DOI: 10.5061/dryad.tht76hf17
title: Data from: Multivariate selection mediated by aridity predicts divergence of drought resistant traits along natural aridity gradients of an invasive weed

description: Geographic variation in the environment underpins selection for local
 adaptation and evolutionary divergence among populations. Because many
 environmental conditions vary across species’ ranges, identifying the
 specific environmental variables underlying local adaptation is profoundly
 challenging. We tested whether natural selection mediated by aridity
 predicts clinal divergence among invasive populations of capeweed
 (Arctotheca calendula) that established and spread across southern
 Australia during the last two centuries. Using common garden experiments
 with two environmental treatments (wet and dry) that mimic aridity
 conditions across capeweed’s invasive range, we estimated clinal
 divergence and effects of aridity on fitness and multivariate phenotypic
 selection in populations sampled along aridity gradients in Australia. We
 show that: (i) capeweed populations have relatively high fitness in
 aridity environments similar to their sampling locations; (ii) the
 magnitude and direction of selection strongly differs between wet and dry
 treatments, with drought stress increasing the strength of selection; and
 (iii) differences in directional selection between wet and dry treatments
 predict patterns of clinal divergence across the aridity gradient,
 particularly for traits affecting biomass, flowering phenology and
 putative antioxidant expression. Our results suggest that aridity-mediated
 selection contributes to trait diversification among invasive capeweed
 populations, possibly facilitating the expansion of capeweed across
 southern Australia.
description: Two common garden
 experiments (2018 greenhouse; 2019 field) were conducted at Monash
 University (Clayton, Victoria; latitude: -37.9091, longitude:
 145.1411).  <em>Greenhouse
 experiment</em>.<em> <br></em>In the 2018
 experiment, conducted in a greenhouse, we investigated variation in
 drought resistance traits in six populations sampled along a transect
 spanning wet-to-dry capeweed range conditions in Victoria. 
 <em>Field
 experiment</em>. <br>The 2019 experiment was conducted in an
 open field at Jock Marshall Reserve (Monash University, Clayton) to
 estimate selection in a semi-natural environment of capeweed. Seeds for
 this experiment were collected from approximately 30 maternal plants each
 from eight populations distributed along transects in eastern and western
 Australia.  We
 measured 13 traits that are thought to mediate drought resistance in
 annual plants. Drought escape traits included growth rate, maximum
 photosynthetic capacity
 (F<sub>v</sub>/F<sub>m</sub>), photosynthetic
 assimilation rate, final biomass, and days to first flower. Root-to-shoot
 ratio, leaf size, leaf succulence, specific leaf area (SLA), and stomatal
 conductance are linked to plants’ dehydration avoidance strategy. We
 quantified three leaf phenolic compounds that are potentially associated
 with plants’ drought tolerance strategy (chlorogenic acid, an unknown
 phenolic acid, and an unknown flavonoid).