bluuebunny/crossref_metadata_2025_split huggingface dataset:
Evaluation of soil saturation, soil chemistry, and early spring soil and air temperatures as risk factors in yellow‐cedar decline
Authors: D'AMORE D. V. , HENNON P. E. 
Published: March 2006

AbstractYellow‐cedar (Callitropsis nootkatensis(D. Don) Oerst.) is a valuable tree species that is experiencing a widespread decline and mortality in southeast Alaska. This study evaluated the relative importance of several potential risk factors associated with yellow‐cedar decline: soil saturation, soil aluminum (Al) toxicity or calcium (Ca) deficiency, and air and soil temperature. Data were collected from permanent vegetation plots established in two low‐elevation coastal forests exhibiting broad ranges of cedar mortality. Measurements of each risk factor were contrasted among classified forest zones to indicate if there were strong links with decline. Hydrology alone is weakly associated with yellow‐cedar decline, but could have a predisposing role in the decline by creating exposed conditions because of reduced forest productivity. Yellow‐cedar decline is not strongly associated with soil pH and extractable Al and Ca, but there appears to be Ca enrichment of surface soils by feedback from dead yellow‐cedar foliage. Air and soil temperature factors are strongly associated with decline. Based on these results, an hypothesis is presented to explain the mechanism of tree injury where exposure‐driven tree mortality is initiated in gaps created by soil saturation and then expands in gaps created by the tree‐mortality itself. The exposure allows soils to warm in early spring causing premature dehardening in yellow‐cedar trees and subsequent freezing injury during cold events. Yellow‐cedars growing in the protection of shade or snow are not preconditioned by this warming, and thus not as susceptible to cold injury. Yellow‐cedar decline appears to be associated with regional climate changes, but whether the cause of these changes is related to natural or human‐induced climate shifts remains uncertain. Management implications, the possible role of climate, and recommended research are discussed.
Contrasting population changes in sympatric penguin species in association with climate warming
Authors: FORCADA JAUME , TRATHAN P. N. , REID K. , MURPHY E. J. , CROXALL J. P. 
Published: March 2006

AbstractClimate warming and associated sea ice reductions in Antarctica have modified habitat conditions for some species. These include the congeneric Adélie, chinstrap and gentoo penguins, which now demonstrate remarkable population responses to regional warming. However, inconsistencies in the direction of population changes between species at different study sites complicate the understanding of causal processes. Here, we show that at the South Orkney Islands where the three species breed sympatrically, the less ice‐adapted gentoo penguins increased significantly in numbers over the last 26 years, whereas chinstrap and Adélie penguins both declined. These trends occurred in parallel with regional long‐term warming and significant reduction in sea ice extent. Periodical warm events, with teleconnections to the tropical Pacific, caused cycles in sea ice leading to reduced prey biomass, and simultaneous interannual population decreases in the three penguin species. With the loss of sea ice, Adélie penguins were less buffered against the environment, their numbers fluctuated greatly and their population response was strong and linear. Chinstrap penguins, considered to be better adapted to ice‐free conditions, were affected by discrete events of locally increased ice cover, but showed less variable, nonlinear responses to sea ice loss. Gentoo penguins were temporarily affected by negative anomalies in regional sea ice, but persistent sea ice reductions were likely to increase their available niche, which is likely to be substantially segregated from that of their more abundant congeners. Thus, the regional consequences of global climate perturbations on the sea ice phenology affect the marine ecosystem, with repercussions for penguin food supply and competition for resources. Ultimately, variability in penguin populations with warming reflects the local balance between penguin adaptation to ice conditions and trophic‐mediated changes cascading from global climate forcing.
Canopy photosynthesis, evapotranspiration, leaf nitrogen, and transcription profiles of maize in response to CO2 enrichment
Authors: KIM SOO‐HYUNG , SICHER RICHARD C. , BAE HANHONG , GITZ DENNIS C. , BAKER JEFFREY T. , TIMLIN DENNIS J. , REDDY VANGIMALLA R. 
Published: March 2006

