Experimental Validation of Finite Element Analysis of Human Vertebral Collapse Under Large Compressive Strains

Osteoporosis-related vertebral fractures represent a major health problem in elderly populations. Such fractures can often only be diagnosed after a substantial deformation history of the vertebral body. Therefore, it remains a challenge for clinicians to distinguish between stable and progressive potentially harmful fractures. Accordingly, novel criteria for selection of the appropriate conservative or surgical treatment are urgently needed. Computer tomography-based finite element analysis is an increasingly accepted method to predict the quasi-static vertebral strength and to follow up this small strain property longitudinally in time. A recent development in constitutive modeling allows us to simulate strain localization and densification in trabecular bone under large compressive strains without mesh dependence. The aim of this work was to validate this recently developed constitutive model of trabecular bone for the prediction of strain localization and densification in the human vertebral body subjected to large compressive deformation. A custom-made stepwise loading device mounted in a high resolution peripheral computer tomography system was used to describe the progressive collapse of 13 human vertebrae under axial compression. Continuum finite element analyses of the 13 compression tests were realized and the zones of high volumetric strain were compared with the experiments. A fair qualitative correspondence of the strain localization zone between the experiment and finite element analysis was achieved in 9 out of 13 tests and significant correlations of the volumetric strains were obtained throughout the range of applied axial compression. Interestingly, the stepwise propagating localization zones in trabecular bone converged to the buckling locations in the cortical shell. While the adopted continuum finite element approach still suffers from several limitations, these encouraging preliminary results towardsthe prediction of extended vertebral collapse may help in assessing fracture stability in future work.

Pattern and process: competition causes regular spacing of individuals within plant populations

1 We used simulated and experimental plant populations to analyse mortality-driven pattern formation under size-dependent competition. Larger plants had an advantage under size-asymmetric but not under symmetric competition. Initial patterns were random or clumped. 2 The simulations were individual-based and spatially explicit. Size-dependent competition was modelled with different rules to partition overlapping zones of influence. 3 The experiment used genotypes of Arabidopsis thaliana with different morphological plasticity and hence size-dependent competition. Compared with wild types, transgenic individuals over-expressed phytochrome A and had decreased plasticity because of disabled phytochrome-mediated shade avoidance. Therefore, competition among transgenics was more asymmetric compared with wild-types. 4 Density-dependent mortality under symmetric competition did not substantially change the initial spatial pattern. Conversely, simulations under asymmetric competition and experimental patterns of transgenic over-expressors showed patterns of survivors that deviated substantially from random mortality independent of initial patterns. 5 Small-scale initial patterns of wild types were regular rather than random or clumped. We hypothesize that this small-scale regularity may be explained by early shade avoidance of seedlings in their cotyledon stage. 6 Our experimental results support predictions from an individual-based simulation model and support the conclusion that regular spatial patterns of surviving individuals should be interpreted as evidence for strong, asymmetric competitive interactions and subsequent density-dependent mortality.

Experimental Evidence of an Eco-evolutionary Feedback during Adaptive Divergence

Differences in how organisms modify their environment can evolve rapidly and might influence adaptive population divergence [1, 2]. In a common garden experiment in aquatic mesocosms, we found that adult stickleback from a recently diverged pair of lake and stream populations had contrasting effects on ecosystem metrics. These modifications were caused by both genetic and plastic differences between populations and were sometimes comparable in magnitude to those caused by the presence/ absence of stickleback. Lake and streamfish differentially affected the biomass of zooplankton and phytoplankton, the concentration of phosphorus, and the abundance of several prey (e.g., copepods) and non-prey (e.g., cyanobacteria) species. The adult mediated effects on mesocosm ecosystems influenced the survival and growth of a subsequent generation of juvenile stickleback reared in the same mesocosms. The prior presence of adults decreased the overall growth rate of juveniles, and the prior presence of stream adults lowered overall juvenile survival. Among the survivors, lake juveniles grew faster than co-occurring stream juveniles, except in mesocosm ecosystems previously modified by adult lake fish that were reared on plankton. Overall, our results provide evidence for reciprocal interactions between ecosystem dynamics and evolutionary change (i.e., eco-evolutionary feedbacks) in the early stages of adaptive population divergence.

