Environmental control of annual testicular cycles in the lizardAnolis carolinensis. III. Temperature thresholds for photoperiodism
✍ Scribed by Licht, Paul
- Publisher
- John Wiley and Sons
- Year
- 1969
- Tongue
- English
- Weight
- 883 KB
- Volume
- 172
- Category
- Article
- ISSN
- 0022-104X
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✦ Synopsis
Photo-sexual responses in Anolis carolinensis during the fall are highly temperature dependent and show distinct thermal thresholds. If body temperatures are maintained at 32°C (the species' preaerred temperature), day lengths of 13 hours or more stimulate testicular growth, whereas day lengths of 12 hours or less inhibit recrudescence. The testis develops slowly and independently of day length at 25°C or below. With fluctuating body temperatures, photoperiodism depends on both the duration of daily heating to 32°C (the thermoperiod) and the level of nocturnal cooling. Photo-sexual responses occur with thermoperiods of eight hours or more when the nocturnal temperature is 20"C, but longer thermoperiods are required if nocturnal temperatures are reduced. There may be some equivalence between heat and light with regard to photo-sexual responses; the critical day length for photostimulation varies with temperature.
Field observations of behavioral thermoregulation and climatic data for the lizards' habitat (around New Orleans, Louisiana) indicate that body temperatures are high enough to allow photoperiodism i n September. Since the effective day length is 12 hours or less, testicular growth may be photoperiodically inhibited in September and early October. The natural onset of testicular growth in mid-October may be due to a reduction of thermoperiod and nocturnal temperatures which abolishes the photoperiodic responsiveness and to an inherent reduction in photosensitivity.
Studies begun in January confirm that the completion of testicular recrudescence in the spring is determined largely by the elevation of body temperatures and is independent of day length. Testicular development is rapidly completed with only a few hours of daily heating to preferred levels (32°C) even if nights are cold (e.g., 12°C).
Anolis carolinensis, a lizard abundant along the southeastern coastal areas of the United States, shows distinct seasonal variations in testicular activity (Fox, '58). The testes and accessory sexual structures are fully enlarged and sperm are produced throughout the spring and summer, they regress during August and remain involuted and quiescent for about six weeks. Gonadal growth starts in mid-October and proceeds slowly to completion in the spring, around mid-March. Laboratory studies have demonstrated that both temperature and photoperiod may influence testicular growth (Fox and Dessauer, '58; Licht, '66, '67a,b). However, the complex, seasonally changing interaction evident between these two environmental factors (Licht, '67a,b) requires further examination before their role in the regulation of testicular activity can be fully evaluated.
Photoperiod may influence testicular recrudescence in early fall but only if body