bluuebunny/crossref_metadata_2025_split huggingface dataset:
Models of open populations with space‐limited recruitment: extension of theory and application to the barnacle Chthamalus montagui
Authors: Hyder Kieran , Åberg Per , Johnson Mark P. , Hawkins Stephen J. 
Published: March 2003

Summary

Barnacles are a good model organism for the study of open populations with space‐limited recruitment. These models are applicable to other species with open supply of new individuals and resource limitation. The inclusion of space in models leads to reductions in recruitment with increasing density, and thus predictions of population size and stability are possible.
Despite the potential generality of a demographic theory for open space‐limited populations, the models currently have a narrow empirical base. In this study, a model for an open population with space‐limited recruitment was extended to include size‐specific survival and promotions to any size class. The assumptions of this model were tested using data from a pan‐European study of the barnacle Chthamalus montagui Southward. Two models were constructed: a 6‐month model and a periodic annual model. Predicted equilibria and their stabilities were compared between shores.
Tests of model assumptions supported the extension of the theory to include promotions to any size class. Mortality was found to be size‐specific and density independent. Studied populations were open, with recruitment proportional to free space.
The 6‐month model showed a significant interaction between time and location for equilibrium free space. This may have been due to contrasts in the timing of structuring processes (i.e. creating and filling space) between Mediterranean and Atlantic systems. Integration of the 6‐month models into a periodic annual model removed the differences in equilibrium‐free space between locations.
Model predictions show a remarkable similarity between shores at a European scale. Populations were persistent and all solutions were stable. This reflects the apparent absence of density‐dependent mortality and a high adult survivorship in C. montagui. As populations are intrinsically stable, observations of fluctuations in density are directly attributable to variations in the environmental forcing of recruitment or mortality.
Synchrony and second‐order spatial correlation in host–parasitoid systems
Authors: Bjørnstad Ottar N. , Bascompte Jordi 
Published: March 2003

Summary

Recent theoretical studies on population synchrony have focused on the role of dispersal, environmental correlation and density dependence in single species. Trophic interactions have received less attention. We explored how trophic interactions affect spatial synchrony.
We considered a host–parasitoid coupled map lattice to understand how the self‐organizing spatial patterns generated by such dynamics affect synchrony. In particular, we calculated the spatial correlation functions (SCF) associated with travelling waves, spatial chaos and crystal lattices.
Travelling waves were associated with cyclic SCF (called second‐order SCF) that differed greatly from those seen in spatial chaos or crystal lattices. Such U‐shaped patterns of spatial synchrony, which have not been predicted by single‐species models, have been reported recently in real data. Thus, the shape of the SCF can provide a test for trophically generated spatiotemporal dynamics.
We also calculated the cross‐correlation function between the parasitoid and the host. Relatively high parasitoid mobility resulted in high within‐patch synchrony of the dynamics of the two species. However, with relatively high host mobility, the parasitoid dynamics began to lag spatially behind those of the host.
We speculated that this spatial lag between the host and parasitoid is the ultimate source of travelling waves, because the spatial cross‐correlation in turn affects host dynamics.
A new method to estimate the spatial cross‐correlation function between two species was developed as an integral part of the study.
Compartmentalization in plant–insect flower visitor webs
Authors: Dicks L. V. , Corbet S. A. , Pywell R. F. 
Published: March 2003

SummaryInteractions between entomophilous flowering plants and their insect visitors were recorded at two mesotrophic grassland communities in Norfolk, and a diagrammatic quantitative web produced for each community.The systems were analysed for compartmentalization using the method ofRaffaelli & Hall (1992), based on trophic similarity between pairs of species. Good evidence was found for compartmentalization at both sites.Ordination of the data was used to suggest how the species fall into compartments. The likelihood that groups of plants and insects implied by this method represent real compartments in the web was assessed quantitatively, using trophic similarity indices, and qualitatively, by consideration of the species involved.The compartments reflected classic pollination syndromes to some extent, dividing the insect fauna into a group of butterflies and bees, and a group of flies, at both sites. The compartmentalization was also affected by phenology.Dominant interactions fell within compartments in the web, as might be expected in mutualistic systems.
Aggregation, habitat quality and coexistence: a case study on carrion fly communities in slug cadavers
Authors: Woodcock B. A. , Watt A. D. , Leather S. R. 
Published: March 2003

