bluuebunny/crossref_metadata_2025_split huggingface dataset:
Disturbance is the principal α‐scale filter determining niche differentiation, coexistence and biodiversity in an alpine community
Authors: PIERCE SIMON , LUZZARO ALESSANDRA , CACCIANIGA MARCO , CERIANI ROBERTA M. , CERABOLINI BRUNO 
Published: May 2007

Summary

Many current biodiversity theories assume that resource competition determines niche segregation and thus coexistence within communities (i.e. at the α‐scale). However, the action of disturbance, creating heterogeneous environments and suppressing potential dominants, may also be important for biodiversity maintenance.
Hypothesis: subordinate species exhibit primarily opportunistic (ruderal) survival strategies, with increasing disturbance intensity constraining dominant species – favouring opportunistic strategies and thus functional and species diversity.
The diversity, character and frequency of strategies in an alpine sedge‐dominated vascular plant community were quantified in situ using CSR (competitor, stress‐tolerator, ruderal) classification, and compared with a pasture in the same alpine vegetation belt (i.e. with additional disturbance). Adaptive trends were confirmed by independent multivariate analysis [detrended correspondence analysis (DCA) and non‐metric multidimensional scaling (NMDS)].
The extremely stress‐tolerant sedge Carex curvula (C : S : R = 17.2 : 72.9 : 9.9%) dominated the relatively undisturbed community (frequency = 52%), with 32 subordinates (typically < 5%) exhibiting a functional spectrum encompassing stress tolerance to ruderalism, but not competitive strategies. With grazing, the community exhibited weaker co‐dominance by five species, greater biodiversity (76 species) and greater functional diversity, characterized by larger numbers of ruderals and some competitive‐ruderals. The principal variation in both DCA1 and NMDS1 for both communities directly reflected CSR strategy spectra, confirmed by Spearman's correlation.
Dominance by stress‐tolerators and restricted functional diversity demonstrates habitat‐level (β‐scale) functional convergence in response to stress. A spectrum of S to R strategies demonstrates α‐scale functional divergence in response to differential stress and disturbance. Grazing suppresses potentially dominant species and favours diversity, with the additional presence of competitive‐ruderals suggestive of a more intricate niche topology including more relaxed abiotic opportunities.
Natural communities are not necessarily structured according to the rules of resource competition models, as these fail to account for disturbance and facilitation processes.
The carbon costs for host trees of a phloem‐feeding herbivore
Authors: DUNGAN ROGER J. , TURNBULL MATTHEW H. , KELLY DAVE 
Published: May 2007

SummaryThrough its effect on plant productivity and fitness, herbivory can regulate forest diversity and ecosystem productivity. We used the interaction between phloem‐feeding scale insects [Ultracoelostoma assimile(Homoptera: Coelostomidiidae)] and the beech trees [Nothofagus solandrivar.solandri(Hook f.) Oerst.] they feed on to estimate directly the carbon costs of herbivory for a forest tree species over two consecutive years. The scale insects live on the bark of tree trunks and branches, and excrete readily collected droplets of carbon‐rich honeydew – this allows us to make an estimate of the carbon cost of herbivory that is not complicated by feeding damage to leaves and buds.Canopy photosynthesis (A) was estimated with an environmentally driven process‐based model, developed with parameters derived from measurements of photosynthesis on trees with (HD+) and without (HD–) honeydew scale insects during year 1. Honeydew dry matter production (PHD) was estimated from values for air temperature and humidity, and accounting for variation in honeydew production due to host‐tree diameter. The carbon cost of scale insect herbivory,CHD, was estimated asPHD/AHD+× 100%, whereAHD+is canopy photosynthesis for trees with scale insects.Over the two years annual canopy photosynthesis at the site was 1720 g C m−2ground area. In spring–summer, values for parameters describing photosynthesis (Vcmax, the maximum rate of rubisco‐catalysed RuBP carboxylation, andJmax, the rate of electron transport when irradiance is saturating) were 44% and 66% higher, respectively, in infested, as opposed to uninfested, trees. Consequently, for equivalent basal area, annual canopy photosynthesis was 4% greater for infested trees.Assuming that honeydew dry matter was 42% carbon by mass, annual honeydew production was 59 g C m−2ground area, which represents 4% of infested‐tree gross photosynthesis (c. 8% of net photosynthesis). Daily values of honeydew production were highest on cloudy days in summer, when warm humid conditions resulted in high values forPHDbut cloud cover reducedAHD+; on these daysCHDcould be > 50% ofAHD+. Values forPHDare remarkably similar to the differences betweenAHD+andAHD–, suggesting that HD+ trees may be able to compensate fully for the loss of carbon to herbivory. Our modelling results thus suggest that while the honeydew insects harvest relatively large amounts of carbohydrate from their host trees, the consequences of this for tree growth and reproduction may be small.
The role of soil resources in an exotic tree invasion in Texas coastal prairie
Authors: SIEMANN EVAN. , ROGERS WILLIAM E. 
Published: May 2007

