Identification of Genomic Loci Associated with Maturation in Pacific Coho Salmon (Oncorhynchus kisutch)

Reproductive success of salmon is influenced by multiple morphological features, physiological performance, and behavioural mating strategies. While certain male-specific traits such as sperm quality can provide a clear advantage to reproductive success, the role of precocious sexual maturation (smaller body size and absent secondary sexual characteristics) in evolutionary stable strategy is counterintuitive. The genetic basis of early maturation (termed jacking in Pacific salmon and grilsing in Atlantic salmon) was previously thought to polygenic. However, this was revised with the recent identification of vestigial-like-family-member-3 (vgll3) as the main locus for regulating maturation onset in Atlantic salmon. Our current study aims to identify loci associated with jacking and survival in Pacific Coho Salmon, Oncorhynchus kisutch. We conducted a genome-wide-association-study and mapping analysis on six families from a hatchery population (Inch Creek), three of which possessed a high proportion of jacks and three that had a low proportion. Using a Genotype-by-Sequencing approach, EcoT22I reduced representation libraries were generated for 654 individuals and sequenced on the Illumina HiSeq platform. Two female- and male-specific linkage maps were generated, where 3815 and 3415 SNP markers, respectively, were mapped onto 30 linkage groups. Preliminary data revealed significant markers associated with jacking on linkage groups 15 and 21 on both genetic maps. Alignment of early maturation markers to a draft Coho Salmon genome assembly suggests that the genomic loci involved is not the Vgll3. This suggests that the molecular mechanism determining age of male maturation is not fully conserved between Atlantic and Pacific Coho Salmon.