Differences in the sex ratios of offspring originating in the right and left ovaries of Mongolian gerbils (Meriones unguiculatus).

Two experiments were undertaken to investigate the cause of the observed tendency of Mongolian gerbil dams to gestate more male than female fetuses in their right uterine horns and more female than male fetuses in their left uterine horns. It was found in Expt 1 that female gerbils that had both ovaries removed and portions of their right ovary placed in both ovarian capsules gestated significantly more male fetuses than did females that had both ovaries removed and portions of their left ovaries placed in both ovarian capsules. Expt 2 showed that female gerbils that had both their ovaries removed and then returned to their original locations gestated more males in their right uterine horns than in their left, while females that had the positions of their ovaries exchanged gestated more male fetuses in their left uterine horns than in their right. The data were consistent with the hypothesis that lateral asymmetries in gerbil ovaries rather than in gerbil uterine horns cause partial uterine segregation of gerbil fetuses by sex.