CZARNOWSKI, M.R.*; LOMBARDO, M.P.; POWER, H.W.; HASSELQUIST, D.; Rutgers University, New Brunswick; Grand Valley State University; Rutgers University, New Brunswick; Lund University, Sweden: Sudden energetic deficit in male tree swallows (Tachycineta bicolor) has negligible effect on immunocompetence and glucocorticosteroid levels
An organism�s response to a sudden, unpredictable event is integral in determining its current and lifetime fitness. Such events frequently trigger changes in behavior and physiology that might result in cascading effects. Humoral immunocompetence (HIC) is one measure of fitness that is frequently related to physiological condition. The facultative connection between body condition and HIC remains unclear, however, with evidence suggesting that both a lack of energy and/or high levels of circulating glucocorticosteroids play a role. We investigated whether an induced energetic deficit resulted in decreased HIC in short-lived male tree swallows (Tachycineta bicolor) by clipping primary wing feathers. We determined HIC by injecting the birds with a novel, harmless antigen, and measured the specific antibody responses using an enzyme-linked immunosorbent assay. In addition, to investigate hormonal response, we measured circulating levels of corticosterone and testosterone using the same blood samples. Clipped males were clearly energy deficient, as they lost significantly more mass than the control males. Despite that deficiency they showed no difference in HIC, and they did not differ in corticosterone or testosterone levels. This suggests that energy deficiency alone is not sufficient to prevent male tree swallows from mounting an antibody response, and presents a direct contrast to a similar study on female tree swallows (Hasselquist, et al., 2001). Furthermore, since the clipped males show no increase in baseline corticosterone despite their sudden increase in workload, it may be that males are able to strategically suppress the activity of their hypothalamo-pituitary adrenal axis during the breeding season.
