bluuebunny/crossref_metadata_2025_split huggingface dataset:
Evidence for a positive influence of fungivorous soil invertebrates on the seed bank persistence of grassland species
Authors: MITSCHUNAS NADINE , WAGNER MARKUS , FILSER JULIANE 
Published: May 2006

Summary
Seeds in soil seed banks are exposed to a number of mortality factors, including fungal attack. The composition of the soil fungal community is affected by fungus‐feeding soil invertebrates, suggesting that fungus‐feeding soil animals may affect losses of seeds caused by fungal attack. We tested this assumption with a full factorial experiment that examined the effects of fungivorous Collembola and of seed coating with a fungicide on seed longevity of four grassland plant species.
Seeds of Centaurea nigra, Dactylis glomerata, Origanum vulgare and Taraxacum officinale were kept in Petri dishes filled with soil under conditions that stimulate fungal growth but not seed germination. Treatment factors were (i) addition of the collembolan Protaphorura fimata, a soil‐dwelling fungus feeder; and (ii) seed treatment with the fungicide chitosan. After 5 weeks, germination was recorded and viability of the remaining ungerminated seeds was determined.
In three species, the addition of P. fimata resulted in an increase in the number of remaining ungerminated viable seeds. This was due to reduced seed mortality (C. nigra, O. vulgare) or to reduced germination (D. glomerata). Seeds of T. officinale remained unaffected.
For the fungicide treatment, no significant main effect was found in any species, although in two species there was a significant interaction between the addition of Collembola and seed coating with chitosan. There is circumstantial evidence that this interaction may have resulted from a negative effect of chitosan on adult survival of P. fimata.
These results show that fungus‐feeding soil invertebrates affect not only the performance of live plants, as shown in previous studies, but also the persistence of seeds in the soil, and that this effect varies between different plant species.
Our results suggest that by reducing the mortality of seeds due to fungal decay, fungal grazers may influence the dynamics of plant populations and the assembly of plant communities. Further experimentation under more realistic conditions is, however, required to investigate the importance of this process under field conditions.
Effects of habitat deterioration on population dynamics and extinction risk of an endangered, long‐lived perennial herb (Scorzonera humilis)
Authors: COLLING GUY , MATTHIES DIETHART 
Published: May 2006

Summary

Habitat deterioration has resulted in the extinction of many local populations of plants. However, in long‐lived plants there may be a time lag between habitat deterioration and a decline in population size, although some vital rates may be immediately affected.
We studied the dynamics and viability of populations of the endangered, long‐lived perennial Scorzonera humilis to different levels of agricultural intensification in five populations over a period of 4 years at the genet level and for 3 years at the rosette (ramet) level.
Asymptotic growth rates varied little between years and the observed stage structure was very similar to the stable stage structure. Mortality of adult genets of S. humilis was low and their life expectancy was several decades. By contrast, turnover of ramets was high and their life expectancy was less than 4 years.
Calculations based on mean transition matrices indicated that populations at nutrient‐poor sites would grow (λ > 1), whereas those at nutrient‐rich sites would continuously decline (λ < 1) if conditions stayed the same. Life‐table response experiment analysis revealed that the lower growth rate of nutrient‐rich populations was primarily due to a lower survival of large plants, but also due to lower establishment and growth of new plants.
Stochastic simulations indicated that the extinction risk for medium‐sized populations at nutrient‐poor sites is very low, whereas the long‐term survival even of large extant populations at nutrient‐rich sites is unlikely unless favourable conditions for the establishment of young plants are restored.
Fertilization did not influence survival, but an additional cutting early in the season significantly reduced survival of S. humilis. Stochastic simulations indicated that a combination of fertilizing and early cutting drives populations quickly to extinction and that the long‐term survival of late‐cut, NPK‐fertilized populations is also unlikely.
The results suggest that in long‐lived plants, population size may not be a suitable predictor of long‐term viability of populations because of time delays in their response to habitat deterioration. A detailed demographic analysis may therefore be necessary to assess realistically the conservation status of long‐lived perennials.
Pollen‐mediated gene dispersal within continuous and fragmented populations of a forest understorey species, Trillium cuneatum
Authors: GONZALES EVA , HAMRICK J. L. , SMOUSE P. E. , DYER R. J. 
Published: May 2006

