Stress responses in fish: From molecular to evolutionary processes.

In the context of global changes, fish are increasingly exposed to multiple stressors that have cascading effects from molecules to the whole individual, thereby affecting wild fish populations through selective processes. In this review, we synthetize recent advances in molecular biology and evolutionary biology to outline some potentially important effects of stressors on fish across biological levels. Given the burgeoning literature, we highlight four promising avenues of research. First, (1) the exposure to multiple stressors can lead to unexpected synergistic or antagonistic effects, which should be better taken into account to improve our predictions of the effects of actual and future human activities on aquatic organisms. Second, (2) we argue that such interactive effects might be due to switches in energy metabolism leading to threshold effects. Under multiple stress exposure, fish could switch from a "compensation" strategy, i.e. a reallocation of energy to defenses and repair to a "conservation" strategy, i.e. blocking of stress responses leading to strong deleterious effects and high mortality. Third, (3) this could have cascading effects on fish survival and population persistence but multiscale studies are still rare. We propose emerging tools merging different levels of biological organization to better predict population resilience under multiple stressors. Fourth (4), there are strong variations in sensitivity among populations, which might arise from transgenerational effects of stressors through plastic, genetic, and epigenetic mechanisms. This can lead to local adaptation or maladaptation, with strong impacts on the evolutionary trajectories of wild fish populations. With this review, we hope to encourage future research to bridge the gap between molecular ecology, ecotoxicology and evolutionary biology to better understand the evolution of responses of fishes to current and future multiple stressors in the context of global changes.

Adaptive response under multiple stress exposure in fish: From the molecular to individual level.

Aquatic systems are subjected to various sources of stress due to global changes, such as increasing temperature and pollution. A major challenge for the next decade will be to evaluate the combined effects of these multiple stressors on organisms and ecosystems. For organisms submitted to chemical, biological or physical stressors, the capacity to set up an efficient adaptive response is a fundamental prerequisite for their long-term survival and performance. In this study, goldfish (Carassius auratus) were subjected to individual and combined pesticide mixtures and increased temperatures to evaluate their adaptive response in multistress conditions from the molecular to the individual level. Fish were exposed for 16 days to a mixture of pesticides at environmental relevant concentrations (S-metolachlor, isoproturon, linuron, atrazine-desethyl, aclonifen, pendimethalin and tebuconazole) and at two temperatures (22 °C and 32 °C). Three major physiological traits of the stress response were measured: the hormonal response (i.e. plasma cortisol), the metabolic balance from molecular to individuals' levels (metabolomics, cellular energy allocation, energy reserves and global condition indexes), and the cellular defense system induction (SOD, CAT and GST). Results show that (1) environmentally relevant concentrations of pesticides lead to significant responses in fish at all biological levels; (2) the metabolic response depends on the nature of stress (thermal vs. chemical); and (3) fish may be unable to set up an efficient adaptive response when chemical and thermal stresses were combined, with adverse outcomes at the individuals' level.

Proteome response of fish under multiple stress exposure: Effects of pesticide mixtures and temperature increase.

