Competitive effects of non-native plants are lowest in native plant communities that are most vulnerable to invasion

Despite widespread acknowledgment that disturbance favors invasion, a hypothesis that has received little attention is whether non-native invaders have greater competitive effects on native plants in undisturbed habitats than in disturbed habitats. This hypothesis derives from the assumption that competitive interactions are more persistent in habitats that have not been recently disturbed. Another hypothesis that has received little attention is whether the effects of non-native plants on native plants vary among habitats that differ in soil fertility. We documented habitat occurrences of 27 non-native plant species and 377 native plant species encountered in numerous study plots in a broad sample of ecosystems in MS (USA). We then reviewed experimental and regression-based field studies in the scientific literature that specifically examined potential competitive (or facilitative) effects of these non-native species on native species and characterized the habitats in which effects were the greatest. As expected, the non-native species examined here in general were more likely to be associated with severely disturbed habitats than were the native species as a group. In contrast, we found that non-native species with competitive effects on natives were more likely to be associated with undisturbed habitats than with disturbed habitats. When longer term studies involving more resident species were given more weight in the analysis, competitive effects appeared to be the greatest in undisturbed habitats with low soil fertility. These results reinforce the notion that invasion is not synonymous with impact. The environmental conditions that promote invasion may limit competitive effects of invaders on native plant communities following invasion.     

Integrated control of the most damaging pests of peach trees in Greece

In this study, the integrated management of Myzus persicae, Adoxophytes orana, Anarsia lineatella, Grapholita molesta, Panonychus ulmi and Tetranychus urticae was evaluated. The results showed that the population of Myzus persica on integrated systems was significantly lower than untreated control and higher than conventional systems. The population of P. ulmi and T. urticae was relatively low ( < 2 per leaf) in all treatments. Damage to fruit caused from A. orana and A. lineatella were significantly higher on untreated control than integrated or conventional systems. The results also showed that the damages caused from G. molesta were low in both conventional and integrated systems. In contrast, this insect caused significantly higher damage on untreated fruit.     

A constituent-based model of age-related changes in conduit arteries

In the present report, a constituent-based theoretical model of age-related changes in geometry and mechanical properties of conduit arteries is proposed. The model was based on the premise that given the time course of the load on an artery and the accumulation of advanced glycation end-products in the arterial tissue, the initial geometric dimensions and properties of the arterial tissue can be predicted by a solution of a boundary value problem for the governing equations that follow from finite elasticity, structure-based constitutive modeling within the constrained mixture theory, continuum damage theory, and global growth approach for stress-induced structure-based remodeling. An illustrative example of the age-related changes in geometry, structure, composition, and mechanical properties of a human thoracic aorta is considered. Model predictions were in good qualitative agreement with available experimental data in the literature. Limitations and perspectives for refining the model are discussed.     

Evidence that most radiation-induced HPRT mutants are generated directly by the initial radiation exposure.

Radiation-induced HPRT mutants are generally assumed to arise directly from DNA damage that is misrepaired within a few hours after X-irradiation. However, there is the possibility that mutations result indirectly from radiation-induced genomic instability that may occur several days after the initial radiation exposure. The protocols that commonly employ a 5-7 day expression period to allow for expression of the mutant phenotype prior to replating for selection of mutants would not be able to discriminate between mutants that occurred initially and those that arose during or after the expression period. To address this question, we performed a fluctuation analysis in which synchronous or asynchronous populations of human bladder carcinoma cells were treated with single doses of X-irradiation. For comparison, radiation was delivered during the expression period, either from an initial dose of 1.0 Gy followed by two 1.0 Gy doses separated by 24 h or from disintegrations resulting from I125dU incorporated into DNA. The mutation frequency observed at the time of replating was used to calculate the average number of mutants in the initial irradiated culture by assuming that the mutants were induced directly at the time of irradiation. Then, this average number was used to calculate the fraction of the irradiated cultures that would be predicted by a Poisson distribution to have zero mutants. There was reasonably good agreement between the predicted poisson distribution and the observed distribution for the cultures that received single doses. Moreover, as expected, when cultures were irradiated during the expression period, the fraction of the cultures having zero mutants was significantly less than that predicted by a Poisson distribution. These results indicate that most radiation-induced HPRT mutations are induced directly by the initial DNA damage, and are not the result of radiation-induced instability during the 5-7 day expression period.     

