Homogenization of dispersal ability across bird species in response to landscape change

Human land use is known to homogenize biotic communities, increasing similarity in their genetic, taxonomic and functional diversity. Explanations have focused almost exclusively on human‐mediated extinction and range expansion. However, homogenization could also be produced by land use driving selection for similar traits across species. We propose a novel hypothesis to explain how human land use homogenizes dispersal ability across species. With habitat loss and increasing human land use intensities there should be larger increases in the costs of dispersal for dispersive than sedentary species, because dispersive species interact with non‐habitat more frequently. In contrast, the benefits of dispersal should increase more for sedentary than dispersive species, because sedentary species are at greater risk from inbreeding depression, predation and competition associated with habitat loss. Therefore we predict that sedentary species become more dispersive in a human‐altered landscape, and dispersive species more sedentary. We tested this prediction using wing pointedness to estimate the initial dispersal ability and change in dispersal ability for 21 North American passerines over the 20th century. More pointed wings are associated with stronger dispersal ability. Thus our prediction would be supported by a negative cross‐species relationship between these two measurements. We found a strong, negative relationship, as predicted. This resulted in declines in the variability in wing pointedness among species over time. Although other things can cause wing shape to change, including changes in habitat availability, none of these explained the observed relationship. Our result provides the first evidence that human landscape alteration is homogenizing bird communities, driving selection for intermediate dispersal ability across species. It also implies that more dispersive species are more at‐risk from human landscape use because, when rates of landscape alteration are faster than a species’ ability to adapt to that change, the costs of dispersal increase more for dispersive than sedentary species.     

The Anthropology of Infectious Disease: International Health Perspectives and The Kiss of Death: Chagas' Disease in the Americas

The Anthropology of Infectious Disease: International Health Perspectives. Marcia C. Inhorn and Peter J. Brown. eds. Amsterdam: Gordon and Breach, Publishers, 1997. xv+ 495 pp.
The Kiss of Death: Chagas' Disease in the Americas. Joseph William Bastien. Salt Lake City: The University of Utah Press, 1998. xxiv +301 pp.     

SAR studies on a series of N-benzyl-4-heteroaryl-1-(phenylsulfonyl)piperazine-2-carboxamides: potent inhibitors of the polymerase enzyme (NS5B) of the hepatitis C virus

Described herein is the initial optimization of (+/−) N-benzyl-4-heteroaryl-1-(phenylsulfonyl)piperazine-2-carboxamide (1), a hit discovered in a high throughput screen run against the NS5B polymerase enzyme of the hepatitis C virus. This effort resulted in the identification of (S)-N-sec-butyl-6-((R)-3-(4-(trifluoromethoxy)benzylcarbamoyl)-4-(4-(trifluoromethoxy)phenylsulfonyl)piperazin-1-yl)pyridazine-3-carboxamide (2), that displayed potent replicon activities against HCV genotypes 1b and 1a (EC₅₀ 1b/1a = 7/89 nM).     

Landscape size affects the relative importance of habitat amount,habitat fragmentation,and matrix quality on forest birds

It is important to understand the relative effects of landscape habitat loss, habitat fragmentation, and matrix quality on biodiversity, so that potential management options can be appropriately ranked. However, their effects and relative importance may change with the size of the landscape considered because the multiple (and potentially conflicting) ecological processes that are influenced by landscape structure occur at different spatial scales (e.g. dispersal, predation, foraging). We estimated the relative effects of habitat loss, habitat fragmentation, and matrix quality (measured as the amount of forest, the proportion of forest area contained in large core forests, and the density of roads respectively) on fragmentation‐sensitive forest birds in southern Ontario, Canada using a range of landscape sizes (0.8–310 km²). We used three complementary statistical approaches to estimate relative effects of these correlated landscape factors – 1) multiple regression, 2) information theoretic (AIC) estimates of the most parsimonious model, and 3) multi‐model inference to average effects across all supported models. We controlled for spatial autocorrelation, local habitat, roadside sampling bias, time of day, season, habitat heterogeneity, and the interaction between the effects of habitat amount and fragmentation. We found that relative effects of habitat amount and fragmentation were scale dependent; habitat amount had a consistently positive effect that was consistent over more than two orders of magnitude in landscape area (~1–300 km²). In contrast, the effects of habitat fragmentation depended on the size of the landscape considered. Indeed, for veery Catharus fuscescens, habitat fragmentation had positive effects at one scale and negative effects at another. The effects of matrix quality were generally weak and changed little with scale. For the number of fragmentation sensitive species and the presence of veery, habitat amount was most important in large landscapes and habitat fragmentation in small landscapes but for the presence of ovenbird Seiurus aurocapilla, habitat amount was most important at all scales.     

Feasibility of Using Pseudo-Continuous Arterial Spin Labeling Perfusion in a Geriatric Population at 1.5 Tesla

Objectives

To evaluate the feasibility of using pseudo-continuous arterial spin labeling (pCASL) perfusion in a geriatric population at 1.5-Tesla.

