Experimental evolution reveals adaptive limits and evolutionary dynamics of freshwater photoautotrophs under environmental stress

Abstract

Photoautotrophic microorganisms play a key role in freshwater ecosystems, supporting primary production and biogeochemical cycles, but their survival is increasingly threatened by rapid environmental change. Understanding how these photosynthetic organisms respond to stressors such as salinity, temperature, and herbicide exposure is crucial for predicting ecosystem resilience. Here, we explored the adaptive capacity of two widespread photoautotrophs, Microcystis aeruginosa and Chlamydomonas reinhardtii, under multiple environmental stresses using experimental evolution and eco-evolutionary approaches. Our results show that gradual increases in stress facilitated evolutionary rescue through the selection of beneficial spontaneous mutants, whereas abrupt stress often exceded adaptive potential, leading to population collapse. We further found that resistant cells exhibited measurable trade-offs, including reduced growth rates and lower photosynthetic eficiency relative to their wild-type ancestors, suggesting that adaptation can critically compromise primary production. Rather than identifying specific adaptive mechanisms or resistance mutations, our work highlights evolutionary trends that provide insights into how these photoautotrophic populations may respond to future environmental challenges. Overall, we offer a predictive framework for understanding the resilience, limitations, and potential adaptive pathways of primary producers in rapidly changing freshwater ecosystems.