Bayesian analysis suggests that most amino acid replacements in Drosophila are driven by positive selection

One of the principal goals of population genetics is to understand the processes by which genetic variation within species (polymorphism) becomes converted into genetic differences between species (divergence). In this transformation, selective neutrality, near neutrality, and positive selection may each play a role, differing from one gene to the next. Synonymous nucleotide sites are often used as a uniform standard of comparison across genes on the grounds that synonymous sites are subject to relatively weak selective constraints and so may, to a first approximation, be regarded as neutral. Synonymous sites are also interdigitated with nonsynonymous sites and so are affected equally by genomic context and demographic factors. Hence a comparison of levels of polymorphism and divergence between synonymous sites and amino acid replacement sites in a gene is potentially informative about the magnitude of selective forces associated with amino acid replacements. We have analyzed 56 genes in which polymorphism data from D. simulans are compared with divergence from a reference strain of D. melanogaster. The framework of the analysis is Bayesian and assumes that the distribution of selective effects (Malthusian fitnesses) is Gaussian with a mean that differs for each gene. In such a model, the average scaled selection intensity (gamma = N(e)s) of amino acid replacements eligible to become polymorphic or fixed is -7.31, and the standard deviation of selective effects within each locus is 6.79 (assuming homoscedasticity across loci). For newly arising mutations of this type that occur in autosomal or X-linked genes, the average proportion of beneficial mutations is 19.7%. Among the amino acid polymorphisms in the sample, the expected average proportion of beneficial mutations is 47.7%, and among amino acid replacements that become fixed the average proportion of beneficial mutations is 94.3%. The average scaled selection intensity of fixed mutations is +5.1. The presence of positive selection is pervasive with the single exception of kl-5, a Y-linked fertility gene. We find no evidence that a significant fraction of fixed amino acid replacements is neutral or nearly neutral or that positive selection drives amino acid replacements at only a subset of the loci. These results are model dependent and we discuss possible modifications of the model that might allow more neutral and nearly neutral amino acid replacements to be fixed.     

A study of sutural bones in Anatolian-Ottoman skulls

In this study, a total of 302 adult Anatolian-Ottoman skulls were classified into three morphological forms (dolichocephalic, mesocephalic, brachycephalic), and were examined in order to find the incidence of sutural bones in each forms. In addition, the cranial capacity was measured in the skulls with and without sutural bones. Comparison of the incidence of sutural bones in each form of the skulls, and cranial capacity in skulls with and without sutural bones showed no significant difference. In most populations, the average measure of difference between Anatolian-Ottoman and the others was statistically significant. In conclusion, the incidence of sutural bones is well suited for comperative studies as an anthropological marker or an indicator of population distance. This study was presented in the 3rd National Anatomy Congress (6–9 Sept 1995) Izmir, Türkiye.     

A canopy architectural model to study the competitive ability of chickpea with sowthistle

Background and Aims

Improving the competitive ability of crops is a sustainable method of weed management. This paper shows how a virtual plant model of competition between chickpea (Cicer arietinum) and sowthistle (Sonchus oleraceus) can be used as a framework for discovering and/or developing more competitive chickpea cultivars.

