Stefan Fischer

University of Tuebingen | EKU Tübingen · Centre of Applied Geosciences

Biogenic magnetite is a potential biosignature for microbial iron cycling in hydrothermal sulfide systems, critical environments for unraveling the emergence and early evolution of life. However, the preservation potential of biogenic magnetite under hydrothermal conditions is poorly understood. Here, we show that the hydrothermal sulfidation of ab...

Pyrite (FeS 2 ) is a mineral of wide interest due to its importance in the biogeochemical cycling of Fe and S, which is tied to those of carbon and other trace metals and nutrients. The mineral itself has potential applications as biosignatures, for environmental remediation and as semiconductors. Despite being a common authigenic mineral in sedime...

Various chalcidoid wasps can actively steer their terebra (= ovipositor shaft) in diverse directions, despite the lack of terebral intrinsic musculature. To investigate the mechanisms of these bending and rotational movements, we combined microscopical and microtomographical techniques, together with videography, to analyse the musculoskeletal ovip...

Additional file 4. Animation of the rotating segmented 3D model of the musculoskeletal ovipositor system of Lariophagus distinguendus (cf. Figs. 5 and 6).

Additional file 2. Superimposed CLSM images of the ovipositor of Lari- ophagus distinguendus (dorsal view, cf. Fig. 3g, h).

Additional file 3. Animation of the aligned semithin sections through the terebra of Lariophagus distinguendus (from distal to proximal; cf. Fig. 4a–d). The jittering movements of the two halves of the 2nd valvula in the mid- dle of the image stack result from section and compression artefacts.

Additional file 1. Video sequences of female Lariophagus distinguendus parasitizing larvae of Sitophilus granarius in an artificial film chamber (cf. Fig. 2b–p). The terebra bending and rotating movements during host assessment and the alternate movements of the paired 1st valvulae can be observed.

Nano-magnetite is a potential archive for biosignatures and paleoenvironmental proxies in hydrothermal systems. However, sulfidic diagenesis at hydrothermal conditions potentially drives the rapid transformation of magnetite to Fe sulfide minerals. The identity and characteristics of transformation products from these reactions are crucial for inte...

The morphology of pyrite has been used to infer ancient redox states and biogenicity. However, the influence of trace metals on pyrite morphology is poorly understood. Through batch synthesis experiments, we demonstrate that bioessential trace metals (Co, Cu, Mo, Ni, Zn) accelerate pyrite formation. The first precipitate, FeS(am), transformed to an...

The extent of how complex natural microbial communities contribute to metal corrosion is still not fully resolved, especially not for freshwater environments. In order to elucidate the key processes, we investigated rust tubercles forming massively on sheet piles along the river Havel (Germany) applying a complementary set of techniques. In-situ mi...

A hallmark in snails' anatomy is the conspicuous crossing of the pleurovisceral nerve cords present in most basal gastropod clades. This feature is called streptoneury and hitherto near-universally believed to derive from the process of torsion which is, ontogenetically, visible by a 180° horizontal rotation of the cephalopodium relative to the vis...

Microbially mediated iron and sulfur cycling have impacted redox transitions and the bioavailability of nutrients throughout Earth’s history. Here, we incubated Geobacter sulfurreducens in the co-presence of ferrihydrite and S0 at pH 6.5, 7.2 or 8.0. Microbial reduction of Fe(III) and S0 resulted in a shift from ferruginous (Fe2+-rich) to sulfidic...

The red flour beetle Tribolium castaneum is a resource-rich model for genomic and developmental studies. To extend previous studies on Tribolium eye development, we produced transcriptomes for normal-eyed and eye-depleted heads of pupae and adults to identify differentially transcript enriched (DE) genes in the visual system. Unexpectedly, cuticle-...

In permafrost peatlands, up to 20% of total organic carbon (OC) is bound to reactive iron (Fe) minerals in the active layer overlying intact permafrost, potentially protecting OC from microbial degradation and transformation into greenhouse gases (GHG) such as CO2 and CH4. During the summer, shifts in runoff and soil moisture influence redox condit...

In permafrost peatlands, up to 20% of total organic carbon (OC) is bound to reactive iron (Fe) minerals in the active layer overlying intact permafrost, potentially protecting OC from microbial degradation and transformation into greenhouse gases (GHG) such as CO2 and CH4. During the summer, shifts in runoff and soil moisture influence redox condit...

In freshwater wetlands, redox interfaces characterized by circumneutral pH, steep gradients in O2, and a continual supply of Fe(II) form ecological niches favorable to microaerophilic iron(II) oxidizing bacteria (FeOB) and the formation of flocs; associations of (a)biotic mineral phases, microorganisms, and (microbially-derived) organic matter. On...

The Braconidae are a megadiverse and ecologically highly important group of insects. The vast majority of braconid wasps are parasitoids of other insects, usually attacking the egg or larval stages of their hosts. The ovipositor plays a crucial role in the assessment of the potential host and precise egg laying. We used light- and electron-microsco...

Video S1. Animation of the rotated segmented 3D reconstruction of the terebra of Habrobracon hebetor.

