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Evolution of cooperation and conflict in experimental bacterial populations


A fundamental problem in biology is the evolutionary transition from single cells to multicellular life forms1,2,3. During this transition the unit of selection shifts from individual cells to groups of cooperating cells1,3,4. Although there is much theory5,6,7,8,9,10,11,12,13,14,15, there are few empirical studies16. Here we describe an evolutionary transition that occurs in experimental populations of Pseudomonas fluorescens propagated in a spatially heterogeneous environment17. Cooperating groups are formed by over-production of an adhesive polymer18, which causes the interests of individuals to align with those of the group. The costs and benefits of cooperation, plus evolutionary susceptibility to defecting genotypes, were analysed to determine conformation to theory1,3,12. Cooperation was costly to individuals, but beneficial to the group. Defecting genotypes evolved in populations founded by the cooperating type and were fitter in the presence of this type than in its absence. In the short term, defectors sabotaged the viability of the group; but these findings nevertheless show that transitions to higher orders of complexity are readily achievable, provide insights into the selective conditions, and facilitate experimental analysis of the evolution of individuality.

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Figure 1: Growth form and niche preference of studied bacteria.
Figure 2: Evolutionary emergence of defecting genotypes from WS during the course of selection in spatially heterogeneous microcosms.
Figure 3: Population dynamics of WS and defector genotypes in the presence and absence of competition.


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We are grateful to D. S. Wilson and A. Buckling whose comments improved the manuscript. A Biotechnology and Biological Sciences Research Council (UK) Research Fellowship to P.B.R. supported the work.

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Correspondence to Paul B. Rainey.

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Rainey, P., Rainey, K. Evolution of cooperation and conflict in experimental bacterial populations. Nature 425, 72–74 (2003).

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