Analysing quantitative trait loci of sexual antagonism in fruitflies

Evolutionary biologists have long been fascinated by the differences between the sexes. Males and females can differ profoundly in appearance and behaviour, in the example of the mallard so much so that the sexes were initially described as members of different species. Past research has shown that sexual dimorphism has arisen in response to differing male and female reproductive roles. Females usually produce large and energetically costly eggs. Their reproductive performance, or 'fitness', is therefore limited by their ability to acquire resources and survive. Males, in contrast, produce large amounts of tiny and cheap sperm. Accordingly, their fitness is in most cases limited by their ability to attract mates, which can involve bright colouration and extravagant displays or exaggerated weaponry to defend a territory of high quality. While it is understood why the sexes differ, the question of how males and females diverge has not been resolved. The underlying problem is that males and females cannot evolve independently because the sexes generally share almost all of their genes. Thus, any difference between the sexes is not caused by a different content of genes, but rather relies on a different subset of genes being used in males and females. However, recent results indicate that the evolution of this differential use of genes is incomplete. Studies in a variety of organisms, ranging from fruitflies to deer, have demonstrated that genomes that improve performance in males often tend to decrease performance in females and vice versa. This data indicates that there are genes that affect male and female performance in opposite directions but are not differentially expressed in the two sexes. So far, these so-called sexually antagonistic genes have only been indirectly inferred by comparing the performance of males and females that are members of the same family (and hence can be expected to share a proportion of their genes). Nothing is known about the identity of the genes that cause antagonism, or their function in the organism or how they evolve. This project will fill this gap in our knowledge. We will identify the genomic regions that have opposite effects on male and female performance and determine where they are located and which genes they contain. Further, we will investigate to what extent sexual antagonism can prevent genes that code for high performance in one sex from spreading through the population, due to their negative effect on the other sex. Finally, we will study the patterns of DNA evolution of loci involved in antagonism in order identify the exact nucleotide sites responsible for differences in sex-specific performance. Doing so will allow us to infer for how long sexual antagonism has persisted at these loci. By addressing these multiple aspects, our project will provide information that will help us to understand the factors that prevent some genes from being differentially expressed. Thus we will deepen our general understanding of how differences between males and females can evolve.