Plants need to adapt their germination timing to environmental variation. Arabidopsis kamchatica ssp. kamchatica, closely related to the plant model A. thaliana, is a perennial herb distributed over remarkably wide altitudinal range (30 to 3000 m), whilst ssp. kawasakiana is an annual herb limited to only lowland. How do those populations evolutionary adapt their germination traits to such altitudinal difference, which is associated with drastic variation in environmental factors?

We used seeds of laboratory-grown 29 and 9 populations of ssp. kamchatica and ssp. kawasakiana, respectively. Germination timing of those populations was assessed by two experiments: (1) 22 ºC constant, (2) 2 stratification (2 weeks or absence) ´ 2 temperature (increasing from 5 ºC to 35 ºC by 5 ºC in every week, or decreasing backward) ´ 2 light (24D or 12L:12D) = 8 treatments. In experiment (1), populations from lower altitude showed later germination, indicating historical natural selection on germination trait and consequent genetic differentiation along altitude. In Experiment (2), subspecies and populations showed markedly different response to those treatments, indicating genetic differentiation by local adaptation.