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First published online March 17, 2006
Journal of Experimental Biology 209, 1185-1196 (2006)
Published by The Company of Biologists 2006
doi: 10.1242/jeb.02038

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

Glenn J. Tattersall^1,*, Paula C. Eterovick² and Denis V. de Andrade³

¹ Department of Biological Sciences, Brock University, St Catharines, Ontario, Canada
² Programa de Pós Graduação em Zoologia de Vertebrados, PUC Minas Gerais, Belo Horizonte, MG, Brazil
³ Dept Zoologia, UNESP-Rio Claro, SP, Brazil

View larger version (146K): [in a new window]   Fig. 1. Digital images of B. alvarengai taken under various circumstances. (A) A cryptically coloured individual in the field, (B) a non-cryptic individual in the field, (C) a darkly coloured cool (18°C) frog at the beginning of Series III experiments, and (D) the same frog as in C 1 h later after reaching 28°C. Note the dramatic colour differences between individuals in the field under varying circumstances (A,B) and within the same individual (C,D) at different body temperatures.

View larger version (15K): [in a new window]   Fig. 2. Skin colour values (A) and grey scale values (B) for frogs exposed to 20 and 30°C in both the dark and the light (Series I experiments) for at least 1 h each. Values are means ± s.e.m. In A, light grey bars refer to the average red value, dark grey values to the average green value, and black bars to the average blue values. Both light level and temperature had significant effects. *Significant difference from 20°C dark exposed frogs; significant difference from 30°C dark exposed frogs.

View larger version (22K): [in a new window]   Fig. 3. Changes in skin colour intensity (red, open circles; green, grey filled circles; blue, solid filled circles) during 30 min of exposure to the sun from Series II experiments. Values are means ± s.e.m. Frog skin temperature is also shown (filled squares) increasing throughout sun exposure.

View larger version (15K): [in a new window]   Fig. 4. Sample temperature and grey intensity trace from one frog that willingly basked in the sun for 60 min. (A) Rock temperature (solid line), black body temperature (broken line; the surface temperature of a piece of black electrical tape exposed to the sun, but not in contact with substrate), and frog dorsal surface temperature (dotted line). (B) Changes in the frog–stone temperature difference (solid line) and the skin's greyscale value (broken line). (C) Correlation between the frog–stone temperature difference and the skin greyscale value (open circles). Roman numerals (i–iii) refer to (i) an early phase when the skin is dark and the frog warms up rapidly, (ii) a secondary phase when the skin has lightened up considerably and the frog and stone temperature difference diminishes, and (iii) a late phase where the frog is as light as possible and the frog equilibrates with stone temperature and eventually falls below stone temperature, presumably due to increased evaporative water loss.

View larger version (23K): [in a new window]   Fig. 5. Correlations between skin colour (grey intensity) and dorsal surface temperature in field and laboratory conditions. Filled black circles refer to values obtained during collection of frogs in the field (N=7; linear correlation: r2=0.95). Open circles with error bars refer to the average ± s.e.m. changes in skin greyscale intensity and temperature during Series II experiments when frogs were allowed to warm up in the sun. Numbers beside these values refer to the elapsed time in minutes (0–30). The two dotted lines, marked Light and Dark, refer to the minimum and maximum possible range of skin colour values defined by Series I experiments from frogs placed in complete dark or light at 20 and 30°C.