Data from: Multivariate selection mediated by aridity predicts divergence of drought resistant traits along natural aridity gradients of an invasive weed

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.