Simple Experimental Manipulation Research Articles

EEG-representational geometries and psychometric distortions in approximate numerical judgment.

When judging the average value of sample stimuli (e.g., numbers) people tend to either over- or underweight extreme sample values, depending on task context. In a context of overweighting, recent work has shown that extreme sample values were overly represented also in neural signals, in terms of an anti-compressed geometry of number samples in multivariate electroencephalography (EEG) patterns. Here, we asked whether neural representational geometries may also reflect a relative underweighting of extreme values (i.e., compression) which has been observed behaviorally in a great variety of tasks. We used a simple experimental manipulation (instructions to average a single-stream or to compare dual-streams of samples) to induce compression or anti-compression in behavior when participants judged rapid number sequences. Model-based representational similarity analysis (RSA) replicated the previous finding of neural anti-compression in the dual-stream task, but failed to provide evidence for neural compression in the single-stream task, despite the evidence for compression in behavior. Instead, the results indicated enhanced neural processing of extreme values in either task, regardless of whether extremes were over- or underweighted in subsequent behavioral choice. We further observed more general differences in the neural representation of the sample information between the two tasks. Together, our results indicate a mismatch between sample-level EEG geometries and behavior, which raises new questions about the origin of common psychometric distortions, such as diminishing sensitivity for larger values.

Experimental manipulation of selfish genetic elements links genes to microbial community function.

Microbial communities underpin the Earth's biological and geochemical processes, but their complexity hampers understanding. Motivated by the challenge of diversity and the need to forge ways of capturing dynamical behaviour connecting genes to function, biologically independent experimental communities comprising hundreds of microbial genera were established from garden compost and propagated on nitrogen-limited minimal medium with cellulose (paper) as sole carbon source. After 1 year of bi-weekly transfer, communities retained hundreds of genera. To connect genes to function, we used a simple experimental manipulation that involved the periodic collection of selfish genetic elements (SGEs) from separate communities, followed by pooling and redistribution across communities. The treatment was predicted to promote amplification and dissemination of SGEs and thus horizontal gene transfer. Confirmation came from comparative metagenomics, which showed the substantive movement of ecologically significant genes whose dynamic across space and time could be followed. Enrichment of genes implicated in nitrogen metabolism, and particularly ammonification, prompted biochemical assays that revealed a measurable impact on community function. Our simple experimental strategy offers a conceptually new approach for unravelling dynamical processes affecting microbial community function.This article is part of the theme issue ‘Conceptual challenges in microbial community ecology’.

Self-assembly of polyoxometalate-based hybrid molecules into nanoparticles or vesicles regulated by simple experimental manipulation

A polyoxometalate (POM)-cholic acid hybrid was prepared by grafting cholic acid moieties on two sides of the POM cluster. The self-assembly behaviors developed by POM-cholic acid hybrid molecules in a methanol/toluene mixed solution were studied to improve the control of molecular architectures. Under the control conditions, nanoparticles and vesicles in solution systems were formed using simple experimental manipulation. The nanoparticles were prepared with hybrid molecules using ultrasonic manipulation, while the vesicles were formed through aging manipulation. More specifically, these different morphologies were thoroughly studied by transmission electron microscopy (TEM), atomic force microscopy (AFM), Fourier-transform infrared (FTIR), and X-ray diffraction (XRD) analyses. The results revealed that the self-assembly behaviors of hybrid molecules can be readily regulated through simple experimental manipulations. Additionally, we also propose the mechanisms of formation of nanoparticles and vesicles. This work may provide a smart approach to the effective design and fabrication of multifunctional supramolecular materials with adjustable structural architectures.

ChemInform Abstract: A General Aminocatalytic Method for the Synthesis of Aldimines.

A general and efficient biomimetic method for the synthesis of aldimines from aldehydes and compounds bearing the NH2 group in the presence of pyrrolidine as a catalyst has been developed. These organocatalytic reactions, based on the application of the concept of nucleophilic catalysis, proceed with outstanding yields in the absence of acids and metals under simple conditions and minimum experimental manipulation. The method has been mainly applied to the synthesis of N-sulfinyl and N-sulfonyl imines, but its general validity has been proven with the preparation of representative N-phosphinoyl, N-alkyl, and N-aryl imines. These unprecedented reactions, which presumably occur via iminium activation without requiring acidic conditions, are an interesting and competitive alternative to the classical methods for preparing aldimines.

