Evolution of the olfactory system in Myriapoda

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Myriapods represent an arthropod lineage that, originating from a marine arthropod ancestor, most likely conquered land independently from hexapods. The successful transition from marine to terrestrial life requires a number of physiological adaptations that are important for survival out of water. The sensory organs of terrestrial species must be able to function in air rather than in water. In chemoreception, establishing aerial olfaction means that molecules need to be detected in gas phase instead of in water solution. In general, the neuroethology of myriapods and the architecture of their central nervous systems are poorly understood. In a set of preliminary experiments with the centipede Scutigera coleoptrata we analyzed the morphology of the antennae and the central olfactory pathway with scanning electron microscopy, serial semithin sectioning combined with 3D reconstruction, antennal backfilling with neuronal tracers, and immunofluorescence combined with confocal laser-scan microscopy. Furthermore, the ability of this animal to respond to airborne stimuli was tested in behavioral assays and electroantennogram recordings. These experiments collectively indicate a good sense of aerial olfaction in this species. Furthermore, the architecture of its olfactory neuropils is clearly distinct from hexapods and also from terrestrial crustaceans indicating an independent evolution of its olfactory sense in response to the conquest of land. We propose here to study the morphology of the central olfactory pathway in a broad range of other myriapods covering Chilopoda, Progoneata, Symphyla and combine these studies with behavioral essays. We will also include Scorpions as an outgroup. In a neurophylogenetic approach, our data will also be compared to the morphology of the olfactory systems in hexapods and crustaceans in order to extract data for reconstructing arthropod phylogeny and for understanding the evolution of arthropod olfactory systems.