Malic enzyme, an “old-new player” in age at maturity in Atlantic salmon

Traditional genetic markers based on allozyme variation had indicated that in Atlantic salmon the genetic variation found for the locus coding for mMEP-2* could be adaptive, with the variation being related to river water temperature, growth, and maturation. More recently, SNP panels used to search for genes related to maturation in Atlantic salmon identified several genes, including the vgll3 gene related to early maturation. However, none of the analyses performed found an association between maturation and the already known locus coding for mMEP-2*. Recently, a method has been developed to characterize the different alleles of the locus coding for mMEP-2* using molecular techniques. In this work we use this method to study the salmon population of the Bidasoa River, located in the Iberian Peninsula, which is the limit of distribution of the species. We found a relationship between the presence of SNP G, equivalent to the 125* allele, and early maturation of Atlantic salmon in both males and females. It is possible that the relationship between the different alleles of this locus and maturation is not direct but is produced by differential growth during the juvenile and/or adult phase. It is also plausible that this association is exclusive to the salmon populations of the Iberian Peninsula.