The brain of Cataglyphis ants: Neuronal organization and visual projections

Abstract

Cataglyphis ants are known for their outstanding navigational abilities. They return to their inconspicuous nest after far‐reaching foraging trips using path integration, and whenever available, learn and memorize visual features of panoramic sceneries. To achieve this, the ants combine directional visual information from celestial cues and panoramic scenes with distance information from an intrinsic odometer. The largely vision‐based navigation in Cataglyphis requires sophisticated neuronal networks to process the broad repertoire of visual stimuli. Although Cataglyphis ants have been subjected to many neuroethological studies, little is known about the general neuronal organization of their central brain and the visual pathways beyond major circuits. Here, we provide a comprehensive, three‐dimensional neuronal map of synapse‐rich neuropils in the brain of Cataglyphis nodus including major connecting fiber systems. In addition, we examined neuronal tracts underlying the processing of visual information in more detail. This study revealed a total of 33 brain neuropils and 30 neuronal fiber tracts including six distinct tracts between the optic lobes and the cerebrum. We also discuss the importance of comparative studies on insect brain architecture for a profound understanding of neuronal networks and their function.

Johnston's organ and its central projections in Cataglyphis desert ants

“…To label the afferents of sensory neurons of the JO in the pedicel of C. nodus , a double anterograde staining procedure was performed using a combination of techniques previously applied in the honeybee (e.g., double staining (Kirschner et al, 2006) and bilateral staining (Ai et al, 2007)) and Cataglyphis (Habenstein, Amini, Grübel, el Jundi, & Rössler, 2020). The head of cold‐anesthetized ants was fixed with dental wax.…”

“…(b and c) The JO in the worker antenna comprises 40 scolopidia (n = 4), (e and f) the JO of a queen comprises 42 scolopidia (n = 1), and (h and i) the JO of a male comprises 48 scolopidia in the JO (n = 1). In Cataglyphis, both the VX and VLP receive visual input from the primary optic ganglia (medulla, lobula) via the posterior (POC) and inferior (IOC) optic commissures (Habenstein et al, 2020). In the honeybee, similar visual projections into this area were found (Maronde, 1991).…”

“…Synapsin is present in presynaptic terminals and highly conserved among invertebrates. The specificity of the antibody has been characterized previously for Cataglyphis ants (Schmitt, Stieb, Wehner, & Rössler, 2016;Schmitt, Vanselow, Schlosser, Wegener, & Rössler, 2017;Stieb, Hellwig, Wehner, & Rössler, 2012;Stieb, Muenz, Wehner, & Rössler, 2010) and most recently for C. nodus (Habenstein et al, 2020).…”

“…(d and e) At the most posterior end, antennal afferents terminate the posterior slope (PS), and some fibers proceed down into the gnathal ganglia (GNG). (f) Reconstruction of the C. nodus brain showing synapsin-rich neuropils and their boundaries at roughly the same depth as in (d) (image from Habenstein et al, 2020). Please note that the section in (d) is slightly tilted compared to the section from the C. nodus brain atlas (f), which was taken into account for the identification of synapsin-rich central neuropils.…”

“…Raw confocal, histology, scanning-electron microscopy images and 3D data are available from the authors upon reasonable request. For comparison of brain data, 3D data of the brain of Cataglyphis nodus (from Habenstein et al, 2020) are available at the Insect Brain Database website (https://www.insectbraindb.org/).…”