Long-term balancing selection: From ecological mechanisms to genetic footprints

平衡选择的概念是指生态和进化机制，可以保持两个或两个以上的等位基因在一个种群的基因座。这种机制的重要例子是杂合子优势，选择压力在时间和空间上的变化，基因型竞争资源和应对竞争的方式的差异，以及宿主-寄生虫相互作用。这些机制不一定是相互排斥的;例如，一些时间异质性的情况下，杂合子有一个更高的几何平均健身比纯合子。根据生态情景和遗传结构，等位基因可以通过新的突变（等位基因更替）定期再生，或者在极长的时间内稳定维持，甚至跨物种或属。这种反式特异性多态性最近在许多分类学类群中被发现，包括果蝇属和植物属拟南芥。然而，目前尚不清楚如何区分基于遗传数据的多样性维持的各种可能机制。在这个项目中，我们将结合联合收割机从进化生态学（适应动力学）和群体遗传学（结合理论）的建模方法，以获得预期的遗传足迹平衡选择下的时空异质性，繁荣-萧条竞争的情况下，宿主-寄生虫的协同进化-机制，已牵连在果蝇和拟南芥的多样性维持。基于这些结果，我们将开发一个生态情景的分类框架，这将突出从遗传数据中推断长期平衡选择机制的潜力和局限性。使用这个框架，我们将推断或缩小果蝇和拟南芥中反式特异性多态性的可能解释。

The concept of balancing selection refers to ecological and evolutionary mechanisms that can maintain two or more alleles at a locus in a population. Important examples for such mechanisms are heterozygote advantage, selection pressures varying across time and space, differences in the way genotypes compete for resources and respond to competition, and host-parasite interactions. These mechanisms are not necessarily mutually exclusive; for example some of the temporally heterogeneous scenarios cause heterozygotes to have a higher geometric mean fitness than homozygotes. Depending on ecological scenario and genetic architecture, alleles can be regularly regenerated by new mutations (allelic turnover) or stably maintained over extremely long time periods, even across species or genera. Such trans-specific polymorphisms have recently been found in many taxonomic groups, including the fruit fly genus Drosophila and the plant genus Arabidopsis. However, it is currently unclear how to distinguish between the various possible mechanisms of diversity maintenance based on genetic data. In this project, we will combine modeling approaches from evolutionary ecology (adaptive dynamics) and from population genetics (coalescent theory) to derive the expected genetic footprints of balancing selection under spatio-temporal heterogeneity, boom-bust competition scenarios, and host-parasite coevolution - mechanisms that have been implicated in diversity maintenance in Drosophila and Arabidopsis. Based on these results, we will develop a classification framework of ecological scenarios, which will highlight the potential and the limitations for inferring mechanisms underlying long-term balancing selection from genetic data. Using this framework, we will then infer or narrow down possible explanations for trans-specific polymorphism in Drosophila and Arabidopsis.