Plant and Invertebrate Ecology, Rothamsted Research, Harpenden Herts, UK.
Heredity (Edinb). 2011 May;106(5):798-807. doi: 10.1038/hdy.2010.121. Epub 2010 Oct 6.
Studying host-based divergence naturally maintained by a balance between selection and gene flow can provide valuable insights into genetic underpinnings of host adaptation and ecological speciation in parasites. Selection-gene flow balance is often postulated in sympatric host races, but direct experimental evidence is scarce. In this study, we present such evidence obtained in host races of Aphidius ervi, an important hymenopteran agent of biological control of aphids in agriculture, using a novel fusion-fission method of gene flow perturbation. In our study, between-race genetic divergence was obliterated by means of advanced hybridisation, followed by a multi-generation exposure of the resulting genetically uniform hybrid swarm to a two-host environment. This fusion-fission procedure was implemented under two contrasting regimes of between-host gene flow in two replicated experiments involving different racial pairs. Host-based genetic fission in response to environmental bimodality occurred in both experiments in as little as six generations of divergent adaptation despite continuous gene flow. We demonstrate that fission recovery of host-based divergence evolved faster and hybridisation-induced linkage disequilibrium decayed slower under restricted (6.7%) compared with unrestricted gene flow, directly pointing at a balance between gene flow and divergent selection. We also show, in four separate tests, that random drift had no or little role in the observed genetic split. Rates and patterns of fission divergence differed between racial pairs. Comparative linkage analysis of these differences is currently under way to test for the role of genomic architecture of adaptation in ecology-driven divergent evolution.
研究由选择和基因流平衡自然维持的基于宿主的分歧，可以为寄生虫宿主适应和生态物种形成的遗传基础提供有价值的见解。选择-基因流平衡通常在同域宿主群体中被假设，但直接的实验证据很少。在这项研究中，我们使用一种新的基因流干扰融合-裂变方法，在农业中重要的膜翅目生物防治剂桃蚜茧蜂的宿主群体中提供了这样的证据。在我们的研究中，通过先进的杂交手段消除了种族间的遗传分歧，然后将产生的遗传上均匀的杂交群体在双宿主环境中暴露多代。在涉及不同种族对的两个重复实验中，在两种不同的宿主间基因流条件下实施了这种融合-裂变程序。尽管存在连续的基因流，但在短短 6 代的分歧适应后，在两个实验中都发生了对环境双峰性的基于宿主的遗传分裂。我们证明，与不受限制的基因流相比，在限制（6.7%）的基因流下，基于宿主的分歧的裂变恢复更快，杂交诱导的连锁不平衡衰减更慢，这直接指向了基因流和分歧选择之间的平衡。我们还在四个单独的测试中表明，随机漂变在观察到的遗传分裂中没有或几乎没有作用。裂变分歧的速度和模式在种族对之间有所不同。目前正在进行这些差异的比较连锁分析，以检验适应的基因组结构在生态驱动的分歧进化中的作用。
