nils-herrmann/clean_scirepeval huggingface dataset:
Integrative biomechanics for tree ecology: beyond wood density and strength.
Venue: Journal of Experimental Botany

Functional ecology has long considered the support function as important, but its biomechanical complexity is only just being elucidated. We show here that it can be described on the basis of four biomechanical traits, two safety traits against winds and self-buckling, and two motricity traits involved in sustaining an upright position, tropic motion velocity (MV) and posture control (PC). All these traits are integrated at the tree scale, combining tree size and shape together with wood properties. The assumption of trait constancy has been used to derive allometric scaling laws, but it was more recently found that observing their variations among environments and functional groups, or during ontogeny, provides more insights into adaptive syndromes of tree shape and wood properties. However, oversimplified expressions have often been used, possibly concealing key adaptive drivers. An extreme case of oversimplification is the use of wood basic density as a proxy for safety. Actually, as wood density is involved in stiffness, loads, and construction costs, the impact of its variations on safety is non-trivial. Moreover, other wood features, especially the microfibril angle (MFA), are also involved. Furthermore, wood is not only stiff and strong, but it also acts as a motor for MV and PC. The relevant wood trait for this is maturation strain asymmetry. Maturation strains vary with cell-wall characteristics such as MFA, rather than with wood density. Finally, the need for further studies about the ecological relevance of branching patterns, motricity traits, and growth responses to mechanical loads is discussed.
Die Spiegeloptik des Flußkrebsauges
Venue: Journal of Comparative Physiology A-neuroethology Sensory Neural and Behavioral Physiology

SummaryIn the superposition eye of the crayfish (Astacus leptodactylus), images are formed by radial plane mirrors arranged in an orthogonal pattern. The optical structure of the crayfish eye can be described as a family of virtual reflecting cone envelopes concentric around each direction in space. There exist two reflection mechanisms: total internal reflection at the sides of the crystalline cones and reflection by multilayer mirrors attached to the distal parts of the cones. Image-forming rays have to be reflected twice in the general case, and once in the case of perpendicular position of the plane of incidence and the mirror plane. For rays incident at small angles to the ommatidial axis, this condition is almost satisfied due to a particular axial variation of the refractive index of the crystalline cone, and for rays incident at large angles, due to the spectral reflecting properties of the multilayer reflector.
The narrow-leaf syndrome: a functional and evolutionary approach to the form of fog-harvesting rosette plants
Venue: Oecologia

Plants that use fog as an important water-source frequently have a rosette growth habit. The performance of this morphology in relation to fog interception has not been studied. Some first-principles from physics predict that narrow leaves, together with other ancillary traits (large number and high flexibility of leaves, caudices, and/or epiphytism) which constitute the “narrow-leaf syndrome” should increase fog-interception efficiency. This was tested using aluminum models of rosettes that differed in leaf length, width and number and were exposed to artificial fog. The results were validated using seven species of Tillandsia and four species of xerophytic rosettes. The total amount of fog intercepted in rosette plants increased with total leaf area, while narrow leaves maximized interception efficiency (measured as interception per unit area). The number of leaves in the rosettes is physically constrained because wide-leafed plants can only have a few blades. At the limits of this constraint, net fog interception was independent of leaf form, but interception efficiency was maximized by large numbers of narrow leaves. Atmospheric Tillandsia species show the narrow-leaf syndrome. Their fog interception efficiencies were correlated to the ones predicted from aluminum-model data. In the larger xerophytic rosette species, the interception efficiency was greatest in plants showing the narrow-leaf syndrome. The adaptation to fog-harvesting in several narrow-leaved rosettes was tested for evolutionary convergence in 30 xerophytic rosette species using a comparative method. There was a significant evolutionary tendency towards the development of the narrow-leaf syndrome the closer the species grew to areas where fog is frequently available. This study establishes convergence in a very wide group of plants encompassing genera as contrasting as Tillandsia and Agave as a result of their dependence on fog.
The mechanism of floral heliotropism in the snow buttercup, Ranunculus adoneus
Venue: Plant Cell and Environment

We designed field experiments using solar-trackingRanunculus adoneusflowers to determine where photo-reception occurred, which organs responded, and howmovement was achieved. Flower peduncles bend eastwardin the morning and gradually unbend over the course ofthe day. Peduncles were found to bend significantly morefrequently in the middle region near the floral bracts,1–3 cm below the flower, than elsewhere on the peduncle.Because the peduncle tip continued to track the sun evenafter the flower itself was removed, our experiments con-centrated on shielding (or conversely, exposing) variousportions of peduncles from (or to) sunlight. Photo-reception occurred primarily in the portion of the stemjust beneath the floral receptacle. By following the posi-tion of landmarks applied to the stem, we found that 40%more growth occurred on the shaded side of bent pedun-cles, compared to the sunlit side. In contrast, top-shieldedpeduncles did not solar track well and grew only 25%more on the shaded side than on the sunlit side. Thisgrowth differential corresponded to differences in celllength on the two sides of bent peduncles, with signifi-cantly longer epidermal cells occurring on the shaded sidethan on the sunlit side. Ranunculus adoneus; snow buttercup; helio-tropism; phototropism; solar tracking.
Carrion-feeding on the sediment surface at nocturnal low tides by the polychaete Phyllodoce mucosa
Venue: Marine Biology

