Insect Navigation Research Articles

Path integration, views, search, and matched filters: the contributions of Rüdiger Wehner to the study of orientation and navigation.

Rüdiger Wehner's work on insect orientation and navigation has influenced many scientists studying navigation, not only in ants and bees, but in other animals as well. We review the scientific legacy of six topics arising from Wehner's work on navigation. The polarisation compass is a chapter with a lot of behavioural and neurobiological detail. It has influenced the study of polarisation vision in other systems, and led Wehner to formulate the concept of a matched filter. The matched filter has probably had earlier formulations, but Wehner's paper on it has been much cited in studies on navigation and in other fields. The polarisation compass serves the task of path integration in insects. Work on path integration took off in the 1980s with work on desert ants and rodents. The use of terrestrial visual cues, landmarks or the panorama in view-based matching is another major theme of navigational research today. Search strategies were also well described in desert ants, and this line of research helped to launch theoretical and empirical developments in searching behaviour, now a lively area of research. Finally, robotic work has often drawn inspiration from work on insect navigation. We end with some discussion of current research directions.

What is the relationship between visual environment and the form of ant learning-walks? An in silico investigation of insect navigation

The learning walks of ants are an excellent opportunity to study the interaction between brain, body and environment from which adaptive behaviour emerges. Learning walks are a behaviour with the specific function of storing visual information around a goal in order to simplify the computational problem of visual homing, that is, navigation back to a goal. However, it is not known at present why learning walks take the stereotypical shapes they do. Here we investigate how learning-walk form, visual surroundings and the interaction between the two affect homing performance in a range of virtual worlds when using a simple view-based homing algorithm. We show that the ideal form for a learning walk is environment-specific. We also demonstrate that the distant panorama and small objects at an intermediate distance, particularly when the panorama is obscured, are important aspects of the visual environment both when determining the ideal learning walk and when using stored views to navigate. Implications are discussed in the context of behavioural research into the learning walks of ants.

A biologically inspired navigation concept based on the Landmark-Tree map for efficient long-distance robot navigation

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Benchmark 3D Models of Natural Navigation Environments @ www.InsectVision.org

A number of models for insect navigation have been developed to explain the results of behavioural experiments and to be tested in simulations or on robotic platforms. However, it remains difficult to evaluate these models in a generic and objective way, beyond the specific results they have been developed to explain and beyond the specific environments and applications for which they have been developed. Here we introduce a realistic and controllable environment, that allows one to test visual navigation algorithms in natural and complex conditions and that can be shared with the research community. We have launched a publicly accessible service at www.insectvision.org that allows users to render panoramic views at any position within 3D models of natural habitats and to filter them with the sampling array of honeybee compound eyes. Using 3D laser scans and multi-camera images, we generate 3D models of environments (see accompanying abstract “Mapping the Navigational Information Content of Insect Habitats” by Sturzl et al.). These models allow us to render views of the scene from arbitrary viewpoints within the acquired workspace. We can then move a virtual insect, in our case a bee, through this environment along any path and reconstruct a view from the cockpit of the insect, including a model of its compound eye sampling array, if available (see Fig. 1). This not only allows us to investigate visual navigation mechanisms in insects, but also the performance of specific models of navigation under real-life conditions. The currently available 3D model is based on data acquired in the habitat of ground nesting wasps and bees. We recorded learning and homing flights, which are also available online. We see this work as the first step towards a growing database that can be used for comparative analysis and for rigorous tests of insect navigation models. The platform can also be used for benchmarking navigation and flight-control models in biology and robotics.

