bluuebunny/crossref_metadata_2025_split huggingface dataset:
Impacts of rain forest fragmentation on butterflies in northern Borneo: species richness, turnover and the value of small fragments
Authors: BENEDICK S. , HILL J. K. , MUSTAFFA N. , CHEY V. K. , MARYATI M. , SEARLE J. B. , SCHILTHUIZEN M. , HAMER K. C. 
Published: August 2006

SummaryWidespread and rapid losses of tropical rain forests have made understanding the responses of species to rain forest fragmentation an area of major concern. In this study we examined the impacts of habitat fragmentation on the species richness and faunal composition of butterflies in tropical rain forests in Sabah, Borneo. We analysed patterns of both α‐ and β‐diversity to assess the relative importance of differences in patch size, isolation and vegetation structure on the diversity and similarity of species assemblages. We used additive partitioning to assess the relative contributions of intact forest and forest remnants to overall species richness at a landscape scale and we examined which traits of species best predicted their responses to fragmentation.Species richness and diversity in rain forest remnants was significantly positively related to remnant size and significantly negatively related to isolation, in keeping with theories of island biogeography. Species assemblages at different sites were significantly nested, with those species most adversely affected by forest fragmentation having a narrow range of larval host‐plants and, to a lesser extent, being large‐bodied. No species endemic to Borneo was recorded in forest remnants smaller than 4000 ha, but even the smallest remnant (120 ha) supported species with geographical distributions confined within Sundaland (West Malaysia and the islands of the Sunda Shelf).Although assemblages were significantly nested, they departed substantially from perfect nestedness, with some species recorded only or predominantly in small, relatively depauperate remnants. As a result there was substantial β‐diversity among sites, which was related to variation in both fragment size and vegetation structure. At the landscape scale, diversity within sites was less than that between sites, and the majority of the diversity between sites was related to variation in fragment size.Synthesis and applications. Substantial diversity was added to the assemblage of butterflies in Bornean rain forests by virtue of species differences among fragments, which were related mainly to differences in patch size and vegetation structure. The data reported indicate that, despite having lower species richness, relatively small and isolated remnants of rain forest make a substantial contribution to regional diversity. Small isolated forest remnants are generally accorded low conservation status and given little protection, with the result that they often disappear over time because of continued anthropogenic disturbance. The results of this study indicate that the conservation value of small remnants of forest, in particular their contribution to environmental heterogeneity, should not be overlooked.
Using the stable isotope marker 44Ca to study dispersal and host‐foraging activity in parasitoids
Authors: WANNER HEIKE , GU HAINAN , HATTENDORF BODO , GÜNTHER DETLEF , DORN SILVIA 
Published: August 2006

Summary

Dispersal and host‐foraging activity are important behavioural characteristics for parasitoid species used as biological control agents. Appropriate marking techniques are often needed for field investigations into these behaviours because of the small size of parasitoids. This study developed a novel technique using the rare stable calcium isotope 44Ca to mark parasitoids.
As demonstrated with a tri‐trophic model system consisting of cabbage plant Brassica oleracea, caterpillar Pieris brassicae and gregarious parasitoid Cotesia glomerata, marking parasitoids with the isotope 44Ca is systemic and non‐disruptive. Significant uptake and translocation of 44Ca occurred in cabbage plants after being drenched with 50 mMol aqueous isotope solution, and the isotope was transferred to wasps emerging from the parasitized host caterpillars that fed on the isotope‐enriched plant. The isotope enrichment did not adversely influence the survivorship of hosts or the development of parasitoids.
The 44Ca‐enriched female wasps could pass the isotope marker further via oviposition into the parasitized host caterpillars, hence allowing the marker to be transferred across parasitoid generations. Greenhouse release experiments validated the transferability of 44Ca from the enriched wasps to hosts through parasitism. The 95% upper confidence limit for the mean 44Ca/40Ca isotope ratio in the hosts without 44Ca enrichment (control) could be used as a statistical marking criterion to identify reliably the individual parasitized hosts within the first 3 days of parasitism.
Synthesis and applications. We have, for the first time, documented the efficient transfer of a stable isotope marker from enriched parasitoids to host insects through parasitism. This isotope technique enables the study of dispersal and host‐foraging activity of parasitoids in the field without having to recapture marked individual parasitoids. Information on the dispersal pattern and host‐foraging activity of the parasitoid species concerned is obtained from the spatial distribution of the parasitized marked host insects. Furthermore, this isotope technique can be used to quantify the efficacy of parasitism by the parasitoids released in the field.
Beyond control: wider implications for the management of biological invasions
Authors: HULME PHILIP E. 
Published: August 2006

