Resurrected seeds from herbarium specimens reveal rapid evolution of drought resistance in a selfing annual

Premise of study: Increased aridity and drought associated with climate change are exerting unprecedented selection pressures on plant populations. Whether populations can rapidly adapt, and which life history traits might confer increased fitness under drought, remain outstanding questions. 

Methods: We utilized a resurrection ecology approach, leveraging dormant seeds from herbarium collections to assess whether populations of Plantago patagonica from the semi-arid Colorado Plateau have rapidly evolved in response to approximately ten years of intense drought in the region. We quantified multiple traits associated with drought escape and drought resistance and assessed the survival of ancestors and descendants under simulated drought. 

Key Results: Descendant populations displayed a significant shift in resource allocation, in which they invested less in reproductive tissues and relatively more in both above- and below-ground vegetative tissues. Plants with greater leaf biomass survived longer under terminal drought; moreover, even after accounting for the effect of increased leaf biomass, descendant seedlings survived drought longer than their ancestors. 

Conclusions: Our results document rapid adaptive evolution in response to climate change in a selfing annual and suggest that shifts in tissue allocation strategies may underlie adaptive responses to drought in arid or semi-arid environments. This work also illustrates a novel approach, documenting that under specific circumstances, seeds from herbarium specimens may provide an untapped source of dormant propagules for future resurrection experiments.

Methods
Data files: This upload includes the input data (.csv and .Rdata) and scripts (.R) for primary analyses and figure generation in the manuscript.  See the README.txt file for description of the metadata. These data were generated in series of experiments conducted in a greenhouse common garden.

Location: This research was conducted at the greenhouse at Northern Arizona University, using seeds collected from 5 locations in Northern Arizona, as well as seeds previously collected from these sites as part of herbarium voucher specimens.