Computation of spiking activity for a stochastic spatial neuron model: effects of spatial distribution of input on bimodality and CV of the ISI distribution

We obtain computational results for a new extended spatial neuron model in which the neuronal electrical depolarization from resting level satisfies a cable partial differential equation and the synaptic input current is also a function of space and time, obeying a first order linear partial differential equation driven by a two-parameter random process. The model is first described explicitly with the inclusion of all biophysical parameters. Simplified equations are obtained with dimensionless space and time variables. A standard parameter set is described, based mainly on values appropriate for cortical pyramidal cells. When the noise is small and the mean voltage crosses threshold, a formula is derived for the expected time to spike. A simulation algorithm, involving one-dimensional random processes is given and used to obtain moments and distributions of the interspike interval (ISI). The parameters used are those for a near balanced state and there is great sensitivity of the firing rate around the balance point. This sensitivity may be related to genetically induced pathological brain properties (Rett's syndrome). The simulation procedure is employed to find the ISI distribution for some simple patterns of synaptic input with various relative strengths for excitation and inhibition. With excitation only, the ISI distribution is unimodal of exponential type and with a large coefficient of variation. As inhibition near the soma grows, two striking effects emerge. The ISI distribution shifts first to bimodal and then to unimodal with an approximately Gaussian shape with a concentration at large intervals. At the same time the coefficient of variation of the ISI drops dramatically to less than 1/5 of its value without inhibition.     

An experimental test of the prolonged brood care model in the tufted titmouse (Baeolophus bicolor)

The prolonged brood care model rests on the assumption thatretaining an offspring through the winter months in the faceof a limited food supply should have a cost for parents. Wetested this idea with a New World permanent-resident bird,the tufted titmouse (Baeolophus bicolor). Using DNA fingerprinting,we assessed the degree of relatedness between adult and juvenilebirds in 17 winter groups, finding that in 8 of the groups noyoung bird was the offspring of the territorial pair. We comparedthe nutritional condition of territorial adult birds in smallforest fragments from which their own offspring and other younghad been removed with the nutritional condition of controlbirds from unmanipulated fragments. Contrary to the model'sassumption, the nutritional condition of adults in treatmentgroups (young removed) appeared to be worse, not better, thanin groups where a related juvenile was present. These resultssuggest that the prolonged brood care model may not be universalin its application and that under some ecological conditions,retaining offspring through the winter can result in a netbenefit for territorial adults despite the necessity of sharingresources.     

RATP: a model for simulating the spatial distribution of radiation absorption, transpiration and photosynthesis within canopies: application to an isolated tree crown

The model RATP (radiation absorption, transpiration and photosynthesis) is presented. The model was designed to simulate the spatial distribution of radiation and leaf-gas exchanges within vegetation canopies as a function of canopy structure, canopy microclimate within the canopy and physical and physiological leaf properties. The model uses a three-dimensional (3D) representation of the canopy (i.e. an array of 3D cells, each characterized by a leaf area density). Radiation transfer is computed by a turbid medium analogy, transpiration by the leaf energy budget approach, and photosynthesis by the Farquhar model, each applied for sunlit and shaded leaves at the individual 3D cell-scale. The model typically operates at a 20–30 min time step. The RATP model was applied to an isolated, 20-year-old walnut tree grown in the field. The spatial distribution of wind speed, stomatal response to environmental variables, and light acclimation of leaf photosynthetic properties were taken into account. Model outputs were compared with data acquired in the field. The model was shown to simulate satisfactorily the intracrown distribution of radiation regime, transpiration and photosynthetic rates, at shoot or branch scales.     

Evaluating drought effect on MODIS Gross Primary Production (GPP) with an eco-hydrological model in the mountainous forest, East Asia

Surface soil moisture dynamics is a key link between climate fluctuation and vegetation dynamics in space and time. In East Asia, precipitation is concentrated in the short monsoon season, which reduces plants water availability in the dry season. Furthermore, most forests are located in mountainous areas because of high demand for agricultural land, which results in increased lateral water flux and uneven distribution of plant available water. These climatic and topographic features of the forests make them more vulnerable to drought conditions. In this study, the eco‐hydrological model (Regional Hydro‐Ecological Simulation System) is validated with various water and carbon flux measurements in a small catchment in Korea. The model is then extended to the regional scale with fine‐resolution remote sensing data to evaluate the Moderate Resolution Imaging Radiometer (MODIS) leaf area index and gross primary productivity (GPP) products. Long‐term model runs simulated severe drought effect in 2001 well, which is clearly shown in the ring increment data. However, MODIS GPP does not capture this drought effect in 2001, which might be from a simplified treatment of water stress in the MODIS GPP algorithm. This study shows that the MODIS GPP products can potentially overestimate carbon uptake specifically during drought conditions driven by soil water stress.     

