The redoubtable cell

The cell theory—the thesis that all life is made up of one or more cells, the fundamental structural and physiological unit—is one of the most celebrated achievements of modern biological science. And yet from its very inception in the nineteenth century it has faced repeated criticism from some biologists. Why do some continue to criticize the cell theory, and how has it managed nevertheless to keep burying its undertakers? The answers to these questions reveal the complex nature of the cell theory and the cell concept on which it is based. Like other scientific ‘laws’, the assertion that all living things are made of cells purchases its universality at the expense of abstraction. If, however, this law is regarded merely as a widely applicable empirical generalization with notable exceptions, it still remains too important to discard. Debate about whether the cell or the organism standpoint provides the more correct account of anatomical, physiological, and developmental facts illustrates the tension between our attempts to express the truth about reality in conceptual terms conducive to a unified human understanding.     

Living matter—nexus of physics and biology in the 21st century

Cells are made up of complex assemblies of cytoskeletal proteins that facilitate force transmission from the molecular to cellular scale to regulate cell shape and force generation. The “living matter” formed by the cytoskeleton facilitates versatile and robust behaviors of cells, including their migration, adhesion, division, and morphology, that ultimately determine tissue architecture and mechanics. Elucidating the underlying physical principles of such living matter provides great opportunities in both biology and physics. For physicists, the cytoskeleton provides an exceptional toolbox to study materials far from equilibrium. For biologists, these studies will provide new understanding of how molecular-scale processes determine cell morphological changes.The distinction between being “alive” or “not alive” has been a long-standing question for those interested in our natural world. In many ancient cultures, the difference between living organisms and inorganic matter was thought to be due to innate differences arising from a “vital force,” such that biology operated with different fundamental properties than the physical world. The ability to disprove such theories came about over the course of the 17th to the 19th centuries, as scientists developed theories of atoms and were able to synthesize organic matter from inorganic constituents. Over the past 100 years, developments in molecular biology and biochemistry have provided a wealth of information on the structure and function of biological molecules, much of which was acquired in collaborations between physical and biological scientists. Application of X-ray–scattering techniques first developed to study metals enabled discovery of the structure of complicated biological molecules ranging from DNA to ion channels. Use of laser trapping techniques first developed to trap and cool atoms enabled precise force spectroscopy measurements of single molecular motors. We now know that biological molecules, while more complicated than their inorganic counterparts, must obey the rules of physics and chemistry.This wealth of molecular-scale information does not directly inform the behaviors of living cells. The organelles within cells are made up of complex and dynamic assemblies of proteins, lipids, and nucleic acids, all immersed within an aqueous environment. These assemblies are somehow able to build materials that can robustly facilitate the plethora of morphological and physical behaviors of cells at the subcellular (intracellular transport), cellular (division, adhesion, migration), and multicellular (tissue morphogenesis, wound healing) length scales. The dynamic cytoskeleton transmits information and forces from the molecular to the cellular length scales. But what is it about the behaviors of biological molecules that endow cells with the ability to respirate, move, and replicate themselves robustly—all qualities we consider essential to “life”? For these questions, understanding of the physics and chemistry of systems of biological molecules is needed. Interactions that occur within ensembles of molecules lead to emergent properties and behaviors that cannot be predicted at the single-molecule level. These emergent chemical and physical properties of living matter are likely fundamentally different from inorganic or “dead” materials. Discovering the underlying principles of living matter provides fantastic opportunities to learn new physics and biology.The fields of condensed matter physics and materials science study the physical properties that emerge when objects (e.g., atoms, molecules, grains of sand, or soap bubbles) are placed in sufficiently close proximity, such that interactions between them cannot be ignored. Interatomic or intermolecular interactions give rise to emergent properties that are not seen in isolated species. Familiar examples involve electron transport across a material or a material''s response to externally applied magnetic fields or mechanical forces. These emergent properties, such as conductivity, elasticity, and viscosity, enable us to predict the behavior of a collection of objects in these condensed phases. In this paper, I will focus on my perspective of how approaches to understanding the mechanical properties of physical materials can inform understanding of the mechanical properties of living matter found within cells.In a crystal of metal, precisely organized atoms are located nanometers apart, and the energies of their interactions are on the scale of an electron volt (40-fold larger than thermal energy or twice the energy released on the hydrolysis of a single ATP molecule). These give rise to an energy