A new biological species forms when a species splits into two populations that gradually become more distinct and, after sufficient time, become reproductively isolated, i.e. matings between the two forms can not produce fertile offspring. However, how this process plays out at the molecular level is an open question. In mammals, sex chromosomes play a strong role. Males that carry an X and a Y chromosome are always the sex where hybrids first become infertile. This indicates a rapid accumulation of incompatibilities between the X and the Y in diverging populations. The purpose of the project is to identify such incompatibilities. The study system is the primates that constitute about 500 species. Many species can still (rarely) hybridise and produce offspring, sometimes with reduced male fertility. To identify emerging incompatibilities between the X and the Y, we study the evolution of genes expressed during spermatogenesis. We need to get testis samples from many individuals of many species and use single-cell approaches to understand changes to gene regulation. The hypothesis is that sex chromosomes can easily be hi-jacked by selfish genetic elements favouring the transmission of either the X or the Y in spermatogenesis. This process is called meiotic drive and is expected to cause rapid spread of these selfish elements, a transient change in the sex ratio of offspring, even if they harm spermatogenesis to some extent. Meiotic drive is known in other species, such as Drosophila and mouse, but has not yet been demonstrated in primates. We wish to use comparative evolutionary analysis of genes in spermatogenesis, identify potential drivers, and study their behaviour in natural hybrid zones of different primate species. The goal is to demonstrate a general mechanism of speciation.
