Die AG Cytologie und Evolutionsbiologie befasst sich mit der Evolution des Nervensystems und anderer Organsystem in Bilateria, wobei ein klarer Schwerpunkt auf den Arthropoda liegt. So interessieren uns insbesondere die Architektur des Gehirns und der Sinnesorgane sowie die Struktur von Drüsensystemen in Vertretern der Crustacea, Myriapoda und Chelicerata. Dabei kommen an Methoden die immunhistochemische Lokalisierung von neuronalen Antigenen verbunden mit Fluoreszenzmikroskopie und confocaler Laser-Scan Mikroskopie zum Einsatz, sowie die gesamte Bandbreite der elektronenmikroskopischen Methoden.
Ein weiterer methodischer Schwerpunkt ist die 3D Rekonstruktion bestimmter Organsysteme aus Dünnschnittserien. Unsere Arbeiten stehen vor dem Hintergrund konkurrierender Hypothesen zur Stammesgeschichte der Arthropoda. Für die Verknüpfung von neurobiologischen Fragestellungen mit evolutiven Aspekten haben wir den Begriff „Neurophylogenie“ geprägt.
DFG Graduiertenkolleg RTG 2010 - Projekt B3: Effects of environmental stress on neurogenesis in crustacean larvae
Associated scientists: Franziska Spitzner, Andy Sombke & Steffen Harzsch
State of the art: Climate change already has a major impact on marine ecosystems including plankton communities (Prog. Oceanograph. 81: 207). In particular semi-enclosed seas (e.g. the Baltic Sea) will be increasingly affected by rising surface temperatures and decreasing salinity due to a higher river runoff (J. Exp. Mar. Biol. Ecol. 400: 52). Decapod crustaceans may be particularly sensitive to such changes, owing to their complex life cycle including a pelagic larval and a benthic juvenile-adult stage. Here, larval survival critically depends on the ability to respond appropriately to chemical, mechanosensory and visual cues to control tidal transport and onshore recruitment (Invert. Reprod. Dev. 49: 175). Larval settlement is of utmost importance for colonisation and population survival, relying on e.g. odour identification indicating preferred habitats and the presence of conspecifics (Mar. Freshwater Behav. Physiol. 39: 269). Hence, the ability to sense environmental cues is an ecologically important trait intimately associated with fitness. However, larval growth and bioenergetics in decapod larvae are strongly affected by thermal and osmotic stress (Invert. Reprod. Dev. 33: 159). While concomitant effects on growth patterns are well understood, knowledge on the effects of abiotic stress on the development of specific, energy-demanding organs such as the nervous system and hence on behavioural performance is lacking. Therefore, we will here explore the effect of abiotic stress on the development of the larval olfactory system and olfactory-guided behaviour.
Working hypotheses and work plan: Current climate change may expose crustacean planktonic larvae to increasing abiotic stress (see above). We hypothesise that (1) thermal and salinity stress will negatively affect neurogenesis and thereby larval behavioural performance, and that (2) negative effects will differ depending on the respective species’ ability to tolerate challenging environmental conditions. To this end, we will study the effects on osmotic and thermal stress on the development of the olfactory system in larvae of six European decapod crustaceans, which are known to differ in their stress tolerance (Aquat. Biol. 21: 249). Investigations will include (1) in vivo incorporation of an s-phase specific mitosis marker to quantify neurogenesis; (2) immunohistochemistry against neuropeptides and confocal laser-scan microscopy to analyse the formation of neuronal networks within the central olfactory pathway, (3) scanning and transmission electron microscopy to analyse the ontogeny of the chemosensory organs; (4) bioessays to analyse larval responses and sensitivity ranges to environmental stimuli. A major part of the breeding experiments will be carried out at the “Biologische Anstalt Helgoland”, a marine biological station on the island of Helgoland/North Sea (http://www.awi.de/de/institut/standorte/helgoland/) in cooperation with Dr. Gabriela Torres and Dr. Luis Gimenez (Bangor, Wales).
