Past selection explains differentiation in flowering phenology of nearby populations of a common alpine plant

The timing of and relative investment in reproductive events are crucial fitness determinants for alpine plants, which have limited opportunities for reproduction in the cold and short growing seasons at high elevations. We use the alpine Anthyllis vulneraria to study whether flowering phenology and reproductive allocation have been under diversifying selection, and to assess genetic diversity and plastic responses to drought in these traits. Open-pollinated maternal families from three populations in each of two regions from the Swiss Alps with contrasting precipitation were grown in low and high soil moisture in a common garden. We measured onset, peak, and end of flowering, as well as vegetative and reproductive aboveground biomass. Population differentiation for each character (Q ST) was compared to differentiation at neutral microsatellite loci (F ST) to test for past selection. We found population differentiation in onset and peak of flowering which results from natural selection according to Q ST–F ST. End of flowering and biomass were not significantly differentiated among populations. Reduced soil moisture had no consistent effect on mean onset of flowering, and advanced peak and end of flowering by less than 1 week. Reproductive biomass was strongly decreased by lowered soil moisture. No genetic variation within or among populations was found for plasticity in any trait measured. The results suggest past heterogeneous selection on onset and peak of flowering in alpine Anthyllis vulneraria and potentially indicate local adaptation to differences in snowmelt date over distances <5 km. Limited variation in plastic responses to reduced soil moisture suggests that soil moisture might not vary between populations.