AbstractPollen movement plays a critical role in the distribution of genetic variation within and among plant populations. Direct measures of pollen movement in the large, continuous populations that characterize many herbaceous plant species are often technically difficult and biologically unreliable. Here, we studied contemporary pollen movement in four large populations of Trillium cuneatum. Three populations, located in the Georgia Piedmont, are exposed to strong anthropogenic disturbances, while the fourth population, located in the Southern Appalachian Mountains, is relatively undisturbed. Using the recently developed TwoGener analysis, we extracted estimates of the effective number of pollen donors (Nep), effective mating neighbourhood size (Aep) and the average distance of pollen movement (δ) for each population. We extended the TwoGener method by developing inference on the paternal gametic contribution to the embryo in situations where offspring genotypes are inferred from seeds and elaiosomes of species with bisporic megagametogenesis. Our estimates indicate that maternal plants do not sample pollen randomly from a global pool; rather, pollen movement in all four populations is highly restricted. Although the effective number of pollen donors per maternal plant is low (1.22–1.66) and pollen movement is highly localized in all populations, Nep in the disturbed Piedmont populations is higher and there is more pollen movement than in the mountains. The distance pollen moves is greater in disturbed sites and fragmented populations, possibly due to edge effects in Trillium habitats.
Rangewide molecular structuring in the Utah sucker (Catostomus ardens)
Authors: MOCK K. E. , EVANS R. P. , CRAWFORD M. , CARDALL B. L. , JANECKE S. U. , MILLER M. P. 
Published: May 2006

AbstractThe Utah sucker (Catostomus ardens) is endemic to the Bonneville Basin and the upper Snake River drainage in western North America, and is thought to hybridize with the federally endangered June sucker (Chasmistes liorus mictus) in Utah Lake (Bonneville Basin). Here we describe the discovery of a major subdivision in Utah suckers (4.5% mitochondrial sequence divergence) between the ancient Snake River drainage and the Bonneville Basin. This boundary has not previously been recognized in Utah suckers based on morphologic variation, but has been recently described in two endemic cyprinids in the region. Populations in valleys east of the Wasatch Mountains in Utah clustered with the Snake River populations, suggesting that these valleys may have had an ancient hydrologic connection to the Snake River. We also found evidence of population isolation within the Bonneville Basin, corresponding to two Pleistocene sub‐basins of the ancient Lake Bonneville. In contrast, we found no molecular evidence for deep divergence between Utah suckers and June suckers in Utah Lake or for a history of hybridization between divergent lineages in that population, although we recognize that demographic events may have obscured this signal. These findings suggest that the morphological differences between Utah and June suckers in Utah Lake may be the result of strong, and relatively recent, ecological selection. In summary, morphological and molecular characters seem to vary along different axes in different portions of the range of this taxon, providing an interesting system for studying the contributions of neutral and adaptive variation to species diversity.
Evolutionary relationships of Drosophila mojavensis geographic host races and their sister species Drosophila arizonae
Authors: REED L. K. , NYBOER M. , MARKOW T. A. 
Published: May 2006

AbstractThe cactophilic Drosophila mojavensis species group living in the deserts and dry tropical forests of the southwestern United States and Mexico provides a valuable system for studies in diversification and speciation. Rigorous studies of the relationships between host races of D. mojavensis and the relationships among the members of the species group (D. mojavensis, Drosophila arizona, and Drosophila navojoa) are lacking. We used mitochondrial CO1 sequence data to address the phylogenetics and population genetics of this species group. In this study we have found that the sister species D. mojavensis and D. arizonae share no mitochondrial haplotypes and thus show no evidence for recent introgression. We estimate the divergence time between D. mojavensis and D. arizonae to be between 1.91 and 2.97 million years ago. D. arizonae shows little structure in our population genetic analyses but there is phylogenetic differentiation between southeastern and northern populations of D. arizonae. Drosophila mojavensis shows significant population and phylogenetic structure across the four geographic regions of its distribution. The mitochondrial data support an origin of D. mojavensis on the mainland with early differentiation into the populations now found in the Mojave Desert and the Mainland Sonoran Desert and later colonization of the Baja Peninsula, in contrast to previous models. Also, the sister clade to D. mojavensis/D. arizonae includes D. navojoa and Drosophila huaylasi. By defining the genetic relationships among these populations, we provide a foundation for more sophisticated hypothesis testing regarding the timing of early speciation events and host switches in this species group.
Bacteriophage WO‐B andWolbachiain natural mosquito hosts: infection incidence, transmission mode and relative density
Authors: CHAUVATCHARIN N. , AHANTARIG A. , BAIMAI V. , KITTAYAPONG P. 
Published: May 2006

