Methylation changes associated with early maturation stages in the Atlantic salmon

AFLPs statistical analysis showed that there was no significant differentiation between rivers or a significant differentiation between maturation states in each river. MSAP statistical analysis showed that among the three tissues sampled, the gonads had the highest number of significant single-locus variation among populations with 74 loci followed by brain with 70 and finally liver with only 12. Principal components analysis (PCA) of the MSAP profiles revealed different profiles among different tissues (liver, brain and testis) clearly separating maturation states in the testis tissue when compared to the liver.Our results reveal that genetically-similar mature and immature salmon parr present high levels of DNA methylation variation in two of the three analyzed tissues. We hypothesize that early maturation may be mostly mediated by epigenetic processes rather than by genetic differences between parrs. To our knowledge this is the first study that attempt to link phenotypic plasticity in salmonids and epigenetic changes.Atlantic salmon populations are anadromous with the only exception of those that inhabit rivers or lakes where there are physical impediments to seaward migration [1]. Eggs develop over winter and hatch in the following spring. After hatching, the fry stay for one to several years in the river and become parr. During spring-early summer, immature parrs undergo parr-smolt transformation and migrate downstream to the sea. After spending several years in the sea, the adults return to spawn in their native river in November-December [2]. Alternatively, during the first or second year in freshwater Atlantic salmon male parr can precociously mature.During the reproductive season, mature male parr compete with the larger anadromous males for access to anadromous females during spawning and are able to fertilize high proportions of eggs [3-9] and as consequence, the effective size of Atlantic salmon populations, increases [10].Early maturation is observed