Photoperiodic control of reproduction in the male lizardAnolis carolinensis

Effects of nightbreak, T-cycle, and resonance lighting schedules on the pineal melatonin rhythm of the lizard Anolis carolinensis: correlations with the reproductive response

Experiments were conducted to determine if a correlation exists between any aspect of the pineal melatonin rhythm (such as its duration or phase) in the lizard Anolis carolinensis and the reproductive response to photoperiod. The rhythm of pineal melatonin content was determined in anoles exposed to nightbreak lighting protocols (10L:5D:1L:8D, 10L:10D:1L:3D), resonance lighting cycles (LD 11:13, LD 11:25), and T-cycle lighting protocols (LD 11:7, LD 11:9, LD 11:13, LD 11:15, LD 11:19) and compared with the testicular response to these lighting protocols as determined previously [Underwood and Hyde, (1990) J. Comp. Physiol. (A) 167:231-243]. Different T-cycles and nightbreak cycles elicited changes in both the duration of the melatonin peak and the phase of the melatonin peak relative to these light cycles. The response to the resonance cycle (LD 11:25) was complex, probably due to the overlapping patterns of two groups whose pineal melatonin rhythms were entrained approximately 12 hr out of phase with each other. No correlation was observed between the duration, or the amplitude, of the nocturnal melatonin peaks seen on the various light cycles and the reproductive response to these cycles. A correlation was observed between the phase of the pineal melatonin rhythm and the reproductive response. Light cycles were inductive (stimulated testicular growth) when the entrained melatonin rhythm peaked near the light-to-dark or the dark-to-light transition, but they were not inductive when the melatonin rhythm peaked during the middle third of the night. These results suggest that if melatonin is involved in the transduction of photoperiodic information in Anolis, neither the duration nor amplitude of the nocturnal melatonin pulse is involved in the measurement of day length. Instead, the phase-relationship of the melatonin rhythm to the rest of the circadian system may determine photoperiodic responsiveness.

Photoperiodic time measurement during the termination of photorefractoriness in the starling (Sturnus vulgaris L.)

Groups of photorefractory male European starlings have been kept under Nanda-Hamner LD schedules ranging from LD 6:6 to LD 6:54 for about 6 weeks. Subsequently, when transferred to LD 13:11, all birds of groups LD 6:18 and LD 6:42 went through a complete cycle of testicular growth and regression. Furthermore, they carried out a postnuptial molt, indicating that they have been able to terminate photorefractoriness under these LD schedules. In contrast, no positive responses could be detected in groups LD 6:6, LD 6:30, LD 6:36, and LD 6:54. Groups LD 6:12, LD 6:24, and LD 6:48 were intermediate in their reactions. Only part of these birds showed gonadal recrudescence when tested for photosensitivity. Changes in plasma testosterone levels were closely related to variations in testicular diameter. These results clearly suggest a strong circadian component in photoperiodic time measurement during the termination of photorefractoriness in the starling. Positive or negative responses were completely in line with predictions derived from the model of external coincidence. A comparison with the results of a similar experiment previously done with photosensitive birds failed to detect basic differences in the interpretation of the various LD cycles. These findings suggest that the same photoperiodic time measurement system is used at both phases of the starling's annual cycle.

Effect of photoperiod on testicular function in blinded and non-blinded marbled newts, Triturus marmoratus (caudata, salamandridae)

Adult male marbled newts (Triturus marmoratus) were collected at the beginning of the spermatogenetic period and exposed to different photoperiods (natural photoperiod with progressively increasing daylengths, total darkness, 8L:16D, 12L:12D, 16L:8D, and continuous light) for 3 months at 20°C. To evaluate the effect of photoperiodic input via pineal gland photoreceptors, two additional groups of newts were blinded by a non-aggressive method (an elastic rubber cap was adjusted to the head to cover the eyes but not the pineal photoreceptors). These animals were exposed either to the natural photoperiod or to 12 hr of light per day. Quantitative histologic studies on testicular development and germ-cell volume revealed no significant differences between non-blinded and blinded animals. Testicular size and germ-cell development increased in the following order: total darkness, constant light, 8L:12D, natural photoperiod, 12L:12D, and 16L:8D. These results suggest that (1) long photoperiods enhance testicular development, whereas short photoperiods or an environment of continuous light have the opposite effects and (2) the effect of photoperiods on testicular function in newts is independent of the ocular photoreceptors.