Quantitative genetic variation in the control of ovarian apoptosis under different environments

Fertility loss in otherwise healthy individuals can be an evolutionary conundrum. Most studies on the evolution of post-reproductive lifespan focus on the fitness effects of survival past the age of last reproduction. A complementary approach, which has been largely neglected, is to develop an understanding of the nature of variation in the mechanism underlying loss of fertility, ovarian apoptosis. Variation in the genetics underlying the regulation of ovarian apoptosis could hold the key to understanding the evolution of midlife fertility loss. We estimated quantitative genetic variation in the regulation of ovarian apoptosis in females of the cockroach Nauphoeta cinerea, an insect with reproductive cycles. We have earlier shown that delaying reproduction incites loss of fertility. Here, we forced females to delay reproduction under conditions of excess or limited food and examined apoptosis under both conditions. We found substantial additive genetic variation in levels of apoptosis when females experienced a limited period of starvation during sexual maturation but not when females had unlimited access to food. Hence, selection could act on the regulation of ovarian apoptosis to change the rate of fertility loss with age at least under some environmental circumstances. Our results suggest that an understanding of how loss of fertility evolves requires an understanding of the interaction between genes involved in the regulation of apoptosis and environmental factors such as diet.