Sociosexual and hormonal changes in aging female bonnet macaques.

A comparison of younger mature and older perimenopausal female bonnet macaques showed differences in sexual interaction with males. Older females evoked significantly fewer copulations than did younger females. Although older females were cycling regularly, the midcycle (estrus) peaking of sexual interaction and levels of plasma estradiol were less pronounced in older than in younger females. Younger females were mounted more during estrus than during the luteal phase of their cycles, and the frequency of ejaculations and duration of intromissions were significantly greater during estrus. These cycle-phase differences were not observed with older females. The results suggest that aging in the female macaque is associated with reduction in sexual attractiveness to males. The possibility that changes in female proceptivity and receptivity contribute to this effect remains to be investigated.