The major histocompatibility complex (MHC) genes code for key immune receptors responsible for recognition of intra- and extracellular pathogens (MHC class I and class II, respectively). It was hypothesized that MHC polymorphism can be maintained via fluctuating selection resulting from between-habitat variation in pathogen regimes. We examined associations between MHC class I and class II genes and habitat structure in an apex avian predator, the white-tailed eagle, Haliaeetus albicilla. We genotyped MHC class I and class II genes in ca. 150 white-tailed eagle chicks from nearly 100 nesting territories distributed across 3 distinct populations in Poland. Habitat structure was quantified at the level of foraging territories and directly at the nest sites. We found strong support for associations of habitat traits with diversity and allelic composition at the MHC class II. Forest area within territory and forest productivity were identified as the major habitat predictors of MHC class II polymorphism, whereas other habitat traits (distance to nearest open water, grassland, and water area within territory or understory presence) showed fewer associations with class II alleles. In contrast, there was little support for associations between MHC class I genes and habitat structure. All significant associations were apparent at the within-population level rather than between populations. Our results suggest that extracellular (rather than intracellular) pathogens may exert much stronger selective pressure on the white-tailed eagle. Associations of habitat structure with MHC class II may reflect fluctuating (balancing) selection, which maintains MHC diversity within populations.

中文翻译：

---

MHC 反映白尾鹰、Haliaeetus albicilla 的精细栖息地结构

主要组织相容性复合体 (MHC) 基因编码负责识别细胞内和细胞外病原体（分别为 MHC I 类和 II 类）的关键免疫受体。据推测，MHC 多态性可以通过由病原体状态的栖息地间变异引起的波动选择来维持。我们检查了顶级鸟类捕食者白尾鹰 Haliaeetus albicilla 中 MHC I 类和 II 类基因与栖息地结构之间的关联。我们在 ca 中对 MHC I 类和 II 类基因进行了基因分型。来自近 100 个筑巢地区的 150 只白尾鹰雏鸟分布在波兰的 3 个不同种群中。栖息地结构在觅食区域和直接在巢穴位置进行量化。我们在 MHC II 类中发现了对栖息地特征与多样性和等位基因组成的关联的强烈支持。领土内的森林面积和森林生产力被确定为 MHC II 类多态性的主要栖息地预测因子，而其他栖息地特征（到最近的开阔水域、草地和领土内的水域或林下存在的距离）与 II 类等位基因的关联较少。相比之下，几乎没有支持 MHC I 类基因与栖息地结构之间的关联。所有显着的关联在人群内而不是人群之间都是明显的。我们的研究结果表明，细胞外（而不是细胞内）病原体可能对白尾鹰施加更强的选择压力。