Changes in serum and urinary corticosterone and testosterone during short-term capture and handling in the cane toad (Rhinella marina)

- Patterns of serum and urinary CORT and T are comparable in amphibians.
- Serum CORT increased between 0-0.5 h, reaching maximal levels at 6-8 h.
- Urinary CORT increased with a lag-time of 1 h.
- Serum T decreased between 0-7 h and increased between 7-8 h.
- Urinary T decreased with a lag-time of 0.5 h, with no change between 4-8 h.

Non-invasive endocrine monitoring with minimally invasive biological samples, such as urine, is being used widely for conservation biology research on amphibians. Currently, it is unknown how closely urinary measurements correspond with the traditional serum hormone measurements. We compared urinary and serum concentrations of corticosterone (CORT) and testosterone (T) in adult male cane toads (Rhinella marina) using a standard capture and handling (short-term stressor) protocol. Free-living male cane toads were captured and sampled for baseline urine (0 h) with a second urine sample taken at 0.5 h and hourly between 1 and 8 h. A single blood sample was collected from each toad after the final urine sampling and capture handling. The mean serum CORT concentration increased between 0 and 0.5 h, reaching the highest level between 6 and 8 h. The mean urinary CORT concentration increased with a lag-time of 1 h and continued to increase up to 8 h. The mean level of serum T decreased between 0 and 7 h and increased between 7 and 8 h. Mean urinary T concentration decreased with a lag-time of 0.5 h. Urinary T levels did not change between 4 and 8 h. Mean serum T levels reached 50% of the original 0 h value at 1 h while mean serum CORT levels reached 200% of the original 0 h value within 0.5 h. Mean urinary T levels reached 50% of the original 0 h value within 3 h while mean urinary CORT levels reached 200% of the original 0 h value within 3 h. The inter-individual variation in baseline serum and urinary CORT and T levels were highly comparable, suggesting that baseline urine sample provides a reliable indicator of the physiological status of the animal. Overall, the results have demonstrated that urine sampling and standard capture handling protocol provide reliable measures of baseline corticosterone and testosterone, as well as short-term stress hormone responses in amphibians.