Contrasted sex chromosome evolution in primates with and without sexual dimorphism

The human sex chromosomes provide a striking example of how sex chromosomes can become modified in gene content and structure (i.e. become heteromorphic). Why sex chromosomes in humans and other lineages can reach such levels of heteromorphy is not clear. One hypothesis posits that mutations with antagonistic effects between males and females can drive recombination suppression and subsequent divergence between X and Y chromosomes. Here, we tested this hypothesis by focusing on strepsirrhine primates (lemurs and lorises) that have much lower sexual dimorphism and opportunities for sexually antagonistic mutations than haplorrhines (apes and monkeys). We sequenced seven strepsirrhine species and identified the pseudoautosomal boundary (PAB), the border between recombining and non-recombining regions on the sex chromosomes. We found that during primate evolution, the PAB has remained unchanged in strepsirrhines whereas several recombination suppression events have occurred in haplorrhines, suggesting that sexually antagonistic mutations might have driven sex chromosomes heteromorphy in primates.