Data from: Blood parasites shape extreme MHC diversity in a migratory passerine.

Pathogens are one of the main forces driving the evolution and maintenance of the highly polymorphic genes of the vertebrate major histocompatibility complex (MHC). Although MHC proteins are crucial in pathogen recognition, it is still poorly understood how pathogen-mediated selection promotes and maintains MHC diversity, and especially so in host species with highly duplicated MHC genes. Sedge warblers (Acrocephalus schoenobaenus) have highly duplicated MHC genes and using data from high-throughput MHC genotyping we were able to investigate to what extent avian malaria parasites explain temporal MHC class I supertype fluctuations in a long-term study population. We investigated infection status and infection intensities of two different strains of Haemoproteus, i.e. avian malaria parasites that are known to have significant fitness consequences in sedge warblers. We found that prevalence of avian malaria in carriers of specific MHC class I supertypes was a significant predictor of their frequency changes between years. This finding suggests that avian malaria infections partly drive the temporal fluctuations of the MHC class I supertypes. Furthermore, we found that individuals with a large number of different supertypes had higher resistance to avian malaria, but there was no evidence for an optimal MHC class I diversity. Thus, the two studied malaria parasite strains appear to select for a high MHC class I supertype diversity. Such selection may explain the maintenance of the extremely high number of MHC class I gene copies in sedge warblers, and possibly also in other passerines where avian malaria is a common disease.

病原体是推动脊椎动物主要组织相容性复合体（major histocompatibility complex, MHC）高度多态基因演化与维持的主要选择动力之一。尽管MHC蛋白在病原体识别过程中发挥核心作用，但学界对病原体介导的选择如何促进并维持MHC多样性的机制仍知之甚少，在MHC基因高度重复的宿主物种中这一问题尤为突出。芦莺（Acrocephalus schoenobaenus）的MHC基因存在大量重复拷贝，本研究借助高通量MHC基因分型数据，针对长期监测的研究种群，探究了禽疟原虫对MHC I类超型（supertype）时间波动的解释程度。我们针对两株不同的血变原虫（Haemoproteus，一类已被证实会对芦莺适合度产生显著影响的禽疟原虫）的感染状态与感染强度展开了分析。研究发现，携带特定MHC I类超型的个体的禽疟感染率，是其种群频率年度变化的显著预测因子。该结果表明，禽疟感染在一定程度上驱动了MHC I类超型的时间动态波动。此外，本研究发现，携带不同超型数量较多的个体对禽疟的抵抗力更强，但未发现存在最优MHC I类多样性的证据。综上，本研究中的两株疟原虫似乎对高MHC I类超型多样性存在选择压力。这种选择机制或可解释芦莺体内极多的MHC I类基因拷贝的维持原理，在禽疟高发的其他雀形目鸟类中或许同样适用。