Comparative neuroanatomy within the context of deep metazoan phylogeny

Comparative invertebrate neuroanatomy has seen a renaissance in recent years. Highly conserved neuroarchitectural traits offer a wealth of hitherto largely unexploited characters that can make valuable contributions in inferring phylogenetic relationships in cases where phylogenetic analyses of molecular or morphological data sets yield trees with conflicting or weakly supported topologies. Conversely, in those cases where robust phylogenetic trees exist, neuroanatomical features can be mapped onto the trees, helping to shed light on the evolution of the central nervous system. This thesis aims to provide detailed neuroanatomical data for a hitherto poorly studied invertebrate taxon, the segmented worms (Annelida). Drawing on the wealth of investigations into the architecture of the brain in different arthropods, the study focuses on the identification and description of possibly homologous brain centers (i.e. neuropils) in annelids. The thesis presents an extensive survey of the internal architecture of the brain of the ragworm Nereis diversicolor (Polychaeta, Annelida). Based upon confocal laser scanning microscope analyses, the distribution of neuroactive substances in the brain is described and the architecture of two major brain compartments, namely the paired mushroom bodies and the central optic neuropil, is characterized in detail. It is concluded that the central optic neuropil cannot be confidently homologized with similarly unpaired neuropils in the arthropod brain, but that annelid and arthropod mushroom bodies are probably homologues. This proposed homology is further explored by comparing 3D reconstructions of mushroom body neuropils and associated structures in the polychaete species Nereis diversicolor, Harmothoe areolata, and Lepidonotus clava with a 3D model of the mushroom bodies in the insect representative Leucophaea maderae. The neuropils are found to share a common principal organization and a similar neuroarchitectural integration. Lastly, the occurrence of unpaired midline neuropils, mushroom bodies, and associated structures is investigated in a broad taxonomic survey, including more than 20 representatives from major groups of the annelid radiation. Considerably complex brains, sometimes comprising mushroom bodies and other subcompartments, are only observed in errant polychaetes but not in sedentary polychaete species, nor in clitellates representatives. The implications of an assumed homology between annelid and arthropod mushroom bodies are discussed in light of the "new animal phylogeny". It is concluded that the homology of mushroom bodies in distantly related groups has to be interpreted as a plesiomorphy, pointing towards a considerably complex neuroarchitecture inherited from the last common ancestor, Urbilateria. Within the annelid radiation, the lack of mushroom bodies in certain groups is explained by wide-spread secondary reductions owing to selective pressures unfavorable for the differentiation of elaborate brains. Evolutionary trajectories of mushroom body neuropils in errant polychaetes remain enigmatic.

Grantor dc:publisher

Publikationsserver der RWTH Aachen University

Year dc:date

2010

Author dc:creator

• Heuer, Carsten Michael

Contributors dc:contributor

• Loesel, Rudolf

• info:eu-repo/classification/ddc/570
• Zoologie
• Morphologie <Biologie>
• Systematik
• Neuroanatomie
• Gehirn
• Gliederfüßer
• Ringelwürmer
• Pilzkörper
• Konfokale Mikroskopie
• Biowissenschaften, Biologie
• CLSM
• Neurophylogenie
• Annelida
• neurophylogeny
• brain
• mushroom bodies

Statement dc:rights

• info:eu-repo/semantics/openAccess

Language dc:language

eng

Identifier

https://publications.rwth-aachen.de/search?p=id:%22RWTH-CONV-114009%22

OAI record oai:identifier

https://publications.rwth-aachen.de/oai2d?verb=GetRecord&metadataPrefix=oai_dc&identifier=oai%3Apublications.rwth-aachen.de%3A51751