density, or elastic modulus, on the order of gigapascals, which underlies the rigidity of metals. For small deformations, the restoring force between atoms means that this metal behaves like an elastic spring: after a force is applied, the metal returns to its original shape. Understanding force transmission through crystalline metals was facilitated by the development of elasticity theory in the 16th and 17th centuries. Fluids, such as water, lack crystalline order, but predictive understanding of fluid flows and forces was captured through development of theories of fluid dynamics. Now think of another material, Silly Putty, which behaves elastically at short timescales (it bounces like a rubber ball) but then oozes and flows at long timescales, acting like a viscous fluid. Silly Putty is made of long polymers that are trapped by one another at short timescales, but thermal energy is sufficient to allow them to diffuse and translocate at long timescales. Silly Putty is also a “soft material,” in that the polymer''s interaction energies are at the thermal energy level, and its length scale is at the micrometer level. Materials like Silly Putty were thought to be too complicated for analytical theory. It was only in the middle of the 20th century that the theoretical framework to understand these “messy” and “disorganized” polymer-based materials was developed.The most powerful theories for understanding these vastly different forms of physical matter were developed in the absence of even the simplest of computers. The theories relied on developing physical properties or parameters to describe the material with a “mean field,” a type of coarse-graining that identifies the essential properties of individual constituents and interactions but ignores many other details. These mean fields give us new intuitions concerning the origin of material properties and give rise to definitions of physical parameters, such as elasticity and viscosity. However, these theories also require materials that do not jostle around a lot and remain close to equilibrium. In fact, understanding materials “far from equilibrium” has been identified as a major challenge in physics for the next century (National Research Council, 2007) .Materials formed by dynamic protein assemblies in the cytoskeleton are disorganized, heterogeneous, and driven far from equilibrium. Motor proteins generate local stresses, and their activity is spatially modulated. The polymerization and depolymerization of cytoskeletal polymers is controlled by a myriad of regulatory proteins. All these dynamic molecular processes endow the cytoskeletal assemblies with unique behaviors that enable them to support complex physiological tasks. It is likely these dynamics also provide underlying robustness of the cells in response to fluctuating and changing environments. These properties make living cells exquisite materials that cannot be captured by existing frameworks of physical matter. I suspect that we have not yet identified the important parameters needed to characterize their properties. The rich dynamics created by active biological matter present a formidable challenge in the area of materials science.How do we hope to understand the properties of these complex cytoskeletal assemblies and materials? It may seem as though understanding cytoskeletal machinery is an insurmountable feat, the approaches that have been successful for physical materials will not work, and we must rely on complex simulations that require modeling of all individual components. This may be true. However, I think that this is a pessimistic view. Just consider how complicated physical materials would be if we did not have the appropriate parameters to describe the macroscopic responses and had instead became obsessed about knowing the details of all the interactions between underlying atoms and molecules? In the same vein, I believe that predictive insights into biological matter will emerge through development of new physical theories that use mean-field approaches to understanding materials that contain active components and are driven far from equilibrium. The burgeoning field of active-matter physics is currently considering these questions (Ramaswamy, 2010) . However, these theoretical approaches require physical measurements of cells and cellular proteins that may not be clearly linked to a physiological process or have a clear biological context. Materials built from cytoskeletal proteins in vitro should also provide an excellent source of experimental measurements, but closer collaboration with theorists working in this field and collaboration between biochemists and experimental physical scientists is needed to develop control over such materials. Developing predictive physical theories of the cytoskeleton will elucidate principles of why “the whole is more than the sum of its parts” that will provide greater control and design over living matter, in the same way that engineering has provided great advances in applications of materials from the physical world.What do biologists gain from theories of living matter? These theories will provide a crucial link between molecular and cellular length scale behaviors and will provide insight into the mechanisms of why specific molecular perturbations alter cell behavior. Moreover, they should provide us with general design principles of living matter. What are the basic aspects of a machine needed to separate chromosomes, establish polarity, or generate contractile forces that is utilized across different cell types? Can knowing these aspects provide insight into the evolution of cellular machines and the robustness of cell behavior? Thus, study of cellular materials both provides new opportunities for physicists and will provide crucial predictive understanding of cell physiology.Open in a separate windowMargaret L. Gardel     

