Showing papers by "University of Georgia published in 1996"

Effects of life history traits on genetic diversity in plant species

Abstract: Seven two-trait combinations (e.g. breeding system and seed dispersal mechanism) of five life history characteristics were used to analyse interspecific variation in the level and distribution of allozyme genetic diversity in seed plants. Highly significant differences were seen among categories for all seven comparisons. Life form and breeding system had highly significant influences on genetic diversity and its distribution. Regardless of other traits, outcrossing species tended to be more genetically diverse and had less genetic differentiation among their populations. Similarly, woody plants have less among population differentiation and somewhat more genetic diversity than non-woody species with similar life history traits. An analysis of twelve plant families indicated that species within families with predominately outcrossing, woody species had more genetic diversity and less interpopulation differentiation than species within families with predominately herbaceous species.

Command and Control and the Pathology of Natural Resource Management

Abstract: As the human population grows and natural resources decline, there is pressure to apply increas- ing levels of topdown, command, and~control management to natural resources. This is manifested in at- tempts to control ecosystems and in socioeconomic institutions that respond to erratic or surprising ecosystem behavior with more control Command and control, however, usually results in unforeseen consequences for both natural ecosystems and human welfare in the form of collapsing resources, social and economic strife, and losses of biological diversity. We describe the "pathology of natural resource management, " defined as a loss of system resilience when the range of natural variation in the system is reduced encapsulates the unsustain- able environmental, social, and economic outcomes of command~and~ontrol resource management. If natu- ral levels of variation in system behavior are reduced through command-and~ontrol, then the system be- comes less resilient to external perturbations, resulting in crises and surprises. We provide several examples of this pathology in management. An ultimate pathology emerges when resource management agencies, through initial success with command and control, lose sight of their original purposes, eliminate research and monitoring, and focus on efficiency of control They then become isolated from the managed systems and inflexible in structure. Simultaneously, through overcapitalization, society becomes dependent upon com- mand and control, demands it in greater intensity, and ignores the underlying ecological change or collapse that is developing. Solutions to this pathology cannot come from further command and control (regulations) but must come from innovative approaches involving incentives leading to more resilient ecosystems, more flexible agencies, more self-reliant industries, and a more knowledgeable citizenry. We discuss several aspects of ecosystem pattern and dynamics at large scales that provide insight into ecosystem resilience, and we pro- pose a "Golden Rule" of natural resource management that we believe is necessary for sustainabllity: man- agement should strive to retain critical types and ranges of natural variation in resource systems in order to maintain their resiliency.

Search for past life on Mars: possible relic biogenic activity in martian meteorite ALH84001.

Abstract: Fresh fracture surfaces of the martian meteorite ALH84001 contain abundant polycyclic aromatic hydrocarbons (PAHs). These fresh fracture surfaces also display carbonate globules. Contamination studies suggest that the PAHs are indigenous to the meteorite. High-resolution scanning and transmission electron microscopy study of surface textures and internal structures of selected carbonate globules show that the globules contain fine-grained, secondary phases of single-domain magnetite and Fe-sulfides. The carbonate globules are similar in texture and size to some terrestrial bacterially induced carbonate precipitates. Although inorganic formation is possible, formation of the globules by biogenic processes could explain many of the observed features, including the PAHs. The PAHs, the carbonate globules, and their associated secondary mineral phases and textures could thus be fossil remains of a past martian biota.

Cation exchange capacity and exchange coefficients.

Abstract: The origin of cation exchange capacity (CEC) lies in the negative charges carried by soil particles, usually clay, organic matter and sesquioxides. A full discussion of the origin and nature of these charges is presented in Chapter 41 (Zelazny et aI., 1996). Basically these charges fall into two distinct categories, being either permanent or variable (i.e., pH dependent) depending on whether or not ambient conditions (pH or salts) in the soil solution affect their magnitude. Much confusion in the literature concerning the measurement and interpretation of CEC has stemmed from the lack of recognition that these charges fall into two distinct categories exhibiting different behavior. These problems will be addressed in the discussion of the methods for the determination of CEC.

