Small-scale variability in growth and condition of dab Limanda limanda (L.) larvae in relation to an Irish Sea tidal-mixing front off the west coast of the Isle of Man

The small-scale variability in condition and growth of dab Limanda limanda larvae was investigated in relation to a tidal-mixing front (Manx West Coast front) off the west coast of the Isle of Man, Irish Sea. RNA:DNA ratios and otolith microincrement analysis were used to estimate nutritional status and recent growth rates of larvae captured on 5 May 1999 in mixed, frontal and stratified waters associated with this front. RNA:DNA ratios were significantly higher at the Manx West Coast front compared to mixed waters, although recent growth rates did not vary significantly with water column stability. More favourable feeding conditions associated with frontal waters from previously reported large-scale investigations in the Irish Sea were reflected on a smaller spatial scale. Although frontal accumulation of dab larvae was not observed in the current study, dab larvae found in the stratified and frontal waters were significantly larger than those captured in the mixed waters. This pattern could suggest an offshore movement of dab larvae into more favourable waters as they develop.     

Dynamic aspects of the structured cell population in a swarming colony of Proteus mirabilis

Proteus mirabilis forms a concentric-ring colony by undergoing periodic swarming. A colony in the process of such synchronized expansion was examined for its internal population structure. In alternating phases, i.e., swarming (active migration) and consolidation (growth without colony perimeter expansion), phase-specific distribution of cells differing in length, in situ mobility, and migration ability on an agar medium were recognized. In the consolidation phase, the distribution of mobile cells was restricted to the inner part of a new ring and a previous terrace. Cells composing the outer part of the ring were immobile in spite of their ordinary swimming ability in a viscous solution. A sectorial cell population having such an internal structure was replica printed on fresh agar medium. After printing, a transplant which was in the swarming phase continued its ongoing swarming while a transplanted consolidation front continued its scheduled consolidation. This shows that cessation of migration during the consolidation phase was not due to substances present in the underlying agar medium. The ongoing swarming schedule was modifiable by separative cutting of the swarming front or disruption of the ring pattern by random mixing of the pattern-forming cell population. The structured cell population seemed to play a role in characteristic colony growth. However, separation of a narrow consolidation front from a backward area did not induce disturbance in the ongoing swarming schedule. Thus, cells at the frontal part of consolidation area were independent of the internal cell population and destined to exert consolidation and swarming with the ongoing ordinary schedule.     

Localised depletion of polymerised actin at the front of Walker carcinosarcoma cells increases the speed of locomotion

Spontaneously migrating Walker carcinosarcoma cells usually form lamellipodia at the front. Combined treatment with 10(-5)M colchicine and 10(-7)M latrunculin A produces large defects in the cortical F-actin layer at the leading front and suppresses lamellipodia. However, the cortical actin layer at the rear is intact and shows myosin IIA accumulation. These cells, showing no or little detectable cortical F-actin at the front and no morphologically recognisable protrusions, migrate faster than control cells with lamellipodia and an intact cortical actin layer. This documents that the cortical actin layer or actin-powered force generation at the front is redundant for locomotion. Colchicine and latrunculin A have synergistic effects in compromising the cortical layer at the front and in increasing the speed of locomotion, but antagonistic effects on the relative amount of F-actin per cell. Colchicine but not latrunculin A, can increase the proportion of polarised and locomoting cells under appropriate conditions. Locomotion and polarity of cells treated with latrunculin A and colchicine is inhibited at latrunculin A concentrations >10(-7)M, by the myosin inhibitor BDM or the ROCK inhibitor Y-27632. Colchicine and Y-27632 have antagonistic effects on polarity and the speed of locomoting cells. The data show that locomotion of metazoan cells, which normally form lamellipodia, can be driven by actomyosin contraction behind the front (cell body, uropod). They are best compatible with a cortical contraction/frontal expansion model, but they are not compatible with models implying that actin polymerisation or actomyosin contraction at the front drive locomotion of the cells studied.     

