Coexistence in an inhomogeneous environment

We examine the two-dimensional extension of the model of Kessler and Sander of competition between two species identical except for dispersion rates. In this class of models, the spatial inhomogeneity of reproduction rates gives rise to an implicit cost of dispersal, due to the tendency to leave favorable locations. Then, as in the Hamilton-May model with its explicit dispersal cost, the tradeoff between dispersal case and the beneficial role of dispersal in limiting fluctuations, leads to an advantage of one dispersal rate over another, and the eventual extinction of the disadvantaged species. In two dimensions we find that while the competition leads to the elimination of one species at high and low population density, at intermediate densities the two species can coexist essentially indefinitely. This is a new phenomenon not present in either the one-dimensional form of the Kessler-Sander model nor in the totally connected Hamilton-May model, and points to the importance of geometry in the question of dispersal

Transcriptional responses to polycyclic aromatic hydrocarbon-induced stress in Arabidopsis thaliana reveal the involvement of hormone and defense signaling pathways

Background: Polycyclic aromatic hydrocarbons (PAHs) are toxic, widely-distributed, environmentally persistent, and carcinogenic byproducts of carbon-based fuel combustion. Previously, plant studies have shown that PAHs induce oxidative stress, reduce growth, and cause leaf deformation as well as tissue necrosis. To understand the transcriptional changes that occur during these processes, we performed microarray experiments on Arabidopsis thaliana L. under phenanthrene treatment, and compared the results to published Arabidopsis microarray data representing a variety of stress and hormone treatments. In addition, to probe hormonal aspects of PAH stress, we assayed transgenic ethylene-inducible reporter plants as well as ethylene pathway mutants under phenanthrene treatment.Results: Microarray results revealed numerous perturbations in signaling and metabolic pathways that regulate reactive oxygen species (ROS) and responses related to pathogen defense. A number of glutathione S-transferases that may tag xenobiotics for transport to the vacuole were upregulated. Comparative microarray analyses indicated that the phenanthrene response was closely related to other ROS conditions, including pathogen defense conditions. The ethylene-inducible transgenic reporters were activated by phenanthrene. Mutant experiments showed that PAH inhibits growth through an ethylene-independent pathway, as PAH-treated ethylene-insensitive etr1-4 mutants exhibited a greater growth reduction than WT. Further, phenanthrene-treated, constitutive ethylene signaling mutants had longer roots than the untreated control plants, indicating that the PAH inhibits parts of the ethylene signaling pathway.Conclusions: This study identified major physiological systems that participate in the PAH-induced stress response in Arabidopsis. At the transcriptional level, the results identify specific gene targets that will be valuable in finding lead compounds and engineering increased tolerance. Collectively, the results open a number of new avenues for researching and improving plant resilience and PAH phytoremediation.University of Massachusetts BostonNational Science Foundation/IBN-0343856

Borrowed alleles and convergence in serpentine adaptation

ACKNOWLEDGMENTS. We thank members of the L.Y. and K.B. laboratories for helpful discussions. This work was supported through the European Research Council Grant StG CA629F04E (to L.Y.); a Harvard University Milton Fund Award (to K.B.); Ruth L. Kirschstein National Research Service Award 1 F32 GM096699 from the NIH (to L.Y.); National Science Foundation Grant IOS-1146465 (to K.B.); NIH National Institute of General Medical Sciences Grant 2R01GM078536 (to D.E.S.); and Biotechnology and Biological Sciences Research Council Grant BB/L000113/1 (to D.E.S.)Peer reviewedPublisher PD

Intelligent chilled mirror humidity sensor

A new, intelligent, chilled mirror humidity instrument has been designed for use on buoys and ships. The design goal is to make high quality dew point temperature measurements for a period of up to one year from an unattended platform, while consuming as little power as possible. Nominal system accuracy is 0.3°C, and a measure of data quality is provided to indicate possible drift in calibration. Energy consumption is typically 800 Joules per measurement; standby power consumption is 0.05 watts. Control of the instrument is managed by an onboard central processing unit which is programmable in BASIC, and communication to an external data logger is provided through an RS232 compatible interface. This report describes the preliminary sensor tests that led to this new design and provides the complete technical description required for fabrication.Funding was provided by the Office of Naval Research under contract Number N00014-84-C-0134, and the National Science Foundation through grant Number OCE87- 09614

Cellular mechanisms of myocardial infarct expansion.