Chemosensory responses of juvenile Coho salmon, Oncorhynchus kisutch, Dolly Varden, Salvelinus malma, and sculpins (Cottus spp.) to eggs and other tissues from adult Pacific salmon

The carcasses of semelparous Pacific salmon (Oncorhynchus spp.) provide nutrients that enter aquatic ecosystems by various pathways, including direct consumption of tissue by fishes. Salmonids and other species frequently eat eggs and other tissues from dead salmon but the roles of vision and olfaction are unclear, as is the relative attraction to different tissues. Accordingly, we conducted a series of in situ experiments using minnow traps in two natural streams in Alaska to test the relative roles of chemosensory and visual cues in attraction of fishes to eggs from adult Pacific salmon, and then compared catch rates of traps baited with eggs, muscle, liver, and testis. Experiments indicated that chemical traces were necessary and sufficient to attract juvenile Dolly Varden (Salvelinus malma), coho salmon (Oncorhynchus kisutch), and sculpins (Cottus spp.) into traps. Combining both sites, 70 salmonids and 19 sculpins were trapped using visual and chemical cues, and 53 and 21, respectively, for traps with only chemical cues. Traps with only the sight of eggs caught no salmonids and only 5 sculpins, comparable to empty control traps. In addition, eggs were markedly more attractive than the other tissues, trapping 68?% of the salmonids and 69?% of the sculpins, compared to 14?% and 15?% for muscle tissue, 12?% and 11?% for liver, and 6?% and 5?% for the testis. Visual cues undoubtedly play a role in egg consumption in streams, but these experiments indicated a very important role of chemical traces in attracting fish to the vicinity of the eggs, and selective attraction of eggs over other salmon tissues.     

Hylomorphism and the Metabolic Closure Conception of Life

This paper examines three exemplary theories of living organization with respect to their common feature of defining life in terms of metabolic closure: autopoiesis, (M, R) systems, and chemoton theory. Metabolic closure is broadly understood to denote the property of organized chemical systems that each component necessary for the maintenance of the system is produced from within the system itself, except for an input of energy. It is argued that two of the theories considered—autopoiesis and (M, R) systems—participate in a hylomorphist pattern of thinking which separates the “form” of the living system from its “matter.” The analysis and critique of hylomorphism found in the work of the philosopher Gilbert Simondon is then applied to these two theories, and on the basis of this critique it is argued that the chemoton model offers a superior theory of minimal life which overcomes many of the problems associated with the other two. Throughout, the relationship between hylomorphism and the understanding of living things as machines is explored. The paper concludes by considering how hylomorphism as a background ontology for theories of life fundamentally influences the way life is defined.     

Waste Treatment and Assessment of Long-Term Emissions (8pp)

