bluuebunny/crossref_metadata_2025_split huggingface dataset:
Inter‐sexual combat and resource allocation into body parts in the spider, Stegodyphus lineatus
Authors: MAKLAKOV ALEXEI A. , BILDE TRINE , LUBIN YAEL 
Published: October 2006

Abstract 1. Sexual conflict, which results from the divergence of genetic interests between males and females, is predicted to affect multiple behavioural, physiological, and morphological traits.2. Sexual conflict over mating may interact with population density to produce predictable changes in resource allocation into inter‐sexual armament.3. In the spider Stegodyphus lineatus, males fight with females over re‐mating. The outcome of the fight is influenced by the cephalothorax size of the contestants. The investment in armament – the cephalothorax, may be traded‐off against investment in abdomen, which is a trait that affects survival and fecundity. Pay‐offs may depend on population density. Both sexes are expected to adjust resource allocation into different body parts accordingly.4. Males had increased cephalothorax/body size ratio in low densities where probability of finding another receptive female is low and females had increased cephalothorax/body size ratio in high densities where cumulative costs of multiple mating are high.5. The results support the theoretical conjecture that population density affects resource allocation into inter‐sexual armament and call for further research on the interaction between sexual selection and population density.
Ecological distribution and niche segregation of sibling species: the case of bean beetles, Acanthoscelides obtectus Say and A. obvelatus Bridwell
Authors: ALVAREZ NADIR , MERCIER LÉNY , HOSSAERT‐MCKEY MARTINE , CONTRERAS‐GARDUÑO JORGE , KUNSTLER GEORGES , AEBI ALEXANDRE , BENREY BETTY 
Published: October 2006

Abstract 1. Molecular techniques have greatly added to the number of known sympatric cryptic species in insects. Ecological differences between these newly distinguished species are little explored, but niches often appear to overlap strongly. These cases are good models for exploring new ideas about species coexistence and community structure.2. Acanthoscelides obtectus and A. obvelatus are two sister species of bean bruchids, which have been confused until the last decade. One important ecological difference between them has emerged, however: A. obtectus is multivoltine and now distributed worldwide, whereas A. obvelatus is univoltine and restricted to Mesoamerica. Where their ranges overlap, the two species share the same host plants and larvae can sometimes complete development in the same seed.3. The analysis of 27 622 Mexican individuals of the two species in 2001‐2002 and 2002‐2003 indicates that their niches overlap, but are differentiated with respect to altitude and the kind of beans (wild vs. domesticated). The principal patterns in their relative abundance in different habitats, and at different seasons, were constant from one year to the next.4. As sympatry of these species seems to be of recent origin, the observed niche differentiation may not have evolved in response to competition, but could instead be the consequence of physiological differences, evolved independently in each species in allopatry, that pre‐adapted them for different altitudes and kinds of resources.5. The combination of biological and historical factors thus appears to allow these two sibling species to coexist in sympatry, despite their broadly overlapping ecological niches.
Effects of organic matter and calcium on soil structural stability
Authors: Wuddivira M. N. , Camps‐Roach G. 
Published: October 2006

SummaryThe cationic bridging effect of the calcium ion (Ca2+) and the flocculating ability of clay and organic matter are crucial in the formation and stability of soil aggregates. They are therefore likely to influence the soil’s saturated hydraulic conductivity (Ks). We tested the individual effects of these factors on aggregate stability and related hydraulic properties, and studied the influence of clay mineralogy also. Samples from the surface (0–10 cm) of three contrasting soils in Trinidad were used. The soils were treated with three levels of Ca2+ and three levels of organic matter in a 3 × 3 × 3 factorial design and incubated for 14 days. Both aggregate stability and saturated hydraulic conductivity were influenced by all factor combinations. Interactions between soil type and Ca2+ revealed the importance of polyvalent cations in aggregate stability of soils with low activity minerals. The influence of organic matter varied with quantity; the more there was, the more stable the soil became, particularly in the soil containing little clay. Clay dispersion and slaking of expanding minerals occurred even with large additions of Ca2+ and organic matter, emphasizing the overall influence of mineralogy in determining the response of soils to stability treatments.
Inference about soil variability from the structure of the best wavelet packet basis
Authors: Lark R. M. 
Published: October 2006

