DOI: 10.5061/dryad.pnvx0k6q1
title: Data from: Rapid-cycling Brassica rapa evolves even earlier flowering under experimental drought

description: Premise Changes in climate can impose selection on populations and may
 lead to rapid evolution. One such climatic stress is drought, which plant
 populations may respond to with escape (rapid growth and early flowering)
 or avoidance (slow growth and efficient water use). However, it is unclear
 if drought escape would be a viable strategy for populations that already
 flower early from prior selection. Methods In an experimental evolution
 study, we subjected rapid-cycling Brassica rapa (RCBr), which was
 previously selected for early flowering, to four generations of
 experimental drought or watered conditions. We then grew ancestral and
 descendant populations concurrently under drought and watered conditions
 to assess evolution, plasticity, and adaptation. Results RCBr evolved
 under drought had earlier flowering and lower water-use efficiency than
 RCBr evolved under watered conditions, indicating evolutionary divergence.
 The drought descendants also had a trend of earlier flowering compared to
 ancestors, indicating evolution. Evolution of earlier flowering under
 drought followed the direction of selection and increased fitness, and was
 consistent with studies in natural and experimental populations of this
 species, suggesting adaptive evolution. Conclusions We found evidence for
 rapid adaptive evolution of drought escape in RCBr and little evidence for
 constraints on flowering, even though RCBr already flowers extremely
 early. Our results suggest that some populations may harbor sufficient
 genetic variation for evolution even after strong selection has occurred.
 Our study also illustrates the utility of combining artificial selection,
 experimental evolution, and the resurrection approach to study the
 evolution of functional traits.
description: We began this experiment with Wisconsin fast plant lines of
 rapid-cycling <em>Brassica rapa</em> (field mustard), which we
 grew and crossed to generate maternal lines of known maternity and
 paternity. We assigned one seed from each of 48 maternal lines to each of
 the 12 experimental populations (N=48 per population). We then assigned 4
 populations for storage as ancestors, 4 to receive four generations of
 experimental drought, and 4 to receive four generations of experimental
 well-watered conditions. During these four generations of experimental
 evolution, drought populations received a drought treatment aimed to
 shorten the growing season while well-watered populations were watered
 every other day.<br>After experimental evolution, we grew all
 experimental populations (ancestors included) under unstressed
 (well-watered) conditions to reduce maternal and storage condition effects
 across the different regimes. We then grew two seeds
 (siblings) from each individual grown in the refresher generation while
 applying a watering treatment with one sibling from each individual under
 each treatment in what was the test generation. This design allowed us to
 assess evolutionary responses (ancestor-descendant regime comparisons) and
 plasticity (watered-drought treatment comparisons) to experimental
 drought.<br>Detailed methods, statistical analysis, and results are
 discussed in the assocated manuscript published in American Journal of
 Botany.