Goal, Scope and Background The disposal phase of a product’s life cycle in LCA is often neglected or based on coarse indicators like ‘kilogram waste’. The goal of report No. 13 of the ecoinvent project (Doka 2003) is to create detailed Life Cycle Inventories of waste disposal processes. The purpose of this paper is to give an overview of the models behind the waste disposal inventories in ecoinvent, to present exemplary results and to discuss the assessment of long-term emissions. This paper does not present a particular LCA study. Inventories are compiled for many different materials and various disposal technologies. Considered disposal technologies are municipal incineration and different landfill types, including sanitary landfills, hazardous waste incineration, waste deposits in deep salt mines, surface spreading of sludges, municipal wastewater treatment, and building dismantling. The inventoried technologies are largely based on Swiss plants. Inventories can be used for assessment of the disposal of common, generic waste materials like paper, plastics, packaging etc. Inventories are also used within the ecoinvent database itself to inventory the disposal of specific wastes generated during the production phase. Inventories relate as far as possible to the specific chemical composition of the waste material (waste-specific burdens). Certain expenditures are not related to the waste composition and are inventoried with average values (process-specific burdens). Methods The disposal models are based on previous work, partly used in earlier versions of ecoinvent/ETH LCI data. Important improvements were the extension of the number of considered chemical elements to 41 throughout all disposal models and new landfill models based on field data. New inventories are compiled for waste deposits in deep salt mines and building material disposal. Along with the ecoinvent data and the reports, also Excel-based software tools were created, which allow ecoinvent members to calculate waste disposal inventories from arbitrary waste compositions. The modelling of long-term emissions from landfills is a crucial part in any waste disposal process. In ecoinvent long-term emissions are defined as emissions occurring 100 years after present. They are reported in separate emission categories. The landfill inventories include long-term emissions with a time horizon of 60’000 years after present. Results and Discussion As in earlier studies, the landfills prove to be generally relevant disposal processes, as also incineration and wastewater treatment processes produce landfilled wastes. Heavy metals tend to concentrate in landfills and are washed out to a varying degree over time. Long-term emissions usually represent an important burden from landfills. Comparisons between burdens from production of materials and the burdens from their disposal show that disposal has a certain relevance. Conclusion The disposal phase should by default be included in LCA studies. The use of a material not only necessitates its production, but also requires its disposal. The created inventories and user tools facilitate heeding the disposal phase with a similar level of detail as production processes. The risk of LCA-based decisions shifting burdens from the production or use phase to the disposal phase because of data gaps can therefore be diminished. Recommendation and Perspective Future improvements should include the modelling of metal ore refining waste (tailings) which is currently neglected in ecoinvent, but is likely to be relevant for metals production. The disposal technologies considered here are those of developed Western countries. Disposal in other parts of the World can differ distinctly, for logistic, climatic and economic reasons. The cross-examination of landfill models to LCIA soil fate models could be advantageous. Currently only chemical elements, like copper, zinc, nitrogen etc. are heeded by the disposal models. A possible extension could be the modelling of the behaviour of chemical compounds, like dioxins or other hydrocarbons.     

Defining the role of matrix compliance and proteolysis in three-dimensional cell spreading and remodeling

Recent studies have identified extracellular matrix (ECM) compliance as an influential factor in determining the fate of anchorage-dependent cells. We explore a method of examining the influence of ECM compliance on cell morphology and remodeling in three-dimensional culture. For this purpose, a biological ECM analog material was developed to pseudo-independently alter its biochemical and physical properties. A set of 18 material variants were prepared with shear modulus ranging from 10 to 700 Pa. Smooth muscle cells were encapsulated in these materials and time-lapse video microscopy was used to show a relationship between matrix modulus, proteolytic biodegradation, cell spreading, and cell compaction of the matrix. The proteolytic susceptibility of the matrix, the degree of matrix compaction, and the cell morphology were quantified for each of the material variants to correlate with the modulus data. The initial cell spreading into the hydrogel matrix was dependent on the proteolytic susceptibility of the materials, whereas the extent of cell compaction proved to be more correlated to the modulus of the material. Inhibition of matrix metalloproteinases profoundly affected initial cell spreading and remodeling even in the most compliant materials. We concluded that smooth muscle cells use proteolysis to form lamellipodia and tractional forces to contract and remodel their surrounding microenvironment. Matrix modulus can therefore be used to control the extent of cellular remodeling and compaction. This study further shows that the interconnection between matrix modulus and proteolytic resistance in the ECM may be partly uncoupled to provide insight into how cells interpret their physical three-dimensional microenvironment.     

