Meeting Abstract
The surface temperature of tree branches in the tropical rainforest canopy can reach up to 55°C. Ants and other small cursorial organisms must maintain adequate adhesive performance in this extreme microenvironment to forage effectively and prevent falling. Tarsal adhesion in ants is partly dependent upon liquid secretions (e.g., hydrocarbons) that vary in viscosity with temperature. Thus, we predicted that adhesive performance of canopy ants would decrease linearly with increasing surface temperature. We measured tarsal adhesion in 580 workers representing 11 species of canopy ants from Barro Colorado Island, Panama. We quantified shear loads by dragging ants individually across a glass plate heated to various temperatures spanning the range observed in the field (23°C to 55°C). Absolute loads ranged 0.1-5.6 g among species (up to 1,250 times their body mass). Adhesive performance showed three general trends: 1) a linear decrease with increasing temperature, 2) no relationship with temperature, and 3) nonlinear dynamics resembling classical thermal performance curves with a peak around 30°C. The mechanisms for these large interspecific differences remain to be determined, but likely reflect variation in tarsal pad morphology, and the volume or chemistry of the secreted fluid. Understanding such differences will reveal the diverse ways that ants cope with highly variable and often unpredictable thermal conditions in the forest canopy.
