Patterns in species associations in plant communities: the importance of scale

Abstract. Present discussions on competitive interactions and the occurrence of predictable patterns in species composition – including assembly rules – are likely to benefit from appropriate analyses of the spatial structure in plant communities. We suggest such an analysis when we specifically want to detect scale regions where fine-scale local processes may affect the spatial pattern of species composition. We combine indirect ordination in the form of Detrended Correspondence Analysis (DCA) and geostatistics in the form of variography. The species abundance data in the sampled quadrats are summarized as positions on the axes in the ordination. Each axis is used as a regionalized variable in the variography to obtain the spatial dependence of the quadrats. The spatial pattern found will suggest the relevant scale region in which to perform an analysis of species associations. A significant spatial dependence (the ‘range’ in geostatistical jargon) will define the size of a sampling plot that will minimize both the problem of being too small and thus having the risk of oversampling of e.g. clonal individuals and of being too large which will risk including individuals that do not interact. We also suggest that plots are spaced at least a ‘range’ apart to insure spatial and statistical independence. Comparisons of species compositions in such plots will reveal any positive or negative associations between species on a scale where these should reflect species-species interactions. To illustrate the method it is applied to three different data sets from two different plant communities.     

Fine structure and fluorescence morphology of adrenergic nerves after 6-hydroxydopamine in vivo and in vitro

Summary In parallel fine structural, fluorescence histochemical and biochemical experiments the effect of 6-OH-DA administered in vivo and in vitro on the adrenergic nerves in the mouse iris was studied. As seen in the electron microscope, in vivo administration of 6-OH-DA causes a selective, rapid degeneration of the adrenergic axon terminals similar to that found after axotomy, whereas the cholinergic nerves are unaffected at all time intervals studied. Already 1 hr after the injection of 6-OH-DA the axonal enlargements swell and the size of the dense core of the granular vesicles is strongly reduced. Since the NA stores are almost completely depleted at this time interval, the small core present may be due to a reaction between 6-OH-DA and the fixative. From 2–4 hr after the injection increasing numbers of axonal enlargements with a high electron density are observed in the Schwann cell cytoplasm, which later are digested and completely absent about 48–72 hr after the 6-OH-DA injection. During the following weeks adrenergic axons reappear. This time course of degeneration obtained is considerably faster than that seen after axotomy in other studies. After incubation in 6-OH-DA containing media similar changes were observed in the axonal enlargements, starting already after 30 min of incubation. At this time-point there is a considerable reduction of endogenous NA and a severe damage of the membrane pump uptake mechanism. Incubation with 6-OH-DA and subsequent rinsing for 2 hr caused marked changes, including partly swelling of axons and partly shrinking of the axons into electron dense bodies.The fluorescence histochemical and biochemical results are in good agreement with the ultrastructural studies demonstrating a rapid loss of NA from the adrenergic nerve terminals and main axons and a long lasting depletion of the NA, with a gradual recovery to 75% 6 weeks after the injection.The investigation has been supported by research grants from the Swedish Medical Research Council (14X-2295, 14X-2887 and 04X-3881) Karolinska Institutet, Magnus Bergvalls and Carl-Berthel Nathorst Stiftelser. For generous supplies of drugs we are indebted to the following companies: AB Hässle (6-OH-DA, through Dr H. Corrodi), Pfizer (Niamid^®), Ciba (Serpasil^®). The skilful technical assistance of Miss Bodil Flock, Mrs Waltraut Hiort and Mrs Eva Lindqvist is gratefully acknowledged.     

Nitric Oxide and Blood Pressure in Mice Lacking Extracellular-Superoxide Dismutase

Nitric oxide is a major vasorelaxant and regulator of the blood pressure. The blood vessels contain several active sources of the superoxide radical, which reacts avidly with nitric oxide to form noxious peroxynitrite. There are large amounts of extracellular-superoxide dismutase (EC-SOD) in the vascular wall. To evaluate the importance of EC-SOD for the physiology of nitric oxide, here we studied the blood pressure in mice lacking the enzyme. In chronically instrumented non-anaesthetized mice there was no difference in mean arterial blood pressure between wild-type controls and EC-SOD mutants. Extensive inhibition of nitric oxide synthases with N -monomethyl- l -arginine however resulted in a larger increase in blood pressure, and infusion of the nitric oxide donor nitrosoglutathione caused less reduction in blood pressure in the EC-SOD null mice. We interpret the alterations to be caused by a moderately increased consumption of nitric oxide by the superoxide radical in the EC-SOD null mice. One role of EC-SOD may be to preserve nitric oxide, a function that should be particularly important in vascular pathologies, in which large increases in superoxide formation have been documented.     