AbstractThe effects of CO2 enrichment on the growth and physiology of maize were investigated at the molecular, biochemical, leaf, and canopy levels. Maize plants were grown in sunlit soil–plant–atmosphere research (SPAR) chambers at ambient (370 μmol mol−1) or elevated (750 μmol mol−1) atmospheric carbon dioxide concentration (Ca) under well‐watered and fertilized conditions. Canopy gas exchange rates and leaf temperatures were monitored continuously during the growing season. CO2 enrichment did not enhance the growth or canopy photosynthesis of maize plants. However, canopy evapotranspiration rates decreased by 22% and daytime leaf temperatures were increased about 1°C in response to CO2 enrichment. Leaf carboxylation efficiency and leaf nitrogen concentration also decreased at elevated Ca. Transcription profiling using maize cDNA microarrays revealed that approximately 5% of tested genes responded to CO2 enrichment. Of the altered transcripts, several were known to encode proteins involved in stomatal development or photosynthesis. For the majority of the altered transcripts, however, it was difficult to link their functions with specific physiological factors partly because many of these genes encoded unknown proteins. We conclude that maize did not exhibit enhanced growth or photosynthesis in response to CO2 enrichment but a number of molecular and physiological processes including those involved in stomatal relations were affected by growth in elevated Ca.
Elevated CO2increases the long‐term decomposition rate ofQuercus myrtifolialeaf litter
Authors: HALL MYRA C. , STILING PETER , MOON DANIEL C. , DRAKE BERT G. , HUNTER MARK D. 
Published: March 2006

AbstractDecomposition ofQuercus myrtifolialeaf litter in a Florida scrub oak community was followed for 3 years in two separate experiments. In the first experiment, we examined the effects CO2and herbivore damage on litter quality and subsequent decomposition. Undamaged, chewed and mined litter generated under ambient and elevated (ambient+350 ppm V) CO2was allowed to decompose under ambient conditions for 3 years. Initial litter chemistry indicated that CO2levels had minor effects on litter quality. Litter damaged by leaf miners had higher initial concentrations of condensed tannins and nitrogen (N) and lower concentrations of hemicellulose and C : N ratios compared with undamaged and chewed litter. Despite variation in litter quality associated with CO2, herbivory, and their interaction, there was no subsequent effect on rates of decomposition under ambient atmospheric conditions. In the second experiment, we examined the effects of source (ambient and elevated) of litter and decomposition site (ambient and elevated) on litter decomposition and N dynamics. Litter was not separated by damage type. The litter from both elevated and ambient CO2was then decomposed in both elevated and ambient CO2chambers. Initial litter chemistry indicated that concentrations of carbon (C), hemicellulose, and lignin were higher in litter from elevated than ambient CO2chambers. Despite differences in C and fiber concentrations, litter from ambient and elevated CO2decomposed at comparable rates. However, the atmosphere in which the decomposition took place resulted in significant differences in rates of decomposition. Litter decomposing under elevated CO2decomposed more rapidly than litter under ambient CO2, and exhibited higher rates of mineral N accumulation. The results suggest that the atmospheric conditions during the decomposition process have a greater impact on rates of decomposition and N cycling than do the atmospheric conditions under which the foliage was produced.
Expression profiling and local adaptation of Boechera holboellii populations for water use efficiency across a naturally occurring water stress gradient
Authors: KNIGHT CHARLES A. , VOGEL HEIKO , KROYMANN JUERGEN , SHUMATE ALICE , WITSENBOER HANNEKE , MITCHELL‐OLDS THOMAS 
Published: March 2006

AbstractWe studied the physiological basis of local adaptation to drought in Boechera holboellii, a perennial relative of Arabidopsis thaliana, and used cDNA–AFLPs to identify candidate genes showing differential expression in these populations. We compared two populations of B. holboellii from contrasting water environments in a reciprocal transplant experiment, as well as in a laboratory dry‐down experiment. We continuously measured the water content of soils using time domain reflectometery (TDR). We compared populations for their water use efficiency (WUE), root/shoot ratios (R:S) and leaf mass per unit area (LMA) in the field and in the laboratory, and identified candidate genes that (i) responded plastically to water stress and (ii) were differentially expressed between the two populations. Genotypes from the drier site had higher WUE, which was attributable to a large reduction in transpirational water loss. The xeric‐adapted population also had increased investment in root biomass and greater leaf mass per unit area. Reciprocal transplants in the field had significantly greater survival in their native habitat. In total, 450 cDNA‐AFLP fragments showed significant changes between drought and control treatments. Furthermore, some genes showed genotype (population)‐specific patterns of up‐ or down‐regulation in response to drought. Three hundred cDNA‐AFLP bands were sequenced leading to the identification of cDNAs coding for proteins involved in signal transduction, transcriptional regulation, redox regulation, oxidative stress and pathways involved in stress adaptation. Some of these proteins could contribute a physiological advantage under drought, making them potential targets for natural selection.
Variation within and among species in gene expression: raw material for evolution
Authors: WHITEHEAD ANDREW , CRAWFORD DOUGLAS L. 
Published: March 2006