Models of visual navigation in ants

Event Abstract Back to Event Models of visual navigation in ants Andrew Philippides1*, Antoine Wystrach1, Michael Mangan2, Bart Baddeley1 and Paul Graham1 1 University of Sussex, Centre for Computational Neuroscience and Robotics, United Kingdom 2 University of Edinburgh, Informatics, United Kingdom Here we present a model of visually guided navigation in ants that captures the known properties of real behaviour whilst retaining mechanistic simplicity and thus biological plausibility. For an ant, the coupling of movement and viewing direction means that a familiar view specifies a familiar direction of movement. Since the views experienced along a habitual route will be more familiar, route navigation can be re-cast as a search for familiar views. This search can be performed with a simple scanning routine, a behaviour ants have been observed to perform. We test our model in a realistic simulation of a desert ant’s environment and also with images viewed by ants during behavioural experiments. Our results indicate that, not only is the approach successful, but also that the resultant behaviour shows characteristics of the paths of ants. As such, we believe the model provides a general demonstration that visually guided routes can be produced with parsimonious mechanisms that do not specify when or what to learn, nor separate routes into sequences of waypoints. Finally, we contrast our approach with the classical ‘snapshot’ model in which views are used as attractors to a point in space. This presentation summarises results from Baddeley et al. (2012) and Wystrach et al. (2013). Acknowledgements This work was funded by the the EPSRC, BBSRC and the Fyssen Foundation References Baddeley, B., Graham, P., Husbands, P. and Philippides, A. (2012) A Model of Ant Route Navigation Driven by Scene Familiarity. PLoS Computational Biology, 8 (1). e1002336. Wystrach, A., Mangan, M., Philippides, A. and Graham, P. Snapshots in ants? New interpretations of paradigmatic experiments. J Exp Biol online: jeb.082941 Keywords: insect navigation, Visual homing, Desert ants, Modelling of Behaviour, Computational Biology Conference: International Conference on Invertebrate Vision, Fjälkinge, Sweden, 1 Aug - 8 Aug, 2013. Presentation Type: Oral presentation preferred Topic: Navigation and orientation Citation: Philippides A, Wystrach A, Mangan M, Baddeley B and Graham P (2019). Models of visual navigation in ants. Front. Physiol. Conference Abstract: International Conference on Invertebrate Vision. doi: 10.3389/conf.fphys.2013.25.00060 Copyright: The abstracts in this collection have not been subject to any Frontiers peer review or checks, and are not endorsed by Frontiers. They are made available through the Frontiers publishing platform as a service to conference organizers and presenters. The copyright in the individual abstracts is owned by the author of each abstract or his/her employer unless otherwise stated. Each abstract, as well as the collection of abstracts, are published under a Creative Commons CC-BY 4.0 (attribution) licence (https://creativecommons.org/licenses/by/4.0/) and may thus be reproduced, translated, adapted and be the subject of derivative works provided the authors and Frontiers are attributed. For Frontiers’ terms and conditions please see https://www.frontiersin.org/legal/terms-and-conditions. Received: 19 Feb 2013; Published Online: 09 Dec 2019. * Correspondence: Dr. Andrew Philippides, University of Sussex, Centre for Computational Neuroscience and Robotics, Brighton, United Kingdom, andrewop@sussex.ac.uk Login Required This action requires you to be registered with Frontiers and logged in. To register or login click here. Abstract Info Abstract The Authors in Frontiers Andrew Philippides Antoine Wystrach Michael Mangan Bart Baddeley Paul Graham Google Andrew Philippides Antoine Wystrach Michael Mangan Bart Baddeley Paul Graham Google Scholar Andrew Philippides Antoine Wystrach Michael Mangan Bart Baddeley Paul Graham PubMed Andrew Philippides Antoine Wystrach Michael Mangan Bart Baddeley Paul Graham Related Article in Frontiers Google Scholar PubMed Abstract Close Back to top Javascript is disabled. Please enable Javascript in your browser settings in order to see all the content on this page.

