Abstract
Spatial patterns of adaptation provide important insights into agents of selection and expected responses of populations to climate change. Robust inference into the geographic scale of adaptation can be gained through reciprocal transplant experiments that combine multiple source populations and common gardens. To quantify the scale of local adaptation and examine the consequences of a warming climate on the species’ range, we performed reciprocal transplant experiments at four common gardens with 22 populations sampled across a ~1200 km latitudinal gradient within the native range of common ragweed, Ambrosia artemisiifolia. We found evidence of local adaptation at the northernmost common garden, but maladaptation at the two southern gardens, where more southern populations outperformed local populations. Overall, the spatial scale of climate adaptation was large — at the three gardens where distance between source populations and gardens explained variation in fitness, it took an average of 820 km for fitness to decline to 50% of its predicted maximum. However, fitness declined more sharply with distance in southern transplant sites. Taken together, these results suggest that climate change has already caused maladaptation, especially across the southern portion of the range, and may result in northward range contraction over time.
Competing Interest Statement
The authors have declared no competing interest.
