Department of Entomology, Max-Planck-Institute for Chemical Ecology, Jena, Germany.
BMC Evol Biol. 2010 Feb 24;10:60. doi: 10.1186/1471-2148-10-60.
A molecular population genetics understanding is central to the study of ecological and evolutionary functional genomics. Population genetics identifies genetic variation and its distribution within and among populations, it reveals the demographic history of the populations studied, and can provide indirect insights into historical selection dynamics. Here we use this approach to examine the demographic and selective dynamics acting of a candidate gene involved in plant-insect interactions. Previous work documents the macroevolutionary and historical ecological importance of the nitrile-specifier protein (Nsp), which facilitated the host shift of Pieridae butterflies onto Brassicales host plants approximately 80 Myr ago.
Here we assess the microevolutionary dynamics of the Nsp gene by studying the within and among-population variation at Nsp and reference genes in the butterfly Pieris rapae (Small Cabbage White). Nsp exhibits unexpectedly high amounts of amino acid polymorphism, unequally distributed across the gene. The vast majority of genetic variation exists within populations, with little to no genetic differentiation among four populations on two continents. A comparison of synonymous and nonsynonymous substitutions in 70 randomly chosen genes among P. rapae and its close relative Pieris brassicae (Large Cabbage White) finds Nsp to have a significantly relaxed functional constraint compared to housekeeping genes. We find strong evidence for a recent population expansion and no role for strong purifying or directional selection upon the Nsp gene.
The microevolutionary dynamics of the Nsp gene in P. rapae are dominated by recent population expansion and variation in functional constraint across the repeated domains of the Nsp gene. While the high amounts of amino acid diversity suggest there may be significant functional differences among allelic variants segregating within populations, indirect tests of selection could not conclusively identify a signature of historical selection. The importance of using this information for planning future studies of potential performance and fitness consequences of the observed variation is discussed.
分子群体遗传学的理解是研究生态和进化功能基因组学的核心。群体遗传学识别遗传变异及其在种群内和种群间的分布，揭示所研究种群的人口历史，并能提供对历史选择动态的间接了解。在这里，我们使用这种方法来研究参与植物-昆虫相互作用的候选基因的种群和选择动态。以前的工作记录了腈特指定蛋白（Nsp）的宏观进化和历史生态重要性，它促进了凤蝶科蝴蝶大约 8000 万年前转移到十字花科植物上。
在这里，我们通过研究凤蝶 Pieris rapae（小菜蛾）中 Nsp 和参照基因的种群内和种群间变异来评估 Nsp 基因的微观进化动态。Nsp 表现出出人意料的高氨基酸多态性，在整个基因中分布不均。绝大多数遗传变异存在于种群内部，在两个大陆的四个种群之间几乎没有遗传分化。在 70 个随机选择的基因中比较了 P. rapae 及其近缘种 Pieris brassicae（大菜粉蝶）的同义和非同义替换，发现 Nsp 与管家基因相比，其功能约束明显放松。我们发现有强烈的证据表明最近发生了种群扩张，而且 Nsp 基因没有强烈的纯化或定向选择作用。
Nsp 基因在 P. rapae 中的微观进化动态主要由近期的种群扩张和 Nsp 基因重复结构域的功能约束变化所决定。虽然氨基酸多样性的大量存在表明，在种群内分离的等位基因变体之间可能存在显著的功能差异，但对选择的间接测试不能明确确定历史选择的特征。讨论了利用这一信息来规划未来研究观察到的变异对潜在性能和适应性影响的重要性。
