Seasonal changes in plasma levels of sex hormones in a promiscuous bird: the greater rhea (Rhea americana)

VALDEZ, D. J.; VERA CORTEZ, M; DELLA COSTA, N.; LECHE, A.; HANSEN C.; NAVARRO, J.L; MARTELLA, M.B.

Congreso; XXVI IOC; 2014

The greater rhea (Rhea americana) is a ratite species native to South America that reproduces seasonally and has a complex and "promiscuous" mating system. For that reason, this study is aimed at analyzing the endocrine basis of reproduction in greater rheas and its relation to their mating system. We used HPLC and electrochemiluminescence techniques to identify and measure plasmatic testosterone and estradiol levels in 21 breeding adults (6 males and 15 females) and 10 greater rhea chicks (5 males and 5 females) as a control, bred in captivity at an experimental farm in Córdoba Zoo, Argentina. Our results show show that the sex hormones testosterone and estradiol fluctuate throughout the year in adult males and females, respectively. Lower levels of these hormones were observed during the non-reproductive season (February to July), whereas maxima were reached in September for males and November-December for females. By contrast, male and female rhea chicks had constant levels of sex hormones, which indicate that there is no seasonal control on gonadal function due to their sexual immaturity. As expected for species with a promiscuous mating system and male parental care, the high testosterone levels exhibited during incubation did not inhibit parental behavior in males, while high estradiol levels in females would be needed to maintain egg-laying behavior during the reproductive season.