Immunogenetic variation shapes the gut microbiome in a wild vertebrate population. Gut microbiome variation in the Seychelles warbler (Acrocephallus seychellinsis)

The gut microbiome (GM) can influence many biological processes in the host, impacting its health and survival, but the GM can also be influenced by the host’s traits. In vertebrates, Major Histocompatibility Complex (MHC) genes play a pivotal role in combatting pathogens and are thought to shape the host’s GM. However, despite this - and the documented importance of both GM and MHC variation to individual fitness - few studies have investigated the association between the GM and MHC in the wild. Here, we characterised MHC class I (MHC-I), MHC class II (MHC-II), and GM variation across individuals in a wild population of the Seychelles warbler, Acrocephalus sechellensis. Our results show that the presence of specific MHC alleles, but not MHC diversity, influences both the diversity and composition of the GM in this population. To our knowledge this is the first-time individual MHC-I variation has been shown to be associated with differences in GM characteristics in a wild population. More widely, host–microbiome coevolution may play a role in maintaining functional immunogenetic variation, potentially explaining how variation is maintained at the MHC.