Significant Population Differences Research Articles

The effect of test speed on the motion characteristics of the lumbar spine during an A-P flexion-extension test

Measurements of trunk flexibility have frequently been used to aid in diagnostic, prognostic and therapeutic processes. However, the speed at which these tests should be performed has not been established. Some authors have performed range of motion studies with subjects moving at their maximum speed, whilst others have asked subjects to move at slow speeds. McIntyre et al. (1991) suggested that tests of human performance should be performed at the subject’s preferred speed, since this is a more reliable measure of function. However, the influence of speed on movement characteristics has received limited attention. In addition the impact of speed on repeatability of measures of motion is unclear. The impact of test speed was investigated in a sample of normal control subjects and low back pain subjects with known spinal stenosis. Measurements of lumbar spine motion were obtained using a triaxial potentiometric analysis system (CA ∼ 6000 Spinal Motion Analyser, OSI, USA) during a simple antero-posterior flexion-extension test. Each subject was asked to perform a series of three flexion-extension tests at three different speeds; as fast as they could, slowly and at their preferred/ normal rate of movement. The results demonstrated that in both study populations the speed at which the test was performed had no significant effect on the resultant ROM of flexion. However, in the normal population it did have an influence on ROM extension, with the tests performed at a fast speed producing a significantly greater ROM extension ( p< 0.05) than tests performed at the subject’s preferred speed or at a slow speed. Not surprisingly the mean velocity characteristics of each test speed showed significant differences in both populations. In terms of test repeatability however, the results indicated that testing at a subject’s preferred speed produced more consistent readings of motion characteristics (in terms of both ROM and velocity). In addition all parameters of motion were significantly impaired in the spinal stenosis group with p< 0.01.

The 2nd:4th digit ratio, sexual dimorphism, population differences, and reproductive success: evidence for sexually antagonistic genes?

The ratio between the length of the 2nd and 4th digit (2D:4D) is sexually dimorphic, with mean male 2D:4D lower than mean female 2D:4D. It recently was suggested that 2D:4D is negatively correlated with prenatal testosterone and positively correlated with prenatal estrogen. It is argued that high prenatal testosterone and low estrogen (indicated by low 2D:4D) favors the male fetus and low prenatal testosterone and high estrogen (indicated by high 2D:4D) favors the female fetus. The patterns of expression of 2D:4D are interpreted in terms of sexually antagonistic genes. We report data on the following. (a) reproductive success and 2D:4D from England, Germany, Spain, Hungary (ethnic Hungarians and Gypsy subjects), Poland, and Jamaica (women only). Significant negative associations were found between 2D:4D in men and reproductive success in the English and Spanish samples and significant positive relationships between 2D:4D in women and reproductive success in the English, German, and Hungarian samples. The English sample also showed that married women had higher 2D:4D ratios than unmarried women, suggesting male choice for a correlate of high ratio in women, and that a female 2D:4D ratio greater than male 2D:4D predicted high reproductive success within couples. Comparison of 2D:4D ratios of 62 father:child pairs gave a significant positive relationship. This suggested that genes inherited from the father had some influence on the formation of the 2D:4D ratio. Waist:hip ratio in a sample of English and Jamaican women was negatively related to 2D:4D. (b) Sex and population differences in mean 2D:4D in samples from England, Germany, Spain, Hungary (including ethnic Hungarians and Gypsy subjects), Poland, Jamaica, Finland, and South Africa (a Zulu sample). Significant sex and population differences in mean 2D:4D were apparent.

Cytokine expression and specific lymphocyte proliferation in two strains of Cryptosporidium parvum-infected gamma-interferon knockout mice.

