Back to the future: The use of historical samples to assess and predict the consequences of climate change on the genetic resources of fish

Einar Eg Nielsen, Nina Overgaard Therkildsen, Sara Bonanomi and Jakob Hemmer-Hansen. Technical University of Denmark, National Institute of Aquatic Resources, Vejlsøvej 39, 8600  Silkeborg. een@aqua.dtu.dk

Global change has altered the environmental conditions for many fish species. In order to avoid extinction fish can respond to the transformed environment in several ways. They can stay put and modify their phenotype through plastic responses, migrate to other areas where more favorable conditions prevail or adapt genetically to the new conditions. Thus the impact on the genetic resources depends on the relative importance of these processes in time and space. Historical samples of fish, such as scales and otoliths, have for more than a century been used for age and growth determination in fish. New methodological developments now allow for retrospective analysis of DNA from such samples at a genomic scale.  We here present a number of cases applying spatiotemporal population genomics in cod populations, which allow for identification of the relative effects of migration and selection on shaping the patterns of genomic variation in space and time. We discuss general insights and generate predictions from these studies in relation to genetic resources in fish, and present a framework for using “genetic monitoring” to demonstrate adaptive responses to climate change and other human activities. Finally, we point to new avenues for applying spatiotemporal population genomics for assessing changes in genomic resources of fish.