Prior Experience with Photostimulation Enhances Photo-Induced Reproductive Response in Female House Finches

Abstract In vertebrates, reproductive output often increases with age. Unlike older birds, first-year photoperiodic birds lack experience with the reproduc-tively stimulatory effects of long day lengths (photostimulation). We examined whether age-related differences in annual reproductive development could be partially attributed to previous experience with photostimulation in the photo-periodic house finch (Carpodacus mexicanus). By manipulating photoperiod, we generated 2 groups of first-year females: a photo-experienced group that underwent 1 photoperiodically induced cycle of gonadal development and regression and a photo-naïve group exposed to long days since hatch. We trans-ferred both groups from long to short days and then photostimulated and exposed them to male birdsong prior to sacrifice. Following concurrent photo-stimulation, both groups exhibited similar plasma luteinizing hormone surges and hypothalamic vasoactive intestinal polypeptide immunoreactivity. In con-trast, hypothalamic gonadotropin-releasing hormone immunoreactivity and circulating vitellogenin levels were higher in photo-experienced birds, and yol