Abstract

Microbes often live in association with dense multicellular aggregates, especially biofilms, and the construction of these aggregates typically requires microbial cells to produce public goods, such as enzymes and signaling molecules. Public-goods producers are, in turn, vulnerable to exploitation by free-rider cells that consume the public goods without paying for their production costs. The cell population of a biofilm or other microbial aggregates are expected to pass through bottlenecks due to a wide range of factors, such as antibiotic treatments and dispersal. The goal of this article is to make the case for the relevance of population bottlenecks at shaping the social interactions within microbial aggregates. The effect of bottlenecks on microbial aggregates is complex in that bottlenecks can favor producers under certain circumstances, but not in others. The concept of the Volunteer’s Dilemma from game theory will be used to motivate the hypothesis that this partly occurs because of how bottlenecks alter the risk of being a producer in a microbial aggregate. Finally, the role of bottlenecks in the microbial world impacts key issues in evolutionary biology, including the importance of ecology at shaping social evolution, and the evolution of multicellularity from unicellular ancestors.