卡车与卡车前部碰撞驾驶员与前排乘车人损伤特征的研究

目的：研究道路交通事故卡车与卡车前部碰撞驾乘人员损伤特征,分析比较驾乘人员的损伤及损伤分布特点。方法：应用统计学方法对2001年-2010年昆明地区卡车与卡车200例前部碰撞人员损伤的法医学鉴定资料进行系统分析性研究。结果：1.驾驶员易发生损伤的部位是下肢、头颈部,其次为胸、腹部损伤。驾驶员易发生右下肢的损伤及骨折。驾驶员易发生颅骨骨折和肋骨骨折。2.前排乘车人员易发生损伤的部位是上肢、头颈部,其次为下肢,而胸腹部损伤较少见。前排乘车人员易发生上肢的损伤及双侧尺桡骨的骨折。前排乘车人员左侧头颈部受伤的几率大于驾驶员的相对部位。前排乘车人员易发生右肱骨骨折。结论：1.与前排乘车人相比,驾驶员易造成胸部、腹部及盆部、右侧下肢的损伤及右股骨胫腓骨的骨折,发生双侧上肢的体表损伤及尺桡骨骨折均明显少。在身体体表出现胸部、腹部及盆部多部位连续的损伤,有助于提高认定卡车驾驶员的准确性。2.与驾驶员相比,前排乘车人易形成左侧头颈部的损伤,上肢双侧尺桡骨骨折,右侧肱骨的骨折。当损伤位于身体左侧头颈部且有右侧肱骨的骨折,有助于提高认定卡车前排乘车人的准确性。     

Testing motor functions of the frontal zonein the locomotion of Amoeba proteus

The hypothesis which attributes the motive power to the frontal zone has been tested by cinematographic analysis of the movements of amoeba, in which the front was either blocked by negative stimuli or destroyed. Partial inhibition and consecutive reorganization of the frontal activity by a beam of light had minor effect on the retraction of other body parts. Micrurgical destruction of the whole frontal zone had no effect on the functions of more posteriorly situated cell regions, which continue to contract and squeeze the endoplasm out into the external medium.     

Possible mechanisms of delay in the voluntary movement initiation

A delay in the movement initiation was shown to entail an augmentation of the N2 wave ascending front and a delay in the ERPs P3 wave in frontal leads in healthy subjects and in parkinsonian patients. The modulation of the N2 wave seems to reflect inhibitory processes in frontal areas of the brain.     

Spatial Assortment of Mixed Propagules Explains the Acceleration of Range Expansion

Range expansion of spreading organisms has been found to follow three types: (i) linear expansion with a constant rate of spread; (ii) bi-phase expansion with a faster linear expansion following a slower linear expansion; and (iii) accelerating expansion with a continuously increasing rate of spread. To date, no overarching formula exists that can be applied to all three types of range expansion. We investigated how propagule pressure, i.e., the initial number of individuals and their composition in terms of dispersal ability, affects the spread of a population. A system of integrodifference equations was then used to model the spatiotemporal dynamics of the population. We studied the dynamics of dispersal ability as well as the instantaneous and asymptotic rate of spread. We found that individuals with different dispersal abilities were spatially sorted with the stronger dispersers situated at the expanding range front, causing the velocity of expansion to accelerate. The instantaneous rate of spread was found to be fully determined by the growth and dispersal abilities of the population at the advancing edge of the invasion. We derived a formula for the asymptotic rate of spread under different scenarios of propagule pressure. The results suggest that data collected from the core of the invasion may underestimate the spreading rate of the population. Aside from better managing of invasive species, the derived formula could conceivably also be applied to conservation management of relocated, endangered or extra-limital species.     

Changes of intraocular pressure in patients with open-angle glaucoma in relation to the passage of atmospheric fronts and environmental contamination

Effects of atmospheric frontal passages on intraocular pressure (IOP) in patients with open-angle glaucoma are statistically investigated to show the meteorotropism of this disease. Changes in IOP caused by frontal passages are evident; the response is not identical in all the patients near the day of the passage of a warm front, while on the third day following the passage of the front a well pronounced drop in IOP occurs. Anomalous increases of IOP over several months' duration occurred in the years 1986–7. This finding is explained in relation to the hypothesis of environmental contamination in Central Europe by radioactive cesium nuclides due to the Chernobyl accident.     

