Environment

Prior Experience with Photostimulation Enhances Photo-Induced Reproductive Development in Female European Starlings: A Possible Basis for the Age-Related Increase in Avian Reproductive Performance

Abstract
Reproductive performance in female birds improves with age, and this is generally attributed to experiences obtained during breeding. In temperate-zone species, experience with photostimulation during the first breeding year may prime the hypothalamo-pituitary-gonadal axis to respond to photic cues more rapidly or robustly in subsequent years. To test this idea, we captured 32 photorefractory juvenile (hence naïve to photostimulation) female European starlings (Sturnus vulgaris) and held half of them (naïve group) on a photoperiod of 8-hours-light 16-hours-dark (8L 16D) for 32 weeks and the other half (experienced group) on 8L 16D for 12 weeks, 16L 8D for 12 weeks, and then 8L 16D for 8 weeks. When we subsequently transferred all birds to 16L 8D, the increase in body mass, which may presage egg laying in the wild, was more robust in experienced than in naïve females. Experienced females also showed a more robust elevation in plasma concentrations of the yolk-precursor protein vitellogenin, although naïve females showed an initial rapid but transient rise in vitellogenin that we attribute to their extended exposure to short-day photoperiods prior to photostimulation. Finally, the photo-induced elevation in diameter of the largest ovarian follicle, in plasma concentrations of luteinizing hormone, and in the number of septo-preoptic fibers relative to the number of cell bodies immunoreactive to gonadotropin-releasing hormone was greater in experienced than in naïve females. Thus, prior experience with photostimulation enhances some initial phases of photo-induced reproductive development and may explain, in part, why reproductive performance improves with age in temperate-zone birds.

Key words: Behavior • Environment • Neuroendocrinology • Aging • Seasonal reproduction

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