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

VALDEZ, DIE GO JAVIER; VERA CORTEZ MARILINA; DELLA COSTA NATALIA; LECHE ALVINA; HANSEN CRISTIAN; NAVARRO JOAQUIN LUIS; MARTELLA MONICA BEATRIZ

Tokyo

Congreso; 26th International Ornithological Congress; 2014

The Greater Rhea (Rhea americana), is a ratite species native of 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 its relation with its mating system. We used HPLC and electrochemiluminescence techniques to identify and measure plasmatic levels of testosterone and estradiol in 21 breeding adults Greater rhea (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 adult males and females had oscillations throughout the year of their sex hormones, testosterone and estradiol. Lower levels of these hormones were observed during the non-reproductive season (February to July), whereas maximums 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 this species with a promiscuous mating system and male parental care, the high levels of testosterone 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.