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Abstract：
Many studies have quantified the distribution of heterozygosity and relatedness in natural populations, but few have examined the demographic processes driving these patterns. In this study, we take a novel approach by studying how population structure affects both pairwise identity and the distribution of heterozygosity in a natural population of the self-incompatible plant Antirrhinum majus. Excess variance in heterozygosity between individuals is due to identity disequilibrium, which reflects the variance in inbreeding between individuals; it is measured by the statistic g2. We calculated g2 together with FST and pairwise relatedness (Fij) using 91 SNPs in 22,353 individuals collected over 11 years. We find that pairwise Fij declines rapidly over short spatial scales, and the excess variance in heterozygosity between individuals reflects significant variation in inbreeding. Additionally, we detect an excess of individuals with around half the average heterozygosity, indicating either selfing or matings between close relatives. We use 2 types of simulation to ask whether variation in heterozygosity is consistent with fine-scale spatial population structure. First, by simulating offspring using parents drawn from a range of spatial scales, we show that the known pollen dispersal kernel explains g2. Second, we simulate a 1,000-generation pedigree using the known dispersal and spatial distribution and find that the resulting g2 is consistent with that observed from the field data. In contrast, a simulated population with uniform density underestimates g2, indicating that heterogeneous density promotes identity disequilibrium. Our study shows that heterogeneous density and leptokurtic dispersal can together explain the distribution of heterozygosity.
摘要：
许多研究已经量化了自然种群中杂合性和相关性的分布，但是很少有人研究过推动这些模式的人口统计学过程。在这项研究中,我们采用了一种新颖的方法，通过研究种群结构如何影响自交不亲和植物Antirrrhinummajus的自然种群中的成对同一性和杂合性分布。个体之间杂合性的过度差异是由于身份不平衡，它反映了个体之间近亲繁殖的差异；它由统计量g2衡量。我们使用11年收集的22,353名个体中的91个SNP计算了g2与FST和成对相关性（Fij）。我们发现，成对的Fij在短空间尺度上迅速下降，个体间杂合度的过度变异反映了近交的显著变异。此外,我们检测到超过平均杂合性一半的个体，表明近亲之间的自交或交配。我们使用2种类型的模拟来询问杂合性的变异是否与精细尺度空间种群结构一致。首先,通过使用从一系列空间尺度中提取的父母来模拟后代，我们证明了已知的花粉散粒解释了g2。第二,我们使用已知的散布和空间分布模拟了1000代谱系，发现所得的g2与从野外数据观察到的一致。相比之下,具有均匀密度的模拟种群低估了g2，表明异质密度促进了身份不平衡。我们的研究表明，异质密度和leptokurtic分散可以共同解释杂合性的分布。
