Friends or enemies: Multi-species interactions among biofoulers, endoparasites and their gastropod hosts

Parasites are a crucial factor that shapes the functioning of communities throughout the world, as are gregarious macrofoulers in aquatic ecosystems. However, little is known about the effects of three-way interactions between macrofoulers, endoparasites and their hosts. We predict that macrofouling and parasite infection may act (i) independently of each other, (ii) synergistically, increasing their final negative impact on the host or (iii) antagonistically, the former weakening the negative impact of the latter. We investigated multiway relationships between an invasive freshwater filter-feeding macrofouler (the zebra mussel), digenean endoparasite and their gastropod host, Viviparus viviparus. Furthermore, we checked the recruitment of mussels in living gastropods versus their empty shells. We sampled living V. viviparus and their empty shells with attached dreissenids from a Polish dam reservoir. We counted and weighed attached mussels and determined wet weight, shell height and sex of gastropods. Then we dissected the molluscs to look for digenean larvae and gastropod embryos. We use these parameters to look for reciprocal associations between mussel fouling, parasitic infection and gastropod size and fertility, as well as to infer the most likely mechanisms of the observed relationships. Dreissenid overgrowth was associated with reduced fertility and size of viviparids, but also with a lower prevalence of digenean metacercariae (Leucochloridiomorpha sp.). We did not observe a negative influence of these digeneans on their gastropod hosts. In addition, large living viviparids and their empty shells were equally used as substrates by dreissenids, but small living gastropods were more fouled than shells of the corresponding size. A trade-off exists in the studied system: filter-feeding macrofoulers may bring some profits for their host, reducing the pressure of waterborne parasites (which may be crucial in the case of pathogenic species/life stages), although at the cost of the reduced growth and fertility of the host. Furthermore, mussels attached to mollusc hosts can exert a cascading effect on the reduced prevalence of digeneans in their final hosts, including those of medical or veterinary importance.

Curvature-driven instabilities in thin active shells

Spontaneous material shape changes, such as swelling, growth or thermal expansion, can be used to trigger dramatic elastic instabilities in thin shells. These instabilities originate in geometric incompatibility between the preferred extrinsic and intrinsic curvature of the shell, which may be modified by active deformations through the thickness and in plane, respectively. Here, we solve the simplest possible model of such instabilities, which assumes the shells are shallow, thin enough to bend but not stretch, and subject to homogeneous preferred curvatures. We consider separately the cases of zero, positive and negative Gauss curvature. We identify two types of supercritical symmetry-breaking instability, in which the shell's principal curvature spontaneously breaks discrete up/down symmetry and continuous planar isotropy. These are then augmented by inversion instabilities, in which the shell jumps subcritically between up/down broken symmetry states and rotation instabilities, in which the curvatures rotate by 90° between states of broken isotropy without release of energy. Each instability has a thickness-independent threshold value for the preferred extrinsic curvature proportional to the square root of Gauss curvature. Finally, we show that the threshold for the isotropy-breaking instability is the same for deep spherical caps, in good agreement with recently published data.

A Brief History of Biomineralization Studies

Biomineralization is the process by which living organisms produce minerals. Although the term is recent (∼1970), the study of internal and external skeleton mineralization is older. This article describes the history of biomineralization studies. This story is strongly dependent on, but not only on, the history of analytical technique development. Events are chronologically described to easily track progress and connections between people. The background of the people who contributed to the progress is also briefly described.

'From soil to chocolate bar': identifying critical steps in the journey of cadmium in a Colombian cacao plantation

Regulation of maximum levels of cadmium in chocolate is an issue for cacao exportation from many parts of Latin America, including Colombia. These limits are related to the final product, but buyers often request maximum levels of Cd in the beans. However, to date, there is neither a clear understanding of the relationship between the specified levels of Cd in chocolate and cocoa derivatives and levels in harvested beans or soil nor of the effect of post-harvest processes on the levels of Cd in the final product. To address this, the fate of Cd concentration from soil to chocolate bar was followed in a single farm in Santander district, Colombia. The concentration of Cd in soils was measured using ICP-OES and correlated with soil pH, soil organic matter (SOM), and the use of P-based fertilisers. Cd concentrations were also measured in unfermented seeds, fermented and dried beans, shell, nibs, and chocolate. SOM (2.93-3.78%), soil pH (4.7-4.9), soil P concentration (120-132 mg kg^-1) affect Cd availability. However, it is still unclear whether Cd concentration of P-based fertilisers (3-30 mg kg^-1) is important or not. While post-harvest treatments did not affect the Cd concentration of beans (4.17 ± 0.8 mg kg^-1 on average), the removal of the shell (6.57 mg kg^-1) from the nibs (3.28 mg kg^-1), as well as the percentage of cocoa mass used contributes to a reduction in Cd concentration in the chocolate bar (1.60 mg kg^-1). This study provides clear indications on where research into mitigation measures should be focussed, as well as indicating the importance of carrying out analyses for Cd in the nib or cacao mass, rather than the whole bean, reducing Cd concentration by up to 40%.