Differences in the immune response between 2 strains of interferon-gamma knockout mice (BALB/c-GKO and C57BL/6-GKO) infected with Cryptosporidium parvum were examined because the course of infection among these 2 strains is markedly different. Infection of the BALB/c-GKO with C. parvum (2 X 10(6) oocysts/mouse) resulted in slight weight loss, oocyst shedding, and recovery from infection by 2 wk postinfection (PI). Infection with 100 oocysts in the C57BL/6-GKO mice resulted in significant weight loss, oocyst shedding, and death by day 10 PI. Splenocytes from infected mice were able to proliferate in a dose-dependent manner to soluble C. parvum-sporozoite antigen (SAg). In vitro stimulation with SAg resulted in an increase in interleukin (IL)-2, IL-4, IL-5, and tumor necrosis factor-alpha mRNA cytokine expression from splenocytes of infected BALB/cGKO mice. In contrast, only IL-5 mRNA expression was increased in the splenocytes from C. parvum-infected C57BL/6-GKO mice. Phenotypic analysis indicated no significant differences in the splenic cell populations. Previous studies indicated that susceptibility to C. parvum is dependent on CD4+ T cells and interferon-gamma production. The present study indicates that although both of these strains of knockout mice become infected with C. parvum, resolution of infection may be in part dependent on the expression of Th2 cytokines.

Ecology of Earthworms under the ‘Haughley Experiment’ of Organic and Conventional Management Regimes

ABSTRACT Significant differences in earthworm populations and soil properties were found in three sections of a farm at Haughley in Suffolk that, since 1939, had either an organic, a mixed conventional, or a stockless intensive arable regime. Compared with the mean earthworm population of a 1,000 year old permanent pasture of 424.0 m−2; an organic field had 178.6 m−2; a mixed field 97.5 m−2; and a stockless field 100.0 m−2. Species recorded were: Allolobophora chlorotica, accounting for most of the increase in the organic section; Aporrectodea caliginosa, dominant in the stockless section; Aporrectodea icterica; Ap, longa; Ap. nocturna; Ap. rosea; and Lumbricus terrestris. Soil analyses showed the organic soil had higher moisture, organic C, and mineral N, P, K, and S compared with soil from the stockless field. The organic soil also had lower bulk density and good crumb structure whereas the stockless soil was cloddy and subject to puddling. The properties of the mixed field soil were intermediate to the others. Winter wheat (Triticum aestivum) in the organic field had significantly longer shoots (by 11.3% and 13.9%) and roots (by 5.4% and 10.8%) compared with the mixed and stockless fields, respectively. Choice chambers offering the three field soils, with and without organic amendments, showed an earthworm preference for the organic soil (total 96 headcounts) compared to the mixed and stockless soils (75 and 73 headcounts). Adding organic matter tended to override this trend and indicated that food supply was an important determinant in earthworm distribution in the laboratory.

Bacteremia by Gram-Negative Bacilli in Patients with Hematologic Malignancies

To compare the characteristics of bacteremic infections by different aerobic gram-negative bacilli (GNB) in patients with hematologic malignancies, we studied 54 consecutive monomicrobial bacteremias by Enterobacteriaceae (EB), 15 by Pseudomonas aeruginosa, 43 by other non-glucose-fermenting GNB (NGFGNB) and 11 by other GNB. Patients with EB and P. aeruginosa bacteremia usually developed the infection after intensive chemotherapy for leukemia or during a hematopoietic stem cell transplantation, while most infections in outpatients off therapy were due to NGFGNB. A significant proportion of bacteremias by EB (37%) and P. aeruginosa (40%) were accompanied by severe morbidity (septic shock, pneumonia or deep-seated organ infections) vs. only 7% of other NGFGNB (p < 0.01). Most infections by these latter bacteria were catheter-related bacteremias (80 vs. 2% of EB, p < 0.005), while most EB infections (61%) were uncomplicated bacteremias of unknown source (vs. 14% of other NGFGNB, p < 0.005). Appropriate antibiotics alone cured 98% of EB and 73% of P. aeruginosa bacteremias but only 26% of other NGFGNB (p < 0.005 for both differences), which were cured by catheter removal in 70%, usually after failure of antibiotic treatment. In conclusion, our results suggest that there are significant differences in the patient populations and clinical characteristics of bacteremic infections by the classic GNB (EB and P. aeruginosa) and the new NGFGNB in adults with hematologic malignancies.

