1) Comparative ultrastructure of tip-pore sensilla in millipedes and spiders

In hexapods, hair sensilla with wall pores (including sensilla basiconica) are important and well-studied organs of the sense of smell. Outside the Hexapoda, however, these multi-pored sensilla are rare (in millipedes) or entirely absent (spiders). Nevertheless, biochemical, ethological, and/or electrophysiological data indicate that representatives of both arthropod groups are capable of perceiving olfactory stimuli. In this context, sensilla possessing a terminal pore and a specially structured, but non-perforated, shaft cuticle are of interest. Examples of such olfactory sensilla are being examined using TEM on the antennae,  walking legs, and terminal legs of the tarantula Scutigera coleoptrata, as well as on the distal podomeres of the walking legs of the wolf spider (Argiope spp.). In addition to addressing questions of evolutionary morphology, we are also interested in elucidating alternative mechanisms by which odorants access the sensille fluid and the receptors located therein.

Collaborators:

Anne-Sarah Ganske (Naturhistorisches Museum Wien, Zoologische Abteilung, Wien, Österreich)

Dr. Andy Sombke (University of Greifswald, Department of Cytology and Evolutionary Biology)

2) Sensory Equipment of the Distal Portions of Spider Palps

Until recently, the bulbs—which serve as sperm carriers during copulation—were considered non-sensory projections of the male palp. However, according to recent transmission electron microscopy (TEM) analyses, this basic assumption can no longer be upheld, as small or large aggregates of embedded sensilla were found at the base of the embolus of some spider species (Sentenska et al. 2017, Scientific Reports 7: 12209). Ultrastructurally, these sensilla resemble the tarsal organs documented in the tarsal segments of the walking legs of various spiders. The discovery is accompanied by the identification of a previously unknown bulb nerve. This nerve contains both afferents from the embedded sensilla cluster and three distinct efferent neurite bundles that innervate, among other things, embolus-associated glandular epithelia. Current TEM analyses aim to localize the pore openings of the embedded sensilla on the embolus. Scanning electron microscopy (SEM) observations in this context indicate a series of mound-like protuberances in the distal third of the embolus. The specific ultrastructure of the dendrite tips (e.g., the presence of a tubular body as an indication of mechanoreception) may provide clues as to whether these sensilla are chemoreceptors or mechanoreceptors.

Collaborators:

Dr. Lenka Sentenská (Masaryk University, Dept. of Botany and Zoology, Brno, Tschechien) 
 

3) Potential applications of the Biowave for optimal chemical fixation of delicate arthropod tissues for TEM

Als beste aller möglichen Methoden für die Konservierung des Cytosols gilt die Cryofixierung, die besonders in der funktionellen Ultrastrukturforschung vielfach mit Erfolg eingesetzt wird. Allerdings sinkt die Effizienz der Cryofizierung mit der Zunahme der Größe bzw. des Durchmessers zu fixierender Gewebe bzw. Körperteile. Auch die glutardialdehyd-basierte Chemofixierung birgt Risiken, da in oder auf den Geweben befindliche Diffusionsbarrieren den Importerfolg des Glutardialdehyds herabsetzen. Dies ist insbesondere bei den Arthropoden ein Problem, welche von einer stark skleroritisierten, ggf. verkalkten Cuticula gepanzert sind. Werden epidermale Sinnes- oder Drüsenorgane mit intracuticulären Anteilen untersucht, dann sind zusätzlich die Möglichkeiten der Präparation eingeschränkt, da die strukturelle Integrität der Zielorgane geschädigt werden kann. Ein klassisches Beispiel für solcherart heikle Untersuchungsobjekte sind die Cheliceren, Palpen oder die Laufbein-Podomere von Spinnen. Der Erfolg einer Chemofixierung kann durch den Einsatz von Mikrowellenstrahlung gesteigert werden. Allerdings ist diese Kombinationsmethode noch nicht feinmorphologische Studien an Spinnen etabliert. Daher wird hier unter Mitwirkung einer technischen Assistentin des Imaging-Zentrums der Fachrichtung Biologie (Leitung: Frau Dr. Rabea Schlüter) eine vergleichende TEM-Studie durchgeführt, in der die Chemofixierungsqualitäten von Beingeweben (Epidermis, Sinnesorgane, Muskulatur) mit und ohne Einsatz einer PELCO BioWave Pro getestet wird. Untersucht werden hierbei distale Laufbeinpodomere der Wespenspinne Argiope blanda. Ziel ist unter anderem die Erstellung eines robusten Präparations- und Fixierungsprotokolls, welches zumindest auch für Vertreter weiterer Teiltaxa der Arachnida angewandt werden kann

4) Vergleichende Ultrastruktur und Evolution von Giftdrüsen bei Hundertfüßern (Chilopoda)

The presence of a single pair of postcephalic venomous claws (maxillipeds) is interpreted as an apomorphy of centipedes. Although there is a fairly accurate understanding of the disparity and evolutionary transformation of maxillipeds within this animal group, an invasive morphological correlate regarding the venom glands located within the maxillipeds is still lacking. Together with colleagues from the University of Greifswald and the University of Queensland (Brisbane, Australia), I am reconstructing the modular structure of the venom glands using selected representatives from all five subgroups of millipedes. A broad spectrum of invasive and non-invasive morphological analysis methods is employed (µ-CT, TEM, immunohistochemistry, semi-thin section histology, paraffin section-based spectroscopy). Accompanying transcriptomic and proteomic analyses are intended to provide insight into the chemical composition of the toxins produced by specific taxa.

