What goes in … … part 2

In the same way that the sensory system of an animal can influence navigational behaviour – the information available in the world can also influence navigational behaviour. Here we have two papers that highlight this point, one through behavioural experiments and one through modelling. Hunt et al observed the trajectories of colonies of Temnothorax ants as part of a nest migration. In their experimental variations to arena within which ants were migrating was surrounded by black wall-like landmarks, with either a flat or sloped top. The paths of migrating where quantifiably different in the two conditions, with ants producing straighter paths when one of the wall-like landmarks had a sloped top. Straighter routes are presumably more efficient and adaptive for the ants. This suggests that the sloped landmark reduces visual homogeneity and either directly provides more information to the ants or allows for symmetry breaking.

Müller et al address the question of how the environment can influence navigation in a more theoretical way. They ask the question of whether some locations are easier to find than others, when using visual information. Not surprisingly, their modelling shows that this is the case. The important piece of the story is that information that can be gained locally, correlates with the ability to navigate to a place from further away. This means that it is theoretically possible for an insect (or robot) to choose locations that will be easier to visually navigate back to. An idea that has biological implications in terms of nest choice, especially for those species that do not have conspicuous nests.

Hunt, E. R., Kendall, C., Stanbury, E., Sendova-Franks, A. B., & Franks, N. R. (2018). Two route landmarks are more useful to navigating ant colonies when they are dissimilar. Behavioural processes.

Müller, M. M., Bertrand, O. J., Differt, D., & Egelhaaf, M. (2018). The problem of home choice in skyline-based homing. PloS one, 13(3), e0194070.

Categories: Papers from 2018

What goes in … …

Although it is self-evident that the sensory input available to an insect is going to influence subsequent behaviour, it is not true that there will be a simple relationship between the two. Ecological constraints and evolutionary history might result in complex relationships between sensors and navigational behviours. We have two papers here that address this issue in terms of resolution: Palavalli-Nettimi and Narendra; and also, colour: Aksoy and Camlitepe.

Abstract: “Evolution of smaller body size in a given lineage, called miniaturisation, is commonly observed in many animals including ants. It affects various morphological features and is hypothesized to result in inferior behavioural capabilities, possibly owing to smaller sensory organs. To test this hypothesis, we studied whether reduced spatial resolution of compound eyes influences obstacle detection or obstacle avoidance in five different species of ants. We trained all ant species to travel to a sugar feeder. During their return journeys, we placed an obstacle close to the nest entrance. We found that ants with higher spatial resolution exited the corridor, the area covered between either ends of the obstacle, on average 10 cm earlier suggesting they detected the obstacle earlier in their path. Ants with the lowest spatial resolution changed their viewing directions only when they were close to the obstacle. We discuss the effects of miniaturisation on visual navigational competence in ants.”
Palavalli-Nettimi, R., & Narendra, A. (2018). Miniaturisation decreases visual navigational competence in ants. Journal of Experimental Biology, jeb-177238.

Abstract: “Ants constitute one of the most intriguing animal groups with their advanced social lifes, different life histories and sensory modalities, one of which is vision. Chemosensation dominates all other modalities in the accomplishment of different vital tasks, but vision, varying from total blindness in some species to a relatively well-developed vision providing ants the basis for visually-guided behaviors, is also of importance. Although studies on ant vision mainly focused on recognition of and guidance by landmark cues in artificial and/or natural conditions, spectral sensitivities of their compound eyes and ocelli were also disclosed, but to a lesser extent. In this review, we have tried to present current data on the spectral sensitivities of the different ant species tested so far and the different methodological approaches. The results, as well as the similarities and/or discrepancies of the methodologies applied, were compared. General tendencies in ants’ spectral sensitivities are presented in a comparative manner and the role of opsins and ant ocelli in their spectral sensitivity is discussed in addition to the sensitivity of ants to long wavelengths. Extraocular sensitivity was also shown in some ant species. The advantages and/or disadvantages of a dichromatic and trichromatic color vision system are discussed from an ecological perspective.”
Aksoy, V., & Camlitepe, Y. (2018). Spectral sensitivies of ants–a review. Animal Biology. doi: 10.1163/15707563-17000119

Categories: Papers from 2018

Ariadne’s thread and Hansel-and-Gretel’s pebbles.

