Route learning during tandem running in the rock ant Temnothorax albipennis

Differential response by tandem leaders and followers to landmark-rich and landmark-poor environments

When animals use the same route repeatedly, they have the opportunity to update information that might help them to navigate more quickly and more accurately. Here we analyse ants involved in tandem running, in which the leader has evaluated a new nest and decided to recruit to it while the follower has chosen to be led and shown the route. We used a motorised gantry equipped with a camera to track the movements of tandem members on their tandem and return trips in a landmark-rich and a landmark-poor environment. Although the amount of visual navigational information did not affect the movements of leaders or followers on their tandem trip, the paths of followers were significantly more tortuous and their speeds significantly slower than those of leaders on their return trips in the landmark-poor environment. By contrast, there were no such differences between the followers and leaders on their return trips in the landmark-rich environment even though the return paths of followers in the landmark-rich environment were significantly more tortuous than that of leaders in the landmark-poor environment. Indeed, in the landmark-rich environment, the majority of the leaders' return paths had loops while most were straight in the landmark-poor environment. Thus, the availability of more information when many landmarks are present may induce tandem leaders to make the loops, typically associated with the paths of tandem followers. This suggests knowledgeable individuals slow down to update navigational information and has implications for the formation of leader oligarchies in tandem running.

Moving as a group imposes constraints on the energetic efficiency of movement

Movement is a key part of life for many species. In solitary animals, the energetic costs of movement can be mitigated through energetically efficient strategies that produce faster, straighter movements. However, little is known about whether moving as part of a collective enhances or limits the ability of individual group members to express such strategies. Drawing on 6 years of population-level, high-resolution (1 Hz) GPS tracking of group-living vulturine guineafowl (Acryllium vulturinum), we detected 886 events from 94 tagged individuals where their groups made large, range-shifting displacements in response to changing environmental conditions. We contrasted these movements with data from 94 similarly large displacement events by 19 lone, dispersing individuals. Our results suggest that individuals in groups can significantly reduce their energetic cost of transport when making large displacements (15.3% more efficient relative to their normal daily ranging) by increasing the speed and straightness of their movements. However, even during their most efficient movements, individuals in groups could not achieve or maintain comparable increases in speed to lone individuals, resulting in significantly limited efficiency gains (35.7% less efficient than solitary individuals). Overall, this study provides evidence for a substantial energetic cost arising from collective movement.

Do They Know What They Are Doing? Cognitive Aspects of Rescue Behaviour Directed by Workers of the Red Wood Ant Formica polyctena to Nestmate Victims Entrapped in Artificial Snares

Ant rescue behaviour belongs to the most interesting subcategories of prosocial and altruistic behaviour encountered in the animal world. Several studies suggested that ants are able to identify what exactly restrains the movements of another individual and to direct their rescue behaviour precisely to that object. To shed more light on the question of how precise the identification of the source of restraint of another ant is, we investigated rescue behaviour of red wood ant Formica polyctena workers, using a new version of an artificial snare bioassay in which a nestmate victim bore two wire loops on its body, one (acting as a snare) placed on its petiole and an additional one on its leg. The tested ants did not preferentially direct their rescue behaviour towards the snare. Moreover, the overall strategy adopted by the most active rescuers was not limited to precisely targeted rescue attempts directed towards the snare, but consisted of frequent switching between various subcategories of rescue behaviour. These findings highlight the importance of precise identification of cognitive processes and overall behavioural strategies for better understanding of causal factors underlying animal helping behaviour in light of new facts discovered by testing of various successive research hypotheses.

Dynamics, statistics, and task allocation of foraging ants

Ant foraging is one of the most fascinating examples of cooperative behavior observed in nature. It is well studied from an entomology viewpoint, but there is currently a lack of mathematical synthesis of this phenomenon. We address this by constructing an ant foraging model that incorporates simple behavioral rules within three task groups of the ant colony during foraging (foragers, transporters, and followers), pheromone trails, and memory effects. The motion of an ant is modeled as a discrete correlated random walk, with a characteristic zigzag path that is congruent with experimental data. We simulate the foraging cycle, which consists of ants searching for food, transporting food, and depositing chemical trails to recruit and orient more ants (en masse) to the food source. This allows us to gain insights into the basic mechanism of the cooperative interactions between ants and the dynamical division of labor within an ant colony during foraging to achieve optimal efficiency. We observe a disorder-order phase transition from the start to the end of a foraging process, signaling collective motion at the population level. Finally, we present a set of time delay ODEs that corroborates with numerical simulations.

