BASKING BEHAVIOR, SWEATING AND THERMAL ECOLOGY OF THE INDIAN TREE FROG, POLYPEDATES MACULATUS

We reported previously that Indian tree frogs, Polypedates maculatus, periodically wipe themselves with mucus-borne lipids secreted from cut aneous mucous glands. When dried, these skin secretions decrease water loss but provide only modest resistance to cutaneous evaporation when compared with lipid barriers of so-called ''waterproof'' species of t ree frogs. Aqueous mucous secretions also allow frogs to increase evap orative water loss when they are expelled repetitively during sweating . In P. maculatus, spontaneous sweating of mucous secretions was shown to begin at threshold body temperatures of approximately 30 C, compar ed with 39-40 C in the waterproof species. Here we report that Indian tree frogs voluntarily tolerate body temperatures in the range 28-38 C when they are normally hydrated and exposed to direct sunlight In con trast, dehydrated tree frogs (approximately 16% of body mass) avoid di rect sunlight when body temperatures increase above the 30 C threshold for sweating. Basking tree frogs respond to thermal stress by sweatin g, panting, and adopting lighter skin coloration, with the result that body temperatures are maintained 10-15 C lower than equilibrial tempe ratures of a dry model frog in sunlight. Both held and laboratory obse rvations suggest that during periods of combined heat and drought, P. maculatus secludes itself in sheltered microenvironments where body te mperature equilibrates below 30 C to avoid rapid losses of water to th ermally induced sweating. This behavior contrasts with that of the ''w aterproof'' anuran species which remain more exposed and tolerate cons iderably higher body temperatures without sweating.