Sex-biased gene expression evolution during transitions to separate sexes in the Silene genus

Sexual dimorphism is widespread among species with separate sexes and its extent is thought to be governed by the differential expression of thousands of genes between males and females (known as Sex-Biased Genes, hereafter SBGs). SBGs have been studied in numerous species, but rarely in a comparative way, which curtails our understanding of their evolution, especially during multiple independent transitions to separate sexes. We sequenced the transcriptomes of nine dioecious species, two gynodioecious species (separate females and hermaphrodites) and two hermaphrodite species from the Silene genus. Our dataset provides access to three independent transitions to dioecy. We demonstrated that male-biased expression emerges first while a transition to separate sexes, later followed by female-biased genes. Furthermore, we showed that natural selection significantly impacts the evolution of some SBGs. This study provides new insights on the causes of SBG evolution during transitions to separate sexes.