William H. Gehrmann

Do Panther Chameleons Bask to Regulate Endogenous Vitamin D3 Production

Basking by ectothermic vertebrates is thought to have evolved for thermoregulation. However, another beneficial effect of sunlight exposure, specifically the ultraviolet B (UV‐B) component, includes endogenous production of vitamin D3. In the laboratory, panther chameleons exhibited a positive phototaxis to greater visible, ultraviolet A (UV‐A) and UV‐B light. However, with equivalent high irradiances of UV‐A or UV‐B, their response to UV‐B was significantly greater than it was to UV‐A. Exposure of in vitro skin patches of panther chameleons to high UV‐B (90 μW/cm2) for 1 h significantly enhanced vitamin D3 concentration. Voluntary exposure to higher UV‐B irradiance (70 vs. 1 μW/cm2) resulted in greater circulating 25‐hydroxyvitamin D3 in female panther chameleons (604 vs. 92 ng/mL). Depending on dietary intake of vitamin D3, chameleons adjusted their exposure time to UV‐B irradiation as if regulating their endogenous production of this vital hormone. When dietary intake was low (1–3 IU/g), they exposed themselves to significantly more UV‐producing light; when intake was high (9–129 IU/g), they exposed themselves to less. Vitamin D3 photoregulation seems to be an important additional component of the function of basking.

Photobiosynthetic Opportunity and Ability for UV-B Generated Vitamin D Synthesis in Free-Living House Geckos (Hemidactylus turcicus) and Texas Spiny Lizards (Sceloporus olivaceous)

Abstract The opportunity and ability to photobiosynthesize vitamin D3 by exposing skin to ultraviolet-B (UVB) irradiation from the sun was compared using the nocturnal/crepuscular Mediterranean House Gecko Hemidactylus turcicus and the diurnal Texas Spiny Lizard Sceloporus olivaceous. Texas spiny lizards had a greater opportunity for photobiosynthetic production of vitamin D3 than geckos. This was revealed by vitamin D3 photoproduct production in models (ampoules containing an alcohol solution of vitamin D3 precursor) placed at locations inhabited by free-living lizards at similar times of occupancy. Alternatively, geckos seemed able to maximize their limited photobiosynthetic opportunity with a higher rate of conversion of provitamin D3 to photoproducts. This was revealed by photoproduct conversion in patches of lizard skin exposed to ultraviolet lamps in the laboratory. Stomach-content analysis showed the spiny lizards to have dietary sources of vitamin D3, the geckos may or may not. This is the first documentation that mostly nocturnal geckos may rely on photobiosynthesis of vitamin D3 and that they might have a more sensitive mechanism than diurnal lizards to compensate for their limited exposure to natural UVB radiation. Future studies should investigate sexual, seasonal, age, and species differences in photobiosynthetic opportunity and ability.

Ultraviolet Exposure and Vitamin D Synthesis in a Sun‐Dwelling and a Shade‐Dwelling Species of Anolis: Are There Adaptations for Lower Ultraviolet B and Dietary Vitamin D3 Availability in the Shade?

We compared the natural ultraviolet B (UV‐B) exposure, dietary vitamin D, and skin‐generated vitamin D synthesis for adult males of two species of Jamaican anoles. The more shade‐tolerant and thermal‐conforming Anolis lineotopus merope, rarely exposed to full sun, experienced less UV‐B irradiation in its shady environment than the more heliophilic and thermophilic Anolis sagrei, which frequently basked in full sun during the morning hours (0800–1100 hours). Both species obtained detectable levels of vitamin D3 in their diet, but the heliophilic A. sagrei obtained more. To compensate for less availability of UV‐B and dietary vitamin D, the skin of A. lineotopus merope seems to have acquired a greater sensitivity than that of A. sagrei regarding UV‐B‐induced vitamin D3 photobiosynthesis. We assessed this by observing a greater conversion of provitamin D to photoproducts in skin exposed to UV‐B from a sunlamp. The reduced skin sensitivity of A. sagrei regarding vitamin D photobiosynthesis may reflect a correlated response associated with less need for vitamin D photobiosynthesis and greater need for UV‐B screening capacity as an adaptation to a more damaging UV‐B environment. However, the possibility that adaptations for photobiosynthesis of vitamin D and for protection from skin damage could involve independent mechanisms needs investigation. Also, the ability to behaviorally regulate UV‐B exposure, as shown for the panther chameleon, would benefit both species of Anolis and should be investigated.

