280 
P.C. Withers 
a bright white colour (A.R. Main, pers. comm.). 
The light skin colour increases cutaneous 
reflectance and decreases the radiative heat load. 
For example, dorsal skin reflectance increases from 
18.8% for dark L. rubella to 31.8 % for light 
individuals (Figure 2); the effective solar 
reflectance (corrected for the spectral energy 
distribution of solar radiation; Bakken et al. 1978) is 
similar, at 19.7% for dark frogs and 34.7% for light 
frogs, because of the similar spectral pattern in 
both reflectance and solar energy distribution. This 
change is similar in pattern to that reported for 
other light-adapted and dark-adapted frogs 
(Deanin and Steggerda 1948), but is greater in 
magnitude. 
In many amphibians, skin colour is matched to 
the background colour by dispersion or 
aggregation of the dermal and epidermal 
melanophores (Waring 1963). However, reed frogs 
(Hyperolius spp.) blanch to a bright white colour 
when exposed to dry air (Withers et al. 1982b) 
regardless of their background colour, although the 
physiological significance of this is not immediately 
apparent as colour does not directly influence the 
EWL. Similarly, the desert tree frog Litoria rubella, 
blanches when exposed to dry air, regardless of 
previous background colour (Table 2). I suggest 
that this colour change is a response to basking 
conditions (exposure to dry air) that results in an 
adapative increase in reflectance which is an 
important response to a related basking condition, 
exposure to incident solar radiation. Colour change 
in response to humidity does also occur in other 
frogs, but the effect is minor compared with 
background matching and temperature effects 
(Hogben and Slome 1931; Waring 1963). 
ACKNOWLEDGEMENTS 
I gratefully acknowledge Professor Bert Main for 
discussions regarding the desert tree frog, and for 
allowing me to cite his observations as pers. comm. 
I thank Mr John Dell for the loan of tree frogs for 
photography. Professor Don Bradshaw provided 
the field opportunity for collection of tree frogs that 
formed the basis of this study. The comments of 
two reviewers are gratefully acknowledged. 
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