SummaryThe plausibility of the assumption that soil variation can be treated as a realization of a random spatial process that is stationary in the variance can break down in various ways. It is possible to test the assumption using methods based on the wavelet transform. To date these approaches have been applied using the discrete wavelet transform. A drawback of this approach is that it uses a partition of the spatial frequencies represented in the data into intervals (scales) that are arbitrarily defined in advance and are not necessarily suitable for the representation of the variation of the data in question. A solution to this problem is to identify the best basis for the data from a wavelet packet library. An interesting question is whether the structure of this best basis is in itself informative about the plausibility of the stationarity assumption. In this paper, I show that this is indeed the case. The best basis for a stationary random variable from some packet library is the basis on the maximum dilation of the mother wavelet, which gives the finest resolution in the frequency domain. I propose the ratio of the entropy cost functional for this basis to that of the empirical best basis as a measure of evidence against the null hypothesis of stationarity in the variance. Critical values of this statistic may be obtained by Monte Carlo methods. I demonstrate the method using data on the clay content of soil on a transect in central England. The null hypothesis of stationarity in the variance may be rejected. Tests for the uniformity of variance can then be applied to wavelet packets in the best basis. The dominant local feature that is reflected in this behaviour is the unique pattern of variation in alluvium around a drainage channel that crosses the transect. This variation contrasts with that seen at most positions on the transect, variation that arises from a more or less regular pattern of boundaries between contrasting Jurassic strata.
Comparison of methods for estimating the spread of a non‐indigenous species
Authors: Tobin Patrick C. , Liebhold Andrew M. , Anderson Roberts E. 
Published: October 2006

AbstractAim To compare different quantitative approaches for estimating rates of spread in the exotic species gypsy moth,Lymantria disparL., using county‐level presence/absence data and spatially extensive trapping grids.Location USAMethods We used county‐level presence/absence records of the gypsy moth's distribution in the USA, which are available beginning in 1900, and extensive grids of pheromone‐baited traps, which are available in selected areas beginning in 1981. We compared a regression approach and a boundary displacement approach for estimating gypsy moth spread based on these sources of data.Results We observed relative congruence between methods and data sources in estimating overall rates of gypsy moth spread through time, and among regions.Main conclusions The ability to estimate spread in exotic invasive species is a primary concern in management programmes and one for which there is a lack of information on the reliability of methods. Also, in most invading species, there is generally a lack of data to explore methods of estimating spread. Extensive data available on gypsy moth in the USA allowed for such a comparison. We show that, even with spatially crude records of presence/absence, overall rates of spread do not differ substantially from estimates obtained from the more costly deployment of extensive trapping grids. Moreover, these methods can also be applied to the general study of species distributional changes, such as range expansion or retraction, in response to climate change or other environmental effects.
Modern pollen–vegetation relationships in subarctic southern Greenland and the interpretation of fossil pollen data from the Norselandnám
Authors: Edward Schofield J. , Edwards Kevin J. , Andy McMullen J. 
Published: October 2006