Adenoviruses use lactoferrin as a bridge for CAR-independent binding to and infection of epithelial cells

Most adenoviruses bind to the coxsackie- and adenovirus receptor (CAR). Surprisingly, CAR is not expressed apically on polarized cells and is thus not easily available to viruses. Consequently, alternative mechanisms for entry of coxsackievirus and adenovirus into cells have been suggested. We have found that tear fluid promotes adenovirus infection, and we have identified human lactoferrin (HLf) as the tear fluid component responsible for this effect. HLf alone was found to promote binding of adenovirus to epithelial cells in a dose-dependent manner and also infection of epithelial cells by adenovirus. HLf was also found to promote gene delivery from an adenovirus-based vector. The mechanism takes place at the binding stage and functions independently of CAR. Thus, we have identified a novel binding mechanism whereby adenovirus hijacks HLf, a component of the innate immune system, and uses it as a bridge for attachment to host cells.     

Latitudinal clines in life-history variables of anadromous brown trout in Europe

Based on published data, we reviewed clinal variations in life-history characteristics of anadromous brown trout Salmo trutta from 102 European rivers at latitudes between 54 and 70° N. Growth rate in fresh water, mean smolt age, mean sea age at first sexual maturity, proportion of repeal spawners among adults, longevity, and length of adult life span exhibited latitudinal clines. Brown trout grew faster in fresh water, smolted and matured younger, lived fewer years but spawned more times in the south than in the north. The life-history traits studied were often correlated. Longevity, smolt age and sea age at maturity were negatively and smolt length and proportion of repeat spawners among adults were positively correlated with growth rate in fresh water. Longevity was positively correlated with smolt age and sea age at maturity. The latter also increased with increasing smolt age. None of these significant correlations among life history variables, except for those between smolt age and parr growth and proportion of repeat spawners and parr growth, are latitudinal effects. We do not know to what extent the latitudinal variation in life–history traits reflects phenotypic plasticity and to what extent it is caused by inherited differences among populations.     

Effect of Metalaxyl on the incidence and severity of Pearl millet downy mildew disease in Northern Nigeria

Pearl millet downy mildew (DM) incidence, severity and yield losses of two pearl millet varieties (local and improved) due to the disease were determined in the field. Significant differences in the disease incidence and severity were recorded in the plots sown with metalaxyl-treated seeds and those sown with non-treated seeds, indicating the efficacy of the fungicide on the fungus. Yield losses due to non-treatment of seeds with metalaxyl was 40.88 and 45.39% in a local variety and 43.00 and 18.60% in an improved variety in the 2000 and 2001 cropping seasons respectively. Significant differences between plots sown with metalaxyl-treated and those sown with non-treated seeds were obtained for other yield components such as 1000-grains weight, panicle length and weight.     

Genetic divergence of climatically marginal populations of Vicia pisiformis on the Scandinavian Peninsula

Vicia pisiformis L. is a perennial leguminous plant with a main distribution in broadleaved forest-steppes of eastern Europe. The species is classified as endangered (EN) according to the IUCN red-lists in both Norway and Sweden, due to severe fragmentation, small population sizes and continuing population decline. The populations on the Scandinavian Peninsula constitute the northern limit of the species distribution and are mostly restricted to warm stony slopes with predominantly southern aspects. In this study we used the AFLP method, which is a high-resolution genetic fingerprint method. Samples were collected from 22 Scandinavian populations. The overall genetic structure was analysed in an AMOVA, in a Mantel test and through constrained correspondence analysis (CCA). The ordination scores representing non-geographic genetic divergence were extracted from the CCA and analysed in a linear model using habitat variables and population size as explanatory variables. We found (i) a strong geographic structure, (ii) significant genetic divergence between populations, (iii) that this genetic divergence remained significant even after removing the effect of geography in a partial CCA and (iv) that the remaining non-geographic part of genetic divergence (distance from the ordination centre) was associated with aspect, populations with a northern aspect were more genetically divergent. Aspect explains more variation than population size and is the only variable retained in the minimal adequate model. We suggest that local adaptation has caused this divergence from an expected geographical pattern of genetic variation. This explanation is further supported by the association between aspect and specific AFLP fragments.     

