Population genomics of grass rockfish. Sebastes rastrelliger

Variation at the genomic level is important for understanding a species’ demographic and phylogenetic history, in addition to identifying candidate regions that may be under selection and important to local adaptation. We used restriction-site associated DNA (RAD) sequencing to sample the grass rockfish (Sebastes rastrelliger) genome via single nucleotide polymorphisms (SNPs) to assess range-wide patterns of population structure and test for signatures of selection (i.e. outlier loci). 6,572 SNPs were genotyped in over 70% of 112 individuals from six sampling areas using RAD loci. Global FST across sampling sites is 0.0009 for all loci. A Bayesian method (BAYESCAN) did not identify any outlier loci while a frequency-based method (FDIST2) identified 180 FST outliers. FST estimate for these 178 outlier loci was 0.055. A Bayesian clustering analysis, STRUCTURE, revealed genetic structure by sampling locality with FST outlier loci presumed to be under selection and this pattern was not apparent with the entire dataset. These results suggest high levels of gene flow for this species across its range and the pattern observed in FST outlier loci may indicate weak local adaptation in grass rockfish, a nearshore marine species, in the face of high gene flow.