Showing papers by "University of Missouri published in 1998"

Inflammation, Pravastatin, and the Risk of Coronary Events After Myocardial Infarction in Patients With Average Cholesterol Levels

Abstract: Background —We studied whether inflammation after myocardial infarction (MI) is a risk factor for recurrent coronary events and whether randomized treatment with pravastatin reduces that risk. Methods and Results —A nested case-control design was used to compare C-reactive protein (CRP) and serum amyloid A (SAA) levels in prerandomization blood samples from 391 participants in the Cholesterol and Recurrent Events (CARE) trial who subsequently developed recurrent nonfatal MI or a fatal coronary event (cases) and from an equal number of age- and sex-matched participants who remained free of these events during follow-up (control subjects). Overall, CRP and SAA were higher among cases than control subjects (for CRP P =0.05; for SAA P =0.006) such that those with levels in the highest quintile had a relative risk (RR) of recurrent events 75% higher than those with levels in the lowest quintile (for CRP RR=1.77, P =0.02; for SAA RR=1.74, P =0.02). The study group with the highest risk was that with consistent evidence of inflammation (elevation of both CRP and SAA) who were randomly assigned to placebo (RR=2.81, P =0.007); this risk estimate was greater than the product of the individual risks associated with inflammation or placebo assignment alone. In stratified analyses, the association between inflammation and risk was significant among those randomized to placebo (RR=2.11, P =0.048) but was attenuated and nonsignificant among those randomized to pravastatin (RR=1.29, P =0.5). Conclusions —Evidence of inflammation after MI is associated with increased risk of recurrent coronary events. Therapy with pravastatin may decrease this risk, an observation consistent with a nonlipid effect of this agent.

C. Elegans II

Abstract: Why should one study a worm? This simple creature is one of several “model” organisms that together have provided tremendous insight into how all organisms are put together. It has become increasingly clear over the past two decades that knowledge from one organism, even one so simple as a worm, can provide tremendous power when connected with knowledge from other organisms. And because of the experimental accessibility of nematodes, knowledge about worms can come more quickly and cheaply than knowledge about higher organisms.

The determinants of export performance: a review of the empirical literature between 1987 and 1997

Abstract: Export performance research has proliferated in the last decade. Significant progress has been made in developing better theory and knowledge of the export performance of firms. However, the field of inquiry is characterized by a diversity of conceptual, methodological, and empirical approaches that inhibit the development of clear conclusions regarding the determinants of export performance. In this article, an updated review and synthesis of the empirical literature on determinants of export performance between 1987 and 1997 is offered. Using a combination of the narrative and vote‐counting approaches, 50 studies were identified, reviewed, and synthesized. Major directions for future research are also discussed.

Actual Share Reacquisitions in Open‐Market Repurchase Programs

Abstract: Unlike Dutch auction repurchases and tender offers, open-market repurchase programs do not precommit firms to acquire a specified number of shares. In a sample of 450 programs from 1981 to 1990, firms on average acquire 74 to 82 percent of the shares announced as repurchase targets within three years of the repurchase announcement. We find that share repurchases are negatively related to prior stock price performance, suggesting that firms increase their purchasing depending on its degree of perceived undervaluation. In addition, repurchases are positively related to levels of cash flow, which is consistent with liquidity arguments.

Renal and intestinal absorptive defects in mice lacking the NHE3 Na + /H + exchanger

