Carotenoid supplementation and GnRH challenges influence female endocrine physiology, immune function, and egg-yolk characteristics in Japanese quail (Coturnix japonica)

Abstract

Androgens and antioxidants circulating in plasma affect the physiology and behavior of vertebrates. Much is known about control mechanisms and functions of each of these substances, yet their interactive effects are still not well understood. Her we examine possible independent and interactive effects of maternal testosterone and antioxidants on female endocrine physiology, immunocompetence, and deposition into egg yolks. We simultaneously manipulated levels of testosterone (via gonadotropin-releasing hormone ?GnRH- challenges) and carotenoids (via diet supplementation) in captive female Japanese quail (Coturnix japonica) and examined how plasma circulating levels related to deposition patterns in yolks. Forty-eight females were randomly assigned to one of four treatments: carotenoid supplementation, GnRH-challenge, GnRH challenge+carotenoid supplementation, and control. Carotenoid supplementation significantly increased plasma circulating carotenoid levels, and acquired immune-system performance, but not innate immunity. GnRH-challenges elevated circulating testosterone and carotenoid levels, and induced immunosuppression in females. However, females in the GnRH-challenge+carotenoid supplementation treatment mounted higher cell-mediated immune responses than control females and similar responses to those mounted by carotenoid-supplemented females. Hence, availability of carotenoids in female quail seemed to counteract immunosuppressive effects of GnRH-challenges. Our results provide further evidence for synergistic effects of carotenoids and T on endocrine physiology and immune function of female birds. Elevated plasma testosterone or carotenoids levels resulted in increased deposition of those compounds to eggs, respectively. Furthermore, because we found that concentrations of testosterone and antioxidants in yolks were correlated within each treatment group, differential deposition of hormones and antioxidants in eggs may not only respond to surrounding social and environmental conditions, but also to other components of the egg.