Rapid and adaptive evolution of mHC genesunder parasite selection in experimentalvertebrate populations

摘要

The genes of the major histocompatibility complex are the most polymorphic genes invertebrates, with more than 1,000 alleles described in human populations. How this polymorphismis maintained, however, remains an evolutionary puzzle. major histocompatibility complexgenes have a crucial function in the adaptive immune system by presenting parasite-derivedantigens to T lymphocytes. Because of this function, varying parasite-mediated selection hasbeen proposed as a major evolutionary force for maintaining major histocompatibility complexpolymorphism. A necessary prerequisite of such a balancing selection process is rapid majorhistocompatibility complex allele frequency shifts resulting from emerging selection by a specificparasite. Here we show in six experimental populations of sticklebacks, each exposed to oneof two different parasites, that only those major histocompatibility complex alleles providingresistance to the respective specific parasite increased in frequency in the next host generation.This result demonstrates experimentally that varying parasite selection causes rapid adaptiveevolutionary changes, thus facilitating the maintenance of major histocompatibility complexpolymorphism.