EFFECTS OF WAVELENGTH AND INTENSITY OF LIGHT IN INITIATION OF BODY FATTENING AND GONADAL GROWTH IN A MIGRATORY BUNTING UNDER COMPLETE AND SKELETON PHOTOPERIODS

A series of experiments investigated the effects of wavelength and int ensity of light in initiation of body fattening (gain in body weight) and gonadal growth in migratory blackheaded bunting under complete and skeleton photoperiods. Using fluorescent light at an intensity simila r to 700 lx, the first experiment compared the inductiveness of a comp lete (13 h continuous light coupled with 11 h darkness; 13L:11D) and a skeleton (two light pulses of 6 and 1 h at 6 h apart; 6L:6D:1L:11D) p hotoperiod. Observations at the beginning and after 3, 8, 10, and 13 w eeks of the treatment indicated that both photoperiods were fully indu ctive but that birds under 13L photoperiod fattened and lost body weig ht significantly earlier than birds under skeleton photoperiod. In the second experiment, bunting were subjected to 13L:11D (L = 100 lx; D = 0 lx) of white, green (528 nm), and red (654 Mn) light for a period o f 5 weeks. Birds gained weight and testes grew in all groups except fo r an inconsistent fattening response in the white light group. The thi rd experiment tested if the inductive effects of 1-h light pulse in a skeleton photoperiod were intensity dependent. Groups of bunting were exposed to 6L:6D:1L:11D (intensity of 1-h white light pulse = 2, 10, 5 0, or 100 lux) and examined at the beginning and after 3 and 8 weeks o f the treatment. Photoinduction occurred at a slower rate and only at 50- and 100-lx intensities. The fourth experiment was similar to the t hird in design but it employed 1-h light pulse of two different wavele ngths (green = 528 nm, and red = 654 nm) at 50- and 100-lx intensities . Birds fattened and testes grew only under red light. The last experi ment varied the wavelength and intensity of the first (6 h) light puls e of the skeleton photoperiod (6L:6D:1L:11D): 6-h entraining light pul se of white, green (528 nn), or red (654 nm) colour at 10- or 50-lx in tensity was used with 1-h inducing light pulse of white light at simil ar to 700-lx intensity. Testes grew in all groups but significant fatt ening occurred only in birds entrained to 50-lx light intensity. These results indicate i) the dissociation of body weight and gonadal respo nses, in the sense that the timing of photostimulation and/or magnitud e of photoperiod-induced body weight and testicular responses differed under various photoperiodic manipulations, and ii) the circadian proc esses involved in photoperiod-induced responses have differential spec tral and intensity sensitivity.