Splenectomy attenuates superoxide anion release into the hepatic sinusoids after lipopolysaccharide challenge

Background/Aims: The aim of this study was to determine whether the spleen contributes to superoxide anion release into the hepatic sinusoids and subsequent damage to endothelial cells of the hepatic sinusoids after lipopolysaccharide challenge. Methods: Rats were given 2 mg/kg body weight lipopolysaccharide. Three hours after the treatment, superoxide anion release into the hepatic sinusoids was examined in a liver perfusion model using the cytochrome C method. Damage to endothelial cells of the hepatic sinusoids was assessed from the purine nucleoside phosphorylase/glutamic-pyruvic transaminase ratio in the liver perfusate. To further characterize the mechanisms behind these changes, these studies were done in rats given superoxide dismutase or an anti-TNFα antibody. To study whether the spleen plays a role in the mechanisms, experiments with splenectomized rats were performed. Results: Lipopolysaccharide challenge resulted in superoxide anion release into the hepatic sinusoids and damage to endothelial cells of the hepatic sinusoids. These changes were significantly attenuated by the treatments with superoxide dismutase or an antibody against TNFα, as well as by splenectomy. The hepatic macrophage and Kupffer cell populations after lipopolysaccharide challenge were significantly smaller in the rats given splenectomy than in those given a sham operation. There were no significant differences in the neutrophil populations between the two groups. Levels of TNFα were significantly lower in the former than the latter, whereas there were no significant differences in levels of Interleukin-8 between the two groups. Conclusions: Splenectomy reduced the superoxide anion release into the hepatic sinusoids caused by the lipopolysaccharide challenge and subsequent damage to endothelial cells of the hepatic sinusoids. This supports the view that splenectomy has a protective effect in lipopolysaccharide-induced liver injury.

Changes in soil microbial communities over time resulting from one time application of zinc: a laboratory microcosm study

Soil microcosms each consisting of approximately 20 kg soil were set up in the laboratory. Three microcosms were amended with 6000 mg zinc kg −1, a concentration chosen to approximate the quantities of total zinc found at a contaminated field site. Three control microcosms received no zinc amendment. Three pH control microcosms received H 2SO 4, adequate to result in the same pH decrease as occurred in the zinc amended soil. Mean soluble zinc contents were 4660 mg kg −1 (amended soils), 1.08 mg kg −1 (unamended soils), and 2.10 mg kg −1 (pH adjusted soils). Biological community assessments included culturable bacteria (plate counts), microbial biomass (chloroform fumigation), dehydrogenase activity, proportion of zinc resistant bacteria (plate counts on zinc amended agar), and changes in community structure (BIOLOG and phospholipid fatty acid (PLFA) analysis). After 15 d of incubation, zinc amendment resulted in an 87% decrease in viable counts and a 47% decrease in microbial biomass. Dehydrogenase activity decreased by 95%, and the proportion of zinc resistant bacteria increased from 0.08% to 0.75%. Microbial community structure alteration resulting from zinc amendment was indicated by shifts in both BIOLOG metabolic profiles and PLFA profiles. Effects of zinc on PLFA profiles included relative decreases in indicator fatty acids for arbuscular mycorrhizal fungi and actinomycetes. Some adaptation of the microbial communities to the zinc amendment was suggested by the fact that after 420 d incubation there were no significant differences in culturable bacterial populations or microbial biomass of the control and zinc amended systems. However, other microbial properties measured in this study showed that zinc still affected microbial community structure and activity after 420 d. Dehydrogenase activity of the zinc treated communities remained 93% lower than the controls. The percentage of zinc resistant populations was still significantly higher for the zinc treated communities. Similarly, the BIOLOG and PLFA profiles continued to show differences in the structure of the zinc treated and control microbial communities. Effects of zinc on PLFA profiles at day 420 included a relative decrease in an indicator fatty acid for arbuscular mycorrhizal fungi and a relative increase in an indicator fatty acid for fungi. The comparison of PLFA profiles also showed mixed results for several fatty acid indicators for actinomycetes. The pH control treatment showed similar effects on population size and activity as the zinc treatment, although in most cases there was a much stronger effect with the zinc treatment. In addition, the pH treatment caused changes in BIOLOG and PLFA profiles which were different than the changes seen with zinc treatment.

