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

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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.