Unilateral cross-feeding constrains adaptive evolution, even in the producer without direct fitness effects.

Unidirectional cross-feeding constrains adaptive evolution in both microbial species over 800 generations, with lower mutation fixation and increased dependence observed.

• Why it matters: Understanding how ecological interactions influence microbial evolution is crucial for predicting community stability and function, especially since most natural interactions are unidirectional rather than mutualistic.
• What they did: The study involved experimental evolution of Acinetobacter johnsonii and Pseudomonas putida in co-culture and monoculture over 800 generations, analyzing mutation patterns, lineage diversity, and fitness changes through genome sequencing.
• The result: Co-cultures showed stronger purifying selection and reduced lineage diversity compared to monocultures, with P. putida becoming more dependent on A. johnsonii, indicating ecological interactions can limit adaptive evolution even without direct fitness benefits.