Predictability of plant species composition from environmental conditions is constrained by dispersal limitation

Despite recent modelling approaches integrating the effects of niche-based processes and dispersal-based processes on local plant species composition, their relative importance is still not clear. We test whether the predictability of local species composition from environmental conditions is influenced by dispersal traits. We analyzed a large database with co-occurrence data, using ordination techniques (DCA and CCA) to identify the major environmental determinants of species composition. The percentage of explained variance in occurrence was quantified for individual species with CCA. Effects of life-history traits on the predictability of occurrence patterns were tested by means of regression analysis, using a generalized linear models approach. The results reveal close correlations between species composition and environmental conditions, implying that the predictability of the set of species that might occur in a given environmental setting ("habitat species pool") is high. The habitat species pool, however, reflects the potential species composition, and not the actual local situation. At the level of individual species, a large proportion (>90%) of the variation in occurrence remained unexplained. Predictability of species occurrence patterns was increased by a greater capacity for long-distance dispersal, greater adult longevity and the capacity to build a persistent seed bank. The results indicate that the predictability of species composition from environmental conditions is reduced by a few orders of magnitude by dispersal limitation and that poor dispersers are underrepresented.     

Structure-activity relationship study on a novel series of cyclopentane-containing macrocyclic inhibitors of the hepatitis C virus NS3/4A protease leading to the discovery of TMC435350

SAR analysis performed with a limited set of cyclopentane-containing macrocycles led to the identification of N-[17-[2-(4-isopropylthiazole-2-yl)-7-methoxy-8-methylquinolin-4-yloxy]-13-methyl-2,14-dioxo-3,13-diazatricyclo [13.3.0.0^4,6]octadec-7-ene-4-carbonyl](cyclopropyl)sulfonamide (TMC435350, 32c) as a potent inhibitor of HCV NS3/4A protease (K_i = 0.36 nM) and viral replication (replicon EC₅₀ = 7.8 nM). TMC435350 also displayed low in vitro clearance and high permeability, which were confirmed by in vivo pharmacokinetic studies. TMC435350 is currently being evaluated in the clinics.     

Patterns of electrical propagation in the intact pregnant guinea pig uterus

Previous studies have reported on propagation of individual spikes in isolated segments of the pregnant uterus, but there is no information on patterns of spike propagation in the intact organ. There is also no information on propagation of myometrial burst. The aim of this study was to record, at high resolution, patterns of propagation of electrical activities in the pregnant uterus. Sixteen timed-pregnant guinea pigs were euthanized at term, and their uteruses isolated. Fetuses were removed and replaced by an equal amount of Tyrode. A 240-electrode array was positioned at various locations along the organ, all signals were recorded simultaneously, and the electrical propagations were reconstructed. In the intact pregnant uterus at term, spikes propagated with high velocity in longitudinal (6.8 +/- 2.4 cm/s) and slower velocity in circular direction (2.8 +/- 1.0 cm/s; P < 0.01). Direction of propagation and frequency of activity were highly variable but showed similar patterns at the ovary or cervical end and along the anterior, posterior, and antimesometrial borders. Along mesometrium, spike propagation was sparse and fractionated. Migration of burst (0.6 +/- 0.4 cm/s) was significantly much slower than that of individual spikes (P < 0.001). Initial burst activity was located at variable locations along the ovarial end of the antimesometrial border, while the latest excitation occurred at the cervical end (1.2 +/- 0.9 min). In conclusion, high resolution electrical mapping of the intact pregnant uterus reveals fundamental properties in spatial and temporal patterns of spike and burst propagation that determine the contraction of the organ.     

Age-related changes in the biomechanics of left ventricular twist measured by speckle tracking echocardiography

The increasing number and proportion of aged individuals in the population warrants knowledge of normal physiological changes of left ventricular (LV) biomechanics with advancing age. LV twist describes the instantaneous circumferential motion of the apex with respect to the base of the heart and has an important role in LV ejection and filling. This study sought to investigate the biomechanics behind age-related changes in LV twist by determining a broad spectrum of LV rotation parameters in different age groups, using speckle tracking echocardiography (STE). The final study population consisted of 61 healthy volunteers (16-35 yr, n=25; 36-55 yr, n=23; 56-75 yr, n=13; 31 men). LV peak systolic rotation during the isovolumic contraction phase (Rot(early)), LV peak systolic rotation during ejection (Rot(max)), instantaneous LV peak systolic twist (Twist(max)), the time to Rot(early), Rot(max), and Twist(max), and rotational deformation delay (defined as the difference of time to basal Rot(max) and apical Rot(max)) were determined by STE using QLAB Advanced Quantification Software (version 6.0; Philips, Best, The Netherlands). With increasing age, apical Rot(max) (P<0.05), time to apical Rot(max) (P<0.01), and Twist(max) (P<0.01) increased, whereas basal Rot(early) (P<0.001), time to basal Rot(early) (P<0.01), and rotational deformation delay (P<0.05) decreased. Rotational deformation delay was significantly correlated to Twist(max) (R(2)=0.20, P<0.05). In conclusion, Twist(max) increased with aging, resulting from both increased apical Rot(max) and decreased rotational deformation delay between the apex and the base of the LV. This may explain the preservation of LV ejection fraction in the elderly.     