AbstractHeritable variation in regulatory or coding regions is the raw material for evolutionary processes. The advent of microarrays has recently promoted examination of the extent of variation in gene expression within and among taxa and examination of the evolutionary processes affecting variation. This review examines these issues. We find: (i) microarray‐based measures of gene expression are precise given appropriate experimental design; (ii) there is large inter‐individual variation, which is composed of a minor nongenetic component and a large heritable component; (iii) variation among populations and species appears to be affected primarily by neutral drift and stabilizing selection, and to a lesser degree by directional selection; and (iv) neutral evolutionary divergence in gene expression becomes nonlinear with greater divergence times due to functional constraint. Evolutionary analyses of gene expression reviewed here provide unique insights into partitioning of regulatory variation in nature. However, common limitations of these studies include the tendency to assume a linear relationship between expression divergence and species divergence, and failure to test explicit hypotheses that involve the ecological context of evolutionary divergence.
Parentage analysis detects cryptic precapture dispersal in a philopatric rodent
Authors: WASER PETER M. , BUSCH JOSEPH D. , McCORMICK CORY R. , DEWOODY J. ANDREW 
Published: March 2006

AbstractLocating birthplaces using genetic parentage determination can increase the precision and accuracy with which animal dispersal patterns are established. We re‐analyse patterns of movement away from the birthplace as a function of time, sex and population density for a sample of 303 banner‐tailed kangaroo rats,Dipodomys spectabilis.We located birth sites using a combination of likelihood‐based parentage analysis with live‐trapping of mothers during the breeding season. The results demonstrate that natal‐breeding site distances are density dependent in this species; in particular, both sexes emigrate earlier in the year, and females disperse farther than males, at low population densities. Banner‐tailed kangaroo rats were chosen as a study system because live‐trapping easily detects maternal and offspring locations; nevertheless, parentage analysis reveals that some offspring evade early detection and move substantial distances before their first capture. In a few cases, the approach even detects dispersal out of the natal ‘deme’ prior to first capture. Parentage analysis confirms the extreme philopatry of both sexes but indicates that prior estimates of median dispersal distance were too low. ForD. spectabilis, more accurate location of individual birthplaces clarifies patterns of sex bias and density dependence in dispersal, and may resolve apparent discrepancies between direct and indirect estimates of dispersal distance. For species in which mothers can be more reliably trapped than juveniles, using offspring genotypes to locate parents is a novel way that genetic techniques can contribute to the analysis of animal dispersal.
High genetic diversity and no inbreeding in the endangered copper redhorse,Moxostoma hubbsi(Catostomidae, Pisces): the positive sides of a long generation time
Authors: LIPPÉ CATHERINE , DUMONT PIERRE , BERNATCHEZ LOUIS 
Published: March 2006

AbstractThe evolutionary potential of a species is determined by its genetic diversity. Thus, management plans should integrate genetic concerns into active conservation efforts. The copper redhorse (Moxostoma hubbsi) is an endangered species, with an endemic distribution limited to the Richelieu River and a short section of the St Lawrence River in Quebec, Canada. The population, gradually fragmented since 1849, is characterized by a decline in population size and a lack of recruitment. A total of 269 samples were collected between 1984 and 2004 and genotyped using 22 microsatellite loci, which indicated that these fish comprise a single population, with a globalFSTvalue of only 0.0038. Despite a small census size (∼500), a high degree of genetic diversity was observed compared to common values for freshwater fishes (average number of 12.5 alleles/locus and averageHOof 0.77 ± 0.08). No difference was observed between expected and observed pairwise values of relatedness (rxy: −0.00013 ± 0.11737), suggesting an outbred population. Long‐termNewas estimated at 4476 whereas contemporaryNevalues ranged from 107 to 568, suggesting a pronounced yet gradual demographic decline of the population, as no bottleneck could be detected for the recent past. By means of simulations, we estimatedNewould need to remain at more than ∼400 to retain 90% of the genetic diversity over 100 years. Overall, these observations corroborate other recent empirical studies confirming that long generation times may act as a buffering effect contributing to a reduction in the pace of genetic diversity erosion in threatened species.
Contrasting effects of heterozygosity on survival and hookworm resistance in California sea lion pups
Authors: ACEVEDO‐WHITEHOUSE KARINA , SPRAKER TERRY R. , LYONS EUGENE , MELIN SHARON R. , GULLAND FRANCES , DELONG ROBERT L. , AMOS WILLIAM 
Published: March 2006

