Résumé
Genes of the major histocompatibility complex (MHC) encode proteins that
recognize foreign antigens and are thus crucial for immune response. In a
population of a single host species, parasite-mediated selection drives
MHC allelic diversity. However, in a community-wide context, species
interactions may modulate selection regimes because the prevalence of a
given parasite in a given host may depend on its prevalence in other
hosts. By combining network analysis with immunogenetics, we show that
host species infected by similar parasites harbour similar alleles with
similar frequencies. We further show, using a Bayesian approach, that the
probability of mutual occurrence of a functional allele and a parasite in
a given host individual is nonrandom and depends on other host–parasite
interactions, driving co-evolution within subgroups of parasite species
and functional alleles. Therefore, indirect effects among hosts and
parasites can shape host MHC diversity, scaling it from the population to
the community level.