Divergent selection in low and high elevation populations of a perennial herb in the Swiss Alps

Abstract

Mountain plant species with wide elevational ranges are expected to be exposed to different selection pressures at low and high elevation. Estimating the extent of genetic population differentiation contributes to our understanding of selective forces shaping phenotypic variation of plants in response to changing climate conditions. Using a common garden experiment, we measured narrow-sense heritability (h 2) and quantitative trait differentiation (Q ST) in several growth-related, reproductive and phenological traits among low and high elevation populations of the semi-dry grassland species Ranunculus bulbosus from the Swiss Alps. Q ST values were compared to neutral genetic differentiation (F ST) based on AFLP markers and indicated divergent selection in most traits among all populations as well as among low and high elevation populations separately. Furthermore, pairwise Q ST and F ST estimates were not correlated suggesting that neutral marker differentiation is not a valuable proxy for quantitative trait differentiation. Neutral molecular differentiation increased with geographical distance whereas quantitative genetic differentiation did not follow an isolation by distance pattern. Plant traits did mostly not differ among low and high populations and pairwise Q ST–F ST comparisons indicated no divergent selection between the two elevations. Differing levels of trait differentiation in low and high elevation populations, however, indicated that different selective forces acted on plants at contrasting elevations suggesting that selection regimes might alter under climate warming.