Pennington, L. K.; Sexton, J. P.

Montane plant populations are experiencing novel conditions due to climate change. Furthermore, climate change is causing increased climate perturbations, such as the 2012-2016 drought in the western US, remarkable in its aridity, longevity, and warmer temperatures. This drought provided an opportunity to understand how montane populations respond to extreme perturbations, including at range limits. We resurrected seeds of the endemic annual plant Erythranthe laciniata, collected in 2008 or earlier (before the drought) and in 2014 (the height of the drought), in a common garden experiment to understand how drought influenced evolution in contemporary field conditions. The study included nine populations across the species range, including range edges. Over 2,100 replicates were sown in three common gardens at natural populations at low, central, and high elevations. We recorded phenology and flower production to estimate lifetime fitness. This experiment took place in 2021, a year with low precipitation and high temperatures. We found higher fitness in the drought generation at the high garden, while both generations showed similar fitness at the central and low gardens. We detected climate adaptation at the low and high gardens, and rapidly evolved faster phenology at the high garden. Lifetime fitness was substantially lower at lower gardens overall, even for low-elevation populations. Low-elevation populations outperformed central populations at the central garden, suggesting adaptive mismatch. Together, these results indicate rapid contemporary adaptation that is beneficial at the leading edge of the species range. Nevertheless, low fitness at lower elevations may foreshadow range contraction under continued climate change.