Pericentric inversion of chromosome 19: prenatal diagnosis and genetic counselling

During prenatal diagnosis for advanced maternal age, a pericentric inversion of a chromosome 19 was detected in a male fetus. The inversion was familial, transmitted to the fetus by the phenotypically normal mother. The pregnancy resulted in a term birth of a phenotypically normal male infant. Inversion 19 appears to be a rare abnormality with only seven families reported thus far including ours. Infants with duplication deficiencies for chromosome 19 have not been reported in these families. This may suggest an apparent suppression of crossing over and recombination within the inverted segment of chromosome 19 during meiosis.     

Optimal copula duration in dungflies: effects of frequency dependence and female mating status

Summary The addition of frequency dependence to the marginal value theorem (MVT) model of the dung fly (Scatophaga stercoraria) male's optimal copula duration makes virtually no difference to the predicted competitive optimum (ESS). However, this evolutionarily stable strategy (ESS) version allows an explicit solution for the optimum. In a general sense, MVT optima will be close to their ESS equivalent when the cycle duration (expected time between the starts of two successive patch exploitations) is long relative to the plausible patch exploitation times. The optimal copula duration for male dung flies will depend on the ratio of virgin to mated females arriving at the droppings and on whether a male can discriminate between the two sorts of female. In nature, we found only an average of 3% of the total females arriving at the droppings to be virgins, rather less than had been estimated. This means that matings away from droppings (extra-dung matings) must be much commoner than previously suspected. Cumulative gains through copulation time rise much more steeply with virgins than with mated females, and so if males are able to discriminate, on the present model, we calculate that the ESS copula durations (at 20° C) would be around 42 min for non-virgins and 11 min for virgins. If they do not discriminate, the ESS is to copulate for a fixed duration of 41.5 min, i.e. very close to the optimum for mated females. The data indicate that copula duration does not differ for the two types of mating (mated females; virgins), suggesting that males cannot discriminate (or that the copula duration with virgins is not optimised to male interests). ESS copula durations with discrimination are almost entirely independent of the frequency of virgins in the population of females arriving at the droppings; without discrimination the optimal copula duration shifts between the ESS for mated females and that for virgins as the virgin frequency increases from 0 to 1. But at their naturally occurring frequency of only 3%, virgins can be ignored from calculations of optimal copula duration without significant loss of precision.Correspondence to: G.A. Parker     

Large Mammalian Herbivores and the Conservation of Arid Acacia Stands in the Middle East

Abstract: High mortality and poor recruitment in Acacia tree populations in many parts of the Middle East may result in loss of biodiversity. Human activities in recent decades have caused drastic changes in the water regime and the abundance of wild and domestic ungulates, which may negatively affect these trees. We studied the effects of large mammalian herbivores on the establishment of young Acacia raddiana and A. tortilis in the Arava Valley between the Red Sea and the Dead Sea, Israel. Seed accumulation under trees was high when large herbivores were excluded, and direct observations confirmed that ungulates were the main seed dispersers of these Acacia species. Insect seed predators (bruchid beetles) damaged more than 95% of seeds not consumed by ungulates. Seed germination was facilitated by gut passage through ungulates. Seedling survival was determined largely by water availability and was independent of herbivore density. Under present conditions, several years of high rainfall are necessary for successful establishment of young trees. Under severe browsing pressure by ungulates, growth in juvenile trees was delayed and smaller sizes were overrepresented. There was no evidence, however, of effects on the long-term demography of Acacia trees, perhaps because ungulates increased seedling densities by enhancing the viability and germination of seeds. We conclude that large mammalian herbivores are essential components of arid Acacia savannas and that wild and domestic ungulates must be included in future conservation plans.     

