Effect of terrain structure on food transport in the ant Pheidole boruca
Alejandro Gustavo Farji-Brener, Ezequiel Vanderhoeven , Pablo Muñoz , Ronny Hernández , Ruben Darío Palacio , Yesenia Jasso
Lab. Ecotono, INIBIOMA-CONICET, Universidad del Comhaue, Argentina; CONICET ; Brenesii SRL, San José, Costa Rica ; Brenesii SRL, San José, Costa Rica ; Independient ; Instituto de Ecología, AC, Xalapa, Veracruz, Mexico
Food transport is a major challenge in ants. Foragers often need to carry food of different size and shape through the forest floor, which represent a heterogeneous scenario full of obstacles that difficult the smooth movement of loaded ants. Since the fitness of the colony depends on the food input to the nest, ants should show flexible behaviors to improve the transport of food through different terrain structures. To improve the transport of food ants can theoretically transport loads individually or collectively, and in both situations transport loads by lifting, dragging or pushing. We evaluated whether the ant Pheidole boruca exhibits flexibility in food transport behavior, testing the hypothesis that the way ants carry food depends on terrain structure. Particularly, we expect that for a given terrain structure, ants will perform more frequently the most efficient transport strategy (i. e., the fastest). We performed a manipulative field experiment in the Pacific highlands of southern Costa Rica. We measured the velocity and the relative frequency of load transport behavior (lifting, dragging, or pushing) at which ants (n=268 ants from 12 ant nests) removed half grains of rice from four treatments representing common terrain types in their natural environment: uphill (cone), downhill (inverted cone), rough (sandpaper) and control (flat paper). Ants changed their way of food transport according the terrain structure. While in flat landscapes ants carried loads by dragging and lifting in similar proportion, in the other treatments lifting was the most frequent transport behavior. We found that during individual transport the most frequent behavior was not the fastest, but that during collective transport the fastest behavior (lifting) was the most frequently employed. Our results demonstrate how ants can adapt their transport behavior according to the terrain structure, illustrating also the key role of cooperative work in this process.