COS 104-1 - Understanding organismal responses to climate change using sky islands: Empirical support from local to global scales

Abstract: Climate-induced evolution will determine population persistence in a changing world. However, finding natural systems in which to study these responses has been a barrier to estimating the impact of global change on a broad scale. Isolated sky islands (SI) and adjacent mountain chains (MC) can serve as a comparative natural laboratory for studying the impact of long-term climatic pressures on real populations. We used genetic replicates of the dominant, riparian tree Populus angustifolia grown in a common garden to determine: 1) whether SI populations exposed to hot and dry climates since the Pleistocene have diverged from MC populations in reproductive and productivity traits; 2) if SI populations from a large geographic range have converged in these traits; and 3) the evolutionary mechanism driving trait differences(i.e., genetic drift or natural selection). We also conducted a comprehensive global literature review of ecological and evolutionary patterns and processes dominant on SI across all life forms and demonstrate the empirical utility of the SI-MC comparison with seven case studies.

We show: 1) isolated SI are significantly hotter and drier than adjacent MC; 2) populations of P. angustifolia from SI have diverged from MC, but have converged across SI, in reproductive and productivity traits, 3) these quantitative traits (cloning and aboveground biomass, respectively) are significantly correlated, and 4) the observed phenotypic change is driven by both natural selection and genetic drift. These results suggest that long-lived tree populations on distantly related SI have evolved in response to long-term selective pressures towards potentially beneficial phenotypes for population persistence in a changing world. Globally, SI isolation often results in lineage formation, reduced genetic variation, and trait evolution, including that driven by altered species interactions on the isolated mountain peaks. We also show support for divergent evolutionary pressures and resultant ecological patterns across diverse taxa using seven comparative SI-MC studies. Operable on most continents, the SI-MC comparison may be an advantageous natural laboratory and predictive framework for studying ecological and evolutionary responses to climate change, from genes to ecosystems, across the globe.