Easy breezey

One of the features of insect navigation is the redundant use of multiple sources of information. Here we see in the dung beetle model system that individuals use wind cues as well as celestial information.

Abstract “South African ball-rolling dung beetles exhibit a unique orientation behavior to avoid competition for food: after forming a piece of dung into a ball, they efficiently escape with it from the dung pile along a straight-line path. To keep track of their heading, these animals use celestial cues, such as the sun, as an orientation reference. Here we show that wind can also be used as a guiding cue for the ball-rolling beetles. We demonstrate that this mechanosensory compass cue is only used when skylight cues are difficult to read, i.e., when the sun is close to the zenith. This raises the question of how the beetles combine multimodal orientation input to obtain a robust heading estimate. To study this, we performed behavioral experiments in a tightly controlled indoor arena. This revealed that the beetles register directional information provided by the sun and the wind and can use them in a weighted manner. Moreover, the directional information can be transferred between these 2 sensory modalities, suggesting that they are combined in the spatial memory network in the beetle’s brain. This flexible use of compass cue preferences relative to the prevailing visual and mechanosensory scenery provides a simple, yet effective, mechanism for enabling precise compass orientation at any time of the day.”

 

Marie Dacke, Adrian T. A. Bell, James J. Foster, Emily J. Baird, Martin F.Strube-Bloss, Marcus J. Byrne, Basil el Jundi (2019) Multimodal cue integration in the dung beetle compass. PNAS, 201904308; DOI:10.1073/pnas.1904308116

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What you see is what you know

To understand the interactions between visual homing and the information provided by different visual environments, we need as many studies as possible that relate navigational behaviour to detailed analysisof the visual world. Here, Freas and Cheng present one such study on the navigation of nocturnal bull ants.

Abstract: Nocturnal ants forage and navigate during periods of reduced light, making detection of visual cues difficult, yet they are skilled visual navigators. These foragers retain visual panoramic memories both around the nest and along known routes for later use, to return to previously visited food sites or to the nest. Here, we explore the navigational knowledge of the nocturnal bull ant Myrmecia midas by investigating differences in nestward homing after displacement of three forager groups based on similarities in the panoramas between the release site and previously visited locations. Foragers that travel straight to the foraging tree or to trees close to the nest show reduced navigational success in orienting and returning from displacements compared with individuals that forage further from the nest site. By analysing the cues present in the panorama, we show that multiple metrics of forager navigational performance correspond with the degree of similarity between the release site panorama and panoramas of previously visited sites. In highly cluttered environments, where panoramas change rapidly over short distances, the views acquired near the nest are useful only over a small area and memories acquired along foraging routes become critical.

Freas, C. A., & Cheng, K. (2019). Panorama similarity and navigational knowledge in the nocturnal bull ant Myrmecia midas. Journal of Experimental Biology, 222(11), jeb193201.

The many uses of optic flow

For flying insects, optic flow is used to measure distances, speed, altitude and distance to objects; It is a flexible piece of sensory input. Here we have two papers that relate to these uses of optic flow. Chatterjee et al show tha the distance information used in waggle dances actually represents averages of a few preceding journeys, which could be a noise reduction mechanism or perhaps an ecological tuning to send bees to the centre of the patch of recently rewarding resources. Lecoeur et al look at the specialisations whereby information from different parts of the visual field is used for different behaviours.

Abstract: Flight through cluttered environments, such as forests, poses great challenges for animals and machines alike because even small changes in flight path may lead to collisions with nearby obstacles. When flying along narrow corridors, insects use the magnitude of visual motion experienced in each eye to control their position, height, and speed but it is unclear how this strategy would work when the environment contains nearby obstacles against a distant background. To minimise the risk of collisions, we would expect animals to rely on the visual motion generated by only the nearby obstacles but is this the case? To answer this, we combine behavioural experiments with numerical simulations and provide the first evidence that bumblebees extract the maximum rate of image motion in the frontal visual field to steer away from obstacles. Our findings also suggest that bumblebees use different optic flow calculations to control lateral position, speed, and height.
Lecoeur, J., Dacke, M., Floreano, D., & Baird, E. (2019). The role of optic flow pooling in insect flight control in cluttered environments. Scientific reports, 9(1), 7707.

Abstract: Honey bees can communicate navigational information which makes them unique amongst all prominent insect navigators. Returning foragers recruit nest mates to a food source by communicating flight distance and direction using a small scale walking pattern: the waggle dance. It is still unclear how bees transpose flight information to generate corresponding dance information. In single feeder shift experiments, we monitored for the first time how individual bees update dance duration after a shift of feeder distance. Interestingly, the majority of bees (86%) needed two or more foraging trips to update dance duration. This finding demonstrates that transposing flight navigation information to dance information is not a reflexive behavior. Furthermore, many bees showed intermediate dance durations during the update process, indicating that honey bees highly likely use two memories: (i) a recently acquired navigation experience and (ii) a previously stored flight experience. Double-shift experiments, in which the feeder was moved forward and backward, created an experimental condition in which honey bee foragers did not update dance duration; suggesting the involvement of more complex memory processes. Our behavioral paradigm allows the dissociation of foraging and dance activity and opens the possibility of studying the molecular and neural processes underlying the waggle dance behavior.
Chatterjee, A., George, E. A., Prabhudev, M. V., Basu, P., & Brockmann, A. (2019). Honey bees flexibly use two navigational memories when updating dance distance information. Journal of Experimental Biology, jeb-195099.

