Radwan Jacek, Kuduk Katarzyna, Levy Esther, LeBas Natasha, Babik Wiesław
Institute of Environmental Sciences, Jagiellonian University, Gronostajowa 7, 30-387, Kraków, Poland.
Mol Ecol. 2014 Dec;23(24):5966-78. doi: 10.1111/mec.12984. Epub 2014 Nov 24.
Major histocompatibility complex (MHC) gene polymorphism is thought to be driven by host-parasite co-evolution, but the evidence for an association between the selective pressure from parasites and the number of MHC alleles segregating in a population is scarce and inconsistent. Here, we characterized MHC class I polymorphism in a lizard whose habitat preferences (rock outcrops) lead to the formation of well-defined and stable populations. We investigated the association between the load of ticks, which were used as a proxy for the load of pathogens they transmit, and MHC class I polymorphism across populations in two types of habitat: undisturbed reserves and agricultural land. We hypothesized that the association would be positive across undisturbed reserve populations, but across fragmented agricultural land populations, the relationship would be distorted by the loss of MHC variation due to drift. After controlling for habitat, MHC diversity was not associated with tick number, and the habitats did not differ in this respect. Neither did we detect a difference between habitats in the relationship between MHC and neutral diversity, which was positive across all populations. However, there was extensive variation in the number of MHC alleles per individual, and we found that tick number was positively associated with the average number of alleles carried by lizards across reserve populations, but not across populations from disturbed agricultural land. Our results thus indicate that local differences in selection from parasites may contribute to MHC copy number variation within species, but habitat degradation can distort this relationship.
主要组织相容性复合体（MHC）基因多态性被认为是由宿主 - 寄生虫共同进化驱动的，但寄生虫的选择压力与种群中分离的MHC等位基因数量之间存在关联的证据却很少且不一致。在这里，我们对一种蜥蜴的MHC I类多态性进行了表征，这种蜥蜴的栖息地偏好（岩石露头）导致形成了明确且稳定的种群。我们调查了蜱虫负载量（用作它们传播的病原体负载量的替代指标）与两种栖息地（未受干扰的保护区和农田）中不同种群的MHC I类多态性之间的关联。我们假设，在未受干扰的保护区种群中这种关联将是正向的，但在碎片化的农田种群中，由于遗传漂变导致的MHC变异丧失会使这种关系发生扭曲。在控制了栖息地因素后，MHC多样性与蜱虫数量无关，并且在这方面两种栖息地没有差异。我们也未检测到MHC与中性多样性之间的关系在不同栖息地存在差异，这种关系在所有种群中都是正向的。然而，每个个体的MHC等位基因数量存在广泛变异，并且我们发现蜱虫数量与保护区种群中蜥蜴携带的平均等位基因数量呈正相关，但与受干扰农田种群中的蜥蜴携带的平均等位基因数量无关。因此，我们的结果表明，寄生虫选择的局部差异可能导致物种内MHC拷贝数变异，但栖息地退化会扭曲这种关系。