For further details on the project and participating partners, see the following link.

5) Structural Diversity and Evolution of the Terminal Legs of Centipedes (Chilopoda)

Segmented legs (arthropodia) are an evolutionary innovation (apomorphy) of the arthropods (Arthropoda). Multiple modifications of what were originally likely two-branched swimming legs led to the development of a wide variety of forms of jointed appendages, including sensory appendages such as antennae and cerci, predatory, defensive, and filtering legs, or grasping organs. Unbranched walking legs (stenopods) evolved independently on multiple occasions. While the antennae of crustaceans, myriapods, and hexapods have been studied quite extensively, knowledge regarding the sensory equipment of the walking legs and hind thoracic legs is comparatively sparse in many arthropod groups. Particularly little is known to date about the terminal legs of centipedes (Chilopoda), although it is precisely these legs—which are usually significantly elongated or thickened—that exhibit a high degree of structural and functional diversification. As part of a DFG project (SO1289/1), various structural specializations are currently being documented using multimodal microscopy (cLSM, immunohistochemistry, SEM, TEM, and semi-thin section histology). The analysis focuses on the antenna-like, multitarsal terminal legs of scutigeromorphs (Scutigeromorpha) and representatives of the centipede genus Newportia (Scolopendromorpha). Ultrastructure-based typological characterizations of the terminal leg sensilla are supplemented by visualizations of the associated neural pathways and electrophysiological recordings from individual sensilla. A comparison with complementary data from the antenna aims to determine whether and to what extent similarly shaped and functionally specialized appendages also exhibit similarities in their sensory equipment and innervation patterns.

For further details on the project and participating partners, see the following link.

1) Neuro- and sensophylogeny of arrow worms (Chaetognatha)

Documentation and ultrastructural reconstruction of ciliary sensory organs (corona ciliata, ciliary fence and tuft organs, eyes); cilia-induced flow patterns over the corona ciliata; Ultrastructural analysis of ventral glandular papillae in Spadellidae; (immuno)histochemical characterization of the peripheral and central nervous systems of selected Sagittidae and Spadellidae; redescription of the species Spadella valsalinae from the northern Adriatic Sea; biogeography of European Spadellidae.

Collaborators:

Prof. Dr. Steffen Harzsch (University of Greifswald, Cytology & Evolutionary Biology)

Dr. Yvan Perez (Aix-Marseille Université, Marseille)

2) Microstructural reconstruction and evolution of epidermal organs in spiny worms (Sipuncula, Annelida)

Description of the sensory and glandular components in smooth and papillary epidermal organs, as well as holdfast papillae in Phascolion cf. strombus; conceptualization of epidermal organs as a new character complex for reconstructing the internal and external phylogeny of the Sipuncula (including bimodal secretory cells).

Collaborators:

PD Dr. Peter Michalik (University of Greifswald, Zoological Museum)

Prof. Dr. Jørgen Hylleberg (Aarhus Universitet, Institute for Bioscience)

3) Evolutionary and functional morphology of solitary and aggregated cutaneous glands in myriapods

Comparative ultrastructure of solitary head glands in Scutigeromorpha, Lithobiomorpha, Craterostigmomorpha, Scolopendromorpha, and Geophilomorpha; distribution, function, and evolution of flexocanal and rectocanal glands; spatial and functional coupling of cutaneous glands with individual sensillae or complex ciliary sensory organs.

Collaborators:

Dr. Jörg Rosenberg (Am Kützelbach 3, D-59494 Soest)

Prof. Dr. Gero Hilken (University of Duisburg-Essen, University Hospital Essen, Central Animal Laboratory)

4) Fine-structural organization, function, and evolution of ciliary sensory organs in centipedes (Chilopoda) and millipedes (Diplopoda)

Fine structure of the shaft organ and adjacent pin sensilla on the second basal segment of the antenna of Scutigera coleoptrata (Chilopoda); Disparity of trimodal sensilla (combination of mechanoreception, olfaction, and gustation) on the antennae of Scutigera coleoptrata; fixation-related structural variations of sensilla components (chemo- vs. high-pressure cryofixation); AMIRA-assisted reconstruction of trimodal sensilla based on ssTEM and serial block photography; fine structure and evolution of Tömösváry’s organs in Phryssonotus platycephalus (Penicillata, Diplopoda) and Craterostigmus tasmanianus (Craterostigmomorpha, Chilopoda).

Collaborators:

Dr. Andy Sombke (University of Greifswald, Department of Cytology and Evolutionary Biology)

Dr. Jörg Rosenberg (Am Kützelbach 3, D-59494 Soest)

Prof. Dr. Gero Hilken (University of Duisburg-Essen, University Hospital Essen, Central Animal Laboratory)

Dr. Michael Laue, (Robert Koch Institute, Berlin)

Dr. habil. Thomas Hörnschemeyer (Senckenberg Society for Nature Research, Scientific IT, DMZ, Biodiversity Informatics)

5) Morphology and Evolution of the Light-Sensory Organs of Brachiopods

Ultrastructure of the ciliary photoreceptors in Joania cordata and Argyroteca cuneata; Significance of brachiopod eye structures for understanding eye evolution within the Bilateria, DFG Project: Lu839/5.

Collaborators:

PD Dr. Carsten Lüter (Museum für Naturkunde Berlin, Leibniz Institute for Evolution and Biodiversity Research)