AbstractBacteriophages ofWolbachiabacteria have been proposed as a potential transformation tool for genetically modifying mosquito vectors. In this study, we report the presence of the WO‐B class ofWolbachia‐associated phages among natural populations of several mosquito hosts. Eighty‐eight percent (22/25) ofWolbachia‐infected mosquito species surveyed were found to contain WO‐B phages. WO‐B phageorf7sequence analysis suggested that a single strain of WO‐B phage was found in most singly (23/24) or doubly (1/1)Wolbachia‐infected mosquitoes. However, the singleWolbachiastrain infectingAedes perplexuswas found to harbour at least two different WO‐B phages. Phylogenetic analysis suggested that horizontal transmission of WO‐B phages has occurred on an evolutionary scale between theWolbachiaresiding in mosquitoes. On an ecological scale, a low trend of co‐transmission occurred among specific WO‐B phages withinWolbachiaof each mosquito species. Assessment of the density of WO‐B phage by real‐time quantitative polymerase chain reaction (RTQ‐PCR) revealed an average relative density of 7.76 × 105± 1.61 × 105orf7copies per individual mosquito for a singleWolbachiastrain infecting mosquitoes, but a threefold higher density in the doublyWolbachia‐infectedAedes albopictus. However, the average combined density of WO‐B phage(s) did not correlate with that of theirWolbachiahosts, which varied in different mosquito species. We also confirmed the presence of WO‐B‐like virus particles in the laboratory colony ofAe. albopictus(KLPP) morphologically, by transmission electron microscopy (TEM). The viral‐like particles were detected after purification and filtration ofAe. albopictusovary extract, suggesting that at least one WO‐B‐like phage is active (temperate) within theWolbachiaof this mosquito vector. Nevertheless, the idea of utilizing these bacteriophages as transformation vectors still needs more investigation and is likely to be unfeasible.
Effects of Pleistocene glaciations on population structure of North American chestnut‐backed chickadees
Authors: BURG THERESA M. , GASTON ANTHONY J. , WINKER KEVIN , FRIESEN VICKI L. 
Published: May 2006

AbstractThe postglacial recolonization of northern North America was heavily influenced by the Pleistocene glaciation. In the Pacific Northwest, there are two disjunct regions of mesic temperate forest, one coastal and the other interior. The chestnut‐backed chickadee is one of the species associated with this distinctive ecosystem. Using seven microsatellite markers we found evidence of population structure among nine populations of chestnut‐backed chickadees. High levels of allelic variation were found in each of the populations. Northern British Columbia and central Alaska populations contained a large number of private alleles compared to other populations, including those from unglaciated regions. The disjunct population in the interior was genetically distinct from the coastal population. Genetic and historical records indicate that the interior population originated from postglacial inland dispersal. Population structuring was found within the continuous coastal population, among which the peripheral populations, specifically those on the Queen Charlotte Islands and the central Alaska mainland, were genetically distinct. The pattern of population structure among contemporary chickadee populations is consistent with a pioneer model of recolonization. The persistence of genetic structure in western North American chestnut‐backed chickadees may be aided by their sedentary behaviour, linear distribution, and dependence on cedar–hemlock forests.
Loss of both Holliday junction processing pathways is synthetically lethal in the presence of gonococcal pilin antigenic variation
Authors: Sechman Eric V. , Kline Kimberly A. , Seifert H. Steven 
Published: May 2006