Harsh physical conditions in the intertidal zone are the cause of an ample amount of dead macroinvertebrates, which constitute a food source for carrion-feeders. In the European Wadden Sea, this trophic guild includes decapod crustaceans and fish when the tide is in, while during nocturnal low tides the polychaete Phyllodoce mucosa is attracted in large numbers by dead mollusks, crabs or worms on the sediment surface. Within 10 s worms emerged to the surface, crawled as far as 15 m on mucus trails towards the carcass, sucked in tissue up to one-third of their own weight, and then quickly retreated to below the surface. Abundance of P. mucosa was highest in the lower intertidal zone and winter. The seaward high abundance pattern, however, did not continue into the shallow subtidal. In summer, few were attracted during daytime or when the tide was in. However, up to 447 worms aggregated at a single crushed mussel within 20 min at dusk during low-tide exposure. This study suggests that during winter carrion-feeding is an important trophic niche on cold-temperate, intertidal mud flats occupied by a phyllodocid polychaete that is segregated in feeding time from most other scavengers and benefits from cold-sensitive benthic invertebrates.
Giant siliceous spicules from the deep-sea glass sponge Monorhaphis chuni.
Venue: International Review of Cell and Molecular Biology

Only 13 years after realizing, during a repair of a telegraph cable pulled out from the deep sea, that the depth of the ocean is plentifully populated with a highly diverse fauna and flora, the Challenger expedition (1873-1876) treasured up a rich collection of vitreous sponges (Hexactinellida). They had been described by Schulze and represent the phylogenetically oldest class of siliceous sponges (phylum Porifera); they are eye-catching because of their distinct body plan, which relies on a filigree skeleton. It is constructed by an array of morphologically determined elements, the spicules. Soon after, during the German Deep Sea Expedition "Valdivia" (1898-1899), Schulze could describe the largest siliceous hexactinellid sponge on Earth, the up to 3-m high Monorhaphis chuni, which develops the equally largest bio-silica structure, the giant basal spicules (3 mx10 mm). Using these spicules as a model, basic knowledge on the morphology, formation, and development of the skeletal elements could be achieved. They are formed by a proteinaceous scaffold (composed of a 27-kDa protein), which mediates the formation of the siliceous lamellae, into which the proteins are encased. The high number of 800 of 5-10 microm thick lamellae is concentrically arranged around the axial canal. The silica matrix is composed of almost pure silicon oxide, providing it with unusually optophysical properties, which are superior to those of man-made waveguides. Experiments might suggest that the spicules function in vivo as a nonocular photoreception system. In addition, the spicules have exceptional mechanical properties, combining mechanical stability with strength and stiffness. Like demosponges, also the hexactinellids synthesize their silica enzymatically, via the enzyme silicatein (27-kDa protein). It is suggested that these basic insights will surely contribute to a further applied utilization and exploration of silica in bio-material/biomedical science.
Transformation mechanism of amorphous calcium carbonate into calcite in the sea urchin larval spicule
Venue: Proceedings of the National Academy of Sciences of the United States of America

Sea urchin larval spicules transform amorphous calcium carbonate (ACC) into calcite single crystals. The mechanism of transformation is enigmatic: the transforming spicule displays both amorphous and crystalline properties, with no defined crystallization front. Here, we use X-ray photoelectron emission spectromicroscopy with probing size of 40–200 nm. We resolve 3 distinct mineral phases: An initial short-lived, presumably hydrated ACC phase, followed by an intermediate transient form of ACC, and finally the biogenic crystalline calcite phase. The amorphous and crystalline phases are juxtaposed, often appearing in adjacent sites at a scale of tens of nanometers. We propose that the amorphous-crystal transformation propagates in a tortuous path through preexisting 40- to 100-nm amorphous units, via a secondary nucleation mechanism.
Feeling Small: Exploring the Tactile Perception Limits
Venue: Scientific Reports