The remarkable navigational performance of insects is the reason many of us are so interested in studying them, and we often comment on how insects achieve this performance despite small brains and presumed efficient neural mechanisms. However, this dogma is worth challenging as has often been the case with claims that experiments with bees show insects to be capable of constructing and navigating with a metric cognitive map. Whether or not a particular behavioural observation implies the use of a cognitive map is a difficult argument to win and Hoinville and Wehner enter the fray armed with a neat model. They show that an architecture using simply PI and local visual guidance, with each weighted by reliability at each time step, can recreate a range of cue-conflict experiments. The authors reach for a mythical metaphor in their conclusion: “As if equipped with both Ariadne’s thread and Hansel-and-Gretel’s pebbles, insects seem to know where to go rather than where they are on a map.”

Thierry Hoinville and Rüdiger Wehner (2018) Optimal multiguidance integration in insect navigation. PNAS. https://doi.org/10.1073/pnas.1721668115

Categories: Papers from 2018

The birds and the bees II – updated

Well, what do you know. After writing the post below, I got news of another paper from this team, again discussing concepts and ideas developed through insect navigation research, that can (should?) be applied to vertebrate studies. This is a weighty paper, with very thorough sections on the history of insect navigation research and the ideas that have emerged from that research. It looks like tit will be a very useful resource, especially for early career researchers looking to get a handle on the historical literature.

Pritchard, D.J. & Healy, S.D. Learn Behav (2018). https://doi.org/10.3758/s13420-018-0314-5

You wait ages for an excuse to use a good title and then two papers come along at once, and from the same authors as well. Previously Pritchard et al. talked about the connections in foraging ecology between hummingbirds and bees. This is enhanced by their new Animal Behaviour paper. In studies that are reminiscent of the classic Cartwright and Collett papers with bees, birds are tested for where they search for a feeder, whose position was previously defined relative to local landmarks. Whilst it is accepted that panoramic views are important for insects, the spatial behaviour of vertebrates has more often been described with reference to learnt vectors associated to individual landmarks. However, in these experiments the behaviour of birds was consistent with the use of views but not vectors.

Pritchard, D. J., Hurly, T. A., & Healy, S. D. (2018). Wild hummingbirds require a consistent view of landmarks to pinpoint a goal location. Animal Behaviour, 137, 83-94.

Categories: Papers from 2018

What does it look like from up there?

Many ant species forage in trees and this presents an interesting navigational problem. When moving vertically, celestial information will not fall on the normal region of the eye and views will be dominated by canopy or the ground, both of which are likely to be informationally sparse. Freas et al investigated this issue of orienting whilst travelling on a tree trunk, firstly they showed that ants are adept at recovering from displacement to different faces of a tree trunk, such that they are usually oriented back towards their nest by the time they have descended the tree on a homeward trip. This ability is disrupted if the tree is surrounded by a shield that masks the ants’ view of the surroundings – this suggests that views are being used. It seems that to use views, ants occasionally perform a kind of “press-up” such that they hold their body horizontally, a position from which they can match stored views that may even have been stored when the ant was on the ground.

Freas, C. A., Wystrach, A., Narendra, A., & Cheng, K. (2018). The view from the trees: Nocturnal bull ants, Myrmecia midas, use the surrounding panorama while descending from trees. Frontiers in Psychology, 9, 16.

Categories: Papers from 2018

What do bees know about what they are learning?

We all know that when leaving an important location insects perform learning flights or walks as a way of picking up important environmental information. However, the requirements for learning about food locations might be different from the requirements of a nest entrance. Here, Robert et al. look at these differences. Using bumblebee foragers in a controlled situation they were able to make the vicinity of both the nest entrance and a reliable feeder, look identical. Thus when performing the learning flight, the only difference was the “state” or motivation of the individual forager. Differences in learning flights were evident, with flights at the nest longer (befitting its importance perhaps) and flights at feeders/flowers more focussed on the feeder itself, reflecting the value in learning about a flower as an object that might appear in different locations. Intriguingly, this might reflect an active vision difference between object learning and place learning.

