Measuring rates of sexual development in female Mongolian gerbils.

In previous experiments, we have shown that age at vaginal introitus predicts adult patterns of reproductive, maternal, and aggressive behavior of female Mongolian gerbils. In the present series of studies, we explored the relationship in gerbils between age at vaginal patency and three other indices of rate of female sexual development: ovarian weight, occurrence of vaginal estrus, and onset of attractiveness to males. We found that female gerbils, classified on the basis of their ages at vaginal introitus as early-maturing: (a) exhibited greater ovarian weights throughout development than did their late-maturing, female sibs; (b) exhibited estrus and Diestrus I stage vaginal smears and, by inference, ovulation at an earlier age than did late-maturing females; and (c) elicited mounting by males at an earlier mean age than did late-maturing females. The data were consistent with the hypothesis that age at vaginal introitus is a reliable indicator of rate of sexual development in female Mongolian gerbils.