Heritability of Age at Maturity in Wild and Hatchery Origin Chinook Salmon (Oncorhynchus tshawytscha)

Chinook salmon (Oncorhynchus tshawytscha) exhibit tremendous life history variation, among which is variation in the age at which they reach sexual maturity.  Fish that reach maturation at a later age achieve a greater body size and are more fecund than smaller and younger maturing fish.  Furthermore sexual selection favors larger males the wild, providing them with more breeding opportunities and an overall higher fitness.  In a hatchery environment sexual selection may no longer play a role in the fitness of larger older fish.  With relaxed selection against early maturation it is purported that hatchery supplementation programs will cause an increase in younger maturation within populations.  In order to test this hypothesis we assess the heritability of age at sexual maturation in wild and hatchery derived Chinook salmon from Johnson Creek, a tributary to the South Fork Salmon River in central Idaho, U.S.A.  We use a suite of microsatellite markers to reconstruct pedigrees in hatchery and wild spawned fish, from which we estimate the additive genetic variance for age at maturation and fork length at maturation, as well as the genetic correlation between these traits.  We also assess the contribution of several factors on shaping the age at sexual maturation in hatchery and wild spawned fish in order to dissect the basis of this trait.