Summary

Variation in resource requirements among plant species may cause changes in community composition when resource supply rates vary. Because exotic plants may differ in their requirements compared with native plants, changes in resource levels or ratios may change their invasive potential. The concentration hypothesis, nutrient balance hypothesis and resource ratio hypothesis make different predictions regarding the effects of nutrient additions on plant communities and the success of invaders.
We investigated these hypotheses using Chinese tallow tree (Sapium sebiferum), which is an aggressive invader of grasslands in the southern USA. Soil nitrogen, phosphorus and potassium were manipulated in a full factorial field experiment in a Texas coastal prairie.
Survival of Sapium seedlings over three growing seasons was independent of all three types of nutrient additions, alone or in any combination. Adding nitrogen or potassium increased the mass and height of Sapium seedlings. Adding phosphorus increased the mass and height of Sapium seedlings only when nitrogen was also added. These results support the nutrient balance hypothesis, which assumes that higher tissue concentrations of a nutrient reflect a greater ability of a plant species to take up and/or conserve that nutrient.
The above‐ground biomass of background prairie vegetation was independent of the addition of each type of nutrient alone or in any combination. However, the functional composition of the community shifted from graminoids to forbs with the addition of nitrogen and from graminoids to woody plants with the addition of phosphorus. These results support the concentration hypothesis, which assumes that higher tissue concentrations of a nutrient reflect a greater requirement for that nutrient. The contrasting responses of native woody vegetation and Sapium to phosphorus addition suggest that Sapium may have unusually low demands for phosphorus relative to nitrogen for a woody plant in this community.
These results show that potassium or nitrogen addition, perhaps in combination with phosphorus addition, has the potential to accelerate the invasion of Sapium into Texas coastal prairies. Because anthropogenic nutrient additions are common in grasslands worldwide, this may help to explain the frequent success of woody species invading grasslands.
Parenting by persons with intellectual disability: an explorative study in the Netherlands
Authors: Willems D. L. , De Vries J.‐N. , Isarin J. , Reinders J. S. 
Published: May 2007

AbstractBackground  As a sequel to a report by the Health Council of the Netherlands on contraception in persons with intellectual disabilities (IDs), a fierce debate about parenthood by such persons occurred, in which a lack of knowledge about parenting competences became clear. Therefore, the Ministry of Health commissioned a study investigating examples of ‘successful parenthood’ by persons with IDs.Methods  In conformity with the literature and with legal categories, we defined ‘successful parenthood’ as ‘good enough parenthood’, meaning no indications for child abuse and/or neglect, no dealings with child protection agencies and no legal custody. We combined a nationwide quantitative questionnaire study with a qualitative interview study. Questionnaires were sent to all institutions involved in caring for persons with ID, interviews were held with ‘good enough’ parents and their professional caregivers, selected on the basis of returned questionnaires.Results  Parenthood occurs in around 1.5% of persons with ID in the Netherlands and is mostly restricted to those with mild handicaps. In total, 51% of the cases were regarded, by caregivers, as not‐good‐enough parenthood, 33% were clearly good enough and 16% were doubtful. Predicting factors included the ability and the willingness to follow advice, the quality of the social network and the acceptance of parenting in the community. However, there is not one decisive predicting factor; particularly, the predictive value of the IQ alone is small.Conclusions  A general policy of discouragement of parenthood, as advocated by the Dutch Ministry, is not supported by our results; moreover, it would probably be impossible and have negative effects on social acceptance of parents with ID. The overall conclusion from the study therefore is that some kind of balancing model, in which positive and negative factors are weighed, may be useful to predict success and need for support.
Symbols can improve the reading comprehension of adults with learning disabilities
Authors: Jones F. W. , Long K. , Finlay W. M. L. 
Published: May 2007

