Urinary corticosterone responses and haematological stress indicators in the endangered Fijian ground frog (Platymantis vitiana) during transportation and captivity

Physiological stress assessment is important for in-situ conservation and captive management of threatened wildlife. Leukocyte (white blood cell) evaluation, especially the neutrophil:lymphocyte (N:L) ratio, provides a logical representation of experimentally elevated corticosterone (stress hormone) in amphibians. Urinary corticosterone enzyme-immunoassay (EIA) is a rapid non-invasive tool for assessing stress responses in amphibians. To our knowledge, no one has explored the relationship between N:L ratio and urinary corticosterone in wild amphibians in a non-experimental way. This study provides a comparative assessment of relative leukocyte numbers, N:L ratios and urinary corticosterone responses of the endangered Fijian ground frog (Platymantis vitiana) during transportation and captivity. Adult frogs (n≤40) were collected from Viwa, Fiji Island for captive breeding. Frogs showed significant changes in leukocyte proportions during transportation and captivity. N:L ratios were higher 6h after transportation and over 5 and 15 days in captivity. Urinary corticosterone responses of the frogs were also higher 6h after transportation and after 5 and 15 days in captivity. All leukocyte proportions, N:L ratios and urinary corticosterone concentrations of the frogs returned near baseline levels after the frogs were kept in an environmentally enriched outdoor enclosure for over 25 days. These results highlight the value of leukocyte evaluation and urinary corticosterone EIAs as physiological tools for evaluating stress in amphibians.