bluuebunny/crossref_metadata_2025_split huggingface dataset:
Successional dynamics of woody seedling communities in wet tropical secondary forests
Authors: CAPERS ROBERT S. , CHAZDON ROBIN L. , BRENES ALVARO REDONDO , ALVARADO BRAULIO VILCHEZ 
Published: August 2005

Summary

Chronosequence studies have found that shrubs and lianas are generally more abundant in early stages of tropical forest succession, whereas canopy trees and palms become more abundant and species‐rich in older stages and mature forests.
We analysed changes in woody seedling communities over 5 years in four second‐growth forests (initially 13–26 years after pasture abandonment) in Costa Rica. We recorded community‐level changes in woody seedling density, species density, species richness and composition in six woody life‐forms: canopy trees, subcanopy trees, canopy palms, understorey palms, shrubs and lianas. We evaluated these changes in relation to annualized recruitment and mortality rates for each life‐form.
Seedling density declined in all four sites over the 5 years, whereas Shannon diversity and the proportion of rare species increased. Species richness and evenness increased in all but the oldest site.
Canopy palm, understorey palm and canopy tree seedlings increased in species richness and relative abundance, whereas shrub and liana relative abundance declined. Canopy trees accounted for 34–42% of all new recruits. Detrended correspondence analysis showed that species composition was initially highly distinct within each forest site and remained distinct over the 5‐year period.
Shifts in life‐form were correlated with declining light availability during succession. Across sites, median light availability at the end of the study period in 2003 was positively correlated with recruitment rates of understorey palms, shrubs and lianas, and was negatively correlated with mortality rates of canopy trees and palms.
Observed changes among seedling communities mirrored those described in chronosequence studies on plants in larger size classes, lending support to the assumptions of chronosequence studies in Neotropical forests.
The results demonstrate the importance of seedling recruitment and mortality in determining the course of succession. Convergence occurs in some community properties, such as relative abundance within life‐forms, but not in others, such as species composition. Finally, the results illustrate the value of studying plant community dynamics at the level of woody life‐forms, especially in hyperdiverse systems such as tropical forests.
Experimental invasion by legumes reveals non‐random assembly rules in grassland communities
Authors: TURNBULL LINDSAY A. , RAHM SABINE , BAUDOIS OKSANA , EICHENBERGER‐GLINZ SUSANN , WACKER LUCA , SCHMID BERNHARD 
Published: August 2005

Summary

Although experimental studies usually reveal that resistance to invasion increases with species diversity, observational studies sometimes show the opposite trend. The higher resistance of diverse plots to invasion may be partly due to the increased probability of a plot containing a species with similar resource requirements to the invader.
We conducted a study of the invasibility of monocultures belonging to three different functional groups by seven sown species of legume. By only using experimentally established monocultures, rather than manipulating the abundance of particular functional groups, we removed both species diversity and differences in underlying abiotic conditions as potentially confounding variables.
We found that legume monocultures were more resistant than monocultures of grasses or non‐leguminous forbs to invasion by sown legumes but not to invasion by other unsown species. The functional group effect remained after controlling for differences in total biomass and the average height of the above‐ground biomass.
The relative success of legume species and types also varied with monoculture characteristics. The proportional biomass of climbing legumes increased strongly with biomass height in non‐leguminous forb monocultures, while it declined with biomass height in grass monocultures. Trifolium pratense was the most successful invader in grass monocultures, while Vicia cracca was the most successful in non‐leguminous forb monocultures.
Our results suggest that non‐random assembly rules operate in grassland communities both between and within functional groups. Legume invaders found it much more difficult to invade legume plots, while grass and non‐leguminous forb plots favoured non‐climbing and climbing legumes, respectively. If plots mimic monospecific patches, the effect of these assembly rules in diverse communities might depend upon the patch structure of diverse communities. This dependency on patch structure may contribute to differences in results of research from experimental vs. natural communities.
Lipopolysaccharide Increases γ‐Aminobutyric Acid Synthesis in Medial Preoptic Neurones in Association with Inhibition of Steroid‐Induced Luteinising Hormone Surge in Female Rats
Authors: Akema T. , He D. , Sugiyama H. 
Published: September 2005

