Comparative analysis of deutocerebral neuropils in Chilopoda (Myriapoda): implications for the evolution of the arthropod olfactory system and support for the Mandibulata concept
- Equal contributors
1 Ernst Moritz Arndt University of Greifswald, Zoological Institute and Museum, Cytology and Evolutionary Biology, 17487 Greifswald, Germany
2 Max Planck Institute for Chemical Ecology, Department of Evolutionary Neuroethology, 07745 Jena, Germany
3 Ernst Moritz Arndt University of Greifswald, Zoological Institute and Museum, General Zoology and Zoological Systematics, 17487 Greifswald, Germany
4 RWTH Aachen University, Institute of Biology II, Unit of Developmental Biology and Morphology of Animals, 52065 Aachen, Germany
BMC Neuroscience 2012, 13:1 doi:10.1186/1471-2202-13-1Published: 3 January 2012
Originating from a marine ancestor, the myriapods most likely invaded land independently of the hexapods. As these two evolutionary lineages conquered land in parallel but separately, we are interested in comparing the myriapod chemosensory system to that of hexapods to gain insights into possible adaptations for olfaction in air. Our study connects to a previous analysis of the brain and behavior of the chilopod (centipede) Scutigera coleoptrata in which we demonstrated that these animals do respond to volatile substances and analyzed the structure of their central olfactory pathway.
Here, we examined the architecture of the deutocerebral brain areas (which process input from the antennae) in seven additional representatives of the Chilopoda, covering all major subtaxa, by histology, confocal laser-scan microscopy, and 3D reconstruction. We found that in all species that we studied the majority of antennal afferents target two separate neuropils, the olfactory lobe (chemosensory, composed of glomerular neuropil compartments) and the corpus lamellosum (mechanosensory). The numbers of olfactory glomeruli in the different chilopod taxa ranged from ca. 35 up to ca. 90 and the shape of the glomeruli ranged from spheroid across ovoid or drop-shape to elongate.
A split of the afferents from the (first) pair of antennae into separate chemosensory and mechanosensory components is also typical for Crustacea and Hexapoda, but this set of characters is absent in Chelicerata. We suggest that this character set strongly supports the Mandibulata hypothesis (Myriapoda + (Crustacea + Hexapoda)) as opposed to the Myriochelata concept (Myriapoda + Chelicerata). The evolutionary implications of our findings, particularly the plasticity of glomerular shape, are discussed.