Early life stages contribute strongly to local adaptation in Arabidopsis thaliana

Significance Organisms are often adapted to local environmental conditions. Yet, the contribution of genetic differences expressed during early life stages to the magnitude and genetic basis of local adaptation are poorly known. We planted seeds of recombinant inbred lines derived from a cross between populations of the model plant Arabidopsis thaliana in Italy and Sweden at the parental sites, and mapped quantitative trait loci (QTL) for fitness and its components. Natural selection strongly favored the local genotype during seedling establishment, and QTL for establishment contributed to local adaptation and genetic fitness tradeoffs. The results demonstrate that adaptive differentiation during early life stages can be strong and should be considered for a full understanding of the ecology and genetics of local adaptation.