Regulation of the Annual Testis Cycle by Photoperiod and Temperature in the Lizard Anolis Carolinensis

Males of the lizard Anolis carolinensis are potentially continuous breeders but an annual testicular cycle is induced by seasonal climatic changes. Both photoperiod and temperature are involved as proximate factors in the regulation of testes activity but the importance of each varies with the phase of the cycle. The regenerative phase of spermatogenesis between late fall and spring is controlled primarily by temperature, whereas, the maintenance and eventual regression of the testis in late summer depends primarily on photoperiod. The male reproductive system shows a discrete period of photosensitivity; in nature the lizard shows photo—sexual responses only between late June and mid—October. It is the reduction in day length below about 13.5 hours (the critical day length) in August that induces gonadal regression. The onset and rate of regression is slightly retarded by high temperatures (32 degrees C). The critical day length and temperature dependence of these photoperiodic responses gradually change during the 4—month photosensitive period; and some photorefractoriness is evident early in this period. The factors that determine the onset of the photosensitive phase are poorly understood; short day lengths appear to be important for the termination of this phase. Photoperiod may also affect appetite and growth but these photoperiodic responses differ in several respects from the photo—sexual responses. The two types of photoperiodic responses have different seasonalities, critical day lengths and temperature dependencies. Analysis of the photo—thermal relations of testis activity in A. carolinensis in light of phenological and experimental data for testis cycles in other species indicates that considerable interspecific variation exists in saurian physiological adaptations.