AbstractLipopolysaccharide (LPS), an endotoxin produced by Gram‐negative bacteria, inhibits gonadotrophin secretion and ovulation in female mammals. The present study was undertaken to examine whether γ‐aminobutyric acid (GABA)‐synthesising neurones in the medial preoptic area (mPOA) may be involved in the inhibition by LPS of progesterone‐induced luteinising hormone (LH) surge in ovariectomised oestrogen‐primed rats. An intravenous injection of LPS (10 µg) at noon significantly increased the content of glutamic acid decarboxylase 67 (GAD67), a GABA‐synthesising enzyme, in brain tissues including the mPOA. LPS treatment also significantly increased the number of detectable GAD67‐immunoreactive (ir) as well as GABA‐ir cells in the mPOA, compared to control rats. The same LPS challenge completely eliminated the steroid‐induced LH surge, which was normally induced in control rats in the afternoon. A local injection of muscimol (100 ng), a GABAA receptor agonist, into the mPOA also significantly attenuated the LH surge, mimicking the effect of LPS. These results suggest that LPS stimulates GABA synthesis in preoptic neurones, which in turn inhibit the LH surge in female rats. The results also support the hypothesis that diminution of the GABAergic suppressive activity in the mPOA permits the LH surge to be induced.
Importance of genetic drift during Pleistocene divergence as revealed by analyses of genomic variation
Authors: KNOWLES L. LACEY , RICHARDS CORINNE L. 
Published: September 2005

AbstractDetermining what factors affect the structuring of genetic variation is key to deciphering the relative roles of different evolutionary processes in species differentiation. Such information is especially critical to understanding how the frequent shifts and fragmentation of species distributions during the Pleistocene translates into species differences, and why the effect of such rapid climate change on patterns of species diversity varies among taxa. Studies of mitochondrial DNA (mtDNA) have detected significant population structure in many species, including those directly impacted by the glacial cycles. Yet, understanding the ultimate consequence of such structure, as it relates to how species divergence occurs, requires demonstration that such patterns are also shared with genomic patterns of differentiation. Here we present analyses of amplified fragment length polymorphisms (AFLPs) in the montane grasshopper Melanoplus oregonensis to assess the evolutionary significance of past demographic events and associated drift‐induced divergence as inferred from mtDNA. As an inhabitant of the sky islands of the northern Rocky Mountains, this species was subject to repeated and frequent shifts in species distribution in response to the many glacial cycles. Nevertheless, significant genetic structuring of M. oregonensis is evident at two different geographic and temporal scales: recent divergence associated with the recolonization of the montane meadows in individual sky islands, as well as older divergence associated with displacements into regional glacial refugia. The genomic analyses indicate that drift‐induced divergence, despite the lack of long‐standing geographic barriers, has significantly contributed to species divergence during the Pleistocene. Moreover, the finding that divergence associated with past demographic events involves the repartitioning of ancestral variation without significant reductions of genomic diversity has intriguing implications — namely, the further amplification of drift‐induced divergence by selection.
Introgression in natural populations of bioindicators: a case study of Carabus splendens and Carabus punctatoauratus
Authors: STREIFF R. , VEYRIER R. , AUDIOT P. , MEUSNIER S. , BROUAT C. 
Published: September 2005

AbstractThe evolutionary importance of hybridization in wild plants and animals has become increasingly widely recognized in the last decade. In practical terms, hybridization provides an exceptionally tough set of problems for conservation biologists. We illustrate this in a case study of two Carabidae species widely used to evaluate the impact of human activities on biodiversity. These two species live in a complex mosaic of sympatry/allopatry and are known to hybridize in controlled conditions. Hybridization has not been quantified in natural populations to date due to the lack of a simple set of phenotypic traits for identifying hybrids. We thus screened for hybrids in natural populations, by multilocus genotyping at nine microsatellite loci. A high level of genetic differentiation between these two taxa was observed, as shown by allelic frequency distributions. Two Bayesian assignment procedures without obligatory pure taxon references were used to infer different classes of hybrids (F1, F2 and backcrosses) and mixture proportions between the two species. A low level of hybridization (F1 genotypes) was observed in natural populations, contrasting with results obtained in controlled conditions. A high level of introgression was, however, detected at three of 12 sites, as revealed by the detection of backcrossed genotypes. This interspecific gene flow was detected in a limited zone of the common geographical range of the two species and was not related to the pattern of sympatry/allopatry. We then considered the origin and repercussions of this introgression, based on intraspecific genetic diversity and geographical structure.
A fork‐clearing role for UvrD
Authors: Florés Maria‐José , Sanchez Nicolas , Michel Bénédicte 
Published: August 2005