Materials and Methods

In 17 participants (mean age 78.8±1.63 years) we assessed; 1) inter-session repeatability and reliability of resting state perfusion in 27 brain regions; 2) brain activation using finger-tapping as a means to evaluate the ability to detect flow differences; 3) reliability by comparing cerebral blood flow (CBF) with pCASL to CBF with phase contrast (PC-MR).

Results

The CBF (mean±standard deviation (SD)) for the whole brain grey matter (GM) was 40.6±8.4 and 41.4±8.7 ml/100g/min for the first and second scan respectively. The within-subject standard deviation (SDw), the repeatability index (RI) and intra-class correlation coefficient (ICC) across the 27 regions ranged from 1.1 to 7.9, 2.2 to 15.5 and 0.35 to 0.98 respectively. For whole brain GM the SDw, RI and ICC were 1.6, 3.2 and 0.96 respectively. The between-subject standard deviation (SD_B) was larger than the SDw for all regions. Comparison of CBF at rest and activation on a voxel level showed significantly higher perfusion during finger tapping in the motor- and somatosensory regions. The mean CBF for whole brain GM was 40.6±8.4 ml/100g/min at rest and 42.6±8.6 ml/100g/min during activation. Finally the reliability of pCASL against the reference standard of PC-MR was high (ICC = 0.80). The mean CBF for whole brain measured with PC-MRI was 54.3±10.1 ml/100g/min and 38.3±7.8 ml/100g/min with pCASL.

Conclusions

The results demonstrate moderate to high levels of repeatability and reliability for most brain regions, comparable to what has been reported for younger populations. The performance of pCASL at 1.5-Tesla shows that region-specific perfusion measurements with this technique are feasible in studies of a geriatric population.     

The effect of light on the production of Heimia alkaloids

Alkaloid extracts obtained from light- and dark-grown shoot cultures of Heimia salicifolia were partially fractionated and semi-quantitatively analysed for phenyl- and biphenylquinolizidine alkaloids. The concentrations of the two structural types of alkaloids in extracts of shoots grown with illumination increase over a 4 week culture period. In extracts obtained from shoots grown in darkness for 4 weeks, however, we observed substantial decreases in the concentrations of both the phenyl- and biphenylquinolizidine alkaloids. We observed that growth in the dark for periods of up to 9 weeks resulted in a further reduction in the levels of biphenyl alkaloids relative to those of the phenylquinolizidinols.     

A Suppressor of snf1 Mutations Causes Constitutive High-Level Invertase Synthesis in Yeast

The SNF1 gene product of Saccharomyces cerevisiae is required to derepress expression of many glucose-repressible genes, including the SUC2 structural gene for invertase. Strains carrying a recessive snf1 mutation are unable to ferment sucrose. We have isolated 30 partial phenotypic revertants of a snf1 mutant that were able to ferment sucrose. Genetic characterization of these revertants showed that the suppressor mutations were all recessive and defined eight complementation groups, designated ssn1 through ssn8 (suppressor of snf1 ). The revertants were assayed for secreted invertase activity, and although activity was detected in members of each complementation group, only the ssn6 strains contained wild-type levels. Synthesis of secreted invertase in ssn6 strains was found to be constitutive, that is, insensitive to glucose repression; moreover, the ssn6 mutations also conferred constitutivity in a wild-type ( SNF1 ) genetic background and are, therefore, not merely suppressors of snf1 . Pleiotropic defects were observed in ssn6 mutants. Genetic analysis suggested that the ssn6 mutations are allelic to the cyc8 mutation isolated by R. J. Rothstein and F. Sherman, which causes increased production of iso-2-cytochrome c. The data suggest a regulatory function for SSN6 .     

Inhibition of the Plaquing Efficiency of T4r+ Bacteriophage by Subtilisin

The mechanism by which the replicative cycle of T4r(+) phage is inhibited by certain nonhost bacterial systems was investigated. Some Bacillaceae, especially Bacillus subtilis, decreased the plaquing efficiency of this virus more than 95% within 24 hr of exposure. Sarcina lutea and Micrococcus sp. both failed to cause any significant change in the infectivity of T4r(+) phage. Preliminary investigations into the nature of the inhibitory substance(s) suggested that an extracellularly elicited protein was at least partially responsible for this effect. Further analysis has implicated subtilisin, an exoprotease from B. subtilis, as the cause of some, if not all, of the observed decrease in plaquing efficiency. Gel-filtration chromatography of control and treated (14)C-labeled T4r(+) phage showed a wide dispersal of phage-specific material of these particles after 24 hr of exposure to pure subtilisin or to expended medium exoprotease from B. subtilis. It was concluded that B. subtilis exoprotease is capable of chemically altering the structure of the phage capsid, thus causing a decrease in its plaquing efficiency.