A Molecular and Co-Evolutionary Context for Grazer Induced Toxin Production in Alexandrium tamarense

Abstract

Marine dinoflagellates of the genus Alexandrium are the proximal source of neurotoxins associated with Paralytic Shellfish Poisoning. The production of these toxins, the toxin biosynthesis and, thus, the cellular toxicity can be influenced by abiotic and biotic factors. There is, however, a lack of substantial evidence concerning the toxins' ecological function such as grazing defense. Waterborne cues from copepods have been previously found to induce a species-specific increase in toxin content in Alexandrium minutum. However, it remains speculative in which context these species-specific responses evolved and if it occurs in other Alexandrium species as well. In this study we exposed Alexandrium tamarense to three copepod species (Calanus helgolandicus, Acartia clausii, and Oithona similis) and their corresponding cues. We show that the species-specific response towards copepod-cues is not restricted to one Alexandrium species and that co-evolutionary processes might be involved in these responses, thus giving additional evidence for the defensive role of phycotoxins. Through a functional genomic approach we gained insights into the underlying molecular processes which could trigger the different outcomes of these species-specific responses and consequently lead to increased toxin content in Alexandrium tamarense. We propose that the regulation of serine/threonine kinase signaling pathways has a major influence in directing the external stimuli i.e. copepod-cues, into different intracellular cascades and networks in A. tamarense. Our results show that A. tamarense can sense potential predating copepods and respond to the received information by increasing its toxin production. Furthermore, we demonstrate how a functional genomic approach can be used to investigate species interactions within the plankton community.

Current Knowledge and Recent Advances in Marine Dinoflagellate Transcriptomic Research

“…Although this study found that grazers induced toxin production in dinoflagellates and this is supported by several studies on grazing effect to the toxin production in dinoflagellates, two upregulated genes that could be annotated in this study are unlikely to be directly involved in PSP toxin synthesis [48,[58][59][60].…”

Intraspecific facilitation by allelochemical mediated grazing protection within a toxigenic dinoflagellate population

“…If cooperative traits governing intraspecific interactions are common in mixed Alexandrium populations, the high phenotypic and genotypic diversity of these populations may be explained for example, by compatibility among these beneficial phenotypic traits in different strains. Such alternative traits may include for instance, chain formation, swimming speed, nutrient uptake capabilities, intrinsic growth rate and PST content [22,23,[69][70][71]. Indeed, the non-lytic strain Alex5 in our experiment contained the highest amount of PSTs (data not shown), a trait that potentially allows protection against grazing by copepods [22,23,69].…”

Predator lipids induce paralytic shellfish toxins in bloom-forming algae

“…2B). A. minutum cells show species specific responses to copepod cues, where some copepods induce a several-fold increase in toxicity and others trigger weaker responses (10,12). The most potent inducer, Centropages typicus, was confirmed to have the highest proportion of the more potent copepodamides A-C, whereas weaker inducers had approximately three times lower proportion of copepodamides A-C.…”