The control of an invasive bivalve, Corbicula fluminea, using gas impermeable benthic barriers in a large natural lake.

Anoxia can restrict species establishment in aquatic systems and the artificial promotion of these conditions can provide an effective control strategy for invasive molluscs. Low abundances (2-20 m(-2)) of the nonnative bivalve, Asian clam (Corbicula fluminea), were first recorded in Lake Tahoe, CA-NV in 2002 and by 2010 nuisance-level population densities (>10,000 m(-2)) were observed. A non-chemical control method using gas impermeable benthic barriers to reduce dissolved oxygen (DO) concentrations available to C. fluminea was tested in this ultra-oligotrophic natural lake. In 2009, the impact of ethylene propylene diene monomer (EPDM) sheets (9 m(2), n = 6) on C. fluminea beds was tested on 1-7 day intervals over a 56 day period (August-September). At an average water temperature of 18 °C, DO concentrations under these small barriers were reduced to zero after 72 h resulting in 100 % C. fluminea mortality after 28 days. In 2010, a large EPDM barrier (1,950 m(2)) was applied to C. fluminea populations for 120 days (July-November). C. fluminea abundances were reduced over 98 % after barrier removal, and remained significantly reduced (>90 %) 1 year later. Non-target benthic macroinvertebrate abundances were also reduced, with variable taxon-specific recolonization rates. High C. fluminea abundance under anoxic conditions increased the release of ammonium and soluble reactive phosphorus from the sediment substrate; but levels of unionized ammonia were low at 0.004-0.005 mg L(-1). Prolonged exposure to anoxia using benthic barriers can provide an effective short term control strategy for C. fluminea.

Lake warming favours small-sized planktonic diatom species.

Diatoms contribute to a substantial portion of primary production in the oceans and many lakes. Owing to their relatively heavy cell walls and high nutrient requirements, planktonic diatoms are expected to decrease with climate warming because of reduced nutrient redistribution and increasing sinking velocities. Using a historical dataset, this study shows that diatoms were able to maintain their biovolume with increasing stratification in Lake Tahoe over the last decades; however, the diatom community structure changed. Increased stratification and reduced nitrogen to phosphorus ratios selected for small-celled diatoms, particularly within the Cyclotella genus. An empirical model showed that a shift in phytoplankton species composition and cell size was consistent within different depth strata, indicating that altered nutrient concentrations were not responsible for the change. The increase in small-celled species was sufficient to decrease the average diatom size and thus sinking velocity, which strongly influences energy transfer through the food web and carbon cycling. Our results show that within the diverse group of diatoms, small-sized species with a high surface area to volume ratio were able to adapt to a decrease in mixing intensity, supporting the hypotheses that abiotic drivers affect the size structure of planktonic communities and that warmer climate favours small-sized diatom cells.

Small GTPase Cdc42 is required for multiple aspects of dendritic morphogenesis.

The study of dendritic development in CNS neurons has been hampered by a lack of complex dendritic structures that can be studied in a tractable genetic system. In an effort to develop such a system, we recently characterized the highly complex dendrites of the vertical system (VS) neurons in the Drosophila visual system. Using VS neurons as a model system, we show here using loss-of-function mutations that endogenous Cdc42, a member of Rho family of small GTPases, is required for multiple aspects of dendritic morphogenesis. Cdc42-mutant VS neurons display normal complexity but increased dendritic length compared with wild type and have defects in dendrite caliber and stereotyped dendritic branch positions. Remarkably, Cdc42 mutant neurons also show a 50% reduction in dendritic spine density. These results demonstrate that Cdc42 is a regulator for multiple aspects of dendritic development.

Dendritic development of Drosophila high order visual system neurons is independent of sensory experience.