SummaryThe inactivation of a replication protein causes the disassembly of the replication machinery and creates a need for replication reactivation. In several replication mutants, restart occurs after the fork has been isomerized into a four‐armed junction, a reaction called replication fork reversal. The repair helicase UvrD is essential for replication fork reversal upon inactivation of the polymerase (DnaE) or the β‐clamp (DnaN) subunits of the Escherichia coli polymerase III, and for the viability of dnaEts and dnaNts mutants at semi‐permissive temperature. We show here that the inactivation of recA, recFOR, recJ or recQ recombination genes suppresses the requirement for UvrD for replication fork reversal and suppresses the lethality conferred by uvrD inactivation to Pol IIIts mutants at semi‐permissive temperature. We propose that RecA binds inappropriately to blocked replication forks in the dnaEts and dnaNts mutants in a RecQ‐ RecJ‐ RecFOR‐dependent way and that UvrD acts by removing RecA or a RecA‐made structure, allowing replication fork reversal. This work thus reveals the existence of a futile reaction of RecA binding to blocked replication forks, that requires the action of UvrD for fork‐clearing and proper replication restart.
Inferring the genetic network of m‐xylene metabolism through expression profiling of the xyl genes of Pseudomonas putida mt‐2
Authors: Velázquez Francisco , Parro Víctor , de Lorenzo Víctor 
Published: August 2005

SummaryA subgenomic array of structural and regulatory genes of the TOL plasmid pWW0 of Pseudomonas putida mt‐2 has been constructed to sort out the interplay between m‐xylene catabolism and the environmental stress brought about by this aromatic chemical. To this end, xyl sequences were spotted along with groups of selected P. putida genes, the transcription of which become descriptors of distinct physiological conditions. The expression of the TOL pathway in response to pathway substrates was thus profiled, uncovering a regulatory network that overcomes and expands the predictions made by projecting known data from individual promoters. First, post‐transcriptional checks appear to mitigate the burden caused by non‐productive induction of the TOL operons. Second, the fate of different segments of the polycistronic mRNAs from the upper and lower TOL operons varies depending on the metabolism of their inducers. Finally, m‐xylene triggers a noticeable heat shock, the onset of which does interfere with optimal expression of catabolic genes. These results reveal a degree of regulatory partnership between TOL plasmid‐encoded functions and host physiology that go beyond transcription initiation control.
Antibiotic‐induced expression of a cryptic cpb2 gene in equine β2‐toxigenic Clostridium perfringens
Authors: Vilei Edy M. , Schlatter Yvonne , Perreten Vincent , Straub Reto , Popoff Michel R. , Gibert Maryse , Gröne Andrea , Frey Joachim 
Published: August 2005

SummaryThe cpb2 gene of β2‐toxigenic Clostridium perfringens isolated from horses, cattle, sheep, human and pigs was sequenced. The cpb2 gene of equine and other non‐porcine isolates differed from porcine isolates by the absence of an adenine in a poly A tract immediately downstream of the start codon in all non‐porcine C. perfringens strains. This deletion involved formation of a cryptic gene harbouring a premature stop codon after only nine amino acid codons, while the full β2‐toxin protein consists of 265 amino acids. Immunoblots carried out with antibodies directed against a recombinant β2‐toxin showed the absence of expression of the β2‐toxin in equine and the other non‐porcine strains under standard culture conditions. However, treatment of C. perfringens with the aminoglycosides gentamicin or streptomycin was able to induce expression of the cpb2 gene in a representative equine strain of this group, presumably by frameshifting. The presence of the β2‐toxin was revealed by immunohistology in tissue samples of small and large intestine from horses with severe typhlocolitis that had been treated before with gentamicin. This result may explain the finding that antibiotic treatment of horses affected by β2‐toxigenic C. perfringens leads to a more accentuated and fatal progression of equine typhlocolitis. Clinical observations show a reduced appearance of strong typhlocolitis in horses with intestinal complications admitted to hospital care since the standard use of gentamicin has been abandoned. This is the first report on expression of a bacterial toxin gene by antibiotic‐induced ribosomal frameshifting.
The Yersinia pestis type III secretion needle plays a role in the regulation of Yop secretion
Authors: Torruellas Julie , Jackson Michael W. , Pennock Jeffry W. , Plano Gregory V. 
Published: August 2005

