Stereochemistry affects sesquiterpene lactone bioactivity against an herbivorous grasshopper

Sesquiterpene lactones are defensive compounds which protect plants against a variety of herbivores and other natural enemies. Sesquiterpene lactones from higher plants can be divided into two groups based on the stereochemistry of their lactone ring junction, either cis-fused or trans-fused. It is unclear whether and how this variation affects potentially important ecological interactions. To investigate whether stereochemical variation in sesquiterpene lactone ring junctions can influence resistance to herbivorous insects, we performed controlled feeding trials with two pairs of diastereomeric sesquiterpene lactones and examined the deterrent effect of each compound on feeding by the polyphagous grasshopper Schistocerca americana (Drury). Sesquiterpene lactone stereochemistry and concentration significantly influenced feeding behavior with grasshoppers consuming less of the trans-fused compounds than the cis-fused compounds. To our knowledge, this is the first demonstration that sesquiterpene lactone ring junction stereochemistry influences the feeding behavior of herbivores. Because this stereochemical trait polymorphism is widely distributed in nature, it could have substantial consequences for the ecology and evolution of large groups of plants, particularly the Asteraceae.     

GIS Methodology for Quantifying Channel Change in Las Vegas,Nevada1

Abstract:  This study applies spatial analyses to examine the consequences of accelerated urban expansion on a hydrologic system over a period of 24 years. Three sets of historical aerial photos are used in a GIS analysis to document the geomorphic history of Las Vegas Wash, which drains the rapidly growing Las Vegas urban area in southern Nevada. New spatial techniques are introduced to make quantitative measurements of the erosion at three specific time intervals in the hydrologic evolution of the channel and floodplain. Unlike other erosion studies that use two different elevation surfaces to assess erosion, this study used a single elevation surface to remove systematic and nonsystemic elevation errors. The spatial analysis quantifies channel changes for discrete time periods, calculates erosion volumes, and provides a foundation to examine how the specific mechanisms related to urban expansion have affected Las Vegas Wash. The erosion calculated over 24 years is the largest documented sediment loss attributed to the effect of rapid urban growth.     

Foliage responses of spruce trees to long-term low-grade sulfur dioxide deposition

Foliage on spruce trees (Picea rubens Sarg.) growing on dry SO(2) deposition zones (dry SO(2) deposition ranging from 0.5 and 8.5 S kg ha(-1) year(-1)) downwind from a SO(2) emission source was analyzed to assess chronic effects of long-term low-grade SO(2) deposition on net photosynthesis, stomatal conductance, dark respiration, stomatal antechamber wax structures, elemental concentrations in and on foliage (bulk and surficial concentrations), and types of epiphytic fungi that reside in the phylloplane. Elemental distributions on stomatal antechambers, on fungal colonies, and on smooth surfaces between stomates and fungus colonies were determined with a scanning electronic microscope (SEM) by way of X-ray scanning. It was found that net photosynthesis of newly developed spruce foliage (current-year, and 1-year-old) was not significantly affected by the local SO(2) deposition rates. Sulfur dioxide deposition, however, may have contributed to the gradual decrease in net photosynthesis with increasing needle age. Dark respiration rates were significantly higher on foliage taken from high SO(2) deposition zones. Stomatal rod-web structures deteriorated to flakes with increasing needle age and increasing SO(2) deposition. Further inspection of the needle surfaces revealed an increasing abundance of fungal colonies with increasing needle age. Many fungal taxa were isolated and identified. It was found that black yeasts responded positively, and Xylohypha pinicola responded negatively to high rates of SO(2) deposition. Surficial concentrations of elements such as P, S, K, Cl, Ca were about 10 times higher on fungal colonies than on smooth needle surfaces. Surficial Ca contents on 4 or 5-year-old needles decreased with increasing SO(2) deposition, but surficial S concentrations remained the same. In contrast, bulk foliar Ca and S concentrations increased with increasing SO(2) deposition.     