Abstract: NHE3 is one of five plasma membrane Na+/H+ exchangers and is encoded by the mouse gene Slc9a3. It is expressed on apical membranes of renal proximal tubule and intestinal epithelial cells and is thought to play a major role in NaCl and HCO3- absorption. As the distribution of NHE3 overlaps with that of the NHE2 isoform in kidney and intestine, the function and relative importance of NHE3 in vivo is unclear. To analyse its physiological functions, we generated mice lacking NHE3 function. Homozygous mutant (Slc9a3-/-) mice survive, but they have slight diarrhoea and blood analysis revealed that they are mildly acidotic. HCO3- and fluid absorption are sharply reduced in proximal convoluted tubules, blood pressure is reduced and there is a severe absorptive defect in the intestine. Thus, compensatory mechanisms must limit gross perturbations of electrolyte and acid-base balance. Plasma aldosterone is increased in NHE3-deficient mice, and expression of both renin and the AE1 (Slc4a1) Cl-/HCO3- exchanger mRNAs are induced in kidney. In the colon, epithelial Na+ channel activity is increased and colonic H+,K+-ATPase mRNA is massively induced. These data show that NHE3 is the major absorptive Na+/H+ exchanger in kidney and intestine, and that lack of the exchanger impairs acid-base balance and Na+-fluid volume homeostasis.

A Physiologically Based Approach To the Study of Bisphenol a and Other Estrogenic Chemicals On the Size of Reproductive Organs, Daily Sperm Production, and Behavior:

Abstract: Two chemicals previously shown to have estrogenic activity, bisphenol A and octylphenol, were examined for their effects on accessory reproductive organs and daily sperm production in male offspring of mice fed these chemicals during pregnancy. These chemicals are used in the manufacture of plastics and other products, and have been detected in food and water consumed by animals and people. From gestation day 11-17 female mice were fed an average concentration (dissolved in oil) of bisphenol A or octylphenol of 2 ng/g body weight (2 ppb) and 20 ng/g (20 ppb). The 2 ppb dose of bisphenol A is lower than the amount reported to be swallowed during the first hour after application of a plastic dental sealant (up to 931 micrograms; 13.3 ppb in a 70 kg adult). We found that the 2 ng/g dose of bisphenol A permanently increased the size of the preputial glands, but reduced the size of the epididymides; these organs develop from different embryonic tissues. At 20 ng/g, bisphenol A significantly decreased efficiency of sperm production (daily sperm production per g testis) by 20% relative to control males. The only significant effect of octylphenol was a reduction in daily sperm production and efficiency of sperm production at the 2 ng/g dose. A new approach to studying physiologically relevant doses of environmental endocrine disruptors is discussed, particularly with regard to the development of the reproductive organs, the brain, and behavior.

Boron in plant structure and function

Abstract: ▪ Abstract New and exciting developments in boron research in the past few years greatly contributed to better understanding of the role of boron in plants. Purification and identification of the first boron-polyol transport molecules resolved much of the controversy about boron phloem mobility. Isolation and characterization of the boron-polysaccharide complex from cell walls provided the first direct evidence for boron crosslinking of pectin polymers. Inhibition and recovery of proton release upon boron withdrawal and restitution in plant culture medium demonstrated boron involvement in membrane processes. Rapid boron-induced changes in membrane function could be attributed to boron-complexing membrane constituents. Boron may affect metabolic pathways by binding apoplastic proteins to cis-hydroxyl groups of cell walls and membranes, and by interfering with manganese-dependent enzymatic reactions. In addition, boron has been implicated in counteracting toxic effects of aluminum on root growth of dicotyle...

Effects of inhaled nitric oxide in patients with acute respiratory distress syndrome: results of a randomized phase II trial. Inhaled Nitric Oxide in ARDS Study Group.