Short Communication Seasonal distribution of Rhipicephalus sanguineus ticks (Acari: Ixodidae) on dogs in an urban area of Morelos, Mexico

Between 1993 and 1995, we examined 1742 dogs at two veterinary clinics in Cuernavaca City in Mexico for the presence of Rhipicephalus sanguineus ticks. The overall tick infestation prevalence was 20% and there were no significant differences (p > 0.05) between different years. The prevalence was somewhat higher in spring, summer and autumn (20% or more) than in winter (13.7%). A positive correlation (p < 0.01) was found between prevalence of ticks and rainfall in spring, summer and autumn, whereas in winter there was only a correlation with temperature. Different stages of the tick were found and it was calculated that 2.5 generations could be completed each year. It is concluded that the enviromental conditions of Cuernavaca City favour development and maintenance of R. sanguineus ticks throughout the year and that its role as a vector of diseases poses a threat to dogs and may have potential zoonotic risks. © Rapid Science Ltd. 1998     

Feeding by the aquatic heteropteran,Diplonychus rusticum (Belostomatidae): an effect of prey density on meal size

The behaviour of Diplonychus rusticum feeding on chironomid larvae has been investigated under laboratory conditions. Changes in the percentage of material extracted from prey indicated that feeding for the first two minutes enabled the predator to obtain approximately 33% of the available food; feeding for 10 minutes resulted in only 60% extraction. Comparing the percentage of each prey consumed by D. rusticum exposed to various prey densities, it was apparent that predators were more wasteful and ate less of each prey as chironomid density increased. Because the rate of food intake declined as a greater proportion of each prey was extracted, predators exposed to high chironomid densities reduced the amount of each prey consumed thereby conforming to a simple optimal feeding model.     

不同土壤类型蔗区甘蔗三高施肥优化研究

采用二次正交旋转组合设计 ,在砖红壤旱地蔗区和冲积土水田蔗区进行施肥优化试验 ,通过建立数学模型、模拟和寻优 ,初步建立了各类蔗区的优化施肥方案 .根据模型回归系数、单项性状指标的施肥方案和综合性状指标的优化施肥方案 ,对肥料三要素及其施用水平对蔗茎产量、蔗茎蔗糖分和净产值的影响进行了比较分析 .     

Histo-cytological study of the liver of the cabrilla sea bass, Serranus cabrilla (Teleostei, Serranidae), an available model for marine fish experimental studies

Livers of juvenile cabrilla sea basses ( Serranus cabrilla ) were subjected to light and electron transmission microscopy following different periods of maintenance in an aquarium. Since this fish is easy to feed in captivity and the hepatic structure was found to be comparable at the four periods tested (0, 5, 10 and 20 days), both at the histological and ultrastructural level, the liver of S. cabrilla could be an available model for marine contamination experimental studies. As in other fish species, it is not possible to distinguish the portal lobules and the triads. The Melano-Macrophage Centres contain tipofuscins, ceroids and haemosiderin, but they do not contain any melanin. The hepatocytes are arranged in cords (two cells thick), and, at the ultrastructural level, they show numerous microvilli in the perisinusoidal and canalicular areas. The hyaloplasm includes a considerable amount of glycogen and some lipid droplets are occasionally observed. Mitochondria, rough endoplasmic reticulum and the Golgi apparatus are relatively scarce.     

A temperature-dependent developmental model for a nucleopolyhedrosis virus of the velvetbean caterpillar,Anticarsia gemmatalis (Lepidoptera: Noctuidae)

Developmental times and rates of nucleopolyhedrosis virus infection in third-instar velvetbean caterpillar, Anticarsia gemmatalis, larvae were studied in the laboratory at a variety of constant and variable temperatures. Developmental time was considered to be time from inoculation until death. Viral infection exhibited a temperature optimum of ca. 30°C and was inhibited at 10 and 40°C. Mean developmental time of the virus ranged from 18.1 days (15°C) to 5.5 days (30°C). Means and standard deviations of viral developmental rates (= development time^?1) were used as inputs into a previously derived absolute reaction rate model designed to generate a set of kinetic constants usable in predicting developmental times. Actual distributions of viral cohort developmental times were compared to distributions generated by the model. Reasonable agreement between predicted and actual distributions was found at three of four temperatures tested.     

