Experimental heating of Macrotermes bellicosus (Isoptera, Macrotermitinae) mounds: what role does microclimate play in influencing mound architecture?

Abstract

Mounds of the fungus-cultivating termite Macrotermes bellicosus (Smeathman) in the Comoe-National Park (Ivory Coast, West Africa) differ in architecture between habitats. Mounds in the cooler, but thermally more stable gallery forest have been shown to be dome-shaped with thick walls, whereas mounds in the shrub savanna are more complex with many ridges and thin walls. In this investigation, we performed heating experiments to determine the thermal properties of the mounds in both habitats in order to test the hypothesis of a thermoregulatory significance of mound architecture. These experiments revealed that each mound had its characteristic individual heating up behavior that depends on its dimensions (height, surface, volume). In addition, habitat-specific traits were demonstrated: mounds of the gallery forest had higher thermal inertia, measured by the thermal capacity, than mounds of the shrub savanna. Thus, the dome-shaped mounds with thick walls in the gallery forest, with its suboptimal low temperatures, reduce loss of heat to the environment.