Summary

Government departments, environmental managers and conservationists are all facing escalating pressure to address and resolve a diversity of invasive alien species (IAS) problems. Yet much research to date is primarily concerned with quantifying the scale of the problem rather than delivering robust solutions and has not adequately addressed all stages of the invasion process, and only a few studies embrace the ecosystem approach.
Three successive steps, prevention, eradication and control, form the cornerstones of recommended best practices aimed at managing IAS. The goal of such actions is the restoration of ecosystems to preserve or re‐establish native biodiversity and functions.
Prevention is widely promoted as being a more environmentally desirable strategy than actions undertaken after IAS establishment, yet is hindered by the difficulty in separating invasive from non‐invasive alien species. Furthermore, the high number of candidate IAS, the investment required in taxonomic support and inspection capacity, and the expense of individual risk assessments may act against the net benefits of prevention. More rewarding avenues may be found by pursuing neural networks to predict the potential composition of pest assemblages in different regions and/or model introduction pathways to identify likely invasion hubs.
Rapid response should be consequent on early detection but, when IAS are rare, detection rates are compromised by low occurrence and limited power to discern significant changes in abundance. Power could be increased by developing composite indicators that track trends in a suite of IAS with similar life histories, shared pathways and/or habitat preferences.
The assessment of management options will benefit from an ecosystem perspective that considers the manipulation of native competitors, consumers and mutualists, and reviews existing management practices as well as mitigates other environmental pressures. The ease with which an IAS can be targeted should not only address the direct management effects on population dynamics but also indirect effects on community diversity and structure. Where the goal is to safeguard native biodiversity, such activities should take into account the need to re‐establish native species and/or restore ecosystem function in the previously affected area.
Synthesis and applications. A comprehensive approach to IAS management should include consideration of the: (i) expected impacts; (ii) technical options available; (iii) ease with which the species can be targeted; (iv) risks associated with management; (v) likelihood of success; and (vi) extent of public concern and stakeholder interest. For each of these issues, in addition to targeting an individual species, the management of biological invasions must also incorporate an appreciation of other environmental pressures, the importance of landscape structure, and the role of existing management activities and restoration efforts.
What controls the population dynamics of the invasive thistle Carduus nutans in its native range?
Authors: JONGEJANS EELKE , SHEPPARD ANDY W. , SHEA KATRIONA 
Published: August 2006