Mapping the Navigational Information Content of Insect Habitats

For developing and validating models of insect navigation it is essential to identify the visual input insects experience in their natural habitats. Here we report on the development of methods to reconstruct what insects see when making navigational decisions and critically assess the current limitations of such methods. We used a laser-range finder as well as camera-based methods to capture the 3D structure and the appearance of outdoor environments. Both approaches produce coloured point clouds that allow within the model scale the reconstruction of views at defined positions and orientations. For instance, we filmed bees and wasps with a high-speed stereo camera system to estimate their 3D flight paths and gaze direction. The high-speed system is registered with a 3D model of the same environment, such that panoramic images can be rendered along the insects’ flight paths (see accompanying abstract “Benchmark 3D-models of natural navigation environments @ www.InsectVision.org” by Mair et al.). The laser-range finder (see figure A) is equipped with a rotating camera that provides colour information for the measured 3D points. This system is robust and easy-to-use in the field generating high resolution data (about 50 × 106 points) with large field of view, up to a distance of 80 m at typical acquisition times of about 8 minutes. However, a large number of scans at different locations has to be recorded and registered to account for occlusions. In comparison, data acquisition in camera-based reconstruction from multiple view-points is fast, but model generation is computationally more complex due to bundle adjustment and dense pair-wise stereo computation (see figure B, C for views rendered from a 3D model based on 6 image pairs). In addition it is non-trivial and often time-consuming in the field to ensure the acquisition of sufficient information. We are currently developing the tools that will allow us to combine the results of laser-scanner and camera-based 3D reconstruction methods.

Bio-inspired polarized skylight-based navigation sensors: a review.

Animal senses cover a broad range of signal types and signal bandwidths and have inspired various sensors and bioinstrumentation devices for biological and medical applications. Insects, such as desert ants and honeybees, for example, utilize polarized skylight pattern-based information in their navigation activities. They reliably return to their nests and hives from places many kilometers away. The insect navigation system involves the dorsal rim area in their compound eyes and the corresponding polarization sensitive neurons in the brain. The dorsal rim area is equipped with photoreceptors, which have orthogonally arranged small hair-like structures termed microvilli. These are the specialized sensors for the detection of polarized skylight patterns (e-vector orientation). Various research groups have been working on the development of novel navigation systems inspired by polarized skylight-based navigation in animals. Their major contributions are critically reviewed. One focus of current research activities is on imitating the integration path mechanism in desert ants. The potential for simple, high performance miniaturized bioinstrumentation that can assist people in navigation will be explored.

Cognition in insects

A traditional view of cognition is that it involves an internal process that represents, tracks or predicts an external process. This is not a general characteristic of all complex neural processing or feedback control, but rather implies specific forms of processing giving rise to specific behavioural capabilities. In this paper, I will review the evidence for such capabilities in insect navigation and learning. Do insects know where they are, or do they only know what to do? Do they learn what stimuli mean, or do they only learn how to behave?

Collective navigation of cargo-carrying swarms

Much effort has been devoted to the study of swarming and collective navigation of micro-organisms, insects, fish, birds and other organisms, as well as multi-agent simulations and to the study of real robots. It is well known that insect swarms can carry cargo. The studies here are motivated by a less well-known phenomenon: cargo transport by bacteria swarms. We begin with a concise review of how bacteria swarms carry natural, micrometre-scale objects larger than the bacteria (e.g. fungal spores) as well as man-made beads and capsules (for drug delivery). A comparison of the trajectories of virtual beads in simulations (using different putative coupling between the virtual beads and the bacteria) with the observed trajectories of transported fungal spores implies the existence of adaptable coupling. Motivated by these observations, we devised new, multi-agent-based studies of cargo transport by agent swarms. As a first step, we extended previous modelling of collective navigation of simple bacteria-inspired agents in complex terrain, using three putative models of agent-cargo coupling. We found that cargo-carrying swarms can navigate efficiently in a complex landscape. We further investigated how the stability, elasticity and other features of agent-cargo bonds influence the collective motion and the transport of the cargo, and found sharp phase shifts and dual successful strategies for cargo delivery. Further understanding of such mechanisms may provide valuable clues to understand cargo-transport by smart swarms of other organisms as well as by man-made swarming robots.

