title: The effect of duration of exposure to short days on the gonadal response to long days in male starlings (Sturnus vulgaris).
abstract: Photorefractory male starlings (Sturnus vulgaris) were transferred from a photoperiodic schedule of 18 h light:6 h dark to 8 h light:16 h dark for 2, 4, 6 or 10 weeks, and then photostimulated by exposure to 18 h light:6 h dark. Testicular dimensions were measured at regular intervals by laparotomy. There was no change in testicular volume in birds photostimulated after 2 weeks under a photoperiod of 8 h light:16 h dark, but a cycle of testicular growth followed by regression occurred in the other groups. Testicular volume was increased significantly by 20 days under 18 h light:6 h dark in all three groups; regression began after 45, 65 and 75 days in birds pre-exposed to 8 h light:16 h dark for 4, 6 and 10 weeks, respectively. These results are discussed in relation to other evidence for the progressive development of photosensitivity.
mesh_terms: D000818:Animals; D001717:Birds / Q000502:physiology*; D008297:Male; D017440:Photoperiod; D013737:Testis / Q000033:anatomy & histology / Q000254:growth & development*; D013997:Time Factors