Explorer Resource supply and the evolution of public - goods cooperation in bacteria

Background: Explaining public-goods cooperation is a challenge for evolutionary biology. However, cooperation is expected to more readily evolve if it imposes a smaller cost. Such costs of cooperation are expected to decline with increasing resource supply, an ecological parameter that varies widely in nature. We experimentally tested the effect of resource supply on the evolution of cooperation using two well-studied bacterial public-good traits: biofilm formation by Pseudomonas fluorescens and siderophore production by Pseudomonas aeruginosa. Results: The frequency of cooperative bacteria increased with resource supply in the context of both bacterial public-good traits. In both cases this was due to decreasing costs of investment into public-goods cooperation with increasing resource supply. Conclusion: Our empirical tests with bacteria suggest that public-goods cooperation is likely to increase with increasing resource supply due to reduced costs of cooperation, confirming that resource supply is an important factor in the evolution of cooperation. Background Public-goods cooperation is widespread in nature but explaining this is a challenge for evolutionary biologists [1-3]. The central problem is that investment in the public-good is costly to individuals yet the public-good may be used by others, thus, all else being equal, cheats that reap the rewards of cooperation without making any investment should be able to invade a population of cooperators [2]. Kin selection provides a general solution to this social dilemma [3-5]: public-goods cooperation can be favoured if the benefits of cooperation are directed towards relatives with whom the cooperator shares genes. This is captured in Hamilton's rule which states that cooperation is favoured when rb > c, where c is the personal fitness cost for the actor, b is the fitness benefit to the recipient, and r is the genetic relatedness between the actor and recipient. Thus, provided that the indirect benefit (rb) accruing from cooperation exceeds the direct cost (c) of investment, then public-goods cooperation can evolve. While the importance of relatedness for the evolution of public-goods cooperation has been demonstrated in several recent empirical studies of microbes [6-8], the effect of variation in the cost of cooperation remains less well explored. Published: 14 May 2008 BMC Biology 2008, 6:20 doi:10.1186/1741-7007-6-20 Received: 17 August 2007 Accepted: 14 May 2008 This article is available from: http://www.biomedcentral.com/1741-7007/6/20 © 2008 Brockhurst et al; licensee BioMed Central Ltd. This is an Open Access article distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/2.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. BMC Biology 2008, 6:20 http://www.biomedcentral.com/1741-7007/6/20