Local adaptation of seed and seedling traits along a natural aridity gradient may both predict and constrain adaptive responses to climate change (American Journal of Botany 2022)

Premise of study: Variation in seed and seedling traits underlies how plants interact with their environment during establishment, a crucial life history stage.  We quantified genetic-based variation in seed and seedling traits in populations of the annual plant Plantago patagonica across a natural aridity gradient, leveraging natural intraspecific variation to predict how populations might evolve in response to increasing aridity associated with climate change in the Southwestern U.S.

Methods: We quantified seed size, seed size variation, germination timing, and specific leaf area in a greenhouse common garden, and related these traits to the climates of source populations.  We then conducted a terminal drought experiment to determine which traits were most predictive of survival under early-season drought.

Key Results:  All traits showed evidence of clinal variation – seed size decreased, germination timing accelerated, and specific leaf area increased with increasing aridity.  Populations with more variable historical precipitation regimes showed greater variation in seed size, suggestive of past selection shaping a diversified bet-hedging strategy mediated by seed size.  Seedling height, achieved via larger seeds or earlier germination, was a significant predictor of survival under drought.

Conclusions: We documented substantial interspecific trait variation as well as clinal variation in several important seed and seedling traits, yet these slopes were often opposite to predictions for how individual traits might confer drought tolerance.  This work shows that plant populations may adapt to increasing aridity via correlated trait responses associated with alternative life history strategies, but that trade-offs might constrain adaptive responses in individual traits.

Keywrds: climate change, drought, intraspecific trait variation, life history strategies, local adaptation, Plantago, precipitation variability, seed size, trade-offs

Data files:  This upload includes all of the input data (.csv and .Rdata) and scripts (.R) for analysis and figure generation in the manuscript.  See the included README.txt file for details.

Location: This research was conducted at the greenhouse at Nothern Arizona University, using seeds collected from 12 locations in nothern Arizona and southern Utah.

These data were collected in the greenhouse and lab (see Methods in the manuscript).

All analyses and figure generation were conducted in R.