Toward a unified tolerance–resistance framework across biological stressors and scales

Erik van Bergen, Sara Magalhães, Élio Sucena, Elvira Lafuente 

Ecotoxicology and immunology both explore how organisms cope with external stressors that disrupt homeostasis, yet these fields have developed largely in parallel. While immunology has formalized the distinction between resistance (i.e reducing stressor burden) and disease tolerance (i.e. mitigating damage without reducing burden), ecotoxicology has traditionally focussed on stressor fate, trophic transfer, and ecosystem-level consequences without consistently discriminating between these mechanistic strategies. Here, we argue that explicitly separating resistance from tolerance provides the conceptual clarity necessary to connect mechanistic, ecological, and evolutionary perspectives across these disciplines and bridge different biological scales.
Using examples from host-pathogen interactions and pollutant systems, we show that distinguishing between mechanisms that reduce stressor burden and those that mitigate damage enables more accurate predictions about contaminant persistence, bioaccumulation, transmission, and recovery. Conversely, ecological perspectives developed in ecotoxicology may extend resistance-tolerance theory and practice by incorporating stressor redistribution, food-web dynamics, and eco-evolutionary feedbacks into the host-pathogen interaction research programme. Finally, we discuss how resistance and tolerance evolve under different selective contexts, emphasizing the roles of reciprocal coevolution, stressor persistence, cross-talk between mechanisms, and eco-evolutionary feedbacks. By integrating mechanistic and ecological perspectives, propelled by a clear and shared definition of resistance and tolerance, we propose a unified framework for understanding how organisms deal with biotic and abiotic stressors across scales.