During the Deepwater Horizon oil well blowout in the Gulf of Mexico, the application of 7 million liters of chemical dispersants aimed to stimulate microbial crude oil degradation by increasing the bioavailability of oil compounds. However, the effects of dispersants on oil biodegradation rates are debated. In laboratory experiments, we simulated environmental conditions comparable to the hydrocarbon-rich, 1,100 m deep plume that formed during the Deepwater Horizon discharge. The presence of dispersant significantly altered the microbial community composition through selection for potential dispersant-degrading Colwellia, which also bloomed in situ in Gulf deep waters during the discharge. In contrast, oil addition to deepwater samples in the absence of dispersant stimulated growth of natural hydrocarbon-degrading Marinobacter. In these deepwater microcosm experiments, dispersants did not enhance heterotrophic microbial activity or hydrocarbon oxidation rates. An experiment with surface seawater from an anthropogenically derived oil slick corroborated the deepwater microcosm results as inhibition of hydrocarbon turnover was observed in the presence of dispersants, suggesting that the microcosm findings are broadly applicable across marine habitats. Extrapolating this comprehensive dataset to real world scenarios questions whether dispersants stimulate microbial oil degradation in deep ocean waters and instead highlights that dispersants can exert a negative effect on microbial hydrocarbon degradation rates.

Phosphorus has been identified as an important determinant of nutritionrelated biological variation. The macronutrients protein (P) and carbohydrates (C), both alone and interactively, are known to affect animal performance. No study, however, has investigated the importance of phosphorus relative to dietary protein or carbohydrates, or the interactive effects of phosphorus with these macronutrients, on fitness-related traits in animals. We used a nutritional geometry framework to address this question in adult field crickets (Gryllus veletis). Our results showed that lifespan, weight gain, acoustic mate signalling and egg production were maximized on diets with different P : C ratios, that phosphorus did not positively affect any of these fitness traits, and that males and females had different optimal macronutrient intake ratios for reproductive performance. When given a choice, crickets selected diets that maximized both lifespan and reproductive performance by preferentially eating diets with low P : C ratios, and females selected diets with a higher P : C ratio than males. Conversely, phosphorus intake was not regulated. Overall, our findings highlight the importance of disentangling the influences of different nutrients, and of quantifying both their individual and interactive effects, on animal fitness traits, so as to gain a more integrative understanding of their nutritional ecology.

During the 2010 Deepwater Horizon (DWH) oil spill, 1.84 M gallons of chemical dispersant was applied to oil released in the subsurface and to oil slicks at the surface. We used liquid chromatography with tandem mass spectrometry to quantify the anionic surfactant DOSS (dioctyl sodium sulfosuccinate) in samples collected from environments known to contain oil persisting from the DWH oil spill. DOSS was found to persist in variable quantities in deep-sea coral communities (6−9000 ng/g) 6 months after the spill and on Gulf of Mexico beaches (1−260 ng/g) 26−45 months after the spill. These results indicate that the applied dispersant, which was thought to undergo rapid degradation in the water column, remains associated with oil in the environment and can persist for ∼4 years.

No abstract

The majority of patients with IC can be managed conservatively. Right-sided IC, guarding, lack of bleeding per rectum and chronic constipation are associated with severe IC.

Visual appearance depends upon the resolution of ambiguities that arise when 2D retinal images are interpreted as 3D scenes. This resolution may be characterized as a form of Bayesian perceptual inference, whereby retinal sense data combine with prior belief to yield an interpretation. Under this framework, the prior reflects environmental statistics, so an efficient system should learn by changing its prior after exposure to new statistics. We conjectured that a prior would only be modified when sense data contain disambiguating information, such that it is clear what bias is appropriate. This conjecture was tested by using a perceptually bistable stimulus, a rotating wire-frame cube, as a sensitive indicator of changes in the prior for 3D rotation direction, and by carefully matching perceptual experience of ambiguous and unambiguous versions of the stimulus across three groups of observers. We show for the first time that changes in the prior—observed as a change in bias that resists reverse learning the next day—is affected more by ambiguous stimuli than by disambiguated stimuli. Thus, contrary to our conjecture, modification of the prior occurred preferentially when the observer actively resolved ambiguity rather than when the observer was exposed to environmental contingencies. We propose that resolving stimuli that are not easily interpreted by existing visual rules must be a valid method for establishing useful perceptual biases in the natural world.

The direction of rotation of a wire-frame (Necker) cube, which is perceptually bistable, can be trained to depend on stimulus location (Q. Haijiang, J. A. Saunders, R. W. Stone, & B. T. Backus, 2006). However, it is not known which aspects of “location” are important to this learning. We therefore explored “location” in a series of experiments that separately assessed testing venue, location relative to the observer, and location in the retinal image as types of location signal that could potentially be recruited by the visual system. Subjects were trained using wire-frame cubes with rotation direction disambiguated by depth cues. Training cubes were presented at two locations, rotating in opposite directions. On interleaved test trials, ambiguous monocular cubes were presented at the same two locations. The extent to which test cubes were perceived to rotate according to the trained location-rotation contingency was our measure of location-cue recruitment. We found that only retinal position was recruited as a cue for apparent rotation direction. Furthermore, the learned retinal location cue was robust to ocular transfer. Our findings are consistent with a relatively low-level site of learning, such as MT.

The integration of spatially distinct elements into coherent objects is a fundamental process of vision. Yet notwithstanding an extensive literature on perceptual grouping, we still lack a clear understanding of the representational consequences of grouping disparate visual locations. We investigated this question in a feature comparison task; subjects identified matching features that belonged either to the same apparent object (within-object condition) or to different apparent objects (between-object condition). The stimulus was backward-masked at a variable SOA, to examine the consequences of changes in the perceptual organization of the segments over time. Critical to our aims, the two objects composing our stimulus were occluded to a variable extent, so that differences in within-object and between-object performance could be unequivocally related to the formation of objects. For certain stimulus arrangements, we found superior performance for within-object matches. The pattern of performance was, however, highly dependent on the stimulus orientation and was not related to the strength of the object percept. Using an oblique stimulus arrangement, we observed superior between-object comparisons that did vary with the object percept. We conclude that performance in our feature comparison task is strongly influenced by spatial relations between features that are independent of object properties. Indeed, this dominating effect may hide an underlying mechanism whereby formation of a visual object suppresses comparison of distinct features within the object.