High rates of evolution preceded shifts to sex-biased gene expression in Leucadendron, the most sexually dimorphic angiosperms

• Published in: eLife Vol. 10
• Main Authors: Scharmann, Mathias, Rebelo, Anthony G, Pannell, John R
• Format: Journal Article
• Language: English
• Published: England eLife Sciences Publications Ltd 02.11.2021; eLife Sciences Publications, Ltd
• Subjects: Angiosperms; Animal reproduction; Biological Evolution; Chromosomes and Gene Expression; Comparative analysis; evolution; Evolution & development; Evolutionary Biology; Evolutionary genetics; Females; Gender differences; Gene Expression; Genes, Plant; Leucadendron; Males; Morphology; Phylogenetics; Physiology; plant; Plant Leaves - metabolism; Pollinators; proteaceae; Proteaceae - genetics; Seeds; sex-biased gene expression; Sexes; Sexual dimorphism; Sexual selection; Species; Species Specificity; Success; evolutionary biology; proteaceae; Leucadendron; chromosomes; plant; evolution; gene expression; sexual dimorphism; sex-biased gene expression
• ISSN: 2050-084X; 2050-084X
• DOI: 10.7554/eLife.67485

Differences between males and females are usually more subtle in dioecious plants than animals, but strong sexual dimorphism has evolved convergently in the South African Cape plant genus Leucadendron . Such sexual dimorphism in leaf size is expected largely to be due to differential gene expression between the sexes. We compared patterns of gene expression in leaves among 10 Leucadendron species across the genus. Surprisingly, we found no positive association between sexual dimorphism in morphology and the number or the percentage of sex-biased genes (SBGs). Sex bias in most SBGs evolved recently and was species specific. We compared rates of evolutionary change in expression for genes that were sex biased in one species but unbiased in others and found that SBGs evolved faster in expression than unbiased genes. This greater rate of expression evolution of SBGs, also documented in animals, might suggest the possible role of sexual selection in the evolution of gene expression. However, our comparative analysis clearly indicates that the more rapid rate of expression evolution of SBGs predated the origin of bias, and shifts towards bias were depleted in signatures of adaptation. Our results are thus more consistent with the view that sex bias is simply freer to evolve in genes less subject to constraints in expression level.