Reproductive biology of the tiger shark (Galeocerdo cuvier) in Hawaii

The tiger shark (Galeocerdo cuvier) is the largest shark in the family Carcharhinidae and the only carcharhinid with aplacental viviparous (ovoviviparous) reproduction. Despite its size and prevalence, many details of tiger shark reproductive biology are unknown. Size at maturity and litter size have been reported by several authors, but a lack of large numbers of pregnant females has made it difficult to determine gestation period, seasonality, and timing of the female reproductive cycle. Here we analyze data from shark control program fishing and incidental catches in Hawaii (n = 318) to construct the most complete picture of tiger shark reproduction to date. Males reached maturity at approximately 292 cm total length (TL) based on clasper calcification, whereas females matured between 330 and 345 cm TL based on oviducal gland and uterus widths. Litter sizes ranged from 3 to 57 with a mean of 32.6 embryos per litter. Data from 23 litters from various months of the year indicate that tiger sharks are usually 80–90 cm TL at birth, and that the gestation period is 15–16 months. Mating scars were observed in January–February and sperm is presumably stored for 4–5 months until ovulation takes place in May–July. Gestation begins in June–July and pups are born in September–October of the following year. Our data suggest that female tiger sharks in Hawaii give birth only once every three years. This could have major implications for conservation and management of this species, as it suggests that tiger shark fecundity is 33% lower than previously thought. This could greatly reduce the ability of this species to rebound from fishing pressure.

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Vacuum sampling techniques for industrial hygienists, with emphasis on beryllium dust sampling

The U.S. Department of Energy (DOE) Chronic Beryllium Disease Prevention Program Rule, 10 CFR Part 850 became effective in 2000 in response to the prevalence of Chronic Beryllium Disease (CBD) in workers. The rule requires surface and air monitoring for beryllium to determine exposure levels and the evaluation of the effectiveness of controls used to minimize or eliminate that risk. The most common methods for surface sampling use wet or dry wipes. Wipe sampling techniques may be impractical for many surfaces common to most buildings such as cinder block, textured wall surfaces, fabric and carpet. Vacuum sampling methods have been developed for the evaluation of lead or pesticides on residential surfaces such as carpets, bare floors and window sills. However, the current vacuum methods may be impractical for many workplace situations such as sampling of protective clothing, complex facility structures, or equipment surfaces. Recent work using vacuum sampling for potential bio-terrorism agents such as anthrax spores may have significant application to industrial hygiene evaluations of the workplace and may be extendable for use in sampling of metals such as beryllium. Validated vacuum sampling methods that provide meaningful data would be of great value to industrial hygienists in identifying areas having surface contamination, evaluating existing controls and work practices and determining the potential of toxic material on surfaces to become airborne and present a potential risk to workers and the public. This article discusses various vacuum sampling methodologies and recommends harmonization of sampling methods.     

Development of Regional Curves for Hydrologic Landscape Regions (HLR) in the Contiguous United States

Regional curves relate drainage area to the bankfull channel characteristics discharge, cross‐sectional area, width, and mean depth. These curves are used for a variety of purposes, including aiding in the field identification of bankfull elevation and in the natural channel design process. When developing regional curves, the degree to which landform, geology, climate, and vegetation influence stream systems within a single physiographic province may not be fully considered. This study examined the use of the U.S. Geological Survey's Hydrologic Landscape Regions (HLR), as well as data from 2,856 independent sites throughout the contiguous United States (U.S.), to develop a set of regional curves (bankfull discharge, cross‐sectional area, width, and mean depth) for (1) the contiguous U.S., (2) each of the 20 HLRs, (3) each of the eight physiographic divisions, (4) 22 of the 25 physiographic provinces, and (5) individual HLRs within the physiographic provinces. These regional curves were then compared to each other, as well as those from the literature. Regional curves developed for individual HLRs, physiographic divisions, and physiographic provinces tended to outperform the contiguous U.S. indicating increased stratification was beneficial. Further stratifying physiographic provinces by HLR markedly improved regional curve reliability. Use of HLR as a basis of regional curve development, rather than physiographic region alone, may allow for the development of more robust regional curves.     

