The metabolic demands of swimming behavior influence the evolution of skeletal muscle fiber design in the brachyuran crab family Portunidae

We investigated the influence of intracellular diffusion on muscle fiber design in several swimming and non-swimming brachyuran crabs. Species with sustained swimming behavior had aerobic dark fibers subdivided into small metabolic functional units, creating short diffusion distances necessary to support the high rates of aerobic ATP turnover associated with endurance activity. This dark fiber design was observed in all swimming species including Ovalipes ocellatus, which has apparently evolved swimming behavior independently of other Portunidae. In addition, we observed fiber and subdivision size-dependent differences in organelle distribution. Mitochondria, which rely on oxygen to function, were uniformly distributed in small fibers/subdivisions, but were clustered at the fiber periphery in larger fibers. The inverse pattern was observed for nuclei, which are not oxygen dependent, but rely on the transport of slow diffusing macromolecules. Phylogenetically independent contrast analysis revealed that these relationships were largely independent of phylogeny. Our results demonstrate cellular responses to diffusion that were necessary for the evolution of swimming and that are likely to be broadly applicable.     

USE OF PEBBLE COUNTS TO EVALUATE FINE SEDIMENT INCREASE IN STREAM CHANNELS1

ABSTRACT: The pebble count, a quick and simple technique for characterizing streambed materials, has long been used by geomorphologists, hydrologists, and river engineers. This paper describes how pebble counts have been used to monitor fine sediment (particles less then 6 mm in size) on the Boise National Forest. Data from two watersheds subjected to major wildfires and the failure of a dam are discussed. Following wildfires, pebble count data showed increases in streambed fines followed by improvement of the stream substrate with time as the watersheds recovered. For the dam failure, pebble count data showed an increase in fines in the stream below the failure and were used to track the distance of sediment movement downstream. Pebble counts may be best used where fine sediment on channel substrates are a concern, such as in granitic watersheds where coarse sands are a large component of bedload and land-disturbing activities introduce fine sediment into streams. Pebble counts are found to be a simple and rapid monitoring method that can be used to help determine whether or not land management activities or land disturbances are introducing fine sediment into streams.     

Effects of ozone impact on the gas exchange and chlorophyll fluorescence of juvenile birch stems (Betula pendula Roth.)

Effects of ozone impact on gas exchange and chlorophyll fluorescence of juvenile birch (Betula pendula) stems and leaves were investigated. Significant differences in the response of leaves and stems to ozone were found. In leaves, O3 exposure led to a significant decline in photosynthetic rates, whereas stems revealed an increased dark respiration and a concomitant increase in corticular photosynthesis. In contrast to birch leaves, corticular photosynthesis appeared to support the carbon balance of stems or even of the whole-tree under O3 stress. The differences in the ozone-response between leaves and stems were found to be related to ozone uptake rates, and thus to inherent differences in leaf and stem O3 conductance.     

Characterization of turf practices in five North Carolina communities

Limited information exists on specific urban lawn care practices in the United States. We conducted a door-to-door lawn care survey in five North Carolina communities to determine suburban fertilizer, pesticide, and water use. These communities, Cary, Goldsboro, Kinston, New Bern, and Greenville, are mostly located within the Neuse River basin, a nutrient-sensitive water resource. Residents in Cary used lawn care companies more than twice as frequently as residents in the other communities (43 compared with 20%). Cary had the smallest mean lawn size (445 m2), while the largest was in Goldsboro (1899 m2). Tall fescue [Festuca arundinacea Schreb.] was the predominant grass type in Cary (99%), and centipedegrass [Eremochloa ophiuroides (Munro) Hack.] or centipedegrass mixtures were the predominant grass types in Greenville and New Bern. Kinston had the lowest fertilizer usage with only 54% of the residents using fertilizer; Cary had the highest rate of 83%. The average N fertilizer rate applied to the lawns was dissimilar ranging from 24 to 151 kg N ha(-1). Analysis of variance results for fertilizer rates and household income indicated a significant difference (P < 0.05) in application rate between high- and medium-income levels and the low-income level. Cary, Goldsboro, and Greenville had approximately the same number of fertilizer applications per year (1.5), whereas the average number of fertilizer applications per year in New Bern was 3.0. Most household residents (53%) used instructions on the bag and either grass type and/or lawn area to guide them on fertilizer application rates.     

Overcoming Endpoint Bias in Climate Change Communication: The Case of Arctic Sea Ice Trends

Unusually cold winters, a slowing in upward global temperatures, or an increase in Arctic sea ice extent are often falsely cast as here-and-now disconfirmation of the scientific consensus on climate change. Such conclusions are examples of “end point bias,” the well documented psychological tendency to interpret a recent short-term fluctuation as a reversal of a long-term trend. End point bias poses a challenge to those trying to communicate cross-decade climate warming trends. In this study, we demonstrate that exposure to misleading scientific information on FoxNews.com that evokes end point bias can affect the beliefs of liberals and moderates as well as conservatives. We also show that the leveraging-involving-visualizing-analogizing communication model can reduce the effects of endpoint bias among moderates and liberals at the same time as it dampens both the ideological and endpoint biasing of conservatives.     

