Variability of foraging in highshore habitats: dealing with unpredictability

Intertidal areas are habitats at the border of two very different environments: the marine environment and the terrestrial environment. In contrast to many habitats at borders, intertidal areas are very variable in space and time. They have upshore and alongshore gradients of environmental conditions, which change through time in predictable (due to changing tides) and unpredictable (due to changing weather) ways. Because most animals and plants on rocky shores are marine in origin, extreme highshore levels are generally considered more harsh and unpredictable environments than are mid- or lowshore levels. In this study, the linear distances and directions dispersed by the littorinid Littorina unifasciata while foraging were compared across randomly-chosen mid- and highshore replicated sites to test the hypothesis that movement during foraging was more variable from place to place in complex midshore habitats. Experiments were repeated on different days to test the hypothesis that temporal variability in movement was greater at high- than at midshore levels because environmental conditions necessary for foraging were more variable high on the shore. Finally, the data were used to test models about differences in variability among individuals in the same patch of habitat according to their recent history of submersion/emersion. In contrast to expectations, dispersal was more variable in space and time within and among highshore sites. The implications of such variable behaviour are discussed with respect to the generalization of patterns of behaviour from sparse data and the levels of replication needed in the design of experiments to investigate behaviour of intertidal animals.     

A quantum of neurotransmitter causes minis in multiple postsynaptic cells at the Caenorhabditis elegans neuromuscular junction

The polyadic synapse, where a single presynaptic active zone associates with two or more postsynaptic cells, exists in both mammals and invertebrates. An important but unresolved question is whether synaptic transmission occurs between the presynaptic site and its various postsynaptic partners. Using the dual whole-cell voltage clamp technique, we analyzed miniature postsynaptic currents (mPSCs or minis) at the C. elegans neuromuscular junction (NMJ), which is a polyadic synapse. We found that neighboring muscle cells at the same position along the body axis had high frequencies of concurrent mPSCs, which could not be explained by pure chance. Although body-wall muscle cells are electrically coupled, the high frequency of concurrent mPSCs was not due to electrical coupling because there was no correlation between the frequency of concurrent mPSCs and the degree of electrical coupling; the rise time of concurrent mPSCs was identical to that of nonconcurrent mPSCs but distinct from that of junctional currents (I(j)); and a mutant defective in electrical coupling showed normal frequency of concurrent mPSCs. Our analyses suggest that a single quantum of neurotransmitter may cause mPSCs in multiple postsynaptic cells at polyadic synapses, and that high-fidelity synaptic transmission occurs between the presynaptic site and its various postsynaptic partners. Thus, polyadic synapses could be a distinct mechanism for synaptic divergence and for synchronizing activities of postsynaptic cells.     

Blood Collection Procedure of Laboratory Primates: A Neglected Variable in Biomedical Research

A survey of 75 biomedical articles dealing with stress-dependent blood parameters in caged primates revealed that the conditions under which blood collection occurred were in most cases described either not at all or so haphazardly that it would be impossible to determine if humane handling procedures were used and basic principles of scientific methodology applied. These findings were unexpected because there is ample scientific evidence not only that stress-sensitive research data are influenced by traditional blood sampling procedures, but also that those data-biasing effects can be avoided. If dependent variables of the blood collection procedure are not controlled, data variability will increase, automatically increasing the number of animals needed for statistical analysis. For ethical and scientific reasons, it was recommended that editors of biomedical journals require authors to provide sufficient information of the blood collection--and, when applicable, the sedative injection--procedure to ensure that the experiment was done with the smallest number of animals possible to achieve statistical significance and that the investigation can be replicated reliably in another laboratory and the research data interpreted with reasonable accuracy.     