Summary

The aggregation model of coexistence for discrete patches of ephemeral resources was tested with Diptera communities in slug cadavers.
Slugs were exposed to the necrophagous fauna present at each of 32 birch woodlands. After 3 days the slugs were removed and emerging adult insects were retained and identified.
Density‐specific aggregation (J), association between species (Cxy) and the necessary and sufficient condition for coexistence (Txy) were used to test the model. Woodlands were ranked on the basis of habitat quality that was defined by the diversity of species associated with each site.
Overall community and species‐specific responses to resource mass were investigated. Results provided evidence for multispecies coexistence by interspecific aggregation, although there was also evidence of alternative mechanisms that promote coexistence.
Differences aggregation and interspecific association were found between high and low quality sites. The implications of these findings are discussed with particular reference to how differences in habitat quality affect aggregation and interspecific association.
Helping does not enhance reproductive success of cooperatively breeding rufous vanga in Madagascar
Authors: Eguchi Kazuhiro , Yamagishi Satoshi , Asai Shigeki , Nagata Hisashi , Hino Teruaki 
Published: March 2003

SummaryIn many studies on cooperative breeding, helping by auxiliary individuals is considered to enhance the reproductive success of breeders. However, confounding factors other than helping could cause the differences.The endemic Madagascan rufous vangaSchetba rufa(Vangidae) is known as a cooperatively breeding species. In order to evaluate the effect of helping in this species, we compared the reproductive success of breeding pairs helped by auxiliary birds, and pairs breeding alone, based on a 6‐year study of an individually colour‐banded population in the Ampijoroa Forest Station, western Madagascar.This species is single‐brooded. Brood reduction was rare and most cases of nesting failure were due to total loss of clutches and broods, probably as a result of predation.Monogamous pairs with one to four auxiliary birds comprised 24–43% of all breeding groups. Most auxiliary birds were male offspring remaining in their natal territory. Auxiliary males provided a considerable contribution towards antipredator defence, territory defence and to the provisioning of nestlings. In about one‐third of the groups, however, the auxiliary males did not help at all. Male offspring may remain in their natal territory in order to avoid harassment by other territorial individuals, and to increase the probability of territory acquisition and of copulation with unrelated breeding females.The probability of breeding successfully was higher, and the number of fledglings produced was larger among pairs with auxiliary birds than among those breeding alone. However, provisioning by auxiliaries neither enhanced the growth rate of nestlings, nor reduced the number of days they required to fledge.A pair‐match comparison of the same pairs between years with and without auxiliaries showed no effect of group size on their reproductive success. Even provisioning by auxiliaries did not affect the reproductive success.Pairs accompanied by auxiliary birds for more than 1 year enjoyed higher reproductive success even in those years when they were without auxiliaries than did pairs always breeding alone.Neither the simple presence of auxiliaries nor their helping behaviour enhanced the reproductive success of breeding pairs. The quality of the breeding pair and/or their territory may have affected their reproductive success and, as a result, increased the number of auxiliaries.
Glutathione decreases in dopaminergic PC12 cells interfere with the ubiquitin protein degradation pathway: relevance  for Parkinson's disease?
Authors: Jha Nandita , Kumar M. Jyothi , Boonplueang Rapee , Andersen Julie K. 
Published: March 2003

AbstractParkinson's disease (PD) is characterized by the presence of proteinaceous neuronal inclusions called Lewy bodies in susceptible dopaminergic midbrain neurons. Inhibition of the ubiquitin‐proteasome protein degradation pathway may contribute to protein build‐up and subsequent cell death. Ubiquitin is normally activated for transfer to substrate proteins by interaction with the E1 ubiquitin ligase enzyme via a thiol ester bond. Parkinson's disease is also characterized by decreases in midbrain levels of total glutathione which could impact on E1 enzyme activity via oxidation of the active site sulfhydryl. We have demonstrated that increasing reductions in total glutathione in dopaminergic PC12 cells results in corresponding decreases in ubiquitin‐protein conjugate levels suggesting that ubiquitination of proteins is inhibited in a glutathione‐dependent fashion. Decreased ubiquitinated protein levels appears to be due to inhibition of E1 activity as demonstrated by reductions in endogenous E1‐ubiquitin conjugate levels as well as decreases in the production of de novo E1‐ubiquitin conjugates when glutathione is depleted. This is a reversible process as E1 activity increases upon glutathione restoration. Our data suggests that decreases in cellular glutathione in dopaminergic cells results in decreased E1 activity and subsequent disruption of the ubiquitin pathway. This may have implications for neuronal degeneration in PD.
Substrate specificity, inhibition and enzymological analysis of recombinant human glutamate carboxypeptidase II
Authors: Barinka Cyril , Rinnová Markéta , Šácha Pavel , Rojas Camilo , Majer Pavel , Slusher Barbara S. , Konvalinka Jan 
Published: March 2003

