The organization of societal conflicts by pavement antsTetramorium caespitum: an agent-based model of amine-mediated decision making

Abstract

Ant colonies self-organize to solve complex problems despite the simplicity of an individual ant’s brain. Pavement ant Tetramorium caespitum colonies must solve the problem of defending the territory that they patrol in search of energetically rich forage. When members of 2 colonies randomly interact at the territory boundary a decision to fight occurs when: 1) there is a mismatch in nestmate recognition cues and 2) each ant has a recent history of high interaction rates with nestmate ants. Instead of fighting, some ants will decide to recruit more workers from the nest to the fighting location, and in this way a positive feedback mediates the development of colony wide wars. In ants, the monoamines serotonin (5-HT) and octopamine (OA) modulate many behaviors associated with colony organization and in particular behaviors associated with nestmate recognition and aggression. In this article, we develop and explore an agent-based model that conceptualizes how individual changes in brain concentrations of 5-HT and OA, paired with a simple threshold-based decision rule, can lead to the development of colony wide warfare. Model simulations do lead to the development of warfare with 91% of ants fighting at the end of 1 h. When conducting a sensitivity analysis, we determined that uncertainty in monoamine concentration signal decay influences the behavior of the model more than uncertainty in the decision-making rule or density. We conclude that pavement ant behavior is consistent with the detection of interaction rate through a single timed interval rather than integration of multiple interactions.

Neuromodulation of Nestmate Recognition Decisions by Pavement Ants

“…A pavement ant worker will decide to fight a non-nestmate ant if two conditions are met: 1) there is a mismatch between information detected in cuticular hydrocarbon nestmate recognition cues and a template and 2) the ant has had a recent history of interactions with its fellow nestmates [19]. The probability that any pavement ant fought a non-nestmate increased with the density of nestmates (beta regression; p < 0.0001; n = 18; Fig 1A).…”

“…An agent-based model describing decisions to fight by pavement ants provides evidence that interactions with nestmate ants, prior to interacting with a non-nestmate, leads to increases in the monoamines 5-HT and OA; when levels exceed a threshold, a worker is likely to fight a non-nestmate ant [19]. Here we present a novel neurophysiological mechanism employed by pavement ants that leads to collective organization into aggressive competitions with neighboring societies.…”

“…Pavement ant workers perform random walks to search colony territory for foods high in sugar and fat content [13; 18]. In order to secure territory boundaries, pavement ant workers organize conspicuous wars, involving thousands of ants, against neighboring colonies [19–20]. In these wars, fighting is ritualized and few ants die [20].…”

“…Most workers fight in pairs, or dyads, grasping mandibles or other body parts and remain engaged for up to 12 hours. A worker is likely to fight a non-nestmate ant if it antennates the other ant, detects mis-matches in nestmate chemical recognition cues, and has had a recent history of interaction with nestmate ants [19]. Other ants recruit workers from colonies to the war using pheromone trails and wars establish quickly, within about 30 minutes [20].…”

“…Other ants recruit workers from colonies to the war using pheromone trails and wars establish quickly, within about 30 minutes [20]. Pavement ant wars are likely ritualized tournaments to display colony size at territorial boundaries [19–20]. …”