Struggle for phosphorus and the Devonian overturn

Organisms with external phosphatic shells diversified and became abundant at the beginning of the Early Paleozoic but gradually declined and were rare by its end. The decreasing availability of phosphorus in oceans is thought to be responsible for this evolutionary trend. Responses of organisms to changes in the phosphorus cycle can be traced to the late Neoproterozoic, and likely had a significant role in the Cambrian explosion, the Great Ordovician Biodiversification Event (GOBE), and the Devonian nekton revolution. Effective use of phosphorus by vertebrates during the Devonian nekton revolution caused the phosphorus pool to shift from benthic external shells to the skeletons of pelagic vertebrates, and moved the marine faunas toward the dominance patterns and ecological structure of the Modern Evolutionary Fauna.

Avoiding Degradation by Using Hydrophobic Polymer Shells

The stunning optical properties of upconverting nanoparticles (UCNPs) have inspired promising biomedical technologies. Nevertheless, their transfer to aqueous media is often accompanied by intense luminescence quenching, partial dissolution by water, and even complete degradation by molecules such as phosphates. Currently, these are major issues hampering the translation of UCNPs to the clinic. In this work, a strategy is developed to coat and protect β-NaYF₄ UCNPs against these effects, by growing a hydrophobic polymer shell (HPS) through miniemulsion polymerization of styrene (St), or St and methyl methacrylate mixtures. This allows one to obtain single core@shell UCNPs@HPS with a final diameter of ≈60-70 nm. Stability studies reveal that these HPSs serve as a very effective barrier, impeding polar molecules to affect UCNPs optical properties. Even more, it allows UCNPs to withstand aggressive conditions such as high dilutions (5 µg mL^-1 ), high phosphate concentrations (100 mm), and high temperatures (70 °C). The physicochemical characterizations prove the potential of HPSs to overcome the current limitations of UCNPs. This strategy, which can be applied to other nanomaterials with similar limitations, paves the way toward more stable and reliable UCNPs with applications in life sciences.

Material Design for Optimal Postbuckling Behaviour of Composite Shells

Lightweight thin-walled structures are crucial for many engineering applications. Advanced manufacturing methods are enabling the realization of composite materials with spatially varying material properties. Variable angle tow fibre composites are a representative example, but also nanocomposites are opening new interesting possibilities. Taking advantage of these tunable materials requires the development of computational design methods. The failure of such structures is often dominated by buckling and can be very sensitive to material configuration and geometrical imperfections. This work is a review of the recent computational developments concerning the optimisation of the response of composite thin-walled structures prone to buckling, showing how baseline products with unstable behaviour can be transformed in stable ones operating safely in the post-buckling range. Four main aspects are discussed: mechanical and discrete models for composite shells, material parametrization and objective function definition, solution methods for tracing the load-displacement path and assessing the imperfection sensitivity, structural optimisation algorithms. A numerical example of optimal material design for a curved panel is also illustrated.

A Commentary on the Use of Bivalve Mollusks in Monitoring Metal Pollution Levels

The objective of this commentary is to promote the use of bivalves as biomonitors, which is a part of the continual efforts of the International Mussel Watch. This commentary is an additional discussion on "Bivalve mollusks in metal pollution studies: From bioaccumulation to biomonitoring" by Zuykov et al., published in Chemosphere 93, 201-208. The present discussion can serve as a platform for further insights to provide new thoughts and novel ideas on how to make better use of bivalves in biomonitoring studies. The certainty of better and more extensive applications of mollusks in environmental monitoring in the future is almost confirmed but more studies are urgently needed. With all the reported studies using bivalves as biomonitors of heavy metal pollution, the effectiveness of using Mussel Watch is beyond any reasonable doubts. The challenge is the development of more accurate methodologies for of heavy metal data interpretation, and the precision of the biomonitoring studies using bivalves as biomonitors, whether in coastal or freshwater ecosystems. Lastly, inclusion of human health risk assessment of heavy metals in commercial bivalves would make the research papers of high public interest.

