Evidence for parallel evolution and site-specific selection of serpentine tolerance in Cerastium alpinum during the colonization of Scandinavia

The effects of Ni and Mg, two factors involved in the infertility of serpentine soils, were studied in the alpine plant Cerastium alpinum. Root growth of plants from adjacent serpentine and non-serpentine populations in Scandinavia, representing an eastern and western postglacial immigration lineage and the hybrid zone between them, were compared to study the adaptation of C. alpinum populations. Seedlings were placed in solutions with low or high concentrations of Ni and Mg in a full factorial experiment according to a randomized block design. The growth of roots was analyzed and discussed in relation to the soil content. The serpentine populations showed higher tolerance to Ni and Mg stress than non-serpentine populations. The degree of metal tolerance differed among the serpentine populations and was related to the effective concentrations of Ni and Mg in the soil at each site. The results suggest that serpentine tolerance is locally evolved in C. alpinum and that tolerance has arisen in parallel during the postglacial colonization of Scandinavia on serpentine soils with similar composition.