Environmental control of annual testicular cycles in the lizard <i>Anolis carolinensis</i>. II. Seasonal variations in the effects of photoperiod and temperature on testicular recrudescence

Abstract

Abstract The effects of photoperiod and changing body temperature on testicular growth in Anolis carolinensis vary seasonally. Both a photo‐ and thermal‐refractoriness are evident. During September and October, 14‐hour day‐lengths accelerated testicular recrudescence in lizards at 32°C; a more rapid response occurred during October, suggesting a “relative” photorefractoriness. Photoperiod had little influence on the testicular cycle after October, once testis development started. Day‐lengths between 12 and 16 hours had no effect during any month if body temperatures were kept at 20°C. Exposures to high temperatures (32°C) in September delayed testicular recrudescence when day‐lengths were 12 hours or less, but after mid‐October, high temperatures accelerated gonadal development, independent of day‐length. These data suggest a thermal refractoriness during September that might be important in preventing premature testicular hypertrophy. A differential temperature sensitivity was evident among various testicular activities. The testes became abnormally enlarged but spermatogenic development was retarded at 20°C. Spermiation and androgen production appear especially temperature‐sensitive. These temperature sensitivities account for the long (3 month) arrest of spermatogenic development in nature during the winter. The rapid completion of testicular development during the two weeks following emergence from hibernation is probably dependent on elevations in body temperature and not on increased day‐lengths. Temperature, not photoperiod, appears to be the primary factor in controlling testicular recrudescence once it has started. A similar environmental control may explain testicular cycles among other species of lizards.