DENSITY DEPENDENCE AND COOPERATION: THEORY AND A TEST WITH BACTERIA

Adin Ross-Gillespie*, Andy Gardner, Angus Buckling, Stuart A. West, Ashleigh S. Griffin

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

83 Citations (Scopus)

Abstract

Although cooperative systems can persist in nature despite the potential for exploitation by noncooperators, it is often observed that small changes in population demography can tip the balance of selective forces for or against cooperation. Here we consider the role of population density in the context of microbial cooperation. First, we account for conflicting results from recent studies by demonstrating theoretically that: (1) for public goods cooperation, higher densities are relatively unfavorable for cooperation; (2) in contrast, for self-restraint-type cooperation, higher densities can be either favorable or unfavorable for cooperation, depending on the details of the system. We then test our predictions concerning public goods cooperation using strains of the pathogenic bacterium Pseudomonas aeruginosa that produce variable levels of a public good-iron-scavenging siderophore molecules. As predicted, we found that the relative fitness of cheats (under-producers) was greatest at higher population densities. Furthermore, as assumed by theory, we show that this occurs because cheats are better able to exploit the cooperative siderophore production of other cells when they are physically closer to them.

Original languageEnglish
Pages (from-to)2315-2325
Number of pages11
JournalEvolution
Volume63
Issue number9
DOIs
Publication statusPublished - Sept 2009

Keywords

  • Kin selection
  • population structure
  • Pseudomonas aeruginosa
  • public goods
  • siderophores
  • AMEBA DICTYOSTELIUM-DISCOIDEUM
  • GROUP-BENEFICIAL TRAITS
  • PSEUDOMONAS-AERUGINOSA
  • PUBLIC-GOODS
  • GROUP-SIZE
  • SOCIAL AMEBA
  • EVOLUTIONARY BIOLOGY
  • PATHOGENIC BACTERIA
  • GROUP SELECTION
  • ALTRUISM

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