The order of DNA replication in mammalian cells : A modified density labelling procedure for isolating sequences replicated at specific times

These experiments were directed towards establishing a procedure for isolation of the DNA sequences replicated at different times in S phase for further study. Primary considerations were thus for a method that gave fairly large quantities of cells as well synchronized in S phase as possible. The use of Chinese hamster ovary (CHO) cells synchronized by isoleucine starvation followed by exposure to hydroxyurea [1] seemed to be most promising and was explored in detail. During the course of this work, a labelling scheme was developed that involved exposure to BrdUrd during the same time window in two sequential S phases. Only those regions of the genome replicated in the same interval in each S period contained BrdUrd in both strands and these were readily isolated in CsCl gradients. As applied in the present experiments, this labelling procedure showed no untoward effects on cell-cycle traverse and gave DNA distributions in density gradients that closely approximated those that would be expected for the conditions employed.     

Noninvasive markers of bone metabolism in the rhesus monkey: Normal effects of age and gender

Abstract: Measurement of bone turnover in conditions such as osteoporosis has been limited by the need for invasive iliac bone biopsy to reliably determine parameters of bone metabolism. Recent advances in the area of serum and urinary markers of bone metabolism have raised the possibility for noninvasive measurements; however, little nonhuman primate data exist for these parameters. The purpose of this experiment was to define the normal range and variability of several of the newer noninvasive bone markers which are currently under investigation in humans. The primary intent was to determine age and gender variability, as well as provide some normative data for future experiments in nonhuman primates. Twenty-four rhesus macaques were divided into equal groups of male and female according to the following age groupings: 3 years, 5–10 years, 15–20 years, and > 25 years. Urine was collected three times daily for a four-day period and measured for several markers of bone turnoverm including pyridinoline (PYD), deoxypyrodinoline (DPD), hydroxyproline, and creatinine. Bone mineral density measurements of the lumbar spine were performed at the beginning and end of the study period. Serum was also obtained at the time of bone densitometry for measurement of osteocalcin levels by radioimmunoassay. There were no significant differences in bone mineral density, urine PYD, or urine DPD based on gender. Bone density was lowest in the youngest animals, peaked in the 15–20-year group, but again decreased in the oldest animals. The osteocalcin, PYD, and DPD levels followed an inversely related pattern to bone density. The most important result was the relative age insensitivity of the ratio of PYD:DPD in monkeys up to age 20 years. Since bone density changes take months or years to become measurable and iliac biopsies are invasive, the PYD/DPD marker ratio may have important implications for rapid noninvasive measurement of the effects of potential treatments for osteoporosis in the non-human primate model.     

The Impact of Mathematical Proficiency on the Number-Space Association

A specific instance of the association between numerical and spatial representations is the SNARC (Spatial Numerical Association of Response Codes) effect. The SNARC effect describes the finding that during binary classification of numbers participants are faster to respond to small/large numbers with the left/right hand respectively. Even though it has been frequently replicated, important inter-individual variability has also been reported. Mathematical proficiency is an obvious candidate source for inter-individual variability in numerical judgments, but studies investigating its influence on the SNARC effect remain scarce. The present experiment included a total of 95 University students, divided into three groups differing significantly in their mathematical proficiency levels. Using group analyses, it appeared that the three groups differed significantly in the strength of their number-space associations in a parity judgment task. This result was further confirmed on an individual level, with higher levels in arithmetic leading to relatively weaker SNARC effects. To explain this negative relationship we propose accounts based on differences in access to qualitatively different numerical representations and also consider more domain general factors, with a focus on inhibition capacities.     

