Underground nest building: the effect of CO2 on digging rates, soil transport and choice of a digging site in leaf-cutting ants
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By reacting to local environmental stimuli, ant workers excavate a nest that offers suitable climatic conditions. Workers may face increasing CO2 levels while digging across the soil profile, and it is an open question whether these levels are used as cues during nest excavation. Here, we explored the influence of different underground CO2 concentrations on digging behavior in the leaf-cutting ant Acromyrmex lundii. We first quantified digging rates and transport of excavated material as a function of CO2 levels, ranging from atmospheric values to 11% CO2. The mass of both the excavated soil and the pellets transported out of the digging chamber were quantified. CO2 preferences for excavation were investigated in a second experiment, in which workers were presented with a choice of two digging sites that differed in their CO2 levels, ranging from atmospheric to 4% CO2, and the mass of excavated material was quantified. Digging rates were similar for all tested CO2 levels up to 7%, and only significantly lower for 11%. The transport of excavated soil increased with increasing CO2 levels up to 7%, and then decreased at 11%. Workers preferred digging at 1% CO2 and avoided levels of 4%. We suggest that the observed CO2 preferences are likely driven by the requirements of their symbiotic fungus, and could be one of the reasons why colonies of A. lundii excavate superficial nest chambers.
KeywordsCarbon dioxide Nest excavation Cue Self-organization Nest architecture
We would like to thank David Urbaniec, Lisa Weidner and Baris Düdükcü for their help during the experiments, and Griselda Roces for the ant drawing. We are grateful to two anonymous reviewers, whose comments greatly improved the manuscript. Daniela Römer was supported by a grant from the Postdoc Plus funding program of the Graduate School of Life Sciences (GSLS) of the University of Würzburg, Germany, and a Grant of the Agencia Nacional de Investigación e Innovación (ANII, Grant Number PD_NAC_2015_1_108641), Uruguay. Florian Halboth was supported by a Grant from the German Excellence Initiative to the Graduate School of Life Sciences, University of Würzburg.
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