The effect of experience on collective decision-making

Social groups repeatedly solving a complex task can improve their collective performance. To study the mechanisms of collective improvement, we tested the effect of experience on collective decision-making using acorn ants (Temnothorax ambiguus). During a six-emigration training phase, colonies in the choice treatment gained experience choosing to move into one of two nests varying in quality, while colonies in the no-choice treatment had only a single available nest. Both treatments were tested in a subsequent test with two nests of varying quality. We found that experience improved decision-making speed, regardless of treatment. We also found that colonies of the choice treatment were more proficient by carrying a larger proportion of individuals directly into the better-quality nest. However, there was no steady improvement in proficiency throughout their training. Using social network analysis, we quantified changes in group performance over successive emigrations. We found that network density, our measure for social connectedness, and the coefficient of variation of out-strength distribution, our measure for workload distribution, did not differ between treatments and remained stable over successive emigrations. We conclude that collective experience with decision-making may improve subsequent group performance, but the mechanisms of improvement remain unclear. Further research on decision-making in house-hunting ants will advance our understanding of the mechanisms underpinning collective improvement.

Robotic communication with ants

We used a robotic gantry to test the hypothesis that tandem running in the ant Temnothorax albipennis can be successful in the absence of trail laying by the leader. Pheromone glands were placed on a pin attached to a gantry. This set-up substituted for the leader of a tandem run. Neither the pin nor the glands touched the substrate and thus the ant following the robot was tracking a plume of airborne pheromones. The robot led individual workers from their current nest to a potential new one. The robotic gantry was programmed to allow for human intervention along its path to permit the following ant to stop and survey its surroundings and then catch up with its mechanical leader. The gantry then automatically tracked the precise route taken by each ant from the new nest back to the old one. Ants led by the robot were significantly more successful at finding their way home than those we carried to the new nest that had no opportunity to learn landmarks. The robot was programmed to take either a straight or a sinusoidal path to the new nest. However, we found no significant difference in the abilities of ants that had been led on such direct or sinuous paths to find their way home. Here, the robot laid no trail but our findings suggest that, under such circumstances, the following ant may lay a trail to substitute for the missing one.

Highlighted Article: During tandem running, a leading ant teaches a follower the route to a resource. Key features of real tandem runs were successfully reproduced using a gantry as a robotic leader.

Ants’ Personality and Its Dependence on Foraging Styles: Research Perspectives

The paper is devoted to analyzing consistent individual differences in behavior, also known as “personalities,” in the context of a vital ant task—the detection and transportation of food. I am trying to elucidate the extent to which collective cognition is individual-based and whether a single individual’s actions can suffice to direct the entire colony or colony units. The review analyzes personalities in various insects with different life cycles and provides new insights into the role of individuals in directing group actions in ants. Although it is widely accepted that, in eusocial insects, colony personality emerges from the workers’ personalities, there are only a few examples of investigations of personality at the individual level. The central question of the review is how the distribution of behavioral types and cognitive responsibilities within ant colonies depends on a species’ foraging style. In the context of how workers’ behavioral traits display during foraging, a crucial question is what makes an ant a scout that discovers a new food source and mobilizes its nestmates. In mass recruiting, tandem-running, and even in group-recruiting species displaying leadership, the division of labor between scouts and recruits appears to be ephemeral. There is only little, if any, evidence of ants’ careers and behavioral consistency as leaders. Personal traits characterize groups of individuals at the colony level but not performers of functional roles during foraging. The leader-scouting seems to be the only known system that is based on a consistent personal difference between scouting and foraging individuals.