178 Differences in Grape Phylloxera-related Grapevine Root Damage in Organically and Conventionally Managed Vineyards in California

Secondary infection of roots by fungal pathogens is a primary cause of vine damage in phylloxera-infested grapevines. In summer and fall surveys in 1997 and 1998, grapevine root samples were taken from organically managed vineyards (OMVs) and from conventionally managed vineyards (CMVs), all of which were phylloxera-infested. In both years, root samples from OMVs showed significantly less fungal pathogen-caused root necrosis than samples from CMVs, averaging 9% in OMVs and 31% in CMVs. There was no significant difference in phylloxera populations per 100 g of root between OMVs and CMVs, although there was a trend toward higher populations in CMVs. Soil characteristics, percent organic matter, total nitrogen, nitrate, and percent sand/silt/clay were not significantly different between the two regimes. Cultures of necrotic root tissue showed significantly higher levels of the benefical fungus Trichoderma in OMVs in 1997 but not in 1998, and there were significantly higher levels of the pathogens Fusarium oxysporum and Cylindrocarpon spp. in CMVs in 1998 but not in 1997. Implications for further research and viticulture are discussed.

Effect of organic nitrogen fertilizers on microbial populations associated with bermudagrass putting greens

Four natural organic fertilizers, alone or in combination with the synthetic organic fertilizer isobutylidene diurea (IBDU), were compared with IBDU alone for their effect on soil/root microbial populations associated with bermudagrass grown on a golf course putting green in southern Florida, USA. Populations of total fungi, total bacteria, fluorescent pseudomonads, Stenotrophomonas maltophilia, actinomycetes and heat-tolerant bacteria were monitored every 3 months during the 2-year study. On only one sampling date and for only one bacterial population (S. maltophilia) was a significant difference in microbial populations obtained among the fertilizer treatments. However, the S. maltophilia populations associated with the natural organic fertilizer treatments were not significantly different from the synthetic organic IBDU fertilizer treatment.

Carbon isotope composition, water-use efficiency and biomass productivity of Eucalyptus microtheca populations under different water supplies

Variation in carbon isotope composition (δ13C), water-use efficiency (WUE) and biomass productivity were compared among three populations of Eucalyptus microtheca F. Muell. in a greenhouse. Seedlings were maintained under one well-watered (Control, keeping the soil at field capacity) and two different water deficit conditions (Drought stress I, keeping the same soil water content; Drought stress II, keeping the same soil water supply). In each treatment, significant population differences in δ13C, WUE, and dry matter accumulation and allocation were detected. A negative correlation between WUE and biomass productivity was detected under control and drought stress I, but a positive correlation under drought stress II. The results suggested that there were different water-use strategies among the populations, the southeastern population with lower WUE may employ a prodigal water-use strategy, whereas the northwestern and central populations with higher WUE may employ a conservative water-use strategy. This knowledge may be useful as criteria for genotype selection within a breeding program for this species.

Analysis of Rainbow Trout Peripheral Blood Leucocytes Separated by Flow Cytometry Cell Sorting.

The characterization of rainbow trout peripheral blood leucocytes (PBL) was carried out by flow cytometry (FCM) analysis and by transmission electron microscopy. Two major cell populations were identified in FCM analysis. One population showed small values in both forward scatter (FS) and side scatter (SS), and the other population showed large values in both parameters. These major populations were divided into two sub-regions each (A/B and C/D). There was no significant difference in cell populations between sub-regions A and B. However, a difference was observed in the small and large lymphocyte percentages between sub-regions C and D. The majority of regions (A and B) were constituted by neutrophils (56% and 66%, respectively), and monocytes accounted for 9% and 7% of the cells, respectively. Large and small lymphocytes were also present in these regions, accounting for 26% and 6% of the cells in sub-region A and 14% and 7% in sub-region B, respectively. In sub-regions C and D, cells were mainly constituted by large and small lymphocytes (33% and 49% in C, and 7% and 70% in D, respectively) and thrombocytes (14% and 23%).

