Ritland Kermit, Ganders Fred R
Department of Botany, University of Toronto, Toronto, ON, M5S 1A1, Canada.
Department of Botany, University of British Columbia, Vancouver, BC, V6T 2B1, Canada.
Evolution. 1987 Jul;41(4):772-786. doi: 10.1111/j.1558-5646.1987.tb05852.x.
The joint effects of parental gene fixation and consanguinity of mates upon the fitness of matings was examined in Mimulus guttatus. Plants from four populations were crossed at five levels of genetic relatedness, and five viability characters were scored in progeny. Parental gene fixation at 12 polymorphic allozyme loci was partitioned into local, subpopulation, and population components. A model is proposed wherein parental gene fixation influences distance-dependent crossing success. At a fixed locus, inbreeding is favored if natural selection caused allele fixation, or is disfavored if gene fixation was random. The distance between mates required to eliminate gene fixation depends upon patch size of fixation. When selective fixation and patch size differ among loci, an optimal crossing distance is possible. In M. guttatus, progeny viability generally decreased with greater relatedness between mates, but this decrease was often heterogeneous among populations. The highest pollen viability and the lowest seed set were found at an intermediate relatedness between mates. To determine whether parental gene fixation influences these crossing patterns, a type of mutational-load analysis was performed. Progeny fitness was regressed on parent F and fitness estimated at F = 1. This was done for each component of F, for a) crosses that maintain gene fixation and b) crosses that eliminate gene fixation. A multiplicative, composite measure of fitness indicates that, in M. guttatus, genes fixed during local or population differentiation favor outbreeding, while genes fixed during subpopulation differentiation favor inbreeding. This predicts that random mating within subpopulations confers highest progeny fitness, exclusive of between-population matings. However, predictions did not fit the observed patterns of crossing success very well, perhaps because gene fixation was relatively low or was not adequately measured at loci influencing fitness.
在沟酸浆属植物中研究了亲本基因固定和配偶间亲缘关系对交配适合度的联合效应。来自四个种群的植株在五个遗传相关水平上进行杂交，并对后代的五个活力性状进行评分。在12个多态性等位酶位点上的亲本基因固定被划分为局部、亚种群和种群组分。提出了一个模型，其中亲本基因固定影响距离依赖性杂交成功率。在一个固定位点，如果自然选择导致等位基因固定，则近亲繁殖是有利的；如果基因固定是随机的，则近亲繁殖是不利的。消除基因固定所需的配偶间距离取决于固定的斑块大小。当不同位点的选择固定和斑块大小不同时，可能存在一个最佳杂交距离。在沟酸浆属植物中，后代活力通常随着配偶间亲缘关系的增加而降低，但这种降低在不同种群中往往是不均匀的。在配偶间中等亲缘关系时发现了最高的花粉活力和最低的结实率。为了确定亲本基因固定是否影响这些杂交模式，进行了一种突变负荷分析。将后代适合度对亲本F进行回归，并估计F = 1时的适合度。对F的每个组分都这样做，分别针对a）维持基因固定的杂交和b）消除基因固定的杂交。一种适合度的乘法复合度量表明，在沟酸浆属植物中，在局部或种群分化过程中固定的基因有利于远交，而在亚种群分化过程中固定的基因有利于近交。这预测亚种群内的随机交配赋予后代最高的适合度，不包括种群间的交配。然而，预测结果与观察到的杂交成功模式不太吻合，可能是因为基因固定相对较低，或者在影响适合度的位点上没有得到充分测量。