Summary

The invasive thistle Carduus nutans causes major economic losses in the Americas, Australia and New Zealand. For the first time, we have modelled its population dynamics in its native range, Eurasia, where it rarely reaches problematic densities, in order to identify ways to improve management strategies for this weed in the invaded range.
In particular, we investigated whether specialist enemies in the thistle's native range suppress thistle populations, as predicted by the enemy‐release hypothesis, and, if so, how this effect relates to other factors that may limit population growth.
We constructed population transition matrix models with data from three French populations. A vital rate elasticity analysis revealed that reproduction determines between 33% and 61% of the projected growth rate of the populations, and thus is a key driver of the population dynamics of this monocarpic short‐lived perennial.
Decreases in population size were predicted by the models for all three populations (λ < 1). Using limiting factor omission analyses, we showed that the suite of native insect herbivores causing seed losses had a larger impact than the joint effects of rosette damage by sheep and summer drought acting on seedling establishment. Removal of insect herbivores increased the native population growth rate by 166% on average; removal of sheep damage and summer drought from the model increased population growth by 51%. Specialist herbivores and drought interacted synergistically to affect reproduction.
Synthesis and applications. We show that vital rate elasticity analysis provides more management information than elasticity analysis on the level of matrix elements, particularly when management options affect only certain vital rates. For example, it can be used to make predictions about the effectiveness of predispersal floral herbivores in control management. The model can also help identify ways in which biocontrol can be augmented using integrated weed management that reduces seedling establishment probabilities, for example by preventing overgrazing. This method illustrates how native range studies of invasive species can be used to generate insights into managing populations in the invaded range.
Secondary metabolic gene cluster silencing in Aspergillus nidulans
Authors: Bok Jin Woo , Noordermeer Daan , Kale Shubha P. , Keller Nancy P. 
Published: August 2006

SummaryIn contrast to most primary metabolism genes, the genes involved in secondary metabolism and certain nutrient utilization pathways are clustered in fungi. Recently a nuclear protein, LaeA, was found to be required for the transcription of several secondary metabolite gene clusters in Aspergillus nidulans. Here we show that LaeA regulation does not extend to nutrient utilization or the spoC1 sporulation clusters. One of the secondary metabolite clusters regulated by LaeA contains the positive regulatory (i.e. aflR) and biosynthetic genes required for biosynthesis of sterigmatocystin (ST), a carcinogenic toxin. Analysis of ST gene cluster expression indicates LaeA regulation of the cluster is location specific as transcription of genes bordering the ST cluster are unaffected in a ΔlaeA mutant and placement of a primary metabolic gene, argB, in the ST cluster resulted in argB silencing in the ΔlaeA background. ST cluster gene expression was remediated when an additional copy of aflR was placed outside of the cluster but not when placed in the cluster. Site‐specific mutation of an s‐adenosyl methionine (AdoMet) binding site in LaeA generated a ΔlaeA phenotype suggesting the protein to be a methyltransferase.
Eukaryotic cyclophilin as a molecular switch for effector activation
Authors: Coaker Gitta , Zhu George , Ding Zhaofeng , Van Doren Steven R. , Staskawicz Brian 
Published: August 2006

SummaryGram‐negative phytopathogenic bacteria, such as Pseudomonas syringae, deliver multiple effector proteins into plant cells during infection. It is hypothesized that certain plant and mammalian effector proteins need to traverse the type III secretion system unfolded and are delivered into host cells as inactive enzymes. We have previously identified cyclophilin as the Arabidopsis eukaryotic activator of AvrRpt2, a P. syringae effector that is a cysteine protease. Cyclophilins are general folding catalysts and possess peptidyl‐prolyl cis/trans isomerase (PPIase) activity. In this paper, we demonstrate the mechanism of AvrRpt2 activation by the Arabidopsis cyclophilin ROC1. ROC1 mutants lacking PPIase enzymatic activity were unable to activate AvrRpt2. Furthermore, nuclear magnetic resonance spectroscopy revealed a structural change in AvrRpt2 from an unfolded to a folded state in the presence of ROC1. Using in vitro binding assays, ROC1's consensus binding sequence was identified as GPxL, a motif present at four sites within AvrRpt2. The GPxL motifs are located in close proximity to AvrRpt2's catalytic triad and are required for protease activity both in vitro and in planta. These data suggest that after delivery into the plant cell during infection, cyclophilin binds AvrRpt2 at four sites and properly folds the effector protein by peptidyl‐prolyl cis/trans isomerization.
Attenuation of penicillin resistance in a peptidoglycan O‐acetyl transferase mutant of Streptococcus pneumoniae
Authors: Crisóstomo M. Inês , Vollmer Waldemar , Kharat Arun S. , Inhülsen Silja , Gehre Florian , Buckenmaier Stephan , Tomasz Alexander 
Published: August 2006