A systematic review of community-based participatory research interventions in pediatric and adolescent populations

Background. Community-based participatory research (CBPR) is a collaborative approach to research actively involving community members in all aspects of the research process. CBPR is not a new research method, but an approach that has gained increased attention in the field of public health over the last several years. Recognition of the inequalities in health status associated with social and environmental factors have led to calls for a renewed focus on ecological approaches to research. Ecological approaches acknowledge that the health of the community is dependent on an interaction between behavioral and environmental factors affecting the entire population. While many published studies document the benefits of CBPR in difficult-to-reach populations and describe successful implementation of this approach in adult populations, relatively few studies have been conducted in child and adolescent populations. Given that children and adolescents are particularly sensitive to the effects of their physical environments and may also be distrustful of outsiders, ecological approaches involving the community as partners, such as CBPR, may be especially useful in this population. ^ Objective. This thesis reviews published studies using a community-based participatory research approach in children and adolescents to assess the appropriateness of this approach in this population. ^ Method. Studies using CBPR in youth populations were identified using Medline and other Internet searches through both MeSH heading and text-word searches. ^ Results. A total of 16 studies were identified and analyzed for this review. Nine of the sixteen studies were experimental or quasi-experimental design, with Asthma being the most commonly studied disease. ^ Conclusions. While many studies using CBPR were not conducted with the level of scientific rigor typically found in clinical trial research, the studies reviewed each contributed to a greater understanding of the problems they investigated. Furthermore, interventional studies provided lasting benefits to communities under study above what would be found in studies using more traditional research approaches. While CBPR may not be appropriate for all research situations due to the time and resources required, we conclude that is a useful approach and should be considered when conducting community-based research for pediatric and adolescent populations.^

Percentage of cultured cell-populations that stained positively and/or negatively for apoptotic markers cleaved caspase-3 and cleaved PARP, following DNA damage treatments induced by doxorubicin and TNF-alpha co-treatments

The present dataset contains the source data for Figure 2B of Tentner et al. (2012). The data shows the percentage of cultured cell-populations that stained positively and/or negatively for apoptotic markers cleaved caspase-3 and cleaved PARP, following DNA damage treatments induced by various doses of doxorubicin (0, 2 and 10 µmole/L) in the presence (100 ng/mL) or absence (0 ng/mL) of TNF-alpha co-treatment. For the six treatment conditions investigated, cell counts were made by flow cytometry at times 6, 12, 24, and 48 h following treatment; CULTURE DETAILS: U2OS cells were obtained from ATCC were maintained at 21% oxygen and 5% CO2 in Dulbecco's modified Eagle medium supplemented with 10% fetal bovine serum, penicillin, streptomycin, 2mM L-glutamine, and used within 15-20 passages. The first thymidine block was released by washing the plates three times with PBS, and incubating them in fresh thymidine-free media for 12 h. A second thymidine block was then performed by re-addition of thymidine to 2.5 mM followed by incubation for an additional 18 h. Media was aspirated, plates were washed 3 with PBS, and replaced with fresh media in the presence or absence of 10 mM aphidicolin; ANALYSIS DETAILS: See supplementary journal publication; RESULT: The authors of the supplementary journal publication conclude that TNF enhances dose-dependent cell death following doxorubicin-induced DNA damage with minimal affect on dose-dependent cell-cycle arrest.

Experimental assessment of sediment burial in eelgrass Zostera marina in Kiel Bight

Seagrass meadows, one of the world's most important and productive coastal habitats, are threatened by a range of anthropogenic actions. Burial of seagrass plants due to coastal activities is one important anthropogenic pressure leading to the decline of local populations. In our study, we assessed the response of eelgrass Zostera marina to sediment burial from physiological, morphological, and population parameters. In a full factorial field experiment, burial level (5-20cm) and burial duration (4-16 weeks) were manipulated. Negative effects were visible even at the lowest burial level (5 cm) and shortest duration (4 weeks), with increasing effects over time and burial level. Buried seagrasses showed higher shoot mortality, delayed growth and flowering and lower carbohydrate storage. The observed effects will likely have an impact on next year's survival of buried plants. Our results have implications for the management of this important coastal plant.