Variability patterns differ between standing stock and process rates

Standing stocks are typically easier to measure than process rates such as production. Hence, stocks are often used as indicators of ecosystem functions although the latter are generally more strongly related to rates than to stocks. The regulation of stocks and rates and thus their variability over time may differ, as stocks constitute the net result of production and losses. Based on long‐term high frequency measurements in a large, deep lake we explore the variability patterns in primary and bacterial production and relate them to those of the corresponding standing stocks, i.e. chlorophyll concentration, phytoplankton and bacterial biomass. We employ different methods (coefficient of variation, spline fitting and spectral analysis) which complement each other for assessing the variability present in the plankton data, at different temporal scales. In phytoplankton, we found that the overall variability of primary production is dominated by fluctuations at low frequencies, such as the annual, whereas in stocks and chlorophyll in particular, higher frequencies contribute substantially to the overall variance. This suggests that using standing stocks instead of rate measures leads to an under‐ or overestimation of food shortage for consumers during distinct periods of the year. The range of annual variation in bacterial production is 8 times greater than biomass, showing that the variability of bacterial activity (e.g. oxygen consumption, remineralisation) would be underestimated if biomass is used. The P/B ratios were variable and although clear trends are present in both bacteria and phytoplankton, no systematic relationship between stock and rate measures were found for the two groups. Hence, standing stock and process rate measures exhibit different variability patterns and care is needed when interpreting the mechanisms and implications of the variability encountered.     

How to estimate variability in affinity relationships in partially observed groups of domestic herbivores?

Animal sociability measurements based on inter-individual distances or nearest-neighbour distributions can be obtained automatically with telemetry collars. So far, all the indices that have been used require the whole group to be observed. Here, we propose an index of the variability in affinity relationships in groups of domestic herbivores, whose definition does not depend on group size and that can be used even if some data are missing. This index and its estimators are based on a function that measures how frequently an animal is closer than another one from a third animal. When no data are missing, we show that our estimator and the variance of the sociability matrixsensu Sibbald (considered as the reference method) are strongly correlated. We then consider two cases of missing data. In the first case, some animals are randomly missing, that is, to account for random breakdown of telemetry collars. Our estimator is unbiased by such missing data and its variance decreases as the number of observation dates increases. In the second case, the same animals are missing at all observation dates, that is, in large herds where there are more individuals to be observed than available telemetry collars. Our estimator of affinity variance within a group is biased by such missing data. Thus, it requires changing animals equipped with telemetry collars regularly during the experiment. Conversely, the estimator remains unbiased at the population level, that is, if several independent groups are being analysed. We finally illustrate how this estimator can be used by investigating changes in the variability of affinities according to group size in grazing heifers.     

Evaluation of an EIA method for measuring serum levels of the estrogen metabolite 2-hydroxyestrone in adults

Two-hydroxyestrone (2OHE-1) and 16alpha-hydroxyestrone (16OHE-1) are two estrogen metabolites that may play important roles in the development or promotion of breast cancer. Our study assessed the reliability of a newly developed kit procedure for measuring 2OHE-1. Although under certain conditions the assay would not distinguish 2OHE-1 from estriol, or possibly 2-methoxyestrone, steroids such as 17beta-estradiol, estrone and 16OHE-1 should not interfere with the test. Our study evaluated the precision of this enzyme immunoassay (EIA) kit for measuring 2OHE-1 levels in serum obtained from healthy men and women. As a result of several replicate analyses of specimens obtained from 18 men and 20 women, we found that the within-run coefficients of variation (CVs) were approximately 20% and the among run CVs, 30%. Because the SD for the procedure is high, the limit of detection (LOD) was also high (130 ng/l). Nonetheless the assay could distinguish between 2OHE-1 levels in men (128 ng/l) and women (332 ng/l) because we performed a large number of analyses on each specimen. Improving the reproducibility of the assay would reduce the: 1. LOD; number of replicates needed to obtain reliable estimates of 2-OHE-1 levels; amount of time, effort, and cost for each analysis; and greatly improve the reliability of the method. Because the within-run variability is relatively smaller than the total variability (among run + within run), use of the assay for determining differences among groups could be justified only when measurements were made in a single run.     