How ants find their way

Summary Insects use a wide range of tools for orientation, including visual memory, smell, and counting steps. The tricky question is how they combine and compute different kinds of inputs, and whether their methods can help us understand more complex brains or create artificial ones. Michael Gross investigates.

What can we learn from studies of insect navigation?

The remarkable navigational abilities of social insects are proof that small brains can produce exquisitely efficient, robust navigation in complex environments. Because social insects produce specialist foragers that are amenable to field and laboratory studies, they have been productive model systems for studies of navigation. Ideas derived from these studies of insect navigation have shown how simple mechanisms can produce robust and seemingly complex behaviour. This is important for a general understanding of spatial cognition as these ‘insect-like’ navigational behaviours are probably phylogenetically widespread. Current insect research is helping to show how simple panoramic views, without the need for cognitive processes such as object identification or labelling, can provide explanations for many findings, including behaviours that in the vertebrate literature have traditionally drawn conclusions about sophisticated high-level spatial modules or learning rules. Recent insect navigation research has only been possible because of techniques enabling the recording of visual scenes from the perspective of the insect. Without such techniques one has to intuit an animal's point of view (its Umwelt) and we discuss how this may lead to unhelpful assumptions about the cues available for navigation.

Spatial Reorientation by Geometry in Bumblebees

Human and non-human animals are capable of using basic geometric information to reorient in an environment. Geometric information includes metric properties associated with spatial surfaces (e.g., short vs. long wall) and left-right directionality or ‘sense’ (e.g. a long wall to the left of a short wall). However, it remains unclear whether geometric information is encoded by explicitly computing the layout of surface geometry or by matching images of the environment. View-based spatial encoding is generally thought to hold for insect navigation and, very recently, evidence for navigation by geometry has been reported in ants but only in a condition which does not allow the animals to use features located far from the goal. In this study we tested the spatial reorientation abilities of bumblebees (Bombus terrestris). After spatial disorientation, by passive rotation both clockwise and anticlockwise, bumblebees had to find one of the four exit holes located in the corners of a rectangular enclosure. Bumblebees systematically confused geometrically equivalent exit corners (i.e. corners with the same geometric arrangement of metric properties and sense, for example a short wall to the left of a long wall). However, when one wall of the enclosure was a different colour, bumblebees appeared to combine this featural information (either near or far from the goal) with geometric information to find the correct exit corner. Our results show that bumblebees are able to use both geometric and featural information to reorient themselves, even when features are located far from the goal.

Ants’ searching behaviour can be biased by recent experience of familiar scenes: a newly observed interaction between innate strategies and learnt information

