Evolutionary specialization of neuronal core circuits in arthropod olfactory systems: structure and function of convergence/divergence in crustaceans versus insects

Steffen Harzsch - Universität Greifswald
Martin Nawrot - Universität Köln
Jürgen Rybak - MPI for Chemical Ecology, Jena

The main chemosensory organ of insects and crustaceans for distance olfaction is the most anterior pair of head appendages, the deutocerebral antennae. Olfactory sensory neurons associated with sensilla on the antennae project their axons into the brain’s primary olfactory centres, the bilaterally paired antennal lobes (insects)/olfactory lobes (crustaceans). There, sensory olfactory afferents synapse with two classes of olfactory interneurons (OSNs), the local olfactory interneurons (LNs) and the olfactory projection neurons (PNs), within specialized neuropil compartments, the olfactory glomeruli. Although the principle wiring pattern within the glomeruli of crustaceans and insects share many similarities, there also exist pronounced difference of these olfactory core circuits. Therefore, this system can be seen as an ideal playground for those interested in analysing evolutionary diversification of neuronal core circuits. By comparing insects and crustaceans we can analyse the end point of past evolutionary optimization processes by analyzing which potential alternative solutions arthropods have found for olfactory circuits. This project brings together two experts on the functional and evolutionary morphology of crustacean (HAR) and insect (RYB) olfactory system and a computational neuroscientist with a strong background in arthropod olfactory systems (NAW). We want to gain detailed insights into the neuroanatomy of the central olfactory pathway beyond the well studied model system D. melanogaster. By quantifying the numbers of the involved neuronal elements (olfactory sensory neurons, local olfactory interneurons, projection neurons, olfactory glomeruli) and by analysing architectural characteristics such as volume, shape and geometrical properties of olfactory glomeruli we will gain additional insights into divergence versus convergence and evolutionary specialization of the central olfactory pathways in arthropod lineages with a known evolutionary history. Furthermore, by obtaining connectome-level data we will understand the evolutionary optimization of local circuit motifs, specifically the connectivity of OSNs to PNs. Finally, by developing a mathematical model of information processing within olfactory glomeruli of different arthropod lineages, we want to understand possible differences of olfactory coding mechanisms in insects versus crustaceans.