Negatively correlated firing: the functional meaning of lateral inhibition within cortical columns

Lateral inhibition is a well documented aspect of neural architecture in the main sensory systems. Existing accounts of lateral inhibition focus on its role in sharpening distinctions between inputs that are closely related. However, these accounts fail to explain the functional role of inhibition in cortical columns, such as those in V1, where neurons have similar response properties. In this paper, we outline a model of position tracking using cortical columns of integrate-and-fire and Hodgkin-Huxley-type neurons which respond optimally to a particular location, to show that negatively correlated firing patterns arise from lateral inhibition in cortical columns and that this provides a clear benefit for population coding in terms of stability, accuracy, estimation time and neural resources.     

Effect of steady torque twisting on the orientation of cortical microtubules in the epidermis of the sunflower hypocotyl

Orientation of cortical microtubules (cMTs) is suggested to be affected by mechanical stress existing in cell walls. However, in mutants exhibiting helical (chiral) growth, there is a correlation between orientation of cMTs in outer tissues and helical growth direction. The aim of this research was to examine the effect of a chiral mechanical stimulation on cMTs. For this purpose, the orientation of cMTs was investigated in hypocotyls subjected to either a right- or a left-handed twist, resulting from a steady torque. cMTs were visualised in fixed material using the immunofluorescence method. The cMTs in untouched control hypocotyls were mostly transverse with respect to the cell long axis. In immobilised, but not twisted control hypocotyls, the transverse orientation was also most frequent, while applied twisting resulted in a change in cMT orientation from transverse to oblique. The data provide additional evidence that changes in tissue stress can be reorganized by cortical microtubules.     

The effects of supraoptimal temperatures on population growth and cortical patterning in Tetrahymena pyriformis and Tetrahymena thermophila: a comparison

In this investigation, we compare the multiplication rates and morphogenetic responses of the two most studied Tetrahymena species, T. pyriformis and T. thermophila, at supraoptimal temperatures. Although the upper temperature limits differ greatly in the two species, the pattern of growth responses to high temperature is for the most part similar, with some differences in detail. The transient recovery of cell division at the highest temperature that allows cell division, characteristic of T. pyriformis, is observed in a less distinct form in T. thermophila. Moreover, there is a remarkable difference in developmental response, with drastic abnormalities in patterning of oral structures during the transient recovery of cell division in T. pyriformis, and far more limited abnormalities under similar conditions in T. thermophila. The abnormalities result from spatial disorder in the alignment and orientation of basal body pairs within the early oral primordium, followed by failures in the realignment that normally occurs as oral structures (membranelles and undulating membrane) mature. Both the initial spatial disorder and the failures in realignment are far more severe in T. pyriformis than in T. thermophila.     

DFT/MM modeling of the five-membered ring in 3,6-anhydrogalactose derivatives and its influence on disaccharide adiabatic maps

Different conformations of methyl 3,6-anhydro-4-O-methyl-alpha-d-galactoside (1) and 3,6-anhydro-4-O-methylgalactitol (2) were studied by molecular mechanics (using the program mm3) and by quantum mechanical (QM) methods at the B3LYP/6-31+G( * *) and MP2/6-311++G( * *) levels, with and without solvent emulation. In 2, where the five-membered ring is free to move, two main stable conformations of this ring were found, identified as North (N) and South (S). The latter appears to be more stable, by either calculation, though the energy difference is reduced when emulating solution behavior. In order to find out the possible influence of a glycosidic bond over its shape, and to explain the marked NMR chemical shift displacements observed by opening of the ring, the adiabatic maps of two disaccharides carrying an analog of beta-galactoside linked to O-4 of 1 and 2 were generated. It was shown that the characteristics of the 3,6-AnGal terminal influence the characteristics of the map, especially at lower dielectric constants. On the other hand, different glycosidic angles also promote distinct stable conformations of the five-membered ring, changing from N to S, or even variants. Comparison with experimental results leads to the idea of highly flexible disaccharides, with variable values for both the five-membered ring and the glycosidic angles.     