AbstractBackground  This study aimed to test the hypothesis that adding symbols to written text can improve its comprehensibility for adults with learning disabilities.Methods  Nineteen adults with mild or borderline learning disabilities attempted to read four short passages of text, two of which had Widgit Rebus symbols added to them. Following each passage, they were asked questions to test their comprehension. A counterbalanced design was employed.Results  Participants’ comprehension scores were significantly higher for the symbolized passages than the non‐symbolized ones.Conclusions  Adding symbols to written text can make comprehension easier for some adults with mild and borderline learning disabilities. Future research, exploring how to do this most effectively, would be worthwhile.
Understanding of facial expressions of emotion by children with intellectual disabilities of differing aetiology
Authors: Wishart J. G. , Cebula K. R. , Willis D. S. , Pitcairn T. K. 
Published: May 2007

AbstractBackground  Interpreting emotional expressions is a socio‐cognitive skill central to interpersonal interaction. Poor emotion recognition has been reported in autism but is less well understood in other kinds of intellectual disabilities (ID), with procedural differences making comparisons across studies and syndromes difficult. This study aimed to compare directly facial emotion recognition skills in children with fragile X syndrome (FXS), Down's syndrome (DS) and non‐specific intellectual disability (NSID), contrasting ability and error profiles with those of typically developing (TD) children of equivalent cognitive and linguistic status.Methods  Sixty children participated in the study: 15 FXS, 15 DS, 15 NSID and 15 TD children. Standardised measures of cognitive, language and socialisation skills were collected for all children, along with measures of performance on two photo‐matching tasks: an ‘identity‐matching’ task (to control for basic face‐processing ability) and an ‘emotion‐matching’ task (happiness, sadness, anger, surprise, fear or disgust).Results  Identity‐matching ability did not differ across the four child groups. Only the DS group performed significantly more poorly on the emotion‐matching task and only in comparison to the TD group, with fear recognition an area of particular difficulty.Conclusion  Findings support previous evidence of emotion recognition abilities commensurate with overall developmental level in children with FXS or NSID, but not DS. They also suggest, however, that syndrome‐specific difficulties may be subtle and detectable, at least in smaller‐scale studies, only in comparison with TD matches, and not always across syndromes. Implications for behavioural phenotype theory, educational interventions and future research are discussed.
TUP1 disruption in Cryptococcus neoformans uncovers a peptide‐mediated density‐dependent growth phenomenon that mimics quorum sensing
Authors: Lee Hyeseung , Chang Yun C. , Nardone Glenn , Kwon‐Chung Kyung J. 
Published: May 2007

Summary Cryptococcus neoformans is a pathogenic yeast that causes life‐threatening meningoencephalitis and grows well on mycological media regardless of inoculum size. Interestingly, a deletion of the global repressor TUP1 in C. neoformans uncovered a density‐dependent growth phenotype reminiscent of the quorum‐sensing phenomenon. An inoculum size of lower than 103 cells of the tup1Δ strain failed to form colonies on agar media while inocula of 105−106 cells per plate formed a lawn. This phenotype, expressed as the inability to grow at low cell densities, was rescued by the culture filtrate from a high cell density tup1Δ culture and the active molecule in this culture filtrate was identified to be an oligopeptide composed of 11 amino acids. Activity assays, using a synthetic version of the peptide with strains harbouring a deletion of the corresponding gene, proved that the oligopeptide functioned as an autoregulatory molecule responsible for the density‐dependent phenotype. Although a density‐dependent growth phenotype has been reported in several species of Ascomycetes, no peptide has been reported to function as an autoregulator in the Kingdom Fungi. The identification of an 11‐mer peptide as an autoregulatory molecule in C. neoformans suggests that a diverse mechanism of cell‐to‐cell communication exists in the Kingdom Fungi.
SapB and the chaplins: connections between morphogenetic proteins in Streptomyces coelicolor
Authors: Capstick David S. , Willey Joanne M. , Buttner Mark J. , Elliot Marie A. 
Published: May 2007

