Temperature-Dependent Color Change in Kenyan Chameleons

Skin reflectance at different body temperatures was measured in three species of Kenyan chameleons (Chamaeleo dilepis, Chamaeleo jacksonii, and Chamaeleo ellioti). Total reflectance, calculated by averaging reflectances measured at 290 through 2,600 nm, was significantly greater at 35°C than at 20°C in C. dilepis (31% at 20°C to 46% at 35°C) and in C. jacksonii (7% at 20°C to 11% at 35°C). Reflectance changes with temperature were not the same at all wavelengths. Significant change was largely confined to visible and near-infrared spectral regions (600-1,000 nm). Chamaeleo ellioti did not show a significant change in total reflectance with temperature. Energy balance equations and climatic data representing long-term averages for each month of the year were used to assess the potential for alteration of equilibrium body temperature and rate of radiant heat gain by temperature-dependent color change in C. dilepis and C. jacksonii. The observed changes in reflectance produced changes in estimated equilibrium body temperature of 0.7°C in C. dilepis and 0.2°C in C. jacksonii, as averaged over the entire year. Dark chameleons are predicted to heat more rapidly than light chameleons. The dark coloration observed frequently during morning basking in chameleons may serve to reduce the basking period and, hence, reduce time spent at suboptimal performance temperatures.