Population genetics of a transformable bacterium: The influence of horizontal genetic exchange on the biology of Neisseria meningitidis

Abstract Information on the biochemistry and genetics of bacterial species, usually obtained by the study of single isolates, is enhanced by studies of populations of bacteria. Recent advances in molecular technology, particularly polymerase chain reaction-based nucleotide sequence analysis, provide powerful for the study of population genetics. Data obtained by such techniques indicate that, while some bacterial species have a clonal population structure, others are non-clonal or panmictic. Clonal populations are a consequence of asexual reproduction by binary fission; panmictic population structures results from 'horizontal' exchange of genetic material between clones. A consequence of horizontal genetic exchange is mosaic gene structures, recognisable by comparisons of nucleotide sequences. In transformable bacteria, for example the human pathogen Neisseria meningitidis , several different genes, including the gene encoding the class 1 outer membrane protein, a major surface antigen, are mosaics. This genetic process has implications both for vaccine design and in the interpretation of epidemiological data.     

The influence of the frequency of periodic disturbances on the maintenance of phytoplankton diversity

The influence of periodic disturbances of various frequency on the maintenance of the phytoplankton diversity was studied by semicontinuous competition experiments. Disturbances consisted of dilution events, which meant both addition of fresh nutrients and elimination of organisms. The intervals between dilution events varied from 1 to 14 days. Diversity was found to increase with increasing intervals between disturbances. coexisting species belonged to different strategy types: (a) species with rapid growth under enriched conditions, (b) species with good competitive abilities under impoverished conditions, (c) species with the ability to build up storage pools of the limiting nutrient. An increase of the number of coexisting species over the number that would have coexisted in steady state was only found when the interval exceeded one generation time.     

The influence of population,fire and time of dissemination on the germination of Betula pendula seeds

The Betula pendula Roth. seeds used in this study were collected from three different natural populations in the province of Lugo (NW Spain). Three samplings were obtained from each population during the dispersal period of the species. The objective of our research was to assess the germination response of the seeds from each population and sampling when exposed to some of the most important effects of fires: high temperatures, ash and their joint effect.Significant differences have been found in the germination percentages of the seeds from the different populations and also from the three samplings. However, the tested effects of fire: heat, ash and their joint effect did not significantly affect the germination percentage of this species.     

The influence of seed dispersal mechanisms on the genetic structure of tropical tree populations

Seed dispersal mechanisms should have a direct impact on the genetic structure of populations. Species whose seeds are dispersed near the maternal plant (e.g. gravity or wind dispersal) or species whose seeds are deposited in clumps or patches should have more fine-scale genetic structure than species whose seeds are dispersed singly by mobile animals. Furthermore, due to the overlap of seed shadows, species with high adult densities should have less genetic structure than species with lower densities. Allozyme analyses of three tropical tree species belonging to the moist tropical forest of Barro Colorado Island, Republic of Panama, were used to describe variation in the scale and intensity of genetic structure within their populations. The genetic structure of seedlings and immature trees in the low-density, wind-dispersed species (Platypodium elegans) was the coarsest and strongest whereas genetic structure in a population of Swartzia simplex var. ochnacea (high density, bird-dispersed) was both the finest and the weakest. The genetic structure of Alseis blackiana, a high-density, wind-dispersed species was intermediate in both degree and scale. In P. elegans and A. blackiana, which had J shaped size distributions, the significant genetic structure seen in the smaller and intermediate diameter classes disappeared in the largest diameter class. The loss of genetic structure was not observed in S. simplex, a species with a more even size distribution.     

The oac gene encoding a lipopolysaccharide O-antigen acetylase maps adjacent to the integrase-encoding gene on the genome of Shigella flexneri bacteriophage Sf6.