Abstract: Objectives To evaluate the safety and physiologic response of inhaled nitric oxide (NO) in patients with acute respiratory distress syndrome (ARDS). In addition, the effect of various doses of inhaled NO on clinical outcome parameters was assessed. Design Prospective, multicenter, randomized, double-blind, placebo-controlled study. Setting Intensive care units of 30 academic, teaching, and community hospitals in the United States. Patients Patients with ARDS, as defined by the American-European Consensus Conference, were enrolled into the study if the onset of disease was within 72 hrs of randomization. Interventions Patients were randomized to receive placebo (nitrogen gas) or inhaled NO at concentrations of 1.25, 5, 20, 40, or 80 ppm. Measurements and main results Acute increases in PaO2, decreases in mean pulmonary arterial pressure, intensity of mechanical ventilation, and oxygenation index were examined. Clinical outcomes examined were the dose effects of inhaled NO on mortality, the number of days alive and off mechanical ventilation, and the number of days alive after meeting oxygenation criteria for extubation. A total of 177 patients were enrolled over a 14-month period. An acute response to treatment gas, defined as a PaO2 increase > or =20%, was seen in 60% of the patients receiving inhaled NO with no significant differences between dose groups. Twenty-four percent of placebo patients also had an acute response to treatment gas during the first 4 hrs. The initial increase in oxygenation translated into a reduction in the FIO2 over the first day and in the intensity of mechanical ventilation over the first 4 days of treatment, as measured by the oxygenation index. There were no differences among the pooled inhaled NO groups and placebo with respect to mortality rate, the number of days alive and off mechanical ventilation, or the number of days alive after meeting oxygenation criteria for extubation. However, patients receiving 5 ppm inhaled NO showed an improvement in these parameters. In this dose group, the percentage of patients alive and off mechanical ventilation at day 28 (a post hoc analysis) was higher (62% vs. 44%) than the placebo group. There was no apparent difference in the number or type of adverse events reported among those patients receiving inhaled NO compared with placebo. Four patients had methemoglobin concentrations >5%. The mean inspired nitrogen dioxide concentration in inhaled NO patients was 1.5 ppm. Conclusions From this placebo-controlled study, inhaled NO appears to be well tolerated in the population of ARDS patients studied. With mechanical ventilation held constant, inhaled NO is associated with a significant improvement in oxygenation compared with placebo over the first 4 hrs of treatment. An improvement in oxygenation index was observed over the first 4 days. Larger phase III studies are needed to ascertain if these acute physiologic improvements can lead to altered clinical outcome.

The coming of age of self-mutilation.

Abstract: Self-mutilation (SM), the deliberate, nonsuicidal destruction of one's own body tissue, occurs in such culturally sanctioned practices as tattooing; body piercing; and healing, spiritual, and order-preserving rituals. As a symptom, it has typically been regarded as a manifestation of borderline behavior and misidentified as a suicide attempt. It has begun to attract mainstream media attention, and many more who suffer from it are expected to seek treatment. This review suggests that SM can best be understood as a morbid self-help effort providing rapid but temporary relief from feelings of depersonalization, guilt, rejection, and boredom as well as hallucinations, sexual preoccupations, and chaotic thoughts. Major SM includes infrequent acts such as eye enucleation and castration, commonly associated with psychosis and intoxication. Stereotypic SM includes such acts as head banging and self-biting most often accompanying Tourette's syndrome and severe mental retardation. Superficial/moderate SM includes compulsive acts such as trichotillomania and skin picking and such episodic acts as skin-cutting and burning, which evolve into an axis I syndrome of repetitive impulse dyscontrol with protean symptoms.

Identification of a family of zinc transporter genes from Arabidopsis that respond to zinc deficiency

Abstract: Millions of people worldwide suffer from nutritional imbalances of essential metals like zinc. These same metals, along with pollutants like cadmium and lead, contaminate soils at many sites around the world. In addition to posing a threat to human health, these metals can poison plants, livestock, and wildlife. Deciphering how metals are absorbed, transported, and incorporated as protein cofactors may help solve both of these problems. For example, edible plants could be engineered to serve as better dietary sources of metal nutrients, and other plant species could be tailored to remove metal ions from contaminated soils. We report here the cloning of the first zinc transporter genes from plants, the ZIP1, ZIP2, and ZIP3 genes of Arabidopsis thaliana. Expression in yeast of these closely related genes confers zinc uptake activities. In the plant, ZIP1 and ZIP3 are expressed in roots in response to zinc deficiency, suggesting that they transport zinc from the soil into the plant. Although expression of ZIP2 has not been detected, a fourth related Arabidopsis gene identified by genome sequencing, ZIP4, is induced in both shoots and roots of zinc-limited plants. Thus, ZIP4 may transport zinc intracellularly or between plant tissues. These ZIP proteins define a family of metal ion transporters that are found in plants, protozoa, fungi, invertebrates, and vertebrates, making it now possible to address questions of metal ion accumulation and homeostasis in diverse organisms.