Methods

The virtual plant models were developed using the L-systems formalism, parameterized according to measurements taken on plants at intervals during their development. A quasi-Monte Carlo light-environment model was used to model the effect of chickpea canopy on the development of sowthistle. The chickpea–light environment–sowthistle model (CLES model) captured the hypothesis that the architecture of chickpea plants modifies the light environment inside the canopy and determines sowthistle growth and development pattern. The resulting CLES model was parameterized for different chickpea cultivars (viz. ‘Macarena’, ‘Bumper’, ‘Jimbour’ and ‘99071-1001’) to compare their competitive ability with sowthistle. To validate the CLES model, an experiment was conducted using the same four chickpea cultivars as different treatments with a sowthistle growing under their canopy.

Results and Conclusions

The growth of sowthistle, both in silico and in glasshouse experiments, was reduced most by ‘99071-1001’, a cultivar with a short phyllochron. The second rank of competitive ability belonged to ‘Macarena’ and ‘Bumper’, while ‘Jimbour’ was the least competitive cultivar. The architecture of virtual chickpea plants modified the light inside the canopy, which influenced the growth and development of the sowthistle plants in response to different cultivars. This is the first time that a virtual plant model of a crop–weed interaction has been developed. This virtual plant model can serve as a platform for a broad range of applications in the study of chickpea–weed interactions and their environment.Key words: Plant architecture, virtual plant modelling, L-systems formalism, crop/weed competition, integrated weed management, chickpea, Cicer arietinum, sowthistle, Sonchus oleraceus     

Identifying genes that contribute most to good classification in microarrays

Background  

The goal of most microarray studies is either the identification of genes that are most differentially expressed or the creation of a good classification rule. The disadvantage of the former is that it ignores the importance of gene interactions; the disadvantage of the latter is that it often does not provide a sufficient focus for further investigation because many genes may be included by chance. Our strategy is to search for classification rules that perform well with few genes and, if they are found, identify genes that occur relatively frequently under multiple random validation (random splits into training and test samples).     

Iron levels in the human brain: A post-mortem study of anatomical region differences and age-related changes

The link between brain iron homeostasis and neurodegenerative disease has been the subject of extensive research. There is increasing evidence of iron accumulation during ageing, and altered iron levels in some specific brain regions in neurodegenerative disease patients have been reported.Using graphite furnace atomic absorption spectrometry after microwave-assisted acid digestion of the samples, iron levels were determined in 14 different areas of the human brain [frontal cortex, superior and middle temporal, caudate nucleus, putamen, globus pallidus, cingulated gyrus, hippocampus, inferior parietal lobule, visual cortex of the occipital lobe, midbrain, pons (locus coeruleus), medulla and cerebellum (dentate nucleus)] of n = 42 adult individuals (71 ± 12 years old, range: 53–101 years old) with no known history or evidence of neurodegenerative, neurological or psychiatric disorders.It was found that the iron distribution in the adult human brain is quite heterogeneous. The highest levels were found in the putamen (mean ± SD, range: 855 ± 295 μg/g, 304–1628 μg/g) and globus pallidus (739 ± 390 μg/g, 225–1870 μg/g), and the lowest levels were observed in the pons (98 ± 43 μg/g, 11–253 μg/g) and medulla (56 ± 25 μg/g, 13–115 μg/g).Globally, iron levels proved to be age-related. The positive correlation between iron levels and age was most significant in the basal ganglia (caudate nucleus, putamen and globus pallidus).Compared with the age-matched control group, altered iron levels were observed in specific brain areas of one Parkinson's disease patient (the basal ganglia) and two Alzheimer's disease patients (the hippocampus).     

