title: Predator exposure alters stress physiology in guppies across timescales.
abstract: In vertebrates, glucocorticoids mediate a wide-range of responses to stressors. For this reason, they are implicated in adaptation to changes in predation pressure. Trinidadian guppies (Poecilia reticulata) from high-predation environments have repeatedly and independently colonized and adapted to low-predation environments, resulting in parallel changes in life history, morphology, and behavior. We validated methods for non-invasive waterborne hormone sample collection in this species, and used this technique to examine genetic and environmental effects of predation on basal glucocorticoid (cortisol) levels. To examine genetic differences, we compared waterborne cortisol levels in high- and low-predation fish from two distinct population pairs. We found that fish from high-predation localities had lower cortisol levels than their low-predation counterparts. To isolate environmental influences, we compared waterborne cortisol levels in genetically similar fish reared with and without exposure to predator chemical cues. We found that fish reared with predator chemical cues had lower waterborne cortisol levels than those reared without. Comparisons of waterborne and whole-body cortisol levels demonstrated that populations differed in overall cortisol levels in the body, whereas rearing conditions altered the release of cortisol from the body into the water. Thus, evolutionary history with predators and lifetime exposure to predator cues were both associated with lower cortisol release, but depended on distinct physiological mechanisms.
authors.affiliation: Department of Biology, Colorado State University, Fort Collins, CO 80523, USA. Electronic address: eva.fischer@colostate.edu.
authors.forename: Eva K
authors.initials: EK
authors.lastname: Fischer
authors.affiliation: Department of Integrative Biology, Institute for Cellular & Molecular Biology, The University of Texas at Austin, 78712, USA.
authors.forename: Rayna M
authors.initials: RM
authors.lastname: Harris
authors.affiliation: Department of Integrative Biology, Institute for Cellular & Molecular Biology, The University of Texas at Austin, 78712, USA; Institute for Neuroscience, The University of Texas at Austin, 78712, USA.
authors.forename: Hans A
authors.initials: HA
authors.lastname: Hofmann
authors.affiliation: Department of Biology, Colorado State University, Fort Collins, CO 80523, USA.
authors.forename: Kim L
authors.initials: KL
authors.lastname: Hoke
mesh_terms: D000818:Animals; D005075:Biological Evolution; D006854:Hydrocortisone / Q000032:analysis*; D008297:Male; D011036:Poecilia / Q000502:physiology*; D011235:Predatory Behavior; D013312:Stress, Physiological / Q000502:physiology*; D014867:Water / Q000737:chemistry*
chemical_list: D014867:Water; D006854:Hydrocortisone
keywords: Adaptive evolution; Cortisol; Glucocorticoids; Poecilia reticulata; Predation; Stress