Genetic and environmental influences on zebrafish sex ratios

Abstract

Zebrafish has become a well established model in many areas of research. However, a basic aspect of its biology, i.e., how sex is determined, is still not known. In contrast to other vertebrates, fish exhibit a wide range of sex determining systems, and whether an animal develops as a male or a female depends on the interplay between genetic, physiological and environmental influences. Although it is well established that the zebrafish is an undifferentiated gonochorist, studies aimed at identifying its sex determining mechanism are equivocal, as are the gene pathways supposedly involved. Thus, sex determination and differentiation are far from being clear. Further, the presence of non-Fisherian sex ratios, usually male biased, in facilities all over the world has puzzled researchers. Here, we report experiments involving different zebrafish families, exposure to different temperatures, as well as rearing at different population densities. Our results show a wide interfamily variation in sex ratios under control conditions, conserved sex ratios in successive broods of the same parents, a strong masculinizing effect of high temperature, the existence of genetic x environment interactions, and a relationship between density, growth and sex ratios. Changes in phenotype were confirmed by changes in in the expression of genes related to sexual differentiation and DNA methylation. Together, these results support a polygenic sex determining system with environmental influences for the zebrafish, with the possibility that the phenotype is discordant with the genotype. Thus, more attention should be paid to these genetic and environmental components in studies where whatever is being investigated may be linked to the sexual phenotype