Scrambled eggs: mechanical forces as ecological factors in early development

Many ecological interactions involve, at some level, mechanical forces and the movements or structural deformations they produce. Although the most familiar examples involve the functional morphology of adult structures, all life history stages (not just the adults) are subject to the laws of physics. Moreover, the success of every lineage depends on the success of every life history stage (again, not just the adults). Therefore, insights gained by using mechanical engineering principles and techniques to study ecological interactions between gametes, embryos, larvae, and their environment are essential to a well-rounded understanding of development, ecology, and evolution. Here I draw on examples from the literature and my own research to illustrate ways in which mechanical forces in the environment shape development. These include mechanical forces acting as selective factors (e.g., when coral gamete size and shape interact with turbulent water flow to determine fertilization success) and as developmental cues (e.g., when plant growth responds to gravity or bone growth responds to mechanical loading). I also examine the opposite cause-and-effect relationship by considering examples in which the development of organisms impacts ecologically relevant mechanical forces. Finally, I discuss the potential for ecological pattern formation as a result of feedback loops created by such bidirectional interactions between developmental processes and mechanical forces in the environment.     

Heat island effects in urban life cycle assessment: Novel insights to include the effects of the urban heat island and UHI‐mitigation measures in LCA for effective policy making

Urbanization often entails a surge in urban temperature compared to the rural surroundings: the Urban Heat Island (UHI) effect. Such a temperature increase triggers the formation of pollutants worsening the urban air quality. Jointly, bad air quality and UHI affect ecosystems and human health. To alleviate the impacts on the population and the environment, it is crucial to design effective UHI‐mitigation measures. Life Cycle Assessment (LCA) is an assessment tool able to capture the complexity of urban settlements and quantify their impact. Yet, as currently implemented, LCA neglects the interactions between the built environment and the local climate, omitting the resulting impacts. This study reviews the existing literature, showing the lack of studies that organically include interactions between the built environment and local climate in LCA. This forms the basis to identify the unsuitability of the current LCA framework for comprehensively capturing the impact of urban settlements. To overcome this limitation, this research offers a pathway to expand the LCA methodology, indicating the necessity to (a) couple the LCA methodology with climate models or physical relations that quantify the interactions between the local climate and the built environment; (b) include novel impact categories in LCA to address such interactions; and (c) use existing or ad hoc developed characterization factors to assess the impacts related to the UHI effect. The LCA community can build on the frame of reference offered by this research to overcome the current limitations of LCA and enable its use for a comprehensive assessment of the impacts of UHI and its mitigation measures.     

Rheology of filamentous fermentations

The performance of a bioreactor containing a filamentous fermentation broth is greatly influenced by the rheological properties of the broth. These properties are determined mainly by the concentration of biomass, its growth rate and morphology. Included in the morphology are such factors as the geometry of hyphae (length, diameter, branching frequency), hyphal flexibility and hyphal-hyphal interactions, which can all be affected by the operational design of the reactor. Thus, correlations describing viscosity as a function of biomass only are of limited value. A better understanding of the relations between morphology and rheology may be achieved by a combination of rheological and morphological studies.Rheological properties are normally determined using off-line measurements in-spite of associated problems with sample treatment influencing the results. Equipment for dynamic, on-line, measurement of morphology and rheology is available, but little used in filamentous fermentations. Controlling the rheological properties of mycelial fermentations may be difficult because of the great number of factors influencing mycelial development and/or hyphal-hyphal interactions.Polymer solutions are often used to simulate flow behaviour of filamentous fermentations and scale-up and mass transfer considerations are based on these studies. Although much information has been gained this way, the predictions developed do not include the effect of an active biomass on the mass transfer and flow properties of the culture. It is important to carry out studies on the non-homogeneous fermentation fluids, and develop correlations based on these studies.     

A Computational Model of the Fluid Dynamics of Undulatory and Flagellar Swimming

We present a mathematical model and numerical method designedto study the fluid dynamics of swimming organisms. The fullNavier— Stokes equations are solved in a domain of fluidwithin which an organism undergoing time—dependent motionsis immersed. Of interest are both the dynamics of a single organismand the relationship of its morphology to its motility properties,as well as the collective hydrodynamic interactions of groupsof swimmers with each other and their environment. Biologicalapplications include spermatozoa motility in the reproductivetract, swimming of non-smooth filaments, and collective swimmingof algal cells.     

