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Comparative neuroanatomy within the context of deep metazoan phylogeny [Elektronische Ressource] / vorgelegt von Carsten Michael Heuer

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109 pages
Comparative Neuroanatomy within the Context of Deep Metazoan Phylogeny Von der Fakultät für Mathematik, Informatik und Naturwissenschaften der Rheinisch-Westfälischen Technischen Hochschule Aachen zur Erlangung des akademischen Grades eines Doktors der Naturwissenschaften genehmigte Dissertation vorgelegt von Diplom-Biologe Carsten Michael Heuer aus Düsseldorf Berichter: Herr Universitätsprofessor Dr. Peter Bräunig Herr Privatdozent Dr. Rudolf Loesel Tag der mündlichen Prüfung: 08.03.2010 Diese Dissertation ist auf den Internetseiten der Hochschulbibliothek online verfügbar. Summary 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).
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Comparative Neuroanatomy within the
Context of Deep Metazoan Phylogeny



Von der Fakultät für Mathematik, Informatik und Naturwissenschaften
der Rheinisch-Westfälischen Technischen Hochschule Aachen
zur Erlangung des akademischen Grades
eines Doktors der Naturwissenschaften
genehmigte Dissertation

vorgelegt von

Diplom-Biologe
Carsten Michael Heuer
aus Düsseldorf


Berichter:
Herr Universitätsprofessor Dr. Peter Bräunig
Herr Privatdozent Dr. Rudolf Loesel


Tag der mündlichen Prüfung: 08.03.2010


Diese Dissertation ist auf den Internetseiten der Hochschulbibliothek online verfügbar. Summary

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.
Contents

Introduction ................................................................................................. ..9
Deep Metazoan Phylogeny – old views and new hypotheses ...... .11
The contribution of neurophylogeny ........................................................................... .13
Arthropod neuroarchitecture outlined .......... .15
Thesis aims .................................................................................................................. .18

Neuroanatomy of the polychaete Nereis diversicolor ............................... 23
Introduction ................................................................................................................. .25
Material and Methods .................................................................................................. .26
Immunohistochemistry ........................ .26
Retrograde staining ............................................................................................. .27
Results ......................................................... .27
Immunoreactivity ................................................................................................. .29
Central optic neuropil ......................... .33
Mushroom bodies .34
Discussion .................................................................................................................... .37
Mushroom bodies ................................ .37
Central optic neuropil ......................................................................................... .39

3D reconstruction of annelid mushroom body neuropils ........................ 43
Introduction ................................................................................................................. .45
Material and Methods .................................................................................................. .46
Immunohistochemistry ........................ .46
Image acquisition and Computer reconstruction ................................................ .46
Assembling and Embedding the 3D model .......................... .48
Results .......................................................................................................................... .48
Nereis diversicolor ............................... .48
Harmothoe areolata ............................................................................................. .51
Lepidonotus clava ................................ .54
Discussion .................................................................................................................... .55

Annelid neuroanatomy: tracing higher brain centers
in segmented worms ..................................................................................... 59
Introduction .................................................. .61
Material and Methods ................................................................... .62
Results .......................................................................................... .62
Arenicola marina ................................................................. .62
Ophelia limacina .................................. .64
Scalibregma inflatum ........................................................... .64
Eupolymnia nebulosa ................................ .64
Sabella penicillus ................................................................. .66
Tomopteris helgolandica ..................................................... .66
Nereis diversicolor ............................................................... .66
Phyllodoce maculata ............................................................ .68
Nephtys hombergii ............................... .68
Eunice torquata .................................................................................................... .68
Lumbrineris cf. fragilis ........................ .70
Odontosyllis cf. fulgurans .................................................................................... .70
Hesione pantherina .............................. .72
Harmothoe areolata ............................................................................................. .72
Lumbricus terrestris .72
Hirudo medicinalis .............................. .73
Discussion .................................................................................................................... .74
Mushroom bodies ................................. .76
Olfactory glomeruli .............................................................................................. .79
Unpaired midline neuropils ................. .80 General discussion ....................................................................................... 83

References .................................................................................................... 93

Acknowledgements .................................................................................... 107

Curriculum vitae ....................................................................................... 109








Introduction