生物行为变化研究的新模式——工蜂

蜜蜂群体由1只蜂王、几百只雄蜂和数千只工蜂组成,工蜂数量巨大,除蜂王和雄蜂共同完成生殖任务,巢内外活动均由工蜂完成,其行为呈现多样性。工蜂发育经过卵、幼虫、蛹、成虫4个阶段,其活动范围由温度、湿度相对稳定的巢内环境发展到复杂的巢外自然环境。随发育阶段和生活环境的变化,工蜂的生理、行为等方面也发生相应变化,这种变化为综合研究生物行为的分子机理提供了可能。又因工蜂数量多、体积较大易于观察、标记、饲养管理简单,而且目前对其形态、发育、生理、分子生物学、神经、社会生态等各方面的研究比较充分,所以工蜂成为研究生物体行为变化、发育机理和个体与群体关系的理想模式生物。该文介绍工蜂活动由巢内发展到巢外时出现的一系列变化以及部分变化的机制,主要包括行为的变化、激素的分泌、代谢活动、飞行能力、神经系统等。     

The cytoplasmic sites of the snRNP protein complexes are punctate structures that are responsive to changes in metabolism and intracellular architecture

Five anti-Sm monoclonal antibodies, Y12, 7.13, KSm4, KSm6, and 128, stain similar discrete punctate structures distributed throughout the cytoplasm of hamster fibroblasts in addition to the expected intense nuclear staining. Several criteria suggest the cytoplasmic staining reflects the cytoplasmic pools of snRNP core proteins. The relative intensity of the cytoplasmic staining is similar to the 30% relative abundance of the cytoplasmic snRNP core proteins compared to the nuclear snRNP core proteins based on cell-fractionation studies. Moreover, the cytoplasmic staining is removed by the same extraction conditions that solubilize the pools of cytoplasmic snRNP core proteins. The cytoplasmic sites of staining are typically spherical but heterogeneous in diameter (0.2-0.5 microm). The larger particles greatly exceed the diameter of individual snRNP core particles and are likely to represent centers of many snRNP proteins or snRNP protein complexes. The staining, though punctate, is evenly dispersed throughout the cytoplasm with no evidence of major compartmentalization. The cytoplasmic staining pattern collapses into larger foci of intensely staining structures when cellular energy levels are depleted or when cells are exposed to hypertonic medium. Unlike the normal sites of snRNP protein cytoplasmic staining, these larger collapsed foci resist detergent extraction. These results suggest that the cytoplasmic staining identified with the anti-Sm monoclonal antibodies represents the large pools of snRNP core proteins in the cytoplasm.     

A new experimental animal for the study of age-related changes in serotonergic neuronal activity in the brain cortex

Calcium uptake by the cortical synaptosomes in a rodent (Fischer rat) and an insectivore shrew (Suncus murinus) was detected as a parameter reflecting molecular dysfunction of the aging brain. The change in calcium uptake by the cortical synaptosomes in both species was concomitant which showed less than half the capacity at 24 months old animals compared with those at 8 months old. On the other hand, 5-hydroxytryptamine binding and imipramine binding to the membrane fraction of aging rat brain cortex was not altered in terms of binding capacity along with aging, while, in Suncus, the binding of both serotonergic ligands declined with aging. In order to elucidate decreased serotonergic activity in human demented aged brain, together with declining activity in neurotransmitting systems detectable as a function of calcium uptake by the cortical synaptosomes, Suncus may be an appropriate animal model for studying physiological aging processes in the mammalian brain cortex.Special Issue Dedicated to Dr. Abel Lajtha.     

Chronic low dose exposure to hydrogen peroxide changes sensitivity of V79 cells to different damaging agents

Chinese hamster V79 cells were repeatedly exposed to a low dose of hydrogen peroxide (H2O2) over several weeks and then exposed to H2O2, cisplatin or ultraviolet (UV) light. Cell killing was examined by colony formation, following these treatments. It was seen that cells conditioned by multiple low doses of H2O2 showed resistance to killing in case of H2O2 and cisplatin but the sensitivity to UV light was same as the control cells. Apoptosis was also determined in these cells after the same treatments. UV light failed to induce apoptosis in both conditioned and in control cells, but in case of cells treated with H2O2 and with cisplatin, there was less apoptosis in the conditioned cells compared to the control cells. From our observation we can say that the enhanced survival of cells after treatment with H2O2 or cisplatin could be due to inhibition of apoptosis.