What’s Wrong with MHC Mate Choice Experiments?

Abstract

It has been convincingly demonstrated that mice can discriminate MHC-related odors among congenic strains under laboratory conditions (see Yamaguchi et al. 1981). There is, however, debate about the use of these MHC-related odors as mate choice cues (Partridge, 1988; Klein et al., 1990; Nei and Hughes, 1991). MHC-based mate choice has been postulated to function either to produce presumably more fit MHC heterozygous offspring (Doherty and Zinkernagel, 1975) or to avoid close inbreeding (Brown, 1983). In either case, mating should be disassortative. Data from semi-natural half-wild enclosure studies (Potts et al., 1991) suggest that disassortative matings produce an excess (from random mating expectations) of MHC heterozygous progeny. Behavioral observations also suggest that these disassortative matings are due primarily to female choice. In a subset of 305 pups of known maternity, those in litters of mixed paternity (30 out of 58 litters) show a significant excess of heterozygotes over what would have been produced if females had mated only with their territorial males. Those litters sired only by the female’s territorial male did not deviate from the number of heterozygotes expected. This suggests that an important factor in producing more MHC heterozygous progeny is extra-territorial matings. In 41 observations of mating pairs, all matings took place on the territory of the male. All 13 extra-pair matings observed involved females who had left their nesting territory to travel to the territory of the male with which they were mating. No male was ever observed mating off of his territory. For details see Potts et al. this volume.