DUFFY, D.L.*; BALL, G.F.: Effects of Photoperiod and Testosterone on Immunity in Starlings

One of the tenets of the immunocompetence handicap hypothesis (ICHH; Folstad & Karter, 1992) is that testosterone (T) is immunosuppressive. A previous report by our laboratory (Duffy et al., 2000) revealed that exogenous T reduced cell-mediated (CMI) and humoral immunity (HI) in European starlings, Sturnus vulgaris. The present study investigated whether reproductive condition and T interact to affect immunity in starlings. Male birds were wild-caught, castrated and housed in the laboratory under different photoperiodic regimens resulting in 3 reproductive conditions: photosensitive, photostimulated, and photorefractory, simulating reproductive conditions characteristic of late winter, early spring, and late summer, respectively. Birds in each condition received either empty or T-filled silastic implants and 6 weeks later CMI was assessed by measuring wing web swelling responses to phytohemagglutinin (PHA) 24 and 48 h post-injection. Next, HI was assessed by measuring antibody responses to keyhole limpet hemocyanin (KLH) via an ELISA. In contrast to prior results, T treatment enhanced CMI responses in photorefractory and photosensitive birds. HI responses were reduced by T in photosensitive and photostimulated birds, but not in photorefractory birds as previously reported. It is possible that differences in whether CMI was assessed before (present study) or after (previous study) the induction of the antibody response to KLH may account for the discrepancies in the effects of T on CMI. These results offer mixed support for the ICHH in that T treatment consistently suppresses HI in starlings; however, the data regarding T effects on CMI remain equivocal and require further study. Funded by a NSF graduate student fellowship to DLD and a NIH grant (NS35467) to GFB.