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

Abstract

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.

Costs of reproduction under experimental climate change across elevations in the perennial forbBoechera stricta

“…Climate change has increased aridity in this system through reductions in snowpack and accelerations of snowmelt [ 41 , 50 , 58 ], which could exacerbate costs of reproduction at the lower end of the elevational gradient. Concordant with our results, drought stress imposed a strong growth cost of reproduction in B. stricta in a greenhouse experiment [ 59 ]. We suggest that these costs will become more apparent as climate change continues to augment drought stress in this landscape.…”

The Boechera model system for evolutionary ecology

“…Subsequent greenhouse experiments documented that trait divergence aligns with the niche models, such that water availability—and other selective pressures—likely underlie local adaptation (Lee and Mitchell‐Olds, 2013). A separate greenhouse manipulation of water and nutrient availability found that fitness declined with source elevation for Colorado accessions exposed to drought stress (MacTavish and Anderson, 2020), which is consistent with local adaptation of low‐elevation accessions to restricted water availability (Anderson and Wadgymar, 2020). Finally, a field study in five Colorado gardens revealed local adaptation to historical winter snowpack, again highlighting the importance of water in exerting selection on natural populations (Anderson and Wadgymar, 2020).…”

“…Phylogeographic data suggest that B. stricta likely recolonized high-elevation and highlatitude sites rapidly after the retreat of the Pleistocene glaciers (Song et al, 2006;Kiefer et al, 2009), suggesting that this species quickly responded to episodes of climate change in the geological past. Furthermore, manipulative experiments in the field, greenhouse, and growth chamber can expose diverse accessions to historical, contemporary, and future climatic conditions (Wadgymar et al, 2018a(Wadgymar et al, , 2018Bemmels and Anderson, 2019;Anderson and Wadgymar, 2020;MacTavish and Anderson, 2020). These studies evaluate how climate change could alter the adaptive landscape and whether populations could keep pace with novel conditions via plasticity or adaptation.…”

Experimental warming reduces body mass but not reproductive investment

“…However, prioritizing reproduction at the cost of additional fat storage could increase the likelihood of mortality before the second breeding season or potentially limit future reproduction. Moreover, stressful or resource‐limited environments typically cause the highest costs for survival and reproduction and the strongest trade‐offs between life history traits (Boggs, 2009; MacTavish & Anderson, 2020; Stearns, 1989). Although males in our study had negligible fat stores, and fat and testes mass did not differ across temperature treatments, males may experience other reproductive costs of warming, including lower energy available for courtship, attractiveness of body size relative to other mates, and sperm quality.…”