Do Panther Chameleons Bask to Regulate Endogenous Vitamin D₃Production?

Abstract

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 D(3). 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 microW/cm(2)) for 1 h significantly enhanced vitamin D(3) concentration. Voluntary exposure to higher UV-B irradiance (70 vs. 1 microW/cm(2)) resulted in greater circulating 25-hydroxyvitamin D(3) in female panther chameleons (604 vs. 92 ng/mL). Depending on dietary intake of vitamin D(3), 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 D(3) photoregulation seems to be an important additional component of the function of basking.

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 have shown that some lizards are capable of precisely regulating their exposure to UVB Karsten et al, 2009]. Ferguson et al [2003] showed that panther chameleons exposed to UVB gradients, that were not linked to thermal gradients and were generated using artificial fluorescent lamps in the laboratory, can regulate UVB exposure independently from temperature regulation. Nevertheless, lizards in the field readily seek refuge from the sun, which is a strong UVB and heat source, when their thermal requirements are satisfied (Figs.…”

“…While one species, the panther chameleon, has been shown to do this with great precision Ferguson et al, 2003;Karsten et al, 2009] and other species may have this ability [Bernard et al, 1991;Aucone et al, 2003], careful laboratory and field research is required to document this ability in other species. If a species can self-regulate its UVB exposure to maintain optimal vitamin D 3 status, then providing a suitable species-specific UVB gradient in the vivarium may be all that is necessary for this to occur.…”

“…In contrast to tissue and DNA damage, exposure of many vertebrate species, including reptiles, to UVB radiation results in positive consequences, including the endogenous production of vitamin D 3 [MacLaughlin et al, 1982;Chen et al, 1993;Holick et al, 1995;Tian et al, 1996;Laing and Fraser, 1999;Carman et al, 2000;Laing et al, 2001;Aucone et al, 2003;Ferguson et al, 2003, Acierno et al, 2006, 2008.Vitamin D 3 is the precursor of a vital hormone (1,25 dihydroxy-vitamin D 3 or calcitriol) that regulates calcium-phosphorus balance and immune responses [Holick, 1999;Brames, 2007].…”

Tribute to R. G. Boutilier: Skin colour and body temperature changes in baskingBokermannohyla alvarengai(Bokermann 1956)

“…Basking behaviour for thermoregulatory purposes (Ferguson et al, 2003) is a relatively uncommon behaviour in amphibians (Hutchison and Dupré, 1992) due to their usually highly permeable skin, which allows for high rates of evaporative water loss (EWL) (Jameson, 1966;Shoemaker et al, 1992). Although some amphibians can tolerate up to 45% body water loss from evaporation alone (Shoemaker et al, 1992), water loss is thought to be a major constraining factor in many aspects of amphibian ecology (Beuchat et al, 1984).…”

A comparison of responses by three broadband radiometers to different ultraviolet‐B sources

“…The currently available Model DMX from Spectronics Corp. (Westbury, NY), has a resolution of 10 mW/cm 2 and may not be able to adequately differentiate among irradiance levels from low wattage lamps. The older model (DM-300N), which did measure at the desired resolution, is no longer available, but literature reporting baseline data using this meter exist [Gehrmann, 1987;Ferguson et al, 2002Ferguson et al, , 2003. Most broadband radiometers tend to underestimate the actual irradiance within a band because they progressively undervalue the irradiances toward the two boundaries of the band.…”