Abstract
Testicular activity in reptiles is controlled primarily by thermal and thermoperiodic factors; however, little is known about the relative contribution of daily heating and nightly cooling in these processes. This question was addressed in the lizard Lacerta vivipara whose cycle is characterized by a 6 month hibernation followed by a single spring spermiogenesis and a summer spermatogenesis. From the autumnal equinox on, lizards were maintained under a constant 12L/12D photoperiod and acclimated to different 24 hour thermoperiodic regimes. Treatments combined a short or a long thermophase (2 or 6 hr basking) in alternation with either a warmer (19β21Β°C) or a colder cryophase (3β7Β°C). Testicular activity was monitored by histological examination of the testis and epididymis in late December and in early March. Heat provided daily during either 2 or 6 hour phases advanced spermiogenesis and spermiation by 3β4 months. Cryophase temperatures had no significant effects on the date of onset of spermiogenesis whereas they greatly affected its speed of completion. Thus, the full testicular cycle, from one spermatogenetic wave to the next, was completed within 6 months under warmer cryophases alternating with either long or short thermophases. In contrast, only part of the cycle was completed in lizards experiencing colder cryophases since active spermiogenesis and spermiation were maintained for at least 2 months as under natural conditions. The functional significance of heat and cold per 24 hour cycles in the regulation of the testicular cycle is discussed.