School of Biological Sciences, Washington State University, P.O. Box 644236, Pullman, Washington 99164-4236 USA.
Am J Bot. 2000 Jun;87(6):783-92.
Rare species are typically considered to maintain low levels of genetic variation, and this view has been supported by several reviews of large numbers of isozyme studies. Although these reviews have provided valuable data on levels of variability in plant species in general, and rare species in particular, these broad overviews involve comparisons that may confound the effects of rarity with a multitude of other factors that affect genetic variability. Additionally, the statistical analyses employed assume the data to be independent, which is not the case for organisms that share a common phylogenetic history. As the role of evolutionary history and historical constraints has become better understood, more researchers have studied widespread congeners when investigating the genetic diversity of rare species in an effort to control for these effects. We summarize the available data from such studies, comparing for rare and widespread congeners (1) the levels of genetic variability at the population and species levels and (2) measures of population substructuring. At the population level, we summarized data for percentage polymorphic loci (%P(pop)), mean number of alleles per locus (A(pop)), and observed heterozygosity (H(o)). Species-level measures used were percentage polymorphic loci (%P(spp)), mean number of alleles per locus (A(spp)), and total genetic diversity (H(T)). Indices of population subdivision (either F(ST) or G(ST)) were also examined. Using Wilcoxon signed rank tests, we found significant, but small, differences between rare and widespread species for all diversity measures except H(T). However, there does not appear to be a difference between rare and widespread congeners in terms of how genetic variation is partitioned within and among populations. Levels of diversity, for all measures examined, between rare and widespread congeners are highly correlated.
稀有物种通常被认为遗传变异水平较低，这一观点得到了许多同工酶研究大量综述的支持。尽管这些综述为一般植物物种，特别是稀有物种的变异水平提供了有价值的数据，但这些广泛的综述涉及的比较可能会将稀有物种的影响与影响遗传可变性的众多其他因素混淆。此外，所采用的统计分析假设数据是独立的，而对于具有共同系统发育历史的生物体则不是这样。随着进化历史和历史约束作用的理解不断加深，越来越多的研究人员在研究稀有物种的遗传多样性时，研究了广泛的同属种，以控制这些影响。我们总结了这些研究中可用的数据，比较了稀有和广泛同属种之间的（1）种群和物种水平的遗传变异水平和（2）种群亚结构的衡量标准。在种群水平上，我们总结了多态性基因座百分比（%P(pop)）、每个基因座平均等位基因数（A(pop)）和观测杂合度（H(o)）的数据。物种水平的衡量标准包括多态性基因座百分比（%P(spp)）、每个基因座平均等位基因数（A(spp)）和总遗传多样性（H(T)）。种群划分指数（F(ST)或 G(ST)）也进行了研究。使用 Wilcoxon 符号秩检验，我们发现除 H(T)外，所有多样性衡量标准在稀有和广泛物种之间存在显著但较小的差异。然而，在遗传变异在种群内部和种群之间的分配方式方面，稀有和广泛同属种之间似乎没有差异。在所有检查的衡量标准中，稀有和广泛同属种之间的多样性水平高度相关。
