Data from: Lack of evidence for selection favouring MHC haplotypes that combine high functional diversity

High rates of gene duplication and the highest levels of functional
allelic diversity in vertebrate genomes are the main hallmarks of the
major histocompatibility complex (MHC), a multigene family with a
primordial role in pathogen recognition. The usual tight linkage among MHC
gene duplicates may provide an opportunity for the evolution of haplotypes
that associate functionally divergent alleles and thus grant the
transmission of optimal levels of diversity to coming generations. Even
though such associations may be a crucial component of disease resistance,
this hypothesis has been given little attention in wild populations. Here,
we leveraged pedigree data from a barn owl (Tyto alba) population to
characterize MHC haplotype structure across two MHC class I (MHC-I) and
two MHC class IIB (MHC-IIB) duplicates, in order to test the hypothesis
that haplotypes’ genetic diversity is higher than expected from randomly
associated alleles. After showing that MHC loci are tightly linked within
classes, we found limited evidence for shifts towards MHC haplotypes
combining high diversity. Neither amino acid nor functional
within-haplotype diversity were significantly higher than in random sets
of haplotypes, regardless of MHC class. Our results therefore provide no
evidence for selection towards high-diversity MHC haplotypes in barn owls.
Rather, high rates of convergent evolution may constrain the evolution of
high-diversity haplotypes at MHC-I, while, in contrast, for MHC-IIB, fixed
differences among loci may provide barn owls with already optimized
functional diversity. This suggests that at the MHC-I and MHC-IIB,
respectively, different evolutionary dynamics may govern the evolution of
within-haplotype diversity.