Temperature and predator-mediated regulation of plasma cortisol and brain gene expression in juvenile brown trout ( Salm
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RESEARCH
Open Access
Temperature and predator-mediated regulation of plasma cortisol and brain gene expression in juvenile brown trout (Salmo trutta) Karl Filipsson* , Eva Bergman, Larry Greenberg, Martin Österling, Johan Watz and Ann Erlandsson
Abstract Background: Temperature affects many aspects of performance in poikilotherms, including how prey respond when encountering predators. Studies of anti-predator responses in fish mainly have focused on behaviour, whereas physiological responses regulated through the hypothalamic-pituitary-interrenal axis have received little attention. We examined plasma cortisol and mRNA levels of stress-related genes in juvenile brown trout (Salmo trutta) at 3 and 8 °C in the presence and absence of a piscivorous fish (burbot, Lota lota). Results: A redundancy analysis revealed that both water temperature and the presence of the predator explained a significant amount of the observed variation in cortisol and mRNA levels (11.4 and 2.8%, respectively). Trout had higher cortisol levels in the presence than in the absence of the predator. Analyses of individual gene expressions revealed that trout had significantly higher mRNA levels for 11 of the 16 examined genes at 3 than at 8 °C, and for one gene (retinol-binding protein 1), mRNA levels were higher in the presence than in the absence of the predator. Moreover, we found interaction effects between temperature and predator presence for two genes that code for serotonin and glucocorticoid receptors. Conclusions: Our results suggest that piscivorous fish elicit primary stress responses in juvenile salmonids and that some of these responses may be temperature dependent. In addition, this study emphasizes the strong temperature dependence of primary stress responses in poikilotherms, with possible implications for a warming climate. Keywords: Anti-predator, Burbot, Climate change, HPI axis, mRNA, Salmonid, Stress, Winter
Background Outcomes of predator-prey interactions depend on the relative performance of predator and prey, which can be strongly temperature dependent in poikilotherms [1–4]. Therefore, temperature is predicted to have strong effects on anti-predator responses [1, 3–5]. Prey fishes, such as juvenile salmonids, typically respond to the presence of piscivorous fish [6–12] and the strength of these * Correspondence: [email protected] River Ecology and Management, Department of Environmental and Life Sciences, Karlstad University, Universitetsgatan 2, SE-651 88 Karlstad, Sweden
responses may change with water temperature [13–17]. Temperature effects on anti-predator responses in fish have mainly been studied in tropical and warmtemperate systems and rarely under winter conditions [12]. Although temperatures all over the Earth are increasing as a result of climate change, global warming is pronounced in boreal and Arctic regions, especially during the winter season [18–23]. Hence, elevated winter temperatures can possibly have major effects on antipredator responses of fishes.
© The Author(s). 2020 Open Access This
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