Competition between species can drive public-goods cooperation within a species

Background/Question/Methods

Costly cooperative strategies are vulnerable to exploitation by cheats. Microbial studies have suggested that cooperation can be maintained in nature by mechanisms such as reciprocity, spatial structure and multi-level selection. So far, however, almost all laboratory experiments aimed at understanding cooperation have relied on studying a single species in isolation. In contrast, species in the wild live within complex communities where they interact with other species. Little effort has focused on understanding the effect of interspecies competition on the evolution of cooperation within a species. The goal of this study was to test this relationship by using sucrose metabolism of budding yeast as a model cooperative system. 

Results/Conclusions

We co-cultured yeast populations (cooperator plus cheater cells) along with a bacterial competitor, Escherichia coli, and tracked the frequency of cooperator individuals over time within the yeast populations. We found that when co-cultured with a bacterial competitor, yeast populations become more cooperative compared to isolated yeast populations. We show that this increase in cooperator frequency within yeast is driven by the bacterial competition for both essential nutrients in the culture media and the public-goods produced by cooperators. Our results show that a thorough understanding of species interactions is important for explaining the maintenance and evolution of cooperation in nature.