Adaptation limits ecological diversification and promotes ecological tinkering during the competition for substitutable resources

Journal Article · 15 October 2018 · Proceedings of the National Academy of Sciences of the United States of America

DOI: https://doi.org/10.1073/pnas.1807530115 · OSTI ID:1543912

Good, Benjamin H. ^[1]; Martis, Stephen ^[1]; Hallatschek, Oskar  ^[1]

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1. Univ. of California, Berkeley, CA (United States)

Microbial communities can evade competitive exclusion by diversifying into distinct ecological niches. This spontaneous diversification often occurs amid a backdrop of directional selection on other microbial traits, where competitive exclusion would normally apply. Yet despite their empirical relevance, little is known about how diversification and directional selection combine to determine the ecological and evolutionary dynamics within a community. To address this gap, we introduce a simple, empirically motivated model of eco-evolutionary feedback based on the competition for substitutable resources. Individuals acquire heritable mutations that alter resource uptake rates, either by shifting metabolic effort between resources or by increasing the overall growth rate. While these constitutively beneficial mutations are trivially favored to invade, we show that the accumulated fitness differences can dramatically influence the ecological structure and evolutionary dynamics that emerge within the community. Competition between ecological diversification and ongoing fitness evolution leads to a state of diversification–selection balance, in which the number of extant ecotypes can be pinned below the maximum capacity of the ecosystem, while the ecotype frequencies and genealogies are constantly in flux. Interestingly, we find that fitness differences generate emergent selection pressures to shift metabolic effort toward resources with lower effective competition, even in saturated ecosystems. Here, we argue that similar dynamical features should emerge in a wide range of models with a mixture of directional and diversifying selection.

• Research Organization: Lawrence Berkeley National Laboratory (LBNL), Berkeley, CA (United States). National Energy Research Scientific Computing Center (NERSC); Univ. of California, Oakland, CA (United States)
• Sponsoring Organization: USDOE Office of Science (SC)
• Grant/Contract Number: AC02-05CH11231
• OSTI ID: 1543912
• Journal Information: Proceedings of the National Academy of Sciences of the United States of America, Vol. 115, Issue 44; ISSN 0027-8424
• Publisher: National Academy of Sciences, Washington, DC (United States)Copyright Statement
• Country of Publication: United States
• Language: English