Science Daily, original paper reference below.
Cheating is a behavior not limited to humans, animals and plants. Even microscopically small, single-celled algae do it, a team of University of Arizona researchers has discovered.
Driscoll isolated several strains of the species, Prymnesium parvum, and noticed that some grew more quickly and do not produce any of the toxins that protect the algae against competition from other species of algae.
"When those 'cheaters' are cultured with their toxic counterparts, they can still benefit from the toxins produced by their cooperative neighbors -- they are true 'free riders,'" Driscoll explained.
I like the paper title too: ALLELOPATHY AS AN EMERGENT, EXPLOITABLE PUBLIC GOOD IN THE BLOOM-FORMING MICROALGAPRYMNESIUM PARVUM.