SummaryActivation of bacterial virulence‐associated type III secretion systems (T3SSs) requires direct contact between a bacterium and a eukaryotic cell. In Yersinia pestis, the cytosolic LcrG protein and a cytosolic YopN‐TyeA complex function to block T3S in the presence of extracellular calcium and prior to contact with a eukaryotic cell. The mechanism by which the bacterium senses extracellular calcium and/or cell contact and transmits these signals to the cytosolic compartment is unknown. We report here that YscF, a small protein that polymerizes to form the external needle of the T3SS, is essential for the calcium‐dependent regulation of T3S. Alanine‐scanning mutagenesis was used to identify YscF mutants that secrete virulence proteins in the presence and absence of calcium and prior to contact with a eukaryotic cell. Interestingly, one of the YscF mutants that exhibited constitutive T3S was unable to translocate secreted proteins across the eukaryotic plasma membrane. These data indicate that the YscF needle is a multifunctional structure that participates in virulence protein secretion, in translocation of virulence proteins across eukaryotic membranes and in the cell contact‐ and calcium‐dependent regulation of T3S.
ABC‐type neutral amino acid permease N‐I is required for optimal diazotrophic growth and is repressed in the heterocysts of Anabaena sp. strain PCC 7120
Authors: Picossi Silvia , Montesinos María Luz , Pernil Rafael , Lichtlé Christiane , Herrero Antonia , Flores Enrique 
Published: August 2005

SummaryAnabaena sp. strain PCC 7120 is a filamentous cyanobacterium that can fix N2 in differentiated cells called heterocysts. The products of Anabaena open reading frames (ORFs) all1046, all1047, all1284, alr1834 and all2912 were identified as putative elements of a neutral amino acid permease. Anabaena mutants of these ORFs were strongly affected (1–12% of the wild‐type activity) in the transport of Pro, Phe, Leu and Gly and also impaired (17–30% of the wild‐type activity) in the transport of Ala and Ser. These results identified those ORFs as the nat genes encoding the N‐I neutral amino acid permease. According to amino acid sequence homologies, natA (all1046) and natE (all2912) encode ATPases, natC (all1047) and natD (all1284) encode transmembrane proteins, and natB (alr1834) encodes a periplasmic substrate‐binding protein of an ABC‐type uptake transporter. The natA, natC, natD and natE mutants showed defects in Gln and His uptake that were not observed in the natB mutant suggesting that NatB is not a binding protein for Gln or His. The nat mutants released hydrophobic amino acids to the medium, and amino acid release took place at higher levels in cultures incubated in the absence of combined N than in the presence of nitrate. Alanine was the amino acid released at highest levels, and its release was impaired in a mutant unable to develop heterocysts. The nat mutants were also impaired in diazotrophic growth, with natA, natC, natD and natE mutants showing more severe defects than the natB mutant. Expression of natA and natC, which constitute an operon, natCA, as well as of natB was studied and found to take place in vegetative cells but not in the heterocysts. These results indicate that the N‐I permease is necessary for normal growth of Anabaena sp. strain PCC 7120 on N2, and that this permease has a role in the diazotrophic filament specifically in the vegetative cells.
Cytoplasmic degradation of ssrA‐tagged proteins
Authors: Farrell Christopher M. , Grossman Alan D. , Sauer Robert T. 
Published: August 2005