Sex ratio, sexual dimorphism and mating structure in bethylid wasps

Sexual dimorphism has been linked to parasitoid mating structure by several authors. In turn mating structure has an important influence on predicted sex ratio optima. Here we test the relationship between sexual dimorphism and sex ratio using data from 19 species of bethylid wasps. Using phylogenetically based comparative methods we confirm the findings of a previous cross-species analysis that sex ratio (proportion of males) is strongly and negatively correlated with clutch size. Using cross-species comparisons we show an additional positive correlation of sex ratio and relative male size, as predicted. The relationship however is not significant when using phylogenetically based methods. The cross-species result is largely due to differences between two bethylid sub-families: the Epyrinae have relatively large males and relatively high sex ratios, whereas the Bethylinae have relatively small males and lower sex ratios. Our study illustrates the benefits and drawbacks of using cross-species versus phylogenetically based comparisons. Received: 13 May 1997 / Accepted after revision: 12 January 1998     

Thermal tolerance of early development in tropical and temperate sea urchins: inferences for the tropicalization of eastern Australia

The thermal envelope of development to the larval stage of two echinoids from eastern Australia was characterized to determine whether they fill their potential latitudinal ranges as indicated by tolerance limits. The tropical sand dollar, Arachnoides placenta, a species that is not known to have shifted its range, was investigated in Townsville, northern Australia (19°20′S, 146°77′E), during its autumn spawning season (May 2012). The subtropical/temperate sea urchin, Centrostephanus rodgersii, a species that has undergone poleward range expansion, was investigated in Sydney, southern Australia (33°58′S, 151°14′E), during its winter spawning season (August 2012). The thermal tolerance of development was determined in embryos and larvae reared at twelve temperatures. For A. placenta, the ambient water temperature near Townsville and experimental control were 24 °C and treatments ranged from 14 to 37 °C. For C. rodgersii, ambient Sydney water temperature and experimental control were 17 °C, and the treatment range was 9–31 °C. A. placenta had a broader developmental thermal envelope (14 °C range 17–31 °C) than C. rodgersii (9 °C range 13–22 °C). Both species developed successfully at temperatures well below ambient, suggesting that cooler water is not a barrier to poleward migration for either species. Both species presently live near the upper thermal limits for larval development, and future ocean warming could lead to contractions of their northern range limits. This study provides insights into the factors influencing the realized and potential distribution of planktonic life stages and changes to adult distribution in response to global change.     

Photosynthetic carbon reduction: high rates in the sea-surface microlayer

The ocean is a significant sink for increasing anthropogenic carbon dioxide emissions. The sea-surface microlayer (upper 50 m layer) serves as the primary point for exchange of materials, including carbon dioxide, between the atmosphere and hydrosphere. We determined microalgal standing stocks and activities in microlayer and subsurface water from areas with (S) and without (NS) visible natural surface slicks in Sequim Bay, Washington, USA, in July 1984. Enrichment ratios (microlayer concentration: subsurface bulkwater concentration) were: phytoneuston population abundance, 37 (NS) to 154 (S); total chlorophylls, 1.3 (NS) to 18 (S); particulate carbon fixation, 2 (NS) to 52 (S); and dissolved carbon excretion, 17 (NS) to 63 (S). Photoinhibition of 36 to 89% occurred in phytoneuston under natural summer light-intensities. Slick samples had greater standing stocks and rates of primary production than non-slick samples. The species composition of phytoneuston was distinctly different from that of phytoplankton. These results suggest that phytoneuston form a unique community. Although carbon fixation in summer was less per individual in phytoneuston than in phytoplankton, because of their overall abundance at the air-sea interface, phytoneuston may play an important role in the transfer of CO₂ from the atmosphere into ocean surface-water.     

The toxicology of the three commercial polybrominated diphenyl oxide (ether) flame retardants

Three commercial polybrominated diphenyl oxide flame retardants (PBDPO, PBDE) are manufactured: decabromodiphenyl oxide (DBDPO), octabromodiphenyl oxide (OBDPO) and pentabromodiphenyl oxide (PeBDPO). The composition, production volumes, uses and toxicology of the three products differ. In 1999, DBDPO accounted for approximately 82% of the global PBDPO usage. DBDPO has been extensively tested. DBDPO was not acutely toxic, was not irritating to the skin or eye, and did not induce skin sensitization. No evidence of genotoxic effects was detected in the Ames Salmonella, chromosome aberration, mouse lymphoma, or sister chromatid exchange tests. No cytogenic changes were observed in the bone marrow of rats (parents and offspring) undergoing a one-generation reproduction test. DBDPO did not adversely affect development or reproduction in rats. DBDPO's no-adverse-effect-level (NOAEL) in repeated dose studies was > or = 1000 mg/kg body weight. No, equivocal, or some evidence of carcinogenicity, dependent on genus and sex, was found in mice and rats at 2.5% and 5% of the diet administered for 2 years. DBPDO was poorly absorbed from the gastrointestinal tract (< 0.3-2% oral dose), had a short half-life (< 24 h) compared to PCB 153 (only 2% of an oral dose eliminated by rats in 21 days), and was rapidly eliminated via the feces (> 99% in 72 h). In contrast, components of the PeBDPO product were well absorbed and slowly eliminated, OBDPO's effect level in a 90-day study was approximately 100 mg/kg, PeBDPO's no-effect-level (NOEL) in a 30-day study was 1 mg/kg, and OBDPO induced developmental toxicity in the rat. In aquatic species, neither DBDPO nor OBDPO were toxic to aquatic organisms or bioconcentrating. Components of the PeBDPO product bioconcentrated in fish but produced little evidence of adverse effects.