Optimal Design of Plated/Shell Structures under Flutter Constraints-A Literature Review

Aeroelastic optimization has become an indispensable component in the evaluation of divergence and flutter characteristics for plated/shell structures. The present paper intends to review the fundamental trends and dominant approaches in the optimal design of engineering constructions. A special attention is focused on the formulation of objective functions/functional and the definition of physical (material) variables, particularly in view of composite materials understood in the broader sense as not only multilayered laminates but also as sandwich structures, nanocomposites, functionally graded materials, and materials with piezoelectric actuators/sensors. Moreover, various original aspects of optimization problems of composite structures are demonstrated, discussed, and reviewed in depth.

Architectural modification of shells by terrestrial hermit crabs alters social dynamics in later generations

Organisms architecturally modify environments and these modifications may persist across generations, potentially strongly shaping social behavior. However, few experiments have directly tested the impact of architectural modifications from earlier generations on social behavior in later generations. Here, I report experiments using extremely durable resources, shells, which endure for decades to centuries in stable form. Terrestrial hermit crabs (Coenobita compressus) architecturally remodel shells and pass these modified shelters to subsequent generations, which reuse them long after the original architect's death. I conducted controlled field experiments in a population of these crabs in which shells have been individually marked and tracked for a decade. I examined the impact of architectural modifications by contrasting social behavior around introduced shells, either remodeled shells (whose internal architecture was modified by earlier generations) or unremodeled shells (whose architecture had never been modified). Remodeled shells generated radically different social dynamics than unremodeled shells, catalyzing vacancy chains in which shells were socially redistributed across the population. Social groups that formed around remodeled shells consisted of size-ordered queues, with precise timing and social coordination required if individuals were to acquire superior shells. Interestingly, comparative experiments in two non-architect species (Clibanarius albidigitus and Calcinus obscurus) failed to show any impact of architectural modifications on social behavior; such impacts were only found in the architect species (C. compressus). Broadly, architecture from earlier generations can thus play a major role in driving social dynamics among later generations.

Get off my back: vibrational assessment of homeowner strength

Animals may use a variety of sensory modalities to assess ownership and resource-holding potential (RHP). However, few studies have experimentally tested whether animals can assess these key variables through a purely vibrational modality, exclusively involving substrate-borne vibrations. Here we studied social terrestrial hermit crabs ( Coenobita compressus), where competitors assess homeowners by climbing on top of a solid external structure-an architecturally remodelled shell home, inside of which the owner then produces vibrations. In the field, we used a miniature vibratory device, hidden within an empty shell, to experimentally simulate a 'phantom owner', with variable amplitudes of vibration representing different levels of homeowner strength. We found that assessors could use these vibrations to deduce the owner's RHP: for strong vibrations (indicative of a high RHP owner) assessors were least likely to escalate the conflict; for weak vibrations (indicative of a low RHP owner) assessors showed intermediate escalation; and in the absence of vibration (indicative of an extremely weak or absent owner) assessors were most likely to escalate. These results reveal that animals can assess homeowner strength based solely on substrate vibrations, thereby making important decisions about whether to escalate social conflicts over property.

Form and function of F-actin during biomineralization revealed from live experiments on foraminifera

Unicellular organisms form endless variability of complex skeletons that serve as archives of Earth’s history and play a crucial role in global geochemical cycles. A longstanding question is how single cells control morphogenesis and mineralization of skeletal structures. Although already addressed by Sir D’Arcy W. Thompson, this problem is still unsolved. Shell emerges from a controlled cascade of interactions at different levels of cellular organization. To gain insight into its morphogenesis, we apply live fluorescent imaging to observe cytoskeleton structures during shell formation in foraminifera. Our live experiments on calcifying foraminiferal chambers show that dynamic F-actin structures are involved in shaping and controlling mineralization.

Although the emergence of complex biomineralized forms has been investigated for over a century, still little is known on how single cells control morphology of skeletal structures, such as frustules, shells, spicules, or scales. We have run experiments on the shell formation in foraminifera, unicellular, mainly marine organisms that can build shells by successive additions of chambers. We used live imaging to discover that all stages of chamber/shell formation are controlled by dedicated actin-driven pseudopodial structures. Successive reorganization of an F-actin meshwork, associated with microtubular structures, is actively involved in formation of protective envelope, followed by dynamic scaffolding of chamber morphology. Then lamellar dynamic templates create a confined space and control mineralization separated from seawater. These observations exclude extracellular calcification assumed in selected foraminiferal clades, and instead suggest a semiintracellular biomineralization pattern known from other unicellular calcifying and silicifying organisms. These results give a challenging prospect to decipher the vital effect on geochemical proxies applied to paleoceanographic reconstructions. They have further implications for understanding multiscale complexity of biomineralization and show a prospect for material science applications.

