Cooperative behaviour among individuals is common, despite apparent fitness costs for the individual. The green‐beard mechanism can foster such cooperation: When a set of linked genes encodes both a cooperative trait and a phenotypic marker (green beard), carriers of that cooperative trait can selectively direct their cooperative actions to other carriers of this trait. This paper explored an extreme green‐beard scenario between two unrelated bacterial species P. aeruginosa and B. cenocepacia, which both produce the public good pyochelin (the cooperative trait) and an iron-pyochelin uptake receptor (the green beard). Competition experiments between these phylogenetically unrelated species revealed that the green‐beard cooperation effect collapses in this scenario, indicating that selection for competitive traits might overrule selection for cooperation in inter‐species interactions.
See Sathe & Kümmerli, Journal of Evolutionary Biology