Shared and unique patterns of embryo development in extremophile poeciliids

Background: Closely related lineages of livebearing fishes have independently adapted to two extreme environmental factors: toxic hydrogen sulphide (H2S) and perpetual darkness. Previous work has demonstrated in adult specimens that fish from these extreme habitats convergently evolved drastically increased head and offspring size, while cave fish are further characterized by reduced pigmentation and eye size. Here, we traced the development of these (and other) divergent traits in embryos of Poecilia mexicana from benign surface habitats (“surface mollies”) and a sulphidic cave (“cave mollies”), as well as in embryos of the sister taxon, Poecilia sulphuraria from a sulphidic surface spring (“sulphur mollies”). We asked at which points during development changes in the timing of the involved processes (i.e., heterochrony) would be detectible. Methods and Results: Data were extracted from digital photographs taken of representative embryos for each stage of development and each type of molly. Embryo mass decreased in convergent fashion, but we found patterns of embryonic fat content and ovum/embryo diameter to be divergent among all three types of mollies. The intensity of yellow colouration of the yolk (a proxy for carotenoid content) was significantly lower in cave mollies throughout development. Moreover, while relative head size decreased through development in surface mollies, it increased in both types of extremophile mollies, and eye growth was arrested in mid-stage embryos of cave mollies but not in surface or sulphur mollies. Conclusion: Our results clearly demonstrate that even among sister taxa convergence in phenotypic traits is not always achieved by the same processes during embryo development. Furthermore, teleost development is crucially dependent on sufficient carotenoid stores in the yolk, and so we discuss how the apparent ability of cave mollies to overcome this carotenoid-dependency may represent another potential mechanism explaining the lack of gene flow between surface and cave mollies

Size scaling in bi-crystalline Cu micropillars containing a coherent twin boundary

The impact of a coherent twin boundary (CTB) on the size scaling of the shear stress in micropillar compression tests has been investigated through microcompression of bi-crystalline pillars containing a vertical CTB, as well as single-crystalline pillars in three different nominal diameters of 1, 3 and 5 µm. While both, single- and bi-crystalline pillar results follow the size scaling trend typically observed in micropillars, namely “smaller is stronger”, we could identify a size-dependent contribution of the CTB in the increase of the shear stress at 2% strain (τ2%). A probabilistic analysis was performed to quantify the magnitude of the effect and to separate the CTB contribution from the single crystal size scaling contribution of the strength increase. The CTB-related strengthening was most prominent for smaller pillars and tended to be small for larger pillar diameters. The behavior can be explained by attributing an excess dislocation curvature in the scaling law according to the double-hump dislocation line shape model for bi-crystals, which requires parallel alignment of the dislocation line and the Burgers vector at the CTB

Sex-specific local life-history adaptation in surface- and cave-dwelling Atlantic mollies (Poecilia mexicana)

Cavefishes have long been used as model organisms showcasing adaptive diversification, but does adaptation to caves also facilitate the evolution of reproductive isolation from surface ancestors? We raised offspring of wild-caught surface- and cave-dwelling ecotypes of the neotropical fish Poecilia mexicana to sexual maturity in a 12-month common garden experiment. Fish were raised under one of two food regimes (high vs. low), and this was crossed with differences in lighting conditions (permanent darkness vs. 12:12 h light:dark cycle) in a 2 × 2 factorial design, allowing us to elucidate potential patterns of local adaptation in life histories. Our results reveal a pattern of sex-specific local life-history adaptation: Surface molly females had the highest fitness in the treatment best resembling their habitat of origin (high food and a light:dark cycle), and suffered from almost complete reproductive failure in darkness, while cave molly females were not similarly affected in any treatment. Males of both ecotypes, on the other hand, showed only weak evidence for local adaptation. Nonetheless, local life-history adaptation in females likely contributes to ecological diversification in this system and other cave animals, further supporting the role of local adaptation due to strong divergent selection as a major force in ecological speciation

A new and morphologically distinct population of cavernicolous Poecilia mexicana (Poeciliidae: Teleostei)

The cave molly, Poecilia mexicana, from the Cueva del Azufre, a sulfur cave in Tabasco, Mexico, ranks among the best-studied cave fishes worldwide, despite being known from a single population only. Here we describe a newly discovered second population of cave-dwelling P. mexicana from a nearby, but mostly non-sulfidic cave (Luna Azufre). Despite apparent similarities between the two populations (such as reduced eye diameter and reduced pigmentation), a geometric morphometric analysis revealed pronounced morphological differentiation between the two cave form

Chemical vapor deposition and infiltration for the production of tungsten fiber reinforced tungsten composite material

Contribution submission to the conference Regensburg 2016Chemical vapor deposition and infiltration for the productionof tungsten fiber reinforced tungsten composite material —∙Martin Aumann1, Jan Willem Coenen1, Hanns Gietl2, TillHoeschen2, Johann Riesch2, Klaus Schmid2, Rudolf Neu2, andChristian Linsmeier1 — 1Forschungszentrum Juelich GmbH, Institutfür Energie- und Klimaforschung, 52425 Juelich — 2Max-Planck-Institut für Plasmaphysik, 85748 GarchingDue to its high melting point, high corrosion resistance and its preferableproperties in terms of hydrogen retention, tungsten is a promisingcandidate in future nuclear fusion devices. However, the mechanicalbehavior of tungsten is crucial, as it is inherently brittle at room temperature.As possibility to overcome this brittleness, a composite materialcan be formed, which shows pseudo-ductility and therefore avoidscatastrophic failure of the material. A possibility to produce such aWf/W-composite is chemical vapor deposition and chemical vapor infiltration,where tungsten is deposited on small tungsten wires throughthe reaction of WF6 and H2. With ongoing infiltration time, pores areformed between the fibers, which decrease in size through the chemicalreaction. For better process understanding, a pore model was established,which solves the mass balance inside the pore and the resultingpore diameter simultaneously. It shows a significant difference in diameterfor longer infiltration times. This behavior shall be proved inexperiments with an experimental pore, which is similar to the simulatedone. Furthermore also kinetic investigations on the chemicalsurface reaction are carried out to increase the process understanding.Part: MMType: Vortrag;TalkTopic: Transport (Diffusion, Leitfähigkeit,Wärme)/ Transport (Diffusion,conductivity, heat)Email: [email protected]

Microstructure, mechanical behaviour and fracture of pure tungsten wire after different heat treatments

Plastic deformation of tungsten wire is an effective source of toughening tungsten fibre-reinforced tungsten composites (Wf/W) and other tungsten fibre-reinforced composites. To provide a reference for optimization of those composites, unconstrained pure tungsten wire is studied after various heat treatments in terms of microstructure, mechanical behaviour and fracture mode. Recrystallization is already observed at a relatively low temperature of 1273 K due to the large driving force caused by a high dislocation density. Annealing for 30 min at 1900 K also leads to recrystallization, but causes a rather different microstructure. As-fabricated wire and wire recrystallized at 1273 K for 3 h show fine grains with a high aspect ratio and a substantial plastic deformability: a clearly defined tensile strength, high plastic work, similar necking shape, and the characteristic knife-edge-necking of individual grains on the fracture surface. While the wire recrystallized at 1900 K displays large, almost equiaxed grains with low aspect ratios as well as distinct brittle properties. Therefore, it is suggested that a high aspect ratio of the grains is important for the ductile behaviour of tungsten wire and that embrittlement is caused by the loss of the preferable elongated grain structure rather than by recrystallization. In addition, a detailed evaluation of the plastic deformation behaviour during tensile test gives guidance to the design and optimization of tungsten fibre-reinforced composites