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

Rate of photoproduct (previtamin D3 plus vitamin D3) formation at different times of day for in vitro models at the free-living locations of three Texas spiny lizards (TSL) (Sceloporus olivaceous) and three house geckos (Hemidactylus turcicus) in Fort Worth, Texas in July and August 1997. TSL locations photoproduct formation was greater than that of the gecko locations. Maximum TSL location photoproduct formation occurred at midday

Mean percent of photoproduct conversion versus duration of skin exposure for 5 × 5 mm patches of Texas spiny lizard (TSL) and gecko skin exposed to a UV bulb (90 uW/cm2 UVB). Vertical bars show two standard errors. There was a significant trend for increase in photoproduct conversion (time effect) as well as a significant difference between the two species (group effect; time-group interaction). See text for statistical detail. In this experiment, the conversion in TSL skin was weak and not significant