Scent of death: Evolution from sea to land of an extreme collective attraction to conspecific death

All living organisms must eventually die, though in some cases their death can bring life-giving opportunities. Few studies, however, have experimentally tested how animals capitalize on conspecific death and why this specialization would evolve. Here, we conducted experiments on the phylogenetically most closely-related marine and terrestrial hermit crabs to investigate the evolution of responses to death during the sea-to-land transition. In the sea, death of both conspecifics and heterospecifics generates unremodeled shells needed by marine hermit crabs. In contrast, on land, terrestrial hermit crabs are specialized to live in architecturally remodeled shells, and the sole opportunity to acquire these essential resources is conspecific death. We experimentally tested these different species' responsiveness to the scent of conspecific versus heterospecific death, predicting that conspecific death would have special attractive value for the terrestrial species. We found the terrestrial species was overwhelmingly attracted to conspecific death, rapidly approaching and forming social groupings around conspecific death sites that dwarfed those around heterospecific death sites. This differential responsiveness to conspecific versus heterospecific death was absent in marine species. Our results thus reveal that on land a reliance on resources associated exclusively with conspecifics has favored the evolution of an extreme collective attraction to conspecific death.

Private parts for private property: evolution of penis size with more valuable, easily stolen shells

Evolution has generated enormous diversity in animal genitalia. However, the importance of private property in driving penis size evolution has rarely been explored. Here, I introduce a novel hypothesis, the 'private parts for private property' hypothesis, which posits that enlarged penises evolved to prevent the theft of property during sex. I tested this hypothesis in hermit crabs, which carry valuable portable property (a shell) and which must emerge from this shell during sex, risking social theft of their property by eavesdroppers. I measured relative penis size (penis-to-body ratio) for N = 328 specimens spanning nine closely related species. Species carrying more valuable, more easily stolen property had significantly larger penis size than species carrying less valuable, less easily stolen property, which, in turn, had larger penis size than species carrying no property at all. These patterns in penis size remained even when phylogeny was controlled for, and the patterns were not explained by alternative hypotheses. Instead, the results suggest larger penises evolved as morphological adaptations to facilitate safe sex, in which individuals retain their valuable property by extending a long penis outside the shell to copulate. This hypothesis may likewise apply to other taxa, including those with valuable but non-portable property.

In Vitro Assembly of Diverse Bacterial Microcompartment Shell Architectures

Bacterial microcompartments (BMCs) are organelles composed of a selectively permeable protein shell that encapsulates enzymes involved in CO2 fixation (carboxysomes) or carbon catabolism (metabolosomes). Confinement of sequential reactions by the BMC shell presumably increases the efficiency of the pathway by reducing the crosstalk of metabolites, release of toxic intermediates, and accumulation of inhibitory products. Because BMCs are composed entirely of protein and self-assemble, they are an emerging platform for engineering nanoreactors and molecular scaffolds. However, testing designs for assembly and function through in vivo expression is labor-intensive and has limited the potential of BMCs in bioengineering. Here, we developed a new method for in vitro assembly of defined nanoscale BMC architectures: shells and nanotubes. By inserting a "protecting group", a short ubiquitin-like modifier (SUMO) domain, self-assembly of shell proteins in vivo was thwarted, enabling preparation of concentrates of shell building blocks. Addition of the cognate protease removes the SUMO domain and subsequent mixing of the constituent shell proteins in vitro results in the self-assembly of three types of supramolecular architectures: a metabolosome shell, a carboxysome shell, and a BMC protein-based nanotube. We next applied our method to generate a metabolosome shell engineered with a hyper-basic luminal surface, allowing for the encapsulation of biotic or abiotic cargos functionalized with an acidic accessory group. This is the first demonstration of using charge complementarity to encapsulate diverse cargos in BMC shells. Collectively, our work provides a generally applicable method for in vitro assembly of natural and engineered BMC-based architectures.

Multi-parameter actuation of a neutrally stable shell: a flexible gear-less motor

We have designed and tested experimentally a morphing structure consisting of a neutrally stable thin cylindrical shell driven by a multi-parameter piezoelectric actuation. The shell is obtained by plastically deforming an initially flat copper disc, so as to induce large isotropic and almost uniform inelastic curvatures. Following the plastic deformation, in a perfectly isotropic system, the shell is theoretically neutrally stable, having a continuous set of stable cylindrical shapes corresponding to the rotation of the axis of maximal curvature. Small imperfections render the actual structure bistable, giving preferred orientations. A three-parameter piezoelectric actuation, exerted through micro-fibre-composite actuators, allows us to add a small perturbation to the plastic inelastic curvature and to control the direction of maximal curvature. This actuation law is designed through a geometrical analogy based on a fully nonlinear inextensible uniform-curvature shell model. We report on the fabrication, identification and experimental testing of a prototype and demonstrate the effectiveness of the piezoelectric actuators in controlling its shape. The resulting motion is an apparent rotation of the shell, controlled by the voltages as in a 'gear-less motor', which is, in reality, a precession of the axis of principal curvature.