Thesis topic: Effects of abiotic stress on neurogenesis in the developing brain of crustacean larvae
DFG Projekt: Persistent neurogenesis in the crustacean brain: comparative aspects (HA 2540/16-1)
Applicant: Prof. Dr. Steffen Harzsch (Greifswald)
Cooperation Partner: Prof. Dr. Barbara S. Beltz (Wellesley)
The central olfactory pathway of the crayfish brain is characterized by persistent, life-long neurogenesis. Adult neurogenesis is driven by a neurogenetic niche on the surface of the brain that generates 1st generation precursor cells. These cells leave the niche and move along an anteriorly and a medially directed migratory stream towards an anterior and a medial proliferation zone, both associated with the central olfactory pathway. During their migration, the cells undergo additional mitoses and evolve into 2nd and 3rd generation precursor cells. The medial proliferation zone contributes new local olfactory interneurons whereas the lateral proliferation zone generates olfactory projection neurons. The cellular machinery in this system that is collectively called the “deutocerebral proliferative system” (DPS) displays strong similarities to the system that drives adult neurogenesis in mammals. In these animals, a neurogenetic niche, the subventricular zone, generates progeny that migrate along the rostral migratory streams towards the olfactory bulb where the neurons are integrated into existing neuronal circuits. This projects sets out to examine the phenomenon of persistent neurogenesis in the crustacean olfactory system in a broad comparative context and against an evolutionary background. We want to know if the mechanisms of adult neurogenesis described for the crayfish hold for other malacostracan crustaceans too and will analyse possible variations in order to gain insights into the possible function of this system. With this comparative approach we will follow an evolutionary experiment and explore the solutions which crustaceans evolved for the task „life-long neurogenesis“. To that end we will study ca. 10 – 15 representative of all major taxa of Malacostraca with immunohistochemical techniques, in vivo labelling with combinations of mitosis markers, pulse-chase experiments and transmission electron microscopy. Specifically, we will analyze A) general arrangement of the DPS components; B) ultrastructure of the neurogenetic niche; C) dynamics of the directed movement in the migratory streams; D) integration of the new olfactory interneurons into the central olfactory pathway; E) persistent neurogenesis associated with the hemiellipsoid bodies in the lateral protocerebrum. This study will lay the foundations for a future project that will in more depth explore the function of persistent neurogenesis in suited model crustaceans specifically with regard to the question how the new neurons are wired up into the network of the functional, adult olfactory system.
DFG Projekt: An integrative analysis of olfaction in terrestrial versus marine hermit crabs. (HA 2540/13-1)
Applicants: Prof. Dr. Steffen Harzsch (Greifswald), Prof. Dr. Bill S. Hansson (Jena)
In parallel to insects, terrestrial Crustacea provide a fascinating chance to participate in a wonderful evolutionary experiment by analyzing which potential alternative solutions arthropods have evolved to explore the terrestrial olfactory landscape. General questions of our approach include:
• Have terrestrial Crustacea successfully established aerial olfaction at all, and which subgroups?
• How have they solved the task of detecting airborne stimuli at the level of olfactory sensory neurons and their receptors?
• Have they evolved insect-like odorant binding proteins and agents with anti-fouling functions to fight epibionts?
• How have the dramatic changes in selection pressure on the sensory systems reshaped and modified peripheral and central olfactory pathways?
• Does their antenna display ultrastructural specializations that may play a role for odorants to get in contact with olfactory sensory neurons?
• To what odor components do they respond and are the response profiles different from those of insects?
• Which tracking strategies do they use to locate odor sources and do these resemble those of walking or flying insect odor trackers?
• Have they evolved insect-like behaviors to track odor sources and which role does air flow play in their tracking behavior?
• Which mechanosensors do they use to detect flow?
• Which role do differences in sensor spans play in terrestrial crustaceans of different sizes?
DFG Projekt - The chemical sense of marine isopod crustaceans (HA 2540/9-1)
Applicant: Prof. Dr. Steffen Harzsch, Dipl. Biol. Matthes Kenning
Cooperation Partner: Dr. Magnus Lindström (University of Helsinki)
Our current knowledge on both the morphology of the crustacean olfactory pathway and on chemically guided behavior is heavily biased towards members of the Decapoda. In the current project, we want to gain more insights into olfaction in another major group of malacostracan crustaceans, the marine Isopoda by analysing the architecture of the peripheral and central olfactory pathway and by conducting behavioral essays. To that end we propose here to analyze, in a wide range of isopods, the morphology of the antennae and the central olfactory pathway with neuroanatomical methods such as scanning electron microscopy, serial semithin sectioning combined with 3D reconstruction, antennal backfilling with neuronal tracers, focal application of dextrans to label populations of olfactory interneurons, and immunofluorescence combined with confocal laser-scan microscopy. We will try to analyse representatives from a wide range of different habitats including the deep sea, the Arctic and Antartica, the Tropics, and from different life styles including scavengers and parasitic species. Furthermore, olfactory-guided behavior and navigation strategies to odor sources will be tested in behavioral assays using the omnivorous isopod Saduria entomon which is common in the Baltic as a model. In a neurophylogenetic approach, our data will be compared to the morphology of the olfactory systems in other malacostracan crustaceans and hexapods in order to extract data for understanding the evolution of arthropod olfactory systems in general.
DFG Projekt - Evolution of the olfactory system in Myriapoda: insights from neuroanatomy and behavior (HA 2540/8-2)
Applicant: Prof. Dr. Steffen Harzsch, Dr. Andy Sombke
Cooperation Partner: Prof. Dr. Bill S. Hansson (MPI Jena)
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.
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