Voluntary Exposure of Some Western-Hemisphere Snake and Lizard Species to Ultraviolet-B Radiation in the Field: How Much Ultraviolet-B Should a Lizard or Snake Receive in Captivity?

Studies of voluntary exposure to ultraviolet-B (UVB) radiation from the sun in the field were conducted in the southern US and Jamaica for 15 species of lizards and snakes occupying various habitats. Species were sorted into four zones of UVB exposure ranging from a median UV index of 0.35 for zone 1 to 3.1 for zone 4. Guidelines for UVB exposure in captivity of these and species occupying similar light environments are presented. Data for most species were collected during mid-day during the spring breeding season, which appeared to be the time of maximum exposure. For two species of Sceloporus studied more intensively there was significant variation of exposure among times of the day and among seasons. So, all-day studies over the entire active season are necessary to fully understand the pattern of natural exposure for a particular diurnal species. Environmental and body temperature and thermoregulation as well as UVB/vitamin D photoregulation influences exposure to UVB. Regressions allowing the inter-conversion of readings among some meters with different detector sensitivities are presented. Readings of natural sunlight predict the same photobiosynthetic potential for vitamin D as the same reading from artificial sources whose wavelength distribution within the UVB band of the source is comparable to that of sunlight. Research approaches to further increase our understanding of vitamin D and UVB use and requirements for squamate reptiles in captivity are outlined.

Evaluation of UVB reduction by materials commonly used in reptile husbandry

Ultraviolet B (UVB) irradiation (285-320 nm) is considered important for metabolic processes and reproduction in many reptile species by facilitating the synthesis of vitamin D(3). In captivity, UVB radiation reaching an animal may be diminished by the properties of the materials used in enclosure construction. We investigated the UVB-attenuating properties of 14 materials commonly used in cage tops for reptile enclosures. Irradiances were measured by two types of hand-held broadband radiometers and the D(3)-synthesizing potential was assessed by the use of an in vitro model. For UV-transmitting acrylic, a significant discrepancy between meter irradiances and in vitro model values for D(3)-synthesizing ability was observed, with meter readings underestimating the blocking effect. In contrast, attenuation of UVB irradiances by air-permeable materials, such as wire screen, measured with meters was generally comparable to the attenuation of D(3)-synthesizing ability as measured by in vitro models. Relatively simple meter readings can therefore be used to reflect reduction of D(3)-synthesizing ability through air-permeable materials. Zoo Biol 26:417-423, 2007. (c) 2007 Wiley-Liss, Inc.

Ultraviolet Light and Reptiles, Amphibians

Ultraviolet lighting is integral for the growth and maintenance of many reptile and amphibian species. But providing an adequate source of light can be challenging. Many disease processes seen by veterinarians are attributed to ultraviolet lighting deficiencies. In mammals, disease due to excess ultraviolet lighting has been noted, and some veterinarians feel this may be a potential issue in reptiles and amphibians.

Comparison of Two Artificial Ultraviolet Light Sources used for Chuckwalla, Sauromalus obesus, Husbandry

ABSTRACT Two studies were conducted to determine the suitability of the Westron Corp. self-ballasted mercury vapor lamps in the captive maintenance of the chuckwalla lizard, Sauromalus obesus. Initially, preference for basking under either a Westron lamp or an incandescent flood lamp was measured in a separate enclosure involving five individuals selected from a group of eight juveniles. Following this, the eight chuckwallas were divided into two groups and maintained for fifteen months in indoor enclosures illuminated with either an incandescent flood lamp and fluorescent Sylvania 350 BL combination or a single Westron self-ballasted mercury vapor lamp. Snout-to-vent length (SVL), body mass, and cloacal body temperatures were measured every two weeks. After nine months, the lizards were radiographed to assess bone density and blood was collected for assay of 25-hydroxyvitamin D. No significant differences in SVL and body mass growth rates, cloacal body temperatures or bone densities were observed between...

