Genetic characterization of clonality in expanding populations of arctic willow (Salix spp) shrubs

The ability to reproduce vegetatively can allow clonal plants to colonize and survive areas when conditions are too extreme for sexual reproduction. In arctic Alaska, warming climate has occurred concomitantly with an increase in the area covered by deciduous shrubs. Repeat photographic analysis and experimental warming has revealed shrub expansion of existing sites and the colonization of new sites. It is thought that zones with growing conditions once too extreme for shrub growth are now marginally improved, facilitating only limited sexual reproduction, but sufficiently adequate for clonal growth. Despite recent widespread arctic shrub expansion and a sustained increase in temperatures, little research has been conducted on the relative contributions of clonal growth and seed reproduction. Here we use molecular genetic markers to explore the extent of clonal growth in the arctic shrubs Salix pulchra and Salix lanata (Salicaceae) along transects at a known expanding shrub site on Alaska’s North Slope. DNA was extracted and microsatellite markers were amplified producing a genetic fingerprint for each sample. Pairwise comparisons of these genetic fingerprints allowed for the identification of clones. Preliminary results demonstrate no clonal growth within patches of S. lanata and small clones within patches of S. pulchra. Colonization by seed may serve as the primary mechanism for the maintenance and expansion of willow populations, implying a lower threshold of abiotic conditions necessary for seedling persistence or greater biological significance of current arctic warming than previously predicted.