The role of macroinvertebrates in stream ecosystem function.

Abstract: This review focuses on some of the roles of macroinvertebrate functional groups, i.e. grazers, shredders, gatherers, filterers, and predators, in stream-ecosystem processes. Many stream-dwelling insects exploit the physical characteristics of streams to obtain their foods. As consumers at intermediate trophic levels, macroinvertebrates are influenced by both bottom-up and top-down forces in streams and serve as the conduits by which these effects are propagated. Macroinvertebrates can have can important influence on nutrient cycles, primary productivity, decomposition, and translocation of materials. Interactions among macroinvertebrates and their food resources vary among functional groups. Macroinvertebrates constitute an important source of food for numerous fish, and unless outside energy subsidies are greater than in-stream food resources for fish, effective fisheries management must account for fish-invertebrate linkages and macroinvertebrate linkages with resources and habitats. Macroinvertebrates also serve as valuable indicators of stream degradation. The many roles performed by stream-dwelling macroinvertebrates underscore the importance of their conservation.

Seriously considering play: Designing interactive learning environments based on the blending of microworlds, simulations, and games

Abstract: Little attention has been given to the psychological and sociological value of play despite its many advantages to guiding the design of interactive multimedia learning environments for children and adults. This paper provides a brief overview of the history, research, and theory related to play. Research from education, psychology, and anthropology suggests that play is a powerful mediator for learning throughout a person's life. The time has come to couple the ever increasing processing capabilities of computers with the advantages of play. The design of hybrid interactive learning environments is suggested based on the constructivist concept of a microworld and supported with elements of both games and simulations.

The ligninolytic system of the white rot fungus Pycnoporus cinnabarinus: purification and characterization of the laccase.

Abstract: The white rot fungus Pycnoporus cinnabarinus was characterized with respect to its set of extracellular phenoloxidases. Laccase was produced as the predominant extracellular phenoloxidase in conjunction with low amounts of an unusual peroxidase. Neither lignin peroxidase nor manganese peroxidase was detected. Laccase was produced constitutively during primary metabolism. Addition of the most effective inducer, 2,5-xylidine, enhanced laccase production ninefold without altering the isoenzyme pattern of the enzyme. Laccase purified to apparent homogeneity was a single polypeptide having a molecular mass of approximately 81,000 Da, as determined by calibrated gel filtration chromatography, and a carbohydrate content of 9%. The enzyme displayed an unusual behavior on isoelectric focusing gels; the activity was split into one major band (pI, 3.7) and several minor bands of decreasing intensity which appeared at regular, closely spaced intervals toward the alkaline end of the gel. Repeated electrophoresis of the major band under identical conditions produced the same pattern, suggesting that the laccase was secreted as a single acidic isoform with a pI of about 3.7 and that the multiband pattern was an artifact produced by electrophoresis. This appeared to be confirmed by N-terminal amino acid sequencing of the purified enzyme, which yielded a single sequence for the first 21 residues. Spectroscopic analysis indicated a typical laccase active site in the P. cinnabarinus enzyme since all three typical Cu(II)-type centers were identified. Substrate specificity and inhibitor studies also indicated the enzyme to be a typical fungal laccase. The N-terminal amino acid sequence of the P. cinnabarinus laccase showed close homology to the N-terminal sequences determined for laccases from Trametes versicolor, Coriolus hirsutus, and an unidentified basidiomycete, PM1. The principal features of the P. cinnabarinus enzyme system, a single predominant laccase and a lack of lignin- or manganese-type peroxidase, make this organism an interesting model for further studies of possible alternative pathways of lignin degradation by white rot fungi.

