Genomic stability through time despite decades of in cod on both sides of the Atlantic

The mode and extent of rapid evolution and genomic change in response to human harvesting are key conservation issues. Al-though experiments and models have shown a high potential for both genetic and phenotypic change in response to fishing, empirical examples of genetic responses in wild populations are rare. Here, we compare whole-genome sequence data of Atlantic cod (Gadus morhua) that were collected before (early 20th century) and after (early 21st century) periods of intensive exploitation and rapid decline the age of maturation from two geographically distinct populations Newfoundland, Canada, and the northeast Arctic, Norway. Our temporal, genome-wide analyses of 346,290 loci show no substantial loss of genetic diversity and high effective population sizes. Moreover, we do not find distinct signals of strong selective sweeps anywhere in the genome, although we cannot rule out the possibility of highly polygenic evolution. Our observations suggest that phenotypic change in these populations is not constrained by irreversible loss of genomic variation and thus imply that former traits could be reestab-lished with demographic recovery.

Automated summary

This study compared whole-genome sequence data of Atlantic cod from two geographically distinct populations and found that genetic diversity did not substantially decline and effective population sizes remained high after periods of intensive exploitation and rapid decline. The research suggests that phenotypic change in these populations is not constrained by irreversible loss of genomic variation.