Geographical Distribution and Phylogenetic Conservation of the vgll3 Locus in Atlantic Salmon and other Fish Species

The vgll3 locus has been shown to contain genetic variants conferring the age at maturity in Atlantic salmon (Salmo salar). In addition, a SNP in the human VGLL3 locus has also been linked to time at puberty, suggesting a conserved regulatory mechanism for age at maturity in vertebrates. To investigate whether the vgll3 locus could be involved in a conserved mechanism regulating puberty in fish, we have studied the phylogenetic conservation of vgll3 in salmonids and other fish species. Although the exact causative mutations in salmon are not known, two missense SNPs (amino acid replacements) are probable candidates. All the assayed species but Atlantic salmon showed only the late maturity variant for one of the missense SNPs, while the other missense SNP showed more variation. We have studied the geographical distribution of the early and late maturity variants of these missense SNPs in populations of Atlantic salmon from Norway, Canada, Ireland, Spain and Russia, in addition to two landlocked populations from Norway and Sweden. Analysis of the geographical distribution of these missense SNPs showed that the early maturity variants were more prevalent in salmon from Norway and Ireland than those from Spain, Canada or Russia. Interestingly, only the variant for late maturation was found in the landlocked populations. These results indicate that the late maturation variants might be the ancestral state, while the early maturing variants have a more recent origin in salmon. While species evolutionary related to salmonids have only one vgll3 gene, two copies are present in salmonids. This is most likely due to the salmonid specific whole genome duplication occurring ~80 million years ago providing the salmonids the genetic raw material for adaptation.