Urinary corticosterone metabolite responses to capture, and annual patterns of urinary corticosterone in wild and captive endangered Fijian ground frogs (Platymantis vitiana)

Edward Narayan; Frank Molinia; Ketan Christi; Craig Morley; John Cockrem

doi:10.1071/ZO10010

RESEARCH ARTICLE

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Urinary corticosterone metabolite responses to capture, and annual patterns of urinary corticosterone in wild and captive endangered Fijian ground frogs (Platymantis vitiana)

Edward Narayan ^A ^E , Frank Molinia ^B , Ketan Christi ^A , Craig Morley ^C and John Cockrem ^D

+ Author Affiliations

- Author Affiliations

^A Division of Biological Sciences, University of the South Pacific, Private Mail Bag, Suva, Fiji.

^B Landcare Research, Private Bag 92170, Auckland 1142, New Zealand.

^C Department of Conservation, Kauri Coast Office, 150 Colville Road, Dargaville, New Zealand.

^D Institute of Veterinary, Animal and Biomedical Sciences, Massey University, Palmerston North, New Zealand.

^E Corresponding author. Email: edward_nryn@yahoo.com

Australian Journal of Zoology 58(3) 189-197 https://doi.org/10.1071/ZO10010
Submitted: 12 February 2010 Accepted: 12 August 2010 Published: 23 September 2010

Abstract

This study was based on the development of a non-invasive glucocorticoid enzyme-immunoassay for the assessment of stress in wild and captive endangered Fijian ground frogs (Platymantis vitiana). Enzyme-immunoassays were developed and validated for the first time to non-invasively measure both cortisol and corticosterone metabolites in frog urine. Frog urine showed parallel displacement with corticosterone but not cortisol standards, therefore corticosterone enzyme immunoassays were used to examine stress in wild and captive frogs. Urinary corticosterone metabolite concentrations increased in frog urine (n = 4) at 6 h, 1 day and 2 days after injection with adrenocorticotropic hormone (0.44 μg g^–1 bodyweight), indicating that the corticosterone enzyme-immunoassay could detect changes in circulating corticosterone in frogs. Urinary concentrations of corticosterone were measured in wild frogs (n = 18) after capture in the field. The first measurement beyond the initial sample was at 2–3 h. Mean urinary corticosterone concentrations rose after the initial sample and were significantly elevated in samples collected 3–4 h after capture. This is the first demonstration of a urinary corticosterone response to capture in amphibians. Urinary corticosterone metabolite concentrations for all months combined were lower in captive males than in wild males, and differed between vitellogenic, non-vitellogenic and captive females. Concentrations did not differ between captive and wild females. In conclusion, urinary corticosterone enzyme immunoassays can be used in frogs for assessing stress responses to capture and natural stress profiles of both captive and wild populations.

Additional keywords: adrenocorticotropic hormone, capture, stress, urine.

Acknowledgements

The authors thank technical staff of the Division of Biological Sciences of the University of the South Pacific, Fiji, for help with captive management of frogs. We thank the villagers of Viwa Island for permission to access the frogs and for their generous assistance during the 10 months of field work on Viwa. We thank Dr Coralie Munro, Dr Janine Brown and Dr Catherine Morrow for providing reagents and/or helping with assay development. Our appreciation also goes to G. Forrester for statistical assistance and to Dr Ashley Edwards and Associate Professor Jean-Marc Hero for useful comments on the manuscript before submission. The research was supported by a USP scholarship and by an Australia Pacific Science (APSF) Foundation grant.

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Urinary corticosterone metabolite responses to capture, and annual patterns of urinary corticosterone in wild and captive endangered Fijian ground frogs (Platymantis vitiana)

Abstract

Acknowledgements

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