Two Pleiotropic Classes of daf-2 Mutation Affect Larval Arrest, Adult Behavior, Reproduction and Longevity in Caenorhabditis elegans

Abstract: The nematode Caenorhabditis elegans responds to overcrowding and scarcity of food by arresting development as a dauer larva, a nonfeeding, long-lived, stress-resistant, alternative third-larval stage. Previous work has shown that mutations in the genes daf-2 (encoding a member of the insulin receptor family) and age-1 (encoding a PI 3-kinase) result in constitutive formation of dauer larvae (Daf-c), increased adult longevity (Age), and increased intrinsic thermotolerance (Itt). Some daf-2 mutants have additional developmental, behavioral, and reproductive defects. We have characterized in detail 15 temperature-sensitive and 1 nonconditional daf-2 allele to investigate the extent of daf-2 mutant defects and to examine whether specific mutant traits correlate with each other. The greatest longevity seen in daf-2 mutant adults was approximately three times that of wild type. The temperature-sensitive daf-2 mutants fell into two overlapping classes, including eight class 1 mutants, which are Daf-c, Age, and Itt, and exhibit low levels of L1 arrest at 25.5 degrees. Seven class 2 mutants also exhibit the class 1 defects as well as some or all of the following: reduced adult motility, abnormal adult body and gonad morphology, high levels of embryonic and L1 arrest, production of progeny late in life, and reduced brood size. The strengths of the Daf-c, Age, and Itt phenotypes largely correlated with each other but not with the strength of class 2-specific defects. This suggests that the DAF-2 receptor is bifunctional. Examination of the null phenotype revealed a maternally rescued egg, L1 lethal component, and a nonconditional Daf-c component. With respect to the Daf-c phenotype, the dauer-defective (Daf-d) mutation daf-12(m20) was epistatic to daf-2 class 1 alleles but not the severe class 2 alleles tested. All daf-2 mutant defects were suppressed by the daf-d mutation daf-16(m26). Our findings suggest a new model for daf-2, age-1, daf-12, and daf-16 interactions.

Fuzzy decision trees: issues and methods

Abstract: Decision trees are one of the most popular choices for learning and reasoning from feature-based examples. They have undergone a number of alterations to deal with language and measurement uncertainties. We present another modification, aimed at combining symbolic decision trees with approximate reasoning offered by fuzzy representation. The intent is to exploit complementary advantages of both: popularity in applications to learning from examples, high knowledge comprehensibility of decision trees, and the ability to deal with inexact and uncertain information of fuzzy representation. The merger utilizes existing methodologies in both areas to full advantage, but is by no means trivial. In particular, knowledge inferences must be newly defined for the fuzzy tree. We propose a number of alternatives, based on rule-based systems and fuzzy control. We also explore capabilities that the new framework provides. The resulting learning method is most suitable for stationary problems, with both numerical and symbolic features, when the goal is both high knowledge comprehensibility and gradually changing output. We describe the methodology and provide simple illustrations.

Are Small, Isolated Wetlands Expendable?

Abstract: What is most evident in the recent debate concerning new wetland regulations drafted by the U.S. Army Corps of Engineers is that small, isolated wetlands will likely continue to be lost. The critical biological question is whether small wetlands are expendable, and the fundamental issue is the lack of biologically rele- vant data on the value of wetlands, especially so-called "isolated" wetlands of small size. We used data from a geographic information system for natural-depression wetlands on the southeastern Atlantic coastal plain (U.S.A.) to examine the frequency distribution of wetland sizes and their nearest-wetland distances. Our re- sults indicate that the majority of natural wetlands are small and that these small wetlands are rich in am- phibian species and serve as an important source of juvenile recruits. Analyses simulating the loss of small wetlands indicate a large increase in the nearest-wetland distance that could impede "rescue" effects at the metapopulation level. We argue that small wetlands are extremely valuable for maintaining biodiversity, that the loss of small wetlands will cause a direct reduction in the connectance among remaining species pop- ulations, and that both existing and recently proposed legislation are inadequate for maintaining the biodi- versity of wetland flora and fauna. Small wetlands are not expendable if our goal is to maintain present lev- els of species biodiversity. At the very least, based on these data, regulations should protect wetlands as small as 0.2 ha until additional data are available to compare diversity directly across a range of wetland sizes. Furthermore, we strongly advocate that wetland legislation focus not only on size but also on local and re- gional wetland distribution in order to protect ecological connectance and the source-sink dynamics of spe- cies populations.

