Pathway to domestic natural rubber production: a cradle-to-grave life cycle assessment of the first guayule automobile tire manufactured in the United States

The International Journal of Life Cycle Assessment - Guayule (Parthenium argentatum) is a perennial shrub that can be cultivated in the Southwestern US. It produces natural rubber that could be a...     

High-frequency generation of conditional mutations affecting Drosophila melanogaster development and life span.

Genome sequencing reveals that a large percentage of Drosophila genes have homologs in humans, including many human disease genes. The goal of this research was to develop methods to efficiently test Drosophila genes for functions in vivo. An important challenge is the fact that many genes function at more than one point during development and during the life cycle. Conditional expression systems such as promoters regulated by tetracycline (or its derivative doxycycline) are often ideal for testing gene functions. However, generation of transgenic animals for each gene of interest is impractical. Placing the doxycycline-inducible ("tet-on") promoter directed out of the end of the P transposable element produced a mobile, doxycycline-inducible promoter element, named PdL. PdL was mobilized to 228 locations in the genome and was found to generate conditional (doxycycline-dependent), dominant mutations at high frequency. The temporal control of gene overexpression allowed generation of mutant phenotypes specific to different stages of the life cycle, including metamorphosis and aging. Mutations characterized included inserts in the alpha-mannosidase II (dGMII), ash1, and pumilio genes. Novel phenotypes were identified for each gene, including specific developmental defects and increased or decreased life span. The PdL system should facilitate testing of a large fraction of Drosophila genes for overexpression and misexpression phenotypes at specific developmental and life cycle stages.     

Host density influences parasitism of the armyworm Pseudaletia unipuncta in agricultural landscapes

Several studies have shown positive responses of parasitism to either host density or landscape complexity. However, no experiments have manipulated host density in landscapes of differing complexity. Here we report the results of a field experiment conducted to determine how host density and agricultural landscape structure jointly affect parasitism and parasitoid diversity of Pseudaletia unipuncta (Haworth) (Lepidoptera: Noctuidae). Parasitism was assessed by experimentally adding P. unipuncta sentinel larvae at low (1 larvae/plant) and high (3 larvae/plant) densities to detect parasitism in commercial cornfields located in a complex and a simple agricultural landscape. The braconid wasps Glyptapanteles militaris (Walsh) and Meteorus spp. accounted for 98.4% of the observed parasitism. Landscape structure did not influence parasitism (80.2% on average) and contrary to expectations, showed a trend towards increased parasitoid richness and diversity in the simple landscape. Increasing host density revealed a trend of increasing parasitoid richness and diversity, and differentially affected parasitism at the parasitoid specific level. G. militaris parasitized a significantly greater proportion of hosts at low host density, while the opposite occurred for Meteorus spp. (primarily M. communis). These offsetting responses of parasitoids resulted in the lack of an overall host density effect on parasitism. The differential response of these parasitoids to host density is discussed in relation to differences in morphological and life history characteristics. Our results suggest that the specific composition of parasitoid assemblages could significantly alter parasitism at different host densities independently of landscape structural complexity.

Zusammenfassung

Verschiedene Untersuchungen haben gezeigt, dass Parasitismus entweder auf die Wirtsdichte oder die Landschaftskomplexität positiv reagiert. Dennoch haben keine Experimente die Wirtsdichte in Landschaften unterschiedlicher Komplexität manipuliert. Hier berichten wir von den Ergebnissen eines Freilandexperiments, das unternommen wurde, um zu bestimmen, wie die Wirtsdichte und die Struktur der Agrarlandschaft gemeinschaftlich die Parasitierung und die Parasitoidendiversität bei Pseudaletia unipuncta (Haworth) (Lepidoptera: Noctuidae) beeinflussen. Die Parasitierung wurde gemessen indem experimentell P. unipuncta Larven in geringen (1 Larve/Pflanze) und hohen (3 Larven/Pflanze) Dichten hinzugefügt wurden, um die Parasitierung in kommerziellen Kornfeldern zu erfassen, die in komplexen und einfachen Agrarlandschaften lagen. 98.4% der Parasitierung entfiel auf die braconiden Wespen Glyptapanteles militaris (Walsh) und Meteorus spp. Die Struktur der Landschaft beeinflusste die Parasitierung nicht (durchschnittlich 80.2%) und zeigte entgegen den Erwartungen einen Trend zu einer erhöhter Parasitoidenartenzahl und -diversität in der einfachen Landschaft. Eine zunehmende Wirtsdichte ließ einen Trend zu einer erhöhten Parasitoidenartenzahl und -diversität erkennen, und sie beeinflusste die Parasitierung auf dem Artenlevel der Parasitoide unterschiedlich. G. militaris parasitierte einen signifikant höheren Anteil der Wirte bei geringen Wirtsdichten, während für Meteorus spp. (vor allem M. communis) das Gegenteil zutraf. Diese sich ausgleichenden Reaktionen der Parasitoide führten zum Fehlen eines Gesamteffekts der Wirtsdichte auf die Parasitierung. Die unterschiedlichen Reaktionen dieser Parasitoide auf die Wirtsdichte werden in Zusammenhang mit Unterschieden in der Morphologie und Lebensweise diskutiert. Unsere Ergebnisse weisen darauf hin, dass die spezifische Zusammensetzung von Ansammlungen von Parasitoiden die Parasitierung bei unterschiedlichen Wirtsdichten unabhängig von der Komplexität der Landschaftsstruktur signifikant verändern könnte.     