Restoring Vitamin D in Monitor Lizards: Exploring the Efficacy of Dietary and UVB Sources

ABSTRACT We studied the effects of ultraviolet B (UVB) exposure or administration of dietary vitamin D3 on serum vitamin D3, serum 25-hydroxyvitamin D3 (25[OH]D), calcium, and phosphorus in juvenile black-throated monitor lizards (Varanus albigularis) deprived of all sources of vitamin D for 87 days. Deprivation resulted in significant decreases of circulating levels of 25(OH)D (25–35%), vitamin D3 (73–76%), calcium (6%), and phosphorus (16%). The half-life of circulating 25(OH)D during deprivation was estimated to be from 128–139 days. After deprivation, eight monitors were given a single dose of UVB from exposure for 10–20 minutes to a Spectroline UVB lamp. The dose resulted in an average of 14.2% conversion of provitamin D3 to previtamin D3 and photoproducts within in vitro models. When administered once every week for 92 days, the dose failed to significantly modify the decline of serum 25(OH)D; however, the decline of vitamin D3 seemed to level off. The overall effect of the UVB dosing was weak, and ...

Daily and Seasonal Patterns of Natural Ultraviolet Light Exposure of the Western Sagebrush Lizard (Sceloporus graciosus gracilis) and the Dunes Sagebrush Lizard (Sceloporus arenicolus)

Abstract:  We monitored ultraviolet-B (UVB) irradiance exposure (measured using the ultraviolet index [UVI]) of the Western Sagebrush Lizard (Sceloporus graciosus gracilis) in Lassen Volcanic National Park, California, and the related Dunes Sagebrush Lizard (S. arenicolus) in eastern New Mexico. For S. graciosus gracilis, on sunny days between 0900 and 1100 h, average lizard UVI tracked available solar UVI. Periodic shade-seeking between 1100 and 1600 h resulted in lizard UVI being less than the available solar UVI. This daily pattern of exposure was evident for the activity period from June until August. This general pattern was also evident for S. arenicolus except when air temperatures exceeded 37°C; at these times, all S. arenicolus subjects retreated underground for much of the afternoon. Individuals of S. graciosus gracilis exhibited large within-day variations in the durations of time that they basked in full sun, sought shade, and retreated underground. Two lizards followed for most of a day showed very different patterns of UVI exposure, yet the calculated daily UVB dose (irradiance × time) was similar for both individuals. Some, but not all, S. graciosus gracilis periodically retreated underground during their daily activity; retreat was more frequent and UVI exposure more intense on a cooler day at the California study site.

Influence of Constant Illumination on Thermal Preference in the Immature Water Snake, Natrix erythrogaster Transversa

Modification of preferred body temperature in reptiles has been described in a number of instances. During ecdysis for example, a significant decrease in mean body temperature occurs in some snakes (Kitchell 1969). Certain species of reptiles exhibit a thermophilic response after feeding (Regal 1966). McGinnis (1966) has described a decrease in field-recorded preferred body temperature in the fence lizard during the winter, although this seasonal change was not evident under laboratory conditions. Acclimation of the fence lizard to a high temperature results in a lower preferred body temperature relative to those acclimated to lower temperatures (Wilhoft and Anderson 1960). Voluntary nocturnal hypothermia has been described in a few species of lizards (Regal 1967) and is highly suggestive of a light component operating in thermal preference. Although the physiological, and more specifically, the neurophysiological, bases of selected body temperatures in reptiles remains obscure, Hammel, Caldwell, and Abrams (1967) have reported that heating or cooling of the preoptic and anterior hypothalamus in