Genes for sexual body size dimorphism in hybrid tilapia (Oreochromis sp. x Oreochromis mossambicus)

Abstract

Tilapias are important aquaculture species. Male-biased sexual size dimorphism is very common and males are preferred for aquaculture in tilapia. However, the mechanisms underlying sexual dimorphism remain to be elucidated. One hundred and thirty-six sex-biased genes, of which 23 were male-biased and 113 were female-biased, were identified via reanalysis of a muscle transcriptome data using the latest reference genome assembly. These genes were mapped to KEGG pathways that are related to somatic cell metabolism, growth and differentiations, such as MAPK, FoxO4 and metabolism pathways as well as developmental processes responsible for skeletal muscle development. Pathways related to cell growth and proliferations such as MAPK signaling pathways are upregulated in males while pathways regulating cell division such as FoxO4 are upregulated in females. Sex-biased genes in tilapia skeletal muscle have higher evolution rates (dN/dS) compared to unbiased genes. Female-biased and male-biased genes showed 17.4% and 13.5% higher dN/dS, respectively, compared to unbiased genes. Our results suggest that some of the male and female sex-biased genes were under selection pressures. Three SNPs located in the promoter region of one sex-biased gene RASGRF1 on LG1 were associated with bodyweight differences in the hybrid tilapia. These sex-biased genes identified in this study may serve as candidate genes for future functional analysis on sexual size dimorphism and for developing DNA markers for selecting fast-growing saline tilapia in aquaculture. Keywords: Sexual dimorphism, Body size, RNA-Seq, Tilapia, Aquaculture, Evolution