Technical note: calculation of age at formation of radiopaque transverse lines

A simple method for determining the age of an individual at the time of radiopaque transverse (Harris) line formation is presented. To use this method, only two measurements are required: total bone length and distance of line to nearest bone end; these are put into formulae that calculate the percent of total bone growth when the line appeared. The result of this calculation is compared with tables of percent bone growth per year (one to 16 years in females and one to 18 years in males) to arrive at estimations of age at line formation. Since these tables are presented for the femur, tibia, humerus, and radius, this technique can be used on any one of the major long bones exhibiting lines.     

The estimation of age at death and ages of formation of transverse lines from measurements of human long bones

A radiographic method is presented which estimates the age at death from the diaphyseal length of a child's long bone or bones. Mean lengths are calculated from adult males and females separately in the skeletal population under study, and the child's age derived from the proportion of adult length attained at his or her death. The calculations come from double logistic curves originally derived from a sample of Colorado children (McCammon, 1970). In radiographs of immature or adult long bones, similar equations are based on the location of the center of ossification, from which distances to transverse lines yield estimated ages when these lines were formed. In a population, ages at death, ages of attainment of transverse lines, and ages when anomalous enamel is laid down in teeth are all contributions to paleopathology and paleodemography. These equations can predict when spaced transverse lines were annually formed. If such spaced lines can be seen in radiographs of early fossil hominids, their spacing can distinguish between short childhood, as in apes, and the longer immature developmental span found in modern children.     

Low persistence of the induced mutant phenotype in Chinese hamster cells

We have analysed the recovery of individual CHO-derived mutants during the generations immediately following their induction. This characteristic, which we call persistence, was measured by propagating mutagenized cultures in non-selective medium after subdivision into many very small populations, each containing either zero or one mutant. The recovery of most hypoxanthine phosphoribosyltransferase (hprt)-deficient mutants induced by ethyl methanesulphonate was low, and we have previously shown that this was usually due to an apparent rapid loss of the mutant phenotype with continued culture in non-selective medium (Bradley, 1980). A minority of about 15% manifest high persistence. We now show that most adenine phosphoribosyltransferase (aprt)-deficient mutants and some ouabain-resistant mutants had low persistence. Mutants induced by UV irradiation also generally exhibited low persistence but those induced by X-irradiation had significantly higher persistence than what was seen among EMS-induced mutants. Among various sublines of CHO cells which were tested for persistence of induced mutants, only one group consistently yielded mutants of high persistence. These were lines which carried glucose-6-phosphate dehydrogenase mutations which themselves had been originally induced by EMS.     

Effects of landscape and patch-level attributes on regional population persistence

Species responses are influenced by processes operating at multiple scales, yet many conservation studies and management actions are focused on a single scale. Although landscape-level habitat conditions (i.e., habitat amount, fragmentation and landscape quality) are likely to drive the regional persistence of spatially structured populations, patch-level factors (i.e., patch size, isolation, and quality) may also be important. To determine the spatial scales at which habitat factors influence the regional persistence of endangered Ord's kangaroo rats (Dipodomys ordii) in Alberta, Canada, we simulated population dynamics under a range of habitat conditions. Using a spatially-explicit population model, we removed groups of habitat patches based on their characteristics and measured the resulting time to extinction. We used proportional hazards models to rank the influence of landscape and interacting patch-level variables. Landscape quality was the most influential variable followed by patch quality, with both outweighing landscape- and patch-level measures of habitat quantity and fragmentation/proximity. Although habitat conservation and restoration priorities for this population should be in maximizing the overall quality of the landscape, population persistence depends on how this goal is achieved. Patch quality exerted a significant influence on regional persistence, with the removal of low quality road margin patches (sinks) reducing the risk of regional extinction. Strategies for maximizing overall landscape quality that omit patch-level considerations may produce suboptimal or detrimental results for regional population persistence, particularly where complex local population dynamics (e.g., source-sink dynamics) exist. This study contributes to a growing body literature that suggests that the prediction of species responses and future conservation actions may best be assessed with a multi-scale approach that considers habitat quality and that the success of conservation actions may depend on assessing the influences of habitat factors at multiple scales.     