SummaryDegradation of ssrA‐tagged proteins is a central feature of protein‐quality control in all bacteria. In Escherichia coli, the ATP‐dependent ClpXP and ClpAP proteases are thought to participate in this process, but their relative contributions to degradation of ssrA‐tagged proteins in vivo have been uncertain because two adaptor proteins, ClpS and SspB, can modulate proteolysis of these substrates. Here, intracellular levels of these protease components and adaptors were determined during exponential growth and  as  cells  entered  early  stationary  phase.  Levels  of ClpA and ClpP increased about threefold during this transition, whereas ClpX, ClpS and SspB levels remained nearly constant. Using GFP‐ssrA expressed from the chromosome as a degradation reporter, the effects of altered concentrations of different protease components or adaptor proteins were explored. Both ClpXP and ClpAP degraded GFP‐ssrA in the cell, demonstrating that wild‐type levels of SspB and ClpS do not inhibit ClpAP completely. Upon entry into stationary phase, increased levels of ClpAP resulted in increased degradation of ssrA‐tagged substrates. As measured by maximum turnover rates, ClpXP degradation of GFP‐ssrA in vivo was significantly more efficient than in vitro. Surprisingly, ClpX‐dependent ClpP‐independent degradation of GFP‐ssrA was also observed. Thus, unfolding of this substrate by ClpX appears to enhance intracellular degradation by other proteases.
Immunity induced by the radiation‐attenuated schistosome vaccine
Authors: HEWITSON J. P. , HAMBLIN P. A. , MOUNTFORD A. P. 
Published: August 2005

SUMMARY As a paradigm for the development of a vaccine against human schistosomiasis, the radiation‐attenuated (RA) vaccine has enabled the dissection of different immune responses as putative effector mechanisms. This review considers advances made in the past, and updates our knowledge with reference to recent studies that have provided new information relevant particularly to the early innate events after vaccination, and to the nature of the protective effector mechanism. Priming of a protective response by RA larvae is a highly co‐ordinated series of events starting in the skin, draining lymph nodes and lungs, leading to the development of various effector responses, ranging from Th1‐associated cell‐mediated activity, to anti‐parasitic antibodies, all of which contribute to the elimination of challenge larvae to varying extents. In this respect, the RA vaccine elicits a multifaceted immune response, from which we can derive valuable insights relevant to the future design of novel delivery systems and adjuvants for recombinant and subunit vaccines.
Molluscan and vertebrate immune responses to bird schistosomes
Authors: HORÁK P. , KOLÁŘOVÁ L. 
Published: August 2005

SUMMARY There is a growing understanding of risks posed by human contact with the cercariae of bird schistosomes. In general, there are no fundamental biological differences between human and bird schistosomes in terms of their interactions with snail and vertebrate hosts. The penetration of host surfaces is accompanied by the release of penetration gland products and the shedding of highly antigenic surface components (miracidial ciliated plates and cercarial glycocalyx) which trigger host immune reactions. New surface structures are formed during transformation: the tegument of mother sporocysts and the tegumental double membrane of schistosomula. These surfaces apparently serve as protection against the host immune response. Certain parasite excretory–secretory products may contribute to immunosuppression or, on the other hand, stimulation of host immune reactions. Discovery of new species and their life cycles, the characterization of host–parasite interactions (including at the molecular level), the determination of parasite pathogenicity towards the host, the development of tools for differential diagnosis and the application of protective measures are all topical research streams of the future. Regularly updated information on bird schistosomes and cercarial dermatitis can be found at http://www.schistosomes.cz (web pages of Schistosome Group Prague).
Immunology of human schistosomiasis: off the beaten path
Authors: SECOR W. E. 
Published: August 2005

SUMMARY Reviews of the immunology of human schistosomiasis generally address the host's protective responses against infection or the factors associated with development of severe pathology. However, there is a growing recognition that the high number of patients expressing moderate morbidity, rather than the few patients with severe morbidity, accounts for the greatest public health impact of schistosomiasis. Therefore, other aspects of the host immune response that have received relatively little attention may actually provide pivotal answers in our understanding and management of the morbidity associated with human schistosomiasis. This review highlights lines of investigation that focus on how immune responses to schistosomiasis may affect schistosomiasis‐associated anaemia, alter susceptibility or disease progression during co‐infections, and influence effective execution of mass treatment programmes.