A Regional Retrospective Assessment of the Potential Stressors Causing the Decline of the Cherry Point Pacific Herring Run

The Pacific herring stock that spawns at Cherry Point, northwest of Bellingham, WA, has undergone a dramatic decline in the last 20 years. The population decline corresponds with a collapse of the age structure. The Cherry Point area contains three deep water shipping piers, two refineries, an aluminum smelter, and urban development. The Cherry Point Aquatic Reserve was formed initially to protect the spawning habitat of the Cherry Point Pacific herring run. We conducted a retrospective assessment using the relative risk model (RRM) to investigate the causes of the current decline of the Cherry Point run. The RRM combines aspects of the weight-of-evidence (WoE) approach and other methods of establishing causality into a framework that deals with multiple stressors, uncertainty, and spatial scale.

An analysis of the Cherry Point Pacific herring age structure and population dynamics indicates that the loss of reproductive potential of the older age class fish was the population characteristic that led to the decline of the run. Exploitation, habitat alteration and climate change are the risk factors that contribute to the decline of the Cherry Point Pacific herring. The retrospective assessment identified the cyclic nature of climate change, as expressed by the warmer sea surface temperatures associated with a warm Pacific Decadal Oscillation (PDO), as the primary factor altering the dynamics of the Pacific herring. Other factors are ranked accordingly along with the associated uncertainty. Criteria for selecting alternative endpoints for managing the Cherry Point Aquatic Reserve are also provided.

The strengths of the retrospective RRM include its ability to combine a WoE and causality criteria with a multitude of stressors at a regional scale. The difficulties include how to deal with differences in the magnitude of effects, and expressing the uncertainty as distributions.     

Distribution of mutations in human thymidylate synthase yielding resistance to 5-fluorodeoxyuridine

Thymidylate synthase (TS) catalyzes methylation of dUMP to dTMP and is the target of cancer chemotherapeutic agents (e.g. 5-fluorouracil). Here, we used error-prone PCR to mutagenize the full-length human TS cDNA and then selected mutants resistant to 5-fluorodeoxyuridine in a bacterial complementation system. We found that resistant mutants contained 1-5 amino acid substitutions and that these substitutions were located along the entire length of the polypeptide. Mutations were frequent near the active site Cys(195) and in the catalytically important Arg(50) loop; however, many mutations were also distributed throughout the remainder of the cDNA. Mutants containing a single amino acid replacement identified the following 14 residues as unreported sites of resistance: Glu(23), Thr(51), Thr(53), Val(84), Lys(93), Asp(110), Asp(116), Pro(194), Ser(206), Met(219), His(250), Asp(254), Tyr(258), and Lys(284). Many of these residues are distant from the active site and/or have no documented function in catalysis or resistance. We conclude that mutations distributed throughout the linear sequence and three-dimensional structure of human TS can confer resistance to 5-fluorodeoxyuridine. Our findings imply that long range interactions within proteins affect catalysis at the active site and that mutations at a distance can yield variant proteins with desired properties.     

Probing the nature of H2 activation in catalytic asymmetric hydrogenation

Despite many years of intensive study, the natures of turnover-limiting and enantio-determining steps in catalytic asymmetric hydrogenation of prochiral enamides are poorly understood. An intriguing set of studies involving isotopic labeling distributions in catalytic enamide hydrogenation reactions were reported by Brown and Parker (Organometallics, 1 (1982) 950–956) more than a decade ago. In this paper we report the results of studies re-examining the application of isotopic probes to the catalytic hydrogenation enamides. These results provide some insights into the nature of the H₂ activation step in enamide hydrogenation.     

A Regional Multiple-Stressor Rank-Based Ecological Risk Assessment for the Fjord of Port Valdez,Alaska

We conducted an ecological risk assessment of the marine environment of Port Valdez, a fjord in south-central Alaska. Because the assessment was regional rather than site-specific and contained a large number of different stressors in a variety of environments, we required a nontraditional method to estimate risks. We created a Relative Risk Model to rank and sum individual risks numerically within each subarea, from each source, and to each habitat. Application of this model involved division of Port Valdez into 11 subareas containing specific ecological and anthropogenic structures and activities. Within each subarea, the stressor sources were analyzed to estimate exposure of receptors within habitats leading to effects relevant to the chosen assessment endpoints. The subareas were analyzed and compared to form a Port-wide perspective of ecological risk. Available chemical concentrations from sediment and mussels collected from the Port were compared to various toxicological benchmarks as a partial confirmation of the risk analysis. An estimation of the risk of polycyclic aromatic hydrocarbons (PAHs) to marine invertebrates indicated low risk. The municipal boat harbor had the highest estimate, which reflected our relative risk rankings. The Relative Risk Model approach appears robust and has potential for use in situations where multiple stressors are of concern and for assessments covering broad geographic areas. In the Port Valdez assessment the approach provided relative risk rankings for chemical and physical stressors from various sources. But data were available for confirmation of risk estimates only for the chemical stressors. The rankings are relative, and extrapolation beyond the scenario in which they were developed is not warranted. Uncertainty is large, and the numerical scores collapse a multidimensional space into a single value. Use of just the numerical score out of context is more valid than with other indexes. The value of the approach lies in the relative rankings and the accounting of the components of the relative risk score.