Regulation of Exposure to Ultraviolet Light in Bearded Dragons (Pogona vitticeps) in Relation to Temperature and Scalation Phenotype
Exposure to ultraviolet (UV) light has both physiological benefits as well as costs. Many lepidosaur reptiles can behaviorally self-regulate their exposure to UV light in order to take advantage of the benefits of UV light while minimizing the costs. Furthermore, lepidosaur scales have been conceptualized by some as a barrier to the penetration of UV light. Here we examine regulation of self-exposure to UV light in three different phenotypes of Bearded Dragon (Pogona vitticeps): wild type, animals exhibiting scales of reduced prominence (‘Leatherback'), and scaleless animals (‘Silkback'). Silkbacks on average chose to expose themselves to lower levels of UV light irradiation than Leatherbacks or wild types did. Bearded Dragons of all scalation phenotypes on average received higher UV irradiation when they were in the cold section of a UV gradient apparatus compared to when they were in the hot section of the apparatus. This either demonstrates that Bearded Dragons under higher UV irradiances choose cooler temperatures or demonstrates that Bearded Dragons at cooler temperatures choose higher UV irradiances. The relationship between chosen temperature and chosen UV light irradiance was not affected by scalation phenotype. This study highlights external influences on the mechanism that regulates UV self-exposure behavior in lepidosaur reptiles.
The ultraviolet light irradiance gradient apparatus used in this study. The labels on the sides of the apparatus indicate that at this time the Exo Terra Reptile UVB100 26W bulb (Rolf C. Hagen Inc., Baie d'Urfé, QC, Canada) is in the light fixture in the compartment on the upper left, followed clockwise by the Exo Terra Reptile UVB150 26W bulb and the Exo Terra Reptile UVB200 26W bulb. The circle indicates the approximate boundaries of the ‘hot' portion of the apparatus generated by coils of heat cable underneath the apparatus. Beyond this is the ambient temperature ‘cold' portion. Lizards were free to walk beneath a large gap underlying each divider. Scale bar is 10 cm.
The regressions of ultraviolet (UV) light irradiance used in this study to infer an animal's UV light exposure level at each time point of its trial. The regressions model how UV light irradiance changes as a function of horizontal bench top distance from the center of the area underneath the bulb. Regressions were modeled for three different bulbs: an Exo Terra Reptile UVB100 26W bulb, an Exo Terra Reptile UVB150 26W bulb, and an Exo Terra Reptile UVB200 26W bulb (Rolf C. Hagen Inc., Baie d'Urfé, QC, Canada). Regressions were modeled for three different wavelength categories: (A) ultraviolet-A (UVA), (B) ultraviolet-B (UVB), and (C) combined UVA+UVB.
Ultraviolet (UV) light irradiations chosen in a UV light gradient apparatus by Bearded Dragons (Pogona vitticeps) of three different phenotypes: Wild Type (n = 13), animals exhibiting scales of reduced prominence (‘Leatherback'; n = 12), and scaleless animals (‘Silkback'; n = 9). Data are displayed for three different wavelength categories: (A) ultraviolet-A (UVA), (B) ultraviolet-B (UVB), and (C) combined UVA+UVB. Boxes display the median and the first and third quartiles, and whiskers display at maximum 1.5 times the inter-quartile range.
The difference in ultraviolet (UV) light irradiance chosen in a UV light gradient apparatus by Bearded Dragons (Pogona vitticeps; n = 34) when they were in the heated (‘Hot') portion of the apparatus compared to when they were in the ambient temperature (‘Cold') portion of the apparatus. Data are displayed for three different wavelength categories within the UV portion of the photic spectrum: (A) ultraviolet-A (UVA), (B) ultraviolet-B (UVB), and (C) combined UVA+UVB. Boxes display the median and the first and third quartiles, and whiskers display at maximum 1.5 times the inter-quartile range. Lines connect data points from the same individual animal.
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