Event Abstract Back to Event Ants’ searching behaviour can be biased by recent experience of familiar scenes: a newly observed interaction between innate strategies and learnt information Antoine Wystrach1, 2* 1 University of Sussex, Life Sciences, United Kingdom 2 Macquarie University, Biological sciences, Australia Ants can use multiple sources of information to navigate, but do not seem to integrate all this information into a unified representation of the world. Rather, the available information appears to serve three distinct navigational systems: Path Integration, systematic search and the use of learnt information, mainly vision. There is a strong tradition of interpreting ant behaviour as resulting from simple interactions between these independent strategies. However, here we report on a newly observed behaviour which suggests a sophisticated interaction between the components of an ant’s navigational toolkit. We enclosed an ant nest so that the only foraging location was along a narrow 8m “road” to a permanently stocked feeder. Returning ants could be captured at precise locations, so that we had control of the current state of their path integration system, i.e. how far did the ants think they were away from the nest. These ants were then released on an unfamiliar test ground, where there initial headings were recorded. Ants captured close to the nest, so that they had run-off their path integrated vector, did not show the undirected headings we would expect of ants entering into a systematic search. Instead, these ants backtracked in the direction they had just travelled. Interestingly, ants that ran off their Path Integrated vector by being forced to run the first 4m of the route twice, did show undirected headings characteristic of systematic search. Therefore, we see that only ants that have recently seen the familiar visual surrounds close to the nest, will backtrack when placed in unfamiliar terrain. The ecological function of such behaviour is clear, as it increases their chance of returning to familiar terrain. What is interesting is that the decision-making process requires sophisticated interactions between navigational systems. It involves the compass system modulating the initial direction of the search when in unfamiliar terrain on the basis of the recently experienced familiar view. This raises fundamental questions about the cognitive architectures underlying ant navigation. Acknowledgements I thank Sebastian Schwarz, Alice Baniel, Ken Cheng and Paul Graham for constructive discussions and help on the field. Keywords: insect navigation, path integration, Searching behaviour, sensory integration, Visual memories Conference: Tenth International Congress of Neuroethology, College Park. Maryland USA, United States, 5 Aug - 10 Aug, 2012. Presentation Type: Poster (but consider for Participant Symposium) Topic: Orientation and Navigation Citation: Wystrach A (2012). Ants’ searching behaviour can be biased by recent experience of familiar scenes: a newly observed interaction between innate strategies and learnt information. Conference Abstract: Tenth International Congress of Neuroethology. doi: 10.3389/conf.fnbeh.2012.27.00185 Copyright: The abstracts in this collection have not been subject to any Frontiers peer review or checks, and are not endorsed by Frontiers. They are made available through the Frontiers publishing platform as a service to conference organizers and presenters. The copyright in the individual abstracts is owned by the author of each abstract or his/her employer unless otherwise stated. Each abstract, as well as the collection of abstracts, are published under a Creative Commons CC-BY 4.0 (attribution) licence (https://creativecommons.org/licenses/by/4.0/) and may thus be reproduced, translated, adapted and be the subject of derivative works provided the authors and Frontiers are attributed. For Frontiers’ terms and conditions please see https://www.frontiersin.org/legal/terms-and-conditions. Received: 28 Apr 2012; Published Online: 07 Jul 2012. * Correspondence: Dr. Antoine Wystrach, University of Sussex, Life Sciences, Brighton, United Kingdom, antoine.wystrach@univ-tlse3.fr Login Required This action requires you to be registered with Frontiers and logged in. To register or login click here. Abstract Info Abstract The Authors in Frontiers Antoine Wystrach Google Antoine Wystrach Google Scholar Antoine Wystrach PubMed Antoine Wystrach Related Article in Frontiers Google Scholar PubMed Abstract Close Back to top Javascript is disabled. Please enable Javascript in your browser settings in order to see all the content on this page.

