Men in menopause? Experimental verification of the mate choice theory of menopause with Drosophila melanogaster

Abstract

AbstractMenopause is an unusual fertility reducing trait and it goes against natural selection. Group selection-based theories, such as the Grandmother hypothesis can, in principle, explain the evolution of menopause, but they do not explain how a fertility reducing mutation became fixed in populations. A population genetics theory of menopause, Mate Choice Theory, explains the evolution of menopause resulting from asymmetric mating involving older males and younger females leading to accumulation and neutral evolution of infertility causing mutations in older females. In this study we tested the mate choice theory using Drosophila melanogaster. Long term laboratory experiments involving asymmetric mating between young females and old males and vise-versa, were conducted over 40 generations and measurement of fitness parameters affecting female survival, fertility, fecundity, and male survival, fertility and testis length and width, were measured. The results showed, as expected, that younger females mated with older males produced infertile females with fewer ovarioles, fewer matured eggs, and fewer offspring; and younger males mated with older females produced sterile males with thinner testis compared to the control. The outcome of the experiment was symmetrical in that it works irrespective of sex, making both sexes, males and females, menopausal depending on which sex is deprived of reproduction in older age. These results show that change in mates’ behavior, such as preferential mating, can have profound impact on women’s health and could provide a basis for understanding reproductive senescence with age in both aging females and males.