Efficacy of the biocontrol yeast Pichia anomala during long-term storage of moist feed grain under different oxygen and carbon dioxide regimens

The yeast Pichia anomala inhibits the spoilage mold Penicillium roqueforti in laboratory experiments with high-moisture wheat in malfunctioning airtight storage. The ability of P. anomala to prevent mold growth during 14 months of grain storage was evaluated in outdoor silos with different air permeabilities. Freshly harvested wheat in 160-kg portions was inoculated with 10(2) colony-forming units (cfu) g(-1) P. roqueforti, alone or together with 10(4) cfu g(-1) P. anomala. During the first month P. anomala increased to about 10(6) cfu g(-1) in the treated silos to reach 10(7) cfu g (-1) after 9 months. Naturally occurring P. anomala in the untreated silos increased from 10(2) to about 10(3) cfu g(-1) during the first month and reached the same level as the treated silos after 9 months. Oxygen levels were reduced below the detection limit within 1 day, while carbon dioxide levels increased to 80-90% during the first month. P. roqueforti did not grow in wheat treated with P. anomala, regardless of silo permeability, but had increased to 10(5) cfu g(-1) in the untreated silos after 14 months of storage.     

Exploring the Relationship between Skeletal Mass and Total Body Mass in Birds

Total body mass (TBM) is known to be related to a number of different osteological features in vertebrates, including limb element measurements and total skeletal mass. The relationship between skeletal mass and TBM in birds has been suggested as a way of estimating the latter in cases where only the skeleton is known (e.g., fossils). This relationship has thus also been applied to other extinct vertebrates, including the non-avian pterosaurs, while other studies have used additional skeletal correlates found in modern birds to estimate TBM. However, most previous studies have used TBM compiled from the literature rather than from direct measurements, producing values from population averages rather than from individuals. Here, we report a new dataset of 487 extant birds encompassing 79 species that have skeletal mass and TBM recorded at the time of collection or preparation. We combine both historical and new data for analyses with phylogenetic control and find a similar and well-correlated relationship between skeletal mass and TBM. Thus, we confirm that TBM and skeletal mass are accurate proxies for estimating one another. We also look at other factors that may have an effect on avian body mass, including sex, ontogenetic stage, and flight mode. While data are well-correlated in all cases, phylogeny is a major control on TBM in birds strongly suggesting that this relationship is not appropriate for estimating the total mass of taxa outside of crown birds, Neornithes (e.g., non-avian dinosaurs, pterosaurs). Data also reveal large variability in both bird skeletal and TBM within single species; caution should thus be applied when using published mass to test direct correlations with skeletal mass and bone lengths.     

Human C-kit+CD45− cardiac stem cells are heterogeneous and display both cardiac and endothelial commitment by single-cell qPCR analysis

C-kit expressing cardiac stem cells have been described as multipotent. We have previously identified human cardiac C-kit+CD45− cells, but only found evidence of endothelial commitment. A small cardiac committed subpopulation within the C-kit+CD45− population might however be present. To investigate this at single-cell level, right and left atrial biopsies were dissociated and analyzed by FACS. Only right atrial biopsies contained a clearly distinguishable C-kit+CD45− population, which was single-cell sorted for qPCR. A minor portion of the sorted cells (1.1%) expressed early cardiac gene NKX2.5 while most of the cells (81%) expressed late endothelial gene VWF. VWF− cells were analyzed for a wider panel of genes. One group of these cells expressed endothelial genes (FLK-1, CD31) while another group expressed late cardiac genes (TNNT2, ACTC1). In conclusion, human C-kit+CD45− cells were predominantly localized to the right atrium. While most of these cells expressed endothelial genes, a minor portion expressed cardiac genes.