W Chromosome Dynamics in Triportheus Species (Characiformes, Triportheidae): An Ongoing Process Narrated by Repetitive Sequences

Abstract

Characterizing the abundance and genomic distribution of repetitive DNAs provides information on genome evolution, especially regarding the origin and differentiation of sex chromosomes. Triportheus fishes offer a useful model to explore the evolution of sex chromosomes, since they represent a monophyletic group in which all species share a ZZ/ZW sex chromosome system. In this study, we analyzed the distribution of 13 classes of repetitive DNA sequences by FISH, including microsatellites, rDNAs, and transposable elements in 6 Triportheus species, in order to investigate the fate of the sex-specific chromosome among them. These findings show the dynamic differentiation process of the W chromosome concerning changes in the repetitive DNA fraction of the heterochromatin. The differential accumulation of the same class of repeats on this chromosome, in both nearby and distant species, reflects the inherent dynamism of the microsatellites, as well as the plasticity that shapes the evolutionary history of the sex chromosomes, even among closely related species sharing a same sex chromosome system.