AbstractAim The objective of this paper is to explore the relationships that exist between vegetation and modern pollen rain in the open, largely treeless landscape of subarctic Greenland. The implications of these results for the interpretation of fossil pollen assemblages from the time of the Norselandnámare then examined.Location The study area is the sheep farming district of Qassiarsuk in the subarctic, subcontinental vegetational and climatic zone of southern Greenland (61° N, 45° W). Betweenc.ad1000–1500 this region was contained within the Norse Eastern Settlement.Methods Detrended Correspondence Analysis (DCA) of harmonized plant–pollen data sets is used to compare plant cover in 64 vegetation quadrats with pollen assemblages obtained from moss polsters at matching locations. Presence/absence data are also used to calculate indices of association, over‐ and under‐representation for pollen types.Results Good correspondence between paired vegetation–pollen samples occurs in many cases, particularly in locations whereSalix glauca–Betula glandulosadwarf shrub heath is dominant, and across herbaceous field boundaries and meadows. Pollen samples are found to be poor at reflecting actual ground cover where ericales orJuniperus communisare the locally dominant shrubs. Dominant or ubiquitous taxa within this landscape (Betula,Salixand Poaceae) are found to be over‐represented in pollen assemblages, as are several of the ‘weeds’ generally accepted as introduced by the Norse settlers.Main conclusions Due to their over‐representation in the pollen rain, many of the Norse apophytes and introductions (e.g.Rumex acetosaandR. acetosella) traditionally used to infer human activity in Greenland should be particularly sensitive indicators forlandnám, allowing early detection of Norse activity in fossil assemblages. Pteridophyte spores are found to be disassociated with the ground cover of ferns and clubmosses, but are over‐represented in pollen assemblages, indicating extra‐local or regional sources and long residence times in soil/sediment profiles for these microfossils. A pollen record forHordeum‐type registered in close proximity to a field containing barley suggests that summer temperatures under the current climatic regime are, at least on occasion, sufficient to allow flowering.
Neisseria gonorrhoeae requires expression of TonB and the putative transporter TdfF to replicate within cervical epithelial cells
Authors: Hagen Tracey A. , Cornelissen Cynthia Nau 
Published: October 2006

Summary Neisseria gonorrhoeae has evolved a repertoire of iron acquisition systems that facilitate essential iron uptake in the human host. Acquisition of iron requires both the energy‐harnessing cytoplasmic membrane protein, TonB, as well as specific outer membrane TonB‐dependent transporters (TdTs.) Survival within host epithelial cells is important to the pathogenesis of gonococcal disease and may contribute to the persistence of infection. However, the mechanisms by which gonococci acquire iron within this intracellular niche are not currently understood. In this study, we investigated the survival of gonococcal strain FA1090 within ME180 human cervical epithelial cells with respect to high affinity iron acquisition. Intracellular survival was dependent upon iron supplied by the host cell. TonB was expressed in the host cell environment and this protein was critical to gonococcal intracellular survival. Furthermore, expression of the characterized outer membrane transporters TbpA, FetA and LbpA and putative transporters TdfG, TdfH and TdfJ were not necessary for intracellular survival. Conversely, intracellular survival was dependent on expression of the putative transporter, TdfF. Expression of TdfF was detected in the presence of epithelial cell culture media containing fetal bovine serum. Expression was further modulated by iron availability. To our knowledge, this study is the first to demonstrate the specific requirement for a single iron transporter in the survival of a bacterial pathogen within host epithelial cells.
Functional studies of the Ssk1p response regulator protein of Candida albicans as determined by phenotypic analysis of receiver domain point mutants
Authors: Menon Veena , Li Dongmei , Chauhan Neeraj , Rajnarayanan Rajendram , Dubrovska Alla , West Ann H. , Calderone Richard 
Published: October 2006