Concepts of an architectonic approach to transformation morphology

This paper is about a general methodology for pattern transformation. Patterns are network representations of the relations among structures and functions within an organism. Transformation refers to any realistic or abstract transformation relevant to biology, e.g. ontogeny, evolution and phenotypic clines. The main aim of the paper is a methodology for analyzing the range of effects on a pattern due to perturbing one or more of its structures and/or functions (transformation morphology). Concepts relevant to such an analysis of pattern transformation are reviewed and several new ones introduced: pattern unit; direct and indirect functional demands; compatibility and trade-off; integrating, adding and decoupling; functional effectiveness; spatial, profile and other architectonic constraints; domains of structure-function relations; goal and process adaptability; multiple pathways. The paper is written from the the perspective of architectonic morphology, viz. functional morphology focusing on the relation between anatomical coherence and the compatibility of functions. The advantages and disadvantages of inductive and deductive approaches are discussed.     

Molecular ecosystems

Biologists employ a suggestive metaphor to describe the complexities of molecular interactions within cells and embryos: cytological components are said to be part of “ecosystems” that integrate them in a complex network of relations with many other entities. The aim of this essay is to scrutinize the molecular ecosystem, a metaphor that, despite its longstanding history, has seldom be articulated in detail. I begin by analyzing some relevant analogies between the cellular environment and the biosphere. Next, I discuss the applicability of the molecular ecosystem concept in actual scientific practice.     

Neighborhood models of plant population dynamics 3. Models with spatial heterogeneity in the physical environment

Population dynamic models are developed for communities of annual plants in spatially heterogeneous environments. These models are constructed from submodels of the survivorship, fecundity, germination, and dispersal of individual plants. The submodels include the effects of spatially local interactions on plant performance and the spatial variation in performance caused by spatial heterogeneity in the physical environment. It is possible to estimate the submodels from data on experimental communities in either the field or greenhouse and so it is possible to empirically calibrate the population dynamic models developed. Each population dynamic model explicitly includes the spatial distribution of individuals in a plant community.Several two-species models for plants in patchy environments are studied to examine the community-level consequences of spatial heterogeneity in the physical environment. The results fall into two classes. First, community structure is in part determined by a relation between patch size and mean seed dispersal distance. Specifically, coexistence is, in some cases, possible only if patches are sufficiently larger than the mean dispersal distance. Second, community structure is also affected by relations between patch size and the maximum distance over which two plants interact (termed the neighborhood radius). In some cases, coexistence is possible only if patch size is sufficiently larger than the neighborhood radius. In others, the species coexist only if patch size is sufficiently smaller than the neighborhood radius. In still other cases, coexistence is possible only if patch sizes are within critical bounds, where the sizes of the critical bounds are in units of the neighborhood radius. All results involving relations between the neighborhood radius and patch size are direct consequences of the sedentary nature of plants and the fact that individual plants interact primarily with nearby plants.     

Evo-Devo: evolutionary developmental mechanisms

Evolutionary developmental biology (Evo-Devo) as a discipline is concerned, among other things, with discovering and understanding the role of changes in developmental mechanisms in the evolutionary origin of aspects of the phenotype. In a very real sense, Evo-Devo opens the black box between genotype and phenotype, or more properly, phenotypes as multiple life history stages arise in many organisms from a single genotype. Changes in the timing or positioning of an aspect of development in a descendant relative to an ancestor (heterochrony and heterotopy) were two evolutionary developmental mechanisms identified by Ernst Haeckel in the 1870s. Many more have since been identified, in large part because of our enhanced understanding of development and because new mechanisms emerge as development proceeds: the transfer from maternal to zygotic genomic control; cell-to-cell interactions; cell differentiation and cell migration; embryonic inductions; functional interactions at the tissue and organ levels; growth. Within these emergent processes, gene networks and gene cascades (genetic modules) link the genotype with morphogenetic units (cellular modules, namely germ layers, embryonic fields or cellular condensations), while epigenetic processes such as embryonic inductions, tissue interactions and functional integration, link morphogenetic units to the phenotype. Evolutionary developmental mechanisms also include interactions between individuals of the same species, individuals of different species, and species and their biotic and/or abiotic environment. Such interactions link ecological communities. Importantly, there is little to distinguish the causality that underlies these interactions from that which underlies inductive interactions within embryos.     

