Meeting Abstract
In virtually all species, reproduction must be precisely timed to coordinate breeding and rearing of offspring with favorable conditions. In many bird species, early breeders often have greater reproductive success. Specifically, egg lay date in many species is an important predictor of annual reproductive output. An individual’s finite energy budget must be partitioned to various bodily functions when and where it is most needed. For female birds, preparation for breeding, including recrudescence of the ovary, follicular development, yolk deposition and egg laying are energetically demanding processes that require energy allocation be directed towards these processes necessary for reproduction. Mounting an antibody response has been shown to increase metabolic rate in other vertebrates. Thus, females at this critical period may suppress immune activation in response to a pathogen and continue with reproductive preparation and risk death or mount an antibody response, which could negatively impact reproductive timing and success. Keyhole limpet hemocyanin (KLH) is a novel non-pathogenic antigen that generates a robust humoral (antibody) immune response, but does not induce an acute phase response and sickness behavior. Roughly two weeks prior to onset of egg laying wild female dark-eyed juncos (Junco hyemalis) were challenged with an intramuscular injection of KLH (treatment) or received physiological saline (control). Treatment was selected at random. On average KLH-treated females laid their first egg of the season 8 days later than saline-treated females. These data strongly suggest that free-living female birds forced to mount an energetically demanding antibody response delayed egg lay date, indicating a trade-off between investment in immunocompetence and reproduction under natural conditions.