SummaryThe obligate human pathogen Neisseria gonorrhoeae (Gc) has co‐opted conserved recombination pathways to achieve immune evasion by way of antigenic variation (Av). We show that both the RuvABC and RecG Holliday junction (HJ) processing pathways are required for recombinational repair, each can act during genetic transfer, and both are required for pilin Av. Analysis of double mutants shows that either the RecG or RuvAB HJ processing pathway must be functional for normal growth of Gc when RecA is expressed. HJ processing‐deficient survivors of RecA expression are enriched for non‐piliated bacteria that carry large deletions of the pilE gene. Mutations that prevent pilin variation such as recO, recQ, and a cis‐acting pilE transposon insertion all rescue the RecA‐dependent growth inhibition of a HJ processing‐deficient strain. These results show that pilin Av produces a recombination intermediate that must be processed by either one of the HJ pathways to retain viability, but requires both HJ processing pathways to yield pilin variants. The need for diversity generation through frequent recombination reactions creates a situation where the HJ processing machinery is essential for growth and presents a possible target for novel antimicrobials against gonorrhoea.
ppGpp with DksA controls gene expression in the locus of enterocyte effacement (LEE) pathogenicity island of enterohaemorrhagic Escherichia coli through activation of two virulence regulatory genes
Authors: Nakanishi Noriko , Abe Hiroyuki , Ogura Yoshitoshi , Hayashi Tetsuya , Tashiro Kosuke , Kuhara Satoru , Sugimoto Nakaba , Tobe Toru 
Published: May 2006

SummaryFor a new pathogen to emerge, it must acquire both virulence genes and a system for responding to changes in environmental conditions. Starvation of nutrients or growth arrest induces the stringent response in Escherichia coli, via increased ppGpp. We found the adherence capacity of enterohaemorrhagic E. coli (EHEC) and gene expression in the locus of enterocyte effacement (LEE) were enhanced by a downshift in nutrients or by entry into the stationary growth phase, both of which increase the ppGpp concentration. The activation was dependent on relA and spoT, which encode enzymes for the synthesis and degradation of ppGpp, and on dksA, which encodes an RNA polymerase accessory protein required for the stringent response. Upon induction of RelA expression, LEE gene transcription was activated within 20 min, even without starvation. The expression of two LEE transcriptional regulators, Ler and Pch, was activated by ppGpp and essential for the enhancement of LEE gene expression. In addition, the ler and pch promoters were directly activated by ppGpp in an in vitro transcription system. These findings suggest that the regulation of virulence genes in EHEC is integrated with E. coli's stringent response system, through the regulation of virulence regulatory genes.
Ruminal Drinkers: Endocrine and Metabolic Status and Effects of Suckling from a Nipple Instead of Drinking from a Bucket
Authors: Herrli‐Gygi M. , Hammon H. M. , Zbinden Y. , Steiner A. , Blum J. W. 
Published: May 2006

SummaryIn ruminal drinkers (RD) ingested milk is transported into the rumen and not into the abomasum. Because this is followed by changes in digestibility and absorption, we have tested whether this is associated with postprandial metabolic and endocrine changes. Unweaned, bucket‐fed calves (one RD, two controls) were studied on seven farms. On d 1, after metabolic and endocrine 12‐h profiles were studied, RD and one control calf were fed for 10 d by nipple, whereas the other control calf was fed by bucket. On d 11, metabolic and endocrine 12‐h profiles were again studied. On d 1, mean plasma concentrations of glucose, triglycerides, urea, insulin, insulin‐like growth factor‐1 (IGF‐1), 3,5,3′‐triiodothyronine (T3), thyroxine (T4) and leptin were significantly different between RD and controls, whereas mean concentrations of non‐esterified fatty acids (NEFA), total protein, albumin, and glucagon did not differ significantly among groups. In RD concentrations of glucose, NEFA, insulin, growth hormone, IGF‐1, and T4 were higher, and of urea were lower on d 11 than on d 1. Glucose and insulin concentrations increased postprandially in healthy calves on d 1, but barely in RD and remained lower than in controls, and there was no rise of NEFA and triglyceride concentrations on d 1 after the initial postprandial decrease in RD, in contrast to controls. But on d 11 postprandial responses of these four traits were similar in RD and controls and urea and T4 concentrations on d 11 became normalized. However, glucose and T3 concentrations in RD on d 11 were still lower than in one or both control groups. In conclusion, various metabolic and endocrine traits in RD differed from healthy controls. Drinking by floating nipple instead of drinking from bucket for 10 d normalized several metabolic and endocrine traits in RD.
Phenotypic and Genotypic Study of Gelatinase and β‐Haemolysis Activities in Faecal Enterococci of Poultry in Portugal
Authors: Poeta P. , Costa D. , Klibi N. , Rodrigues J. , Torres C. 
Published: May 2006

