BOUGHTON, R.K.*; KAMP, M.F.; BRIDGE, E.; SCHOECH, S.J.; Univ. Memphis: Testosterone, immune function, and energetics in Japanese Quail

Evolutionary theory predicts that the high energetic cost of reproduction will induce a trade-off between reproduction and other physiologic functions, such as the immune system. Though this assumes a cost to maintaining or increasing immune function, few studies have directly examined this assumption. Testosterone (T) mediates male reproductive behavior and physiology and it may underlie immune system suppression during reproduction. We investigated the postulated trade-off between reproduction and immune function by comparing the energetic costs of an immune response in castrated (low T) and intact (high T) Japanese quail (Coturnix coturnix). Immune challenges utilized the phytohemagglutinin (PHA) wing-web swelling test and resting metabolic rate (RMR) was assessed with flow through respirometry. Intact birds had higher pre- and post-immune challenge RMR and significantly lower immune responses than castrates. Intact quail also showed no change in RMR in response to an immune-challenge suggesting that T is both immunosuppressive and energetically costly. Interestingly, castrates not only had a lower pre-challenge RMR than intact birds, they also exhibited a significant decrease in RMR during an immune response, despite having a greater immune response than intact quail. It has been proposed that pro-inflammatory cytokines (e.g., TNF & IL-1β) released during an immune response, such as that induced by PHA, increase somnogenic activity and thereby, conserve energy. The greater wing-web swelling and lower nocturnal RMR in castrates as compared to intact birds is consistent with this hypothesis. It may be, and our data agree, that intact birds have a suppressed immune response as a consequence of their elevated RMR and this may be in part due to the increased metabolic requirements of their reproductive tissues.