Pre-adaptation to climate change through topography-driven evolution of traits and their plasticity

1. Climate change will increase the level of drought stress experienced by
plant communities, but the spatial distribution of projected changes in
dryness remains highly uncertain. Species can, to some extent, deal with
climate uncertainty through natural variation in adaptive responses to
environmental heterogeneity and predictability. Biodiversity conservation
could thus target populations pre-adapted to climatic heterogeneity to
anticipate climate uncertainty. Disentangling evolution of trait means vs.
trait plasticity, however, requires a sampling design with genetic
replicates grown under distinct environmental conditions. 2. Here, we
applied three soil moisture treatments to genetic replicates of Fragaria
vesca plants raised from seeds that were sampled in distinct topographical
settings, to study adaptive trait and plasticity divergence in response to
drought. 3. We demonstrate that various plant traits evolved along
distinct topographical gradients. For example, populations on
south-exposed slopes retained high levels of both flowering and runner
formation under drought stress, while north-faced populations hardly
flowered under reduced soil moisture levels. Aspect but not elevation was
found to coincide with plant traits, suggesting that micro-environmental
variation rather than general clines in elevation drive evolution in
mountainous landscapes. Our results also indicate that traits and their
plasticity can evolve independently in response to distinct topographical
stressors. 4. Synthesis. We conclude that heterogeneous landscapes (i)
harbor micro-refugia of adaptive genetic diversity that protect natural
populations against environmental change, and (ii) represent invaluable
sources of quantitative genetic variation that could support conservation
where climate projections are inconclusive.