Interface Biology of Implants

Implants are widely used in various clinical disciplines to replace or stabilize organs. The challenge for the future is to apply implant materials to specifically control the biology of the surrounding tissue for repair and regeneration. This field of research is highly interdisciplinary and combines scientists from technical and life sciences disciplines. To successfully apply materials for regenerative processes in the body, the understanding of the mechanisms at the interface between cells or tissues and the artificial material is of critical importance. The research focuses on stem cells, design of material surfaces, and mechanisms of cell adhesion. For the third time around 200 scientists met in Rostock, Germany for the international symposium “Interface Biology of Implants.” The aim of the symposium is to promote the interdisciplinary dialogue between the scientists from the different disciplines to develop smart implants for medical use. In addition, researchers from basic sciences, notably cell biology presented new findings concerning mechanisms of cell adhesion to stimulate research in the applied field of implant technology.Key words: interface, implant, stem cells, adhesion, mechanics, surface, biomaterialMedical implants play a growing role in routine clinical practice. In addition to replace or stabilize injured tissue permanently or transiently, the application of implant materials to stimulate the regeneration of tissue is becoming a challenge in the field of regenerative medicine. The use of implant materials is based on the idea that biomaterials function not only as mechanical support for cells and tissue but also provide a matrix to induce signal transduction in the cells that control complex molecular mechanisms responsible for proliferation und differentiation. In this context, the interface between artificial materials and living cells or tissue is an exciting field of great scientific interest and constitutes one of the most dynamic and expanding field in science and technology. Progress in this field is mainly driven by the fundamental importance for clinical applications. The research is characterized by a multidisciplinary collaboration between physics, engineers, biologists and clinicians.In May 2009, for the third time after 2003 and 2006 around 200 scientists met in Rostock-Warnemünde for the symposium “Interface Biology of Implants” to discuss biointerface processes at a fundamental level. The main goals of this symposium are to simulate the interdisciplinary dialogue between scientists of the different disciplines and to introduce current knowledge of basic research in cell biology and material science into the applied field of implant technology. The programme was organized in invited presentations of 20 internationally renowned scientists and complemented by short talks of mostly young scientists selected from the submitted abstracts. In addition, 80 posters presented latest results in this multidisciplinary field.The symposium was opened with a keynote lecture presented by Hartmut Hildebrand (Lille). He gave an overview about the 7,000 years old history of application of implant materials. Rare photographs were shown which demonstrated that in these early times prostheses mainly made from metallic materials were used to restore teeth, extremities and the skull of the human body. These old documents stressed the historical relevance of medical application of implant materials.The symposium on two days was composed of four sessions covering the interdisciplinary research in the field. The session “Stem cells and biomaterials” discussed the biological response and signalling mechanism of stem cells in the interaction with a material surface. The session “Bioactivation of implant surfaces” focussed on the tailoring of surfaces to control the cell physiology. To stimulate the field by recent data in basic cell biology, talks were presented in the third session, dealing with molecular mechanisms involved in cell adhesion. A special session dealt with the role and mechanism of controlling cells by mechanics.     

Gravity: one of the driving forces for evolution

Mechanical load is 10(3) larger for land-living than for water-living organisms. As a consequence, antigravitational material in form of compound materials like lignified cell walls in plants and mineralised bones in animals occurs in land-living organisms preferentially. Besides cellulose, pectic substances of plant cell walls seem to function as antigravitational material in early phases of plant evolution and development. A testable hypothesis including vesicular recycling processes into the tensegrity concept is proposed for both sensing of gravitational force and responding by production of antigravitational material at the cellular level.     

