Contrasting genomic shifts underlie parallel phenotypic evolution in response to fishing

Parallel and idiosyncratic fish adaptation Fish populations respond rapidly to fishing pressure. Within a handful of generations, marked phenotypic change can occur—often to smaller body sizes, because it is the big fish that are usually extracted. Therkildsen et al. examined wild ancestor fish lineages and found that polygenic mechanisms underpin this rapid evolutionary capacity (see the Perspective by Jørgensen and Enberg). Phenotypic change happened in two ways: first, by multiple small parallel changes in hundreds of unlinked genes associated with growth variation in the wild, and second, by shifts in large blocks of linked genes, causing large allele frequency changes at some loci. Science , this issue p. 487 ; see also p. 443