Meeting Abstract

49.1  Sunday, Jan. 5 10:15  Surface swimming in tropical canopy ants YANOVIAK, S P*; FREDERICK, D N; Univ. of Louisville; Univ. of Arkansas, Little Rock steve.yanoviak@louisville.edu

Wingless arthropods (e.g., ants) regularly fall from tropical forest canopies to the ground below. The flooded, fish-inhabited understory typical of many tropical forests presents an especially high probability of mortality for fallen insects. Here we show that several canopy-dwelling ant species use rapid, directed surface swimming to escape from water. We tested the hypothesis that swimming ability is associated with an arboreal lifestyle in tropical ants by dropping workers of a broad range of arboreal and epigeic species individually into natural and experimental aquatic settings. We used Image-J software to quantify swimming velocity and directionality for each species. We similarly quantified leg kinematics for selected species. We conducted experiments with workers of Odontomachus bauri, a common species that swims well, to determine if their aquatic locomotion is directed toward emergent objects (black or white pipe). Swimming ability varied greatly among the species tested. Many simply struggled on the water surface (e.g., Cephalotes atratus), while others were very effective swimmers (e.g., Gigantiops destructor, velocity = 12 cm s^-1). Directional swimming of O. bauri was biased toward dark objects, suggesting that these ants use skototropism for orientation toward tree trunks when on water. Although swimming behavior has been described for ant species associated with specific habitats (e.g., mangroves and phytotelmata), we provide the first evidence that aquatic locomotion is a widespread phenomenon among tropical rainforest ants.