Nonrandom sex composition of gerbil, mouse, and hamster litters before and after birth.

Examining data describing the sex composition of 1074 Caesarean-delivered litters of house mice, 253 Caesarean-delivered and 265 vaginally delivered litters of Mongolian gerbils, and 854 vaginally delivered litters of golden hamsters, we determined whether segregation of sexes between uterine horns and correlations between litter size and litter sex ratio were present in each of the three rodent species studied. Although significant deviations from expected distributions of male and female fetuses were found, these deviations from chance were not the same in any two of the three species examined. Analyses also indicated that the correlation between litter size and litter sex ratio that Huck, Seger, and Lisk (1990) found in vaginally delivered infant hamsters is present in vaginally delivered infant Mongolian gerbils, but not in their Caesarean-delivered colony mates. In gerbils, and perhaps hamsters as well, the correlation between litter size and litter sex ratio appears to be a result of sex-biased perinatal mortality correlated with litter size rather than of sex-biased conception correlated with litter size.