Experimental Manipulation of Body Size to Estimate Morphological Scaling Relationships in <em>Drosophila</em>

The scaling of body parts is a central feature of animal morphology1-7. Within species, morphological traits need to be correctly proportioned to the body for the organism to function; larger individuals typically have larger body parts and smaller individuals generally have smaller body parts, such that overall body shape is maintained across a range of adult body sizes. The requirement for correct proportions means that individuals within species usually exhibit low variation in relative trait size. In contrast, relative trait size can vary dramatically among species and is a primary mechanism by which morphological diversity is produced. Over a century of comparative work has established these intra- and interspecific patterns3,4.Perhaps the most widely used approach to describe this variation is to calculate the scaling relationship between the size of two morphological traits using the allometric equation y=bxα, where x and y are the size of the two traits, such as organ and body size8,9. This equation describes the within-group (e.g., species, population) scaling relationship between two traits as both vary in size. Log-transformation of this equation produces a simple linear equation, log(y) = log(b) + αlog(x) and log-log plots of the size of different traits among individuals of the same species typically reveal linear scaling with an intercept of log(b) and a slope of α, called the 'allometric coefficient'9,10. Morphological variation among groups is described by differences in scaling relationship intercepts or slopes for a given trait pair. Consequently, variation in the parameters of the allometric equation (b and α) elegantly describes the shape variation captured in the relationship between organ and body size within and among biological groups (see 11,12).Not all traits scale linearly with each other or with body size (e.g., 13,14) Hence, morphological scaling relationships are most informative when the data are taken from the full range of trait sizes. Here we describe how simple experimental manipulation of diet can be used to produce the full range of body size in insects. This permits an estimation of the full scaling relationship for any given pair of traits, allowing a complete description of how shape covaries with size and a robust comparison of scaling relationship parameters among biological groups. Although we focus on Drosophila, our methodology should be applicable to nearly any fully metamorphic insect.

Experimental Manipulation of Body Size to Estimate Morphological Scaling Relationships in <em>Drosophila</em>

The scaling of body parts is a central feature of animal morphology1-7. Within species, morphological traits need to be correctly proportioned to the body for the organism to function; larger individuals typically have larger body parts and smaller individuals generally have smaller body parts, such that overall body shape is maintained across a range of adult body sizes. The requirement for correct proportions means that individuals within species usually exhibit low variation in relative trait size. In contrast, relative trait size can vary dramatically among species and is a primary mechanism by which morphological diversity is produced. Over a century of comparative work has established these intra- and interspecific patterns3,4. Perhaps the most widely used approach to describe this variation is to calculate the scaling relationship between the size of two morphological traits using the allometric equation y=bxα, where x and y are the size of the two traits, such as organ and body size8,9. This equation describes the within-group (e.g., species, population) scaling relationship between two traits as both vary in size. Log-transformation of this equation produces a simple linear equation, log(y) = log(b) + αlog(x) and log-log plots of the size of different traits among individuals of the same species typically reveal linear scaling with an intercept of log(b) and a slope of α, called the 'allometric coefficient'9,10. Morphological variation among groups is described by differences in scaling relationship intercepts or slopes for a given trait pair. Consequently, variation in the parameters of the allometric equation (b and α) elegantly describes the shape variation captured in the relationship between organ and body size within and among biological groups (see 11,12). Not all traits scale linearly with each other or with body size (e.g., 13,14) Hence, morphological scaling relationships are most informative when the data are taken from the full range of trait sizes. Here we describe how simple experimental manipulation of diet can be used to produce the full range of body size in insects. This permits an estimation of the full scaling relationship for any given pair of traits, allowing a complete description of how shape covaries with size and a robust comparison of scaling relationship parameters among biological groups. Although we focus on Drosophila, our methodology should be applicable to nearly any fully metamorphic insect.

SPECIES VARIABILITY IN CARDIOVASCULAR RESEARCH: THE EXAMPLE OF ADRENOCORTICOTROPHIN‐INDUCED HYPERTENSION

1. Lawrie Beilin has contributed greatly to international hypertension research through both animal and human studies. 2. Animals are used in biomedical research to gain insights that can be extrapolated ultimately to humans. 3. A simple experimental manipulation, adrenocorticotrophin (ACTH) administration, has a range of different cardiovascular effects in different species. 4. Caution should be exercised in extrapolating data from animals to humans.

Temperature affects longevity and age‐related locomotor and cognitive decay in the short‐lived fish Nothobranchius furzeri

Temperature variations are known to modulate aging and life-history traits in poikilotherms as different as worms, flies and fish. In invertebrates, temperature affects lifespan by modulating the slope of age-dependent acceleration in death rate, which is thought to reflect the rate of age-related damage accumulation. Here, we studied the effects of temperature on aging kinetics, aging-related behavioural deficits, and age-associated histological markers of senescence in the short-lived fish Nothobranchius furzeri. This species shows a maximum captive lifespan of only 3 months, which is tied with acceleration in growth and expression of aging biomarkers. These biological peculiarities make it a very convenient animal model for testing the effects of experimental manipulations on life-history traits in vertebrates. Here, we show that (i) lowering temperature from 25 degrees C to 22 degrees C increases both median and maximum lifespan; (ii) life extension is due to reduction in the slope of the age-dependent acceleration in death rate; (iii) lowering temperature from 25 degrees C to 22 degrees C retards the onset of age-related locomotor and learning deficits; and (iv) lowering temperature from 25 degrees C to 22 degrees C reduces the accumulation of the age-related marker lipofuscin. We conclude that lowering water temperature is a simple experimental manipulation which retards the rate of age-related damage accumulation in this short-lived species.