Increasing physical activity: a quantitative synthesis

Abstract: National policy for increasing leisure physical activity in the United States is impeded by a poor understanding of interventions that can be implemented by community and clinical medicine. To clarify the literature in this area, we conducted a quantitative, meta analysis of 127 studies that examined the efficacy of interventions for increasing physical activity among approximately 131,000 subjects in community, worksite, school, home, and health care settings; 445 effects were expressed as a Pearson correlation coefficient (r) and examined as they varied according to moderating variables important for community and clinical intervention. The mean effect was moderately large, r = 0.34, approximating three-fourths of a standard deviation or an increase in binomial success rate from 50% to 67%. The estimated population effect weighted by sample size was larger, r = 0.75, approximating 2 standard deviations or increased success to 88%. Contrasts between levels of independent moderating variables indicated that effects weighted by sample size were larger when the interventions: 1) employed the principles of behavior modification, 2) used a mediated delivery, 3) targeted groups, 4) of combined ages, 5) sampled apparently healthy people, or 6) measured active leisure, of 7) low intensity, 8) by observation. Independently of sample size, effects were larger when interventions 1) used behavior modification, 2) employed a preor quasi-experimental design, or 3) were of short duration, regardless of features of the people, setting, or physical activity. Our results show that physical activity can be increased by intervention. The optimal ways for selecting intervention components, settings, and population segments to maintain increases in physical activity and the relative contributions by community and clinical medicine toward successful physical activity intervention require experimental confirmation, warranting accelerated attention in clinical trials.

Measuring Leisure Motivation: A Meta-Analysis of the Recreation Experience Preference Scales

Abstract: One approach to studying the motivations for leisure is to focus on the desired goal States that are attained through participation in leisure. The Recreation Experience Preference (REP) scales wer...

Mediators of long-term memory performance across the life span.

Abstract: An individual-differences approach was used to examine the component processes that predict episodic long-term memory performance A total of 301 participants ages 20-90 received a 7-hr cognitive battery across 3 days Key constructs hypothesized to affect long-term memory function were assessed, including multiple measures of working memory and perceptual speed Latent-construct, structural equation modeling was used to examine the relationship of these measures and age to different types of long-term memory tasks Speed was a key construct for all 3 types of memory tasks, mediating substantial age-related variance; working memory was a fundamental construct for free and cued recall but not spatial memory The data suggest that both speed and working memory are fundamental to explaining age-related changes in cognitive aging but that the relative contributions of these constructs vary as a function of the type of memory task

Semantic and schematic similarities between database objects: a context-based approach

Abstract: In a multidatabase system, schematic conflicts between two objects are usually of interest only when the objects have some semantic similarity. We use the concept of semantic proximity, which is essentially an abstraction/mapping between the domains of the two objects associated with the context of comparison. An explicit though partial context representation is proposed and the specificity relationship between contexts is defined. The contexts are organized as a meet semi-lattice and associated operations like the greatest lower bound are defined. The context of comparison and the type of abstractions used to relate the two objects form the basis of a semantic taxonomy. At the semantic level, the intensional description of database objects provided by the context is expressed using description logics. The terms used to construct the contexts are obtained from {\em domain-specific ontologies}. Schema correspondences are used to store mappings from the semantic level to the data level and are associated with the respective contexts. Inferences about database content at the federation level are modeled as changes in the context and the associated schema correspondences. We try to reconcile the dual (schematic and semantic) perspectives by enumerating possible semantic similarities between objects having schema and data conflicts, and modeling schema correspondences as the projection of semantic proximity with respect to (wrt) context.

Strong, constitutive expression of the Arabidopsis ACT2/ACT8 actin subclass in vegetative tissues