Robert, T., Frasnelli, E., de Ibarra, N. H., & Collett, T. S. (2018). Variations on a theme: bumblebee learning flights from the nest and from flowers. Journal of Experimental Biology, jeb-172601.

Categories: Papers from 2018

December Catch-up

Happy New Year to everybody. The first post of 2018 is a catch-up of the papers I didn’t find time to cover in December. Normal service resumed shortly.

The desert ant Cataglyphis fortis inhabits the salt pans of Tunisia. Individual ants leave the nest for foraging trips that can cover distances of more than 1,500 m. Homing ants use path integration, but they also rely on visual and olfactory nest-defining cues to locate the nest entrance. However, nest cues can become ambiguous when they are ubiquitous in the environment. Here we show how ants behave during the nest search when the same cues occur at the nest and along the route. Homing ants focused their search narrowly around a visual or olfactory cue that in training they had experienced only at the nest. However, when ants were trained to the same cue not only at the nest but also repeatedly along the foraging route, they later exhibited a less focused search around the cue. This uncertainty was eliminated when ants had a composite cue at the nest that consisted of two components, one unique to the nest and another that also occurred along the route. Here, the ants focused their search on that part of the binary blend that was presented only at the nest and ignored the other, ubiquitous component. Ants thus not only seem to be able to pinpoint their nest by following learned visual and olfactory cues, but also take into account which cues uniquely specify the nest and which, due to their ubiquity, are less informative and so less reliable.

Huber, R., & Knaden, M. (2017). Homing Ants Get Confused When Nest Cues Are Also Route Cues. Current Biology.

Animals that visit multiple foraging sites face a problem, analogous to the Travelling Salesman Problem, of finding an efcient route. We explored bumblebees’ route development on an array of fve artifcial fowers in which minimising travel distances between individual feeders conficted with minimising overall distance. No previous study of bee spatial navigation has been able to follow animals’ movement during learning; we tracked bumblebee foragers continuously, using harmonic radar, and examined the process of route formation in detail for a small number of selected individuals. On our array, bees did not settle on visit sequences that gave the shortest overall path, but prioritised movements to nearby feeders. Nonetheless, fight distance and duration reduced with experience. This increased efciency was attributable mainly to experienced bees reducing exploration beyond the feeder array and fights becoming straighter with experience, rather than improvements in the sequence of feeder visits. Flight paths of all legs of a fight stabilised at similar rates, whereas the frst few feeder visits became fxed early while bees continued to experiment with the order of later visits. Stabilising early sections of a route and prioritising travel between nearby destinations may reduce the search space, allowing rapid adoption of efcient routes.

Woodgate, J. L., Makinson, J. C., Lim, K. S., Reynolds, A. M., & Chittka, L. (2017). Continuous Radar Tracking Illustrates the Development of Multi-destination Routes of Bumblebees. Scientific reports, 7(1), 17323.

Desert ants that forage solitarily continually update their position relative to the nest through path integration. This is accomplished by combining information from their celestial compass and pedometer. The path integration system can adapt when memories of previous inbound routes do not coincide with the outbound route, through vector calibration. Here, we test the speed and limit of vector calibration in the desert ant Melophorus bagoti by creating directional conflicts between the inbound and outbound routes (45°, 90°, 135°, 180°). The homeward vector appears to calibrate rapidly after training with shifts occurring after three foraging trips, yet the limit of the vector’s plasticity appears to be a maximum of 45°. At 45° conflicts, the vector calibrates the full 45°, suggesting dominance of the previous inbound memories over the outbound cues of the current trip. Yet at larger directional conflicts, vector shifts after training diminish, with foragers in the 90° and 135° conditions showing smaller intermediate shifts between the inbound memories and the current outbound vector. When the conflict is at its maximum (180°), foragers show no calibration, suggesting the outbound vector is dominant. Panorama exposure during training appears to aid foragers orienting to the true nest, but this also appears limited to about a 45° shift and does not improve with training.

Freas, C. A., & Cheng, K. (2017). Limits of vector calibration in the Australian desert ant, Melophorus bagoti. Insectes Sociaux, 1-12.

Categories: Papers from 2017