Ageostrophic Frontal Processes Controlling Phytoplankton Production in the Catalano-Balearic Sea (Western Mediterranean)

Buoyancy-induced unstable boundary currents and the accompanying retrograde density fronts are often the sites of pronounced mesoscale activity, ageostrophic frontal processes, and associated high biological production in marginal seas. Biophysical model simulations of the Catalano-Balearic Sea (Western Mediterranean) illustrated that the unstable and nonlinear southward frontal boundary current along the Spanish coast resulted in a strain-driven frontogenesis mechanism. High upwelling velocities of up to 80 m d^-1 injected nutrients into the photic layer and promoted enhanced production on the less dense, onshore side of the front characterized by negative relative vorticity. Additional down-front wind stress and heat flux (cooling) intensified boundary current instabilities and thus ageostrophic cross-frontal circulation and augmented production. Specifically, entrainment of nutrients by relatively strong buoyancy-induced vertical mixing gave rise to a more widespread phytoplankton biomass distribution within the onshore side of the front. Mesoscale cyclonic eddies contributed to production through an eddy pumping mechanism, but it was less effective and more limited regionally than the frontal processes. The model was configured for the Catalano-Balearic Sea, but the mechanisms and model findings apply to other marginal seas with similar unstable frontal boundary current systems.     

On the accumulation of deleterious mutations during range expansions

We investigate the effect of spatial range expansions on the evolution of fitness when beneficial and deleterious mutations cosegregate. We perform individual‐based simulations of 1D and 2D range expansions and complement them with analytical approximations for the evolution of mean fitness at the edge of the expansion. We find that deleterious mutations accumulate steadily on the wave front during range expansions, thus creating an expansion load. Reduced fitness due to the expansion load is not restricted to the wave front, but occurs over a large proportion of newly colonized habitats. The expansion load can persist and represent a major fraction of the total mutation load for thousands of generations after the expansion. The phenomenon of expansion load may explain growing evidence that populations that have recently expanded, including humans, show an excess of deleterious mutations. To test the predictions of our model, we analyse functional genetic diversity in humans and find patterns that are consistent with our model.     

Microplankton respiration (ETS) in two areas of the Northern Adriatic (Mediterranean Sea)

Respiratory rates in two areas of the North Adriatic Sea were studied in the context of a PRISMA II Project, with the aim of quantifying the oxidative processes occurring in the frontal system caused by strong riverine discharge. In the northern area, higher respiratory rates and seasonal variations occurred with respect to the southern area. On average, respiratory activity sustained the oxidation of 66.9 nM C h(-1) inside the front and 24.4 nM C h(-1) outside the front. In conclusion, organic matter oxidation inside the front resulted 2.7 times higher than outside the front. Oxidative metabolism in the Northern Adriatic Sea appears mainly governed by river inputs.     

What factors shape female phenotypes of a poleward‐moving damselfly at the edge of its range?

Individuals at the expansion front during a climate‐driven range expansion are expected to differ phenotypically from those individuals in core populations. Little information is known about the joint, potentially opposing, effects of stressful conditions at the range edge versus evolutionary changes that take place during range expansion in shaping the phenotypes at the range front. We investigated the effect of range expansion on immune function, body condition and flight‐related morphology (flight muscle ratio, wing loading, and wing aspect ratio) of field‐collected females of the poleward‐moving damselfly Coenagrion scitulum. Individuals at the expansion front had a lower body condition, which indicated more stressful conditions at the range edge. Despite the counteracting effect of the shorter growth season, the higher flight muscle ratios at the expansion front indicated a strong selection for dispersal ability during range expansion. The current study suggests that models need to incorporate the interplay of stressful conditions and evolutionary processes at the expansion front to arrive at robust predictions of future species distributions under global warming. © 2014 The Linnean Society of London, Biological Journal of the Linnean Society, 2014, 112 , 556–568.     