Sky compass orientation in diurnal and nocturnal dung beetles

Event Abstract Back to Event Sky compass orientation in diurnal and nocturnal dung beetles Basil El Jundi1*, Jochen Smolka1, Emily Baird1, Marcus Byrne2, Marie Dacke1 and Eric Warrant1 1 University of Lund, Department of Biology, Sweden 2 University of Witwatersrand, Department of Biology, South Africa To escape from the intense competition at the dung pile, ball-rolling dung beetles have developed a unique and simple orientation behavior in which they roll a dung ball away from the dung pile in a straight line. To keep this straight path, dung beetles use celestial compass cues such as the sun, the moon and the pattern of polarized light formed around these sources (Dacke et al., 2003, Nature, 424: 33). These sky compass cues provide all the precision these insects need to ensure a safe exit from the dung pile. However, whether the relevance of individual sky compass signals varies between diurnal and nocturnal dung beetle is still an open question. Furthermore, nothing is known concerning the neural substrate that allows nocturnal dung beetles to orientate at light levels a million times dimmer than those that allow orientation in their diurnal relatives. To investigate these questions, we analyzed the orientation performance in a diurnal (Scarabaeus nigroaeneus) and a nocturnal (S. satyrus) beetle species to celestial compass signals, both in the laboratory and in their natural habitat in South Africa. We tested whether a change in the orientation of polarized light in the laboratory or a shift of the plane of skylight polarization in the field affects the rolling bearing of the beetles. In addition, we studied how beetles change their bearing in response to a 180° reflection of the sun. Finally, we used a combination of immunohistochemistry, confocal microscopy and 3D reconstruction of different brain areas to show how nocturnality affects the neuroanatomy of the dung beetle brain. Our data show that both diurnal and nocturnal dung beetle species use patterns of polarized light (either artificial or from the sun/moon) and the sun/moon in a similar way for straight line orientation. While brain areas in the optic lobes are remarkably larger in the nocturnal species compared to the diurnal species, our preliminary data suggest that, in the central brain, the relative volumes of brain areas dedicated to visual processing are similar. These results indicate that sky compass signals in the brain of nocturnal beetles converge more strongly towards late processing stages and thus, could lead to a greater sensitivity in dim light conditions. Keywords: Anatomy, Behavior, dung beetle, Insect brain, insect navigation, Orientation, polarized light, sky compass signals Conference: Tenth International Congress of Neuroethology, College Park. Maryland USA, United States, 5 Aug - 10 Aug, 2012. Presentation Type: Poster (but consider for student poster award) Topic: Orientation and Navigation Citation: El Jundi B, Smolka J, Baird E, Byrne M, Dacke M and Warrant E (2012). Sky compass orientation in diurnal and nocturnal dung beetles. Conference Abstract: Tenth International Congress of Neuroethology. doi: 10.3389/conf.fnbeh.2012.27.00231 Copyright: The abstracts in this collection have not been subject to any Frontiers peer review or checks, and are not endorsed by Frontiers. They are made available through the Frontiers publishing platform as a service to conference organizers and presenters. The copyright in the individual abstracts is owned by the author of each abstract or his/her employer unless otherwise stated. Each abstract, as well as the collection of abstracts, are published under a Creative Commons CC-BY 4.0 (attribution) licence (https://creativecommons.org/licenses/by/4.0/) and may thus be reproduced, translated, adapted and be the subject of derivative works provided the authors and Frontiers are attributed. For Frontiers’ terms and conditions please see https://www.frontiersin.org/legal/terms-and-conditions. Received: 30 Apr 2012; Published Online: 07 Jul 2012. * Correspondence: Dr. Basil El Jundi, University of Lund, Department of Biology, Lund, Sweden, basil.el.jundi@ntnu.no Login Required This action requires you to be registered with Frontiers and logged in. To register or login click here. Abstract Info Abstract The Authors in Frontiers Basil El Jundi Jochen Smolka Emily Baird Marcus Byrne Marie Dacke Eric Warrant Google Basil El Jundi Jochen Smolka Emily Baird Marcus Byrne Marie Dacke Eric Warrant Google Scholar Basil El Jundi Jochen Smolka Emily Baird Marcus Byrne Marie Dacke Eric Warrant PubMed Basil El Jundi Jochen Smolka Emily Baird Marcus Byrne Marie Dacke Eric Warrant Related Article in Frontiers Google Scholar PubMed Abstract Close Back to top Javascript is disabled. Please enable Javascript in your browser settings in order to see all the content on this page.

Information processing in the Drosophila Olfactory System: From Odors to Kenyon cells

Information processing in the Drosophila Olfactory System: From Odors to Kenyon cells

Odometry and insect navigation

Animals have needed to find their way about almost since a free-living life style evolved. Particularly, if an animal has a home--shelter or nesting site--true navigation becomes necessary to shuttle between this home and areas of other activities, such as feeding. As old as navigation is in the animal kingdom, as diverse are its mechanisms and implementations, depending on an organism's ecology and its endowment with sensors and actuators. The use of landmarks for piloting or the use of trail pheromones for route following have been examined in great detail and in a variety of animal species. The same is true for senses of direction--the compasses for navigation--and the construction of vectors for navigation from compass and distance cues. The measurement of distance itself--odometry--has received much less attention. The present review addresses some recent progress in the understanding of odometers in invertebrates, after outlining general principles of navigation to put odometry in its proper context. Finally, a number of refinements that increase navigation accuracy and safety are addressed.