Study of Prediagnostic Selenium Level in Toenails and the Risk of Advanced Prostate Cancer

Abstract: Background In a recent randomized intervention trial, the risk of prostate cancer for men receiving a daily supplement of 200 microg selenium was one third of that for men receiving placebo. By use of a nested case-control design within a prospective study, i.e., the Health Professionals Follow-Up Study, we investigated the association between risk of prostate cancer and prediagnostic level of selenium in toenails, a measure of long-term selenium intake. Methods In 1986, 51,529 male health professionals aged 40-75 years responded to a mailed questionnaire to form the prospective study. In 1987, 33,737 cohort members provided toenail clippings. In 1988, 1990, 1992, and 1994, follow-up questionnaires were mailed. From 1989 through 1994, 181 new cases of advanced prostate cancer were reported. Case and control subjects were matched by age, smoking status, and month of toenail return. Selenium levels were determined by neutron activation. All P values are two-sided. Results The selenium level in toenails varied substantially among men, with quintile medians ranging from 0.66 to 1.14 microg/g for control subjects. When matched case-control data were analyzed, higher selenium levels were associated with a reduced risk of advanced prostate cancer (odds ratio [OR] for comparison of highest to lowest quintile = 0.49; 95% confidence interval [CI] = 0.25-0.96; P for trend = .11). After additionally controlling for family history of prostate cancer, body mass index, calcium intake, lycopene intake, saturated fat intake, vasectomy, and geographical region, the OR was 0.35 (95% CI = 0.16-0.78; P for trend = .03). Conclusions Our results support earlier findings that higher selenium intakes may reduce the risk of prostate cancer. Further prospective studies and randomized trials of this relationship should be conducted.

Analysis of Cell Division and Elongation Underlying the Developmental Acceleration of Root Growth in Arabidopsis thaliana

Abstract: To investigate the relation between cell division and expansion in the regulation of organ growth rate, we used Arabidopsis thaliana primary roots grown vertically at 20°C with an elongation rate that increased steadily during the first 14 d after germination. We measured spatial profiles of longitudinal velocity and cell length and calculated parameters of cell expansion and division, including rates of local cell production (cells mm−1 h−1) and cell division (cells cell−1 h−1). Data were obtained for the root cortex and also for the two types of epidermal cell, trichoblasts and atrichoblasts. Accelerating root elongation was caused by an increasingly longer growth zone, while maximal strain rates remained unchanged. The enlargement of the growth zone and, hence, the accelerating root elongation rate, were accompanied by a nearly proportionally increased cell production. This increased production was caused by increasingly numerous dividing cells, whereas their rates of division remained approximately constant. Additionally, the spatial profile of cell division rate was essentially constant. The meristem was longer than generally assumed, extending well into the region where cells elongated rapidly. In the two epidermal cell types, meristem length and cell division rate were both very similar to that of cortical cells, and differences in cell length between the two epidermal cell types originated at the apex of the meristem. These results highlight the importance of controlling the number of dividing cells, both to generate tissues with different cell lengths and to regulate the rate of organ enlargement.

