Age-related decline in ovarian follicle stocks differ between chimpanzees (Pan troglodytes) and humans

Abstract

Similarity in oldest parturitions in humans and great apes suggests that we maintain ancestral rates of ovarian aging. Consistent with that hypothesis, previous counts of primordial follicles in postmortem ovarian sections from chimpanzees (Pan troglodytes) showed follicle stock decline at the same rate that human stocks decline across the same ages. Here, we correct that finding with a chimpanzee sample more than three times larger than the previous one, which also allows comparison into older ages. Analyses show depletion rates similar until about age 35, but after 35, the human counts continue to fall with age, while the change is much less steep in chimpanzees. This difference implicates likely effects on ovarian dynamics from other physiological systems that are senescing at different rates, and, potentially, different perimenopausal experience for chimpanzees and humans.

Fig. 1

Sample size comparisons between the chimpanzee (dark bars) and human (open bars) data used in statistical model comparisons

Fig. 2

A non-linear model best fits the human (circles)—but not the chimpanzee (triangles)—data, highlighting differences between the species. The figure shows log-transformed counts ages 0–51, best-fit models, and their confidence intervals

Fig. 3

Best-fit model comparisons between the chimpanzee and human 0–34-year data, centered by age class means. The chimpanzee model is the solid line, the human model is the dashed line

Fig. 4

Best-fit model comparisons between the chimpanzee and human 35–51-year data, centered by age class means. The chimpanzee model is the solid line, the human model is the dashed line