Population genomics of contemporary adaptation across a species' range
We’re using pool-seq across ~100 populations of Clarkia xantiana — sampled both historically and contemporaneously — to ask how allele frequencies have shifted over recent decades of climate change, and whether the same loci respond to climate across populations and across time. The work leverages long-term demographic and herbarium records from the Moeller and Geber labs, together with newly assembled reference genomes (see Clarkia reference genomes).
With Dave Moeller (Minnesota), Monica Geber (Cornell), and Jacob Landis (Cornell).
Key publications
The spatial scale of adaptation in a native annual plant and its implications for responses to climate change
Amanda J Gorton*, John W Benning*, Peter Tiffin, and David A Moeller
Spatial patterns of adaptation provide important insights into agents of selection and expected responses of populations to climate change. Robust inference into the spatial scale of adaptation can be gained through reciprocal transplant experiments that combine multiple source populations and common gardens. Here, we examine the spatial scale of local adaptation of the North American annual plant common ragweed, Ambrosia artemisiifolia, using data from four common gardens with 22 source populations sampled from across a 1200 km latitudinal gradient within the native range. We found evidence of local adaptation at the northernmost common garden, but maladaptation at the two southern gardens, where more southern source populations outperformed local populations. Overall, the spatial scale of 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. 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.
Rapid evolution during climate change: demographic and genetic constraints on adaptation to severe drought
John W Benning, Alexai Faulkner^, and David A Moeller
Populations often vary in their evolutionary responses to a shared environmental perturbation. A key hurdle in building more predictive models of rapid evolution is understanding this variation - why do some populations and traits evolve while others do not? We combined long-term demographic and environmental data, estimates of quantitative genetic variance components, a resurrection experiment and individual-based evolutionary simulations to gain mechanistic insights into contrasting evolutionary responses to a severe multi-year drought. We examined five traits in two populations of a native California plant, Clarkia xantiana, at three time points over 7 years. Earlier flowering phenology evolved in only one of the two populations, though both populations experienced similar drought severity and demographic declines and were estimated to have considerable additive genetic variance for flowering phenology. Pairing demographic and experimental data with evolutionary simulations suggested that while seed banks in both populations likely constrained evolutionary responses, a stronger seed bank in the non-evolving population resulted in evolutionary stasis. Gene flow through time via germ banks may be an important, underappreciated control on rapid evolution in response to extreme environmental perturbations.
