Divergence among arctic and alpine populations of the annual, Koenigia islandica: morphology, life-history, and phenology

Arctic and alpine habitats occur along complex environmental gradients, and over an extensive geographical range. Despite some selective forces common to these habitats, evolutionary divergence among populations of arctic and alpine plants along this gradient is expected. Of particular significance, both in the context of life-history theory and for implications of climate change, are the few annual species that have adapted to the constraints of an unpredictable, short growing season. In this study, morphological, life-history and phenological characters were found to differ significantly among six widely distributed populations of the arctic-alpine annual Koenigia islandica. On the basis of morphology and life-history traits, populations from high latitudes, with the exception of Svalbard, performed better in simulated arctic conditions, whereas the low latitude alpine plants from Colorado showed enhanced performance under simulated alpine conditions. On the basis of phenology, the six populations can be clearly grouped into arctic, high latitude alpine and alpine populations: arctic plants were found to develop and flower earliest; alpine plants latest. Because these results were obtained using seeds harvested from plants first grown through a complete generation in growth chambers, they indicate strong genetic differentiation. We discuss possible adaptive explanations for observed differences among the six geographically divergent populations.