Information synergy: adding unambiguous quality information rescues social information use in ants

Abstract

Animals have access to many alternative information sources when making decisions, such as private information (e.g. memory) and social information. Social insects make extensive use of social information. However, when intentional social information (e.g. pheromone trails in ants) conflicts with private information (e.g. route memories), insects often follow their private information. Why is this? We propose that an asymmetry in the type of information provided by these two information sources drives the neglect of social information: In ants, workers with certain information about the quality of a food source (memory) ignore valuable social information (pheromone trails) because the pheromone trails encode only a very ambiguous measure of food quality. This leads to a testable hypothesis: the addition of unambiguous quality information should rescue social information following. To test this, we trained ants to a poor quality (0.25M sucrose) food source, and then provided an alternative path along with either 1) no information, 2) a pheromone trail, 3) a 0.2μl 1.5M sucrose droplet, providing unambiguous quality information, or 4) both a trail and a droplet. When either no or only one information source was provided (1-3), most ants (60-75%) continued following their own memory. However, the addition of unambiguous quality information (4) rescued trail following: when both a trail and a droplet were provided, 75% of ants followed the trail. In further experiments, we show that quality information gleaned from direct contact with fed nestmates produced similar effects. Using florescence microscopy, we demonstrate that food (and information) flows from fed workers to outgoing foragers, explaining the frequent contacts on trails. We propose that the type of information an information source can convey, and its ambiguity, is a strong driver of which source of information is attended to.

Copy when uncertain: Lower light levels result in higher trail pheromone deposition and stronger reliance on pheromone trails in the ant Lasius niger

“…Light levels have a large effect on the way in which L. niger foragers make use of, and deposit, pheromone trails. As previously reported [19,22,30], when route memories (private information) and pheromone trails (social information) conflict in bright light (3200 lux), L. niger foragers mostly follow their route memories. However, we found that as light levels decreased to dusk-like levels (10 lux) and on to darkness (0.0007 lux), the rate at which ants relied on private information decreased, until in darkness over half the ants chose to follow a pheromone-marked branch.…”

“…Here, we study the use and provision of social information under different light levels in the ant Lasius niger . Under high light levels, L. niger preferentially follow private route memories over pheromone trails, even if the pheromone trails are very strong [22,30]. We first test confirm that route memories in L. niger are based solely on visual cues (as reported by [36]).…”

“…Insects may be attempting to follow a ‘copy-if-better’ strategy [2], but without accurate quality information, rarely copy. And indeed, when unambiguous quality information about a better food source is provided, Lasius niger ants switch from following memories to following pheromone trails [30]. Another important reversal in social information use was reported by Beugnon & Fourcassie [21,31].…”

Meat ants cut more trail shortcuts when facing long detours

“…Camponotus fellah ants perform at a similar level with ~75-90% correct choices for the rewarded odour after The clear preference for the olfactory modality in conflict situations may give the impression that ants use their private information in a hierarchical way. Hierarchical information use has been suggested for private and social information (Almeida et al 2018), although it is clear that when choosing social or private information, information use strategies are more complex, as environmental conditions or other available information sources affect information use choices (Czaczkes et al 2018;Grüter and Leadbeater 2014;Jones et al in press). The preference found for the olfactory modality is likely strongly linked to the ecology of the investigated species.…”

“…Similarly, an ant can shift to a new food source if it is of better quality than the currently exploited food (Czaczkes et al 2018). Yet, not only the energetic value of a food source is important, but also its other properties.…”