Evolutionary Responses to Historic Drought across the Range of Scarlet Monkeyflower

AbstractAdaptive evolution is a key means for populations to persist under environmental change, yet whether populations across a species' range can adapt quickly enough to keep pace with climate change remains unknown. The breeder's equation predicts the evolutionary change in a trait from one generation to the next as the product of the selection differential and the narrow-sense heritability in that trait. Incorporating these aspects of the breeder's equation, we performed a resurrection study with the scarlet monkeyflower (Mimulus cardinalis) to evaluate whether traits associated with drought adaptation have evolved in populations across a species' range in response to extreme drought. We compared trait and fitness differences of predrought ancestors and postdrought descendants from six populations transplanted into three latitudinally arrayed common gardens and quantified phenotypic selection and trait heritabilities. The strength, direction, and mode of selection varied among traits and gardens. Trait heritabilities were relatively low and did not differ dramatically among populations or gardens. Overall, instances of evolutionary responses between ancestors and descendants were few and small in magnitude, but the magnitude of these evolutionary differences varied among gardens. These results suggest that evolutionary responses to climate change vary among populations in unpredictable ways and that the expression of these responses depend on environmental conditions, hindering our ability to predict evolutionary rescue under changing climate.