Abstract: Arabidopsis has a complex and ancient actin gene family encoding six divergent subclasses of proteins. One subclass is represented by ACT2 and ACT8, which encode nearly identical proteins. These two genes differ significantly in flanking and intron sequences and in silent nucleotide positions within codons. Gene-specific RNA gel blot hybridization and reverse transcriptase-mediated polymerase chain reaction (RT-PCR) assays showed that ACT2 and/or ACT8mRNAs were coordinately and strongly expressed in leaves, roots, stems, flowers, pollen, and siliques. Together they account for greater than 80% of the actin mRNA in most Arabidopsis organs. The 5' flanking regions, including the promoter, the mRNA leader exon, an intron in the mRNA leader, and the first 19 codons, were coupled to a beta-glucuronidase (GUS) reporter gene and transformed into Arabidopsis. The ACT2/GUS construct was expressed strongly in nearly all the vegetative tissues in seedlings, juvenile plants, and mature plants. These activities persisted in older tissues. Little or no expression was observed in seed coats, hypocotyls, gynoecia, or pollen sacs. In contrast, the expression of the ACT8/GUS construct was weaker. It was observed only in a subset of the organs and tissues expressing ACT2/GUS and was not significantly expressed in the flower. ACT2, ACT8, and ACT8/GUS mRNAs were present at moderate to high levels in pollen, and yet neither ACT2/GUS nor ACT8/GUS enzyme expression could be detected in pollen. This suggested a mechanism of translational control affecting ACT2 and ACT8 expression in some tissues. The conservation of protein sequence and overlapping patterns of expression, in spite of significant DNA sequence divergence, suggests that the function and regulation of these two genes have been conserved during the evolution of the Brassicaceae.

Fate of enterohemorrhagic Escherichia coli O157:H7 in bovine feces.

Abstract: Dairy cattle have been identified as a principal reservoir of Escherichia coli O157:H7. The fate of this pathogen in bovine feces at 5, 22, and 37 degrees C was determined. Two levels of inocula (10(3) and 10(5) CFU/g) of a mixture of five nalidixic acid-resistant E. coli O157:H7 strains were used. E. coli O157:H7 survived at 37 degrees C for 42 and 49 days with low and high inocula, respectively, and at 22 degrees C for 49 and 56 days with low and high inocula, respectively. Fecal samples at both temperatures had low moisture contents (about 10%) and water activities ( < 0.5) near the end of the study. E. coli O157:H7 at 5 degrees C survived for 63 to 70 days, with the moisture content (74%) of feces remaining high through the study. Chromosomal DNA fingerprinting of E. coli O157:H7 isolates surviving near the completion of the study revealed that the human isolate strain 932 was the only surviving strain at 22 or 37 degrees C. All five strains were isolated near the end of incubation from feces held at 5 degrees C. Isolates at each temperature were still capable of producing both verotoxin 1 and verotoxin 2. Results indicate that E. coli O157:H7 can survive in feces for a long period of time and retain its ability to produce verotoxins. Hence, bovine feces are a potential vehicle for transmitting E. coli O157:H7 to cattle, food, and the environment. Appropriate handling of bovine feces is important to control the spread of this pathogen.

Pain responses, anxiety and aggression in mice deficient in pre-proenkephalin

Abstract: ENKEPHALINS are endogenous opioid peptides that are derived from a pre-proenkephalin precursor protein1,2. They are thought to be vital in regulating many physiological functions, including pain perception and analgesia, responses to stress, aggression and dominance3–5. Here we have used a genetic approach to study the role of the mammalian opioid system. We disrupted the pre-proenkephalin gene using homologous recombination in embryonic stem cells to generate enkephalin-deficient mice. Mutant enk−/− animals are healthy, fertile, and care for their offspring, but display significant behavioural abnormalities. Mice with the enk−/− genotype are more anxious and males display increased offensive aggressiveness. Mutant animals show marked differences from controls in supraspinal, but not in spinal, responses to painful stimuli. Unexpectedly, enk−/− mice exhibit normal stress-induced analgesia. Our results show that enkephalins modulate responses to painful stimuli. Thus, genetic factors may contribute significantly to the experience of pain.

Effects of concentric and eccentric training on muscle strength, cross-sectional area, and neural activation

Abstract: Higbie, Elizabeth J., Kirk J. Cureton, Gordon L. Warren III, and Barry M. Prior. Effects of concentric and eccentric training on muscle strength, cross-sectional area, and neural activation.J. Appl...