AbstractGlutamate carboxypeptidase II (GCPII, EC 3.4.17.21) is a membrane peptidase expressed in a number of tissues such as kidney, prostate and brain. The brain form of GCPII (also known as NAALADase) cleavesN‐acetyl‐aspartyl glutamate to yield free glutamate. Animal model experiments show that inhibition of GCPII prevents neuronal cell death during experimental ischaemia. GCPII thus represents an important target for the treatment of neuronal damage caused by excess glutamate. In this paper we report expression of an extracellular portion of human glutamate carboxypeptidase II (amino acids 44–750) inDrosophilaSchneider's cells and its purification to homogeneity. A novel assay for hydrolytic activity of recombinant human GCPII (rhGCPII), based on fluorimetric detection of released alpha‐amino groups was established, and used for its enzymological characterization. rhGCPII does not show dipeptidylpeptidase IV‐like activity assigned to the native form of the enzyme previously. Using a complete set of protected dipeptides, substrate specificity of rhGCPII was elucidated. In addition to the previously described substrates, four novel compounds, Ac‐Glu‐Met, Ac‐Asp‐Met and, surprisingly, Ac‐Ala‐Glu and Ac‐Ala‐Met were identified as substrates for GCPII, and their respective kinetic constants determined. The glycosylation of rhGCPII was found indispensable for the enzymatic activity.
The production of macrophage inflammatory protein‐2 induced by soluble intercellular adhesion molecule‐1 in mouse astrocytes is mediated by src tyrosine kinases and p42/44 mitogen‐activated protein kinase
Authors: Otto Vivianne I. , Gloor Sergio M. , Frentzel Stefan , Gilli Urs , Ammann Emerita , Hein Andreas E. , Folkers Gerd , Trentz Otmar , Kossmann Thomas , Morganti‐Kossmann Maria C. 
Published: March 2003

AbstractSevere traumatic brain injury stimulates the release of soluble intercellular adhesion molecule‐1 (sICAM‐1) into CSF. Studies in cultured mouse astrocytes suggest that sICAM‐1 induces the production of macrophage inflammatory protein‐2 (MIP‐2). In the present study, we investigated the underlying mechanisms for MIP‐2 induction. sICAM‐1 induced MIP‐2 in astrocytes lacking membrane‐bound ICAM‐1, indicating that its action is due to heterophilic binding to an undescribed receptor rather than homophilic binding to surface ICAM‐1. Signal transduction may be mediated by src tyrosine kinases, as the src tyrosine kinase inhibitors herbimycin A and PP2 abolished MIP‐2 induction by sICAM‐1. Phosphorylation of p42/44 mitogen‐activated protein kinase (MAPK), but not of p38 MAPK, occurred further downstream, as evidenced by western blot analysis combined with the use of herbimycin A and specific MAPK inhibitors. By contrast, induction of MIP‐2 by tumour necrosis factor‐α (TNF‐α) involved both p42/44 MAPK and p38 MAPK. Following stimulation with either sICAM‐1 or TNF‐α, astrocyte supernatants promoted chemotaxis of human neutrophils and incubation of these supernatants with anti‐MIP‐2 antibodies more efficiently suppressed the migration induced by sICAM‐1 than by TNF‐α. These results show that sICAM‐1 induces the production of biologically active MIP‐2 in astrocytes by heterophilic binding to an undefined receptor and activation of src tyrosine kinases and p42/44 MAPK.
Ceramide activates microglia to enhance the production/secretion of brain‐derived neurotrophic factor (BDNF) without induction of deleterious factors in vitro
Authors: Nakajima Kazuyuki , Tohyama Yoko , Kohsaka Shinichi , Kurihara Tadashi 
Published: March 2003

