From proteins to species ranges: a framework for understanding thermal adaptation during range expansions

Species distributions are governed by both ecological and evolutionary processes. Traditionally, ecological factors have been the primary focus of species distribution studies, but recent work emphasizes the importance of rapid evolution through local adaptation. Here, we focus on adaptation to changing temperatures, which is one of the central challenges populations face today. Importantly, thermal adaptation may be affected by the underlying thermodynamics. Despite many existing models in the fields of thermal biology and spatial evolutionary ecology, there is little integrative theory. However, understanding and modelling the thermodynamic constraints on thermal adaptation is likely essential for more nuanced predictions of the impacts of climate change. By integrating molecular mechanisms and population dynamics in a unified modelling framework, we here study how temperature-dependent processes at the protein level influence the macroecological patterns of range expansions. Our results highlight the importance of the microscopic processes underlying thermal adaptation for capturing the evolutionary ecology of range expansions. Specifically, the molecular bases of thermal adaptation define how and how fast thermal performance can evolve, which determines range expansion speeds. In general, our framework predicts that adaptation to warmer temperatures will be easier than adaptation to cold. Our study underscores the necessity for more interdisciplinary work, combining molecular mechanisms with population dynamics in space in order to improve climate change modeling, enhance prediction accuracy and provide better information for management and conservation of natural populations. Significance StatementAs global temperatures shift, species must adapt to new climates, but how molecular changes scale up to influence population- and ecosystem-level patterns is poorly understood. Here, we link mutations affecting protein stability and enzyme activity to species abilities to expand along temperature gradients. Our models show that adaptation is faster at warmer temperatures and more constrained in the cold, reflecting how mutations shape protein function. Thermodynamic effects amplify the impact of beneficial mutations at higher temperatures, potentially accelerating evolutionary responses. By connecting molecular biophysics to population dynamics and range expansion, this work provides a cross-scale framework for predicting how organisms respond to warming environments.