Genetic adaptation of wild populations under climate change: building up the evidence base

Natalie E. van Dis 

To understand to what extent evolution can contribute to bending the curve of ongoing biodiversity losses, we urgently need to characterize the rate of genetic adaptation in wild populations. However, we lack a comprehensive overview of which species and populations have been tested to date and the strength of evidence these studies provide. In this review, I systematically assessed the evidence of genetic adaptation to climate change on four criteria that together robustly demonstrate that genetic changes are adaptive and driven by climate change. I determined whether strong inference methods were used to (1) test for genetic change over time, (2) show that the observed genetic change is associated with climate change, (3) establish that the fitness of the phenotype / genotype depends on the climatic variable that changed over time, and (4) assess population genetic continuity over time to rule out purely neutral evolution. I identified 44 species that were tested for genetic change under climate change using strong inference methods, with a number of patterns emerging from this overview. The 44 species tested were mostly from the terrestrial realm in temperate regions and encompassed eight higher taxa (16 plants, 7 insects, 7 birds, 5 mammals, 4 fish, 2 crustaceans, 2 molluscs, and 1 alga), with 39 species having evidence that genetic change had occurred in wild populations and 5 species evidence that no genetic change occurred albeit for 4 of these 5 species only one population has been tested so far. In fact, climate change responses were highly population specific, with clear variation within species (152 of the 253 populations tested were found to have genetically changed over time). Finally, in most species, responses to climate change were associated with changes in temperature and/or precipitation, where climate change was found to have both direct effects on survival and reproduction as well as indirect effects through changing species interactions. However, with regard to the strength of evidence, only 3 out of the 44 tested species met the criteria for demonstrating that the observed genetic responses are indeed adaptive and driven by climate change. I urge the field to strengthen the evidence base of genetic adaptation to climate change in wild populations as this is needed before it is possible to draw robust conclusions about the role of genetic adaptation in population persistence. In addition, testing more species to improve taxonomic and geographic representation as well as increasing spatial and temporal replication per species would allow for the exciting opportunity to start empirically testing drivers and constraints that determine the rate of genetic adaptation to climate change.