Influence of breeding season on fecal glucocorticoid levels in captive greater rhea (Rhea americana)

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

ZOO BIOLOGY

WILEY-LISS, DIV JOHN WILEY & SONS INC

Lugar: New York; Año: 2014 vol. 34 p. 71 - 75

0733-3188

Gender, hormonal and stress related changes can be seasonally influenced. We investigatewhether fecal glucocorticoid metabolite (FGM) levels can differ between male and femalecaptive Greater Rheas during breeding and non-breeding season. Over a 3-year-period, freshfecal samples from ten rheas (5 of each sex) were collected during breeding months (October,November and December) and non breeding months (April and June). A total of 960 sampleswere assayed using a commercial radioimmunoassay. Results showed that FGM levels wereaffected by the breeding season in a gender dependent way. Male rheas showed significantlyhigher FGM levels in the breeding months than in the non breeding months (13.44 ± 0.37 vs7.92 ± 0.1 ng/g feces, respectively). In contrast, females did not show FGM seasonal changesthroughout the same sampling periods (7.55 ± 0.14 vs 7.26 ± 0.73 ng/g feces). Moreover, during the breeding season months, males showed higher average FGM levels than their females counterparts (13.44 ± 0.37 vs 7.55 ± 0.14 ng/g feces, respectively), and no differences were found between sexes during the non-breeding season (7.92 ± 0.1 vs 7.26 ± 0.73 ng/g feces, respectively). Our findings suggest that male rheas have a sensitive adrenocortical response to breeding season related changes, probably due to the increased testosterone levels and agonist interactions that are also observed during that phase. Studies aimed to determine the appropriate sex ratio for captive rearing should be carefully considered, to help minimize male agonist encounters and thus to improve welfare of the group.