BEhavioral Experiments in Nature

To study which sensory cues insects use for spatial orientation, we perform behavioral experiments in nature. In collaboration with the Dacke lab (Lund University, Sweden), we perform experiments on dung beetles in field arenas in South Africa. In collaboration with the Merlin lab (Texas A&M University, USA), we conduct flight simulator experiments during the migration of the Monarch butterflies in Texas. In these flight simulator experiments, the butterflies are tethered to a mounting rod at the center of the simulator and are free to head in any desired direction with respect to their environment. By manipulating the sensory world of the Monarch butterflies or dung beetles, we can reveal the relevance of different cues for the insect navigation system.

Dung beetle in a field arena (photo: M. Dacke); Monarch butterfly in a flight simulator (photo: F. Hanslin) 

BEhavioral Experiments in the Lab

To study the insect navigation system in detail, we perform experiments under laboratory conditions, using indoor dung beetle arenas and LED flight simulators. This allows us to present simulated cues under tightly controlled conditions, allowing us to reveal the navigational strategies and orientation mechanisms of the insect compass system. Moreover, these experiments allow us to investigate if the cues used by insects in nature can be reproduced in the laboratory and are being used in the same way under laboratory-conditions, which is important to interpret the relevance of neurophysiological recordings. 

 

General Neuroarchitecture

​To unravel how navigation information is encoded in the brain we study the insect brain anatomically, using immunohistochemical techniques combined with imaging and 3D modelling. By staining brains with an anti-synapsin antibody, we can visualize the brain areas in the insect brain. Using a scanning microscope, the whole brain can then be imaged and reconstructed in 3D. By averaging several brains together, we can generate a representative brain atlas of the brain of an insect. 

Pictures: The Monarch brain (from Heinze and Reppert (2012); The beetle central brain (from Immonen et al. 2017)

NEural CIrcuits

To study the neural network in the insect brain, we perform tracer injections into specific brain areas or into single neurons, and conduct stainings against neurotransmitters (e.g. serotonin). The neurons can then be modelled in 3D and warped into a brain atlas.This allow us to gain a detailed knowledge of the neural circuits in general, and the compass network in particular. ​One main focus of our studies is the analysis of the central-complex network, the brain region that acts as internal compass during insect navigation..

Pictures: The locust central complex (el Jundi et al. 2010); compass network in the locust brain (el Jundi et al. 2011)

 

Single Cell Recordings

​To unravel how compass information is encoded in the brain, we study the insect brain electrophysiologically. To observe the activity of single neurons, we perform intracellular recordings using sharp electrodes. To study if the neurons encode specific orientation cues that we tested behaviorally, we simulate the skylight cues, such as polarized light, or the sun, during recording. In addition to skylight cues, we can also present wind and magentic signals, as well as terrestrial landmark and optic low cues to the insects. After recording, we inject a tracer into the neuron to identify the neuron anatomically and reveal in which brain area the neuron branches.

Left: A tethered Monarch butterfly with an implanted tetrode in its brains (photo: M.J. Beetz)

MultiChannel Tetrode Recordings

We are also monitoring the activity of neurons in the brain using extracellular multichannel tetrode recordings. This has the advantage that we can study the activity of neurons over several hours. In addition, we can perform simultaneous recordings from a population of neurons. Such recordings also allow to perform brain recordings in actively navigating insect.s For instance, we can perform these recordings while a dung beetle is rollling a dung ball in an arena or while a butterfly is tethered to a mounting rod at the center of a flight simulator while presenting simulated orientation cues to the insect.