THE MAJOR HISTOCOMPATIBILITY COMPLEX AND MATE CHOICE - INBREEDING AVOIDANCE AND SELECTION OF GOOD GENES

It has been known for decades that MHC genes play a critical role in t he cellular immune response, but only recent research has provided a b etter understanding of how these molecules might affect mate choice. O riginal studies in inbred mouse strains revealed that mate choice was influenced by MHC dissimilarity. Detection of MHC differences between individuals in these experiments was related to olfactory cues, primar ily in urine. Recent studies in humans have shown an analogous picture of MHC-based mating. Taken together, these findings could support eit her the hypothesis of MHC-based inbreeding avoidance or the hypothesis of MHC-related avoidance of reproductive failure, since studies in mi ce, humans and pig-tailed macaques have shown that parental sharing of certain MHC alleles correlates with frequent spontaneous abortion or prolonged intergestational intervals. Data from many mammalian species clearly demonstrate that reproductive failure occurs as a result of i nbreeding. Therefore, MHC similarity might serve as an indicator of ge nome-wide relatedness. In contrast, increased fitness due to the prese nce of individual MHC alleles in a pathogenic environment could explai n MHC-based selection of currently good genes. Specifically, the physi cal condition of long-living animals depends on the ability to respond to immunological challenge and an individual's MHC alleles determine the response, since, unlike the T cell receptors, MHC alleles are not somatically recombined. Therefore, sexual selection of condition-depen dent traits during mate choice could be used to select successful MHC alleles, thereby providing offspring with a higher relative immunity i n their pathogenic environment.