Seed collection
For the present study, seeds of natural populations of Arabidopsis thaliana (L.) Heynh. were collected at 45 sites in Fennoscandia and Italy (Fig. 1, Table S1 ) between 2005 and 2012. We sampled 28 populations in Fennoscandia (latitude, 55°58’ N – 66°88’ N; longitude 6°62’ E – 24°38’ E) and 17 in Italy (latitude, 37°80’ – 42°39’; longitude 12°00’ – 18°34’E). Seeds were kept in paper bags at room temperature until use. Prior to the present experiment, seed collections had gone through two generations of selfing in the greenhouse to reduce maternal environmental effects.