Widespread contribution of methane-cycle bacteria to the diets of lake profundal chironomid larvae

Reports of unexpectedly 13C-depleted chironomid larvae in lakes have led to an hypothesis that significant transfer of detrital organic matter to chironomid larvae may occur via methane-cycle bacteria. However, to date little is known of how such transfer might vary across species and lakes. We gathered data from 87 lakes to determine how widespread this phenomenon might be and to define boundaries for its likely magnitude. Carbon stable isotope values of chironomid larvae varied greatly between taxa. Very marked 13C-depletion was evident only in certain taxa, especially Chironomus plumosus, C. anthracinus, and C. tenuistylus, all characteristic of eutrophic or dystrophic lakes and known to be tolerant of low oxygen conditions. Furthermore, marked 13C-depletion was only found in larvae from lakes in which late-summer hypolimnetic oxygen depletion near the sediment surface was below an apparent threshold concentration of 2-4 mg O2/L. Similarly, application of a two-source mixing model suggested that methanotrophic bacteria made the greatest contribution to profundal chironomid growth (0-70% of larval carbon) when the late-summer oxygen concentration dropped below approximately 2 mg O2/L. Our study demonstrates that methane-derived carbon is an important, but often neglected, contribution to the flux of carbon through the food webs of many productive or dystrophic lakes.     

The role of marine aggregates in the ingestion of picoplankton-size particles by suspension-feeding molluscs

Suspension-feeding molluscs are important members of coastal communities and a large body of literature focuses on their feeding processes, including the efficiency of particle capture. Some molluscs, such as bivalves, capture individual picoplankton cells (0.2–2.0 μm) with a retention efficiency of less than 50%, leading to the assumption that such particles are not an important food resource. Picoplankton, however, are often concentrated in particle aggregates of much larger size. This study investigates the ability of suspension feeders to ingest picoplankton-size particles (0.2–2.0 μm) bound in marine aggregates. We fed clams (Mercenaria mercenaria), mussels (Mytilus edulis), oysters (Crassostrea virginica), scallops (Argopecten irradians) and slipper snails (Crepidula fornicata) 1.0- and 0.5-μm fluorescent particles (either polystyrene beads or bacteria) that were (1) dispersed in seawater, or (2) embedded within laboratory-made aggregates. Dispersed 10-μm beads were also delivered so that feeding activity could be determined. Ingested fluorescent particles were recovered in feces or isolated digestive glands and quantified. Results indicate that aggregates significantly enhance the ingestion of 1.0- and 0.5-μm beads by all species of bivalves, and enhance the ingestion of bacteria (greatest cell dimension ca. 0.6 μm) by all suspension feeders examined. Differences among species in their ability to ingest aggregates and picoplankton-size particles, however, were evident. Compared to mussels and clams, scallops and oysters ingested fewer aggregates with 1.0-μm beads or bacteria, and slipper snails ingested the most dispersed beads and bacteria. These differences may be a consequence of variations in gill structure and mechanisms of particle processing. Our data demonstrate that suspension feeders can ingest picoplankton-size particles that are embedded within aggregates, and suggest that such constituent particles may be an important food resource.     

Are savannas patch-dynamic systems? A landscape model

Savannas are ecosystems characterized by the coexistence of woody species (trees and bushes) and grasses. Given that savanna characteristics are mainly formed from competition, herbivory, fire, woodcutting, and patchy soil and precipitation characteristics, we propose a spatially explicit model to examine the effects of the above-mentioned parameters on savanna vegetation dynamics in space and time. Furthermore, we investigate the effects of the above-mentioned parameters on tree–bush–grass ratios, as well as the degrees of aggregation of tree–bush–grass biomass. We parameterized our model for an arid savanna with shallow soil depth as well as a mesic one with generally deeper and more variable soil depths. Our model was able to reproduce savanna vegetation characteristics for periods of time over 2000 years with daily updated time steps. According to our results, tree biomass was higher than bush biomass in the arid savanna but bush biomass exceeded tree and grass biomass in the simulated mesic savanna. Woody biomass increased in our simulations when the soil's porosity values were increased (mesic savanna), in combination with higher precipitation. Savanna vegetation varied from open savanna to woodland and back to open savanna again. Vegetation cycles varied over ∼300-year cycles in the arid and ∼220-year cycles in the mesic-simulated savanna. Autocorrelation values indicated that there are both temporal and spatial vegetation cycles. Our model indicated cycling savanna vegetation at the landscape scale, cycles in cells, and patchiness, i.e. patch dynamics.     