Invasive species can't cover their tracks: using microsatellites to assist management of starling (Sturnus vulgaris) populations in Western Australia

Invasive species are known to cause environmental and economic damage, requiring management by control agencies worldwide. These species often become well established in new environments long before their detection, resulting in a lack of knowledge regarding their history and dynamics. When new invasions are discovered, information regarding the source and pathway of the invasion, and the degree of connectivity with other populations can greatly benefit management strategies. Here we use invasive common starling ( Sturnus vulgaris ) populations from Australia to demonstrate that genetic techniques can provide this information to aid management, even when applied to highly vagile species over continental scales. Analysis of data from 11 microsatellites in 662 individuals sampled at 17 localities across their introduced range in Australia revealed four populations. One population consisted of all sampling sites from the expansion front in Western Australia, where control efforts are focused. Despite evidence of genetic exchange over both contemporary and historical timescales, gene flow is low between this population and all three more easterly populations. This suggests that localized control of starlings on the expansion front may be an achievable goal and the long-standing practice of targeting select proximal eastern source populations may be ineffective on its own. However, even with low levels of gene flow, successful control of starlings on the expansion front will require vigilance, and genetic monitoring of this population can provide essential information to managers. The techniques used here are broadly applicable to invasive populations worldwide.     

Dynamism in the upstream invasion edge of a freshwater fish exposes range boundary constraints

Studying the dynamics of species’ borders can provide insight into the mechanisms limiting or promoting range expansion in response to environmental change. In the John Day River, Oregon (USA), rising stream temperatures are facilitating the upstream expansion of invasive smallmouth bass Micropterus dolomieu. Here, where smallmouth bass occupy the upstream limit of its thermal tolerance, we explore population structure and seasonal movement patterns to elucidate the environmental conditions and individual traits that define front edge (where individuals reside year-round) and leading edge (where individuals colonize, but may not establish) limits to its upstream distribution. Reporting on a multi-year, spatially extensive riverscape survey, our results show dramatic ebbs and flows of seasonal occupancies due to individual movement with an overall trend of upstream expansion. We revealed distinct front and leading edge invasion extents, each constrained by different ecological conditions. The front edge is largely constrained by the ability for juveniles to survive an overwinter starvation period, whereas the leading edge is associated with adult growth potential and seasonal hydrological conditions. We also found key morphological traits associated with more mobile individuals. By providing mechanistic insight into the factors that promote or limit range expansion of an invasive riverine species, our study enhances the ability to predict future range shifts and provides critical information to managers tasked with restricting further expansion.     

Genetic signature of the colonisation dynamics along a coastal expansion front in the damselfly Coenagrion scitulum

1. Many insects are expanding their distribution range polewards as a result of climate change, which has been shown to be associated with founder effects leading to a reduction in genetic diversity and an increase in genetic differentiation. These spatial genetic patterns may arise from colonisation from a broad expansion front or a limited neighbourhood after a stepping stone model of dispersal. The temporal persistence of such founder effects are poorly understood, mainly because studies looking at the fine‐scale initial temporal dynamics of the genetic signature of a range expansion are rare. 2. Using microsatellite markers, we performed a detailed spatiotemporal genetic analysis of the range expanding damselfly Coenagrion scitulum (Rambur) along a coastal axis during the first years after colonisation. 3. A decrease was in (private) allelic richness when going northwards along the coastline, which is consistent with a scenario of cumulative founder events. In spite of the spatiotemporal dynamics in the observation records of the species along the coastline, the spatial genetic data indicated a major contribution from the broad expansion front during the colonisation of the coastline rather than a stepping‐stone colonisation process. 4. The fine‐scale temporal dynamics of the range expansion indicated the absence of persistent founder effects and instead showed considerable temporal instability in genetic indices at the more northern edge populations. This may be explained by genetic immigration and admixture from the broad expansion front in this active disperser.     

