The Antarium: A Reconstructed Visual Reality Device for Ant Navigation Research

We constructed a large projection device (the Antarium) with 20,000 UV-Blue-Green LEDs that allows us to present tethered ants with views of their natural foraging environment. The ants walk on an air-cushioned trackball, their movements are registered and can be fed back to the visual panorama. Views are generated in a 3D model of the ants' environment so that they experience the changing visual world in the same way as they do when foraging naturally. The Antarium is a biscribed pentakis dodecahedron with 55 facets of identical isosceles triangles. The length of the base of the triangles is 368 mm resulting in a device that is roughly 1 m in diameter. Each triangle contains 361 blue/green LEDs and nine UV LEDs. The 55 triangles of the Antarium have 19,855 Green and Blue pixels and 495 UV pixels, covering 360◦ azimuth and elevation from −50◦ below the horizon to +90◦ above the horizon. The angular resolution is 1.5◦ for Green and Blue LEDs and 6.7◦ for UV LEDs, offering 65,536 intensity levels at a flicker frequency of more than 9,000 Hz and a framerate of 190 fps. Also, the direction and degree of polarisation of the UV LEDs can be adjusted through polarisers mounted on the axles of rotary actuators. We build 3D models of the natural foraging environment of ants using purely camera-based methods. We reconstruct panoramic scenes at any point within these models, by projecting panoramic images onto six virtual cameras which capture a cube-map of images to be projected by the LEDs of the Antarium. The Antarium is a unique instrument to investigate visual navigation in ants. In an open loop, it allows us to provide ants with familiar and unfamiliar views, with completely featureless visual scenes, or with scenes that are altered in spatial or spectral composition. In closed-loop, we can study the behavior of ants that are virtually displaced within their natural foraging environment. In the future, the Antarium can also be used to investigate the dynamics of navigational guidance and the neurophysiological basis of ant navigation in natural visual environments.We acknowledge financial support from Australian Research Council (ARC) Discovery Project Grants (DP150101172 and DP150102699), an ARC Future Fellowship (FT140100221), the Hermon Slade Foundation (HSF 10/7), the Australian National University Endowment Fund, and private funding. We are grateful to Ken Cheng for providing initial funding during the start phase of this project. TM was supported for part of the work by the Australian Government, via grant AUSMURIB000001 associated with ONR MURI grant N00014- 19-1-2571

How Ants Use Vision When Homing Backward

Ants can navigate over long distances between their nest and food sites using visual cues [1 and 2]. Recent studies show that this capacity is undiminished when walking backward while dragging a heavy food item [3, 4 and 5]. This challenges the idea that ants use egocentric visual memories of the scene for guidance [1, 2 and 6]. Can ants use their visual memories of the terrestrial cues when going backward? Our results suggest that ants do not adjust their direction of travel based on the perceived scene while going backward. Instead, they maintain a straight direction using their celestial compass. This direction can be dictated by their path integrator [5] but can also be set using terrestrial visual cues after a forward peek. If the food item is too heavy to enable body rotations, ants moving backward drop their food on occasion, rotate and walk a few steps forward, return to the food, and drag it backward in a now-corrected direction defined by terrestrial cues. Furthermore, we show that ants can maintain their direction of travel independently of their body orientation. It thus appears that egocentric retinal alignment is required for visual scene recognition, but ants can translate this acquired directional information into a holonomic frame of reference, which enables them to decouple their travel direction from their body orientation and hence navigate backward. This reveals substantial flexibility and communication between different types of navigational information: from terrestrial to celestial cues and from egocentric to holonomic directional memories

The sensory arrays of the ant, Temnothorax rugatulus

Individual differences in response thresholds to task-related stimuli may be one mechanism driving task allocation among social insect workers. These differences may arise at various stages in the nervous system. We investigate variability in the peripheral nervous system as a simple mechanism that can introduce inter-individual differences in sensory information. In this study we describe size-dependent variation of the compound eyes and the antennae in the ant Temnothorax rugatulus. Head width in T. rugatulus varies between 0.4 and 0.7 mm (2.6-3.8 mm body length). But despite this limited range of worker sizes we find sensory array variability. We find that the number of ommatidia and of some, but not all, antennal sensilla types vary with head width. The antennal array of T. rugatulus displays the full complement of sensillum types observed in other species of ants, although at much lower quantities than other, larger, studied species. In addition, we describe what we believe to be a new type of sensillum in hymenoptera that occurs on the antennae and on all body segments. T. rugatulus has apposition compound eyes with 45-76 facets per eye, depending on head width, with average lens diameters of 16.5 μm, rhabdom diameters of 5.7 μm and inter-ommatidial angles of 16.8°. The optical system of T. rugatulus ommatidia is severely under focussed, but the absolute sensitivity of the eyes is unusually high. We discuss the functional significance of these findings and the extent to which the variability of sensory arrays may correlate with task allocation.We acknowledge funding support for a PhD scholarship (FRE) from The Australian National University, from the Australian Research Council's (ARC) Centres of Excellence Scheme (CEO561903, JZ & AN), from the Go8 Australia Germany Joint Research Cooperation Scheme (AN & JZ), ARC DECRA and Future Fellowship Grants to AN (DE120100019, FT140100221) and from the National Science Foundation for NEL's PhD stipend (NSF DGE-1143953)