Resource availability alters fitness trade‐offs: implications for evolution in stressful environments

Premise Industrialization and human activities have elevated temperatures and caused novel precipitation patterns, altering soil moisture and nutrient availability. Predicting evolutionary responses to climate change requires information on the agents of selection that drive local adaptation and influence resource acquisition and allocation. Here, we examined the contribution of nutrient and drought stress to local adaptation, and we tested whether trade‐offs across fitness components constrain or facilitate adaptation under resource stress. Methods We exposed 35 families of Boechera stricta (Brassicaceae) to three levels of water and two levels of nutrient supply in a factorial design in the greenhouse. We sourced maternal families from a broad elevational gradient (2499–3530 m a.s.l.), representing disparate soil moisture and nutrient availability. Results Concordant with local adaptation, maternal families from arid, low‐elevation populations had enhanced fecundity under severe drought over those from more mesic, high‐elevation sites. Furthermore, fitness trade‐offs between growth and reproductive success depended on the environmental context. Under high, but not low, nutrient levels, we found a negative phenotypic relationship between the probability of reproduction and growth rate. Similarly, a negative phenotypic association only emerged between fecundity and growth under severe drought stress, not the benign water treatment levels, indicating that stressful resource environments alter the direction of trait correlations. Genetic covariances were broadly concordant with these phenotypic patterns. Conclusions Despite high heritabilities in all fitness components across treatments, trade‐offs between growth and reproduction could constrain adaptation to increasing drought stress and novel nutrient levels.