Concerning the width of spark channels with different polarities in submicrosecond sliding discharges in noble gases

Previously, the parameters of submicrosecond (with a duration of <200 ns) multichannel high-current discharges sliding along a ceramic surface in Ne, Ar, and Xe were studied only for the negative polarity of the applied voltage. The experimental data indicate that the channels expand in the transverse direction mainly due to electron drift from the channel surface layer under the action of the electric field perpendicular to the channel axis and subsequent gas ionization by these electrons. To investigate mechanisms for the channel development in a sliding discharge—in particular, to determine the contribution of electron drift—it is necessary to carry out experiments similar to those performed earlier for the opposite polarity of the applied voltage. Here, the results of measurements of the widths of the spark channels of negativeand positive-polarity sliding discharges excited in Ne, Ar, and Xe at pressures of 30 and 100 kPa are presented and discussed. It is shown that, depending on the pressure and sort of gas, the averaged optical width of positive-polarity channels is smaller by a factor of 1.27–1.60 than that of negative-polarity channels. The experimental data are analyzed using the theory of propagation of ionization waves with different polarities in gases. Analysis has shown that electron diffusion contributes insignificantly to channel expansion and that, for both polarities, the channel expansion rate exceeds the electron drift velocity in the transverse electric field near the channel. In the framework of the so-called approximation of nonlocalized initial conditions, the measured ratio between of the widths of negativeand positive-polarity channels and their relation to the electron mobility are explained by the channel expansion governed by both electron drift and primary free electrons produced by a short-term source in a narrow region ahead of the front of the expansion wave. Numerical simulations show that the width of this region is comparable with that of the wave front and is more than one order of magnitude smaller than the observed channel radius. Gas photoionization by the channel radiation can serve as a source of primary electrons.     

Distribution of euphausiids in the Kuroshio front and warm water tongue with special reference to the surface aggregation of Euphausia pacifica

The distribution of euphausiids and other macrozooplankton wasinvestigated in and around the Kuroshio front formed in theKa.shima-nada Sea. Japan. during the summer of 1993. Zooplanktonwere dominated by copepods, chaetognaths and euphausiids. andtheir biomass was significantly higher at the frontal stations.Eighteen species belonging to six genera of euphausiids werecollected. The species composition and community structure ofeuphausiids changed drastically with the ‘areas’corresponding to the hydrological conditions. In the area underthe influence of the Kuroshio. most euphausiids were warm-waterspecies. In contrast. euphausiids found in the frontal areawere those usually predominating in subarctic or cold Oyashiowaters. In the area of the warm water tongue. where warm Kuroshiowater lay above cold Oyashio water, the species compositionof euphausiids represented a mixture of both warm- and cold-waterspecies. Surface aggregations of Euphausia pacifica were observedin the frontal area during the night. The biomass and densityof the aggregations ranged between 90 and 136 mg C m^–3and 164 and 238 md. m^–3 respectively. These aggregationswere mostly made up of immature individuals of < 12 mm. Passivetransportation by convergent flow at the front seems to explainthe observed surface aggregations of E.pacifica.     

Plankton distribution across a slope current-induced front in the southern Bay of Biscay