An intermolecular (H2O)10 cluster in a solid-state supramolecular complex

Abstract: Chemical self-assembly is the process by which ‘programmed’ molecular subunits spontaneously form complex supramolecular frameworks1,2. This approach has been applied to many model systems, in which hydrogen bonds3,4, metal–ligand coordination5 or other non-covalent interactions6 typically control the self-assembly process. In biology, self-assembly is generally dynamic and depends on the cooperation of many such non-covalent interactions. Water can play an important role in these biological self-assembly processes, for example by stabilizing the native conformation of biopolymers7,8,9. Hydrogen-bonded (H2O)n clusters10,11 can play an important role in stabilizing some supramolecular species, both natural and synthetic, in aqueous solution. Here we report the preparation and crystal structure of a self-assembled, three-dimensional supramolecular complex that is stabilized by an intricate array of non-covalent interactions involving contributions from solvent water clusters, most notably a water decamer ((H2O)10) with an ice-like molecular arrangement. These findings show that the degree of structuring that can be imposed on water by its surroundings, and vice versa, can be profound.

Achievement loss associated with the transition to middle school and high school

Abstract: To explore the nature of the achievement loss associated with school-to-school transitions from elementary school to middle school and to high school, the author compared 3 groups of 16 school districts in this ex post facto study. A statistically significant achievement loss associated with the transition from elementary school to middle school at 6th grade was found, as compared with K–8 schools that did not have a school-to-school transition at 6th grade. The transition loss in achievement was larger when students from multiple elementary schools were merged into a single middle school during the transition. The students from the middle schools and K–8 elementary schools experienced an achievement loss in the transition to high school at 9th grade. The achievement loss in the transition to high school was larger for middle school students than for K–8 elementary students. High school dropout rates were higher for districts with Grade 6–8 middle schools than for districts with K–8 elementary sc...

Motivations for sex and risky sexual behavior among adolescents and young adults: a functional perspective.

Abstract: The implications of a functionalist perspective for understanding sexual risk taking are explored. Key motivational dimensions thought to underlie human behavior (viz., approach vs. avoidance, autonomy vs. relatedness) were used to identify 4 broad domains of sexual motivations and to develop a measure of specific motives within each of these domains. Data from both college student and community samples are used to demonstrate the psychometric adequacy of these scales and to show that having sex for different reasons predicts distinctive patterns of sexual risk taking both cross-sectionally and longitudinally: that selection into specific types of sexual relationships partially mediates these effects; and that these needs may be differentially expressed, or even suppressed, depending on relationship context. Results provide strong support for the functionalist perspective on behavior and indicate that an adequate understanding of sexual risk-taking behavior must take into account the various needs and goals that such behavior can serve.

Roles of estrogen receptor-alpha gene expression in reproduction-related behaviors in female mice.

Abstract: The role of gene expression of the estrogen receptor-alpha form (ER alpha) in the regulation of female reproductive behavior was investigated in estrogen receptor knockout (ERKO) mice, deficient specifically for the ER alpha, but not the ER beta, gene. Estrogen- or estrogen- plus progesterone-treated gonadectomized ERKO mice did not show any lordosis response. Detailed behavioral analysis revealed that ERKO females were also deficient in sexual behavioral interactions preceding the lordosis response. They were extremely rejective toward attempted mounts by stud male mice, which could not show any intromissions. During resident-intruder aggression tests, gonadally intact ERKO females were more aggressive toward female intruder mice than wild-type (WT) mice. Gonadectomy did not influence the levels of aggressive behavior, and their genotype differences when mice were tested both before and after gonadectomy. However, when mice were tested after gonadectomy for the first time, very few ERKO mice showed aggression. In contrast to aggression, male-type sexual behavior shown by resident mice toward female intruder mice during aggression tests was not different between ERKO and WT mice and was completely abolished after gonadectomy of the resident mice. Finally, it was also found that ERKO females showed greatly reduced levels of parental behavior toward newborn pups placed in their home cage. These changes in parental behavior were not influenced by gonadectomy. ERKO females retrieved significantly fewer numbers of pups with longer latencies compared with wild-type (WT) or heterozygous (HZ) littermates when they were tested as gonadally intact or 20-65 days after gonadectomy. In addition, during parental behavior tests, a significantly higher percentage of ERKO mice exhibited infanticide compared with WT and HZ mice, which rarely showed infanticide. Taken together, these findings suggest that ER alpha gene expression plays a key role in female mice, not only for sexual behavior but also for other interrelated behaviors, such as parental and aggressive behaviors. In addition, persistence of genotype differences in parental and aggressive behavior after gonadectomy indicates that ER alpha activation during neural developmental processes may also be involved in the regulation of these behaviors.