SummaryThe detection of gelatinase and β‐haemolysis activities was carried out in 83 faecal enterococci (43 Enterococcus faecalis, 33 E. faecium, five E. durans and two E. hirae) of poultry origin. In addition, the presence of genes of the gelE–fsrABC locus and of the cyl operon (cylLL, cylLS, cylA, cylB and cylM) were studied by polymerase chain reaction and correlated with gelatinase and β‐haemolysis production, respectively. Most of our E. faecalis isolates were gelatinase‐positive (88%), being this activity not frequent in the other enterococcal species (2.5%). Only one of the 33 E. faecium isolates showed a positive gelatinase reaction. All enterococci that showed gelatinase activity harboured the gelE and fsrABC genes, although these genes were also detected in four E. faecalis and one E. durans gelatinase‐negative isolates. Most of our non‐E. faecalis gelatinase‐negative isolates did not harbour gelE–fsrABC genes. A high proportion of faecal enterococci of poultry origin harboured genes of the cyl operon (71%), although only 7% contained the five cyl tested genes (all of them E. faecalis). Only one isolate of our series could express β‐haemolysis, harbouring the whole cyl operon. The cylLS genotype was the most prevalent in our enterococci (39%) and also the most prevalent among our E. faecalis isolates (60%). Other genotypes detected were the following ones (% of enterococci): cylA + cylB + cylM (13%), cylLL + cylA (4%), cylLL (4%), cylLL + cylA + cylB + cylM (2%), cylLL + cylA + cylM (1%) and cylA + cylM (1%). Both phenotypic and genotypic assays are important to evaluate the virulence potential of enterococci.
The Styrian Salmonella Monitoring Programme for Pork Production
Authors: Köfer J. , Kleb U. , Pless P. 
Published: May 2006

SummaryThe Styrian Salmonella Monitoring Programme for pork production is based on a representative analysis of the current status, serological meat juice monitoring and bacteriological tests of carcass halves and parts and has been in operation since 1999. A total of 34 170 meat juice samples from 3417 finisher herds were tested using the meat juice SALMOTYPE®‐ELISA (Labor Diagnostik, Leipzig, Germany) in the period from 1999 to 2003. More than 95% of the samples investigated were below the negative cut‐off of <20% based on the 5‐year average. The mean extinction values for meat juice samples showed regional differences, which were visualized for epidemiological purposes using the VETGIS® geographical information system (Department of Veterinary Administration, Graz, Austria). Salmonella spp. were detected in only 15 cases (0.13%) of a total of 11 330 bacteriologically tested wipe samples from meat‐processing plants. The Salmonella isolates detected included four S. Typhimurium, two S. Enteritidis PT 4, five S. Infantis, one S. Bredeny, one S. Saintpaul, one S. Brenderup and one S. Livingstone isolates. The proportion of Salmonella‐contaminated pork in the total population estimated from the annual sample showed a falling tendency. It decreased from 0.48% (CI: 0.23 ≤ P ≤ 0.85) in 1999 to 0.14% (CI: 0.07 ≤ P ≤ 0.24) in 2003. The contamination of Styrian pork with Salmonella is extremely low and thus poses a negligible risk of infection to consumers.