Curvature-driven morphing of non-Euclidean shells

We investigate how thin structures change their shape in response to non-mechanical stimuli that can be interpreted as variations in the structure's natural curvature. Starting from the theory of non-Euclidean plates and shells, we derive an effective model that reduces a three-dimensional stimulus to the natural fundamental forms of the mid-surface of the structure, incorporating expansion, or growth, in the thickness. Then, we apply the model to a variety of thin bodies, from flat plates to spherical shells, obtaining excellent agreement between theory and numerics. We show how cylinders and cones can either bend more or unroll, and eventually snap and rotate. We also study the nearly isometric deformations of a spherical shell and describe how this shape change is ruled by the geometry of a spindle. As the derived results stem from a purely geometrical model, they are general and scalable.

The elastic theory of shells using geometric algebra

We present a novel derivation of the elastic theory of shells. We use the language of geometric algebra, which allows us to express the fundamental laws in component-free form, thus aiding physical interpretation. It also provides the tools to express equations in an arbitrary coordinate system, which enhances their usefulness. The role of moments and angular velocity, and the apparent use by previous authors of an unphysical angular velocity, has been clarified through the use of a bivector representation. In the linearized theory, clarification of previous coordinate conventions which have been the cause of confusion is provided, and the introduction of prior strain into the linearized theory of shells is made possible.

A New Type of Low Density Material: Shellular

A new type of cellular material named Shellular, in which cells are composed of a continuous, smooth-curved shell according to the minimal surface theory, is proposed. Shellular specimens are fabricated using 3D lithography with negative templates and hard coating, and exhibit superb strength and stiffness at densities lower than 10(-2) Mg m(-3), incorporating benefits from hierarchical structures and constituent materials with nanosized grains.

Red ochre and shells: clues to human evolution

The 200-kiloannus (ka) use of red ochre and shells by humans is interpreted as a simple clue of symbolic thinking. Integration of multiple lines of evidence supports the opinion that the use of red ochre and shells might have had direct significance for human evolution. Use of seafood and red ochre supplies docosahexaenoic acid (DHA), possibly iron, and other essential nutrients for brain development and reproductive health, improving human fitness and triggering brain growth. The fitness advantages to humans of using shells, and possibly red ochre, might have selected for artistic and symbolic expression, and, thereby, lead to social cohesion. Current global health syndromes show that an adequate supply of seafood and iron continues to play a fundamental role in human health.

Reduced-order models for nonlinear vibrations, based on natural modes: the case of the circular cylindrical shell

Reduced-order models are essential to study nonlinear vibrations of structures and structural components. The natural mode discretization is based on a two-step analysis. In the first step, the natural modes of the structure are obtained. Because this is a linear analysis, the structure can be discretized with a very large number of degrees of freedom. Then, in the second step, a small number of these natural modes are used to discretize the nonlinear vibration problem with a huge reduction in the number of degrees of freedom. This study finds a recipe to select the natural modes that must be retained to study nonlinear vibrations of an angle-ply laminated circular cylindrical shell that the author has previously studied by using admissible functions defined on the whole structure, so that an accuracy analysis is performed. The higher-order shear deformation theory developed by Amabili and Reddy is used to model the shell.

Effective dimensional reduction algorithm for eigenvalue problems for thin elastic structures: a paradigm in three dimensions

We present a methodology for the efficient numerical solution of eigenvalue problems of full three-dimensional elasticity for thin elastic structures, such as shells, plates and rods of arbitrary geometry, discretized by the finite element method. Such problems are solved by iterative methods, which, however, are known to suffer from slow convergence or even convergence failure, when the thickness is small. In this paper we show an effective way of resolving this difficulty by invoking a special preconditioning technique associated with the effective dimensional reduction algorithm (EDRA). As an example, we present an algorithm for computing the minimal eigenvalue of a thin elastic plate and we show both theoretically and numerically that it is robust with respect to both the thickness and discretization parameters, i.e. the convergence does not deteriorate with diminishing thickness or mesh refinement. This robustness is sine qua non for the efficient computation of large-scale eigenvalue problems for thin elastic structures.