Information exchange and use in group decision making: you can lead a group to information, but you can't make it think

Abstract: Organizations often build groups with members from different areas so that a wider range of information and opinions can be considered. When members of such groups share the information they have, the group as a whole can access a larger pool of information than any one member acting alone, potentially enabling them to make better decisions. This experiment studied groups working on a hidden profile task in which each participant received different (but not conflicting) information about the task, which they needed to combine to identify the optimal decision. Verbally interacting groups exchanged only a small portion of the available information and made poor decisions as a result. Groups interacting using a GSS exchanged about 50% more information, providing sufficient information to enable all groups to identify the optimal decision. However, GSS groups did not accurately process this information -- only one GSS group chose the optimal decision. Possible explanations for this lack of information processing are that participants were unable to integrate into their existing base of information the information received during discussions, that the way in which the GSS was used impeded information processing, that the anonymity and delayed feedback in the GSS reduced the credibility of new information so that participants chose not to process it, or that information in the GSS was less salient than verbally contributed information.

Mercuric ion reduction and resistance in transgenic Arabidopsis thaliana plants expressing a modified bacterial merA gene

Abstract: With global heavy metal contamination increasing, plants that can process heavy metals might provide efficient and ecologically sound approaches to sequestration and removal. Mercuric ion reductase, MerA, converts toxic Hg2+ to the less toxic, relatively inert metallic mercury (Hg0) The bacterial merA sequence is rich in CpG dinucleotides and has a highly skewed codon usage, both of which are particularly unfavorable to efficient expression in plants. We constructed a mutagenized merA sequence, merApe9, modifying the flanking region and 9% of the coding region and placing this sequence under control of plant regulatory elements. Transgenic Arabidopsis thaliana seeds expressing merApe9 germinated, and these seedlings grew, flowered, and set seed on medium containing HgCl2 concentrations of 25-100 microM (5-20 ppm), levels toxic to several controls. Transgenic merApe9 seedlings evolved considerable amounts of Hg0 relative to control plants. The rate of mercury evolution and the level of resistance were proportional to the steady-state mRNA level, confirming that resistance was due to expression of the MerApe9 enzyme. Plants and bacteria expressing merApe9 were also resistant to toxic levels of Au3+. These and other data suggest that there are potentially viable molecular genetic approaches to the phytoremediation of metal ion pollution.

The effects of elevated temperature on the photosynthetic efficiency of zooxanthellae in hospite from four different species of reef coral: a novel approach

Abstract: Bleaching of reef corals is a phenomenon linked to temperature stress which involves loss of the symbiotic algae of the coral, which are known as zooxanthellae, and/or loss of algal pigments. The photosynthetic efficiency of zooxanthellae within the corals Montastrea annularis, Agaricia lamarki, Agaricia agaricites and Siderastrea radians was examined by pulse-amplitude modulation fluorometry (PAM) during exposure to elevated temperatures (3-36 degrees C). Zooxanthellae within M. annularis and A. lamarki were found to be more sensitive to elevated temperature, virtually complete disruption of photosynthesis being noted during exposure to temperatures of 32 and 34 degrees C. The photosynthetic efficiency of zooxanthellae within S. radians and A. agaricites decreased to a lesser extent. Differences in the loss of algal cells on an aerial basis and in the cellular chlorophyll concentration were also found between these species. By combining the noninvasive PAM technique with whole-cell fluorescence of freshly isolated zooxanthellae, we have identified fundamental differences in the physiology of the symbionts within different species of coral. Zooxanthellae within M. annularis appear to be more susceptible to heat-induced damage at or near the reaction centre of Photosystem II, while zooxanthellae living in S. radians remain capable of dissipating excess excitation energy through non-photochemical pathways, thereby protecting the photosystem from damage during heat exposure.