Broadband microstrip patch antenna

Abstract: The characteristics of a rectangular microstrip antenna with an L-shaped probe are investigated. A foam layer with a thickness of around 10% of the wavelength is used as the supporting substrate. An impedance bandwidth of 35% and an average gain of 7.5 dBi can be achieved. The radiation pattern is stable across the passband.

The EXPERF Scale: A Cross-National Generalized Export Performance Measure

Abstract: A large number of studies have attempted to identify factors that are correlated with exporting success. However, much controversy exists about the key determinants of export performance and their ...

Call Duration as an Indicator of Genetic Quality in Male Gray Tree Frogs

Abstract: The "good genes" hypothesis predicts that mating preferences enable females to select mates of superior genetic quality. The genetic consequences of the preference shown by female gray tree frogs for long-duration calls were evaluated by comparing the performance of maternal half-siblings sired by males with different call durations. Offspring of male gray tree frogs that produced long calls showed better performance during larval and juvenile stages than did offspring of males that produced short calls. These data suggest that call duration can function as a reliable indicator of heritable genetic quality.

Biological delineation of terrestrial buffer zones for pond-breeding salamanders

Abstract: Many semi-aquatic organisms, such as salamanders, depend on both aquatic and terrestrial habitats to complete their life cycle and maintain viable populations. But current U.S. federal and state regulations protect only the wetland itself or arbitrarily defined portions of terrestrial habitat, if any. Part of the reason terrestrial habitats adjacent to wetlands are not protected is the lack of a clear understanding of the distances from shorelines that are biologically relevant to wetland fauna. Such information is critical for delineation of terrestrial “buffer zones” for wetlands, and thus for the conservation of semi-aquatic organisms. I summarized data from the literature on terrestrial habitat use by one group of pond-breeding salamanders, especially distances individuals traveled away from ponds. The results provide a basis for setting terrestrial buffer zones determined from actual habitat use by adult and juvenile salamanders. The mean distance salamanders were found from the edge of aquatic habitats was 125.3 m for adults of six species and 69.6 m for juveniles of two of these species. Assuming that the mean distance encompasses 50% of the population, a buffer zone encompassing 95% of the population would extend 164.3 m (534 ft) from a wetland’s edge into the terrestrial habitat. Data from other amphibians suggest that this buffer zone is applicable to a range of species, but caution should be taken for taxa suspected to be more vagile. Wetland managers and policymakers must recognize the special needs of semi-aquatic organisms during their entire life cycle, not just during the breeding season. To maintain viable populations and communities of salamanders, attention must be directed to the terrestrial areas peripheral to all wetlands. Data on habitat use from salamanders and other semi-aquatic species make it increasingly apparent that maintaining the connection between wetlands and terrestrial habitats will be necessary to preserve the remaining biodiversity of our vanishing wetlands. Delineacion Biologica de Zonas Terrestres de Amortiguamiento para Salamandras con Reproduccion en Charcas Muchos organismos semi-acuaticos, como son las salamandras, dependen tanto de habitats acuaticos como terrestres para completar su ciclo de vida y mantener poblaciones viables. Sin embargo, las actuales regulaciones federales y estatales en los Estados Unidos protegen unicamente a los humedales o a porciones de habitat terrestres (de ser posible). Parte de las razones por las cuales los habitates terrestres adyacentes a humedales no son protegidos se debe a la carencia de un claro entendimiento de las distancias biologicamente relevantes partiendo de los bordes y que son utilizados por la fuana del humedal. Esta informacion es critica para delinear zonas terrestres de “amortiguamiento” para humedales, y en consecuencia para la conservacion de organismos semi-acuaticos. Resumo datos de la literatura sobre el uso de habitat terrestre por un grupo de salamandras con reproduccion en charcas, especialmente de distancias individuales viajadas hacia afuera de las charcas. Los resultados proveen las bases para establecer zonas terrestres de amortiguamiento determinadas a partir del uso actual del habitat por salamandras adultas y juveniles. La distancia media a partir del borde de los habitats acuaticos en la cual las salamandras fueron encontradas fue de 125.3 m para adultos de seis especies y de 69.6 m para juveniles de dos de estas especies. Asumiendo que la distancia media abarca un 50% de la poblacion, una zona de amortiguamiento que abarque 95% de la poblacion podria extenderse hasta los 164.3 m (534 pies) partiendo del borde del humedal hacia el habitat terrestre. Datos de ostros anfibios sugieren que esta zona de amortiguamiento es aplicable para un rango de especies, pero se deben tomar precauciones para taxes de los que se sospecha se desplazan mas. Manejadores de humedales y estructuradores de politicas deben reconocer las necesidades especiales de organismos semi-acuaticos a lo largo de su ciclo de vida completo, no solo durante la temporada de reproduccion. Se debe dirijir especial atencion a las areas terrestres perifericas a todos los humedales para mantener poblaciones viables y comunidades de salamandras. Datos de uso del habitat por salamandras y otras especies semi-acuaticas hacen mas aparente la necesidad de mantener la coneccion entre humedales y habitats terrestres para conservar la biodiversidad que aun queda en nuestros humedales en desaparicion.