The Effects of Sun, Shade, and Predation on Azalea Lace Bug Populations in Containerized Azaleas

The effects of sun and shade in a small monocultural nursery-like environment and the effect of natural enemies on the population density of azalea lace bugs (Stephanitis pyrioides Scott) on azaleas (Rhododendron L.) in the nursery environment were assessed. A comparison of sun and shade treatments for total number of azalea lace bug eggs collected and eclosed revealed no significant (P &lt; 0.05) differences. Stippling damage did not differ significantly between sun and shade treatments. Therefore, lace bug oviposition or eclosion were not affected by sun or shade. Arthropods collected from 5 weeks of beat samples were divided into four feeding guilds: predator-parasitoid (eight families), chelicerates (six families), chewing herbivores (two families), and piercing-sucking herbivores (nine families). Guilds were not significantly different between sun and shade treatments. In the small monocultures designed for this experiment, the 4 guilds do not appear to show preference for sun or shade habitats. No significant differences in azalea lace bug populations between caged and uncaged azalea cuttings in the nursery environment indicate there were no consequential effects of predation or parasitism on egg eclosion or subsequent instars in the first generation.

Insect Defoliation and Population Dynamics in Blends of Resistant and Susceptible Soybean Cultivars

AbstractPhytophagous insects can cause significant economic yield loss in soybean [Glycine max (L.) Merr.] production areas of the southern United States. Although breeding efforts have resulted in developing insect‐resistant cultivars, the yield potential of these cultivars is generally lower than conventional cultivars under conditions of light insect pressure. The objective of this study was to determine if a blend of insect resistant and insect susceptible cultivars affords some degree of insect control while maintaining high yields under high insect pressure environments. Experiments were conducted on a Labelle soil (Oxyaquic Vertic Argiaquolls) near Beaumont, TX, in 1990 to 1992. The 3‐yr field study included five population ratios of Maturity Group VIII cultivars Dowling (insect susceptible, S) and Crockett (insect resistant, R): 100 S:0 R, 75 S:25 R, 50 S:50 R, 25 S:75 R, and 0 S:100 R. Plots were sampled weekly for insects and percent leaf defoliation when insect populations began to increase in late summer. Data were analyzed with blend treated as a linear trend. Insect counts of six major pests showed that, of 18 possible year‐insect combinations, in only three cases were there significant population differences due to blend. In late season, the percent defoliation of Crockett increased in all 3 yr as the percentage of Crockett in the blend increased. By contrast, as the percentage of Dowling in the blend increased, the percent defoliation of Dowling decreased in 2 of the 3 yr. Therefore, blending Crockett and Dowling did not offer insect defoliation protection for Dowling and may have had an opposite effect. Maximum percent defoliation for Crockett was generally 40 to 50% less than that for Dowling. In 1990 and 1991, blending had no effect on yield or seed quality. In 1992, there was a significant, negative effect on yield (b = −4.46) and seed quality (b = 0.01) as the percentage of Crockett increased in the blend. Blends of these cultivars did not improve yield of Dowling under conditions of insect pressure compared with a pure stand of Dowling. A blend of insect resistant and susceptible cultivars did not appear to be a suitable insect control management strategy in soybean.

Bacterial Abundance and Activity across Sites within Two Northern Wisconsin Sphagnum Bogs

Abstract Bacterial abundance, temperature, pH, and dissolved organic carbon (DOC) concentration were compared across surface sites within and between two northern Wisconsin Sphagnum peatlands over the summer seasons in 1995 and 1996. Sites of interest were the Sphagnum mat surface, the water-filled moat (lagg) at the bog margin, and the bog lake littoral zone. Significant differences in both bacterial populations and water chemistry were observed between sites. pH was highest in the lake and lowest in the mat at both bogs; the opposite was true for DOC. Large populations of bacteria were present in surface interstitial water from the mat; abundance in this site was consistently higher than in the moat or lake. Bacterial abundance also increased across sites of increasing DOC concentration and declining pH. Bacterial activities (rates of [3H]leucine incorporation) and growth in dilution cultures (with grazers removed) were also assessed in lake, moat, and mat sites. Results using these measures generally supported the trends observed in abundance, although high rates of [3H]leucine incorporation were recorded in the moat at one of the bogs. Our results indicate that bacterial populations in Sphagnum peatlands are not adversely affected by acidity, and that DOC may be more important than pH in determining bacterial abundance in these environments.