SummaryMorphogenesis in the streptomycetes features the differentiation of substrate‐associated vegetative hyphae into upwardly growing aerial filaments. This transition requires the activity of bld genes and the secretion of biosurfactants that reduce the surface tension at the colony–air interface enabling the emergence of nascent aerial hyphae. Streptomyces coelicolor produces two classes of surface‐active molecules, SapB and the chaplins. While both molecules are important for aerial development, nothing is known about the functional redundancy or interaction of these surfactants apart from the observation that aerial hyphae formation can proceed via one of two pathways: a SapB‐dependent pathway when cells are grown on rich medium and a SapB‐independent pathway on poorly utilized carbon sources such as mannitol. We used mutant analysis to show that while the chaplins are important, but not required, for development on rich medium, they are essential for differentiation on MS (soy flour mannitol) medium, and the corresponding developmental defects could be suppressed by the presence of SapB. Furthermore, the chaplins are produced by conditional bld mutants during aerial hyphae formation when grown on the permissive medium, MS, suggesting that the previously uncharacterized SapB‐independent pathway is chaplin dependent. In contrast, a bld mutant blocked in aerial morphogenesis on all media makes neither SapB nor chaplins. Finally, we show that a constructed null mutant that lacks all chaplin and SapB biosynthetic genes fails to differentiate in any growth condition. We propose that the biosurfactant activities of both SapB and the chaplins are essential for normal aerial hyphae formation on rich medium, while chaplin biosynthesis and secretion alone drives aerial morphogenesis on MS medium.
Sre1p, a regulator of oxygen sensing and sterol homeostasis, is required for virulence in Cryptococcus neoformans
Authors: Chang Yun C. , Bien Clara M. , Lee Hyeseung , Espenshade Peter J. , Kwon‐Chung Kyung J. 
Published: May 2007

Summary Cryptococcus neoformans is an environmental pathogen requiring atmospheric levels of oxygen for optimal growth. Upon inhalation, C. neoformans disseminates to the brain and causes meningoencephalitis, but the mechanisms by which the pathogen adapts to the low‐oxygen environment in the brain have not been investigated. We found that SRE1, a homologue of the mammalian sterol regulatory element‐binding protein (SREBP), functions in an oxygen‐sensing pathway. Low oxygen decreased sterol synthesis in C. neoformans and triggered activation of membrane‐bound Sre1p by the cleavage‐activating protein, Scp1p. Microarray and Northern blot analysis demonstrated that under low oxygen, Sre1p activates genes required for ergosterol biosynthesis and iron uptake. Consistent with these regulatory functions, sre1Δ cells were hypersensitive to azole drugs and failed to grow under iron‐limiting conditions. Importantly, sre1Δ cells failed to produce fulminating brain infection in mice. Our in vitro data support a model in which Sre1p is activated under low oxygen leading to the upregulation of genes required for sterol biosynthesis and growth in a nutrient‐limiting environment. Animal studies confirm the importance of SRE1 for C. neoformans to adapt to the host environment and to cause fatal meningoencephalitis, thereby identifying the SREBP pathway as a therapeutic target for cryptococcosis.
A novel compartment, the ‘subapical stem’ of the aerial hyphae, is the location of a sigN‐dependent, developmentally distinct transcription in Streptomyces coelicolor
Authors: Dalton Kate A. , Thibessard Annabelle , Hunter James I. B. , Kelemen Gabriella H. 
Published: May 2007

