A unifying concept: the history of cell theory

After the first observations of life under the microscope, it took two centuries of research before the 'cell theory', the idea that all living things are composed of cells or their products, was formulated. It proved even harder to accept that individual cells also make up nervous tissue.     

A unifying evolutionary theory for the biomass–diversity–fertility relationship

Although a widely accepted ecological theory predicts that more diverse plant communities should be better able to capture resources and turn carbon dioxide into biomass, the most productive communities known are low diversity agricultural ones. This paradox has fuelled a long running controversy in ecology surrounding the nature of the relationship between diversity, productivity and fertility. Here, an evolutionary computer model is used which demonstrates that given the opportunity, species-rich communities may evolve under high fertility conditions. In contrast to low diversity, highly productive agricultural communities are shown to probably be a recent phenomenon. In simulations where fertility was applied to communities that had evolved under lower nutrient conditions, a few species had the ability to become ‘dominant’. These species were responsible for the loss of diversity and for the majority of biomass production. These results are consistent with complementarity theory applying in nature in old co-evolved low nutrient communities, whereas in recently established fertile agricultural communities, dominant species appear to regulate biomass production. Understanding the nature of these ‘dominant’ species throws light on our understanding of phenotypic plasticity and the ecology of invasive species. The appendices files are currently available at .     

A unifying concept for the amino acid code

The structure of the genetic code is related to a Gray code, which is a plausible theoretical model for an amino acid code. The proposed model implies that the most important factor in shaping the code was the effects of mistakes in translation, not effects of mutations. Another possible implication is that the preservation of stiffness and flexibility at appropriate places in a protein chain is as important in protein structure as the appropriate placement of hydrophilic (external) and hydrophobic (internal) residues. Other results are a simple conceptualization of the relationships among the 20 amino acids and their relations to their codons. The detailed relationships are summarized in the following ‘similarity alphabet’: ala, thr, gly, pro, ser; asp, asn, glu, gln, lys; his, arg, trp, tyr, phe; leu, met, ile, val, cys; (ATGPS DNEQK HRWYF LMIVC in the one-letter code). This alphabet falls into four groups of amino acids: small, external, large, internal. The approximate relation of the groups to their codons is expressed as: the first base of a codon controls size—a purine means a small amino acid, a pyrimidine means large; the middle base controls cloisterednes—purine means external, pyrimidine means internal. These relationships express the minimum change principle upon which the code appears to be founded.     

Effect of the N/P ratio on biomass productivity and nutrient removal from municipal wastewater

The aim of this study is to investigate the effect of the N/P ratio on biomass growth with the simultaneous removal of nutrients from municipal wastewaters. An optical panel photobioreactor is employed for this investigation because it provides a uniform light distribution within the reactor, which enhances the efficiency of the reactor in the cultivation of microalgae. The N/P ratio is varied over a wide range, i.e., from 5 to 30, for the assessment of its effect on biomass productivity. There is not a strong correlation between biomass productivity and TN removal, and these factors do not seem to be proportional in the wastewater using the microalgae we employed. In contrast, the TP removal depends greatly on both the N/P ratio and biomass productivity. The optimum value of the N/P ratio for biomass productivity in and nutrient removal from municipal wastewater treatment using microalgae varies from 5 to 30, depending on the ecological conditions in the wastewater.     

"Noise" as a unifying concept in the theory of schizophrenia

The psychological effects of pharmacologically active substances can only be adequately described in terms of the psychological processes upon which they act. Psychopharmacology therefore depends on the development of psychological “models”, i.e. formally stated and testable hypotheses concerning the psychological processes required for the performance of any given task. Information theory is not concerned with the physical nature of events but only with those features which confer specificity upon them. It therefore provides a suitable theoretical language in which to describe interactions between biochemical, neurophysiological and psychological events. (i) The first section of this paper defines the information-theory concept of noise. Starting from first principles with the “noisy channel” and progressing to the “noisy system”, some of its psychophysiological implications are explored. (ii) An “order-memory” task is described which was used for three years to study the thinking of acutely disturbed young adult psychiatric patients, including many with acute schizophrenia. On the basis of a simple model, it is possible to calculate the value of a “critical” noise-level which marks the dividing line between two qualitatively different modes of functioning. (iii) A number of results are either reported or summarized, which show the functional significance of a supra-critical noise-level and its connection with the acute schizophrenic state. (iv) A “control-theory” approach to schizophrenia is outlined, which shows how specific and non-specific hereditary factors could be accommodated in the hypothesis but mainly emphasizes the concept of a mutual struggle for control between parent and child, in which the “loser” overloads the regulatory capacity of the other by “going noisy”. In this way the “loser” escapes from control but is more or less disabled by his own cognitive noise.     

