Protective behavior or 'true' tool use? Scrutinizing the tool use behavior of ants.

Gábor Módra,Ádám Lőrincz,Orsolya Juhász,István Maák,Péter János Kiss,Gábor Lőrinczi

doi:10.1002/ece3.6968

Abstract

In the genus Aphaenogaster, workers use tools to transport liquid food to the colony. During this behavior, ants place or drop various kinds of debris into liquids or soft food, and then, they carry the food‐soaked tools back to the nest. According to some authors, this behavior is not "true" tool use because it represents two separate processes: a defense response to cover the dangerous liquid and a transport of food. Here, we investigated the debris dropping and retrieving behavior of the ant Aphaenogaster subterranea to establish which of the two hypotheses is more probable by conducting manipulative experiments. We tested the responses of eight colonies (a) to liquid food (honey‐water) and nonfood liquids (water) in different distances from the nest and (b) to nonthreatening liquids previously covered or presented as small droplets. We also tested whether the nutritional condition of colonies (i.e., starved or satiated) would affect the intensity and rate of debris dropping. Our results were consistent with the tool‐using behavior hypothesis. Firstly, ants clearly differentiated between honey‐water and water, and they directed more of their foraging effort toward liquids farther from the nest. Secondly, ants performed object dropping even into liquids that did not pose the danger of drowning or becoming entangled. Lastly, the nutritional condition of colonies had a significant effect on the intensity and rate of object dropping, but in the opposite direction than we expected. Our results suggest that the foraging behavior of A. subterranea is more complex than that predicted by the two‐component behavior hypothesis and deserves to be considered as "true" tool use.

Highlights

Tool use is “...the exertion of control over a freely manipulable external object with the goal of (a) altering the physical properties of another object, substance, surface or medium via a dynamic mechanical interaction, or (b) mediating the flow of information between the tool user and the environment or other organisms in the environment”
If the purpose of debris dropping is to promote food transport (H2), we can predict that (a) more objects would be dropped into liquid food than into nonfood liquids, (b) more objects would be dropped into liquids farther from the nest than into those closer to the nest, (c) objects would be dropped into liquids previously covered with debris, especially if these objects are more manageable, (d) objects would be dropped into liquids presented as small droplets, and (e) the nutritional condition of colonies would have an effect on the intensity and rate of the dropping of objects
Our study supports that the debris dropping and retrieval behavior of Aphaenogaster subterranea constitute "true" tool use (H2)

Summary

| INTRODUCTION

Tool use is “...the exertion of control over a freely manipulable external object (the tool) with the goal of (a) altering the physical properties of another object, substance, surface or medium (the target, which may be the tool user or another organism) via a dynamic mechanical interaction, or (b) mediating the flow of information between the tool user and the environment or other organisms in the environment” That is, the use of tools to transport food and/or water, is a well-documented phenomenon in some vertebrates (birds and primates), but among nonvertebrate animals is known only in a few ant species including members of the genus Aphaenogaster (Bentley-Condit & Smith, 2010; Shumaker et al, 2011) During this behavior, ants place or drop various debris (e.g., pieces of leaf, soil, and wood) into or over soft or liquid foods, and after an interval, they retrieve and carry the food-soaked tools back to the nest where nestmates can feed on them (e.g., Banschbach et al, 2006; Fellers & Fellers, 1976). If the purpose of debris dropping is to promote food transport (H2), we can predict that (a) more objects would be dropped into liquid food than into nonfood liquids, (b) more objects would be dropped into liquids farther from the nest than into those closer to the nest, (c) objects would be dropped into liquids previously covered with debris, especially if these objects are more manageable, (d) objects would be dropped into liquids presented as small droplets, and (e) the nutritional condition of colonies (i.e., starved or satiated) would have an effect on the intensity and rate of the dropping of objects

| METHODS

Findings

| DISCUSSION