Infarct expansion is acute regional dilatation and thinning of the infarct zone. There are several possibilities for the mechanism of this alteration in cardiac shape: thinning could be caused by 1) cell rupture, 2) a reduction in the intercellular space, or 3) stretching of myocytes or 4) slippage of groups of myocytes so that less cells are distributed across the wall. To determine the relative contributions of these cellular mechanisms of wall thinning and dilatation, detailed study of transverse histological sections of rat hearts with infarct expansion was performed 1, 2, and 3 days after coronary ligation. The number of cells across the wall was determined in six regions within, adjacent to, and remote from the infarct. Cell counting was performed so that the total number of cells across the wall and the number of cells per unit length (cell density) across the wall were determined. The transmural cell count and the cell density were correlated with the wall thickness in each region. Myocyte cross-sectional areas and sarcomere lengths were also measured. The results from the infarct expansion hearts were compared with those of sham-operated control hearts that had been similarly analyzed. To ensure that mechanisms identified in the rat were applicable to human infarct expansion, five hearts from patients who died within 3 days of infarction and two hearts from patients without coronary disease wer

Structure-Dependent Fluorescence Efficiencies of Individual Single-Walled Carbon Nanotubes

Single-nanotube photometry was used to measure the product of absorption cross-section and fluorescence quantum yield for 12 (n,m) structural species of semiconducting SWNTs in aqueous SDBS suspension. These products ranged from 1.7 to 4.5 x 10(-19) cm2/C atom, generally increasing with optical band gap as described by the energy gap law. The findings suggest fluorescent quantum yields of ~8% for the brightest, (10,2) species and introduce the empirical calibration factors needed to deduce quantitative (n,m) distributions from bulk fluorimetric intensities

Obesity and COVID-19 Outcomes in a Primarily Black Population

ABSTRACT Background: Studies have noted higher COVID-19 mortality with more severe obesity in populations that included a small percentage of Black patients. Methods: We retrospectively analyzed COVID-19 outcomes associated with obesity in our largely African American patient population. A total of 1101 symptomatic patients with a positive COVID-19 laboratory test March 5 to June 3, 2020, were categorized into weight groups based on body mass index (BMI). Of these patients, 679 (61.7%) were Black. A total of 355 (32.2%) patients had overweight and 516 (46.9%) had obesity. Results: BMI was an independent risk factor for intubation and an independent predictor for ICU length of stay and intubation days. An unexpected observation was favorable outcomes in mild obesity compared with normal weight and more severe obesity, likely a result of older age and higher Charlson comorbidity index in patients with normal BMI compared with patients with mild obesity. Conclusions: In a diverse primarily Black population, comorbidities were a concern for adverse COVID-19 outcomes and COVID-19 outcomes were significantly worse with moderate and severe obesity

Silk from Crickets: A New Twist on Spinning

Raspy crickets (Orthoptera: Gryllacrididae) are unique among the orthopterans in producing silk, which is used to build shelters. This work studied the material composition and the fabrication of cricket silk for the first time. We examined silk-webs produced in captivity, which comprised cylindrical fibers and flat films. Spectra obtained from micro-Raman experiments indicated that the silk is composed of protein, primarily in a beta-sheet conformation, and that fibers and films are almost identical in terms of amino acid composition and secondary structure. The primary sequences of four silk proteins were identified through a mass spectrometry/cDNA library approach. The most abundant silk protein was large in size (300 and 220 kDa variants), rich in alanine, glycine and serine, and contained repetitive sequence motifs; these are features which are shared with several known beta-sheet forming silk proteins. Convergent evolution at the molecular level contrasts with development by crickets of a novel mechanism for silk fabrication. After secretion of cricket silk proteins by the labial glands they are fabricated into mature silk by the labium-hypopharynx, which is modified to allow the controlled formation of either fibers or films. Protein folding into beta-sheet structure during silk fabrication is not driven by shear forces, as is reported for other silks