C:N:P stoichiometry in soil: is there a “Redfield ratio” for the microbial biomass?

Well-constrained carbon:nitrogen:phosphorus (C:N:P) ratios in planktonic biomass, and their importance in advancing our understanding of biological processes and nutrient cycling in marine ecosystems, has motivated ecologists to search for similar patterns in terrestrial ecosystems. Recent analyses indicate the existence of “Redfield-like” ratios in plants, and such data may provide insight into the nature of nutrient limitation in terrestrial ecosystems. We searched for analogous patterns in the soil and the soil microbial biomass by conducting a review of the literature. Although soil is characterized by high biological diversity, structural complexity and spatial heterogeneity, we found remarkably consistent C:N:P ratios in both total soil pools and the soil microbial biomass. Our analysis indicates that, similar to marine phytoplankton, element concentrations of individual phylogenetic groups within the soil microbial community may vary, but on average, atomic C:N:P ratios in both the soil (186:13:1) and the soil microbial biomass (60:7:1) are well-constrained at the global scale. We did see significant variation in soil and microbial element ratios between vegetation types (i.e., forest versus grassland), but in most cases, the similarities in soil and microbial element ratios among sites and across large scales were more apparent than the differences. Consistent microbial biomass element ratios, combined with data linking specific patterns of microbial element stoichiometry with direct evidence of microbial nutrient limitation, suggest that measuring the proportions of C, N and P in the microbial biomass may represent another useful tool for assessing nutrient limitation of ecosystem processes in terrestrial ecosystems.     

A unifying theory for methods of systematic analysis

A unifying theory for systematic analysis states that a number of methods should be used jointly to cope with various kinds of data; also that groups should be as consistent as possible, be made with least information loss, and where needed, be polythetic. A test of relationship, homogeneity, can use various kinds of data. It can take account of the internal variation of aggregate items such as genera. It can give due emphasis to smaller clusters that have likely important contexts of external items. It helps in analysing trends, cores and hazes in dendrograms. A proposed detector for formal groups can be based on measures of isolation, identifiability and inclusiveness. Non-mathematical, inter-item reaction tests such as hybridization and serology can also be used in grouping. All relationship data are used polythetically to reveal natural groups. This leads to a unified informational concept for taxa. This is more useful than the biological species concept that is restricted to inter-breeding data. All the methods appear to be analogues of the powerful human grouping instinct. The resulting compatibility is important as precise methods are needed mainly when the data are too complex for the mind to use reliably. Cladograms can be made by self-graded deweighting of homogeneity and agglomerative clustering. Unlike classical cladistics this can reveal any polythetic group. Finding the derived states for making cladograms is often much too hypothetical for a fully cladistic approach to be properly precise. Instead, where the evidence is weak, a milder strength of graded deweighting is used for the cladistic properties, which help to show relationships along with the others. Axiomatic failures of other classes of grouping methods are discussed. Unavoidable remnants of instinctive processing lower the precision of all the methods. The Uniter computer program, based on the theory, is tested with finely graded values of artificially ‘evolved’ items and with coarsely coded cladistic data. The results show that with natural data, the program should act as a fairly sensitive probe of past evolutionary branching. Another test shows how specimens from species complexes can be grouped and how distinctions between groups are analysed.     

