Conflicting demands on detoxification pathways influence how common brushtail possums choose their diets

Most herbivores eat more and survive better when they have access to a variety of foods. One explanation involves the detoxification of plant secondary metabolites (PSMs). By feeding from a variety of plants that contain different classes of PSMs, animals can use multiple detoxification pathways and presumably consume more food. Although popular, this theory is difficult to test because it requires knowledge of the detoxification pathways of each PSM in the diet. We established that common brushtail possums (Trichosurus vulpecula) use various combinations of oxidation, hydrolysis, and conjugation with glucuronic acid (GA) or glycine to detoxify six PSMs. Compared to their ingestion of a single PSM, possums ate more when offered a choice between two diets containing PSMs that require apparently independent detoxification pathways (benzoate and 1,8-cineole, benzoate and p-cymene, benzoate and orcinol, benzoate and salicin, or orcinol and 1,8-cineole). However, possums still did not eat as much of these diets as they did of a basal diet free of PSMs. This suggests that detoxification pathways are never independent, but are separated instead by degrees. In contrast, possums offered a choice of two PSMs that require competing detoxification pathways (1,8-cineole and p-cymene, 1,8-cineole and salicin, or orcinol and salicin) ate no more than when offered diets containing one of the compounds. There was an exception: even though both rutin and orcinol are detoxified via conjugation with GA, the feeding behavior of possums did not suggest competition for detoxification pathways. This implies that the supply of GA is not limiting. This study provides the first convincing evidence that herbivorous mammals can eat more by selecting mixed diets with a diversity of PSMs that make full use of their detoxification potential. It also emphasizes that other behavioral and physiological factors, such as transient food aversions, influence feeding behavior.     

Loss of PM2.5 nitrate from filter samples in central California

Evaporative loss of particulate matter (with aerodynamic diameter < 2.5 microm, [PM2.5]) ammonium nitrate from quartz-fiber filters during aerosol sampling was evaluated from December 3, 1999, through February 3, 2001, at two urban (Fresno and Bakersfield) and three nonurban (Bethel Island, Sierra Nevada Foothills, and Angiola) sites in central California. Compared with total particulate nitrate, evaporative nitrate losses ranged from < 10% during cold months to > 80% during warm months. In agreement with theory, evaporative loss from quartz-fiber filters in nitric acid denuded samplers is controlled by the ambient nitric acid-to-particulate nitrate ratio, which is determined mainly by ambient temperature. Accurate estimation of nitrate volatilization requires a detailed thermodynamic model and comprehensive chemical measurements. For the 14-month average of PM2.5 acquired on Teflon-membrane filters, measured PM2.5 mass was 8-16% lower than actual PM2.5 mass owing to nitrate volatilization. For 24-hr samples, measured PM2.5 was as much as 32-44% lower than actual PM2.5 at three California Central Valley locations.     

Do pronghorn mothers reveal the locations of their hidden fawns?

Summary Success of the hider strategy in ungulates depends, in part, on the mother's ability to minimize information she transmits about her young's hiding place while remaining close enough to distract or drive away a predator. We predicted that pronghorn (Antilocapra americana) mothers should: (1) maintain minimum distances from their hidden fawns sufficient to cause the expected energy gain for a ground predator, systematically searching around the mother, to fall below that expected when searching for some other prey; (2) orient the axes of either head or trunk towald the hidden fawn no more frequently than would be expected by chance; (3) schedule behavior so that no activity is more likely than another to occur when a visit to the hidden fawn is imminent. At the National Bison Range, where coyote (Canis latrans) predation on pronghorn fawns is frequent, pronghorn mothers conform to predictions (1) and (3), but not (2). Within the first 10% of their time away from fawns, mothers reached an average distance of 70.4 m from their fawns' biding places and remained at that distance until 95% of their time away was clapsed. At this mother-fawn distance a coyote, using the mother's position to begin a systematic search for the fawn, and searching at a rate of 4 m²/s, would gain energy at a lower rate than it would hunting ground squirrels (Spermophilus columbianus). Mothers pointed both head and trunk toward their hidden fawns more frequently than would be expected by chance and coyotes, able to use this information to establish a 90° quadrant to search, could expect rates of gain higher than those obtainable in 360° search. Mothers especially tended to orient both head and trunk toward their fawns when standing or moving. Coyotes that begin a 90° search based on the mother's head or trunk position only when mothers were standing or moving, could expect rates of energy gain almost double those expected in 360° search or ground squirrel hunting. Maternal activities (stand, feed, recline, or move) were distributed evenly across all mother-fawn distances and across percent total time away from the fawn. Thus, activity was not a good predictor of a mother's likelihood of soon returning to her fawn. Mothers also remained away from their fawns long enough to cause the expected rate of energy gain for a coyote hiding and watching for the mother's return to the fawn to fall well below the rate expected for searching or ground squirrel hunting.     

Respiratory health assessment and exposure to polycyclic aromatic hydrocarbons in Mexican indigenous population

Environmental Science and Pollution Research - Indoor air pollution is an important risk factor for the generation of lung diseases in developing countries. The indigenous population is...     

Herbicides based on 2,4-D: its behavior in agricultural environments and microbial biodegradation aspects. A review

Environmental Science and Pollution Research - One of the main herbicides used in the agricultural environments is 2,4-dichlorophenoxyacetic acid (2,4-D). It is a synthetic plant hormone auxin...     

贾谊为何不被汉文帝所用

贾谊是西汉初杰出的政论家,他提出了一系列切中时弊且影响深远的政治主张,但他却不被汉文帝所重用,究其原因,乃是因为贾谊的主张损害了朝廷重臣等人的既得利益,而汉文帝以藩王身份继承皇位,皇权有限,在强大的政治压力下将他贬为长沙王太傅。之后贾谊被迁升为梁怀王太傅,因其削藩措施不符合汉文帝以诸侯王国拱卫西汉中央王朝的思路,故也不被汉文帝采用。     

A simulator study of driving behavior and mental workload in mixed-use arterial road environments

Objectives: Mixed-use urban environments, such as arterial roads with adjacent commercial land uses, represent crash locations with the highest risk. These locations are often characterized by high volumes of motor vehicle traffic, on-street parking, and interactions with multiple road user groups such as pedestrians, cyclists, and public transportation. The objective of this study was to investigate previously identified crash risk factors for mixed-use urban environments and assess how parking occupancy, center medians, and cyclist volume influence performance and workload in a driving simulator study.

Methods: Thirty participants were recruited for the study. Participants completed 6 drives that presented different combinations of cyclist volume, median condition, and parking occupancy. Incorporated into the simulator drives was a secondary peripheral detection task (PDT) designed to measure mental workload. Participants provided subjective assessments of workload using the Rating Scale Mental Effort (RSME).

Results: Mean lateral lane position was found to significantly vary across the 3 independent variables of parking occupancy, cyclist volume, and median conditions. No significant changes were identified for mean speed across the conditions. Subjective and objective measures of workload identified changes due to the presence of cyclists with slower reaction times for the PDT task when cyclists were present.

Conclusion: The findings provide insight into the interaction of road design elements in mixed-use urban road environments and demonstrate that increasingly complex environments increase driver demand. This has important road design implications for mixed-use arterial roads, which are often characterized by complex interactions between multiple road user groups.