从系统到景观:区域物质流分析的景观取向

物质流过程是考察系统属性的重要维度。区域物质流分析在研究框架、指标体系、数据集成、管理应用等方面的发展困境,都不同程度地反映了"黑箱假设"以及"系统隐喻"等产业生态学理论的应用局限性。基于整合复杂性科学、广义进化论的生态学组织层次理论,对区域物质流分析开展理论探讨,指出应在原有的"系统"思维之外引入"景观"概念,以拓展区域物质流分析的空间与认知维度。基于"从系统到景观"的理念,将景观生态学原理引入区域物质流分析,建构区域物质流分析的景观取向,并从空间结构与认知图式两个方面对这一取向的核心涵义做以解读。结合区域物质流分析的最新研究案例,从多尺度MFA的综合研究框架、物质流动过程的时空集成研究、物质流动过程的空间行为管理等几个方面,对区域物质流分析的景观取向做了进一步探讨。     

Ontoecogenophyloconstraints? The chaos of constraint terminology

The world of evolutionary biology today is being bombarded with all kinds of possible constraints to the process of natural selection. Are we witnessing the end of the neodarwinistic theory of evolution, as some may like to see it, or is it just another whim of giving new names to old things? Here, we attempt to unravel the meaning and name-giving of constraints in a small and nonrandom sample of the literature, and suggest a way out from the present confusion of usages.     

Interface Biology of Implants

Implants are widely used in various clinical disciplines to replace or stabilize organs. The challenge for the future is to apply implant materials to specifically control the biology of the surrounding tissue for repair and regeneration. This field of research is highly interdisciplinary and combines scientists from technical and life sciences disciplines. To successfully apply materials for regenerative processes in the body, the understanding of the mechanisms at the interface between cells or tissues and the artificial material is of critical importance. The research focuses on stem cells, design of material surfaces, and mechanisms of cell adhesion. For the third time around 200 scientists met in Rostock, Germany for the international symposium “Interface Biology of Implants”. The aim of the symposium is to promote the interdisciplinary dialogue between the scientists from the different disciplines to develop smart implants for medical use. In addition, researchers from basic sciences, notably cell biology presented new findings concerning mechanisms of cell adhesion to stimulate research in the applied field of implant technology.     

Egg ejection cost can limit defence strategies against brood parasitism

A cost associated with the evolution of antiparasite strategies is the failure to recognize parasitic eggs, leading the host to evict its own eggs. However, there is evidence that birds recognize their own eggs through imprinting. This leads to the question of why birds accept parasitic eggs if such eggs can be identified. Here, we tested whether egg ejection per se can be costly due to increased predation risk to the remaining clutch and whether olfactory or visual cues of egg ejection increase predation. We carried out three field experiments to answer the following questions: (a) Does ejecting an egg increase nest predation risk? (b) Does the presence of olfactory cues, such as the smell of a broken egg, increase nest predation risk? And (c) Does the presence of visual cues, such as an egg shell below the nest, increase nest predation risk? We found evidence that egg ejection increases nest predation and that olfactory cues alone also increase nest predation. The presence of visual cues did not change predation rates. These data indicate that egg ejection is costly for both host and parasitic eggs that may remain in the nest. Our results suggest why host and parasite eggs are commonly found within the same nests, despite the possibility that hosts recognize and could possibly eject the parasite’s egg.     

Gyrodinium undulans Hulburt, a marine dinoflagellate feeding on the bloom-forming diatomOdontella aurita, and on copepod and rotifer eggs

The marine dinoflagellateGyrodinium undulans was discovered as a feeder on the planktonic diatomOdontella aurita. Every year, during winter and early spring, a certain percentage of cells of this bloom-forming diatom, in the Wadden Sea along the North Sea coast, was regularly found affected by the flagellate. Supplied with the food diatomO. aurita the dinoflagellate could be maintained successfully in clonal culture. The vegetative life cylce was studied, mainly by light microscopy on live material, with special regard to the mode of food uptake. Food is taken up by a so-called phagopod, emerging from the antapex of the flagellate. Only fluid or tiny prey material could be transported through the phagopod. Larger organelles like the chloroplasts ofOdontella are not ingested and are left behind in the diatom cell. Thereafter, the detached dinoflagellate reproduces by cell division, occasionally followed by a second division. As yet, stages of sexual reproduction and possible formation of resting cysts could not be recognized, neither from wild material nor from laboratory cultures. Palmelloid stages (sometimes with a delicate wall) occurring in ageing cultures may at least partly function as temporary resting stages. The winter speciesG. undulans strongly resemblesSyltodinium listii, a summer species feeding on copepod and rotifer eggs. Surprisingly, in a few cases this prey material was accepted byG. undulans as well, at least under culture conditions. When fed with copepod eggs, the dinoflagellate developed into a large trophont, giving rise thereafter by repeated binary fission to 4, 8 or 16 flagellates, as a result of a single feeding act. A re-examination of both species under simultaneous culture conditions is planned.     

