Phenotypic selection on growth rhythm in whitebark pine (Pinus albicaulis) in low elevation common gardens

Abstract

Growth rhythm represents the timing of annual plant growth and development in relation to the environment. Growth rhythm that is well synchronized with the local climate is understood to confer adaptation in plant species. Rapid ongoing climate change threatens to desynchronize growth rhythm for many plant populations, yet knowledge of how plant populations undergo selection on growth rhythm and how they will respond is limited. Therefore, to evaluate phenotypic selection on growth rhythm, seedlings from 49 populations of whitebark pine (Pinus albicaulis), representative of the interior northwestern United States, were grown in two common-garden field tests over a 12-year period under climate (+4.4 to 9.1 °C mean annual temperature) approximating projected climate change in the present century for the sampled species range. In addition, variation in growth rhythm among populations and its relation to the climate of the seed source were evaluated to clarify how growth rhythm varies over the study region. Height at the end of the study was used as the best available measure of fitness. Survival and the unconditional expected value for height were dependent on timing of apical shoot elongation rates within and among growing seasons. Comparison of models using survival versus unconditional expected height as the proxy for fitness showed that survival strongly influenced selection on elongation rates. The form and magnitude of selection on timing and rate of shoot elongation varied between test sites and over time. Analysis of the timing of selection detected directional and stabilizing selection on shoot elongation rates in the earliest years whereas only directional selection was detected for selection on elongation rate in later years. Differences among populations for growth rhythm were mild and were explained to a moderate extent (r2 = 0.08-0.28) by climatic clines. Taken together, these findings suggest that growth rhythm in whitebark pine has been mildly selected for in relation to past climate and will undergo phenotypic selection in response to ongoing climate change.

Parent Publication

• Proceedings of the IUFRO joint conference: Genetics of five-needle pines, rusts of forest trees, and Strobusphere; 2014 June 15–20; Fort Collins, CO

Citation

Warwell, Marcus V. 2018. Phenotypic selection on growth rhythm in whitebark pine (Pinus albicaulis) in low elevation common gardens. In: Schoettle, Anna W.; Sniezko, Richard A.; Kliejunas, John T., eds. Proceedings of the IUFRO joint conference: Genetics of five-needle pines, rusts of forest trees, and Strobusphere; 2014 June 15-20; Fort Collins, CO. Proc. RMRS-P-76. Fort Collins, CO: U.S. Department of Agriculture, Forest Service, Rocky Mountain Research Station. p. 59-62.