Article (refereed) -postprint Prior Experience with Photostimulation Enhances Photo-induced Reproductive Response in Female House Finches: a Potential Basis for Age-related Increase in Reproductive Output , and 4

Prior experience with photostimulation enhances photo-induced reproductive response in female house finches. The NERC and CEH trademarks and logos ('the Trademarks') are registered trademarks of NERC in the UK and other countries, and may not be used without the prior written consent of the Trademark owner. ABSTRACT 24 In many vertebrates parental age is related to reproductive output with older individuals 25 often performing better (e.g., advanced timing, more offspring) than younger ones. First-26 year birds differ from older birds in that they lack previous experience with the 27 reproductively-stimulatory effects of long day lengths (photostimulation). The goal of this 28 study was to examine whether this age-related increase in reproductive output can be 29 attributed, at least in part, to previous experience with photostimulation in a 30 photoperiodic bird, the female house finch (Carpodacus mexicanus). Specifically, we 31 investigated whether previous experience with photostimulation influences the early 32 stages of reproductive development by quantifying plasma luteinizing hormone (LH), 33 plasma vitellogenin, ovarian follicle size, and immunoreactivity of hypothalamic 34 gonadotropin-releasing hormone (GnRH-I) and vasoactive intestinal polypeptide (VIP). 35 By differentially manipulating photoperiod, we generated two groups of first-year female 36 finches: a photo-experienced group that had been through one photoperiodically-37 induced cycle of gonadal development and regression, and a photo-naïve group 38 exposed to long days since hatch. Both groups were then transferred from long to short 39 days for nine weeks, to ensure full photoperiodic responsiveness, and then 40 photostimulated for four weeks and exposed to conspecific or heterospecific male song 41 starting 90 minutes before sacrifice. Following photostimulation, although photo-42 experienced and photo-naïve groups exhibited similar surges in plasma LH 43 concentrations, circulating vitellogenin levels increased in photo-experienced, but not in 44 photo-naïve birds. After four weeks of photostimulation, egg yolk deposition was 45 observed in two of six photo-experienced birds but in none of the photo-naïve birds. 46 3 After four weeks of photostimulation and exposure to conspecific or heterospecific male 47 song, more GnRH-I-ir cells were seen in the septo-preoptic hypothalamus of photo-48 experienced than of photo-naïve birds. In contrast, there were no differences between 49 the photo-experienced and photo-naïve birds, irrespective of the song type they were 50 exposed to, in numbers of visible VIP-ir cells in the mediobasal hypothalamus. Our 51 results demonstrate that previous photo-experience enhances some of the early stages 52 of photo-induced reproductive development, and that the reproductive neuroendocrine 53 …