Mycobacterium tuberculosis persistence in various adipose depots of infected mice and the effect of anti-tubercular therapy

The adipocytes are one of the non-professional phagocytes postulated to be a haven for Mycobacterium tuberculosis during persistence in the human host. The adipocyte – M. tuberculosis interaction data available to date are ex vivo. The present study was primarily aimed to investigate M. tuberculosis infection of adipocytes in course of infection of mouse model. Using primary murine adipocytes, the study first confirmed the infection and immunomodulation of natural adipocytes by M. tuberculosis. The bacilli could be isolated form visceral, subcutaneous, peri renal and mesenteric adipose depots of immunocompetent mice infected with M. tuberculosis intravenously. The bacilli could be isolated from adipocytes and the stromal vascular fraction, even though the numbers were significantly higher in the latter. The bacterial burden in the adipose depots was comparable to those in lungs in the early phase of infection. But with time, the burden in the adipose depots was either decreased or kept under control, despite the increasing burden in the lungs. Infected mice treated with standard anti tubercular drugs, despite effective elimination of bacterial loads in the lungs, continued to harbour M. tuberculosis in adipose depots at loads similar to untreated mice in the late infection phase.     

Effects of colonization asymmetries on metapopulation persistence

Ocean currents, prevailing winds, and the hierarchical structures of river networks are known to create asymmetries in re-colonization between habitat patches. The impacts of such asymmetries on metapopulation persistence are seldom considered, especially rarely in theoretical studies. Considering three classical models (the island, the stepping stone and the distance-dependent model), we explore how metapopulation persistence is affected by (i) asymmetry in dispersal strength, in which the colonization rate between two patches differs in direction, and (ii) asymmetry in connectivity, in which the overall colonization pattern displays asymmetry (circulating or dendritic networks). Viability can be drastically reduced when directional bias in dispersal strength is higher than 25%. Re-colonization patterns that allow for strong local connectivity provide the highest persistence compared to systems that allow circulation. Finally, asymmetry has relatively weak effects when metapopulations maintain strong general connectivity.     

土壤中乙草胺的微生物降解及其对防除稗草持效性的影响

采用气相色谱法和生物测定法,研究了土壤中乙草胺的微生物降解及其对防除稗草持效性的影响.结果表明,在同样的湿度和温度条件下,当添加到土壤中的乙草胺浓度为125、25和5.0 mg·kg^-1时,相同浓度的乙草胺在非灭菌土壤中的半衰期显著短于灭菌土壤,说明土壤微生物对乙草胺有明显的降解作用.三大主要菌群分离培养物降解实验与上述结果一致.生物测定结果表明,乙草胺在非灭菌土壤中防除稗草的持效期显著短于灭菌土壤,微生物的存在缩短了乙草胺在土壤中的滞留时间,从而降低了乙草胺防除稗草的持效性.     

The effect of temporal variability on persistence conditions in rivers

There has been great interest in the invasion and persistence of algal and insect populations in rivers. Recent modeling approaches assume that the flow speed of the river is constant. In reality, however, flow speeds in rivers change significantly on various temporal scales due to seasonality, weather conditions, or many human activities such as hydroelectric dams. In this paper, we study persistence conditions by deriving the upstream invasion speed in simple reaction-advection-diffusion equations with coefficients chosen to be periodic step functions. The key methodological idea to determine the spreading speed is to use the exponential transform in order to obtain a moment generating function. In a temporally periodic environment, the averages of each coefficient function determine the minimal upstream and downstream propagation speeds for a single-compartment model. For a two-compartment model, the temporal variation can enhance population persistence.     

A Petri net approach to the study of persistence in chemical reaction networks

Persistence is the property, for differential equations in R(n), that solutions starting in the positive orthant do not approach the boundary of the orthant. For chemical reactions and population models, this translates into the non-extinction property: provided that every species is present at the start of the reaction, no species will tend to be eliminated in the course of the reaction. This paper provides checkable conditions for persistence of chemical species in reaction networks, using concepts and tools from Petri net theory, and verifies these conditions on various systems which arise in the modeling of cell signaling pathways.     

Top predator persistence in differential equation models of food chains: The effects of omnivory and external forcing of lower trophic levels

Persistence criteria are given for the highest trophic level predator in ordinary differential equation models of food chains exhibiting arbitrary omnivory and external supplementation of food source or an intermediate predator. The results are expressed in terms of inequalities involving the bounds on the intrinsic growth and interaction rates. Whether omnivory or external forcing enhances persistence is discussed, particularly for the examples of three-, four-, and five-link Lotka-Volterra food chains.     

Measuring the persistence length of MCF7 cell microtubules in vitro

The dynamic and mechanical properties of mammalian neural microtubules have been widely studied; however, similar knowledge about these properties is limited for non-neural microtubules, which, unlike neural microtubules, consist of different β-tubulin isotypes. In this study, we report, for the first time, an estimated value for the persistence length of a single non-neural microtubule polymerized from purified tubulin from human breast cancer cell lines (MCF7 tubulin). The method of measurement is based on an analysis of the local curvature of a microtubule as a result of thermal fluctuations. In parallel, we measured the persistence length of a single bovine brain microtubule under similar conditions. The results of our measurements indicate a higher value for the persistence length of MCF7 microtubules in vitro as compared to the persistence length of a neural microtubule. The difference can be associated with different β-tubulin isotypes in the structure of MCF7 microtubules.     