AbstractIn analyzing the regulation of neurotrophin production/secretion from microglia, C8‐ceramide (d‐erythro‐sphingosine, N‐octanoyl‐) was found to induce secretion of brain‐derived neurotrophic factor (BDNF) from microglia in vitro. In the present study, the action of C8‐ceramide in secreting neurotrophic and harmful factors was investigated and compared with the effects of lipopolysaccharide (LPS). C8‐ceramide as well as LPS enhanced the production/secretion of BDNF but, different from LPS, did not induce tumor necrosis factor α, interleukin‐1β, or nitric oxide. The C8‐ceramide‐induced BDNF release was significantly suppressed by protein kinase C (PKC) inhibitor, bisindolylmaleimide, which targets PKC isoforms, α, β, γ, δ and ε. However, it was not suppressed by a specific inhibitor of PKCα. Furthermore, PKCβ and γ were undetected in the microglia. Therefore, PKCδ and/or ε appear to be functioning PKC isoforms. In contrast, none of the mitogen‐activated protein kinases (MAPKs) and none of the transcription factors, including the cAMP response element‐binding transcription factor (CREB) and nuclear factor κB (NFκB) were activated in the microglia in response to C8‐ceramide. These results indicate that ceramide‐induced BDNF release in microglia is mediated by a signaling pathway associated with PKCδ and/or ε, but not with activation of MAPKs, CREB and NFκB.
Refsum's disease: a peroxisomal disorder affecting phytanic acid α‐oxidation
Authors: Wierzbicki Anthony S. , Lloyd Matthew D. , Schofield Christopher J. , Feher Michael D. , Gibberd F. Brian 
Published: March 2003

AbstractRefsum's disease (hereditary motor sensory neuropathy type IV, heredopathia atactica polyneuritiformis) is an autosomal recessive disorder the clinical features of which include retinitis pigmentosa, blindness, anosmia, deafness, sensory neuropathy, ataxia and accumulation of phytanic acid in plasma‐ and lipid‐containing tissues. The transport and biochemical pathways of phytanic acid metabolism have recently been defined with the cloning of two key enzymes, phytanoyl‐CoA 2‐hydroxylase (PAHX) and 2‐hydroxyphytanoyl‐CoA lyase, together with the confirmation of their localization in peroxisomes. PAHX, an iron(II) and 2‐oxoglutarate‐dependent oxygenase is located on chromosome 10p13. Mutant forms of PAHX have been shown to be responsible for some, but not all, cases of Refsum's disease. Certain cases have been shown to be atypical mild variants of rhizomelic chondrodysplasia punctata type 1a. Other atypical cases with low‐plasma phytanic acid may be caused by α‐methylacyl‐CoA racemase deficiency. A sterol‐carrier protein‐2 (SCP‐2) knockout mouse model shares a similar clinical phenotype to Refsum's disease, but no mutations in SCP‐2 have been described to‐date in man. This review describes the clinical, biochemical and metabolic features of Refsum's disease and shows how the biochemistry of the α‐oxidation pathway may be linked to the regulation of metabolic pathways controlled by isoprenoid lipids, involving calcineurin or the peroxisomal proliferator activating α‐receptor.
Timothy growth in Scandinavia: combining quantitative information and simulation modelling
Authors: Höglind M. , Schapendonk A. H. C. M. , Van Oijen M. 
Published: March 2003

SummaryTimothy (Phleum pratense) is the most widely grown sown grass species for silage and hay production in the Nordic countries; it is also common in many other areas with a cold maritime climate. Research on timothy has identified many environmental factors and plant characteristics that determine timothy growth. However, much of the literature that analyses timothy growth presents only qualitative estimates of the importance of the different growth‐determining factors. Here we present a review of quantitative information on timothy. Moreover, we analyse to what extent this quantitative information is sufficient to permit the construction of a simple process‐based model of timothy growth. We then use such a model to identify the major growth‐determining factors. Simulations with the model showed that the major processes to be elucidated in future research on timothy are tillering dynamics and the formation and loss of leaves from tillers. We conclude that a combination of literature review and analysis by means of simulation modelling, such as we attempted here, is an effective approach to identify and prioritize research goals.
Phosphorus modifies the effects of nitrogen on nodulation in split‐root systems of Hippophaë rhamnoides
Authors: Gentili Francesco , Huss‐Danell Kerstin 
Published: March 2003