Lysogens of Shigella flexneri harbouring the temperate bacteriophage, Sf6, have been previously shown to undergo a serotype conversion due to O-acetylation of the O-antigen of the lipopolysaccharide. A partial physical map of the phage genome has been constructed. Analysis of the phage DNA suggests that the phage packages by a headful mechanism and that the mature DNA molecules are terminally redundant. Cloning of the PstI fragments of Sf6 enabled the region encoding the serotype conversion to be localized, showing that this was clearly phage-encoded. The gene was further localized by mutagenesis with Tn5 and the nucleotide sequence of the entire 2693-bp PstI fragment was determined. Two major open reading frames (ORFs) were found capable of encoding proteins of 44.1 and 37.2 kDa. The latter corresponds to the O-antigen acetylase and its gene has been designated oac. The oac gene is capable of converting Sh. flexneri serotypes X, Y, 1a and 4a to 3a, 3b, 1b and 4b, respectively. The Oac protein bears a high degree of homology to the NodX protein of Rhizobium leguminosarum suggesting that it, too, may be a sugar acetylase. The second ORF immediately upstream from oac corresponds to the bacteriophage Sf6 integrase responsible for chromosomal integration and is highly homologous to the integrases of Escherichia coli bacteriophages P4 and phi 80, but less closely related to those of P1, P2, P22, 186 and lambda.     

The influence of contact guidance on the orientation of colonies of subcultured vascular smooth muscle cells

Summary Subcultures of smooth muscle cells derived from rat thoracic aorta were grown on plane plastic substrata and on plastic substrata having ridges molded in them by a heated, ruled template. The cells were found to have a very high degree of contact guidance when distributed sparsely on the ridged substrata. When the cell density increased multilayered, elongated colonies formed. On plane substrata these were irregular, curved, and disposed in all directions. On the ridged substrata, however, the colonies were straight, evenly spaced, and positioned at right angles to the ridges. Supported by Grant MT1011 from the Medical Research Council of Canada.     

The influence of the social environment on sexual maturation of female deermice (Peromyscus maniculatus bairdi)

Population Ecology - Female deermice housed from weaning with groups of five females, five males or five males plus five females had significantly smaller uteri at 35–38 days of age compared...     

Growth and decline of a penguin colony and the influence on nesting density and reproductive success

Colonial breeding is characteristic of seabirds but nesting at high density has both advantages and disadvantages and may reduce survival and fecundity. African penguins (Spheniscus demersus) initiated breeding at Robben Island, South Africa in 1983. The breeding population on the island increased in the late 1990s and early 2000s before decreasing rapidly until 2010. Before the number breeding peaked, local nest density in the areas where the colony was initiated plateaued, suggesting that preferred nests sites were mostly occupied, and the area used by breeding birds expanded. However, it did not contract again as the population decreased, so that nesting density varied substantially. Breeding success was related positively to the prey available to the breeding birds and negatively to local nest density, particularly during the chick-rearing period, suggesting a density-dependence operating through social interactions in the colony, possibly exacerbated by poor prey availability when the breeding population was large. Although nest density at Robben Island was not high, nesting burrows, which probably reduce the incidence of aggressive encounters in the colony, are scarce and our results suggest that habitat alteration has modified the strength of density-dependent relationships for African penguins. Gaining a better understanding of how density dependence affects fecundity and population growth rates in colonial breeders is important for informing conservation management of the African penguin and other threatened taxa.     

The influence of time since introduction on the population growth of introduced species and the consequences for management

Several processes likely act to change the demographic rates of introduced species over time, and this changing demography could influence the optimal management of invasive populations. Optimal management strategies should be derived based on the demography. However, we have a poor understanding of the degree to which the demography of introduced species changes following initial introduction. We used published matrix population models of introduced plant populations to test how population growth rate and elasticity change with time since introduction. We did not find a significant relationship between population growth rate and time since introduction. However, elasticity to stasis increased while elasticity to growth decreased with time since introduction. Broadly, as time since introduction progressed the elasticities of the introduced plant populations became more similar to those that have been reported for native species. These results suggest that the optimal management strategy should be derived incorporating elasticity through time, especially when the time scope of management is long or the available demographic data were obtained in the past.     

