Defining the Role of Operational Sex Ratio in Fitness of Organisms With Sexually Antagonistic Genes

Abstract

In many species, populations vary in size and reproductive sex ratio, producing situations in which small population sizes are paired with strongly skewed effective sex ratios. This imbalance among sexes is particularly important in populations with genes that experience different selective pressures in males and females. Understanding the role selection and drift play in such populations is important in determining the evolution of genetic variation and the role they play in the fitness of organisms. Using forward time population genetic simulations under various conditions, we show that certain conditions will lead to the fixation of genetic variation that benefits the more numerous sex and are deleterious to the rarer sex. These results suggest that in some species the rare sex may be destined to evolve lower fitness. This is of particular concern in cases where a species has a strong imbalance in the numbers of males and females and has reduced population size either due to domesticated production methods, climate change, or habitat loss.