Grounding vision through experimental manipulation.

Experimentation is crucial to human progress at all scales, from society as a whole to a young infant in its cradle. It allows us to elicit learning episodes suited to our own needs and limitations. This paper develops active strategies for a robot to acquire visual experience through simple experimental manipulation. The experiments are oriented towards determining what parts of the environment are physically coherent--that is, which parts will move together, and which are more or less independent. We argue that following causal chains of events out from the robot's body into the environment allows for a very natural developmental progression of visual competence, and relate this idea to results in neuroscience.

Social desirability effects in simulated work teams

Stimulated by disparate empirical findings, an experimental study with federal managers (N = 129) tested for differential effects of Low vs. High Social Desirability (SD) under two “objective” conditions -- simulated membership in a “good” vs. a “bad” work team. A simple and economical experimental manipulation successfully induced the two conditions and, overall, the expected differential effects of SD were observed. Treatment order confounds the interpretation of results, however, and revisions in the design are required for a more definitive test of the present approach.

Hyperoxia and hypoxia in pregnancy: simple experimental manipulation alters the incidence of cleft lip and palate in CL/Fr mice.

This paper describes alterations in the incidence of cleft lip and palate in CL/Fr mice subsequent to experimental manipulation of maternal respiratory oxygen levels during a critical period of pregnancy. Only a few previous studies have shown that the incidence of some "genetically determined" malformations in mammals can be decreased by environmental procedures. In addition to demonstrating a decreased incidence of cleft lip and palate subsequent to maternal hyperoxia on gestational days 10 and 11 in a genetically susceptible strain, the results of the present study show that hypoxia at this time increases the incidence of cleft lip and palate.

Hyperoxia and hypoxia in pregnancy: simple experimental manipulation alters the incidence of cleft lip and palate in CL/Fr mice.

Hyperoxia and hypoxia in pregnancy: simple experimental manipulation alters the incidence of cleft lip and palate in CL/Fr mice.

Age-dependent Excystment of the Protozoan Acanthamoeba castellanii

Summary: Axenic cyst cultures of Acanthamoeba castellanii (Neff strain) maintained in salt medium undergo excystment when transferred into enriched growth medium containing yeast extract and proteose peptone. Both the synchrony and extent of excystment induced in this manner are critically dependent upon the length of time cysts are aged in salt medium prior to the initiation of excystment. Cysts sustained in salt medium for 50 h or less characteristically show only about 10 % excystment even after 70 h in the enriched growth medium. With progressively longer periods of ageing the synchrony and degree of excystment improve such that for cysts of age ≥ 800 h, more than 85 % of the organisms germinate within a period of 12 h. Thus more complete and relatively synchronous excystment can be achieved by this simple experimental manipulation.

Two Cases of Resource Partitioning in an Intertidal Community: Making the Right Prediction for the Wrong Reason

An important ecological goal is understanding patterns of coexistence and exclusion of species in the same geographic area. Because most multispecies ecological systems are exteremely complex, it is probably impossible to describe all the component populations in terms of their physiological status or demographic characteristics such as age distributions and birth and death rates. One current method of studying such ecological systems is to design a generalized model, based on a few premises or simplifying assumptions, which will generate testable predictions. If, upon being tested, these predictions are falsified, the simplifying assumptions are changed accordingly; but if the predictions are verified, the assumptions are often considered to be substantiated. This hypothetico-deductive approach has influenced ecologists to focus on more general questions rather than on specific factors which may have small effects and which, when applied to more general situations, lead to intractable mathematical equations. Here I emphasize, with Levins (1966) and Cohen (1968), that the use of generalized models can be misleading because of uncertainty as to whether a positive result depends on the reality of the model and the simplifying assumptions, or on entirely unrelated factors. I therefore urge that, whenever possible, simplifying assumptions themselves be tested as hypotheses and resultant models be based on a thorough understanding of the relevant natural history and, when possible, on experimental manipulation. Here I will test predictions generated by two models which might be used in the construction of a general competition-based theory of the structure of an intertidal community. In both cases, the predictions generated by these two models are verified, suggesting that their simplifying assumptions are based on parameters sufficient to describe the community process in question. In both cases, however, acceptance of the superficially plausible models is due to inadequate appreciation of natural history. Simple experimental manipulation shows that each model makes the right prediction for the wrong reason.