Change of the persistence lengths in the conformational transitions of pullulan- and amylose-tricarbanilates

With raising temperature in the domain of 20 to 60 degrees C, the intrinsic viscosity [eta] for pullulan-tricarbanilate PTC and amylose-tricarbanilate ATC in solutions was found to decrease, indicating that they exhibited thermal-induced conformational transition from expanded form to compact form. The persistence length P(l) of the chains, evaluated with small-angle X-ray scattering, has also decreased as the temperature is raised and, moreover, it significantly depended on the solvents employed, where as P(l) of pullulan, having no carbanilate groups, has exhibited neither temperature- nor solvent-dependence. The temperature dependence of [eta] for PTC and ATC was well elucidated in terms of the temperature-dependent P(l) with the wormlike chain model. From these results, it is suggested that intramolecular hydrogen bonds would be formed between carbanilate groups neighboring along the backbone chain, but they are gradually and cooperatively collapsed as the temperature is raised, inducing the conformational transition.     

Morphology and evolution of the wing bullae in South American Leptophlebiidae (Ephemeroptera)

Insects were the first animals to take to the skies, and have been flying for over 320 million years. The order Ephemeroptera is, or at least is part of, the most early-diverging lineage of extant winged insects. The extant species present a very short adult life span, mainly dedicated to reproduction and dispersal of eggs. Mating and egg-laying behavior depend on flight. Wings are structures to fly and as such face a number of physical and physiological challenges. The convex curvature along the anterior–posterior axis of the wing generates a camber that must be carefully regulated. One of the most interesting ways of wing bending is provided by the bullae, which have been defined as short sections of flexible chitin, where the flexion lines cross veins. Although the bullae have been frequently used as taxonomic characters, there is no study focused on their morphology, although their prevalence on the wings of mayflies strongly suggests a role in flight. In order to identify evolutionary trends of these structures within Ephemeroptera, we constructed a matrix with comparative anatomy data of the bullae from whole mounts of the wings of 300 specimens belonging to 70 species of several mayfly families, as well as scanning microscopy samples of selected specimens. We also surveyed the number of bullae and their distribution in the wings of the different species within the South American Leptophlebiidae clade. We optimized the characters onto the latest published phylogeny for Leptophlebiidae.     

Developmental schedules and persistence of experimental host-parasitoid systems at two different temperatures

In experimental systems of a bruchid host, Callosobruchus chinensis, and a braconid parasitoid, Heterospilus prosopidis, the effects of changes in developmental schedules were examined in relation to the persistence of the system, or the time to extinction of a component species. We modified the developmental schedules by changing the temperature from 30°C to 32°C. To compare persistence, a long-term system with overlapping generations was set up and the bruchid host resource, azuki beans (Vigna angularis), were renewed every 10 days. The long-term systems showed greater persistence at 30°C than at 32°C. Parasitoid extinction was often observed. We examined differences in life-history characteristics of the component species between the two temperatures by short-term, single-generation experiments. Fecundity and egg hatchability of the host were reduced and the developmental period of the parasitoid was shortened at 32°C. The age at which the host became vulnerable to parasitoid attacks was earlier at 32°C than at 30°C. We constructed a daily based, age-structured model to analyse which life-history change(s) affected the persistence of the long-term systems. The density-dependent population growth of the host was described by a logistic equation and the attack rate of the parasitoid by a type II functional response with mutual interference. The simulation results showed greater persistence at 30°C than at 32°C. Sensitivity analysis showed that there are threshold boundaries in the length of the vulnerable period of the host beyond which system persistence drastically changes. Further, persistence at another temperature, 28°C, was predicted using a model based on short-term data on the host.     

Persistence of Conidia of Metarhizium anisopliae in Sugarcane Fields: Effect of isolate and formulation on persistence over 3.5 years