BACKGROUND: The complex and characteristic structures of dendrites are a crucial part of the neuronal architecture that underlies brain function, and as such, their development has been a focal point of recent research. It is generally believed that dendritic development is controlled by a combination of endogenous genetic mechanisms and activity-dependent mechanisms. Therefore, it is of interest to test the relative contributions of these two types of mechanisms towards the construction of specific dendritic trees. In this study, we make use of the highly complex Vertical System (VS) of motion sensing neurons in the lobula plate of the Drosophila visual system to gauge the importance of visual input and synaptic activity to dendritic development. RESULTS: We find that the dendrites of VS1 neurons are unchanged in dark-reared flies as compared to control flies raised on a 12 hour light, 12 hour dark cycle. The dendrites of these flies show no differences from control in dendrite complexity, spine number, spine density, or axon complexity. Flies with genetically ablated eyes show a slight but significant reduction in the complexity and overall length of VS1 dendrites, although this effect may be due to a reduction in the overall size of the dendritic field in these flies. CONCLUSIONS: Overall, our results indicate no role for visual experience in the development of VS dendrites, while spontaneous activity from photoreceptors may play at most a subtle role in the formation of fully complex dendrites in these high-order visual processing neurons.

Modeling MTBE and BTEX in lakes and reservoirs used for recreational boating.

It is generally recognized that the bulk of fuel-related volatile organic compounds (VOCs) in lakes and reservoirs come from motorized recreational boating, but a quantitative connection between the two has been difficult to establish. A detailed boating use survey was conducted at a Northern California multiple-use lake, and the results were used to quantify daily methyl tert-butyl ether (MTBE) and benzene, toluene, ethylbenzene, and xylene (BTEX) loading from recreational boating. A one-dimensional, process-based numerical model was used to predict VOC levels as a function of the number, type, and activity of marine engines using the lake, the vertical mixing dynamics of the lake, and the volatilization rates of the individual VOCs. The model was validated on two other reservoirs to establish its applicability under a range of climatic and boating conditions. The study further confirmed the link between motorized boating and surface-water VOC contamination. In addition, the results of this study suggest that volatilization alone is inadequate to describe the loss of volatile hydrocarbons from surface waters and that some combination of additional degradation processes is involved. Under low wind conditions, these degradation processes dominate the removal of MTBE. For toluene, these processes are always more dominant than volatilization. The mean relative percent difference (RPD) between measured and simulated VOC concentrations at the study site, accounting only for volatilization losses, was 50.6% for MTBE and 113% for toluene. A first-order submodel was implemented to account for losses other than volatilization, using decay coefficients estimated from the literature. The resulting mean RPDs between measured and modeled concentrations were 14.2% for MTBE and 4.5% for toluene.

A mosaic genetic screen for genes necessary for Drosophila mushroom body neuronal morphogenesis.

Neurons undergo extensive morphogenesis during development. To systematically identify genes important for different aspects of neuronal morphogenesis, we performed a genetic screen using the MARCM system in the mushroom body (MB) neurons of the Drosophila brain. Mutations on the right arm of chromosome 2 (which contains approximately 20% of the Drosophila genome) were made homozygous in a small subset of uniquely labeled MB neurons. Independently mutagenized chromosomes (4600) were screened, yielding defects in neuroblast proliferation, cell size, membrane trafficking, and axon and dendrite morphogenesis. We report mutations that affect these different aspects of morphogenesis and phenotypically characterize a subset. We found that roadblock, which encodes a dynein light chain, exhibits reduced cell number in neuroblast clones, reduced dendritic complexity and defective axonal transport. These phenotypes are nearly identical to mutations in dynein heavy chain Dhc64 and in Lis1, the Drosophila homolog of human lissencephaly 1, reinforcing the role of the dynein complex in cell proliferation, dendritic morphogenesis and axonal transport. Phenotypic analysis of short stop/kakapo, which encodes a large cytoskeletal linker protein, reveals a novel function in regulating microtubule polarity in neurons. MB neurons mutant for flamingo, which encodes a seven transmembrane cadherin, extend processes beyond their wild-type dendritic territories. Overexpression of Flamingo results in axon retraction. Our results suggest that most genes involved in neuronal morphogenesis play multiple roles in different aspects of neural development, rather than performing a dedicated function limited to a specific process.