Linkage Disequilibrium Associated with Oncorhynchus mykiss Adaptive Life-History Variation (Residency vs. Anadromy) along Its Geographic Range

O. mykiss is characterized by an extremely complex life-history, where two ecotypes can be recognized based on its migratory patterns: the anadromous form called “steelhead” and the resident form called “rainbow trout”. Recent research has greatly increased our understanding of the genetic architecture and heritability of this life-history variability. These studies have discovered a specific genomic region of one chromosome (Omy5) that is strongly associated with life-history differentiation in multiple above-barrier populations of rainbow trout and their anadromous steelhead ancestors. The associated loci are in strong linkage disequilibrium, suggesting the presence of a chromosomal inversion or other rearrangement limiting recombination. We assess the effects of this genomic region on the expression of anadromous and resident life-history patterns in coastal O. mykiss population above and below barriers to migration along its distribution range. These results provide evidence of a common genomic basis for life-history variation in O. mykiss in a geographically diverse set of populations, and extend our knowledge of the heritable basis of rapid adaptation of complex traits in novel habitats.