Genes with sex-biased expression in Drosophila are thought to underlie sexually dimorphic phenotypes and have been shown to possess unique evolutionary properties. However, the forces and constraints governing the evolution of sex-biased genes in the somatic tissues of Drosophila are largely unknown. By using population-scale RNA sequencing data, we show that sex-biased genes in the Drosophila brain are highly enriched on the X Chromosome and that most are biased in a species-specific manner. We show that X-linked male-biased genes, and to a lesser extent female-biased genes, are enriched for signatures of directional selection at the gene expression level. By examining the evolutionary properties of gene-flanking regions on the X Chromosome, we find evidence that adaptive cis-regulatory changes are more likely to drive the expression evolution of X-linked male-biased genes than other X-linked genes. Finally, we examine whether constraint owing to broad expression across multiple tissues and genetic constraint owing to the largely shared male and female genomes could be responsible for the observed patterns of gene expression evolution. We find that expression breadth does not constrain the directional evolution of gene expression in the brain. Additionally, we find that the shared genome between males and females imposes a substantial constraint on the expression evolution of sex-biased genes. Overall, these results significantly advance our understanding of the patterns and forces shaping the evolution of sexual dimorphism in the Drosophila brain.

中文翻译：

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果蝇大脑中性别偏向基因表达的演变。

果蝇中具有性别偏向性表达的基因被认为是性二态性表型的基础，并已被证明具有独特的进化特性。然而，在果蝇的体细胞组织中支配性别偏向基因进化的力量和约束是未知的。通过使用人口规模的RNA测序数据，我们显示了果蝇中的性别偏向基因大脑在X染色体上高度富集，并且大多数以特定于物种的方式存在偏见。我们显示X链接的男性偏向的基因，以及程度较小的女性偏向的基因，在基因表达水平上被丰富了定向选择的标记。通过检查X染色体上基因侧翼区域的进化特性，我们发现了适应性顺式与其他X连锁基因相比，调控的变化更可能驱动X连锁男性偏向基因的表达进化。最后，我们研究了由于在多种组织中广泛表达而引起的限制和由于男性和女性基因组共享程度高而导致的遗传限制是否可以负责观察到的基因表达进化模式。我们发现表达广度不会限制基因表达在大脑中的定向进化。此外，我们发现男性和女性之间共享的基因组对性别偏向基因的表达进化施加了实质性的限制。总体而言，这些结果大大提高了我们对果蝇大脑中性二态性进化的模式和力量的理解。