Contractility Measurements on Isolated Papillary Muscles for the Investigation of Cardiac Inotropy in Mice

Papillary muscle isolated from adult mouse hearts can be used to study cardiac contractility during different physiological/pathological conditions. The contractile characteristics can be evaluated independently of external influences such as vascular tonus or neurohumoral status. It depicts a scientific approach between single cell measurements with isolated cardiac myocytes and in vivo studies like echocardiography. Thus, papillary muscle preparations serve as an excellent model to study cardiac physiology/pathophysiology and can be used for investigations like the modulation by pharmacological agents or the exploration of transgenic animal models. Here, we describe a method of isolating the murine left anterior papillary muscle to investigate cardiac contractility in an organ bath setup. In contrast to a muscle strip preparation isolated from the ventricular wall, the papillary muscle can be prepared in toto without damaging the muscle tissue severely. The organ bath setup consists of several temperature-controlled, gassed and electrode-equipped organ bath chambers. The isolated papillary muscle is fixed in the organ bath chamber and electrically stimulated. The evoked twitch force is recorded using a pressure transducer and parameters such as twitch force amplitude and twitch kinetics are analyzed. Different experimental protocols can be performed to investigate the calcium- and frequency-dependent contractility as well as dose-response curves of contractile agents such as catecholamines or other pharmaceuticals. Additionally, pathologic conditions like acute ischemia can be simulated.     

Individual female common cuckoos Cuculus canorus lay constant egg types but egg appearance cannot be used to assign eggs to females

Females of the obligate brood parasitic common cuckoo Cuculus canorus are assumed to lay eggs of consistent colour and pattern and egg characteristics have been used to separate between different individuals. We tested the "constant egg-type hypothesis" in blind tests using test persons who grouped cuckoo eggs into "potential clutches" based on similarity in appearance. A correct classification of eggs laid by known (radiotagged) females supported the hypothesis. However, comparisons between maternity based on visual assessments and DNA-based parentage analyses revealed rather poor concordance between the two methods. Our findings indicate that egg characteristics cannot be used to separate between cuckoo females, even if they lay eggs with constant appearance. The reason is probably that there are only small or negligible variations in egg appearance between some females like mothers and daughters or other closely related individuals.     

Chemical properties allow stingless bees to place their eggs upright on liquid larval food

Abstract. Queen-laid eggs of Melipona bees stand upright on their larval food, in part because the upper part of the egg is covered with a water-repellent layer of fatty acids and C₂₁ to C₂₉ hydrocarbons. The lower, wettable portion does not have these materials. Trophic eggs laid by workers are essentially devoid of this coating and tend to sink in the food, when not detected and consumed by the queen. Reproductive workers' eggs, which have about 50% of the water-repellent coating in comparison with the queen's eggs, are usually laid in the cell after oviposition by the queen, and therefore there are two eggs in the cell. Surface tension forces cause the two eggs to float towards each other so they become attached. When alone inside the cell, the reproductive worker egg often floats at an angle to the surface, reflecting the instability of this kind of egg. Attachment to a queen's egg therefore compensates this instability and enhances the reproductive worker egg's chances to develop. Such reproductive worker eggs have about 50% of the water-repellent coating in comparison with the queen's eggs. The surface of an 'undetermined' egg laid by a worker was much closer in composition to that of a queen's egg, from which it is deduced that this was the rarer type of reproductive worker egg, namely those that are laid before queen oviposition has taken place. The layer of hydrophobic material on a queen's egg is about one molecule thick, and probably orientated with the carboxyl groups toward the chorion of the egg and the hydrocarbon chains perpendicular to the surface.     

