Genome Screens Identify Chromosomal Regions Under Divergent Selection in Steelhead/Rainbow Trout

Rapid adaptation to novel environments may be accompanied by genetic changes in specific genomic regions that contain genes controlling selected traits. Identification of marker loci with greater differentiation between populations than expected by purely neutral genomic processes can localize regions of the genome linked to genes affected by divergent natural selection. In the salmonid species Oncorhynchus mykiss, adaptive divergence between anadromous steelhead and freshwater resident forms at specific loci has recently been documented in several studies, including cases where the two populations are separated by natural or artificial barriers to gene flow. In one such situation, in Scott Creek, CA, we have identified several markers associated with genomic regions that appear to be under strong divergent selection between the resident and anadromous forms. Here we extend our previous results through a combination of hatchery rearing experiments and additional genome-wide SNP and microsatellite data to identify genes under differential selection and determine the developmental differentiation and extent of hybridization between resident and anadromous fish separated by barriers to upstream gene flow. Identification of regions in the genome that are under divergent selection between these life-history forms will extend our knowledge of the genetic basis of rapid adaptation to novel habitats.