MHC diversity, migration and pathogens: effects of host-pathogen interactions on fitness traits in greater flamingos across the Mediterranean basin and west Africa.

长距离迁移和扩散可能在病原体在广泛地理区域的传播中发挥核心作用，这对野生动物、牲畜和人类健康具有重要影响。特别是，长途迁徙和分散的水鸟经常被认为在水传播的胃肠道病原体的广泛地理传播中起着核心作用，这些病原体污染了野生动物和人类活动的关键水体。然而，在长距离分散的物种中，宿主-病原体的相互作用在很大程度上仍然未知。免疫遗传多样性，包括脊椎动物中最多样化的免疫基因，主要组织相容性复合体（MHC）基因，通常被认为与适应潜力相关，并由强大的病原体介导的选择（PMS）形成。PMS如何塑造MHC多样性将取决于鲜为人知的病原体群落在远距离分散时所遇到的时空动态。远距离传播可能使病原体群落在物种分布中均质化，从而导致种群间PMS相似。或者，强烈的环境选择可能在空间和时间上迅速选择病原体，导致对当地适应的强烈选择。此外，病原体和宿主MHC变异性可能对宿主的生存和分散能力都有重要影响。与低病原体负荷相关的MHC变异性可能有利于远距离传播的倾向和能力，这将限制远距离传播宿主物种传播病原体的有效性。迄今为止，还没有研究调查病原体和MHC变异对传播行为的综合影响。大火烈鸟（Phoenicopterus roseus）是一种部分长距离迁徙和分散的水鸟。它是地中海湿地最丰富的鸟类，在大量鸟类在浅水中排便的地区集中觅食，这增加了胃肠道病原体感染的风险。通过结合在地中海盆地和西非地区收集的大量样本（n = 9323）、长期生活史数据集（1995-2017）和最近可用的下一代测序方法，我们提出：(1)测试当地环境和长途传播对地中海盆地和西非繁殖种群胃肠道细菌群落和MHC多样性的影响；(2)鉴定病原体和mhc适应度性状的相关性；(3) MHC等位基因频率和选择随时间变化的检验；(4)检验病原负荷和MHC变异对远距离传播倾向和能力的综合影响。该项目将在了解胃肠道病原体对天然鸟类种群的风险以及它如何影响遗传适应性、个体适应性和种群健康方面发挥关键作用。

Long-distance migration and dispersal is likely to play a central role in the spread of pathogens across wide geographic areas, which have important implications for wildlife, livestock and human health. In particular, long-distance migrating and dispersing waterbirds are often cited as playing a central role in the wide geographic spread of waterborne gastrointestinal pathogens which contaminate crucial waterbodies for wildlife and human activities. However, the host-pathogen interaction in long-distance dispersing species remains largely unknown. Immune genetic diversity, including the most diverse immune genes in vertebrates, major histocompatibility complex (MHC) genes, is generally thought to be correlated with adaptive potential and to be shaped by powerful pathogen-mediated selection (PMS). How PMS shapes MHC diversity will depend on the little known spatial and temporal dynamics of pathogen communities encountered by long-distance dispersing species. Long-distance dispersal may act to homogenise pathogen communities across species distribution, thereby resulting in similar PMS between populations. Alternatively, strong environmental selection may rapidly select pathogens across space and time, resulting in strong selection for local adaptations. Furthermore, pathogens and host MHC variability are likely to have an important impact on both host survival and the ability of the host to disperse. MHC variability associated with low pathogen load may favour long-distance dispersal propensity and ability, which will limit the effectiveness of pathogen spread by long-distance dispersal host species. To date, no study has investigated the combined effects of pathogens and MHC variability on dispersal behaviour. The Greater Flamingo, Phoenicopterus roseus is a partially long-distance migratory and dispersing waterbird species. It is the most abundant avian species in Mediterranean wetlands and feeds intensively in areas where a large number of birds have defecated in shallow waters, which increases the risk of gastrointestinal pathogen infection. By combining a large number of samples collected around the Mediterranean basin and west Africa (n = 9323), a long-term life-history dataset (1995-2017) and recently available next-generation sequencing methods, we propose to: (1) test the effect of the local environment and long-distance dispersal on the gastrointestinal bacterial community and MHC diversity of breeding populations across the Mediterranean basin and west Africa; (2) identify pathogen- and MHC-fitness trait correlations; (3) test for the variation in MHC allele frequencies and selection across time; and, (4) test the combined effects of pathogen loads and MHC variation on long-distance dispersal propensity and ability. This project will play a crucial role in the understanding of the risks of gastrointestinal pathogens on natural avian populations and how it shapes genetic adaptability, individual fitness and population health.