Molecular sexing and population genetic inference using a sex-linked microsatellite marker in the nine-spined stickleback (Pungitius pungitius)

BACKGROUND: Sex-specific DNA markers can serve as tools for molecular sex identification, as well as for population genetic inferences. We investigated the potential utility of a microsatellite marker located on sex chromosomes for molecular sexing of Fennoscandian nine-spined sticklebacks (Pungitius pungitius). In addition, we assessed the patterns of allelic differentiation between X and Y chromosomes across the populations to examine if the sex chromosomes had been highly differentiated prior to the postglacial recolonization of Fennoscandia. FINDINGS: A clear and consistent sex difference in allele size distribution was observed at the Stn19 locus throughout the 15 populations investigated. Males were distinguishable by the presence of distinct male-specific alleles, which were lacking in all females. There was no indication of recombination between sex and the Stn19 locus in the 647 individuals tested. The degree of genetic differentiation between the X and Y chromosomes was much higher than that of interpopulation differentiation in the respective chromosomes. CONCLUSIONS: Our results indicate that the Stn19 locus can be used for molecular sex identification in Fennoscandian nine-spined sticklebacks. The consistent pattern of high allelic differentiation between the X and Y chromosomes in these populations suggests that the sex chromosomes were already highly differentiated prior to the postglacial recolonization of Fennoscandia.