The human finger is exquisitely sensitive in perceiving different materials, but the question remains as to what length scales are capable of being distinguished in active touch. We combine material science with psychophysics to manufacture and haptically explore a series of topographically patterned surfaces of controlled wavelength, but identical chemistry. Strain-induced surface wrinkling and subsequent templating produced 16 surfaces with wrinkle wavelengths ranging from 300 nm to 90 μm and amplitudes between 7 nm and 4.5 μm. Perceived similarities of these surfaces (and two blanks) were pairwise scaled by participants, and interdistances among all stimuli were determined by individual differences scaling (INDSCAL). The tactile space thus generated and its two perceptual dimensions were directly linked to surface physical properties – the finger friction coefficient and the wrinkle wavelength. Finally, the lowest amplitude of the wrinkles so distinguished was approximately 10 nm, demonstrating that human tactile discrimination extends to the nanoscale.
Surface tension propulsion of fungal spores
Venue: The Journal of Experimental Biology

Most basidiomycete fungi actively eject their spores. The process begins with the condensation of a water droplet at the base of the spore. The fusion of the droplet onto the spore creates a momentum that propels the spore forward. The use of surface tension for spore ejection offers a new paradigm to perform work at small length scales. However, this mechanism of force generation remains poorly understood. To elucidate how fungal spores make effective use of surface tension, we performed a detailed mechanical analysis of the three stages of spore ejection: the transfer of energy from the drop to the spore, the work of fracture required to release the spore from its supporting structure and the kinetic energy of the spore after ejection. High-speed video imaging of spore ejection in Auricularia auricula and Sporobolomyces yeasts revealed that drop coalescence takes place over a short distance (∼5 μm) and energy transfer is completed in less than 4 μs. Based on these observations, we developed an explicit relation for the conversion of surface energy into kinetic energy during the coalescence process. The relation was validated with a simple artificial system and shown to predict the initial spore velocity accurately (predicted velocity: 1.2 m s–1; observed velocity: 0.8 m s–1 for A. auricula). Using calibrated microcantilevers, we also demonstrate that the work required to detach the spore from the supporting sterigma represents only a small fraction of the total energy available for spore ejection. Finally, our observations of this unique discharge mechanism reveal a surprising similarity with the mechanics of jumping in animals.
Penguin heat-retention structures evolved in a greenhouse Earth
Venue: Biology Letters

Penguins (Sphenisciformes) inhabit some of the most extreme environments on Earth. The 60+ Myr fossil record of penguins spans an interval that witnessed dramatic shifts in Cenozoic ocean temperatures and currents, indicating a long interplay between penguin evolution and environmental change. Perhaps the most celebrated example is the successful Late Cenozoic invasion of glacial environments by crown clade penguins. A major adaptation that allows penguins to forage in cold water is the humeral arterial plexus, a vascular counter-current heat exchanger (CCHE) that limits heat loss through the flipper. Fossil evidence reveals that the humeral plexus arose at least 49 Ma during a ‘Greenhouse Earth’ interval. The evolution of the CCHE is therefore unrelated to global cooling or development of polar ice sheets, but probably represents an adaptation to foraging in subsurface waters at temperate latitudes. As global climate cooled, the CCHE was key to invasion of thermally more demanding environments associated with Antarctic ice sheets.
Flow, flapping, and photosynthesis ofNereocystis leutkeana: a functional comparison of undulate and flat blade morphologies
Venue: Marine Biology

A number of species of macroalagae possess a flat, strap-like blade morphology in habitats exposed to rapidly-moving water whereas those at protected sites have a wider, undulate blade shape. We have explored the functional consequences of flat, narrow vs. wide, undulate blade morphologies in the giant bull kelpNereocystis luetkeana. Our study focused on the behavior of blades in ambient water currents and the consequences of that behavior to breakage and to photosynthesis. In flowing water, the narrow, flat blades flap with lower amplitude and collapse together into a more streamlined bundle than do wide, undulate blades, and hence experience lower drag per blade area at a given flow velocity. If the algae at current-swept sites had ruffled blades, drag forces would sometimes be sufficient to break the stipes. However, flat blades in a streamlined bundle experience more self-shading than do undulate blades, which remain spread out in water currents. Thus, there is a morphological trade-off between reducing drag and reducing self-shading. Photosynthetic14C-HCO3 uptake rates decrease in slow flow when the boundary layer along the blade surface across which diffusion takes place is relatively thick. However, blade flapping, which stirs water near the blade surface, enhances carbon uptake rates in slow water currents for both the undulate and the flat morphologies.
Directionally Controlled Fluorescence Emission in Butterflies
Venue: Science

Recently developed, high-efficiency, light-emitting diodes use two-dimensional photonic crystals to enhance the extraction of otherwise internally trapped light and multilayer reflectors to control the direction of light emission. This work describes the characterization of a naturally evolved light-extraction system on the wing scales of a small group of Papilio butterflies. The efficient extraction of fluorescence from these scales is facilitated by a two-dimensional photonic crystal slab that uses a multilayer to help control emission direction. Its light-extraction function is analogous to that of the light-emitting diode.
Evidence that dimethyl sulfide facilitates a tritrophic mutualism between marine primary producers and top predators
Venue: Proceedings of the National Academy of Sciences of the United States of America