Frequency of anal sphincter rupture at delivery in Sweden and Finland ‐ result of difference in manual help to the baby's head

Anal sphincter rupture is a serious complication of vaginal delivery and almost half the affected women have persistent defecatory symptoms despite adequate primary repair. During the past decade, the incidence of anal sphincter ruptures has been increasing in Sweden and is currently estimated to occur in 2.5% of vaginal deliveries. The aim of the study was to report the frequency of anal sphincter ruptures in two university hospitals in two Scandinavian countries, Malmö in Sweden and Turku in Finland, and analyze the potential determinants. Retrospective analysis of a population of 30,933 deliveries (26,541 vaginal) during the years 1990 to 1994. The incidence of anal sphincter ruptures in Malmö, Sweden was 2.69%, and in Turku, Finland 0.36%. There were no significant population differences for the known risk factors (fetal weight, nulliparity or fetal head circumference). However, there is a difference in manual support given to the perineum and to the baby's head when crowning through the vaginal introitus between Malmö and Turku. The proportion of operative vaginal deliveries and abnormal presentations was significantly higher in Turku reflected in the lower Apgar score at 5 minutes and longer duration of second phase of labor. When high risk deliveries (operative vaginal delivery, abnormal presentation and newborns over 4,000 g) were excluded, the risk for anal sphincter ruptures was estimated to be 13 times higher in Malmö than in Turku. The difference in the incidence of anal sphincter rupture between Malmö, Sweden and Turku, Finland may be due to the difference in manual control of the baby's head when crowning.

Effect of winter cover crops on populations of southern root-knot and reniform nematodes

Nematicidal effects of decomposing plant amendments have long been known, and many different crops have been shown to suppress a range of species of plant parasitic nematodes. Leguminous winter cover crops such as hairy vetch ( Vicia villosa Roth.) and crimson clover ( Trifolium incarnatum L.) have varying degrees of tolerance to high populations of certain plant parasitic nematodes, but their ability to suppress populations have not been well studied. The objective of this study was to examine the effectiveness of commonly-used winter cover crops to suppress populations of root-knot ( Meloidogyne arenaria) and reniform ( Rotylenchulus reniformis) nematodes in field and greenhouse studies. Common vetch ( Vicia sativa L. cv. `Cahaba White'), hairy vetch and crimson clover were planted in autumn, each at the rate of 22 kg ha −1. Two additional treatments were bare soil (no cover crop) and bare soil plus nitrogen added at a rate equal to the average N content of the incorporated cover crops. Cover crops were incorporated just before planting okra ( Abelmoschus esculentus L. Moench). Few significant differences in nematode populations were noted at any sampling date because of cover crop treatments. When differences occurred, populations of M. arenaria were lower in bare soil treatments in comparison with those with an incorporated cover crop. Okra yield was unaffected by any cover crop. In the greenhouse study, R. reniformis populations were reduced in rye and bare soil treatments, but populations were unaffected in common or hairy vetch treatments.

Patterns of Differentiation in Wiregrass (Aristida beyrichiana): Implications for Restoration Efforts

Aristida beyrichiana (wiregrass) is increasingly being planted in restoration projects across the southeastern coastal plain, with little focus on genetic differences among populations across the region. Local and regional population differentiation for establishment and growth traits were examined in common garden and reciprocal transplant experiments. Seeds from up to 20 plants from each of seven populations were collected in northern and central Florida sites that encompassed gradients of soils, hydrology, and temperature. Reciprocal seed transplants using three of the common garden populations were conducted in two consecutive years. In the common garden, significant population differences were seen in seed weight, seedling emergence and survival, tiller height, number of tillers, the relationship between tiller number and tiller height, and flowering. Variation among maternal families was seen in tiller number and in the relationship between tiller number and tiller height. The reciprocal transplant study did not detect either local adaptation to sites of origin or consistent superiority of one source population or planting site in seedling establishment. These results suggest that the probability of seedling establishment is primarily dependent on environmental conditions rather than genetic differences. Genetic variation for traits related to fitness (e.g., tiller number) may be retained within populations because phenotypically plastic growth responses of seedlings to environmental variation buffer genetic variation against the action of selection. But despite the lack of evidence for genetic influences on initial establishment in wiregrass, our common garden study suggests genetic differences among populations. This result, when combined with previous results indicating local adaptation in later life stages of wiregrass, suggests that restoration efforts involving this species should use local seed sources from sites with similar soil and hydrological conditions.

