Data from: Sexual selection and the evolution of the Major Histocompatibility Complex

The genes of the major histocompatibility complex (MHC) are a key
component of the adaptive immune system and among the most variable loci
in the vertebrate genome. Pathogen-mediated natural selection and
MHC-based disassortative mating are both thought to structure MHC
polymorphism, but their effects have proven difficult to discriminate in
natural systems. Using the first model of MHC dynamics incorporating both
survival and reproduction, we demonstrate that natural and sexual
selection produce distinctive signatures of MHC allelic diversity with
critical implications for understanding host–pathogen dynamics. While
natural selection produces the Red Queen dynamics characteristic of
host–parasite interactions, disassortative mating stabilizes allele
frequencies, damping major fluctuations in dominant alleles and protecting
functional variants against drift. This subtle difference generates a
complex interaction between MHC allelic diversity and population size. In
small populations, the stabilizing effects of sexual selection moderate
the effects of drift, whereas pathogen-mediated selection accelerates the
loss of functionally important genetic diversity. Natural selection
enhances MHC allelic variation in larger populations, with the highest
levels of diversity generated by the combined action of pathogen-mediated
selection and disassortative mating. MHC-based sexual selection may help
to explain how functionally important genetic variation can be maintained
in populations of conservation concern.