Shades of Empire: Police Photography in German South-West Africa

This article looks at a photographic album produced by the German police in colonial Namibia just before World War I. Late 19th- and early 20th-century police photography has often been interpreted as a form of visual production that epitomized power and regimes of surveillance imposed by the state apparatuses on the poor, the criminal and the Other. On the other hand police and prison institutions became favored sites where photography could be put at the service of the emergent sciences of the human body—physiognomy, anthropometry and anthropology. While the conjuncture of institutionalized colonial state power and the production of scientific knowledge remain important for this Namibian case study, the article explores a slightly different set of questions. Echoing recent scholarship on visuality and materiality the photographic album is treated as an archival object and visual narrative that was at the same time constituted by and constitutive of material and discursive practices within early 20th-century police and prison institutions in the German colony. By shifting attention away from image content and visual codification alone toward the question of visual practice the article traces the ways in which the photo album, with its ambivalent, unstable and uncontained narrative, became historically active and meaningful. Therein the photographs were less informed by an abstract theory of anthropological and racial classification but rather entrenched with historically contingent processes of colonial state constitution, socioeconomic and racial stratification, and the institutional integration of photography as a medium and a technology into colonial policing. The photo album provides a textured sense of how fragmented and contested these processes remained throughout the German colonial period, but also how photography could offer a means of transcending the limits and frailties brought by the realities on the ground.     

Do farming conditions influence brominated flame retardant levels in pig and poultry products?

Brominated flame retardants (BFR) are primarily used as flame retardant additives in insulating materials. These lipophilic compounds can bioaccumulate in animal tissues, leading to human exposure via food ingestion. Although their concentration in food is not yet regulated, several of these products are recognised as persistent organic pollutants; they are thought to act as endocrine disruptors. The present study aimed to characterise the occurrence of two families of BFRs (hexabromocyclododecane (HBCDD) and polybrominated diphenyl ethers (PBDE)) in hen eggs and broiler or pig meat in relation to their rearing environments. Epidemiological studies were carried out on 60 hen egg farms (34 without an open-air range, 26 free-range), 57 broiler farms (27 without an open-air range, 30 free-range) and 42 pig farms without an open-air range in France from 2013 to 2015. For each farm, composite samples from either 12 eggs, five broiler pectoral muscles or three pig tenderloins were obtained. Eight PBDE congeners and three HBCDD stereoisomers were quantified in product fat using gas chromatography–high-resolution mass spectrometry, or high-performance liquid chromatography–tandem mass spectrometry, respectively. The frequencies of PBDE detection were 28% for eggs (median concentration 0.278 ng/g fat), 72% for broiler muscle (0.392 ng/g fat) and 49% for pig muscle (0.403 ng/g fat). At least one HBCDD stereoisomer was detected in 17% of eggs (0.526 ng/g fat), 46% of broiler muscle (0.799 ng/g fat) and 36% of pig muscle (0.616 ng/g fat). Results were similar in concentration to those obtained in French surveillance surveys from 2012 to 2016. Nevertheless, the contamination of free-range eggs and broilers was found to be more frequent than that of conventional ones, suggesting that access to an open-air range could be an additional source of exposure to BFRs for animals. However, the concentration of BFRs in all products remained generally very low. No direct relationship could be established between the occurrence of BFRs in eggs and meat and the characteristics of farm buildings (age, building materials). The potential presence of BFRs in insulating materials is not likely to constitute a significant source of animal exposure as long as the animals do not have direct access to these materials.     

Formalism for the neural network of visual systems

A formalism to describe neural interrelations is developed on the exemplary case of the fly visual system. Absolute and relative indices are employed to identify the position of neural elements within the lattices of the visual ganglia. Illustrative applications as the projection of fly retinual cell axons into the lamina are discussed as well as the general feasibility of the formalism to other visual systems.