Nosil Patrik, Egan Scott P, Funk Daniel J
Department of Zoology, University of British Columbia, Vancouver, BC, Canada.
Evolution. 2008 Feb;62(2):316-36. doi: 10.1111/j.1558-5646.2007.00299.x. Epub 2007 Nov 12.
Genetic differentiation can be highly variable across the genome. For example, loci under divergent selection and those tightly linked to them may exhibit elevated differentiation compared to neutral regions. These represent "outlier loci" whose differentiation exceeds neutral expectations. Adaptive divergence can also increase genome-wide differentiation by promoting general barriers to neutral gene flow, thereby facilitating genomic divergence via genetic drift. This latter process can yield a positive correlation between adaptive phenotypic divergence and neutral genetic differentiation (described here as "isolation-by-adaptation"). Here, we examine both these processes by combining an AFLP genome scan of two host plant ecotypes of Timema cristinae walking-sticks with existing data on adaptive phenotypic divergence and ecological speciation in these insects. We found that about 8% of loci are outliers in multiple population comparisons. Replicated comparisons between population-pairs using the same versus different host species revealed that 1-2% of loci are subject to host-related selection specifically. Locus-specific analyses revealed that up to 10% of putatively neutral (nonoutlier) AFLP loci exhibit significant isolation-by-adaptation. Our results suggest that selection may affect differentiation directly, via linkage, or by facilitating genetic drift. They thus illustrate the varied and sometimes nonintuitive contributions of selection to heterogeneous genomic differentiation.
遗传分化在整个基因组中可能具有高度变异性。例如,与中性区域相比,处于趋异选择下的基因座以及与其紧密连锁的基因座可能表现出更高的分化。这些代表了“异常基因座”,其分化超过了中性预期。适应性分化还可以通过促进对中性基因流动的一般障碍来增加全基因组的分化,从而通过遗传漂变促进基因组分化。后一过程可导致适应性表型分化与中性遗传分化之间产生正相关(在此称为“适应性隔离”)。在这里,我们通过结合对克氏细趾螳两个寄主植物生态型的AFLP基因组扫描以及这些昆虫适应性表型分化和生态物种形成的现有数据,来研究这两个过程。我们发现,在多个种群比较中,约8%的基因座是异常基因座。使用相同与不同寄主物种的种群对之间的重复比较表明,1 - 2%的基因座特别受到与寄主相关的选择。基因座特异性分析表明,高达10%的假定中性(非异常)AFLP基因座表现出显著的适应性隔离。我们的结果表明,选择可能通过连锁直接影响分化,或通过促进遗传漂变来影响分化。因此,它们说明了选择对异质基因组分化的多样且有时非直观的贡献。