The bloom-forming diatom Pseudo-nitzschia produces a potent neurotoxin, domoic acid, that may cause closure of fisheries. The reason for its production has long been under debate. In a new study (in collaboration with the Natural History Museum of Denmark) we demonstrate a ‘private-good’ benefit to producing the toxins as toxic cells are more frequently rejected by grazing copepods. However, the production of toxins comes at a cost to the cells in terms of reduced growth rate.
The cosmopolitan diatom Pseudo-nitzschia often form dense blooms with severe consequences to marine ecosystems. The toxin it produces, domoic acid, accumulates in the food web and may lead to mass death of marine mammals such as seals and even whales. Toxin production is upregulated in the presence of copepod predators, suggesting they should have defensive benefits, but so far, the evidence has been but circumstantial. Using video-observations of copepod-phytoplankton interactions, we find that cells with increased toxin content have higher odds of being rejected by the copepods after capture, thus, demonstrating a ‘private-benefit’ of the defense that only the cells producing the toxins enjoys. This mechanism may play a role in allowing these cells to form blooms during times of intense grazing pressure.
Defense mechanisms must come at a cost to the organism, otherwise all phytoplankton would evolve towards the same level of defense. By exposing eight genetically different strains of P. seriata we find that cells that increase their toxin production grow slower, and that the trade-off is similar between strains despite a three-fold different in growth rate.
Read the paper here: https://doi.org/10.1098/rspb.2021.2735
Olesen A.J., F. Ryderheim, B. Krock, N. Lundholm, and T. Kiørboe. 2022. Costs and benefits of predator-induced defense in a toxic diatom. Proc. R. Soc. B. 289: 20212725. doi:10.1098/rspb.2021.2735.