Loiseau Claire, Richard Murielle, Garnier Stéphane, Chastel Olivier, Julliard Romain, Zoorob Rima, Sorci Gabriele
Laboratoire Parasitologie Evolutive, CNRS UMR 7103, Université Pierre et Marie Curie, Paris Cedex 05, France.
Mol Ecol. 2009 Apr;18(7):1331-40. doi: 10.1111/j.1365-294X.2009.04105.x.
Genes of the major histocompatibility complex (MHC) are the most polymorphic loci known in vertebrates. Two main hypotheses have been put forward to explain the maintenance of MHC diversity: pathogen-mediated selection and MHC-based mate choice. Host-parasite interactions can maintain MHC diversity via frequency-dependent selection, heterozygote advantage, and diversifying selection (spatially and/or temporally heterogeneous selection). In this study, we wished to investigate the nature of selection acting on the MHC class I across spatially structured populations of house sparrows (Passer domesticus) in France. To infer the nature of the selection, we compared patterns of population differentiation based on two types of molecular markers: MHC class I and microsatellites. This allowed us to test whether the observed differentiation at MHC genes merely reflects demographic and/or stochastic processes. At the global scale, diversifying selection seems to be the main factor maintaining MHC diversity in the house sparrow. We found that (i) overall population differentiation at MHC was stronger than for microsatellites, (ii) MHC marker showed significant isolation by distance. In addition, the slope of the regression of F(ST) on geographical distance was significantly steeper for MHC than for microsatellites due to a stronger pairwise differentiation between populations located at large geographical distances. These results are in agreement with the hypothesis that spatially heterogeneous selective pressures maintain different MHC alleles at local scales, possibly resulting in local adaptation.
主要组织相容性复合体（MHC）的基因是脊椎动物中已知的多态性最高的基因座。已经提出了两种主要假说来解释MHC多样性的维持：病原体介导的选择和基于MHC的配偶选择。宿主 - 寄生虫相互作用可以通过频率依赖性选择、杂合子优势和多样化选择（空间和/或时间上的异质选择）来维持MHC多样性。在本研究中，我们希望研究在法国家麻雀（Passer domesticus）的空间结构化种群中作用于MHC I类的选择性质。为了推断选择的性质，我们基于两种类型的分子标记比较了种群分化模式：MHC I类和微卫星。这使我们能够测试在MHC基因上观察到的分化是否仅仅反映了人口统计学和/或随机过程。在全球范围内，多样化选择似乎是维持家麻雀MHC多样性的主要因素。我们发现：（i）MHC的总体种群分化比微卫星更强；（ii）MHC标记显示出显著的距离隔离。此外，由于位于大地理距离的种群之间更强的成对分化，F(ST)对地理距离的回归斜率对于MHC来说比微卫星明显更陡。这些结果与以下假设一致，即空间异质的选择压力在局部尺度上维持不同的MHC等位基因，可能导致局部适应。
