Females and males typically differ in many ways in their morphology, physiology and behaviour. How such sex differences, known as sexual dimorphism, evolve is a puzzle because females and males share the same set of genes and an evolutionary change in one sex should cause a correlated change even in the other sex, thereby preventing sex differences from evolving. The new study shows that even small amounts of genetic differences between the sexes can facilitate the evolution of sexual dimorphism such that it can evolve in just a few generations.

 

‘Our experiments show that the autosomes as well as both sex chromosomes, the X and Y, can harbor genetic variation important for sexual dimorphism, but the Y chromosome alone can alter the sex difference in size by as much as 30 percent. This is remarkable because in these beetles the Y chromosome contains just a handful of genes and represents a very small fraction of the genome, just like in humans. Many have thought that the Y only affects the most important reproductive processes in males, namely sperm production. Our findings suggest that the Y chromosome may have a broader role than previously appreciated,’ says Philipp Kaufmann, a PhD student at the Uppsala University’s Department of Ecology and Genetics and the first author of the study.