In natural populations, hybridization is known to occur between a wide range of species. However, its evolutionary significance is less clear. Genes involved in fighting pathogens are considered excellent candidates for studying adaptive introgression, although both introgression and balancing selection can generate similar patterns of diversity and differentiation. Here, we compared DQA and DQB MHC class II and microsatellite allelic diversity of sympatric and parapatric mountain (Lepus timidus) and brown hare (L. europaeus) populations from Switzerland. We detected higher genetic diversity in brown hares compared to mountain hares at both MHC and microsatellite loci. We consider the observed patterns of microsatellite diversity both for L. europaeus and L. timidus as result of stochastic demographic processes while the pattern of MHC polymorphism of the studied hare populations can be explained by pathogen-driven selection. Rare bidirectional gene flow between both hare species seems to occur specifically for MHC alleles. However, the high number of shared alleles showing similar high frequency in both species suggests that reciprocally exchanged MHC alleles are being maintained via balancing selection. Adaptation to similar pathogen communities can also lead to parallel selection of MHC alleles. Positive selection, recombination and mutations have played different roles in shaping the patterns of MHC allelic diversity in and differentiation between both species. Results for the latter evolutionary forces do not show a better matching between the sympatric populations compared to the parapatric ones, suggesting a minor role of introgression for the observed evolutionary patterns of the studied hare species.

在自然种群中，已知多种物种之间会发生杂交。然而，其进化意义尚不清楚。尽管基因渗入和平衡选择都可以产生相似的多样性和分化模式，但参与对抗病原体的基因被认为是研究适应性基因渗入的优秀候选者。在这里，我们比较了 DQA 和 DQB MHC II 类和微卫星等位基因多样性同域和同域山地 (Lepus timidus) 和棕兔 (L. europaeus) 来自瑞士的人口。与山兔相比，我们在 MHC 和微卫星位点上检测到棕色野兔具有更高的遗传多样性。我们考虑了 L 的微卫星多样性的观测模式。欧洲和L。 timidus 是随机人口统计过程的结果，而所研究的野兔群体的 MHC 多态性模式可以通过病原体驱动的选择来解释。两种野兔之间罕见的双向基因流似乎专门针对 MHC 等位基因而发生。然而，两个物种中大量共享等位基因表现出相似的高频率，表明相互交换的 MHC 等位基因是通过平衡选择得以维持的。对相似病原体群落的适应也可能导致 MHC 等位基因的平行选择。正选择、重组和突变在塑造两个物种的 MHC 等位基因多样性模式和分化方面发挥着不同的作用。后一种进化力量的结果并未显示同域种群与近域种群相比具有更好的匹配性，这表明基因渗入对于所研究的野兔物种观察到的进化模式的作用较小。