Heart rate variability in conscious neonatal swine: spectral features and responses to short-term intermittent hypoxia

Background  

Spectral analysis of the cardiac time series has been used as a tool for assessing levels of parasympathetic and sympathetic modulation of the sinoatrial node. In the present investigation we evaluated daily changes in heart rate variability spectra in conscious neonatal piglets that were either neurally intact (n = 5) or had undergone right stellate ganglionectomy (n = 5). The partial stellectomized animals and their intact litter mates were exposed to four days of intermittent hypoxia, each day comprising nine episodes of hypoxia alternating with nine episodes of normoxia. A time control group (n = 7) comprised animals from different litters that were not exposed to intermittent hypoxia. We hypothesized that exposure to intermittent hypoxia would increase sympathetic efferent neuronal modulation of heart rate variability spectra in neurally intact animals and in those with right stellate ganglionectomy, and that his effect would be observed in heart rate variability spectra computed from baseline recordings.     

Individual differences in sensitivity and tolerance to alcohol

Abstract

Human responses to alcohol—especially sensitivity and acute behavioral tolerance—are being studied within a behavioral genetic design involving comparisons of scores from monozygotic twins, dizygotic twins, nontwin siblings, and unrelated (adoptee) pairs reared in the same family from infancy. The planned genetic analyses must await completion of data collection. The present sample is, however, adequate for analyses of means and for some analyses of individual differences in responses. For most of the measures being used, we find the usual mean decrement in performance after alcohol dosing to 0.100 BAC, but individual differences in response to alcohol are large, and a few individuals actually improve in performance after dosing. Also, on two tests, Cancellation and Block Rotations, there is a significant mean improvement in performance immediately after dosing. As yet we do not have a satisfactory explanation for this phenomenon. On most but not all of the tests, performance improves after the initial decrement during a 3‐hour period in which blood alcohol levels are maintained by additional hourly doses. This improvement may be due in part to practice effects, as well as to the development of acute behavioral tolerance to ethanol (ABTE). We are still exploring ways in which these effects may be disentangled, using data from concurrent placebo control subjects and from pre‐dosing test sessions. It is already apparent, nevertheless, that most of the variability in sensitivity and ABTE is related to pre‐existing individual variability rather than to gender, age, height, weight, or drinking history. By mailing annual questionnaires to all participants, we hope to be able to test the hypothesis that those who were relatively insensitive to ethanol or who showed a relatively large amount of ABTE during the test sessions may be at increased risk for heavy alcohol consumption.     

Analysis of host response to bacterial infection using error model based gene expression microarray experiments

A key step in the analysis of microarray data is the selection of genes that are differentially expressed. Ideally, such experiments should be properly replicated in order to infer both technical and biological variability, and the data should be subjected to rigorous hypothesis tests to identify the differentially expressed genes. However, in microarray experiments involving the analysis of very large numbers of biological samples, replication is not always practical. Therefore, there is a need for a method to select differentially expressed genes in a rational way from insufficiently replicated data. In this paper, we describe a simple method that uses bootstrapping to generate an error model from a replicated pilot study that can be used to identify differentially expressed genes in subsequent large-scale studies on the same platform, but in which there may be no replicated arrays. The method builds a stratified error model that includes array-to-array variability, feature-to-feature variability and the dependence of error on signal intensity. We apply this model to the characterization of the host response in a model of bacterial infection of human intestinal epithelial cells. We demonstrate the effectiveness of error model based microarray experiments and propose this as a general strategy for a microarray-based screening of large collections of biological samples.     