Photochemical release of biologically available nitrogen from aquatic dissolved organic matter

Abstract: DISSOLVED organic material in marine and freshwater ecosystems constitutes one of the Earth's largest actively cycled reservoirs for organic matter1. The bacterially mediated turnover of chemically identifiable, low-molecular-mass components of this pool has been studied in detail for nearly three decades, but these compounds constitute less than 20% of the total reservoir2. In contrast, little is known about the fate of the larger, biologically more refractory molecules—including humic substances—which make up the bulk of dissolved organic matter. Here we report results from bacterial bioassays and photochemical studies indicating that exposure to sunlight causes dissolved organic matter to release nitrogen-rich compounds that are biologically available, thus enhancing the bacterial degradation of humic substances. We demonstrate that ammonium is among the nitrogenous compounds released and is produced most efficiently by ultraviolet wavelengths. Photochemical release of ammonium from dissolved organic matter has important implications for nitrogen availability in many aquatic ecosystems, including nitrogen-limited high-latitude environments and coastal oceans, where inputs of terrestrial humic substances are high.

Genome Duplication in Soybean ( Glycine subgenus soja )

Abstract: Restriction fragment length polymorphism mapping data from nine populations (Glycine max X G. soja and G. max X G. max) of the Glycine subgenus soja genome led to the identification of many duplicated segments of the genome. Linkage groups contained up to 33 markers that were duplicated on other linkage groups. The size of homoeologous regions ranged from 1.5 to 106.4 cM, with an average size of 45.3 cM. We observed segments in the soybean genome that were present in as many as six copies with an average of 2.55 duplications per segment. The presence of nested duplications suggests that at least one of the original genomes may have undergone an additional round of tetraploidization. Tetraploidization, along with large internal duplications, accounts for the highly duplicated nature of the genome of the subgenus. Quantitative trait loci for seed protein and oil showed correspondence across homoeologous regions, suggesting that the genes or gene families contributing to seed composition have retained similar functions throughout the evolution of the chromosomes.

The world wide web as an advertising medium

Abstract: This paper discusses the role of the World Wide Web as an advertising medium and its position in the marketing communication mix. It introduces a conceptual framework for measuring the efficiency of a Web site. Efficiency indexes are defined for five Web advertising communication activities, and an overall measure of Web site efficiency measure is presented.

Fourier transform mass spectrometry

Abstract: The fundamental principles of Fourier transform mass spectrometry (FTMS) are presented. The motion of ions in a FTMS analyzer can be understood in terms of the magnetic and electric fields present in the FTMS analyzer cell. Ion motion is illustrated with the results of ion trajectory calculations under both collision-free conditions and at high pressure. Dipolar and quadrupolar excitation are described and compared. Practical considerations in obtaining ultra-high-mass resolution and accuracy are discussed. The FTMS experiment is a series of events (ionization excitation, detection) that occur in sequence. Pulse sequences for mass spectrometric and tandem mass spectrometric experiments are presented.

RFLP and Cytogenetic Evidence on the Origin and Evolution of Allotetraploid Domesticated Peanut, Arachis hypogaea (Leguminosae)

Abstract: Nuclear restriction fragment length polymorphism (RFLP) analysis was used to determine the wild diploid Arachis species that hybridized to form tetraploid domesticated peanut. Results using 20 previously mapped cDNA clones strongly indicated A. duranensis as the progenitor of the A genome of domesticated peanut and A ipaensis as the B genome parent A large amount of RFLP variability was found among the various accessions of A duranensis, and accessions most similar to the A genome of cultivated peanut were identified. Chloroplast DNA RFLP analysis determined that A duranensis was the female parent of the original hybridization event Domesticated peanut is known to have one genome with a distinctly smaller pair of chromosomes ("A"), and one genome that lacks this pair. Cytogenetic analysis demonstrated that A duranensis has a pair of "A" chromosomes, and A. ipaensis does not The cytogenetic evidence is thus consistent with the RFLP evidence concerning the identity of the progenitors RFLP and cytogenetic evidence indicate a single origin for domesticated peanut in Northern Argentina or Southern Bolivia, followed by diversification under the influence of cultivation