AbstractLow genetic heterozygosity is associated with loss of fitness in many natural populations. However, it remains unclear whether the mechanism is related to general (i.e. inbreeding) or local effects, in particular from a subset of loci lying close to genes under balancing selection. Here we analyse involving heterozygosity–fitness correlations on neonatal survival of California sea lions and on susceptibility to hookworm (Uncinaria spp.) infection, the single most important cause of pup mortality. We show that regardless of differences in hookworm burden, homozygosity is a key predictor of hookworm‐related lesions, with no single locus contributing disproportionately. Conversely, the subsequent occurrence of anaemia due to blood loss in infected pups is overwhelmingly associated with homozygosity at one particular locus, all other loci showing no pattern. Our results suggest contrasting genetic mechanisms underlying two pathologies related to the same pathogen. First, relatively inbred pups are less able to expel hookworms and prevent their attachment to the intestinal mucosa, possibly due to a weakened immune response. In contrast, infected pups that are homozygous for a gene near to microsatellite Hg4.2 are strongly predisposed to anaemia. As yet, this gene is unknown, but could plausibly be involved in the blood‐coagulation cascade. Taken together, these results suggest that pathogenic burden alone may not be the main factor regulating pathogen‐related mortality in natural populations. Our study could have important implications for the conservation of small, isolated or threatened populations, particularly when they are at a risk of facing pathogenic challenges.
Comparative phylogeography of two coastal polychaete tubeworms in the Northeast Atlantic supports shared history and vicariant events
Authors: JOLLY M. T. , VIARD F. , GENTIL F. , THIÉBAUT E. , JOLLIVET D. 
Published: March 2006

AbstractThe historic processes which have led to the present‐day patterns of genetic structure in the marine coastal fauna of the Northeast Atlantic are still poorly understood. While tectonic uplifts and changes in sea level may have caused large‐scale vicariance, warmer conditions during glacial maxima may have allowed pockets of diversity to persist to a much wider extent than in the Northwestern Atlantic. The large‐scale geographic distribution of deeply divergent lineages of the coastal polychaete tubeworms Pectinaria koreni (two clades) and Owenia fusiformis (three clades) were compared using a fragment of the mitochondrial cytochrome oxidase I gene (mtCOI). All lineages were present along the biogeographic transition zone on the north coast of Brittany (France) and we found evidence pointing towards congruence in the timing of cladogenic events between Pectinaria sp. (P. auricoma/P. belgica and P. koreni) and Owenia sp., suggesting a shared history of vicariant events. More conserved 16SrRNA sequences obtained from four species of Pectinariidae together with mtCOI sequences of P. koreni seem consistent with an initial establishment of pectinariids in the north, and a southward colonization of the Northeast Atlantic. Phylogeographic patterns in O. fusiformis were also consistent with a north/south pattern of lineage splitting and congruent levels of divergence were detected between lineages of both species. We observed signatures of both persistence in small northern glacial refugia, and of northwards range expansion from regions situated closer to the Mediterranean. However, whether the recolonization of the Northeast Atlantic by both species actually reflects separate interglacial periods is unclear with regards to the lack of molecular clock calibration in coastal polychaete species.
Set regulation in asexual and sexual Plasmodium parasites reveals a novel mechanism of stage‐specific expression
Authors: Pace Tomasino , Olivieri Anna , Sanchez Massimo , Albanesi Veronica , Picci Leonardo , Kiamos Inga Siden , Janse Chris J. , Waters Andrew P. , Pizzi Elisabetta , Ponzi Marta 
Published: March 2006

