Genetic mapping of adaptation reveals fitness tradeoffs in <i>Arabidopsis thaliana</i>

Significance Adaptation to local environmental conditions is common, but the genetic mechanisms of adaptation are poorly known. We produced recombinant inbred lines (RILs) of the model plant Arabidopsis thaliana by crossing populations that inhabit drastically different climates in Sweden and Italy, grew the RILs at the parental sites for 3 y, and genetically mapped quantitative trait loci (QTL) for fitness. The results demonstrate that surprisingly few QTL explain much of the adaptive divergence between the two plant populations. Moreover, we find strong evidence for tradeoffs (i.e., adaptation to one environment reduces performance elsewhere). The results shed light on processes governing the evolution of biological diversity and the potential for adaptive evolution in response to environmental change.