Divergent allele advantage at MHC-DRB through direct and maternal genotypic effects and its consequences for allele pool composition and mating


It is still debated whether main individual fitness differences in naturalpopulations can be attributed to genome-wide effects or to particular lociof outstanding functional importance such as the major histocompatibilitycomplex (MHC). In a long-term monitoring project on Galápagos sea lions (Zalophus wollebaeki), we collected comprehensive fitness and mating datafor a total of 506 individuals. Controlling for genome-wide inbreeding, wefind strong associations between the MHC locus and nearly all fitnesstraits. The effect was mainly attributable to MHC sequence divergenceand could be decomposed into contributions of own and maternal genotypes.In consequence, the population seems to have evolved a pool ofhighly divergent alleles conveying near-optimal MHC divergence even byrandom mating. Our results demonstrate that a single locus can significantlycontribute to fitness in the wild and provide conclusive evidence for the‘divergent allele advantage’ hypothesis, a special form of balancing selectionwith interesting evolutionary implications.


Last updated on 06/09/2013