Genetic variation in threshold reaction norms for alternative reproductive tactics in male Atlantic salmon, Salmo salar

• Published in: Proceedings of the Royal Society B: Biological Sciences
• Main Authors: Piché, Jacinthe, Hutchings, Jeffrey A, Blanchard, Wade
• Format: Article in Journal/Newspaper
• Language: English
• Published: The Royal Society 2008
• Subjects: Atlantic salmon; Salmo salar
• Online Access: http://dx.doi.org/10.1098/rspb.2008.0251; https://royalsocietypublishing.org/doi/pdf/10.1098/rspb.2008.0251; https://royalsocietypublishing.org/doi/full-xml/10.1098/rspb.2008.0251

Alternative reproductive tactics may be a product of adaptive phenotypic plasticity, such that discontinuous variation in life history depends on both the genotype and the environment. Phenotypes that fall below a genetically determined threshold adopt one tactic, while those exceeding the threshold adopt the alternative tactic. We report evidence of genetic variability in maturation thresholds for male Atlantic salmon ( Salmo salar ) that mature either as large (more than 1 kg) anadromous males or as small (10–150 g) parr. Using a common-garden experimental protocol, we find that the growth rate at which the sneaker parr phenotype is expressed differs among pure- and mixed-population crosses. Maturation thresholds of hybrids were intermediate to those of pure crosses, consistent with the hypothesis that the life-history switch points are heritable. Our work provides evidence, for a vertebrate, that thresholds for alternative reproductive tactics differ genetically among populations and can be modelled as discontinuous reaction norms for age and size at maturity.