Maintenance of diversity in the face of long-term eco-evolutionary dynamics in microbial ecosystems

One of the major challenges in organismal biology is to understand long-term eco-evolutionary dynamics in microbial ecosystems. Understanding eco-evolution is challenging because community diversity can change dramatically over time due to eco-evolutionary feedback: new mutants arise during evolution and subsequently cause the extinction of residents via ecological interactions. Here, we simulate eco-evolutionary dynamics in microbial communities using repeated, sequential invasions by closely related mutants in a high-dimensional Microbial Consumer Resource Model (MiCRM) with cross-feeding. We identify an evolutionary quasi-steady state that arises from the interplay of ecological competition, metabolic constraints, and environmental filtering. In this state, strains align along an optimal direction in consumer preference while maintaining diversity in orthogonal directions. We show that this complex behavior can be understood using a simple stochastic model which predicts the dependence of the evolutionary steady-state diversity on the effect size of mutations and environmental variables. Our results suggest that the long-term eco-evolutionary dynamics of complex microbial ecosystems may be understood in terms of simple emergent models.