An evolutionary mechanism for diversity in siderophore-producing bacteria.

Bacteria produce a great diversity of siderophores to scavenge for iron in their environment. We suggest that this diversity results from the interplay between siderophore producers (cooperators) and non-producers (cheaters): when there are many cheaters exploiting a siderophore type it is beneficial for a mutant to produce a siderophore unusable by the dominant population. We formulated and analysed a mathematical model for tagged public goods to investigate the potential for the emergence of diversity. We found that, although they are rare most of the time, cheaters play a key role in maintaining diversity by regulating the different populations of cooperators. This threshold-triggered feedback prevents any stain of cooperators from dominating the others. Our study provides a novel general mechanism for the evolution of diversity that may apply to many forms of social behaviour.