The phenomenon of minimizing the path length to a target site in order to increase transport efficiency is described as path optimization, and it has been observed in many mammals, birds and some invertebrates like honeybees and ants. It has been demonstrated that ants can optimize their foraging path through an emergent process, involving the trail pheromone concentration, without individual ants having to measure and compare distances. In the current study, we investigated if ants that use only tandem running to recruit their nestmates can minimize their path while relocating their entire colony into a new nest. As colony relocation directly impacts the survival of the whole colony, it would be particularly important to optimize their path to the new nest. Using the ponerine ant Diacamma indicum, we conducted relocation experiments, in which ants had to choose between different defined paths and contrasted our findings with open arena experiments, as they navigate to their new nest. After following 4100 unique transports by 450 different transporters, we found that these ants minimize their path. Individual leaders, as well as colonies, choose the shorter path significantly more than the longer path, and they showed a significant preference for the shorter arm at multiple decision points on encountering a combination of paths. Thus, we concluded that tandem leaders are capable of path minimization based on the information they themselves collect. Further investigation into the proximate mechanisms by which they achieve this is required.

Visual inputs are important for navigation, and several studies have investigated its importance in ants in the context of foraging. Little is known about the importance of visual cues when the whole colony engages in the goal‐oriented task of colony relocation. In this study, we investigated the role of vision for a tandem‐running tropical ant Diacamma indicum during colony relocation by impairing the vision in both eyes of all colony members and comparing our findings with ants having unimpaired vision. Colonies relocated successfully under zero‐lux conditions and when all colony mates were visually impaired, without compromising their colony cohesion. On examining 265 tandem runs performed by visually impaired ants, we found that they had lower efficiency as compared to ants with normal vision. They traveled along longer routes at lower speeds and often lost their followers, leading to significant increase in transportation time. The absence of visual inputs did not influence the number of tandem leaders that participated nor did it negatively impact their ability to recruit their visually impaired followers from becoming tandem leaders. Visually impaired tandem leaders were not able to minimize their relocation path in an open arena but were capable of doing so in defined paths. Our results suggest that these ants use thigmotactic or proprioceptive cues in order to navigate to their new nest in the absence of visual inputs. Our understanding of tandem‐running recruitment would be incomplete until we delineate the role of multiple sensory inputs involved in conducting this mode of recruitment successfully.

IntroductionThe cognitive abilities of animals play a crucial role in their capacity to adapt to changing environments. Experiments to understand cognition are usually performed on animals such as non-human primates, canids, or corvids. These studies often use food as the motivating factor. However, in the current study, we used a new paradigm to investigate the ability of ponerine ants, who are solitary foragers, to solve a nature-inspired problem. As pupae are the most invested brood item and are directly associated with the colony’s fitness, we designed an experiment that presented a challenge to colony relocation by imposing restrictions on the transportation of pupae to the new nest.MethodsWe used a narrow nest entrance through which an adult could enter, but it rendered the passage of an adult holding a pupa virtually impossible. Through this, we examined the capacity of these ants to overcome the “pupal insertion” challenge by investigating eight colonies involving 425 pupal insertions performed by 104 uniquely labeled ants. ResultsWe found that 80% of all pupae were inserted into the nest by employing a novel cooperative behavior: one ant pushed the pupa while the other ant(s) inside the nest pulled it. Even though individual ants showed high variability in their performance regarding pupal insertion, the initial three successive insertions showed a significant improvement in their performance. Such improvement was also documented at the colony level, with shorter durations and fewer attempts for subsequent pupal insertions. DiscussionOur study demonstrated that ants can overcome difficult environmental challenges through innovation and subsequently improve their performance without training or reward.