Influence of replacement rate on the welfare of sows introduced to a large dynamic group

This experiment investigated the effects of replacing 10, 20, 30 or 40% of a dynamic group of forty sows on the welfare of newly-introduced animals. The experiment was replicated five times, using a total of 200 multiparous sows. Replacements took place at 3 week intervals, and 3 days prior to sows being added to the group the same number of animals were removed from the group. Sows were added to the dynamic group as pre-formed groups of four animals which had resided together for a period of 5 weeks beginning directly after their piglets were weaned. Replacement rate did not appear to influence overall levels of aggression to which newly-introduced animals were exposed on the day of mixing, however aggression among newly-introduced animals increased significantly as replacement rate increased between 20 and 40% (P<0.05). Injury levels measured 1 week post mixing did not differ significantly between treatments. Newly-introduced sows in the 10% replacement rate treatment spent more time in slatted areas and less time in kennel areas during the first week post mixing than newly-introduced sows in other treatments (P<0.05). In addition, during the first week post mixing when sows in the 10% replacement rate treatment entered kennel areas they spent less time lying down (P<0.05), and when they did lie down they spent less time lying in contact with other animals and more time lying close to the wall (P<0.05) compared to newly-introduced sows in other treatments. It is suggested that this type of behaviour represents intimidation from resident sows. Newly-introduced sows in the 20, 30 and 40% replacement rate treatments showed similar lying behaviour. In all treatments the newly-introduced sows showed a significant increase in the time spent in kennel areas, and the time spent lying in contact with ‘resident’ sows during the first week post mixing, which suggests that the process of social integration with the resident group had begun. The results of the present study suggest that the welfare of newly-introduced sows in dynamic groups may be compromised when replacement rates of 10% are used. There appears to be no additional welfare benefit associated with increasing replacement rate above 20%.     

The interplay of physical and biological factors in maintaining mid-shore and low-shore assemblages on rocky coasts in the north-west Mediterranean

This study examined the interactive effects of grazing by limpets and inclination of the substratum in maintaining differences between mid-shore and low-shore assemblages of algae in the northwest Mediterranean, at different scales of space and through time. Alternative models leading to different predictions about these effects were proposed and tested. Limpets were excluded by fences from areas of the substratum at mid levels on the shore. The response of algal assemblages to this manipulation was compared with control and enclosure plots at the same level, and with unmanipulated plots in the low shore where limpets are less abundant. The effects of limpets were examined at several replicated sites (0.1–4 km apart) for each slope of the substratum (nearly horizontal vs vertical), at different locations (hundreds of kilometres apart) and at different times. Individual taxa responded differently to limpet exclusion. The percentage cover of the coarsely branched and filamentous algae increased significantly in exclosure plots, in some loser reaching values found on the low shore. These patterns, however, varied greatly from shore to shore and significant effects were found both on horizontal and vertical substrata. Multivariate analyses indicated that grazing by limpets accounted for about 20% of the differences between mid-shore and low-shore assemblages. This effect was independent of substratum inclination and was consistent in space and time, suggesting that physical conditions were not as stressful for macroalgae on vertical substrata as initially supposed. Variable recruitment of algae is proposed as a possible explanation for the lack of consistency in the effects of limpets at the scale of the shore. The results of this study emphasize the need for multiple-scale analyses of the interactive effects of physical and biological factors to understand the organization of natural assemblages. Received: 22 June 1999 / Accepted: 15 November 1999     

Collecting Psycholinguistic Response Time Data Using Amazon Mechanical Turk

Researchers in linguistics and related fields have recently begun exploiting online crowd-sourcing tools, like Amazon Mechanical Turk (AMT), to gather behavioral data. While this method has been successfully validated for various offline measures—grammaticality judgment or other forced-choice tasks—its use for mainstream psycholinguistic research remains limited. This is because psycholinguistic effects are often dependent on relatively small differences in response times, and there remains some doubt as to whether precise timing measurements can be gathered over the web. Here we show that three classic psycholinguistic effects can in fact be replicated using AMT in combination with open-source software for gathering response times client-side. Specifically, we find reliable effects of subject definiteness, filler-gap dependency processing, and agreement attraction in self-paced reading tasks using approximately the same numbers of participants and/or trials as similar laboratory studies. Our results suggest that psycholinguists can and should be taking advantage of AMT and similar online crowd-sourcing marketplaces as a fast, low-resource alternative to traditional laboratory research.     

