Many species of phytoplankton release toxins that combat competitors and predators. It has long puzzled researchers how such ‘public good’ toxicity has evolved, because mutant ‘cheaters’ that do not pay the cost of toxin production would benefit equally from the toxicity and thus outcompete the toxin producers. In a new study we describe how toxins as a public good may evolve.
The idea is that as cells divide, daughter cells are near one another. Thus, the two genetically identical siblings may both benefit from toxins produced by their sister cell, while those cells that are further away may not. Thus, kin-selection may function within patches of identical cells, and these clonal cells may benefit collectively from the toxins produced. We demonstrate in an individual-based phytoplankton model that this process of binary fission leads to the formation of patches of toxic and patches of non-toxic cells. Random cell motility and ambient turbulence may cause destruction of patches, but there are realistic conditions of cell motility and ambient turbulence that will allow coexistence of toxic and non-toxic cells and hence facilitate the evolution of toxicity. Thus, blooms of toxic cells often develop near the pycnocline, where turbulent mixing is minimal and spatial patchiness often well developed. The proposed mechanism may explain both the evolution of toxins as a public good and the commonly observed strain diversity and intraspecific variation in toxicity in toxic algal blooms.
Read the paper here
http://rspb.royalsocietypublishing.org/lookup/doi/10.1098/rspb.2022.0393
Ehrlich E, Thygesen UH, Kiørboe T (2022) Evolution of toxins as a public good in phytoplankton. Proc Roy Soc B 20220393.