Glutathione S-Transferase Regulation in Calanus finmarchicus Feeding on the Toxic Dinoflagellate Alexandrium fundyense

Oil-mediated oxidative-stress responses in a keystone zooplanktonic species, Calanus finmarchicus

The copepod Calanus finmarchicus is an ecologically important species in the North Atlantic, Norwegian and Barents seas. Accidental or continuous petroleum pollution from oil and gas production in these seas may pose a significant threat to this low trophic level keystone species. Responses related to oxidative stress, protein damage and lipid peroxidation were investigated in C. finmarchicus exposed to a water-accommodated fraction (WAF) of a naphthenic North Atlantic crude oil. The exposure concentration corresponded to 50% of the 96 h LC₅₀, and samples were obtained at 0, 24, 48, 72 and 96 h after exposure initiation. Gene expressions (superoxide dismutase, catalase, glutathione S-transferase, glutathione synthetase, heat shock protein 70 and 90, ubiquitin and cytochrome P-450 330A1), enzyme activities (superoxide dismutase, catalase, glutathione S-transferase) and concentrations of total glutathione and malondialdehyde were analyzed. Gene expression analyses showed no differences between controls and the exposed animals, however significantly higher glutathione S-transferase activity and malondialdehyde concentrations were found in the exposed group, suggests lipid peroxidation as main toxic effect.

Eco-physiological responses of copepods and pteropods to ocean warming and acidification

We compare physiological responses of the crustacean copepod Calanus pacificus and pelagic pteropod mollusk Limacina helicina to ocean temperatures and pH by measuring biomarkers of oxidative stress, antioxidant defences, and the activity of the respiratory electron transport system in organisms collected on the 2016 West Coast Ocean Acidification cruise in the California Current System. Copepods and pteropods exhibited strong but divergent responses in the same habitat; copepods had higher oxygen-reactive absorbance capacity, glutathione-S-transferase, and total glutathione content. The ratio between reduced to oxidised glutathione was higher in copepods than in pteropods, indicating lower oxidative stress in copepods. Pteropods showed higher activities of glutathione reductase, catalase, and lipid peroxidation, indicating increased antioxidant defences and oxidative stress. Thus, the antioxidant defence system of the copepods has a greater capacity to respond to oxidative stress, while pteropods already face severe stress and show limited capacity to deal with further changes. The results suggest that copepods have higher adaptive potential, owing to their stronger vertical migration behaviour and efficient glutathione metabolism, whereas pteropods run the risk of oxidative stress and mortality under high CO₂ conditions. Our results provide a unique dataset and evidence of stress-inducing mechanisms behind pteropod ocean acidification responses.

Adverse effects of a synthetic pyrethroid insecticide cypermethrin on life parameters and antioxidant responses in the marine copepods Paracyclopina nana and Tigriopus japonicus

To find the adverse effects induced by cypermethrin, the ecotoxicological model copepods Tigriopus japonicus and Paracyclopina nana were exposed under cypermethrin, which is a widely used type-II pyrethroid insecticide in agriculture. Despite its large-scale application as insecticide in agriculture, little information is available on its adverse effects on aquatic invertebrates. In this study, the toxicity of cypermethrin on two copepods was assessed based on life parameters (growth rate and reproduction), oxidative stress and consequent antioxidant enzymatic activities, and gene expression profiles of antioxidants. The acute toxicity alone demonstrated that P. nana is less tolerant and sensitive against cypermethrin, compared to T. japonicus. However, under chronic exposure, life parameters of both P. nana and T. japonicus were severely affected by cypermethrin. Among antioxidant enzymatic activities, superoxide dismutase (SOD) and glutathione S-transferase (GST), in particular, demonstrated significant increase in response to cypermethrin. Furthermore, temporal-mRNA expression profile showed modulations in antioxidant related genes in response to cypermethrin. Our results provide the underlying toxic mechanism of cypermethrin and the oxidative stress defense mechanism and species-specific tolerance against cypermethrin in two model copepods species.

Complementary mechanisms for neurotoxin resistance in a copepod

Toxin resistance is a recurring evolutionary response by predators feeding on toxic prey. These adaptations impact physiological interaction and community ecology. Mechanisms for resistance vary depending on the predator and the nature of the toxin. Potent neurotoxins like tetrodotoxin (TTX) and saxitoxin (STX) that are highly toxic to humans and other vertebrates, target conserved voltage-gated sodium channels (Na_V) of nerve and muscle, causing paralysis. The copepod Calanus finmarchicus consumes the STX-producing dinoflagellate, Alexandrium fundyense with no effect on survival. Using transcriptomic approaches to search for the mechanism that confers resistance in C. finmarchicus, we identified splice variants of Na_Vs that were predicted to be toxin resistant. These were co-expressed with putatively non-resistant form in all developmental stages. However its expression was unresponsive to toxin challenge nor was there any up-regulation of genes involved in multi-xenobiotic resistance (MXR) or detoxification (phases I or II). Instead, adults consistently regulated genes encoding digestive enzymes, possibly to complement channel resistance by limiting toxin assimilation via the digestive process. The nauplii, which were more susceptible to STX, did not regulate these enzymes. This study demonstrates how deep-sequencing technology can elucidate multiple mechanisms of toxin resistance concurrently, revealing the linkages between molecular/cellular adaptations and the ecology of an organism.