Quorum sensing in Pseudomonas aeruginosa controls the production of costly public goods such as exoproteases. This cooperative behavior is susceptible to social cheating by mutants that do not invest in the exoprotease production but assimilate the amino acids and peptides derived by the hydrolysis of proteins in the extracellular media. In sequential cultures with protein as the sole carbon source, these social cheaters are readily selected and often reach equilibrium with the exoprotease producers. Nevertheless, an excess of cheaters causes the collapse of population growth. In this work, using the reference strain PA14 and a clinical isolate from a burn patient, we demonstrate that the initial amount of public goods (exoprotease) that comes with the inoculum in each sequential culture is essential for maintaining population growth and that eliminating the exoprotease in the inoculum leads to rapid population collapse. Therefore, our results suggest that sequential washes should be combined with public good inhibitors to more effectively combat P. aeruginosa infections.

In cooperatively breeding species, helpers take higher risks of getting lower return of investment than breeders due to the incongruity between helping and breeding. Helpers can deal with the risk by curtailing their investment or, if possible, claiming immediate rewards in the cooperation. Given breeders may rely largely on the aid of helpers to raise their offspring, it can be hypothesized that helpers are more likely to make adaptive responses to the incongruity-associated risk in adverse habitats than in good ones. This hypothesis was tested in the giant babax (Babax waddelli) by comparing helpers' provisioning behaviors between two breeding populations in adverse high-altitude and good low-altitude environments. These two populations differed significantly in their egg size and nestlings’ growth patterns. Helpers in both populations made great contributions to the raising of offspring. During provisioning, helpers in the high-altitude population exhibited significantly higher feeding rates but delivered fewer insects per feeding bout than their counterparts in the low-altitude population. Helpers in both populations displayed a cheating strategy of 'non-feeding' to reduce investment in provisioning. They pursued immediate excess rewards via kleptoparasitism of nestling fecal sacs in the high-altitude population but not in the low-altitude one. Accordingly, breeders made different antagonistic actions toward the cheating helpers between populations. Our findings confirm that helpers are prone to deceiving cooperation under poor breeding conditions and that breeders' tolerance of the cheating behavior of helpers is determined by their dependence on the helpers' aid. Methods We collected the dataset in the field. It has been processed according to the methods of different statistical analyses.