%0 Journal Article %A Anna M. O’Brien %A Ruairidh J.H. Sawers %A Jeffrey Ross-Ibarra %A Sharon Y. Strauss %T Extending the Stress-Gradient hypothesis: greater adaptation between teosinte and soil biota at higher stress sites %D 2016 %R 10.1101/031195 %J bioRxiv %P 031195 %X The stress-gradient hypothesis (SGH) predicts that some species interactions grade from being more mutualistic under stressful abiotic conditions to more antagonistic or neutral under benign conditions. We extend these predictions in our Stress-Gradient-Adaptation hypothesis (SGA), positing that as interactions become more mutualistic in stressful environments, fitness benefits of interactors become more aligned and selection should favor greater mutualistic co-adaptation between interacting species. We test our SGA hypothesis using the interaction between teosinte (Zea mays ssp. mexicana) and its rhizosphere soil biota across a climate gradient. In support of predictions stemming from the SGA, we find local adaptation between teosinte and rhizosphere biota at the stressful (cold) end of our climatic gradient but not at the benign (warm) end. Sympatric combinations of plants and biota from cold (stressful) sites both increase plant fitness and generate more locally adapted plant phenotypes. Counterintuitively, warmer-sourced biota provide greater benefit than colder-sourced biota, even for colder-sourced plant populations, a result we argue may be due to the environmental context of our experiment. Overall, our experiment finds some support for our SGA hypothesis and suggests that co-adaptation of interacting partners may be a means of ameliorating stressful environments. %U https://www.biorxiv.org/content/biorxiv/early/2016/04/20/031195.full.pdf