Sight of a Predator Induces a Corticosterone Stress Response and Generates Fear in an Amphibian

Abstract

Amphibians, like other animals, generate corticosterone or cortisol glucocorticoid responses to stimuli perceived to be threatening. It is generally assumed that the corticosterone response of animals to capture and handling reflects the corticosterone response to stimuli such as the sight of a predator that are thought to be natural stressors. Fijian ground frogs ( Platymantisvitiana ) are preyed upon by the introduced cane toads ( Rhinellamarina ), and we used ground frogs to test the hypothesis that the sight of a predator will induce a corticosterone stress response in an amphibian. Urinary corticosterone metabolite concentrations increased in male ground frogs exposed to the sight of a toad for 1, 3 or 6 h, whereas corticosterone did not change in frogs exposed to another male ground frog, a ball, or when no stimulus was present in the test compartment. The frogs exposed to a toad initially moved towards the stimulus then moved away, whereas frogs exposed to another frog moved towards the test frog and remained closer to the frog than at the start of the test. Tonic immobility (TI) was measured as an index of fearfulness immediately after the test exposure of the frogs to a stimulus. The duration of TI was longer in frogs exposed to a toad than to another frog or to a ball. The results provide novel evidence that the sight of a predator can induce a corticosterone response and lead to increased fearfulness in amphibians. In addition, they show that endemic frogs can recognise an introduced predator as a threat.

Stress in biological invasions: Introduced invasive grey squirrels increase physiological stress in native Eurasian red squirrels

“…Extra support to this interpretation is given by the fact that no such increase occurred in red squirrels monitored over the same time‐period in sites that were not colonised. A similar pattern was documented in the only study we found which used experimental approaches to investigate changes in stress levels in the native and endangered Fijian ground frog ( Platymantis vitiana ) caused by the presence of introduced cane toads ( Rhinella marina ) that can prey on the native frogs (Narayan et al., , ). Artificial exposure or introduction of the alien predator resulted in an increase in urinary corticosterone metabolites (Narayan et al., ) and subsequently reduced reproductive success (fewer eggs laid in enclosures which also contained alien predators than in no‐predator enclosures) in the endemic species (Narayan et al., ).…”

“…Although there are many studies on the impact of invasive species on native species, only a few have used glucocorticoid metabolites (before and after the stressor) to investigate the degree of physiological impact of invasive predators on native species (frogs, Platymantis vitiana , Narayan, Cockrem, & Hero, ; Narayan et al., ; iguanas or lizards, Amblyrhynchus cristatus , Berger et al., ; Urosausus ornatus , Graham, Freidenfelds, McCormick, & Langkilde, ; Varanus varius, Anson et al., ; Jessop et al., ).…”

Invasive cane toad triggers chronic physiological stress and decreased reproductive success in an island endemic

“…A species interaction–physiological dysregulation framework predicts how introduced cane toads ( R hinella marina ) could induce competition with endemic Fijian ground frogs ( P latymantis vitiana ) reducing reproduction or survival. High cane toad densities and overlapping habitat requirements invoke fear responses (Narayan, Cockrem & Hero ) and reduced nutritional intake in ground frogs to cause physiological dysregulation. Elevated (+) ground frog glucocorticoid ( GC ) stress hormones and reduced (−) body condition could suppress physiological pathways regulating reproductive success and survival.…”

Revisiting the “visible burrow system”: The impact of the group, social rank, and gender on voles under owl attack

“…Brief exposure of rats to predator odor increased both ACTH and corticosterone levels [53]. Fijian ground frogs showed increased corticosterone levels when exposed to the sight of a predator [54]. Increased fecal corticosterone levels were found in rabbits when directly introduced to a predator [55].…”