择。
