Make your own landmark
We talk a lot about the use of visual information for navigation, but surely life would be easier for navigating insects if they were able to create their own visual landmarks. One way in which this can happen is via nest structures, with one lovely example from ants being the thatched “chimneys” of Acromyrmex. Moreira et al. perform a series of manipulations to ask if these ants use such manufactured nest structures as visual or olfactory guidance cues. The evidence suggests that, in fact, they are visual cues.
Moreira, I. J. S., Santos, M. F., & Madureira, M. S. (2018). Why do Acromyrmex nests have thatched entrance structures? Evidence for use as a visual homing cue. Insectes Sociaux.
Individual Navigation in a Social World
A majority of insect navigation studies rely on solitary foraging species such as desert ants, i.e. those species that don’t rely on pheromones. But obviously most ants have social and individual strategies in their navigational toolkit. One such species is the harvester ant (Veromessor pergandei) which uses shared foraging columns to move away from their nest for a certain distance before individuals spread out to forage in what is described as the foraging fan. In this paper, ants were captured at different positions either along the shared foraging column or in the foraging fan and displaced to a novel location. Their behaviour from the test release point is essentially a test of their Path Integration system and the location that they are aiming for and treating as the PI origin. From the foraging fan, ants head for the end of the shared column and when captured from the end of the column ants they show little orientation. However, when captured from the nest end of the foraging fan, ants show backtracking and head in the nest-feeder direction. Taken together, these data suggest that the PI system is actually directing ants to a point on the shared column. This is similar to findings from a variety of desert ants where PI doesn’t always aim for the nest, but for the familiar side of the nest ,where individuals are most likely to experience familiar environmental cues. That there is a similar but more extreme effect here is perhaps reflective of the pheromone marked shared column being a hyper familiar and “safe” part of the world to navigate back to the nest from.
Plowes, N., Du, Y., Congdon, J. V., Bulitko, V., Soares, E. S., & Spetch, M. L. (2018). Odometry and backtracking: social and individual navigation in group foraging desert harvester ants (Veromessor pergandei). Animal cognition, 1-13.
Desert ant navigation: state of the art and future prospects
Obviously Cataglyphis ants have been important for insect navigation studies, but most of the work over the last decades has involved behavioural studies. This review takes what we know about the mechanisms underpinning ant navigation and asks about possible neural underpinnings and the potential new experimental methods that will lead to ever deeper levels of understanding.
Abstract: “The desert ant Cataglyphis inhabits the arid environment of North Africa where it forages individually for dead arthropods. Because of the ants’ high motivation to find the nest entrance and due to the almost lab-like conditions of their environment — the flat salt pan (where visual information and partly also olfactory information available to a homing ant can be easily manipulated) — Cataglyphis has become an important model for animal navigation. So far, we know a lot about how Cataglyphis uses path integration and learns visual and olfactory cues to return to its nest entrance after far-reaching foraging runs. We know, however, less regarding the neuronal processes involved in both path integration and landmark acquisition. In this article I discuss recent progress in molecular and neurophysiological techniques in other insect species. I furthermore speculate how these techniques might — in a hopefully not too far future — help us pinpointing the neuronal circuits involved in the fascinating navigation and learning capabilities of Cataglyphis.”
Knaden, M. (2019). Learning and processing of navigational cues in the desert ant. Current Opinion in Neurobiology, 54, 140-145.
If in doubt – search.
In discussion of insect navigation strategies, search behaviours are often an afterthought. A strategy of last resort for an insect when the “proper” navigation strategies have failed to lead to the goal. Of course this is an overly simplistic view, not least because search behaviour requires idiothetic path control similarly to Path Integration. Here we have two papers that tackle aspects of search behaviour. Waldner and Merkle take a synthetic approach by developing a parsimonious model that can recreate the optimal search distributions that are seen in ants. Thus demonstrating that the motor output and idiothetic control needed for search might be relatively simple. Corfas and Dickinson tackle the idea of search is a different way. Recently this lab have shown that flies control food searches with a form of idiothetic path control showing the hallmarks of Path Integration. In this paper they use optogenetic stimulation to trigger food sensing neurons, which in turn kickstart search. Therefore it is shown how this method can be used in future studies of the neural basis of PI.
Waldner, F., & Merkle, T. (2018). A simple mathematical model using centred loops and random perturbations accurately reconstructs search patterns observed in desert ants. Journal of Comparative Physiology A, 1-14.
Corfas, R. A., & Dickinson, M. H. (2018). Diverse food-sensing neurons trigger idiothetic local search in Drosophila. bioRxiv, 433771.
How do I know how far to go?
Abstract: Navigation plays an essential role for many animals leading a mobile mode of life, and for central place foragers in particular. One important prerequisite for navigation is the ability to estimate distances covered during locomotion. It has been shown that Cataglyphis desert ants, well-established model organisms in insect navigation, use two odometer mechanisms, namely, stride and optic flow integration. Although both mechanisms are well established, their mode of interaction to build one odometer output remains enigmatic. We tackle this problem by selectively covering the ventral eye parts in Cataglyphis fortis foragers, the eye regions responsible for optic flow input in odometry. Exclusion of optic flow cues was implemented during different sections of outbound and inbound travel. This demonstrated that the two odometers have separate distance memories that interact in determining homing distance. Possible interpretations posit that the two odometer memories (i) take on different relative weights according to context or (ii) compete in a winner-take-all mode. Explanatory values and implications of such interpretations are discussed. We are able to provide a rough quantitative assessment of odometer cue interaction. An understanding of the interaction of different odometer mechanisms appears valuable not only for animal navigation research but may inform discussions on sensor fusion in both behavioural contexts and potential technical applications.
Wolf H, Wittlinger M, Pfeffer SE (2018) Two distance memories in desert ants—Modes of interaction. PLoS ONE 13(10): e0204664. https://doi.org/10.1371/journal.pone.0204664
Bio-inspired engineering
The latest edition of Current Opinions in Insect Science has two really useful looking reviews about different aspects of insect-inspired hardware: neuromorphic computers and visually controlled vehicles.
Julien R. Serres, Stéphane Viollet (2018) Insect-inspired vision for autonomous vehicles. Current Opinions in Insect Science
T. Dalgaty, E. Vianello, B. De Salvo, J. Casas (2018) Insect-inspired neuromorphic computing. Current Opinions in Insect Science
Not all smells are equal
The flexibility and robustness of animal behaviour is often attributed to their ability to use the most valuable information for guiding a particular behaviour. However, animals are not general purpose learning machines and the specific cues that are attended to and learned depend on the behavioural context. Here is a lovely example of the rapid and extensive potential of insect learning – but only applied to a particular context as dictated by the animal’s ecology. Ants were able to rapidly learn a large number of discrete odours that were associated with food, and further, able to retain the information for a lifetime. Ants were also able to associate odours with their nest location, but this ability was much less pronounced and retention times were shorter suggesting different different ecololgical values for these different odour associations.
Huber, R., & Knaden, M. (2018). Desert ants possess distinct memories for food and nest odors. Proceedings of the National Academy of Sciences, 201809433.