Adaptive resemblance: a unifying concept for mimicry and crypsis

Adaptive resemblance (AR) is a broad and inclusive concept which requires that only one condition be met: that members of a species of organism gain fitness due to a selective advantage imparted by a resemblance to some cue or signal in the organism's environment. Essential to the evolution and maintenance of AR is the dynamic and ongoing relationship among model, mimic and selective agent (SA) that provides a complex selective milieu within which evolves resemblance. Because specifics of a resemblance, including phenotypic traits being imitated, the nature of the model, and the function of the resemblance, are not relevant to the concept of AR, the diversity and abundance of such resemblances are limited only by the diversity and abundance of exploitable model-SA relationships. Defined as it is by a single mimic-related criterion, AR thus provides the basis for uniting under one conceptual umbrella diverse resemblances that range from cryptic to sematic, interspecific to intraspecific, organismal to molecular, and material to attributive or implied. The defining criterion excludes incidental resemblances which are contrastingly defined as those which are the result of coincidental phenotypic responses to functional requirements or to other selective influences. Some adaptive resemblances are attributable to more than one selective factor and thus may be categorized in more than one way (having aposematic and procryptic functions, for instance), while some others apparently are due to incidental resemblance as well as adaptive (such as thermoadaptive and procryptic functions).     

A metabolic theory of ecology applied to temperature and mass dependence of N and P excretion by common carp

Our study used a metabolic theory of ecology (MTE) to explore scaling of metabolic rates by body size and temperature, and to predict nutrient excretion by common carp (Cyprinus carpio). At high biomasses, common carp have negative impacts on water quality, and one mechanism is excretion of the nutrients N and P. We measured whole-body and mass-specific excretion rates during summer and winter for fish of different sizes (wet mass range 28–1,196 g) to produce an allometric scaling model capable of predicting excretion at different temperatures. We found positive relationships between both dissolved and total nutrient concentrations and fish wet mass in summer and winter, with greater excretion rates in summer (mean water temperature 24.2°C) than in winter (mean water temperature 9.2°C). Mass-specific excretion rates decreased with increasing fish size, consistent with the MTE, and the temperature-adjusted model explained more variation for N excretion than for P. The proportion of dissolved nutrients (NH₄ and PO₄) to total nutrients increased with increasing fish size. The significance of these models is that they can be used to predict population-based nutrient excretion by common carp when thermal history, fish density and size distribution in a water body are known.     

Effects of light intensity and quality on the relative N and P requirement (the optimum N:P ratio) of marine planktonic algae

The relative requirement of N and P (the optimum N:P ratio)by Dunaliella tertiolecta, Phaeodactylum tricornutum, Prymnesiumparvum and Thalassiosira pseudonana was studied under variouslight intensities and spectra. The ratio was determined as theratio of the minimum cell N and P concentrations (q₀N and q₀pwhen either nutrient was limiting. The ratio varied widely amongspecies; under light-saturation for growth (116 µEin ^m–2s^–1 it ranged from 11.8 in ^D. tertiolecta to 36.6 in P.tricornutum. The ratio appeared to be higher at a sub-saturatingintensity (24 µEin m^–2 s^–1 in all except P.tricornutum, mainly because of higher q_oN with little changein q_oP. In T. pseudonana Q_oP also increased, resulting in aninsignificant change in the ratio. The ratio varied little withinthe range of saturation intensity. Light quality affected q_oNand q_oP as well as the ratio, and the pattern of change variedfrom species to species. The optimum ratio of individual specieswas linearly correlated to their q_oN except in P. tricornutum.q_oN for all species showed a linear correlation with cell proteinconcentrations irrespective of light conditions. The changeof optimum N:P ratios in the three species thus appears to berelated to changes in cell protein contents. The ratio of carbohydratesto protein remained constant regardless of light intensity orquality and was higher in P-limited cultures. We conclude thatchanges in light regime can strongly influence algal nutrientrequirements and species interrelationships by altering theoptimum cellular N:P ratio.     