Polyethism in social interactions in ants

Worker ants, which perform various tasks in their society (division of labour or polyethism), also demonstrate different types of antennal activity in trophallactic interactions. These differences concern the variability in successions of behavioural units performed by the worker in the course of substance transmission as well as in the sequential organization of these units. The antennal activity of an aged worker varies according to whether the ant gives food to another aged worker or to a callow worker. In the latter case, the donor's behaviour does not differ according to its social function (brood-tending worker or forager). A parallel can be established between these results and those obtained in a previous study of aggressive behaviour. This behaviour is liable to appear when a callow worker extracted from its society before hatching and therefore deprived of relations with aged workers of the society, is therefore placed with an aged worker. Polyethism is then manifested in social interactions, and not only in the division of labour between members of the society.     

A MODEL FOR DEVELOPMENT AND EVOLUTION OF COMPLEX MORPHOLOGICAL STRUCTURES

How 'complex' or composite morphological structures like the mammalian craniomandibular region arise during development and how they are altered during evolution are two major unresolved questions in biology. Herein, we have described a model for the development and evolution of complex morphological structures. The model assumes that natural selection acts upon an array of phenotypes generated by variation in a variety of underlying genetic and epigenetic controlling factors. Selection refines the integration of the various morphogenetic components during ontogeny in order to produce a functioning structure and to adapt the organisms to differing patterns of environmental heterogeneity. The model was applied to the development and evolution of the mammalian mandible (which is used as a paradigm of complex morphological structures). The embryology of the mandible was examined in detail in order to identify the fundamental developmental units which are necessary to assemble the final morphological structure. The model is quite general since equivalent units exist for the development of many other biological structures. This model could be applied to many other developing morphological structures as well as other groups of organisms. For example, it can be applied to cell parameters during Drosophila development (Atchley, 1987). The model as discussed in this paper assumes that morphological changes in the mandible result from evolutionary changes in its underlying developmental units. The developmental units relate to characteristics of cellular condensations which are produced from the differentiation of embryonic neural crest cells. The developmental units include: the number of stem cells in preskeletal condensations (n), the time of initiation of condensation formation (t), the fraction of cells that is mitotically active within a condensation (f), the rate of division of these cells (r), and their rate of cell death (d). These units and their derivative structures are discussed in terms of types of tissue differentiation (chondrogenesis, osteogenesis, primary/secondary osteogenesis, intramembranous/endochondral ossification) and growth properties of major morphological regions of the mandible. Variation in these five units provides the developmental basis for ontogenetic and phylogenetic modification of mandibular morphology. We have discussed how these developmental units are influenced by (a) the cell lineage from which they arise, (b) epithelial-mesenchymal (inductive tissue) interactions, (c) regulation of cell differentiation, and (d) extrinsic factors such as muscles, teeth and hormones. Evidence was provided that variation in mandibular morphology is heritable, subject to modification by natural selection, and that divergence among different genetic stocks has apparently occurred through changes in these developmental units and their derivative structures.(ABSTRACT TRUNCATED AT 400 WORDS)     

Seasonal variation in skeletal silicification of Neodenticula seminae,a marine planktonic diatom: Sediment trap experiments in the NW Pacific Ocean (1997–2001)

Neodenticula seminae is an important component of pelagic diatom floras in the subarctic North Pacific and its adjacent seas. We conducted an SEM image analysis of four series of samples collected by sediment traps in the NW Pacific, in order to investigate the relations between its morphology, evolution, and environment. Seasonal variation in the skeletal morphology was common: lightly silicified morphs were dominant during spring blooms and in the summer (under oligotrophic conditions owing to surface water stratification and progressive nutrient limitation), whereas heavily silicified morphs became abundant in the fall and winter, subsequent to the onset of intensive vertical mixing. These observations suggest that the morphology of N. seminae is influenced by environmental factors including the nutrient availability as well as by its reproductive strategy.     

Experimental analysis of the nature of social context in captive groups of squirrel monkeys (Saimiri sciureus)

The nature of social context as a factor affecting grouping behavior is experimentally examined in captive groups of squirrel monkeys by recording the effects of systematic removal and return of individuals on the distributions of non-agonistic interactions and prolonged (huddle) contacts among the remaining group members. Observed changes in the distributions of these interactions among the remaining individuals are analyzed in terms of the age-sex class of the individual(s) removed, age-sex distributions of the individuals remaining, and the classes of dyadic relationships severed by the removals. Results indicate that, at least so far as these spacing-related behaviors are concerned, (1) the social environment does not act as a configurational whole on the grouping behavior of individuals, (2) the effect of social context on grouping behavior may be analyzed as the effects of specific dyadic relationships upon others, and (3) not all dyadic relationships significantly affect all others in a social group, i.e., not all of the social environment is relevant to the interactions between all pairs of individuals.     