Heat shock resistance traits in specimens of the seaweed Gracilaria vermiculophylla originating from native and non-native populations

We compared the responses of native and non-native populations of the seaweed Gracilaria vermiculophylla to heat shock in common garden-type experiments. Specimens from six native populations in East Asia and from eight non-native populations in Europe and on the Mexican Pacific coast were acclimated to two sets of identical conditions before their resistance to heat shock was examined. The experiments were carried out twice - one time in the native range in Qingdao, China and one time in the invaded range in Kiel, Germany - to rule out effects of specific local conditions. In both testing sites the non-native populations survived heat shock significantly better than the native populations, The data underlying this statement are presented in https://doi.pangaea.de/10.1594/PANGAEA.859335. After three hours of heat shock G. vermiculophylla exhibited increased levels of heat shock protein 70 (HSP70) and of a specific isoform of haloperoxidase, suggesting that both enzymes could be required for heat shock stress management. However, the elevated resistance toward heat shock of non-native populations only correlated with an increased constitutive expression of heat shock protein 70 (HSP70). The haloperoxidase isoform was more prominent in native populations, suggesting that not only increased HSP70 expression, but also reduced allocation into haloperoxidase expression after heat shock was selected during the invasion history. The data describing expression of HSP70 and three different isoforms of haloperoxidase are presented in https://doi.pangaea.de/10.1594/PANGAEA.859358.

Estimating the relative roles of top-down and bottom-up forces on insect herbivore populations: A classic study revisited

Although most ecologists agree that both top-down and bottom-up forces (predation and resource limitation, respectively) act in concert to influence populations of herbivores, it has proven difficult to estimate the relative contributions of such forces in terrestrial systems. Using a combination of time–series analysis of population counts recorded over 16 years and experimental data, we present the first estimates of the relative roles of top-down and bottom-up forces on the population dynamics of two terrestrial insect herbivores on the English oak (Quercus robur). Data suggest that temporal variation in winter moth, Operophtera brumata, density is dominated by time-lagged effects of pupal predators. By comparison, spatial variation in O. brumata density is dominated by host–plant quality. Overall, top-down forces explain 34.2% of population variance, bottom-up forces explain 17.2% of population variance, and 48.6% remains unexplained. In contrast, populations of the green oak tortrix, Tortrix viridana, appear dominated by bottom-up forces. Resource limitation, expressed as intraspecific competition among larvae for oak leaves, explains 29.4% of population variance. Host quality effects explain an additional 5.7% of population variance. We detected no major top-down effects on T. viridana populations. An unknown factor causing a linear decline in T. viridana populations over the 16-year study period accounts for most of the remaining unexplained variance. We discuss the observed differences between the insect species and the utility of time–series analysis as a tool in assessing the relative importance of top-down and bottom-up forces on herbivore populations.

Experimental evidence for a behavior-mediated trophic cascade in a terrestrial food chain

Predators of herbivorous animals can affect plant populations by altering herbivore density, behavior, or both. To test whether the indirect effect of predators on plants arises from density or behavioral responses in a herbivore population, we experimentally examined the dynamics of terrestrial food chains comprised of old field plants, leaf-chewing grasshoppers, and spider predators in Northeast Connecticut. To separate the effects of predators on herbivore density from the effects on herbivore behavior, we created two classes of spiders: (i) risk spiders that had their feeding mouth parts glued to render them incapable of killing prey and (ii) predator spiders that remained unmanipulated. We found that the effect of predators on plants resulted from predator-induced changes in herbivore behavior (shifts in activity time and diet selection) rather than from predator-induced changes in grasshopper density. Neither predator nor risk spiders had a significant effect on grasshopper density relative to a control. This demonstrates that the behavioral response of prey to predators can have a strong impact on the dynamics of terrestrial food chains. The results make a compelling case to examine behavioral as well as density effects in theoretical and empirical research on food chain dynamics.

