Behavioral Reduction in the Transmission of Deleterious t Haplotypes by Wild House Mice

About 25% of wild house mice are heterozygous (+/t) for a variable recessive haplotype of the T locus. Although t haplotypes are highly deleterious when homozygous, they are maintained in wild mouse populations because they are associated with transmission-ratio distortion in heterozygous males, which may transmit their t haplotype to 90%-100% of their progeny. In a study of factors affecting variation in male transmission ratio in matings between wild-caught +/t males and +/+ females, we found (1) that male transmission ratio is considerably lower in litters produced as a result of postpartum-estrus matings than in litters produced as a result of cycling-estrus matings, (2) that the frequency of postpartum-estrus litters is much higher when +/t males mate with females caught from the same location as themselves than when they mate with females caught elsewhere, and (3) that, as a result of findings I and 2, the male transmission ratio is considerably lower in within-population matings than in betweenpopulation matings. These data suggest that the frequency of t haplotypes within populations may be correlated with the migration rate and that t haplotypes may be found in high frequencies only in populations for which the migration rate is high.