Summary

The effects of N (ammonium nitrate), P (phosphate) and their interactions on nodulation were studied in the intercellularly infected actinorhizal plant Hippophaë rhamnoides.
A split‐root design, with pots receiving different concentrations of N and P, was used to determine whether the effects of N and P are local or systemic, if they are specific to nodulation or general, and whether P could counteract N inhibition. H. rhamnoides plants were grown for 6–10 wk after inoculation with Frankia.
Inhibition of nodulation by N was systemic for both nodule number and nodule biomass in H. rhamnoides.
By contrast, high P had a systemic stimulation on nodule number and biomass and P prevented systemic, but not local, N inhibition. Stimulation by P was specific to nodulation and not simply mediated via plant growth. Whether N and P alter not only nodulation but also N2‐fixation in the nodules requires further investigation.
Growth depression of mycorrhizal Citrus seedlings grown at high phosphorus supply is mitigated by elevated CO2
Authors: Jifon John L. , Graham James H. , Drouillard Diana L. , Syvertsen James P. 
Published: March 2003

Summary

Gas exchange and growth responses of pot‐grown sour orange (Citrus aurantium) and sweet orange (C. sinensis) were studied at high soil‐P where growth depression is predicted.
Seedlings were either inoculated (AM) with the arbuscular mycorrhizal fungus Glomus intraradices or not inoculated (NM), and grown at elevated (eCO2) or ambient CO2 (aCO2) for 11 wk.
At aCO2, growth of AM sour orange was depressed (18%) compared with NM seedlings, but at eCO2, AM sour orange plants were 15% larger than NM plants. Growth depression coincided with increased rhizosphere respiration, reduced root starch concentration, and lower relative growth rates. Net photosynthesis (Pn) of both genotypes was enhanced by eCO2. For sour orange, the stimulation was greater in AM than in NM seedlings and this may have compensated for the carbon (C) expenditure on mycorrhizas. Gas exchange and growth of sweet orange were unresponsive to colonization by G. intraradices.
Differential responses to treatments suggest that C expenditure on mycorrhizas is more tightly regulated in citrus genotypes of low mycorrhizal dependency (MD) such as sweet orange than in high MD genotypes (e.g. sour orange).
Uptake and metabolism of glucose in the Nostoc–Gunnera symbiosis
Authors: Black K. G. , Parsons R. , Osborne B. A. 
Published: March 2003

Summary

The transition of Nostoc colonies from free‐living to symbiotic conditions, in the Nostoc–Gunnera association, involves increased heterocyst frequency and a reliance on carbon imported from the host for metabolic processes, including N2 fixation.
Here the uptake of a glucose analogue, 3‐[14C]‐O‐methyl‐glucose (14C‐OMG), in freshly isolated symbiotic and free‐living Nostoc cells was characterized. In situ isotope enrichment coupled with GC–MS was used to elucidate the primary pathway(s) of 1‐[13C]‐glucose metabolism in the Nostoc–Gunnera symbiosis.
The characteristics of 14C‐OMG uptake by symbiotic clusters suggested a respiratory driven process mediated by a hexose transporter. However, uptake by various Nostoc isolates decreased with increasing heterocyst frequency and was specifically associated with vegetative cells. In isolated and symbiotically intact Nostoc cells, 1‐[13C]‐glucose was imported and converted to various intermediates of the incomplete citric acid cycle, glycolysis and N2‐assimilating pathways. Labelling profiles indicated that C metabolism was altered in infected, but not in uninfected, rhizome tissue.
Although it has been proposed that cyanobacteria such as Nostoc metabolise glucose using enzymes of the oxidative pentose phosphate cycle, our results suggest that glucose is also metabolised via glycolysis as well as the incomplete citric acid cycle in symbiotic cells.