Studies on the adaptation of influenza virus replicated at low temperature. III. Biochemical studies.

Five strains of influenza viruses A(H3N2) replicated at low temperature passaged in cotton rats were reisolated. The properties of these strains replicated at low temperature were compared before and after passage in susceptible animals to check the stability of some its markers. At the same time original viruses replicated at 37 degrees C--which are different in epidemiological potency--were compared. The following parameters being tested: NA activity, HA titers, heat inactivation NA and Ha, Michaelis constants and optimum pH. We observed some differences between strains both replicated at low temperature after passage in the susceptible animal organism and original viruses from 37 degrees C. Viruses replicated at low temperature from original epidemiostrain are really cold adapted and remained stable after passage in the animals when the others derived from no epidemic strain are not stable.     

Effects of weight, temperature and behaviour on the circadian rhythm of salivary cortisol in growing pigs

In farm animals, salivary cortisol has become a widely used parameter for measuring stress responses. However, only few studies have dealt with basal levels of concentration of cortisol in pigs and its circadian rhythm. The aim of this study was to examine the effects of ambient temperature and thermoregulatory behaviour on the circadian rhythm of salivary cortisol levels in fattening pigs. Subjects were 30 fattening pigs of different weight (60 to 100 kg), kept in six groups in an uninsulated building in pens with partly slatted floors. Saliva samples were taken every 2 h over periods of 24 h at different ambient temperatures at two times in winter and four times in summer. Thermoregulatory behaviour was recorded in the same 24-h time periods. The effect of time of day, body weight, ambient temperature and behaviour on the cortisol level was analysed using a mixed-effects model. Two peaks of cortisol levels per day were found. This circadian pattern became more pronounced with increasing weight and on days where thermoregulatory behaviour was shown. Mean cortisol levels per day were affected by weight but not by thermoregulatory behaviour. From our data, we conclude that long-term variations in cortisol concentration may be influenced by increasing age and weight more than by the respective experimental situation. In assessing animal welfare, it seems more reliable to consider the circadian pattern of cortisol concentration instead of only one value per day.     

THE QUANTIFICATION OF SOME PLANT-TAXA CIRCUMSCRIPTIONS

Intrataxon variability is estimated by the technique of numerical taxonomy. Taxa which had been determined by orthodox taxonomic methods are subjected to analyses by numerical phenetics. Comparisons are made of the amounts of cohesion among the members of different taxa in the Bromeliaceae at several taxonomic levels by computing the degrees of similarities between members of the same taxon and of different taxa. Results of these comparisons with several taxa reveal that the variability of a taxon in terms of phenetic distance computed with a large number of characters does not necessarily agree with a subjective appraisal of variability. The method facilitated difficult taxonomic determinations and provided an estimate of the relative evolutionary ages of different taxonomic groups.     

Are indirect measures of abundance a useful index of population density? The case of red grouse harvesting

Indirect measures of population abundance, such as harvest data, are often used to make inference on long term population dynamics when direct data are either not available or are logistically difficult to obtain. However, when harvesting records are used, a common concern is that they may not reflect actual population abundance. We investigated the extent to which harvest data reflected changes in population density of the red grouse Lagopus lagopus scoticus in Great Britain. We used 92 independently managed populations over the period 1977–2000 and examined the temporal and spatial variability of the hunting records and independently obtained count data from each of these managed estates. Three different analyses support the conclusion that grouse hunting records are a reliable indicator of grouse abundance: 1) the number of red grouse shot in autumn showed a tendency to be linearly related to the density of individuals counted in the summer prior to the harvesting, 2) the relationships between the variance and the mean in the harvesting and corresponding count data, calculated over different populations at the same time, or the same locations at different times, were not statistically distinguishable, 3) similar direct and delayed density dependence patterns were observed in hunting records and count data. Our results suggest that red grouse hunting time series are a good proxy for population abundance.