No Need for a Cognitive Map: Decentralized Memory for Insect Navigation

In many animals the ability to navigate over long distances is an important prerequisite for foraging. For example, it is widely accepted that desert ants and honey bees, but also mammals, use path integration for finding the way back to their home site. It is however a matter of a long standing debate whether animals in addition are able to acquire and use so called cognitive maps. Such a ‘map’, a global spatial representation of the foraging area, is generally assumed to allow the animal to find shortcuts between two sites although the direct connection has never been travelled before. Using the artificial neural network approach, here we develop an artificial memory system which is based on path integration and various landmark guidance mechanisms (a bank of individual and independent landmark-defined memory elements). Activation of the individual memory elements depends on a separate motivation network and an, in part, asymmetrical lateral inhibition network. The information concerning the absolute position of the agent is present, but resides in a separate memory that can only be used by the path integration subsystem to control the behaviour, but cannot be used for computational purposes with other memory elements of the system. Thus, in this simulation there is no neural basis of a cognitive map. Nevertheless, an agent controlled by this network is able to accomplish various navigational tasks known from ants and bees and often discussed as being dependent on a cognitive map. For example, map-like behaviour as observed in honey bees arises as an emergent property from a decentralized system. This behaviour thus can be explained without referring to the assumption that a cognitive map, a coherent representation of foraging space, must exist. We hypothesize that the proposed network essentially resides in the mushroom bodies of the insect brain.

How might ants use panoramic views for route navigation?

Studies of insect navigation have demonstrated that insects possess an interesting and sophisticated repertoire of visual navigation behaviours. Ongoing research seeks to help us understand how these behaviours are controlled in natural complex environments. A necessary complement to behavioural studies is an understanding of the sensory ecology within which an animal behaves. To this end we have analysed ants'-perspective views of a habitat within which desert ant navigation is well studied. Results from our analysis suggest that: parsimonious visual strategies for homing and route guidance are effective over behaviourally useful distances even in cluttered environments; that these strategies can function effectively using only the skyline heights as input; and that the simplicity and efficacy of using stored views as a visual compass makes it a viable and robust mechanism for route guidance.

Vision and Visual Navigation in Nocturnal Insects

With their highly sensitive visual systems, nocturnal insects have evolved a remarkable capacity to discriminate colors, orient themselves using faint celestial cues, fly unimpeded through a complicated habitat, and navigate to and from a nest using learned visual landmarks. Even though the compound eyes of nocturnal insects are significantly more sensitive to light than those of their closely related diurnal relatives, their photoreceptors absorb photons at very low rates in dim light, even during demanding nocturnal visual tasks. To explain this apparent paradox, it is hypothesized that the necessary bridge between retinal signaling and visual behavior is a neural strategy of spatial and temporal summation at a higher level in the visual system. Exactly where in the visual system this summation takes place, and the nature of the neural circuitry that is involved, is currently unknown but provides a promising avenue for future research.

Visual Targeting of Motor Actions in Climbing Drosophila

Drosophila melanogaster flies cross surmountable gaps in their walkway of widths exceeding their body length with an astounding maneuver but avoid attempts at insurmountable gaps by visual width estimation. Different mutant lines affect specific aspects of this maneuver, indicating a high complexity and modularity of the underlying motor control. Here we report on two mutants, ocelliless(1) and tay bridge(1), that, although making a correct decision to climb, fail dramatically in aiming at the right direction. Both mutants show structural defects in the protocerebral bridge, a central complex neuropil formed like a handlebar spanning the brain hemispheres. The bridge has been implicated in step-length control in walking flies and celestial E-vector orientation in locusts. In rescue experiments using tay bridge(1) flies, the integrity of the bridge was reestablished, concomitantly leading to a significant improvement of their orientation at the gap. Although producing directional scatter, their attempts were clearly aimed at the landing site. However, this partial rescue was lost in these flies at a reduced-visibility landing site. We therefore conclude that the protocerebral bridge is an essential part of a visual targeting network that transmits directional clues to the motor output via a known projection system.