SummaryThe level of penicillin resistance in clinical isolates of Streptococcus pneumoniae depends not only on the reduced affinity of penicillin binding proteins (PBPs) but also on the functioning of enzymes that modify the stem peptide structure of cell wall precursors. We used mariner mutagenesis in search of additional genetic determinants that may further attenuate the level of penicillin resistance in the bacteria. A mariner mutant of the highly penicillin‐resistant S. pneumoniae strain Pen6 showed reduction of the penicillin minimum inhibitory concentration (MIC) from 6 to 0.75 μg ml−1. Decrease in penicillin MIC was also observed upon introduction of the mutation (named provisionally adr, for attenuator of drug resistance) into representatives of major epidemic clones of penicillin‐resistant pneumococci. Attenuation of resistance levels was specific for β‐lactams. The adr mutant has retained unchanged (low affinity) PBPs, unaltered murM gene and unchanged cell wall stem peptide composition, but the mutant became hypersensitive to exogenous lysozyme and complementation experiments showed that both phenotypes – reduced resistance and lysozyme sensitivity – were linked to the defective adr gene. DNA sequence comparison and chemical analysis of the cell wall identified adr as the structural gene of the pneumococcal peptidoglycan O‐acetylase.
The cell biology of secondary endosymbiosis – how parasites build, divide and segregate the apicoplast
Authors: Vaishnava Shipra , Striepen Boris 
Published: August 2006

SummaryProtozoan parasites of the phylum Apicomplexa harbour a chloroplast‐like organelle, the apicoplast. The biosynthetic pathways localized to this organelle are of cyanobacterial origin and therefore offer attractive targets for the development of new drugs for the treatment of malaria and toxoplasmosis. The apicoplast also provides a unique system to study the cell biology of endosymbiosis. This organelle is the product of secondary endosymbiosis, the marriage of an alga and an auxotrophic eukaryote. This origin has led to a fascinating set of novel cellular mechanisms that are clearly distinct from those employed by the plant chloroplast. Here we explore how the apicoplast interacts with its ‘host’ to secure building blocks for its biogenesis and how the organelle is divided and segregated during mitosis. Considerable advances in parasite genetics and genomics have transformed apicomplexans, long considered hard to study, into highly tractable model organisms. We discuss how these resources might be marshalled to develop a detailed mechanistic picture of apicoplast cell biology.
Comparative proteomic analysis of two Entamoeba histolytica strains with different virulence phenotypes identifies peroxiredoxin as an important component of amoebic virulence
Authors: Davis Paul H. , Zhang Xiaochun , Guo Jianhua , Townsend R. Reid , Stanley Samuel L. 
Published: August 2006

Summary Entamoeba histolytica is a protozoan intestinal parasite that causes amoebic colitis and amoebic liver abscess. To identify virulence factors of E. histolytica, we first defined the phenotypes of two E. histolytica strains, HM‐1:IMSS, the prototype virulent strain, and E. histolytica Rahman, a strain that was reportedly less virulent than HM‐1:IMSS. We found that compared with HM‐1:IMSS, Rahman has a defect in erythrophagocytosis and the ability to cause amoebic colitis in human colonic xenografts. We used differential in‐gel 2D electrophoresis to compare the proteome of Rahman and HM‐1:IMSS, and identified six proteins that were differentially expressed above a fivefold level between the two organisms. These included two proteins with antioxidative properties (peroxiredoxin and superoxide dismutase), and three proteins of unknown function, grainin 1, grainin 2 and a protein containing a LIM‐domain. Overexpression of peroxiredoxin in Rahman rendered the transgenic trophozoites more resistant to killing by H2O2 in vitro, and infection with Rahman trophozoites expressing higher levels of peroxiredoxin was associated with higher levels of intestinal inflammation in human colonic xenografts, and more severe disease based on histology. In contrast, higher levels of grainin appear to be associated with a reduced virulence phenotype, and E. histolytica HM‐1:IMSS trophozoites infecting human intestinal xenografts show marked decreases in grainin expression. Our data indicate that there are definable molecular differences between Rahman and HM‐1:IMSS that may explain the phenotypic differences, and identify peroxiredoxin as an important component of virulence in amoebic colitis.
Treatment of Chlamydia trachomatis with a small molecule inhibitor of the Yersinia type III secretion system disrupts progression of the chlamydial developmental cycle
Authors: Wolf K. , Betts H. J. , Chellas‐Géry B. , Hower S. , Linton C. N. , Fields K. A. 
Published: August 2006