Ecological complexity for unifying ecological theory across scales: A field ecologist's perspective

The evening session in ecological complexity at the last Joint Meeting of the International Association for Ecology (INTECOL) and the Ecological Society of America (ESA) held in Montreal was an occasion to evaluate the pertinence and upcoming challenges of the complex systems approach (CSA) applied to ecology. Through concepts such as the interaction topology among biological objects, the phenotypic integration of individual traits, the meaning of biological objects and complexity measures in space and time, the management of human dominated ecosystems, and non-equilibrium thermodynamics as a paradigm for the development of ecosystems, the panel members covered some of the most active areas of research in ecological complexity. However, for many ecologists, and particularly field ecologists, a comprehensive framework clearly emphasizing how and why the CSA provides a unique corpus for studying ecosystem functions is missing. The purpose of this article is thus to provide an overview of the different themes visited during the evening session and to emphasize the distinctiveness of the CSA as an alternative to contemporary ecological issues. Examples from functional ecology and food webs are given to support the discussion.     

A unifying theory for genetic epidemiological analysis of binary disease data

Background

Genetic selection for host resistance offers a desirable complement to chemical treatment to control infectious disease in livestock. Quantitative genetics disease data frequently originate from field studies and are often binary. However, current methods to analyse binary disease data fail to take infection dynamics into account. Moreover, genetic analyses tend to focus on host susceptibility, ignoring potential variation in infectiousness, i.e. the ability of a host to transmit the infection. This stands in contrast to epidemiological studies, which reveal that variation in infectiousness plays an important role in the progression and severity of epidemics. In this study, we aim at filling this gap by deriving an expression for the probability of becoming infected that incorporates infection dynamics and is an explicit function of both host susceptibility and infectiousness. We then validate this expression according to epidemiological theory and by simulating epidemiological scenarios, and explore implications of integrating this expression into genetic analyses.

Results

Our simulations show that the derived expression is valid for a range of stochastic genetic-epidemiological scenarios. In the particular case of variation in susceptibility only, the expression can be incorporated into conventional quantitative genetic analyses using a complementary log-log link function (rather than probit or logit). Similarly, if there is moderate variation in both susceptibility and infectiousness, it is possible to use a logarithmic link function, combined with an indirect genetic effects model. However, in the presence of highly infectious individuals, i.e. super-spreaders, the use of any model that is linear in susceptibility and infectiousness causes biased estimates. Thus, in order to identify super-spreaders, novel analytical methods using our derived expression are required.

Conclusions

We have derived a genetic-epidemiological function for quantitative genetic analyses of binary infectious disease data, which, unlike current approaches, takes infection dynamics into account and allows for variation in host susceptibility and infectiousness.     

Adrenoceptors and the pharmacology of affective illness: a unifying theory

Based on recent clinical and preclinical research, it is theorized that antimanic and antidepressant effects of clinically available drugs can be produced through their actions on alpha-1 adrenoreceptor-mediated neurotransmission in the central nervous system. The theory suggests that final effects on alpha-1 mediated neurotransmission may be produced not only by drugs which have direct effects on the alpha-1 receptor or its second messenger, but also by drugs having effects on neurotransmitter systems such as acetylcholine, GABA, and serotonin, among others, which modulate the activity of central norepinephrine neurons or, via feedback mechanisms, by drugs having effects on adrenergic receptors other than the alpha-1 receptor itself.     

Effects of soil C:N:P stoichiometry on biomass allocation in the alpine and arid steppe systems

Soil nutrients strongly influence biomass allocation. However, few studies have examined patterns induced by soil C:N:P stoichiometry in alpine and arid ecosystems. Samples were collected from 44 sites with similar elevation along the 220‐km transect at spatial intervals of 5 km along the northern Tibetan Plateau. Aboveground biomass (AGB) levels were measured by cutting a sward in each plot. Belowground biomass (BGB) levels were collected from soil pits in a block of 1 m × 1 m in actual root depth. We observed significant decreases in AGB and BGB levels but increases in the BGB:AGB ratio with increases in latitude. Although soil is characterized by structural complexity and spatial heterogeneity, we observed remarkably consistent C:N:P ratios within the cryic aridisols. We observed significant nonlinear relationships between the soil N:P and BGB:AGB ratios. The critical N:P ratio in soils was measured at approximately 2.0, above which the probability of BGB:AGB response to nutrient availability is small. These findings serve as interesting contributions to the global data pool on arid plant stoichiometry, given the previously limited knowledge regarding high‐altitude regions.     

