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

VALDÉZ DIEGO; VERA CORTEZ MARILINA; DELLA COSTA, NATALIA SOLEDAD; LÈCHE, ALVINA; HANSEN CRISTIAN; NAVARRO, JOAQUÍN; MARTELLA, MÓNICA BEATRIZ

Tokyo

Congreso; 26th International Ornithological Congress 2014; 2014

The ornithological Society of Japan and Rikkyo University

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 this bird and the relation with its 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 control, bred in captivity at an experimental farm in Córdoba Zoo, Argentina. Our results show that 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 not a 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.