Elsevier

Animal Behaviour

Volume 127, May 2017, Pages 179-185
Animal Behaviour

Tall trails: ants resolve an asymmetry of information and capacity in collective maintenance of infrastructure

https://doi.org/10.1016/j.anbehav.2017.03.018Get rights and content

Highlights

  • Leaf-cutting ants clear trails to transport leaf material from a tree to the nest.

  • Unladen ants create trails for laden ants, creating an information asymmetry.

  • Unladen ants clear trails in response to hindrances of laden ants.

  • Trail clearing was not triggered by visual cues or unladen ants' hindrances.

  • Leaf-cutting ants efficiently clear a trail to resolve an information asymmetry.

Information asymmetry is common in many aspects of natural and economic systems. Collective self-organized behaviour in social insects may involve asymmetries in which an individual may possess information but only another individual is able to act on it. We examined this phenomenon on foraging trails of leaf-cutting ants (Atta colombica) to determine whether workers can resolve such an asymmetry. Cleared trails facilitate the transfer of resources and information but require constant maintenance to remove obstacles that arise in a dynamic environment. Overhead obstructions, which occur frequently along trails, present a specific asymmetry for collective behaviours. Returning foragers carrying leaf fragments above their heads may be hindered by such obstructions but must rely on unladen workers to remove them. Can leaf-cutting ants resolve this asymmetry? Do they do so in an indiscriminate or discriminate fashion? We created experimental overhead obstructions that hindered laden but not unladen ants. Clearing efforts by unladen workers were sensitive to the experience of their laden nestmates; they intensified attacks on a low barrier that impeded traffic but not on an equivalent barrier too high to strike leaf fragments. By contrast, a low barrier in the absence of laden ants or an ineffective visual ‘barrier’ did not elicit increased clearance attempts. Our results demonstrate that leaf-cutting ants can overcome an information asymmetry challenge, in which one group possesses the information that another must act upon. This allows the ants to adaptively modulate their trail-clearing efforts.

Section snippets

Methods

The experiment was performed on Barro Colorado Island (BCI) and mainland Panama during 10 March – 3 April 2014, between 0845 and 1830 hours with colonies of A. colombica. Because of local field conditions at the time, especially a decline in the density of A. colombica colonies on BCI, collecting a broad sample population was not possible. One large colony with multiple trails was the subject of most replicates (N = 23). Additionally, a colony from the mainland was sampled once and a second

Results

The mean (±SD) speed of laden ants during transit of the experimental apparatus was significantly slower for the obstruction treatment (2.03 ± 0.97 cm/s, N = 50) than for the no-obstruction (2.93 ± 1.05 cm/s, N = 52) or visual cue (2.87 ± 0.89 cm/s, N = 52) treatments, while the transit speeds in the latter two treatments did not differ significantly from each other (ANOVA: F2,151 = 6.734, P < 0.001, with Tukey's post hoc tests to confirm pairwise differences at an overall significance level of 0.05). None of the

Discussion

The results demonstrate that unladen ants attempt to remove an overhead obstruction at a significantly higher rate when their laden colonymates are slowed by an obstruction (Fig. 3). Unladen ants were not simply responding at a fixed rate to any potential barrier on or above the trail regardless of whether laden ants were affected, as shown by the significantly higher rate of clearing attacks for the obstruction treatment compared to the no-obstruction treatment (Fig. 3). Secondly, ants are not

Acknowledgments

This work was supported by Monash University Dean's Scholarship to A.I.B. Thanks go to the Smithsonian Institute for providing access to Barro Colorado Island. T.J.C. was funded by an Alexander von Humboldt postdoctoral fellowship and a DFG Emmy Noether group leader grant (grant number CZ 237/1-1).

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