Species-specific differences in phytoplankton responses to N and P enrichments and the N:P ratio in the Archipelago Sea, northern Baltic Sea

A nutrient enrichment experiment was conducted in order to studythe role of nitrogen (N), phosphorus (P) and the N:P ratio onthe early summer phytoplankton community in the ArchipelagoSea, northern Baltic Sea. The phytoplankton community was, interms of chlorophyll a and total biomass, primarily N-limited,but the individual species varied in their responses to thenutrient supply. The recorded overall N limitation was due tofast growth responses of a few N-limited species such as thediatom Chaetoceros wighamii (Brightwell) and the mixotrophicchrysophyte Uroglena sp. Another dominating diatom, Skeletonemacostatum (Greville) Cleve was most clearly P-limited. The N:Pratio had the strongest effect on Uroglena sp., which grew exponentiallyin the enrichments with a high N:P ratio. This can be explainedby the ability of the species to feed on P-rich bacteria, whichgives it a competitive advantage in P-limited conditions. Thespecies-specific differences in the responses to the nutrientenrichments can generally be explained by differences in thespecies physiology and they were consistent with the theoryof resource competition.     

Ionic strength dependence of localized contact formation between membranes: nonlinear theory and experiment.

Erythrocyte membrane surface or suspending phase properties can be experimentally modified to give either spatially periodic local contacts or continuous contact along the seams of interacting membranes. Here, for cells suspended in a solution of the uncharged polysaccharide dextran, the average lateral separation between localized contacts in spatially periodic seams at eight ionic strengths, decreasing from 0.15 to 0.065, increased from 0.65 to 3.4 micrometers. The interacting membranes and intermembrane aqueous layer were modeled as a fluid film, submitted to a disjoining pressure, responding to a displacement perturbation either through wave growth resulting in spatially periodic contacts or in perturbation decay, to give a plane continuous film. Measured changes of lateral contact separations with ionic strength change were quantitatively consistent with analytical predictions of linear theory for an instability mechanism dependent on the membrane bending modulus. Introduction of a nonlinear approach established the consequences of the changing interaction potential experienced by different parts of the membrane as the disturbance grew. Numerical solutions of the full nonlinear governing equations correctly identified the ionic strength at which the bifurcation from continuous seam to a stationary periodic contact pattern occurred and showed a decrease in lateral contact and wave crest separation with increasing ionic strength. The nonlinear approach has the potential to recognize the role of nonspecific interactions in initiating the localized approach of membranes, and then incorporate the contribution of specific molecular interactions, of too short a range to influence the beginning of perturbation growth. This new approach can be applied to other biological processes such as neural cell adhesion, phagocytosis, and the acrosome reaction.     

Dielectrophoretic force: A comparison of theory and experiment

Because of the increasing use of dielectrophoresis in the dielectric characterization and sorting of living cells or their parts, it has become important to establish carefully the theoretical backgrounds for this effect. A comparison with experiment is made of the several versions of the theory for the dielectrophoretic force exerted by nonuniform electric fields upon a neutral object. The three fundamental approaches: the Maxwell-Strattonstress tensor, the effective dipole moment, and the ‘Helmholtz’ energy approach are presented along with the general solution given earlier by Pohl and Crane. These are found to agree closely with experiment in predicting the dielectrophoretic force upon various rods hung in specially shaped (isomotive) field distributions. On the other hand, an alternative formulation based upon a debatable assignment of fields local to the dipoles gave a good fit to the experimental data only for materials of very low permittivity, and fitted poorly in the case of highly polarizable materials. An improved derivation of the theory for stable dielectrophoretic levitation is also presented. This phenomenon is of particular interest in that it is based upon an apparent violation of the Earnshaw's theorem, and is useful in the study of the dielectric properties of individual living cells.