Ecol Evol. 2012 Feb;2(2):341-53. doi: 10.1002/ece3.86.
The ability of natural populations to adapt to new environmental conditions is crucial for their survival and partly determined by the standing genetic variation in each population. Populations with higher genetic diversity are more likely to contain individuals that are better adapted to new circumstances than populations with lower genetic diversity. Here, we use both neutral and major histocompatibility complex (MHC) markers to test whether small and highly fragmented populations hold lower genetic diversity than large ones. We use black grouse as it is distributed across Europe and found in populations with varying degrees of isolation and size. We sampled 11 different populations; five continuous, three isolated, and three small and isolated. We tested patterns of genetic variation in these populations using three different types of genetic markers: nine microsatellites and 21 single nucleotide polymorphisms (SNPs) which both were found to be neutral, and two functional MHC genes that are presumably under selection. The small isolated populations displayed significantly lower neutral genetic diversity compared to continuous populations. A similar trend, but not as pronounced, was found for genotypes at MHC class II loci. Populations were less divergent at MHC genes compared to neutral markers. Measures of genetic diversity and population genetic structure were positively correlated among microsatellites and SNPs, but none of them were correlated to MHC when comparing all populations. Our results suggest that balancing selection at MHC loci does not counteract the power of genetic drift when populations get small and fragmented.
自然种群适应新环境条件的能力对其生存至关重要，部分取决于每个种群中存在的遗传变异。遗传多样性较高的种群比遗传多样性较低的种群更有可能包含适应新环境的个体。在这里，我们使用中性和主要组织相容性复合体 (MHC) 标记来测试小而高度碎片化的种群是否比大种群具有更低的遗传多样性。我们选择了黑松鸡作为研究对象，因为它分布在整个欧洲，并且存在着不同程度的隔离和大小的种群。我们对 11 个不同的种群进行了采样，其中 5 个是连续的，3 个是隔离的，3 个是小而隔离的。我们使用三种不同类型的遗传标记来测试这些种群中的遗传变异模式：9 个微卫星和 21 个单核苷酸多态性 (SNP)，它们都被发现是中性的，以及两个假定受到选择的功能性 MHC 基因。与连续种群相比，小而隔离的种群表现出明显较低的中性遗传多样性。在 MHC 类 II 基因座的基因型中也发现了类似的趋势，但不那么明显。与中性标记相比，MHC 基因的种群分化程度较低。在微卫星和 SNP 之间，遗传多样性和种群遗传结构的测量值呈正相关，但在比较所有种群时，它们与 MHC 均没有相关性。我们的结果表明，当种群变得小而碎片化时，MHC 基因座上的平衡选择并不能抵消遗传漂变的影响。
