Life-history genotype explains variation in migration activity in Atlantic salmon ( Salmo salar ).

One of the most well-known life-history continuums is the fast-slow axis, where 'fast' individuals mature earlier than 'slow' individuals. 'Fast' individuals are predicted to be more active than 'slow' individuals because high activity is required to maintain a fast life-history strategy. Recent meta-analyses revealed mixed evidence for such integration. Here, we test whether known life-history genotypes differ in activity expression by using Atlantic salmon ( Salmo salar ) as a model. In salmon, variation in Vgll3, a transcription cofactor, explains approximately 40% of variation in maturation timing. We predicted that the allele related to early maturation ( vgll3 *E) would be associated with higher activity. We used an automated surveillance system to follow approximately 1900 juveniles including both migrants and non-migrants (i.e. smolt and parr fish, respectively) in semi-natural conditions over 31 days (approx. 580 000 activity measurements). In migrants, but not in non-migrants, vgll3 explained variation in activity according to our prediction in a sex-dependent manner. Specifically, in females the vgll3 *E allele was related to increasing activity, whereas in males the vgll3 *L allele (later maturation allele) was related to increasing activity. These sex-dependent effects might be a mechanism maintaining within-population genetic life-history variation.