Non-invasive monitoring of adrenocortical activity in Greater rhea (Rhea americana) by fecal

LECHE A.; BUSSO, J. M.; NAVARRO, J. L.; HANSEN C.; MARIN, R. H .; MARTELLA M. B.

Journal of Ornithology

SPRINGER DOI 10.1007/s10336-011-0661-x

Año: 2011 vol. 152 p. 839 - 847

1439-0361

The Greater rhea (Rhea americana) is a near-threatened species. Wild populations are affected by human activities, such as illegal hunting, egg harvesting and conversion of natural habitats to croplands. An indicator of disturbances is the increase of glucocorticoid corticosterone, a stress hormone that helps to cope with life-threatening situations. Here we evaluate and characterize adrenocortical function in the Greater rhea by validating the use of a radioimmunoassay (RIA) to asses fecal glucocorticoid metabolite concentrations, and by comparing the time course of plasma corticosterone and fecal immunoreactive glucocorticoid metabolite excretion. An adrenocorticotropic hormone (ACTH) challenge was performed and serial blood and fecal samples (cecal and rectal) were collected and analyzed by RIA. High-pressure liquid chromatography (HPLC) was employed to explore the presence of fecal immunoreactive glucocorticoid metabolites. HPLC analysis revealed the presence of two immunoreactive glucocorticoid metabolites in rectal and cecal rhea feces. Greater rheas responded to the ACTH challenge with a thirty-fold increase in plasma corticosterone concentration 2 h post injection, and a thirty- to forty-fold increase in rectal feces glucocorticoid concentration 4-6 h post injection. However, in cecal feces ACTH challenge produced only an eleven-fold increase and did not reflect the increase observed in plasma, suggesting that glucocorticoids levels would be underestimated in cecal samples. Thus, rectal feces sampling would be recommended for adrenal activity monitoring in this species. The adrenocortical response to ACTH found in rhea was higher than what is usually observed in other birds and might be associated with their flightless condition and the use of running as an antipredator strategy.