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1.  Resource supply and the evolution of public-goods cooperation in bacteria 
BMC Biology  2008;6:20.
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.
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.
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.
PMCID: PMC2409295  PMID: 18479522
2.  Cooperation and virulence in acute Pseudomonas aeruginosa infections 
BMC Biology  2006;4:21.
Efficient host exploitation by parasites is frequently likely to depend on cooperative behaviour. Under these conditions, mixed-strain infections are predicted to show lower virulence (host mortality) than are single-clone infections, due to competition favouring non-contributing social 'cheats' whose presence will reduce within-host growth. We tested this hypothesis using the cooperative production of iron-scavenging siderophores by the pathogenic bacterium Pseudomonas aeruginosa in an insect host.
We found that infection by siderophore-producing bacteria (cooperators) results in more rapid host death than does infection by non-producers (cheats), and that mixtures of both result in intermediate levels of virulence. Within-host bacterial growth rates exhibited the same pattern. Crucially, cheats were more successful in mixed infections compared with single-clone infections, while the opposite was true of cooperators.
These data demonstrate that mixed clone infections can favour the evolution of social cheats, and thus decrease virulence when parasite growth is dependent on cooperative behaviours.
PMCID: PMC1526758  PMID: 16827933

Results 1-2 (2)