Originally published as Genetics Published Articles Ahead of Print on June 18, 2008.

Genetics, Vol. 179, 1559-1575, July 2008, Copyright © 2008
doi:10.1534/genetics.107.084251

The Genetic Basis of Smoltification-Related Traits in Oncorhynchus mykiss

Krista M. Nichols*,{dagger},{ddagger},1, Alicia Felip Edo*,2, Paul A. Wheeler* and Gary H. Thorgaard*

* School of Biological Sciences and Center for Reproductive Biology, Washington State University, Pullman, Washington 99164, {dagger} National Oceanic and Atmospheric Administration, National Marine Fisheries Service, Northwest Fisheries Science Center, Conservation Biology Division, Seattle, Washington 98112 and {ddagger} Departments of Biological Sciences and Forestry and Natural Resources, Purdue University, West Lafayette, Indiana 47907

1 Corresponding author: Departments of Biological Sciences, 915 W. State St., Purdue University, West Lafayette, IN 47907.
E-mail: kmnichol{at}purdue.edu

The timing and propensity for migration between fresh- and seawater is a key theme in the diversity of life histories within the salmonid fishes. Across salmonid species, life-history strategies range from wholly freshwater-resident populations, to migratory and nonmigratory variation within populations, to populations and species that are primarily migratory. Despite the central theme of migration to the evolution of these fishes, the genetic architecture of migration-related processes is poorly understood. Using a genetic cross of clonal lines derived from migratory and nonmigratory life-history types of Onchorhynchus mykiss (steelhead and rainbow trout, respectively), we have dissected the genetic architecture of the complex physiological and morphological transformation that occurs immediately prior to seaward migration (termed smoltification). Quantitative trait loci (QTL) analyses were used to identify the number, effects, and genomic location of loci associated with smoltification-related traits, including growth and condition factor, body coloration, morphology, and osmoregulatory enzymes during the smoltification period. Genetic analyses revealed numerous QTL, but one locus in particular is associated with multiple traits in single and joint analyses. Dissecting the genetic architecture of this highly complex trait has profound implications for understanding the genetic and evolutionary basis of life-history diversity within and among migratory fishes.