Effect of photoperiod and host distribution on the horizontal transmission of Isaria fumosorosea (Hypocreales: Cordycipitaceae) in greenhouse whitefly assessed using a novel model bioassay

A model bioassay was used to evaluate the epizootic potential and determine the horizontal transmission efficiency of Isaria fumosorosea Trinidadian strains against Trialeurodes vaporariorum pharate adults under optimum conditions (25±0.5°C, ~100% RH) at two different photoperiods. Untreated pharate adults were arranged on laminated graph paper at different distributions to simulate varying infestation levels on a leaf surface. Four potential hosts were located 7, 14 and 21 mm away from a central sporulating cadaver simulating high, medium and low infestation levels, respectively. Percent hosts colonized were recorded 7, 12, 14 and 21 days post-treatment during a 16- and 24-h photophase. After 21 days, mean percent hosts colonized at the highest, middle and lowest infestation levels were 93 and 100%, 22 and 58%, 25 and 39% under a 16- and 24-h photophase, respectively. From the results, it was concluded that the longer the photophase, the greater the percentage of hosts colonized, and as host distance increased from the central sporulating cadaver, colonization decreased. The use of this novel model bioassay technique is the first attempt to evaluate the epizootic potential and determine the horizontal transmission efficiency of I. fumosorosea Trinidadian strains under optimal environmental conditions at different photoperiods. This bioassay can be used to assess horizontal transmission efficiency for the selection of fungi being considered for commercial biopesticide development.     

Long-term effect of a simple nest-box on the reproductive efficiency and other life traits of an Aotus lemurinus lemurinus monkey colony: an animal model for malaria research

Background The long‐term effect of a PVC pipe nest‐box on the reproductive efficiency and other life traits of an Aotus monkey‐breeding colony have not been characterized. Methods and Results We analyzed laboratory records of the Gorgas Memorial Institute (GMI) Aotus monkey colony in Panama for the period 1999–2010 and found a 273% increase in the annual mean life births in the following 7 years after the introduction of a PVC pipe nest‐box in 2002, as well as increases in the mean body mass and survival of laboratory‐bred monkeys. Other life traits such as inter‐birth interval, parity, birth sex distribution, mortality, and longevity were also determined. Conclusions The use of a PVC pipe nest‐box significantly improved the reproductive efficiency and other life traits of the GMI Aotus breeding colony.     

Analysis of the vertical distribution of epiphytic lichens on Pinus nigra (Mount Olympos,Greece) along an altitudinal gradient

Epiphytic lichen vegetation was studied in 10 sites along an altitude gradient from 750 to 1510 m on NW-facing slopes of Mount Olympos, Greece to assess the main spatial heterogeneity of microhabitats affecting communities and species composition. Community structure along the gradient was studied by using multivariate techniques. The critical factor for spatial heterogeneity seems to be the height at which the lichen community develops on the tree trunks. Changes in the community structure of the epiphytic lichen vegetation were also detected along the altitudinal gradient and the altitude of 1200 m is considered to be an ecotone. A comparative study of epiphytic lichen communities on Mt. Olympos and in the Thessaloniki area revealed species indicators of air pollution.     

Description of the larva, diagnosis of the nymph and female based on scanning electron microscopy, hosts, and distribution of Ixodes (Ixodes) venezuelensis

Abstract. The larva, nymph, and female of Ixodes (Ixodes) venezuelensis are diagnosed using scanning electron microscopy, and the larva is described for the first time. This ixodid tick is recorded from the northern neotropics as a parasite of five species of didelphid marsupials and eighteen species of rodents (one sciurid, two heteromyids, eleven murids, two dasyproctids, and two echimyids). Collection records of I. venezuelensis are presented for Costa Rica, Colombia, Panama and Venezuela, with the Costa Rican records being new and extending the known range of this tick by at least 300 km. Altitudinally, I. venezuelensis has been collected between elevations of 24 and 2410 m with most collections between 100 and 800m. The possibility that I. venezuelensis may be partheno-genetic is discussed.     

Effect of agronomic factors on the spatial distribution of greyback canegrub, Dermolepida albohirtum (Waterhouse) (Coleoptera: Scarabaeidae), in sugarcane in the Burdekin River Irrigation Area

Abstract A series of studies were undertaken examining the factors that impact on the spatial distribution of greyback canegrub infestations in sugarcane in the Burdekin region of Queensland. Historic records of damage by greyback canegrub showed that sugarcane blocks planted or harvested earlier than surrounding blocks were more likely to be damaged than blocks planted or harvested later. The derived hypothesis that sugarcane height may be the primary determinant of where damage occurs was confirmed in field studies. The tallest sugarcane blocks at the time of oviposition consistently had the highest grub populations. There was no difference in the distribution of damage between the cultivars Q96 and Q117 and the age of these crops also had no impact. The finding that sugarcane height is the primary determinant of where damage occurs on Burdekin farms opens the possibility of using it as a tool to manipulate where canegrubs oviposit and the development of a range of associated cultural control strategies.     

