Photoperiodic and thermoperiodic interaction affecting fat stores and reproductive indexes in the male green anole, Anolis carolinensis

Abstract

Daily fluctuations in warm (30°C) and cold (20°C) temperatures have different effects on fat stores and gonad weights of male Anolis carolinensis than constant warm or cold temperatures; and the effects vary depending on the phase relations of the daily thermoperiod with a daily photoperiod. In addition there is a seasonal change in the thermoperiod-photoperiod interaction. For example an &hour interval of warm temperature beginning eight hours after the onset of a 6-hour daily photoperiod during July is more stimulatory for testicular weights than similar intervals of warm temperature beginning a t 0 or 16 hours after the onset of light, but it is less stimulatory in October. The results suggest that the interaction of thermoperiodic and photoperiodic cycles may have important roles in regulating the annual cycles of reproduction and lipid metabolism.The reproductive system of male green anoles is influenced by both temperature and daylength during the year. GonadaI regression in late summer is primarily dependent on decreasing daylengths. Daily photoperiods of less than 14 hours promote testis involution in late summer but not at other times during the year. In contrast, the regenerative period of the testicular annual cycle seems to depend primarily on temperature. Low constant temperatures (20°C or less) promote the initial stages of spermatogenesis and testis enlargement in late fall and winter independent of daily photoperiod. Higher temperatures approaching the "preferred" temperature of the anole (approximately 32°C) stimulate spermiation in the spring (Licht, '66, '67a,b, '69, '71).The manner in which temperature and daylength interact to influence the reproductive system is apparently complex. Some of the difficulty in interpretation of experimental data may result from the common practice of providing constant temperatures in the laboratories for ectothermic vertebrates including the green anole. However, under natural conditions, daily fluctuations in environmental temperatures (daily thermoperiods) are almost as predictable as the periodicity in light intensity. This study was undertaken to ex-J. EXP. ZOOL., 202: 97-102. plore possible influences on fat stores and reproductive indexes that daily thermoperiods may have when related temporally in different phases with respect to daily photoperiods a t different seasons of the year. MATERIALS AND METHODSAdult male green anoles (Anolis carolinensisl were collected in Baton Rouge, Louisiana, or purchased from a local biological supply house in southern Louisiana. Experimental groups of seven to ten animals were maintained in screen-covered plastic cages. Food (house crickets) and water were provided ad libitum. The cages were kept in incubators equipped with daylight fluorescent fixtures (150-200 lux at cage level) attached to a timer. The lizards were acclimated to the photoperiodic regimen for seven days before the experiments began. A 6L:18D daily schedule was used in all the experiments. This photoperiodic regimen inhibits the release of gona...