Fly brains and social insect behaviour

What we know about Path Integration in insects has mainly be learnt from behaviour studies with ants and bees, but in recent times, studies of neural circuits in flies have given us fascinating clues about how PI might be implemented in the brain. Here in this knowledgeable and broad review, Tom Collett talks about aspects of the social insect behaviour and the computations required. He then discusses how neural circuits might implement these computations. As always with Tom, this is a great read.

Collett, T. S. (2019). Path integration: how details of the honeybee waggle dance and the foraging strategies of desert ants might help in understanding its mechanisms. Journal of Experimental Biology, 222(11), jeb205187.

When to learn?

We know that the learning flights of bees and wasps are crucial for visual homing, but it is still a bit of a mystery as to exactly when during these flights individuals actually learn visual information. Given the immense practical challenges in studying learning flights, modelling can play a role in identifying plausible control rules. Here, in simulations of real world environments, Schulte et al. test such rules for the control of learning flights and how they might relate to subsequent visual homing.

Abstract: “Wasps and bees perform learning flights when leaving their nest or food locations for the first time during which they acquire visual information that enables them to return successfully. Here we present and test a set of simple control rules underlying the execution of learning flights that closely mimic those performed by ground-nesting wasps. In the simplest model, we assume that the angle between flight direction and the nest direction as seen from the position of the insect is constant and only flips sign when pivoting direction around the nest is changed, resulting in a concatenation of piecewise defined logarithmic spirals. We then added characteristic properties of real learning flights, such as head saccades and the condition that the nest entrance within the visual field is kept nearly constant to describe the development of a learning flight in a head-centered frame of reference, assuming that the retinal position of the nest is known. We finally implemented a closed-loop simulation of learning flights based on a small set of visual control rules. The visual input for this model are rendered views generated from 3D reconstructions of natural wasp nesting sites, and the retinal nest position is controlled by means of simple template-based tracking. We show that naturalistic paths can be generated without knowledge of the absolute distance to the nest or of the flight speed. We demonstrate in addition that nest-tagged views recorded during such simulated learning flights are sufficient for a homing agent to pinpoint the goal, by identifying nest direction when encountering familiar views. We discuss how the information acquired during learning flights close to the nest can be integrated with long-range homing models.”

Schulte, P., Zeil, J., & Stürzl, W. (2019). An insect-inspired model for acquiring views for homing. Biological cybernetics, 1-13.

Navigation inside the nest

Summary: “Animal navigation relies on the available environmental cues and, where present, visual cues typically dominate. While much is known about vision-assisted navigation, knowledge of navigation in the dark is scarce. Here, we combine individual tracking, dynamic modular nest structures, and spatially resolved chemical profiling to study how Camponotus fellah ants navigate within the dark labyrinth of their nest. We find that, contrary to ant navigation above ground, underground navigation cannot rely on long-range information. This limitation emphasizes the ants’ capabilities associated with other navigational strategies. Indeed, apart from gravity, underground navigation relies on self-referenced memories of multiple locations and on socially generated chemical cues placed at decision points away from the target. Moreover, the ants quickly readjust the weights attributed to these information sources in response to environmental changes. Generally, studying well-known behaviors in a variety of environmental contexts holds the potential of revealing new insights into animal cognition.”

Heyman, Y., Vilk, Y., & Feinerman, O. (2019). Ants use multiple spatial memories and chemical pointers to navigate their nest. iScience.

Sensory ecology of compass cues

Abstract “To transport their balls of dung along a constant bearing, diurnal savannah-living dung beetles rely primarily on the sun for compass information. However, in more cluttered environments, such as woodlands, this solitary compass cue is frequently hidden from view by surrounding vegetation. In these types of habitats, insects can, instead, rely on surrounding landmarks, the canopy pattern, or wide-field celestial cues, such as polarised skylight, for directional information. Here, we investigate the compass orientation strategy behind straight-line orientation in the diurnal woodland-living beetle Sisyphus fasciculatus. We found that, when manipulating the direction of polarised skylight, Si. fasciculatus responded to this change with a similar change in bearing. However, when the apparent position of the sun was moved, the woodland-living beetle did not change its direction of travel. In contrast, the savannah-living beetle Scarabaeus lamarcki responded to the manipulation of the solar position with a corresponding change in bearing. These results suggest that the dominant compass cue used for straight-line orientation in dung beetles may be determined by the celestial cue that is most prominent in their preferred habitat.”

Khaldy, L., Tocco, C., Byrne, M., Baird, E., & Dacke, M. (2019). Straight-line orientation in the woodland-living beetle Sisyphus fasciculatus. Journal of Comparative Physiology A, 1-9.