title: Sex-biased transcriptome evolution in Drosophila.
abstract: Sex-biased genes are thought to drive phenotypic differences between males and females. The recent availability of high-throughput gene expression data for many related species has led to a burst of investigations into the genomic and evolutionary properties of sex-biased genes. In Drosophila, a number of studies have found that X chromosomes are deficient in male-biased genes (demasculinized) and enriched for female-biased genes (feminized) and that male-biased genes evolve faster than female-biased genes. However, studies have yielded vastly different conclusions regarding the numbers of sex-biased genes and forces shaping their evolution. Here, we use RNA-seq data from multiple tissues of Drosophila melanogaster and D. pseudoobscura, a species with a recently evolved X chromosome, to explore the evolution of sex-biased genes in Drosophila. First, we compare several independent metrics for classifying sex-biased genes and find that the overlap of genes identified by different metrics is small, particularly for female-biased genes. Second, we investigate genome-wide expression patterns and uncover evidence of demasculinization and feminization of both ancestral and new X chromosomes, demonstrating that gene content on sex chromosomes evolves rapidly. Third, we examine the evolutionary rates of sex-biased genes and show that male-biased genes evolve much faster than female-biased genes, which evolve at similar rates to unbiased genes. Analysis of gene expression among tissues reveals that this trend may be partially due to pleiotropic effects of female-biased genes, which limits their evolutionary potential. Thus, our findings illustrate the importance of accurately identifying sex-biased genes and provide insight into their evolutionary dynamics in Drosophila.
authors.affiliation: Department of Integrative Biology, Center for Theoretical Evolutionary Genomics, University of California, Berkeley, USA. rassis@berkeley.edu
authors.forename: Raquel
authors.initials: R
authors.lastname: Assis
authors.forename: Qi
authors.initials: Q
authors.lastname: Zhou
authors.forename: Doris
authors.initials: D
authors.lastname: Bachtrog
mesh_terms: D000818:Animals; D002874:Chromosome Mapping; D016000:Cluster Analysis; D004330:Drosophila / Q000235:genetics*; D004331:Drosophila melanogaster / Q000235:genetics; D019143:Evolution, Molecular; D005260:Female; D015870:Gene Expression; D017344:Genes, Insect; D050172:Genes, X-Linked; D008297:Male; D012727:Sex Characteristics; D059467:Transcriptome / Q000235:genetics*; D014960:X Chromosome / Q000235:genetics