SummaryThe obligate intracellular bacterium Chlamydia trachomatis possesses a biphasic developmental cycle that is manifested by differentiation of infectious, metabolically inert elementary bodies (EBs) to larger, metabolically active reticulate bodies (RBs). The cycle is completed by asynchronous differentiation of dividing RBs back to a population of dormant EBs that can initiate further rounds of infection upon lysis of the host cell. Chlamydiae express a type III secretion system (T3SS) that is presumably employed to establish and maintain the permissive intracellular niche by secretion of anti‐host proteins. We hypothesize that T3SS activity is essential for chlamydial development and pathogenesis. However, the lack of a genetic system has confounded efforts to establish any role of the T3SS. We therefore employed the small molecule Yersinia T3SS inhibitor N’‐(3,5‐dibromo‐2‐hydroxybenzylidene)‐4‐nitrobenzohydrazide, designated compound 1 (C1), to examine the interdependence of the chlamydial T3SS and development. C1 treatment inhibited C. trachomatis but not T4SS‐expressing Coxiella burnetii development in a dose‐dependent manner. Although chlamydiae remained viable and metabolically active, they failed to divide significantly and RB to EB differentiation was inhibited. These effects occurred in the absence of host cell cytotoxicity and were reversible by washing out C1. We further demonstrate that secretion of T3S substrates is perturbed in C1‐treated chlamydial cultures. We have therefore provided evidence that C1 can inhibit C. trachomatis development and T3SS activity and present a model in which progression of the C. trachomatis developmental cycle requires a fully functional T3SS.
Extensive phage dynamics in Staphylococcus aureus contributes to adaptation to the human host during infection
Authors: Goerke Christiane , Wirtz Christiane , Flückiger Ursula , Wolz Christiane 
Published: August 2006

SummaryBacteriophages serve as a driving force in microbial evolution, adaptation to new environments and the pathogenesis of human bacterial infections. In Staphylococcus aureus phages encoding immune evasion molecules (SAK, SCIN, CHIPS), which integrate specifically into the β‐haemolysin (Hlb) gene, are widely distributed. When comparing S. aureus strain collections from infectious and colonizing situations we could detect a translocation of sak‐encoding phages to atypical genomic integration sites in the bacterium only in the disease‐related isolates. Additionally, significantly more Hlb producing strains were detected in the infectious strain collection. Extensive phage dynamics (intragenomic translocation, duplication, transfer between hosts, recombination events) during infection was shown by analysing cocolonizing and consecutive isolates of patients. This activity leads to the splitting of the strain population into various subfractions exhibiting different virulence potentials (Hlb‐production and/or production of immune evasion molecules). Thus, phage‐inducing conditions and strong selection for survival of the bacterial host after phage movement are typical for the infectious situation. Further in vitro characterization of phages revealed that: (i) SAK is encoded not only on serogroup F phages showing a conserved tropism for hlb but also on serogroup B phages which always integrate in a distinct intergenic region, (ii) the level of sak transcription correlates to phage inducibility but is independent of the phage localization in the chromosome, and (iii) phages can be stabilized extra‐chromosomally during their life cycle.