The influence of matrix components on the morphological differentiation of a proliferating hepatocyte line from liver of newborn mice

The differentiation behaviour of a liver epithelial cell line of the newborn mouse cultured on various matrix components (Thermanox pure, Thermanox coated with ECM, dried collagen type I and type II, wet collagen type I and type III and on floating collagen) was investigated by electron microscopy. Only during the last few days of pregnancy and up to day 9 p.p. could these cells be isolated using a very delicate method. The cells were smaller than differentiated hepatocytes and proliferated spontaneously. They resembled the so-called oval liver cells. On Thermanox pure or Thermanox coated with ECM, dried collagen type I or type II a confluent monolayer developed after about 6 days that consisted of rather flat extended cells which were characterized by short contacts and the absence of any morphological indications of differentiation. On wet collagen the extension area was smaller and the cells were taller. The length of the contact area and the number and size of gap junctions and cell organelles increased. On floating collagen multi-layered aggregates of polygonal cells developed that were characterized by extended cell contacts, bile capillary-like structures and highly developed cell organelles, especially rough endoplasmic reticulum. Since differentiation processes can be demonstrated ultrastructurally only on wet collagen, especially on floating collagen, the chemical composition of the substrate and a specific matrix-cell interaction cannot be the only triggering factor. It is assumed that mechanical properties of the substrate, e.g. plasticity, are involved. The change in the shape of the cell, the prolongation or intensification of the cell contact and the adaptation of the cytoskeleton might play a decisive role in this connection.     

A rapid method for constructing precaution maps based on a simple virtual ecology model: a case study on the range expansion of the invasive aquatic species Limnoperna fortunei

Before invasion, or in its early stages, information on the invader in target areas is generally extremely limited. In such situations, managers must select focal areas in which to concentrate control and mitigation efforts. Here, we discuss a rapid method for selecting areas in which to control invasive aquatic species based on limited information. We used a simple cellular automata model that does not require species-specific information, but simulates the process of invasive species expansion and includes observed expansion progress to detect keystone areas. As a case study, we simulated the expansion of an invasive aquatic mussel, Limnoperna fortunei, in Ibaraki Prefecture, Japan, and detected the areas in which control efforts should be concentrated. To some extent, our model was able to predict the expansion of L. fortunei from the initial detected invasion to the current distribution. We predicted areas with a high potential of spreading and areas that would suffer from high propagule pressure. Results revealed a mismatch between areas with high spread potential and those with high propagule pressure. Managers should concentrate their invasion prevention efforts in the former because these are likely to have a greater long-term influence. Additionally, we predicted future expansion from the current distribution and showed that current scattered populations could merge naturally. Our approach is useful for establishing a management plan before or in the early stages of invasion.     

生态条件的多样性变化对蜜蜂生存的影响

蜜蜂在整个生态系统中起着重要的传花授粉作用,是生态链中不可或缺的物种。随着现代农业的发展,蜜蜂赖以生存的环境遭到破坏,继而引发蜜蜂数量大幅减少,影响了蜂种的生存与可持续发展。总结了近年来生态条件的变化,归纳了影响蜜蜂生存的主要因素,分析了蜜蜂生存艰难的原因,提出了蜜蜂生存的关键问题,并展望了未来维持蜜蜂强群的主要研究方向。     

Global phylogeography of the dolphinfish (Coryphaena hippurus): the influence of large effective population size and recent dispersal on the divergence of a marine pelagic cosmopolitan species

Pelagic fish that are distributed circumtropically are characterised by a low population structure level as a result of a high capacity for dispersion and large population sizes. Nevertheless, historical and contemporary processes, including past demographic and/or range expansions, secondary contact, dispersal, gene flow, and the achievement of large effective population sizes, may play a part in the detection of divergence signals, especially in the case of tropical pelagic species, whose distribution range depends strongly on the sea surface temperature. The connectivity and historical demography of Atlantic, Indian, Pacific and Mediterranean populations of dolphinfish (Coryphaena hippurus) was studied using partial sequences of the mitochondrial DNA NADH dehydrogenase subunit 1 (ND1). AMOVA analyses revealed significant inter-oceanic divergence with three phylogroups located in the Indo-Pacific, Eastern Atlantic, and Mediterranean Sea, the last one being the most divergent. However, it was not possible to clearly observe any genetic differentiation between the Indo-Pacific and Atlantic populations, as has been reported for most tropical pelagic species of tuna and billfishes. This supports the assumption of recent dispersal among basins facilitated by the actual continuous distribution of dolphinfish populations. Moreover, the lack of a divergence signal for populations separated by the Panamanian Isthmus reveals that genetic drift does not exert a strong influence on tropical pelagic species with large effective population sizes.     

The influence of landscape and environmental factors on ranavirus epidemiology in a California amphibian assemblage

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