Migration and adaptation in response to natural and experimental climate gradients: Implications for species' responses to climate change from a field transplant experiment
Given the rate and magnitude of contemporary climate change, understanding how plasticity, local adaptation, and migration may facilitate or constrain species’ adaptive responses to climate change is a high priority. Toward this goal, a field transplant experiment investigates the genetic and plastic components of trait variation across climate gradients, response to selection imposed by natural and experimental climate change, and the potential for upward migration of genes or genotypes to facilitate population-level persistence as habitats warm.
Androsace septentrionalis (Primulaceae) seeds collected across a wide elevation/climate gradient were reared in a greenhouse common garden. Reproductive plants were selfed (creating 40 lines from low, mid, and high elevations) and crossed (creating 60 hybrid lines from within and across elevations). All lines were taken through a second greenhouse generation during which plants were allowed to self. 24,400 greenhouse-harvested seeds from across all lines were then planted into transplant gardens across the original elevation gradient and into a 24 year-old climate manipulation experiment where A. septentrionalis has experienced a four-fold decline in response to experimental warming. Transplants were monitored for germination, establishment, drought stress, herbivore damage, growth rate, and first year survival.
In low-elevation gardens, we find evidence for local adaptation. While mid-elevation lines have the highest germination rates, low-elevation lines are most likely to survive. Susceptibility to and ability to recover from drought stress explain differences in survival; low-elevation lines experience less drought stress and have higher drought-stress recovery rates than both mid- and high-elevation lines. These low-elevation patterns mimic what we see in experimentally warmed plots; severe drought stress and high mortality follow rapid germination in response to transient warm, moist conditions.
At higher elevations, we do not find evidence for local adaptation. In mid-elevation gardens, low-elevation lines outperform mid-elevation lines, and mid-low hybrids experience less drought stress and have higher survival than mid-elevation lines. At high elevation, mid-elevation lines outperform high-elevation lines, and mid-high hybrids have higher survival than both mid- and high-elevation lines.
Together, transplant results indicate that contemporary climate change may be disrupting local-adaptation across natural climate gradients. Results also suggest that germination timing and early seedling drought susceptibility play critical roles in transplant success and also explain population-level declines in experimentally warmed plots. Finally, transplant results suggest that migration of genes and/or genotypes from lower elevations may buffer mid- and high-elevation populations from climate-change induced declines.