Genomic imprinting and separate sexes evolution – IMPRINT

Epigenetics is more labile than genetics and mutates more rapidly. An important question in Evolutionary Biology is currently whether epigenetics participates in species adaptation. In this project, I offer to investigate how epigenetics may impact the evolution of separate sexes. In hermaphrodites, a compromise is reached between the female and male function, but, with separate sexes, sexual dimorphism can evolve and sexual antagonism may be resolved (traits advantageous for one sex but deleterious for the other can become sex-specific). I will focus on an epigenetic phenomenon called imprinting, where gene expression is biased for the maternal or the paternal copy. Imprinting has been observed in mammal and plant adult tissues and the evolutionary forces leading to imprinting in adults and its functions remain to be elucidated. A theoretical model proposed that sexual antagonism may lead to imprinting emergence. I propose to empirically this theory by comparing species with separate sexes to closely related hermaphrodite species (two independent species pairs). In a second aim, I will investigate if imprinting drives differential gene expression between sexes (called sex-biased expression). Sex-biased expression is a key phenomenon for the evolution of sexual dimorphism. Plants with separate sexes carry between 1 and 43% of sex-biased genes, but it is currently unknown how this is regulated. Finally, sex chromosomes have convergently evolved imprinting in organisms as diverged as marsupials and the plant S. latifolia, where the two Xs in females have different activity depending on their parental origin. In these organisms, X imprinting is linked to dosage compensation, a phenomenon that compensates for lower Y expression in males. I will investigate how the X imprint is regulated epigenetically in S. latifolia. The young sex chromosomes of S. latifolia may help us understand the early steps of dosage compensation evolution in the old mammalian sex chromosomes.