Summary Streptomyces coelicolor has nine SigB‐like RNA polymerase sigma factors, several of them implicated in morphological differentiation and/or responses to different stresses. One of the nine, SigN, is the focus of this article. A constructed sigN null mutant was delayed in development and exhibited a bald phenotype when grown on minimal medium containing glucose as carbon source. One of two distinct sigN promoters, sigNP1, was active only during growth on solid medium, when its activation coincided with aerial hyphae formation. Transcription from sigNP1 was readily detected in several whi mutants (interrupted in morphogenesis of aerial mycelium into spores), but was absent from all bld mutants tested, suggesting that sigNP1 activity was restricted to the aerial hyphae. It also depended on sigN, thus sigN was autoregulated. Mutational and transcription studies revealed no functional significance to the location of sigN next to sigF, encoding another SigB‐like sigma factor. We identified another potential SigN target, nepA, encoding a putative small secreted protein. Transcription of nepA originated from a single, aerial hyphae‐specific and sigN‐dependent promoter. While in vitro run‐off transcription using purified SigN on the Bacillus subtilis ctc promoter confirmed that SigN is an RNA polymerase sigma factor, SigN failed to initiate transcription from sigNP1 and from the nepA promoter in vitro. Additional in vivo data indicated that further nepA upstream sequences, which are likely to bind a potential activator, are required for successful transcription. Using a nepA–egfp transcriptional fusion we located nepA transcription to a novel compartment, the ‘subapical stem’ of the aerial hyphae. We suggest that this newly recognized compartment defines an interface between the aerial and vegetative parts of the Streptomyces colony and might also be involved in communication between these two compartments.
The Pseudomonas putida Crc global regulator is an RNA binding protein that inhibits translation of the AlkS transcriptional regulator
Authors: Moreno Renata , Ruiz‐Manzano Ana , Yuste Luis , Rojo Fernando 
Published: May 2007

SummaryThe Crc protein is a global regulator that controls the hierarchical assimilation of carbon sources in Pseudomonads by inhibiting expression of several catabolic pathways. Crc does not bind DNA and its mechanism of action has remained elusive. Among other genes, Crc inhibits expression of alkS, the transcriptional activator of the Pseudomonas putida OCT plasmid alkane degradation pathway. AlkS activates expression of its own gene. In the presence of saturating AlkS levels, translational fusions of alkS to the lacZ reporter gene were responsive to Crc, but transcriptional fusions were not. In translational fusions, the first 33 nt of alkS mRNA, which includes up to position +3 relative to the translation start site, were sufficient to confer an efficient response to Crc. In vitro, purified Crc could bind specifically to an alkS mRNA fragment spanning positions +1 to +43, comprising the translation initiation region. We have previously shown that Crc has little effect on the stability of alkS mRNA. We conclude that Crc modulates AlkS levels by binding to the translation initiation region of alkS mRNA, thereby inhibiting translation. Because AlkS is an unstable protein present in limiting amounts, reducing its levels leads to decreased expression of all genes in the pathway.
The rotational dynamics of kinetoplast DNA replication
Authors: Liu Yanan , Englund Paul T. 
Published: May 2007

SummaryKinetoplast DNA (kDNA), from trypanosomatid mitochondria, is a network containing several thousand catenated minicircles that is condensed into a disk‐shaped structure in vivo. kDNA synthesis involves release of individual minicircles from the network, replication of the free minicircles and reattachment of progeny at two sites on the network periphery ∼180° apart. In Crithidia fasciculata, rotation of the kDNA disk relative to the antipodal attachment sites results in distribution of progeny minicircles in a ring around the network periphery. In contrast, Trypanosoma brucei progeny minicircles accumulate on opposite ends of the kDNA disk, a pattern that did not suggest kinetoplast motion. Thus, there seemed to be two distinct replication mechanisms. Based on fluorescence microscopy of the kDNA network undergoing replication, we now report that the T. brucei kinetoplast does move relative to the antipodal sites. Whereas the C. fasciculata kinetoplast rotates, that from T. brucei oscillates. Kinetoplast motion of either type must facilitate orderly replication of this incredibly complex structure.