Intracranial aneurysms: a review of endovascular and surgical treatment in 248 patients.

We reviewed the medium-term results of endovascular treatment of intracranial aneurysms and compared patient selection and results with those of open surgery. Between January 1992 and December 1995, a total of 248 consecutive patients were treated for 297 aneurysms (61 unruptured and 236 ruptured). 162 aneurysms in 142 patients (mean age, 48.5 years) were treated microsurgically and 134 aneurysms in 106 patients (mean age, 54.2 years) were treated by endovascular embolization with Guglielmi detachable coils (GDC). The mean follow-up was 2.6 years (range, 1.5 to 4.5 years). There was no significant difference in patient population and selection in terms of age, sex or location of aneurysms between both methods. Both modalities achieved excellent results (defined as no neurological deficit) in patients with unruptured aneurysms and with no or minor deficits after subarachnoid hemorrhage (SAH) between 71% and 88%. Patients with moderate deficits after SAH had excellent outcomes in 49% after open surgery, and 47% after embolization. Poor grade patients had, equally, as well an acceptable as a pour outcome, between 0% and 50%. There was no significant difference between the outcome of surgical or endovascular patients. We conclude that GDC embolization is not associated with a higher risk of morbidity and mortality than open surgery. This risk may even be lower for lesions in surgically unfavorable locations. The GDC technique is a less invasive, effective option to prevent re-bleeding in early stage, even in poor-grade patients. However, these encouraging medium-term results have to be confirmed by a longer observation period.

Stellar Populations in Three Outer Fields of the Large Magellanic Cloud

We present HST photometry for three fields in the outer disk of the LMC extending approximately four magnitudes below the faintest main sequence turnoff. We cannot detect any strongly significant differences in the stellar populations of the three fields based on the morphologies of the color-magnitude diagrams, the luminosity functions, and the relative numbers of stars in different evolutionary stages. Our observations therefore suggest similar star formation histories in these regions, although some variations are certainly allowed. The fields are located in two regions of the LMC: one is in the north-east field and two are located in the north-west. Under the assumption of a common star formation history, we combine the three fields with ground-based data at the same location as one of the fields to improve statistics for the brightest stars. We compare this stellar population with those predicted from several simple star formation histories suggested in the literature, using a combination of the R-method of Bertelli et al (1992) and comparisons with the observed luminosity function. The only model which we consider that is not rejected by the observations is one in which the star formation rate is roughly constant for most of the LMC's history and then increases by a factor of three about 2 Gyr ago. Such a model has roughly equal numbers of stars older and younger than 4 Gyr, and thus is not dominated by young stars. This star formation history, combined with a closed box chemical evolution model, is consistent with observations that the metallicity of the LMC has doubled in the past 2 Gyr.

Physiological Variation and Allometry in Western Whiptail Lizards (Cnemidophorus tigris) from a Transect across a Persistent Hybrid Zone

A hybrid zone involving Cnemidophorus tigris punctilinealis (formerly gracilis) and C. tigris marmoratus in southwestern New Mexico and adjacent Arizona is narrow and characterized by abrupt and concordant change in both morphological characters and allele frequencies studied by protein electrophoresis. We compared adult C. tigris sampled from three locations that span the hybrid zone. Body mass was positively associated with both treadmill endurance at 1.0 km/h and maximal sprint running speed on a high-speed treadmill, although the largest individuals were not the fastest sprinters. Males and females differed significantly for maximal sprint ruloning speed, liver mass, and kidney mass (ANCOVA with body mass as covariate). We found no statistically significant population differences for body mass, maximal sprint running speed, standard metabolic rate at 40C, blood hematocrit levels, or heart mass. Hybrids tended to have lower treadmill endurance rlnning capacities as compared with the pure forms, but the difference was not statistically significant. Cnemidophorus tigris punctilinealis and the hybrids both had significantly heavier kidneys, relative to body mass, than did C. tigris marmoratus. Hybrid individuals also had significantly heavier livers as compared with either pure population. However, the present data cannot rule out the possibility that the observed differences in organ masses were related to reproductive status as opposed to being genetically based population differences. Thus, our results do not suggest that hybrid individuals differ from nonhybrids with respect to Darwinian fitness.