Complementary landmarks facilitate ant navigation

Edmund R Hunt,Christopher Kendall,Emma Stanbury,Ana B Sendova-Franks,Nigel R Franks

doi:10.1016/j.beproc.2018.03.004

Edmund R Hunt, Christopher Kendall + Show 3 more

Open Access

https://doi.org/10.1016/j.beproc.2018.03.004

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Abstract

Visual landmarks are important navigational aids to many animals, and when more than one is available their juxtaposition can convey valuable new information to a navigator about progress toward a goal, depending on the landmarks’ comparative distinctiveness. We investigated the effect of presenting rock ant colonies (Temnothorax albipennis) with identical horizontal landmarks either side of their route, versus one horizontal landmark paired with a sloping landmark, as they navigated to a new nest site. Our findings suggest that ants can obtain more navigational information from a combination of dissimilar landmarks: the average tortuosity of the route taken between old and new nests was significantly lower when a horizontal landmark was paired with a monotonically downward sloping landmark (the paths were more direct). The impact on available navigational information from the similarity or dissimilarity of nearby landmarks is likely made through more distinctive visual panoramas, and could be an influential factor in individual and collective animal decision-making about which routes are followed. Furthermore, the effect of landmark complementarity may be relevant to a wide range of species, including other insects or birds, and highlights the possibility that there is an intrinsic difference in the informational content of natural vs. artificial environments.

Highlights

If external landmarks are available during navigation to a goal this can greatly reduce uncertainty in a navigator’s position, because position can be estimated through path integration, errors tend to accumulate over time (Cheung et al, 2007)
We found that ant colonies follow less tortuous routes to a new nest site when a sloping landmark was present, and we found a significant interaction between movement speed and landmark treatment
We studied the effect of presenting similar or dissimilar landmarks to Temnothorax worker ants carrying their brood to a new nest site

Summary

Introduction

If external landmarks are available during navigation to a goal this can greatly reduce uncertainty in a navigator’s position, because position can be estimated through path integration, errors tend to accumulate over time (Cheung et al, 2007). Memorised landmarks are of major importance for the navigation of many ant species, either en route (Collett et al, 2001; Collett, 2010; Wystrach et al, 2011b) or as a beacon to be aimed for at the goal (Graham et al, 2003); and trail pheromones are often laid as a complementary source of navigational information (Czaczkes et al, 2015). If two landmarks are identically shaped, this may be less useful to a navigator than if they have distinctive, complementary characteristics. In natural environments such combinations, for example from rocky terrain and lines of trees, are likely to be typical, compared to the symmetrical landmark geometry often found in controlled experiments such as squares

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