Route Retracing: Way-pointing in Trail Following Ants

Maintaining positional estimates of goal locations is a fundamental task for navigating animals. Diverse animal groups, including both vertebrates and invertebrates, can accomplish this through path integration (PI). During PI, navigators integrate movement changes, tracking both distance and direction, to generate a spatial estimate of their start location, or global vector, allowing efficient direct return travel without retracing the outbound route. In ants, PI is accomplished through the coupling of pedometer and celestial compass estimates. Within the PI system, it has been theorized navigators may segment the global vector into local-vectors for way-pointing. However, this is controversial, as these navigators may instead be homing via the view alignment. Here, we present evidence trail-following ants can attend to segments of their global vector to retrace their non-straight pheromone trails, without the confound of familiar views. Veromessor pergandei foragers navigate via directionally distinct segments of their PI by orienting along separate legs of their inbound route at unfamiliar locations, indicating these changes are not triggered by familiar external cues, but by the PI state. These findings contrast with the view of path integration as a singular memory estimate and underscore the systems ability to way-point to intermediate goals along the inbound route. We discuss how the foraging ecology of ant species that rely on non-straight pheromone-marked trails may support attending vector segments to remain on the pheromone rather than attempting straight-line shortcuts back to the nest.