Aquatic systems can be subjected to multiple stressors, including pollutant cocktails and elevated temperature. Evaluating the combined effects of these stressors on organisms is a great challenge in environmental sciences. To the best of our knowledge, this is the first study to assess the molecular stress response of an aquatic fish species subjected to individual and combined pesticide mixtures and increased temperatures. For that, goldfish (Carassius auratus) were acclimated to two different temperatures (22 and 32°C) for 15 days. They were then exposed for 96h to a cocktail of herbicides and fungicides (S-metolachlor, isoproturon, linuron, atrazine-desethyl, aclonifen, pendimethalin and tebuconazole) at two environmentally relevant concentrations (total concentrations of 8.4µgL-1 and 42µgL-1) at these two temperatures (22 and 32°C). The molecular response in liver was assessed by 2D-proteomics. Identified proteins were integrated using pathway enrichment analysis software to determine the biological functions involved in the individual or combined stress responses and to predict the potential deleterious outcomes. The pesticide mixtures elicited pathways involved in cellular stress response, carbohydrate, protein and lipid metabolisms, methionine cycle, cellular functions, cell structure and death control, with concentration- and temperature-dependent profiles of response. We found that combined temperature increase and pesticide exposure affected the cellular stress response: the effects of oxidative stress were more marked and there was a deregulation of the cell cycle via apoptosis inhibition. Moreover a decrease in the formation of glucose by liver and in ketogenic activity was observed in this multi-stress condition. The decrease in both pathways could reflect a shift from a metabolic compensation strategy to a conservation state. Taken together, our results showed (1) that environmental cocktails of herbicides and fungicides induced important changes in pathways involved in metabolism, cell structure and cell cycle, with possible deleterious outcomes at higher biological scales and (2) that increasing temperature could affect the response of fish to pesticide exposure.

Multistress effects on goldfish (Carassius auratus) behavior and metabolism.

Crossed effects between climate change and chemical pollutions were identified on community structure and ecosystem functioning. Temperature rising affects the toxic properties of pollutants and the sensitiveness of organisms to chemicals stress. Inversely, chemical exposure may decrease the capacity of organisms to respond to environmental changes. The aim of our study was to assess the individual and crossed effects of temperature rising and pesticide contamination on fish. Goldfish, Carassius auratus, were exposed during 96 h at two temperatures (22 and 32 °C) to a mixture of common pesticides (S-metolachlor, isoproturon, linuron, atrazine-desethyl, aclonifen, pendimethalin, and tebuconazol) at two environmentally relevant concentrations (total concentrations MIX1 = 8.4 µg L(-1) and MIX2 = 42 µg L(-1)). We investigated the sediment reworking behavior, which has a major ecological functional role. We also focused on three physiological traits from the cellular up to the whole individual level showing metabolic status of fish (protein concentration in liver and muscle, hepatosomatic index, and Fulton's condition factor). Individual thermal stress and low concentrations of pesticides decreased the sediment reworking activity of fish and entrained metabolic compensation with global depletion in energy stores. We found that combined chemical and thermal stresses impaired the capacity of fish to set up an efficient adaptive response. Our results strongly suggest that temperature will make fish more sensitive to water contamination by pesticides, raising concerns about wild fish conservation submitted to global changes.

Neurodevelopmental and behavioral effects of nonylphenol exposure during gestational and breastfeeding period on F1 rats.

Nonylphenols (NP) are endocrine-disruptors known to be widely present in our environment. This study evaluated the effects of 4-n-NP on neurobehavioral development and memory capacity after perinatal exposure on the offspring rats. Dams were gavaged with 4-n-NP (0, 50 and 200mg/kg/day) from gestational day 5 to postnatal day (PND) 21. Dams exposed to the higher dose lost weight during gestation and had a longer gestational duration. Juvenile female pups of the 200mg 4-n-NP/kg/day group were lighter. Their thyroid somatic index (TSI) was also affected. For male pups, a decrease of TSI at weaning for the 200mg 4-n-NP/kg/day group and an increase of GSI for the 50mg 4-n-NP/kg/day group were observed. Physical maturation (incisives and eyes) were likewise affected. In open field (OF) tests, females were more active than males. In the first OF (PND 36), a treatment effect was observed only for males, particularly for the high dose group, which became as active as females. The second OF (PND 71) showed few differences between groups (treated vs control), the gender difference whatever the dose was not abolished. In the Morris Water Maze test, the study of the first 30s showed that females (200mg/kg/day) were mainly affected. Their performances were improved by 4-n-NP. These effects were particularly important for the first short-term memory test and observed to a lesser extent in the second evaluation of the long-term memory (PND 69). These data showed that perinatal 4-n-NP exposure induced behavioral and neuro-developmental impairments from 50mg/kg/day.