Factors controlling the distribution of Marenzelleria cf. viridis, Pygospio elegans and Streblospio shrubsoli (Polychaeta: Spionidae) in the southern Baltic Sea, with special attention for the response to an event of hypoxia

The large-scale distribution patterns of the estuarine spionid polychaetes Marenzelleria cf. viridis, Pygospio elegans, and Streblospio shrubsoli were studied in the Pomeranian Bay (southern Baltic Sea) at 20 stations in April 1993 and their relationship with hydrographic factors and sediment composition investigated. The densities of M. cf. viridis and S. shrubsoli decreased rapidly with increasing distance offshore. A corresponding decrease in phytoplankton concentration offshore is suggested as the main cause for the observed spatial patterns. P. elegans was more evenly distributed. At 10 selected stations further samples were collected between April 1993 and July 1996 to study the response of abundance and biomass of the three polychaetes to changes in environmental conditions and to investigate interspecific interactions within the macrofauna. Salinity, pelagic food supply, and sediment parameters did not change. At three of these stations redox potential of the sediment and macrofauna composition were affected by an unusual hypoxic/anoxic event in July/August 1994. All three spionid species were able to survive moderate seasonal hypoxic conditions, but died after exposure to severe anoxia. Special attention was focused on the re-establishment of the spionids. The rate with which M. cf. viridis and P. elegans re-colonised defaunated stations varied between a few weeks and two years. These differences in rate of re-establishment were attributed to the distance from undisturbed recruitment areas, and to the severity of the oxygen deficiency. Increasing densities of P. elegans and S. shrubsoli after the hypoxic event coincided with a reduced abundance of the bivalve Mya arenaria, suggesting a negative interspecific interaction.     

Testosterone effects on the immune system and parasite infestations in the barn swallow (Hirundo rustica): an experimental test of the immunocompetence hypothesis

The immunocompetence hypothesis predicts that testosterone (T)enhances the expression of male secondary sexual characterswhile exerting a suppressive effect on the immune system therebyexposing hosts to higher intensities of parasite infestations.In a natural population of barn swallow (Hirundo rustica) males,the intensity of infestation by some ectoparasites was negativelycorrelated with tail length and was positively correlated withimmunoglobulin levels, but no clear relationship was observedbetween immune responses (leukocyte counts, immunoglobulins)and tail length. Males implanted with T had higher intensitiesof parasite infestations at the time of recapture than controlmales, and T-implanted males experienced an increase in countsof eosinophils. In T-implanted males, immunoglobulin levelsinitially decreased and then increased as time from implantationelapsed. Among T-implanted males, those with longer tails hada smaller increase in eosinophil counts, tended to experiencea smaller increase of parasite infestations, and were more likelyto survive until the following breeding season than those withshorter tails. The relationships between parasite burden, immunesystem, and exaggeration of tail length in the natural populationof males are consistent with some aspects of the immunocompetencehandicap hypothesis. The results from the manipulation of Tplasma levels are also partly consistent with the hypothesis,since T-implantation resulted in higher levels of parasite infestations,but contradict the assumption of an obligatory immunosuppressiveeffect of T. Higher activation of the immune system of T-implantedmales indicate that high T plasma levels imposed a two-foldcost because of the effects on parasites and the immune responseto parasites, and this suggests that the effect of T on parasitesmight not be mediated by the immune system of the host. Theresults of the manipulation of T plasma levels support the handicapversion of the immunocompetence hypothesis since high quality,long-tailed males paid less in terms of activation of the immunesystem, change in parasite infestations, and chances of survivalthan low-quality, short-tailed males.     

The effects of control on the biomass, carbohydrate content and bud reserves of bracken (Pteridium aquilinum (L.) Kuhn), and an evaluation of a bracken growth model

This paper examines the initial effects of bracken control on frond numbers and biomass, and the biomass, carbohydrate reserves and bud densities of bracken stands cut once per year, twice per year, subject to a single application of asulam or left untreated. The seasonal dynamics of these parameters are displayed; carbohydrate and biomass are both removed from the rhizome system to produce frond tissue, and are replenished at the end of the growing season. Asulam application reduced densities of both active and dormant buds, and both frond biomass and density. It did not significantly reduce rhizome biomass or carbohydrate reserves in the two years after treatment. Cutting, either once or twice per year reduced both rhizome biomass and rhizome carbohydrate reserves, as well as bud densities, though the latter were reduced in proportion to biomass. Cutting twice a year reduced the production of fronds, both in numbers and biomass. The collected data were used to evaluate a model of bracken growth, and subsequently to improve estimates of some of the model parameters. The model simulations of control treatments were compared to field data. The effects of cutting once per year and spraying with asulam were predicted accurately, but the bracken stand was more resilient to cutting twice per year than would be expected from model predictions. The combination of cutting and spraying is discussed as a potential tool in land management and the deficiencies of the model are discussed in relation to the need for future research into the biology of bracken.