Abstract

Predator‐inducible defenses constitute a widespread form of adaptive phenotypic plasticity, and such defenses have recently been suggested linked with the neuroendocrine system. The neuroendocrine system is a target of endocrine disruptors, such as psychoactive pharmaceuticals, which are common aquatic contaminants. We hypothesized that exposure to an antidepressant pollutant, fluoxetine, influences the physiological stress response in our model species, crucian carp, affecting its behavioral and morphological responses to predation threat. We examined short‐ and long‐term effects of fluoxetine and predator exposure on behavior and morphology in crucian carp. Seventeen days of exposure to a high dose of fluoxetine (100 µg/L) resulted in a shyer phenotype, regardless of the presence/absence of a pike predator, but this effect disappeared after long‐term exposure. Fluoxetine effects on morphological plasticity were context‐dependent as a low dose (1 µg/L) only influenced crucian carp body shape in pike presence. A high dose of fluoxetine strongly influenced body shape regardless of predator treatment. Our results highlight that environmental pollution by pharmaceuticals could disrupt physiological regulation of ecologically important inducible defenses.

Highlights

  • Predation is an important structuring force in nature and has selected for the evolution of diverse defense adaptations in prey organisms, including behavioral (Sih, 1980, Ydenberg & Dill, 1986), morphological (Brönmark & Miner, 1992; Young et al, 2004) and chemical defenses (Bakus, 1981, Brodie Jr, 1977, Skelhorn & Rowe, 2005)

  • We evaluated the relative importance of model terms using the multivariate effect size estimate of Wilks's partial η2 (e.g., Langerhans & DeWitt, 2004)

  • After short-­term exposure to a high concentration of FLX, fish became relatively shyer whereas unexposed fish and individuals exposed to a low concentration shifted toward increased boldness

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Summary

| INTRODUCTION

Predation is an important structuring force in nature and has selected for the evolution of diverse defense adaptations in prey organisms, including behavioral (Sih, 1980, Ydenberg & Dill, 1986), morphological (Brönmark & Miner, 1992; Young et al, 2004) and chemical defenses (Bakus, 1981, Brodie Jr, 1977, Skelhorn & Rowe, 2005). Contemporary studies highlight that inducible defense expression may be mediated by physiological stress response mechanisms, predator-­induced activation of the hypothalamus–­ pituitary–­adrenal/interrenal axis (HPA/HPI axis) and associated hormones (mainly glucocorticoids) (Hossie et al, 2010; Maher et al, 2013; Vinterstare et al, 2020). Recent work found a strong effect of endogenous cortisol implants on the expression of predator-­induced traits (body depth and body coloration) in crucian carp (Vinterstare, Hulthén, Nilsson, Nilsson Sköld & Brönmark, 2020), implying that stress physiology and defense expression are linked via the HPA/ HPI axis (Sapolsky et al, 2000). Based on earlier studies (Maher et al, 2013; Vinterstare, Hulthén, Nilsson, Nilsson Sköld & Brönmark, 2020), we predicted that chronic fluoxetine exposure would reduce the magnitude of morphological defense expression in the presence of predator cues

| MATERIAL AND METHODS
| DISCUSSION
Findings
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