THE EFFECTS OF ALTERNATING LONG AND SHORT DAILY PHOTOPERIODS ON GONADAL GROWTH AND PITUITARY GONADOTROPINS IN THE WHITE-CROWNED SPARROW, ZONOTRICHIA LEUCOPHRYS GAMBELII

¹ Department of Zoology, The University, Leeds 2, England.
² Department of Zoology, University of Washington, Seattle 98105.
³ Department of Biology, Occidental College, Los Angeles, California 90041.

The characteristics of the gonadal photoperiodic responses in the White-crowned Sparrow, Zonotrichia leucophrys gambelii, have been examined by the use of cyclic photoperiodic regimes consisting of a day with a long photoperiod followed by n days with short, non-stimulatory daily photoperiod, n with the range 0-5; responses measured were the rates of gonadal growth and the concentration of pituitary gonadotropin. The gonadotropic effect of a single 20-hour photoperiod extends through at least seven days with short (8-hour) non-stimulatory photoperiods. The apparently simplest interpretation of the results of the experiments suggests that there must be separate, although perhaps not completely independent, control schemes for synthesis and release of pituitary gonadotropin.