How much heterogeneity? Flow versus area from a big data perspective

Over the past 10 years, there has been an increased recognition that matrix diffusion processes are a significant factor controlling the success of groundwater remediation. New field techniques and modeling tools have, consequently, been developed to understand how contaminants diffuse into and then out of low‐permeability (“low‐k”) zones and assess the resulting impact on groundwater quality. Matrix diffusion, in turn, is driven by one key factor: geologic heterogeneity. The importance of heterogeneity is being emphasized in the groundwater field by general rules of thumb such as “90% of the mass flux occurs in 10%‐20% of the cross‐sectional area” and conceptual models that show most of the groundwater flow occurs through the aquifer's “mobile porosity” which just a small fraction of commonly used effective porosity values (between 0.02 and 0.10 for mobile porosity vs. 0.25 for effective porosity). For this study, 141 boring logs from 43 groundwater remediation sites were evaluated to develop an empirically based estimate of the groundwater flow versus aquifer cross‐sectional area to confirm or reject the general flow versus area rules of thumb. This study indicated that at these 43 sites, an average of 30% of the cross‐sectional area carried 90% of the groundwater flow. Our flow‐only analysis does provide moderate (but not confirmatory) support for the “mobile porosity” concept with an estimated representative mobile porosity value of about 0.11 at the 43 sites.     

An experimental field test of host-finding mechanisms in a Caribbean gnathiid isopod

Field experiments were conducted from dusk to dawn off St. John (18° 18′ 59.32″ N, 64° 43′ 24.5″ W) and Guana Island (18° 28″ 28.31″ N, 64° 34′ 30.83″ W), Virgin Islands from June through August 2008-2010 to assess the sensory cues used by the nocturnal/crepuscular fish-parasitic gnathiid isopod, Gnathia marleyi, to locate fish hosts. Experimental traps providing both visual and olfactory cues from live French grunts (Haemulon flavioliniatum) attracted significantly more gnathiids than traps providing only visual cues or control traps (empty or with a rock), which were not significantly different from each other. In another experiment, traps providing both cues and only olfactory cues attracted significantly more gnathiids than empty control traps, but were not significantly different from each other. Our findings suggest that during nocturnal and crepuscular periods, visual cues provided by resting or slow-moving fish are not alone sufficient to attract gnathiids, while olfactory cues alone are. The traps designed for this study offer a new method of sampling free-living gnathiid isopods.     

Predictors of occupancy trend across spatial scale

Many explorations of extinction probability have had a global focus, yet it is unclear whether variables that explain the probability of extinction at large spatial extents are the same as those at small spatial extents. Thus, we used nearly annual presence-absence records for the most recent 40 years of a 110-year data set from Palenque, Mexico, an area with ongoing deforestation, to explore which of >200 species of birds have probabilities of extirpation that are likely to increase. We assessed associations between long-term trends in species presence (i.e., detection in a given year) and body size, geographic range size, diet, dependence on forest cover, taxonomy, and ecological specialization. Our response variable was the estimated slope of a weighted logistic regression for each species. We assessed the relative strength of each predictor by means of a model ranking scheme. Several variables associated with high extinction probability at global extents, such as large body size or small geographic range size, were not associated with occurrence of birds over time at our site. Body size was associated with species loss at Palenque, but occurrence trends of both very large and very small species, particularly the latter, have declined, or the species have been extirpated. We found no association between declining occurrence trend and geographic range size, yet decline correlated with whether a species depends on forest (mean occupancy trend =-0.0380, 0.0263, and 0.0186 for, respectively, species with high, intermediate, or low dependence on forest) and with complex combinations of diet and foraging strata (e.g., occurrence of canopy insectivores and terrestrial omnivores has increased, whereas occurrence of mid-level frugivores and terrestrial granivores has decreased). Our findings emphasize that analyses of local areas are necessary to explicate extirpation risk at various spatial extents.