Structure and torsion of the normal and situs inversus totalis cardiac left ventricle. I. Experimental data in humans

In 1926, the famous American pediatric cardiologist, Dr. Helen B. Taussig, observed that in situs inversus totalis (SIT) main gross anatomical structures and the deep muscle bundles of the ventricles were a mirror image of the normal structure, while the direction of the superficial muscle bundles remained unchanged (H. B. Taussig, Bull Johns Hopkins Hosp 39: 199-202, 1926). She and we wondered about the implication of this observation for left ventricular (LV) deformation in SIT. We used magnetic resonance tagging to obtain information on LV deformation, rotation, and torsion from a series of tagged images in five evenly distributed, parallel, short-axis sections of the heart of nine controls and eight persons with SIT without other structural (cardiac) defect. In the controls, during ejection, the apex rotated counterclockwise with respect to the base, when looking from the apex. Furthermore, the base-to-apex gradient in rotation (torsion) was negative and similar at all longitudinal levels of the LV. In SIT hearts, torsion was positive near the base, indicating mirrored myofiber orientations compared with the normal LV. Contrary to expectations, torsion in the apical regions of SIT LVs was as in normal ones, reflecting a normal internal myocardial architecture. The transition zone with zero torsion, found between the apex and base, suggests that the heart structure in SIT is essentially different from that in the normal heart. This provides a unique possibility to study regulatory mechanisms for myocardial fiber orientation and mechanical load, which has been dealt with in the companion paper by Kroon et al.     

Methanethiol degradation in anaerobic bioreactors at elevated pH (8): reactor performance and microbial community analysis

The degradation of methanethiol (MT) at 30 degrees C under saline-alkaline (pH 8-10, 0.5M Na(+)) conditions was studied in a lab-scale Upflow Anaerobic Sludge Blanket (UASB) reactor inoculated with estuarine sediment from the Wadden Sea (The Netherlands). At a sodium concentration of 0.5M and a pH between 8 and 9 complete MT degradation to sulfide, methane and carbon dioxide was possible at a maximum loading rate of 22mmolMTL(-1)day(-1) and a hydraulic retention time of 6h. The presence of yeast extract (100mg/L) in the medium was essential for complete MT degradation. 16S rRNA based DGGE and sequence analysis revealed that species related to the genera Methanolobus and Methanosarcina dominated the archaeal community in the reactor sludge. Their relative abundance fluctuated in time, possibly as a result of the changing operational conditions in the reactor. The most dominant MT-degrading archaeon was enriched from the reactor and obtained in pure culture. This strain WR1, which was most closely related to Methanolobus taylorii, degraded MT, dimethyl sulfide (DMS), methanol and trimethylamine. Its optimal growth conditions were 0.2M NaCl, 30 degrees C and pH 8.4. In batch and reactor experiments operated at pH 10, MT was not degraded.     

Association of <Emphasis Type="Italic">SIRT1</Emphasis> gene variation with visceral obesity

The sirtuin SIRT1 is an important regulator of energy metabolism through its impact on glucose and lipid metabolism and therefore we tested the hypothesis that genetic variation in SIRT1 may have an effect on adiposity in a Belgian case/control association study. This study included 1,068 obese patients (BMI ≥ 30 kg/m²) from the outpatient obesity clinic and 313 lean controls (BMI between 18.5 and 25 kg/m²). Anthropometrics were assessed by classical methods and visceral (VFA), subcutaneous (SFA) and total abdominal (TFA) fat areas were determined by a CT scan. The extent of linkage disequilibrium in SIRT1 allowed us to reduce the number of SNPs to two, sufficient to cover the entire gene. The two tagSNPs (rs7069102 and rs3818292) were analyzed by LightSNiP assays in all subjects. Rs3818292 genotypes were similarly distributed in cases and controls, whereas rs7069102 was different for the additive (P = 0.007) and dominant (P = 0.01) model. The variant C-allele of rs7069102 reduced obesity risk with an OR of 0.74 (P = 0.025; 95% CI 0.57–0.96) under a dominant model. In obese male subjects, this variant allele was associated with increased waist circumference (P = 0.04), WHR (P = 0.02), TFA (P = 0.03) and VFA (P = 0.005) (dominant model; adjusted for age and BMI). Rs3818292 was related to VFA (P = 0.005; adjusted for age and BMI) in obese males while in obese women, no significant associations were detected. Our data suggest that genetic variation in SIRT1 increases the risk for obesity, and that SIRT1 genotype correlates with visceral obesity parameters in obese men. A. V. Peeters and S. Beckers have contributed equally to this work.