The impact of wood smoke on ambient PM2.5 in northern Rocky Mountain valley communities

During the winters of 2006/2007 and 2007/2008, PM_2.5 source apportionment programs were carried out within five western Montana valley communities. Filter samples were analyzed for mass and chemical composition. Information was utilized in a Chemical Mass Balance (CMB) computer model to apportion the sources of PM_2.5. Results showed that wood smoke (likely residential woodstoves) was the major source of PM_2.5 in each of the communities, contributing from 56% to 77% of the measured wintertime PM_2.5. Results of ¹⁴C analyses showed that between 44% and 76% of the measured PM_2.5 came from a new carbon (wood smoke) source, confirming the results of the CMB modeling. In summary, the CMB model results, coupled with the ¹⁴C results, support that wood smoke is the major contributor to the overall PM_2.5 mass in these rural, northern Rocky Mountain airsheds throughout the winter months.     

Design of Experimental Streams for Simulating Headwater Stream Restoration1

Huang, Jung-Chen, William J. Mitsch, and Andrew D. Ward, 2010. Design of Experimental Streams for Simulating Headwater Stream Restoration. Journal of the American Water Resources Association (JAWRA) 1-15. DOI: 10.1111/j.1752-1688.2010.00467.x Abstract: Headwater streams flowing through agricultural fields in the midwestern United States have been extensively modified to accommodate subsurface drainage systems, resulting in deepened, straightened, and widened streams. To restore these headwater streams, partial or total reconstruction of channels is frequently attempted. There are different approaches to reconstructing the channel, yet there is little evidence that indicates which promises more success and there has been no experimental work to evaluate these approaches. This study designs three experimental channels – two-stage, self-design, and straightened channels – on a human-created swale at the Olentangy River Wetland Research Park, Columbus, Ohio, for long-term evaluation of headwater stream evolution after restoration. The swale receives a continuous flow of pumped river water from upstream wetlands. Using streamflow and stage data for the past 12 years, a channel-forming discharge of 0.18 m³/s was estimated from bankfull discharge, effective discharge, and recurrence interval. These stream channels, after construction, will be monitored to evaluate physical, chemical, and biological responses to different channels over a decade-long experiment. We hypothesize that the three stream restoration designs will eventually evolve to a similar channel form but with different time periods for convergence. Monitoring the frequency and magnitude of changes over at least 10 years is needed to document the most stable restored channel form.     

Disaster risk,social vulnerability,and economic development

This paper examines the extent to which economic development decreases a country's risk of experiencing climate‐related disasters as well as the societal impacts of those events. The paper proceeds from the underlying assumption that disasters are not inherently natural, but arise from the intersection of naturally‐occurring hazards within fragile environments. It uses data from the International Disaster Database (EM‐DAT), 1 representing country‐year‐level observations over the period 1980–2007. The study finds that low‐income countries are significantly more at risk of climate‐related disasters, even after controlling for exposure to climate hazards and other factors that may confound disaster reporting. Following the occurrence of a disaster, higher income generally diminishes a country's social vulnerability to such happenings, resulting in lower levels of mortality and morbidity. This implies that continued economic development may be a powerful tool for lessening social vulnerability to climate change.     

The effect of a woodstove changeout on ambient levels of PM2.5 and chemical tracers for woodsmoke in Libby,Montana

Residential woodstoves are the single largest source of PM_2.5 in Libby, MT, resulting in the community being designated as a nonattainment area for PM_2.5. Beginning in 2005, a community-wide woodstove changeout program was implemented that replaced nearly 1200 old stoves with EPA-certified units. In an effort to track the reduction of woodsmoke particles throughout the program, ambient PM_2.5 samples were collected before, during, and after the changeout. These samples were analyzed for seven selected woodsmoke tracers, including vanillin, acetovanillone, guaiacol, 4-ethylguaiacol (methoxyphenols), levoglucosan (sugar anhydride), abietic acid, and dehydroabietic acid (resin acids). Results of the changeout showed that PM_2.5 levels decreased by 20% during the changeout period, while levels of the seven chosen tracer compounds gave variable responses. Levoglucosan levels decreased by 50% while both resin acids increased after the changeout, suggesting a change in the chemistry of the particles. No trend was observed in the levels of methoxyphenols as a group over the changeout period. The results suggest that the concentrations of woodsmoke related PM_2.5 in the Libby airshed have decreased; however, the chemistry of the emitted particles also changed when old woodstoves were replaced with new EPA-certified stoves.