Interdependence, Punitive Capability, and the Reciprocation of Punitive Actions in Channel Relationships:

Abstract: Using data from automobile dealers in the Netherlands, the authors find that dealers’ punitive actions toward their key suppliers are affected by their perceptions of their own and their supplier's...

Evolutionary theories of aging: confirmation of a fundamental prediction, with implications for the genetic basis and evolution of life span.

Abstract: Evolutionary considerations predict that rate of aging should vary in direct relation to the mortality rate of presenescent young adults (extrinsic mortality rate) independently of differences in physiology, such as rate of metabolism. This prediction emerges from theory irrespective of the particular genetic mechanisms responsible for variation in aging. Yet this critical relationship has not been confirmed in comparative studies of natural populations. In the present analysis, rate of aging is estimated by the rate of increase in mortality rate (mx) with age (x). Comparisons between natural and captive populations of birds suggest that the Weibull model (mx = m0 + alphaxbeta) provides a better description of aging than the Gompertz model (mx = m0esigmax). Rate of aging is quantified by the parameter omega (dimension: 1/time), which is calculated from the Weibull parameters alpha and beta (omega = alpha1/(beta+1)). In this analysis, rate of aging in birds and mammals is directly related to extrinsic mortality (estimated by the initial mortality rate, m0) independently of taxonomic group and of variation in body size and, by implication, metabolic rate. When time is expressed in years, rate of senescence is related to initial mortality rate by omega = 0.294m0(0.367). This result implies that natural selection in response to variation among taxa in m0 has resulted in the evolutionary modification of factors that influence the rate of aging in natural populations. The potential strength of selection on factors that could further reduce rate of aging is indicated by the proportion of deaths due to aging-related causes. Although species with low initial mortality rates also exhibit reduced rates of increase in mortality rate with age (i.e., delayed senescence), the relatively high proportion of aging-related deaths in such species suggests that further evolutionary responses leading to long life are severely constrained. This argues against mutation accumulation and antagonistic pleiotropy as genetic mechanisms underlying senescence and suggests, instead, that rate of aging represents a balance between wear and tear, on the one hand, and genetically controlled mechanisms of prevention and repair, on the other. Evidently, remedies for extreme physiological deterioration in old age either are not within the range of genetic variation or are too costly to be favored by selection.