A simple model of dynamic receptor pattern generation

A dynamic pattern generating automaton has been constructed. The rules controlling its function furnish the non-random generation of sub-patterns in consecutive cycles, within a large plane area, covered by four different classes of units of constant mean frequency in each class (standard system). The stabilization of certain specific sub-patterns over 100 subsequent cycles of pattern generation (modified systems) resulted in the modification of the frequency and frequency distribution of the sub-patterns relative to the standard system. Some new types of sub-patterns, not encountered in the standard system, also made appearance in the modified systems. The functioning of the standard and modified systems was analyzed and compared by the methods of mathematical statistics. The automaton was used to model certain features of the cytoplasmic membrane. The latter was regarded as a device by which the cell collects information about its environment. The dynamic generation of sub-patterns was taken as the cell's manner of asking questions, and the complementary chemical structures present in the environment were treated as possible answers to these. The irreversible question-answer interactions were regarded as signals and were modelled by the stabilization of specific sub-patterns. It was found that in a dynamic system like the model presented, it is not necessary to code each possible sub-pattern individually. Precise coding of the relative frequency of units per class and of their possible interactions is sufficient to furnish statistically constant mean frequencies for a given range of sub-patterns. In a dynamic system, the actual range of sub-patterns arisen in a population of identical individuals depends only on the size of the population. If the latter is appropriately large, all possible sub-patterns may be simultaneously present at any time at the average frequencies characteristic of each. Stabilized sub-patterns (signals) seem to modify specifically the frequencies of the other sub-patterns generated by the normal automaton. Some sub-patterns may disappear permanently, while others (new ones) may turn up and persist at given frequencies. Missense signals may definitively put the automaton out of order, i.e. result in the cell's complete misorientation in respect of its relations to the normal tissue structure.Reader of publications in physics, Gondolat Publishing House, Budapest, Hungary     

Quondam Gill-Covers

On the basis of its positional relations to the neuromast and branchial-arch systems, a greater part of the cephalic exoskeleton in teleostome fishes is suggested to have evolved from dermal elements which once provided support for gill-covers. More precisely, the following results are arrived at: parts of the decking of the ethmoid region of the endocranium stem from the branchiostegic exoskeleton of the terminal, or first, branchial unit; the external cheek-plates are made up of modified branchiostegic components of the premandibular (second), mandibular (third), and hyoid (fourth) branchial units; the lower jaws include inferior branchiostegic elements of the mandibular and hyoid branchial units; those branchiostegic elements of the hyoid branchial unit which remained free of the external cheek-plates and the lower jaws gave origin to the exoskeletal support of the hyoidean opercula as well as to the two rows of submandibular bones.     

Role of the human thalamic parafascicular (CM-Pf) complex in neuronal mechanisms of selective attention

Responses of 93 single units of the human thalamic CM-Pf complex to relevant and irrelevant verbal (or sensory) stimuli were studied using microelectrode technique in alert diskinetic patients suffering from the tonic forms of spasmodic torticollis during 11 stereotaxic operations. The response patterns of two types units with irregular unitary (A-type) and low-threshold bursting Ca(2+)-dependent (B-type) spike activity were studied. Three main conclusions emerge from the studies: 1) high reactivity of both A- and B-units to presentation of relevant verbal stimuli with differences of their response patterns as determined by the type of constituent elements; 2) close functional connectivity of these neuronal changes with the level of selective attention; 3) at the moment of attention activation, the appearance of transient interneuronal interactions between adjacent A and B cells characterized by the local synchronization and stabilization of rhythmic oscillations. These data point to considerable contribution of the thalamic CM-Pf complex and its neuronal mechanisms into organization of the human selective attention and triggering verbal-related processing during performance of purposive speech-provoked voluntary acts.     

Human physiology in space

The universality of gravity (1 g ) in our daily lives makes it difficult to appreciate its importance in morphology and physiology. Bone and muscle support systems were created, cellular pumps developed, neurons organised and receptors and transducers of gravitational force to biologically relevant signals evolved under 1g gravity. Spaceflight provides the only microgravity environment where systematic experimentation can expand our basic understanding of gravitational physiology and perhaps provide new insights into normal physiology and disease processes. These include the surprising extent of our body's dependence on perceptual information, and understanding the effect and importance of forces generated within the body's weightbearing structures such as muscle and bones. Beyond this exciting prospect is the importance of this work towards opening the solar system for human exploration. Although both appear promising, we are only just beginning to taste what lies ahead.