SummaryThe Candida albicans response regulator protein Ssk1p regulates oxidant adaptation through the MAPK HOG1 pathway. Deletion mutants lacking SSK1 are oxidant sensitive in vitro and are killed more than wild‐type (WT) cells by human neutrophils. Furthermore, the mutants are avirulent in an invasive murine model, and unable to adhere to human esophageal cells. Transcriptional profiling has indicated that approximately 25% of all changes occur in genes encoding cell wall and stress adaptation functions. In this study, we have investigated the role of amino acid residues in the Ssk1p receiver (or regulatory) domain by constructing point mutants at positions D556 (putative site of protein phosphorylation) and D513 (putative role in divalent metal binding, phosphorylation and conformational switching). For each point mutant, their sensitivity to a variety of oxidant stress conditions was assessed and correlated with in vitro phosphorylation of each Ssk1p receiver domain, phosphorylation of the Hog1p MAP kinase, and translocation to the nucleus. We show that a D556N mutant is sensitive to 5 mM H2O2 or t‐butyl hydroperoxide, similar to a gene knock‐out ssk1 mutant, even though Hog1p is phosphorylated in the D556N mutant. To resolve this apparent paradox, we also demonstrate that Hog1p translocation to the nucleus in the D556N mutant is significantly reduced compared with WT cells (CAF2‐1). In a second point mutant, D513 was changed to a lysine residue (D513K). This mutant had WT levels of resistance to peroxide, but in comparison to WT cells and the D556N mutant, morphogenesis (yeast to hyphae transition) was inhibited in 10% serum or in M‐199 medium at 37°C. In the D513K point mutant, constitutive phosphorylation of Hog1p was observed, suggesting that a non‐conservative change (D513K) traps Ssk1p in an active conformation and therefore constitutive Hog1p phosphorylation. The inhibition of morphogenesis in D513K is related to a downregulation of the transcription factors of morphogenesis, EFG1 and CPH1. Another non‐conserved point mutant (D556R) was also constructed and phenotypically was like the D513K mutant. The receiver domains of the D556N and the D513K mutants could not be appreciably phosphorylated in vitro indicating that constitutive activation of Hog1p occurs in vivo due to the inability of Ssk1p to be phosphorylated at least in the D513K mutant. We speculate that the non‐conservative changes described above in Ssk1p response regulator may cause conformational changes in the Ssk1p that account for phenotype differences compared with the D556N mutant that are also Hog‐independent.
Acyl carrier protein/SpoT interaction, the switch linking SpoT‐dependent stress response to fatty acid metabolism
Authors: Battesti Aurélia , Bouveret Emmanuelle 
Published: October 2006

SummaryBacteria respond to nutritional stresses by producing an intracellular alarmone, guanosine 5′‐(tri)diphosphate, 3′‐diphosphate [(p)ppGpp], which triggers the stringent response resulting in growth arrest and expression of resistance genes. In Escherichia coli, upon fatty acid or carbon starvation, SpoT enzyme activity switches from (p)ppGpp degradation to (p)ppGpp synthesis, but the signal and mechanism for this response remain totally unknown. Here, we characterize for the first time a physical interaction between SpoT and acyl carrier protein (ACP) using affinity co‐purifications and two‐hybrid in E. coli. ACP, as a central cofactor in fatty acid synthesis, may be an ideal candidate as a mediator signalling starvation to SpoT. Accordingly, we show that the ACP/SpoT interaction is specific of SpoT and ACP functions because ACP does not interact with the homologous RelA protein and because SpoT does not interact with a non‐functional ACP. Using truncated SpoT fusion proteins, we demonstrate further that ACP binds the central TGS domain of SpoT, consistent with a role in regulation. The behaviours of SpoT point mutants that do not interact with ACP reveal modifications of the balance between the two opposite SpoT catalytic activities thereby changing (p)ppGpp levels. More importantly, these mutants fail to trigger (p)ppGpp accumulation in response to fatty acid synthesis inhibition, supporting the hypothesis that the ACP/SpoT interaction may be involved in SpoT‐dependent stress response. This leads us to propose a model in which ACP carries information describing the status of cellular fatty acid metabolism, which in turn can trigger the conformational switch in SpoT leading to (p)ppGpp accumulation.
The causes and consequences of variation in offspring size: a case study usingDaphnia
Authors: GUINNEE M. A. , GARDNER A. , HOWARD A. E. , WEST S. A. , LITTLE T. J. 
Published: October 2006