SummaryTransmission of the malaria parasite depends on specialized gamete precursors (gametocytes) that develop in the bloodstream of a vertebrate host. Gametocyte/gamete differentiation requires controlled patterns of gene expression and regulation not only of stage and gender‐specific genes but also of genes associated with DNA replication and mitosis. Once taken up by mosquito, male gametocytes undergo three mitotic cycles within few minutes to produce eight motile gametes. Here we analysed, in two Plasmodium species, the expression of SET, a conserved nuclear protein involved in chromatin dynamics. SET is expressed in both asexual and sexual blood stages but strongly accumulates in male gametocytes. We demonstrated functionally the presence of two distinct promoters upstream of the set open reading frame, the one active in all blood stage parasites while the other active only in gametocytes and in a fraction of schizonts possibly committed to sexual differentiation. In ookinetes both promoters exhibit a basal activity, while in the oocysts the gametocyte‐specific promoter is silent and the reporter gene is only transcribed from the constitutive promoter. This transcriptional control, described for the first time in Plasmodium, provides a mechanism by which single‐copy genes can be differently modulated during parasite development. In male gametocytes an overexpression of SET might contribute to a prompt entry and execution of S/M phases within mosquito vector.
Structural basis for the extended substrate spectrum of CMY‐10, a plasmid‐encoded class C β‐lactamase
Authors: Kim Jae Young , Jung Ha Il , An Young Jun , Lee Jung Hun , Kim So Jung , Jeong Seok Hoon , Lee Kye Joon , Suh Pann‐Ghill , Lee Heung‐Soo , Lee Sang Hee , Cha Sun‐Shin 
Published: March 2006

SummaryThe emergence and dissemination of extended‐spectrum (ES) β‐lactamases induce therapeutic failure and a lack of eradication of clinical isolates even by third‐generation β‐lactam antibiotics like ceftazidime. CMY‐10 is a plasmid‐encoded class C β‐lactamase with a wide spectrum of substrates. Unlike the well‐studied class C ES β‐lactamase from Enterobacter cloacae GC1, the Ω‐loop does not affect the active site conformation and the catalytic activity of CMY‐10. Instead, a three‐amino‐acid deletion in the R2‐loop appears to be responsible for the ES activity of CMY‐10. According to the crystal structure solved at 1.55 Å resolution, the deletion significantly widens the R2 active site, which accommodates the R2 side‐chains of β‐lactam antibiotics. This observation led us to demonstrate the hydrolysing activity of CMY‐10 towards imipenem with a long R2 substituent. The forced mutational analyses of P99 β‐lactamase reveal that the introduction of deletion mutations into the R2‐loop is able to extend the substrate spectrum of class C non‐ES β‐lactamases, which is compatible with the isolation of natural class C ES enzymes harbouring deletion mutations in the R2‐loop. Consequently, the opening of the R2 active site by the deletion of some residues in the R2‐loop can be considered as an operative molecular strategy of class C β‐lactamases to extend their substrate spectrum.
Expression of a putative laccase gene, ZmLAC1, in maize primary roots under stress*
Authors: LIANG MINGXIANG , HAROLDSEN VICTOR , CAI XIAONING , WU YAJUN 
Published: March 2006

ABSTRACTLaccases are multi‐copper‐containing glycoproteins and comprise a multi‐gene family in plants. However, their physiological functions are still not well understood. We obtained sequence information for a putative laccase gene, ZmLAC1, from maize and studied ZmLAC1 expression in detail. The deduced ZmLAC1 protein was 70% identical to LpLAC5‐4, a laccase from ryegrass. ZmLAC1 was expressed in leaves, stems and roots of maize seedlings. In unstressed maize primary roots, a higher ZmLAC1 transcript level was located in the basal region where cell elongation had ceased compared to the apical 5 mm of the roots where cells were rapidly dividing and elongating. A treatment with 300 mm NaCl resulted in a shortened root elongation zone (< 2 mm) and swelling in the apical 5 mm. Associated with the morphological change, the transcript level of ZmLAC1 was enhanced in the apical 5 mm, reaching a level similar to that in the basal region. Other abiotic stresses tested – such as 28.5% polyethylene glycol (PEG), which caused an inhibition of root elongation comparable to 300 mm NaCl – did not affect ZmLAC1 transcript level. Potential roles of ZmLAC1 in the roots responding to NaCl or other high concentration of salts are discussed.