title: An experimental evaluation of the role of the stress axis in mediating predator-prey interactions in wild marine fish.
abstract: The hypothalamic-pituitary-interrenal (HPI) axis, through corticosteroid secretion, is an integral mechanism regulating internal homeostasis when vertebrates are faced with a stressor. However, continued HPI-axis stimulation can produce homeostatic overload, where corticosteroids are detrimental to organismal function. This overload condition may play an important role in mediating predator-prey interactions, because chronically/previously stressed animals may have higher rates of predator-induced mortality. However, the mechanism(s) underlying this observation are unknown. Using fish as models, we hypothesized that chronic stress would increase predation susceptibility owing to a poor physiological state (e.g. homeostatic overload) with corresponding sub-optimal changes in predator-avoidance behaviour. As cortisol is also required in low quantities to help regulate basic metabolic functions in fish, we expected that a glucocorticoid receptor antagonist (GR; e.g. homeostatic failure) may produce similar effects. Schoolmaster snapper (Lutjanus apodus) were given intraperitoneal implants of cocoa butter impregnated with nothing (sham; 5ml/kg body weight (BW)), cortisol (50mg/kg BW) or the GR antagonist RU486 (100mg/kg BW). At 24-h post-implantation, fish were tethered to the seafloor and observed for behavioural metrics associated with predation. Blood samples were collected from a subset of fish to assess the physiological consequences of the implants. Cortisol- and RU486-implanted fish both had significantly higher plasma cortisol concentrations than sham fish, with blood glucose and plasma urea being elevated only in the former. Further, anti-predator behaviours and predation mortality did not differ significantly among treatments. Despite changes in physiological state, predation susceptibility was unaffected, a finding that may reflect the complex relationships linking the physiology and behaviour of an organism as well as potential tethering artefacts.
authors.affiliation: Fish Ecology and Conservation Physiology Laboratory, Department of Biology, Carleton University, Ottawa, ON K1S 5B6, Canada. Electronic address: m_lawrence27@live.ca.
authors.forename: Michael J
authors.initials: MJ
authors.lastname: Lawrence
authors.affiliation: Fish Ecology and Conservation Physiology Laboratory, Department of Biology, Carleton University, Ottawa, ON K1S 5B6, Canada; Department of Ecology, Evolution and Marine Biology, University of California at Santa Barbara, Santa Barbara, CA 93106, USA.
authors.forename: Erika J
authors.initials: EJ
authors.lastname: Eliason
authors.affiliation: Fish Ecology and Conservation Physiology Laboratory, Department of Biology, Carleton University, Ottawa, ON K1S 5B6, Canada.
authors.forename: Jacob W
authors.initials: JW
authors.lastname: Brownscombe
authors.affiliation: Department of Biology, University of Ottawa, Ottawa, ON K1N 6N5, Canada.
authors.forename: Kathleen M
authors.initials: KM
authors.lastname: Gilmour
authors.affiliation: School for the Environment, University of New England, Biddeford, ME 04005, USA; John H. Prescott Marine Laboratory, New England Aquarium, Boston, ME 02110, USA.
authors.forename: John W
authors.initials: JW
authors.lastname: Mandelman
authors.affiliation: Fish Ecology and Conservation Physiology Laboratory, Department of Biology, Carleton University, Ottawa, ON K1S 5B6, Canada.
authors.forename: Steven J
authors.initials: SJ
authors.lastname: Cooke
mesh_terms: D000818:Animals; D006854:Hydrocortisone / Q000494:pharmacology; D007030:Hypothalamo-Hypophyseal System / Q000187:drug effects / Q000378:metabolism*; D015735:Mifepristone / Q000494:pharmacology; D010473:Perciformes / Q000502:physiology*; D011235:Predatory Behavior / Q000187:drug effects / Q000502:physiology*; D013312:Stress, Physiological / Q000187:drug effects
chemical_list: D015735:Mifepristone; D006854:Hydrocortisone
keywords: Cortisol; Homeostatic overload; Lutjanus apodus; Negaprion brevirostris; Predation; RU486