AbstractOffspring size can have large and direct fitness implications, but we still do not have a complete understanding of what causes offspring size to vary.Daphnia(water fleas) generally produce fewer and larger offspring when food is limited. Here, we use a mathematical model to show that this could be explained by either: (1) an advantage of producing larger eggs when food is limited; or (2) a lower boundary on egg volume (below which eggs do not have sufficient resources to be viable), that is similar in volume to the evolutionarily stable egg volume predicted by standard clutch size models. We tested the first possibilities experimentally by placing offspring from mothers kept at two food treatments (high and low – leading to relatively small and large eggs respectively) into two food treatments (same as maternal treatments, in a fully factorial design) and measuring their fitness (reproduction, age at maturity, and size at maturity). We also tested survival under starvation conditions of offspring produced from mothers at low and high food treatments. We found that (larger) offspring produced by low‐food mothers actually had lower fitness as they took longer to reproduce, regardless of their current food treatment. Additionally, we found no survival advantage to being born of a food‐stressed mother. Consequently, our results do not support the hypothesis that there is an advantage to producing larger eggs when food is limited. In contrast, data from the literature support the importance of a lower boundary on egg size.
Brain‐derived neurotrophic factor (BDNF) is required for the enhancement of hippocampal neurogenesis following environmental enrichment
Authors: Rossi Chiara , Angelucci Andrea , Costantin Laura , Braschi Chiara , Mazzantini Mario , Babbini Francesco , Fabbri Maria Elena , Tessarollo Lino , Maffei Lamberto , Berardi Nicoletta , Caleo Matteo 
Published: October 2006

AbstractNeurogenesis continues to occur in the adult mammalian hippocampus and is regulated by both genetic and environmental factors. It is known that exposure to an enriched environment enhances the number of newly generated neurons in the dentate gyrus. However, the mechanisms by which enriched housing produces these effects are poorly understood. To test a role for neurotrophins, we used heterozygous knockout mice for brain‐derived neurotrophic factor (BDNF+/–) and mice lacking neurotrophin‐4 (NT‐4–/–) together with their wild‐type littermates. Mice were either reared in standard laboratory conditions or placed in an enriched environment for 8 weeks. Animals received injections of the mitotic marker bromodeoxyuridine (BrdU) to label newborn cells. Enriched wild‐type and enriched NT‐4–/– mice showed a two‐fold increase in hippocampal neurogenesis as assessed by stereological counting of BrdU‐positive cells in the dentate gyrus and double labelling for BrdU and the neuronal marker NeuN. Remarkably, this enhancement of hippocampal neurogenesis was not seen in enriched BDNF+/– mice. Failure to up‐regulate BDNF accompanied the lack of a neurogenic response in enriched BDNF heterozygous mice. We conclude that BDNF but not NT‐4 is required for the environmental induction of neurogenesis.
Mechanisms involved in modulation of trigeminal primary afferent activity in rats with peripheral mononeuropathy
Authors: Kitagawa Junichi , Takeda Mamoru , Suzuki Ikuko , Kadoi Jun , Tsuboi Yoshiyuki , Honda Kuniya , Matsumoto Shigeji , Nakagawa Hiroshi , Tanabe Aya , Iwata Koichi 
Published: October 2006

AbstractIn order to clarify the mechanisms underlying the changes in primary afferent neurons in trigeminal neuropathic pain, a chronic constriction nerve injury model of the infraorbital nerve (ION‐CCI) was developed in rats. Mechanical allodynia was observed at 3 days after ION‐CCI and lasted more than 14 days. Single‐unit activities were recorded from the ION of anesthetized rats. C‐, Aβ‐ and Aδ‐units were identified on the basis of their conduction velocity. Aδ‐units were frequently encountered at a later period after ION‐CCI. The highest Aδ‐spontaneous activity was recorded at 3 days after ION‐CCI and progressively decreased after that, but spontaneous activity was still higher at 14 days after ION‐CCI than that of naïve rats. Mechanical‐evoked responses of Aδ‐units were also highest at 3 days after ION‐CCI and then gradually decreased. In consideration of these data, patch‐clamp recordings were performed on medium to large size neurons of the dissociated trigeminal ganglion (TRG). Patch‐clamp recordings revealed that the IK (sustained) and IA (transient) in rats with ION‐CCI were significantly smaller than those of naïve rats, and correlated with an increase in duration of repolarization phase and a decrease in duration of depolarization phase, respectively. The hyperpolarization‐activated current (Ih) was significantly larger in TRG neurons of rats with ION‐CCI as compared with those of naïve rats. The present results suggest that Ih, IK and IA in Aδ‐afferent neurons in TRG are significantly involved in the changes in afferent spontaneous activity and mechanically evoked activity that accompany mechanical allodynia produced by trigeminal nerve injury.