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Thermal Imaging in Animal Physiology

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Thermoregulatory Associated Skin Colour Changes

In amphibians solar basking far from water sources is relatively uncommon since the highly permeable amphibian skin does not represent a significant barrier to the accompanying risk of losing water by evaporation.  A South American frog, Bokermannohyla alvarengai (Bokermann, 1956), however, spends a significant amount of the day exposed to full sun and relatively high temperatures.  The means by which this frog copes with potentially high rates of evaporative water loss and high body temperatures is unknown. Thus, in this study, skin colour changes, body surface temperature, and evaporative water loss rates were examined under a mixture of field and laboratory conditions to ascertain whether changes in skin reflectivity play an important role in this animal’s thermal and hydric balance.  Field data demonstrated a tight correlation between the lightness of skin colour and frog temperature, with lighter frogs being captured possessing higher body temperatures.  Laboratory experiments supported this relationship, revealing that frogs kept in the dark or at lower temperature (20°C) had darker skin colours, whereas frogs kept in the light or higher temperatures (30°C) had skin colours of a lighter hue.  Light exhibited a stronger influence on skin colour than temperature alone, suggesting that colour change is triggered by the increase in incident solar energy and in anticipation of changes in body temperature. This conclusion is corroborated by the observation that cold, darkly coloured frogs placed in the sun rapidly became lighter in colour during the initial warming up period (over the first 5 minutes), after which they warmed up more slowly and underwent a further, albeit slower lightening of skin colour. Surprisingly, despite its natural disposition to bask in the sun, this species does not possess a ‘waterproof’ skin, since their rates of evaporative water loss were not dissimilar from many hylid species that live in arboreal or semi-aquatic environments. The natural history of B. alvarengai is largely unknown and, therefore, it is likely that the herein reported colour change and basking behavior represent a complex interaction between thermoregulation and water balance with other ecologically relevant functions, such as crypsis.


Tattersall, G.J., Eterovick, P.C., de Andrade, D.V. 2006. Skin colour and body temperature changes in basking Bokermannohyla alvarengai (Bokermann 1956). Journal of Experimental Biology 209: 1185-1196.

Brock University, Department of Biological Sciences
MacKenzie Chown F242, St. Catharines, Ontario, Canada, L2S 3A1
Tel: 905-688-5550 x4815
Email: Glenn Tattersall
Updated: April 11, 2007
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