Argentine ants (Linepithema humile) use adaptable transportation networks to track changes in resource quality

Abstract

Transportation networks play a crucial role in human and animal societies. For a transportation network to be efficient, it must have adequate capacity to meet traffic demand. Network design becomes increasingly difficult in situations where traffic demand can change unexpectedly. In humans, network design is often constrained by path dependency because it is difficult to move a road once it is built. A similar issue theoretically faces pheromone-trail-laying social insects; once a trail has been laid, positive feedback makes rerouting difficult because new trails cannot compete with continually reinforced pre-existing trails. In the present study, we examined the response of Argentine ant colonies and their trail networks to variable environments where resources differ in quality and change unexpectedly. We found that Argentine ant colonies effectively tracked changes in food quality such that colonies allocated the highest proportion of foragers to the most rewarding feeder. Ant colonies maximised access to high concentration feeders by building additional trails and routes connecting the nest to the feeder. Trail networks appeared to form via a pruning process in which lower traffic trails were gradually removed from the network. At the same time, we observed several instances where new trails appear to have been built to accommodate a surge in demand. The combination of trail building when traffic demand is high and trail pruning when traffic demand is low results in a demand-driven network formation system that allows ants to monopolise multiple dynamic resources.

Verification of Argentine ant defensive compounds and their behavioral effects on heterospecific competitors and conspecific nestmates

“…For example, only nanogram quantities (per centimeter of trail) of dolichodial and iridomyrmecin were found on the Argentine ant recruitment trails 19 while the quantities of iridoids on the cuticular surface of harvester ants in the current study (after being attacked by several Argentine ants) were in microgram quantities (per harvester ant). Studies suggest that the recruitment trail is continuously and uniformly reinforced over a period of time and the concentration of the trail pheromone may be dependent on the resource quality 19 , 54 , 61 . Being able to parsimoniously utilize these iridoids in a variety of behavioral/ecological contexts (e.g., colony maintenance, recruitment, defense, and alarm) may contribute to the Argentine ants’ ability to outcompete several other ant species 57 .…”

Invasive ants fed spinosad collectively recruit to known food faster yet individually abandon food earlier

“…This was likely due to ants which foraged on a novel food source ingesting it faster, and thus return to the nest sooner, than those feeding on a previously experienced food taste. Mass-recruiting ants, such as L. humile , rely on pheromone trails during foraging, with ants laying more pheromone towards higher quality food sources (Latty et al ., 2017). Small initial differences between pheromone trails often result in large recruitment differences and in most cases in preference for one food source over the other, a phenomenon often called symmetry breaking (Beckers et al ., 1990; Sumpter & Beekman, 2003; Detrain & Deneubourg, 2008; Grüter et al ., 2012).…”

Foraging behavior and locomotion of the invasive Argentine ant from winter aggregations

“…Recent work indicates that the volume of L . humile foragers on bidirectional trails is altered in response to changing resource abundance and quality [ 44 ]. We hypothesize that, as in other species (e.g.…”

“…It may be that foraging rate is related to a circadian rhythm that happens to align with a narrow temperature range. Although it is likely that a variety of factors are at play, the 10–15°C thermal window may have provided an improved opportunity, metabolic [ 11 – 14 , 29 ] or environmental [ 44 , 49 ], for L . humile colonies to forage on hemipteran honeydew during a time of reduced resource availability [ 6 , 7 ].…”