Contact rate modulates foraging efficiency in leaf cutting ants

Abstract

Lane segregation is rarely observed in animals that move in bidirectional flows. Consequently, these animals generally experience a high rate of head-on collisions during their journeys. Although these collisions have a cost (each collision induces a delay resulting in a decrease of individual speed), they could also have a benefit by promoting information transfer between individuals. Here we explore the impact of head-on collisions in leaf-cutting ants moving on foraging trails by artificially decreasing the rate of head-on collisions between individuals. We show that head-on collisions do not influence the rate of recruitment in these ants but do influence foraging efficiency, i.e. the proportion of ants returning to the nest with a leaf fragment. Surprisingly, both unladen and laden ants returning to the nest participate in the modulation of foraging efficiency: foraging efficiency decreases when the rate of contacts with both nestbound laden or unladen ants decreases. These results suggest that outgoing ants are able to collect information from inbound ants even when these latter do not carry any leaf fragment and that this information can influence their foraging decisions when reaching the end of the trail.Although fluid-like collective movement are observed in many organisms, only humans and social insects are known to move in bidirectional flows 1 and thus to potentially experience a high rate of collisions during their movement. To avoid these collisions and move more smoothly, humans 2 and some species of ants 3 and open-air foraging termites 4,5 spatially segregate their flows and travel in unidirectional lanes. Most species of ants and termites however do not show lane segregation and this implies a certain cost for their colony. Indeed, each collision induces a short delay in the progression of individuals and thus significantly decreases their speed, which in turn, when summed over the thousands of collisions that occur along a foraging trail, eventually decreases the rate of food return to the nest 6 . These collisions however can also promote information transfer between individuals and thus benefit their colonies. Hence, in the black garden ant Lasius niger repeated contacts with nestmates or with glass beads coated with their cuticular hydrocarbons reinforce path choice 7 and reduce the frequency of trail pheromone deposits by ants, thus acting as a negative feedback allowing the avoidance of traffic congestion on foraging trails 8,9 . In addition to the contacts occurring on foraging trails, the contacts occurring inside the nest galleries prolonging foraging trails can also be important in conveying information about the type of food available outside the nest 10 or in regulating the recruitment to the food sources being exploited. For example, in the seed harvester ant Pogonomyrmex barbatus the departure rate of foragers from the nest depends on the rate of encounters with successful foragers coming back to the nest 11,12 or on the rate at which glass beads coated with a combination of work...

The Ecology of Collective Behavior in Ants

“…The rate at which ants travel on the trail is also influenced by the rate of antennal contact between inbound and outbound foragers (10,31,35). In turn, the rate of contact depends on crowding and trail width (11).…”

The Role of Information Acquisition and Processing in Decision‐Making by Individual within Insects Colonies

“…The contact-dependent interactions have an important role in the regulation of traffic flows in many activities of the colony (Dussutour et al, 2009;Farji-Brener et al, 2010;Bouchebti et al, 2015). For example, in many species of ants, the contact-dependent interactions by antennation or head-on encounters regulate the flow of insects that go foraging and return to the nest avoiding traffic jams on foraging trails (Dussutour et al, 2009;Bouchebti et al, 2015). Long-range communication consists of the direct interactions between insects that do not require physical contact.…”

General scaling in bidirectional flows of self-avoiding agents

“…The Vicsek model for swarming dynamics 16,17 is probably the best known, but many variations and generalizations based on lattice-gas 18,19 or social force 20,21 models have been developed. Additionally, the formation and sustainance of bidirectional (trail) flows represent also an intriguing situation of interest in behavioral biology too, since only a few social species in the animal kingdom are able to exhibit such behavior in natural conditions 22 , ants being the most renowned case 23,24 .…”