Adaptation, differentiation and plasticity of alpine Erysimum capitatum and their implications for responses to climate change

Anthropogenic climate change is expected to alter species distributions and abundances. Organisms at high altitude or latitude are at particular risk. To predict changes in population sizes and viability, responses to changing environments in demography, life history, and physiological traits must be evaluated, as well as their interactions with each other and with specific environmental factors. Although altitudinal variation in diverse traits is well documented in plant species, little information is available on how the demography of alpine plants is expected respond to climate change, and how fundamental life histories of alpine plants will change via phenotypic plasticity and adaptive evolution. Since the alpine environment is expected to become more similar to below tree-line environments, I quantified phenotypic plasticity, population differentiation and local adaptation of Erysimum capitatum populations inhabiting alpine and below tree-line environments.;Plant survival of all life-stages was higher in alpine environments compared to lower-elevation environments, suggesting that climate change can directly reduce population growth rate. Plasticity of physiological and morphological traits may mitigate the decline of alpine populations, but adaptive evolution or migration of low-elevation genotypes is likely required to maintain populations at high altitude because of the limits of phenotypic plasticity.;Life-history differed across altitude, with semelparity predominating at low altitude and iteroparity at high altitude. This differentiation appears adaptive since adult mortality was higher at low altitude. In addition, a tradeoff between juvenile survival and post-reproductive survival was found: the production of more axillary rosettes compromised survival at the pre-reproductive stage under drought conditions like those at low elevation, but axillary rosettes are also required for post-reproductive survival and an iteroparous life history. Thus, evolution or phenotypic plasticity of pre-reproductive traits may influence adult reproductive strategy. Such a change in reproductive strategy induces fundamental changes in population demography.;In summary, alpine populations of E. capitatum are specialized to high-elevation environments, so their sizes are expected to decrease in response to climate change unless migration occurs from populations at lower elevation. Altered natural selection on pre-reproductive traits, moreover, has the potential to alter basic reproductive strategy, which in turn will influence population demography.