Relatively warm (12.50–12.75°C) and high-salinity[<35.640 practical salinity units (PSU)] water flowing eastwardwas detected at the shelf-break during a cruise carried Outin the southern Bay of Biscay in Spring 1987. The slope currentinduced the formation of a convergent front separating well-mixedoceanic waters from haline-stratified coastal waters. Very highconcentrations of dissolved oxygen (295 µmol kg^–1)and chlorophyll a(>4.5 mg m^–3) were found at the outeredge of the frontal boundary. Small autotrophic flagellatesdominated the phytoplankton community. Primary production peakedat the boundary region. Estimated phytoplankton growth ratesindicated that active growth was taking place, with lower turnovertimes integrated over the water column at the frontal station(2.5–5 days) than at coastal (1.5–2.8 days) or oceanic(1.5–3.5 days) stations. The lowest doubling times (1–2days) were calculated for surface frontal populations. Accumulationof zooplankton was also observed associated with the convergentphysical structure, although this relationship was less markedthan for phytoplankton. Copepods, mainly Paracalanus parvus,Acartia clausi and Oithona helgolandica, formed the bulk ofthe mesozooplankton biomass. Compatibility between the sizeof phytoplankton cells and copepod size spectra indicate highfood availability for these animals, particularly in the vicinityof the front. The distribution of fish eggs and fish larvaewas also coupled with the slope current-induced front. Sardinelarvae were more abundant at the coastal side of the front,whereas larval stages of blue whiting reached the highest densitiesat off-shelf stations. Larvae of lamellibranch molluscs andbryozoa were restricted to nearshore waters, as the frontalboundary prevented larval dispersion to the open ocean. Theresults presented in this paper suggest that the Iberian slopecurrent and its associated shelf-break frontal structure werecrucial in controlling phytoplankton primary production, activityof grazers, distribution of larvae of fishes and benthic invertebrates,and ultimately in determining the structure of the pelagic foodweb in the southern Bay of Biscay during the seasonal periodof vertical mixing.     

Quaternary range and demographic expansion of Liolaemus darwinii (Squamata: Liolaemidae) in the Monte Desert of Central Argentina using Bayesian phylogeography and ecological niche modelling

Until recently, most phylogeographic approaches have been unable to distinguish between demographic and range expansion processes, making it difficult to test for the possibility of range expansion without population growth and vice versa. In this study, we applied a Bayesian phylogeographic approach to reconstruct both demographic and range expansion in the lizard Liolaemus darwinii of the Monte Desert in Central Argentina, during the Late Quaternary. Based on analysis of 14 anonymous nuclear loci and the cytochrome b mitochondrial DNA gene, we detected signals of demographic expansion starting at ~55 ka based on Bayesian Skyline and Skyride Plots. In contrast, Bayesian relaxed models of spatial diffusion suggested that range expansion occurred only between ~95 and 55 ka, and more recently, diffusion rates were very low during demographic expansion. The possibility of population growth without substantial range expansion could account for the shared patterns of demographic expansion during the Last Glacial Maxima (OIS 2 and 4) in fish, small mammals and other lizards of the Monte Desert. We found substantial variation in diffusion rates over time, and very high rates during the range expansion phase, consistent with a rapidly advancing expansion front towards the southeast shown by palaeo‐distribution models. Furthermore, the estimated diffusion rates are congruent with observed dispersal rates of lizards in field conditions and therefore provide additional confidence to the temporal scale of inferred phylogeographic patterns. Our study highlights how the integration of phylogeography with palaeo‐distribution models can shed light on both demographic and range expansion processes and their potential causes.     

Toxic red-tide in the Argentine Sea. Phytoplankton distribution and survival of the toxic dinoflagellate Gonyaulax excavata in a frontal area

The association of the first bloom of the toxic dinoflagellateGonyaulax excavata with the frontal system off Peninsula Valds(Argentina), and the presence of resting cysts in sedimentsof the area gave way to the hypothesis of a second bloom duringthe subsequent spring. In this work we report on the resultsobtained after the study of the second bloom. The characteristicsof the frontal system in relation to the development of thephenomenon are analyzed, and latitudinal differences are established.The presence of resting cysts in the plankton of the homogeneousside of the front indicates that the phenomenon is related tothe transportation of these cysts from the sediments to thestratified side of the front, where stability and availabilityof nutrients favor a fast growth. Selection, imposed by turbulence,limits the growth of G. excavata at the homogeneous side wherechain-forming diatoms develop. The presence of the red patchfor a long time suggests a zooplankton-phytoplankton uncoupledinteraction based on the zooplankton exclusion and its replacementby the phagotrophic dinoflagellate Polykrikos schwartzii. Thehighest predation pressure is located at the patch edges ofthe stratified zone.