Sex-Biased Gene Expression and Evolution in the Cerebrum and Syrinx of Chinese Hwamei (Garrulax canorus).

Hua Jiang,Yan-Chun Xu,Li Sun,Jian-Qing Lin,Sheng-Guo Fang

doi:10.3390/genes12040569

Abstract

It is common that males and females display sexual dimorphisms, which usually result from sex-biased gene expression. Chinese hwamei (Garrulax canorus) is a good model for studying sex-biased gene expression because the song between the sexes is quite different. In this study, we analyze cerebrum and syrinx sex-biased gene expression and evolution using the de novo assembled Chinese hwamei transcriptome. In both the cerebrum and syrinx, our study revealed that most female-biased genes were actively expressed in females only, while most male-biased genes were actively expressed in both sexes. In addition, both male- and female-biased genes were enriched on the putative Z chromosome, suggesting the existence of sexually antagonistic genes and the insufficient dosage compensation of the Z-linked genes. We also identified a 9 Mb sex linkage region on the putative 4A chromosome which enriched more than 20% of female-biased genes. Resultantly, male-biased genes in both tissues had significantly higher Ka/Ks and effective number of codons (ENCs) than unbiased genes, and this suggested that male-biased genes which exhibit accelerated divergence may have resulted from positive selection. Taken together, our results initially revealed the reasons for the differences in singing behavior between males and females of Chinese hwamei.

Highlights

Males and females have approximately identical genomes, but they have many markedly different phenotypic traits, including morphology, behavior, and physiology [1], and most of these sexual differences are denoted as sexual dimorphisms [2]
We identified the sex-biased genes in the cerebrum and syrinx tissue of Chinese hwamei by RNA sequencing technology (RNA-Seq)
We sampled eight samples in total. This generated a total of 440,648,252 paired-end 150 bp reads that were generated using the Illumina platform from the eight RNA-Seq libraries of Chinese hwamei

Summary

Introduction

Males and females have approximately identical genomes, but they have many markedly different phenotypic traits, including morphology, behavior, and physiology [1], and most of these sexual differences are denoted as sexual dimorphisms [2].Sexual dimorphism results from natural selection or sex selection for characteristics that have different fitness optima between the sexes [3]. It is assumed that most sexually dimorphic characteristics result from the difference in gene expression between males and females [4,5]. The distribution traits of sex-biased genes on chromosomes are nonrandom, and the sex chromosomes (Z or X chromosome) usually provide the platform for their enrichment [6,11,12]. Genes which may be favorably selective to one sex but harmful to the other, and can result in different optimal characteristics between the sexes, are referred to as sexually antagonistic genes [13,14]. These genes may be enriched on the sex chromosome

Methods

Results

Conclusion