蜥蜴中 MHC 多态性的选择、漂移和基因渗入,Heredity

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蜥蜴中 MHC 多态性的选择、漂移和基因渗入
Heredity ( IF 3.1 ) Pub Date : 2018-09-26 , DOI: 10.1038/s41437-018-0146-2
K Sagonas _{1,

2} , A Runemark _{3,

4} , A Antoniou ₅ , P Lymberakis ₆ , P Pafilis ₇ , E D Valakos ₂ , N Poulakakis _{6,

8} , B Hansson ₃

Affiliation

主要组织相容性复合体（MHC）长期以来一直充当野生种群适应性遗传多样性进化的模型。病原体介导的选择被认为是 MHC 多样性的主要驱动因素，但在其他进化过程（例如遗传漂变和基因渗入）也可能发挥作用的复杂生物地理场景中，选择在多大程度上塑造了 MHC 多样性仍然难以捉摸。在这里，我们重点关注两个密切相关的绿蜥蜴物种，Lacerta trilineata 和 L. viridis，以解决不同生物地理结构种群中 MHC 多样性的进化力量。我们对 MHC I 类外显子 2 和外显子 3 以及中性多样性（微卫星）进行了表征，以研究选择、漂移和基因渗入在塑造 MHC 多样性方面的相对重要性。正如预期的那样，正选择是塑造两个物种 MHC 基因高度多样性的重要力量。此外，基因渗入显着增加了大陆种群的 MHC 多样性，基因流的主要方向是从 L. viridis 到 L. trilineata。最后，我们发现岛屿种群中的 MHC 等位基因明显较少，但保持了 MHC 序列和功能多样性，这表明正选择抵消了漂移的影响。总体而言，我们的数据支持不同的进化过程在不同的生物地理场景中控制 MHC 多样性：正选择广泛发生，而基因渗入则在种群规模减少时以同源和漂移的方式发生。

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Selection, drift, and introgression shape MHC polymorphism in lizards

The major histocompatibility complex (MHC) has long served as a model for the evolution of adaptive genetic diversity in wild populations. Pathogen-mediated selection is thought to be a main driver of MHC diversity, but it remains elusive to what degree selection shapes MHC diversity in complex biogeographical scenarios where other evolutionary processes (e.g. genetic drift and introgression) may also be acting. Here we focus on two closely related green lizard species, Lacerta trilineata and L. viridis, to address the evolutionary forces acting on MHC diversity in populations with different biogeographic structure. We characterized MHC class I exon 2 and exon 3, and neutral diversity (microsatellites), to study the relative importance of selection, drift, and introgression in shaping MHC diversity. As expected, positive selection was a significant force shaping the high diversity of MHC genes in both species. Moreover, introgression significantly increased MHC diversity in mainland populations, with a primary direction of gene flow from L. viridis to L. trilineata. Finally, we found significantly fewer MHC alleles in island populations, but maintained MHC sequence and functional diversity, suggesting that positive selection counteracted the effect of drift. Overall, our data support that different evolutionary processes govern MHC diversity in different biogeographical scenarios: positive selection occurs broadly while introgression acts in sympatry and drift when the population sizes decrease.

更新日期：2018-09-26

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