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Sight of a predator induces a corticosterone stress response and generates fear in an amphibian.

Narayan EJ, Cockrem JF, Hero JM - PLoS ONE (2013)

Bottom Line: 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 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.

View Article: PubMed Central - PubMed

Affiliation: Environmental Futures Centre, School of Environment, Griffith University, Gold Coast Campus, Southport, Australia. e.narayan@ga.griffith.edu.au

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.

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Mean (+ S.E.) locations of the Fijian ground frogs during exposure to a cane toad or another frog.Location 1 was closest to the test compartment and location 6 was furthest away from the test compartment. The location of the frog was recorded at 5, 15, 20, 40 and 60 min after the test began (Fig. 3A, frogs sampled up to 60 min) or 5, 20, 40, 60, 120, 180 (Fig. 3B, frogs sampled up to 180 min) or 5, 20, 40, 60, 120, 180, 240 and 360 min (Fig. 3C, frogs sampled up to 360 min). Sample sizes at each time point were n = 7.
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pone-0073564-g003: Mean (+ S.E.) locations of the Fijian ground frogs during exposure to a cane toad or another frog.Location 1 was closest to the test compartment and location 6 was furthest away from the test compartment. The location of the frog was recorded at 5, 15, 20, 40 and 60 min after the test began (Fig. 3A, frogs sampled up to 60 min) or 5, 20, 40, 60, 120, 180 (Fig. 3B, frogs sampled up to 180 min) or 5, 20, 40, 60, 120, 180, 240 and 360 min (Fig. 3C, frogs sampled up to 360 min). Sample sizes at each time point were n = 7.

Mentions: Adult male ground frogs were usually sitting in the middle of their home container (location number 3) before being subjected to the test stimulus. The locations of the ground frogs changed when the frogs were exposed to some of the test stimuli. Frogs exposed to cane toads moved towards the test compartment within the first 15-20 min and then moved away and stayed as far away as possible for the remainder of the test period (Figure 3). Frogs exposed to a male ground frog in the test compartment moved towards the compartment within the first 15-20 min and stayed close to the test compartment throughout the remainder of the test period (Figure 3). There was little or no change in the locations of the ground frogs in the control group and in the presence of a ball. There was a significant effect of test stimulus (F3,96 = 94.98, p < 0.0001) and time (F3,96 = 3.22, p = 0.026) on the location of the male ground frogs, and a significant interaction between test stimulus and time (F9,96 = 11.39, p < 0.0001). There was a significant difference in locations of frogs over 1, 3 or 6 h between frogs subjected to the toad or another frog (p < 0.05; Figure 3A–C). There was no significant difference in locations of the frogs between those subjected to a ball or a control group (p > 0.05).


Sight of a predator induces a corticosterone stress response and generates fear in an amphibian.

Narayan EJ, Cockrem JF, Hero JM - PLoS ONE (2013)

Mean (+ S.E.) locations of the Fijian ground frogs during exposure to a cane toad or another frog.Location 1 was closest to the test compartment and location 6 was furthest away from the test compartment. The location of the frog was recorded at 5, 15, 20, 40 and 60 min after the test began (Fig. 3A, frogs sampled up to 60 min) or 5, 20, 40, 60, 120, 180 (Fig. 3B, frogs sampled up to 180 min) or 5, 20, 40, 60, 120, 180, 240 and 360 min (Fig. 3C, frogs sampled up to 360 min). Sample sizes at each time point were n = 7.
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Related In: Results  -  Collection

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pone-0073564-g003: Mean (+ S.E.) locations of the Fijian ground frogs during exposure to a cane toad or another frog.Location 1 was closest to the test compartment and location 6 was furthest away from the test compartment. The location of the frog was recorded at 5, 15, 20, 40 and 60 min after the test began (Fig. 3A, frogs sampled up to 60 min) or 5, 20, 40, 60, 120, 180 (Fig. 3B, frogs sampled up to 180 min) or 5, 20, 40, 60, 120, 180, 240 and 360 min (Fig. 3C, frogs sampled up to 360 min). Sample sizes at each time point were n = 7.
Mentions: Adult male ground frogs were usually sitting in the middle of their home container (location number 3) before being subjected to the test stimulus. The locations of the ground frogs changed when the frogs were exposed to some of the test stimuli. Frogs exposed to cane toads moved towards the test compartment within the first 15-20 min and then moved away and stayed as far away as possible for the remainder of the test period (Figure 3). Frogs exposed to a male ground frog in the test compartment moved towards the compartment within the first 15-20 min and stayed close to the test compartment throughout the remainder of the test period (Figure 3). There was little or no change in the locations of the ground frogs in the control group and in the presence of a ball. There was a significant effect of test stimulus (F3,96 = 94.98, p < 0.0001) and time (F3,96 = 3.22, p = 0.026) on the location of the male ground frogs, and a significant interaction between test stimulus and time (F9,96 = 11.39, p < 0.0001). There was a significant difference in locations of frogs over 1, 3 or 6 h between frogs subjected to the toad or another frog (p < 0.05; Figure 3A–C). There was no significant difference in locations of the frogs between those subjected to a ball or a control group (p > 0.05).

Bottom Line: 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 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.

View Article: PubMed Central - PubMed

Affiliation: Environmental Futures Centre, School of Environment, Griffith University, Gold Coast Campus, Southport, Australia. e.narayan@ga.griffith.edu.au

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.

Show MeSH
Related in: MedlinePlus