This study demonstrates that dimethyl sulfide, a chemical cue involved in global climate regulation, mediates a tritrophic mutualistic interaction between marine apex predators and primary producers. Our results imply that marine top predators play a critical role in maintaining both ocean health and global climate. Our results highlight the need for more collaboration and discussion between micro- and macroscale biologists working on global issues in the Southern Ocean. Tritrophic mutualistic interactions have been best studied in plant–insect systems. During these interactions, plants release volatiles in response to herbivore damage, which, in turn, facilitates predation on primary consumers or benefits the primary producer by providing nutrients. Here we explore a similar interaction in the Southern Ocean food web, where soluble iron limits primary productivity. Dimethyl sulfide has been studied in the context of global climate regulation and is an established foraging cue for marine top predators. We present evidence that procellariiform seabird species that use dimethyl sulfide as a foraging cue selectively forage on phytoplankton grazers. Their contribution of beneficial iron recycled to marine phytoplankton via excretion suggests a chemically mediated link between marine top predators and oceanic primary production.
Antipredatory properties of an animal architecture: how complex faecal cases thwart arthropod attack
Venue: Animal Behaviour

Animals create a wide variety of structures to deal with abiotic and biotic challenges. We evaluated an intriguing structure whose function has never been thoroughly tested. Specifically, we evaluated the hypothesis that the body-enclosing ‘faecal case’ created and lived in by the immature stages of Neochlamisus leaf beetles reduces their risk of predation. We especially focus on the case of N. platani, which is externally covered with host-plant trichomes, and includes a distinct trichome-filled chamber (‘attic’) in the case apex. Here, we separately evaluated the effects of case, trichomes and attic on each of several behavioural stages of predator attack using N. platani and N. bimaculatus larvae and pupae. Three generalist predators (crickets, soldier bugs and lynx spiders) that represent different feeding strategies were used in our individual-level repeated observation behavioural trials. Results strongly demonstrated that the faecal case itself greatly reduced predation risk for all combinations of beetle species, life history stage and predator. Additional evidence indicated that both trichomes and attics further and independently reduced predation risk. Variation in results among treatments was also informative. For example, the capacity of faecal case components to reduce predation sometimes varied markedly among predators and between larval versus pupal life stages. Patterns of predator behaviour provided no evidence that caseless larvae have alternative means of defence. This study further presents a rare example of the co-option of a physical plant defence (trichomes) by an herbivore.
The high cost of mutualism: effects of four species of East African ant symbionts on their myrmecophyte host tree.
Venue: Ecology

Three recent meta-analyses of protective plant-ant mutualisms report a surprisingly weak relationship between herbivore protection and measured demographic benefits to ant-plants, suggesting high tolerance for herbivory, substantial costs of ant-mediated defense, and/or benefits that are realized episodically rather than continuously. Experimental manipulations of protective ant-plant associations typically last for less than a year, yet virtually all specialized myrmecophytes are long-lived perennials for which the costs and benefits of maintaining ant symbionts could accrue at different rates over the host's lifetime. To complement long-term monitoring studies, we experimentally excluded each of four ant symbionts from their long-lived myrmecophyte host trees (Acacia drepanolobium) for 4.5 years. Ant species varied in their effectiveness against herbivores and in their effects on intermediate-term growth and reproduction, but the level of herbivore protection provided was a poor predictor of the net impact they had on host trees. Removal of the three Crematogaster species resulted in cumulative gains in host tree growth and/or reproduction over the course of the experiment, despite the fact that two of those species significantly reduce chronic herbivore damage. In contrast, although T. penzigi is a relatively poor defender, the low cost of maintaining this ant symbiont apparently eliminated negative impacts on overall tree growth and reproduction, resulting in enhanced allocation to new branch growth by the final census. Acacia drepanolobium is evidently highly tolerant of herbivory by insects and small browsers, and the costs of maintaining Crematogaster colonies exceeded the benefits received during the study. No experimental trees were killed by elephants, but elephant damage was uniquely associated with reduced tree growth, and at least one ant species (C. mimosae) strongly deterred elephant browsing. We hypothesize that rare but catastrophic damage by elephants may be more important than chronic herbivory in maintaining the costly myrmecophyte habit in this system.
Structural biology: A channel with a twist
Venue: Nature

Mechanosensitive channels release tension in cell membranes by opening 'pressure relief' pores. The structure of a partially open channel suggests a gating mechanism and delivers an unexpected architectural twist. Mechanosensitive channels protect bacteria from osmotic shock by allowing ions to flow across the membrane in response to changes in membrane tension. MscL is one such channel with large conductance, which exhibits several intermediate states between its closed and open forms. The 3.8-Å crystal structure of the Staphylococcus aureus MscL has now been determined in a nonconductive, partially expanded and tetrameric form.