Metarhizium anisopliae is being used in Australia as a biopesticide for control of sugarcane whitegrubs in soil. The field persistence in sugarcane soil of two isolates of M. anisopliae each in four formulations was tested by mixing the formulation with soil which was then placed in PVC rings and buried in sugarcane fields. The two isolates used were FI-1045, M. anisopliae var. anisopliae, the active ingredient in BioCane™ currently used for greyback canegrub control, Dermolepida albohirtum (Coleoptera: Scarabaeidae: Melolonthinae), and FI-147, M. anisopliae var. lepidiotum, being tested as a biopesticide for Lepidiota spp. (Coleoptera: Scarabaeidae: Melolonthinae) and other species of canegrub. The four formulations were rice granules (as in BioCane™), a wettable powder derived from conidia screened from the rice granules, conidia off rice suspended in water and conidia produced on agar plates, dried, and then mixed with water for adding to soil. FI-1045 was tested at three different sites in north Queensland with a range of soil types and climatic conditions while FI-147 was tested at three similarly diverse sites in southern Queensland. The PVC rings were destructively sampled every 6 months for 3.5 years and the number of viable conidia remaining determined by plating onto a selective medium. The exponential decay was determined. Monthly decay rates ranged from 0.0309 to 0.0835 (mean 0.0512). A small proportion of conidia survived the 3.5 years at all sites and all formulations. Overall, isolate FI-147 persisted better than FI-1045, but was used at the more Southerly sites. Rainfall and soil type had negligible effects on persistence. The agar-produced FI-147 conidia declined most slowly, while the two rice-produced but water-formulated conidia gave similar results. Isolate FI-1045 survived best as the BioCane™ formulation and this rice granule formulation was almost as persistent as the agar conidia with FI-147. A small proportion of conidia, in some formulations and at some sites, were recovered from immediately below the rings. This movement was thought to be due to activity of earthworms or mites. The results suggest that 3 years would be the maximum period for a BioCane™ formulation to provide some level of infection in the target pest unless augmented by conidia from infected grubs. The effectiveness of these new conidia may be reduced due to their highly aggregated distribution.     

Absence of persistence and transfer of genetic material by recombinantEscherichia coli in conventional,antibiotic-treated mice

Summary Strain BST-1 is a derivative ofEscherichia coli K-12 that carries a plasmid designated pURA-4 and is the expression system used by The Upjohn Company in the production of recombinant bovine somatotropin (rbSt). This plasmid also encodes an ampicillin resistance gene. The plasmidless carrier strain, BST-1C, contains a gene for tetracycline resistance which is provided by the chromosomal insertion of the transposon Tn10. Therefore, BST-1 is resistant to ampicillin and tetracycline, while BST-1C is resistant only to tetracycline. The Food and Drug Administration requested that we conduct an environmental assessment study to monitor the persistence of the recombinant live K-12E. coli organism compared to the hostE. coli organism. In addition, we were requested to monitor the potential transfer of genetic material from (our) recombinant organism to the indigenous microflora of the mouse gastrointestinal (GI) tract. The differences in persistence were determined by monitoring shedding of BST-1 and BST-1C in the feces of conventionally reared, outbred mice inoculated with either of the two strains. Even with antibiotic selective pressure applied (tetracycline in the water), BST-1 did not persist as well as the non-plasmid carrying parental stain, BST-1C. In the gene transfer experiments, transfer of pURA-4 was monitored by the appearance of the ampicillin resistance marker and/or by hybridization assays for the rbSt gene in indigenous, mouse-colonizingE. coli strains which had been made streptomycin resistant. At the limit of detection, no transfer of pURA-4 was detected either in vitro or in vivo. These data support an interpretation that BST-1 does not present an environmental hazard as measured by colonization/persistence in the gut of conventionally reared mammals.     

The role of food plant and pathogen-induced behaviour in the persistence of a nucleopolyhedrovirus

Insect baculoviruses can survive between epidemics as infectious particles external to the host. Many pathogens persist in reservoirs, i.e., microhabitats where survival is enhanced, for example due to protection from the degrading effects of UV irradiation. However, the probability of infecting new susceptible hosts is usually reduced. Persistence of pathogens and their movement in and out of reservoirs is an important, albeit little understood, aspect of insect pathogen ecology. This study investigated interactions between the behaviour of infected insect hosts, virus distribution and plant species on the persistence of the winter moth (Operophtera brumata) nucleopolyhedrovirus. Habitat influenced the persistence of infectious baculovirus in the field: virus on Sitka spruce (Picea sitchensis) and oak (Quercus robur) in forested areas retained more infectivity than virus on heather (Calluna vulgaris) in an unshaded habitat. Plant species per se did not directly affect the persistence of virus on the foliage of potted seedlings. Virally infected insects had altered behaviour and moved down plants relative to control insects, whereas in other systems larvae show height-seeking behaviour. Consequently, the majority of virus particles were distributed on plant stems. In two experiments (one using winter moth NPV and one Mamestra brassicae NPV) virus persisted better on plant stems relative to foliage. Neonate larvae were shown to be able to acquire infections from tree stems contaminated with a low level of virus. These data suggest that plant stems may be important reservoirs for between-year persistence of this pathogen. The observed virus-induced changes in host behaviour in winter moth could enhance the viral persistence by increasing the deposition of occlusion bodies in these reservoirs.