Biology subjects

Selander, E.

Publications and source records attributed to Selander, E..

3 recordsLinked to original sources

bioRxiv2025

Fear of grazing rivals the toxin induction effect of nitrogen enrichment in marine harmful algae- a meta-analysis

One of the major subfields of chemical ecology is the study of toxins and how they mediate interactions between organisms. Toxins produced by harmful algae, phycotoxins, impact a wide variety of organisms connected to the marine food web. Significant research efforts have thus aimed to identify the ecological and evolutionary drivers behind harmful algal blooms (HABs) to facilitate their forecasting, mitigation, and management. Nutrient availability is a key factor controlling growth and toxin production. Additionally, recent evidence has shown that harmful algae can sense the presence of zooplankton grazers, primarily copepods, and respond by dramatically increasing toxin production. Phycotoxin production is consequently controlled by a combination of bottom-up and top-down drivers, but the relative importance of the two is not understood. Here we conducted a meta-analysis of 113 control-treatment contrasts from 37 peer-reviewed experimental studies, comparing the effects of relative nitrogen enrichment (increased nitrogen:phosphorus ratio) and elevated grazing risk on phycotoxin induction in the two most studied marine HAB-forming genera, Alexandrium dinoflagellates and Pseudo-nitzschia diatoms. We show that phycotoxins are induced in response to both nitrogen enrichment and elevated grazing risk. Although both genera responded similarly to nitrogen enrichment, Pseudo-nitzschia toxins increased four times more in response to grazers than to nitrogen enrichment, and ten times more than Alexandrium toxins did in response to grazers. Grazing risk thus appears to rival, perhaps even supersede, the well-established phycotoxin-inducing effect of nitrogen enrichment in marine harmful algae. Although this analysis is limited to the two most studied marine HAB genera, we conclude that future attempts to understand the evolution and variable production of phycotoxins require integration of bottom-up nutrient availability and top-down selective pressures to fully elucidate phycotoxin dynamics in marine HAB-forming species.

ecology↗

bioRxiv2024

Effects of copepod chemical cues on intra- and extracellular toxins in two species of Dinophysis

Copepods may contribute to harmful algal bloom formation by selectively rejecting harmful cells. Additionally, copepods and the chemical cues they exude, copepodamides, have been shown to induce increased toxin production in paralytic and amnesic toxin producing microalgae. However, it is unknown if diarrhetic shellfish toxin (DST) producers such as Dinophysis respond to copepods or copepodamides in a similar fashion. Here we expose laboratory cultures of Dinophysis sacculus and D. acuminata to direct grazing by Acartia sp. copepods or copepodamides and measure their toxins after three days. Total Dinophysis- produced toxins (DPTs), okadaic acid, pectenotoxin-2, and C9-diol ester of okadaic acid, increased by 8 - 45% in D. sacculus but was significantly different from controls only in the highest (10 nM) copepodamide treatment whereas toxin content was not affected in D. acuminata. Growth rate was low across all groups and explained up to 91% of the variation in toxin content. DPTs were redistributed from internal compartments to the extracellular medium in the highest copepodamide treatments (5 - 10 nM), which were two to three times higher than controls and indicates an active release or passive leakage of toxins. Untargeted analysis of endometabolomes indicated significant changes in metabolite profiles for both species in response to the highest copepodamide treatments, independent of known toxins. However, it is not clear whether these are stress responses or caused by more complex mechanisms. The relatively small grazer-induced effect in Dinophysis observed here, compared to several species of Alexandrium and Pseudo-nitzschia reported previously, suggests that DPT production in Dinophysis is likely not induced by copepods, except perhaps in patches with high copepod densities. Thus, DPTs may, represent either a constitutive chemical defence for Dinophysis, or serve an altogether different purpose.

ecology↗

bioRxiv2023

Copepodamides in marine and freshwater copepods -similar but different

Marine copepods, the most abundant group of zooplankton in the worlds oceans, imprint their surrounding waters with chemical cues, called copepodamides. Copepodamides induce defensive traits such as toxin production, bioluminescence, and colony size plasticity in a variety of marine phytoplankton. The role of copepodamides in freshwater ecosystems is, however, unknown. Here we report the consistent presence of copepodamides in copepods from six Swedish lakes. Copepodamide concentrations in freshwater copepods are similar to those of marine copepods, around 0.1 ppt of dry mass in millimetre sized individuals. The composition substantially overlaps with marine copepodamides but is also distinctly different. Freshwater copepods are largely dominated by one of the two subgroups of copepodamides, the dihydro-copepodamides, whereas marine copepods more commonly contain representatives from both subgroups. We describe 10 new copepodamide structures, four of which only found in freshwater copepods. Taxonomic groups had consistent copepodamide profiles across sampling sites and timepoints, supporting the presence of species specific copepodamide signatures. The presence of copepodamides in freshwater environments warrants study into their potential function as predator alarm cues also in freshwater systems.

ecology↗