Symmetry breaking in mass-recruiting ants: extent of foraging biases depends on resource quality

Abstract

The communication involved in the foraging behaviour of social insects is integral to their success. Many ant species use trail pheromones to make decisions about where to forage. The strong positive feedback caused by the trail pheromone is thought to create a decision between two or more options. When the two options are of identical quality, this is known as symmetry breaking, and is important because it helps colonies to monopolise food sources in a competitive environment. Symmetry breaking is thought to increase with the quantity of pheromone deposited by ants, but empirical studies exploring the factors affecting symmetry breaking are limited. Here, we tested if (i) greater disparity between two food sources increased the degree to which a higher quality food source is favoured and (ii) if the quality of identical food sources would affect the degree of symmetry breaking that occurs. Using the mass-recruiting Pharaoh ant, Monomorium pharaonis, we carried out binary choice tests to investigate how food quality affects the choice and distribution of colony foraging decisions. We found that colonies could coordinate foraging to exploit food sources of greater quality, and a greater contrast in quality between the food sources created a stronger collective decision. Contrary to prediction, we found that symmetry breaking decreased as the quality of two identical food sources increased. We discuss how stochastic effects might lead to relatively strong differences in the amount of pheromone on alternative routes when food source quality is low.Significance statementPheromones used by social insects should guide a colony via positive feedback to distribute colony members at resources in the most adaptive way given the current environment. This study shows that when food resources are of equal quality, Pharaoh ant foragers distribute themselves more evenly if the two food sources are both of high quality compared to if both are of low quality. The results highlight the way in which individual ants can modulate their response to pheromone trails which may lead colonies to exploiting resources more evenly when in a resource rich environment.Electronic supplementary materialThe online version of this article (doi:10.1007/s00265-016-2187-y) contains supplementary material, which is available to authorized users.

Irrational risk aversion in ants is driven by perceptual mechanisms

“…Each colony was presented with two feeders: a stable one, always presenting the same, medium quality sucrose solution (0.55M), and a variable one, presenting alternatively (changing every 3 minutes) either low or high quality sucrose solution (0.1M -1.0M). Almost all trials showed a clear collective decision for one of the two feeders (as is expected due to symmetry breaking in ants collective decisions, see Beckers et al, 1990Beckers et al, , 1993Czaczkes et al, 2015b;Price et al, 2016), but overall colonies were risk-indifferent: half the colonies chose the safe feeder, and half chose the risky one. This is surprising, as positive feedback from the initially best food source should have resulted in symmetry breaking and a collective choice for that feeder (Beckers et al, 1993;Czaczkes et al, 2015b;Detrain and Deneubourg, 2008;Price et al, 2016).…”

Modulation of trail laying in the ant Lasius neglectus (Hymenoptera: Formicidae) and its role in the collective selection of a food source

“…the higher the value of the resources, the less probable the symmetry breaking (I'Anson Price, Grüter, Hughes, & Evison, 2016).…”

Meat ants cut more trail shortcuts when facing long detours

“…The absence of deception tactics and beneficial impact of information sharing in foraging contexts favoured sophisticated communication systems to increase information flow between individuals. Waggle dances in honeybees (Dyer 2002;Riley et al 2005;von Frisch and Jander 1957) and pheromone trail recruitment in ants (Czaczkes et al 2015b) are prominent examples of such systems for information sharing and allow those organisms to decide collectively on the best food sources available (Beckers et al 1990;de Biseau et al 1991;Price et al 2016;Seeley et al 1991).…”