Video S2. Animation of the rotated segmented 3D reconstruction of the proximal region of the terebra of Habrobracon hebetor (cf. Fig. 3), highlighting the 1st and 2nd valvulae, the ligaments, and the duct of the venom gland.

Using two-dimensional top-down view microscopy, researchers have recently described chondrocytes as being spatially arranged in distinct patterns such as strings, double strings, and small and large clusters. Because of the seeming association of these changes with tissue degeneration, they have been proposed as an image-based biomarker for early o...

Stemmata of strepsipteran insects represent the smallest arthropod eyes known, having photoreceptors which form fused rhabdoms measuring an average size of 1.69 × 1.21 × 1.04 μm and each occupying a volume of only 0.97–1.16 μm³. The morphology of the stemmata of the extremely miniaturized first instar larva of Stylops ovinae (Strepsiptera, Stylopid...

A hallmark in snails’ anatomy is the conspicuous crossing of the pleurovisceral nerve cords present in all but the most derived gastropod clades. This feature is called streptoneury and hitherto near-universally believed to derive from the process of torsion which is, ontogenetically, visible by a 180° rotation of the visceral sac relative to the c...

Little morphological information is available about subretinal pigment shields in insect compound eyes, especially ultrastructural information. The latter is however needed in order to detect possible smallest projections that emanate from pigment‐granule‐bearing cells and pass through the basal matrix (BM), but that are not visible in light microg...

Pigment granules, found in different cell types of the retina in insect compound eyes, fulfill important functions. They isolate the individual ommatidia from stray light, regulate the angular sensitivity and restrict the light that reaches the photoreceptor according to ambient light intensities. Descriptions of pigment cells within the retina are...

Existing information on insect compound eyes is mainly limited to two-dimensional information derived from histological or ultrathin sections. These allow a basic description of eye morphology, but are limited in z-axis resolution because of the section thickness or intervals between sections, so that accurate volumetric information cannot be gener...

Solar cells with increased short‐circuit current density and energy conversion efficiency can be realized by integrating moth eye textures in the design of perovskite and amorphous silicon thin film solar cells. Broadband light incoupling in solar cells can be achieved by using hexagonally arranged arrays of nipples or domes with parabolically shap...

Most studies dealing with the limits to miniaturization in insect brains have until now relied on information based on data collected in two dimensions: either histological sections imaged by light microscopy, or electron micrographs of single ultrathin sections imaged by transmission electron microscopy (TEM). To test the validity of transferring...

Due to their small size, diminutive parasitic wasps are outstanding subjects for investigating aspects of body miniaturization. Information on minute compound eyes is still scarce, and we therefore investigated eye morphology in one of the smallest known Hymenopteran species Megaphragma mymaripenne (body size 0.2 mm) relative to Anaphes flavipes (b...

The Acanthopteroctetidae are one of the first-originated family-group lineages within "tongue moths" (Lepidoptera-Glossata). The purpose of this study is to provide a comprehensive account (based on whole mount preparations, serial sections, and Scanning electron microscopy) of the cephalic structure of an adult exemplar of the family, to supplemen...

Superposition and apposition compound eyes are commonly associated with moths and butterflies, respectively. However, recently intermediate eye designs, combining features of both apposition and superposition eyes were found in tiny insects. Here, we examine the eyes of 12 species of moth, ranging from 1.88 to 6.03 mm body size, by scanning and tra...

In spite of the numerous studies on insect compound eyes within the last 100 years, the number of investigations specifically dealing with the eyes of species of small body size is near to negligible. Based on theoretical optical examinations it had been predicted that an unlimited reduction in the size of a compound eye, especially if the latter w...

The two lemon-shaped compound eyes of the moth Cameraria ohridella measure in dorsal–ventral direction 263.0 μm in male and 238.9 μm in female individuals. In anterior–posterior direction no significant differences were found between the sexes, eye length being about 194.6 μm. The eyes of males consist of ca. 417 hexagonal facets, while those of fe...

With a body length of only 2 mm, the nepticulid Stigmella microtheriella (Stainton, 1854) is one of the smallest moths known to date. We investigated the optical design of its lemon-shaped compound eyes, which measure 83.60 μm in anterior-posterior and 119.77 μm in dorso-ventral direction. The eyes consist of about 123 facets, each of the latter ju...

Nipples on the surface of moth eye facets exhibit almost perfect broadband anti-reflection properties. We have studied the facet surface micro-protuberances, known as corneal nipples, of the chestnut leafminer moth Cameraria ohridella by atomic force microscopy, and simulated the optics of the nipple arrays by three-dimensional electromagnetic simu...

With a body length of only 0.3-0.4 mm, the parasitoid wasp Trichogramma evanescens (Westwood) is one of the smallest insects known. Yet, despite its diminutive size, it possesses compound eyes that are of oval shapes, measuring across their long axes in dorsoventral direction 63.39 and 71.11 μm in males and females, respectively. The corresponding...

In the framework of several field excursions to the Balearic Island of Ibiza (Western Mediterranean Sea) conducted every spring and autumn between 1998 and 2007, extensive studies were carried out on the structure, diversity and ecology of the coastal ichthyofauna. The ichthyofaunistic observations were made in the months of March, April, September...