Flower color variation: A model for the experimental study of evolution

We review the study of flower color polymorphisms in the morning glory as a model for the analysis of adaptation. The pathway involved in the determination of flower color phenotype is traced from the molecular and genetic levels to the phenotypic level. Many of the genes that determine the enzymatic components of flavonoid biosynthesis are redundant, but, despite this complexity, it is possible to associate discrete floral phenotypes with individual genes. An important finding is that almost all of the mutations that determine phenotypic differences are the result of transposon insertions. Thus, the flower color diversity seized on by early human domesticators of this plant is a consequence of the rich variety of mobile elements that reside in the morning glory genome. We then consider a long history of research aimed at uncovering the ecological fate of these various flower phenotypes in the southeastern U.S. A large body of work has shown that insect pollinators discriminate against white phenotypes when white flowers are rare in populations. Because the plant is self-compatible, pollinator bias causes an increase in self-fertilization in white maternal plants, which should lead to an increase in the frequency of white genes, according to modifier gene theory. Studies of geographical distributions indicate other, as yet undiscovered, disadvantages associated with the white phenotype. The ultimate goal of connecting ecology to molecular genetics through the medium of phenotype is yet to be attained, but this approach may represent a model for analyzing the translation between these two levels of biological organization.

Founder-effect speciation theory: failure of experimental corroboration.

The theory of founder-effect speciation proposes that colonization by very few individuals of an empty habitat favors rapid genetic changes and the evolution of a new species. We report here the results obtained in a 10-year-long and large-scale experiment with Drosophila pseudoobscura designed to test the theory. In our experimental protocol, populations are established with variable numbers of very few individuals and allowed to expand greatly for several generations until conditions of severe competition for resources are reached and the population crashes. A few random survivors are then taken to start a new population expansion and thus initiate a new cycle of founding events, population flushes, and crashes. Our results provide no support for the theories proposing that new species are very likely to appear as by-products of founder events.

Experimental infections of neonatal mice with cysts of Giardia lamblia clone GS/M-83-H7 are associated with an antigenic reset of the parasite.

Transmission of the protozoan parasite Giardia lamblia from one to another host individuum occurs through peroral ingestion of cysts which, following excystation in the small intestine, release two trophozoites each. Many studies have focused on the major surface antigen, VSP (for variant surface protein), which is responsible for the antigenic variability of the parasite. By using trophozoites of G. lamblia clone GS/M-83-H7 (expressing VSP H7) and the neonatal mouse model for experimental infections, we quantitatively assessed the process of antigenic variation of the parasite on the transcriptional level. In the present study, variant-specific regions identified on different GS/M-83-H7 vsp sequences served as targets for quantitative reverse transcription-PCR to monitor alterations in vsp mRNA levels during infection. Respective results demonstrated that antigenic switching of both the duodenal trophozoite and the cecal cyst populations was associated with a massive reduction in vsp H7 mRNA levels but not with a simultaneous increase in transcripts of any of the subvariant vsp genes analyzed. Most importantly, we also explored giardial variant-type formation and vsp mRNA levels after infection of mice with cysts. This infection mode led to an antigenic reset of the parasite in that a VSP H7-negative inoculum "converted" into a population of intestinal trophozoites that essentially consisted of the original VSP H7 type. This antigenic reset appears to be associated with excystation rather than with a selective process which favors expansion of a residual population of VSP H7 types within the antigenically diversified cyst inoculum. Based on these findings, the VSP H7 type has to be regarded as a predominant variant of G. lamblia clone GS/M-83-H7 which (re-)emerges during early-stage infection and may contribute to an optimal establishment of the parasite within the intestine of the experimental murine host.

Evaluation of the impact of natural enemies on Plutella xylostella L. (Lepidoptera: Yponomeutidae) populations on commercial Brassica farms

1 Accurate assessment of the impact of natural enemies on pest populations is fundamental to the design of robust integrated pest management programmes. In most situations, diseases, predators and parasitoids act contemporaneously on insect pest populations and the impact of individual natural enemies, or specific groups of natural enemies, is difficult to interpret. These problems are exacerbated in agro-ecosystems that are frequently disrupted by the application of insecticides. 2 A combination of life-table and natural enemy exclusion techniques was utilized to develop a method for the assessment of the impact of endemic natural enemies on Plutella xylostella populations on commercial Brassica farms. 3 At two of the experimental sites, natural enemies had no impact on P. xylostella survival, at two other sites, natural enemy impact was low but, at a fifth site, natural enemies drastically reduced the P. xylostella population. 4 The calculation of marginal death rates and associated k-values allowed the comparison of mortality factors between experimental sites, and indicated that larval disappearance was consistently the most important mortality factor, followed by egg disappearance, larval parasitism and pupal parasitism. The appropriateness of the methods and assumptions made to calculate the marginal death rates are discussed. 5 The technique represents a robust and easily repeatable method for the analysis of the activity of natural enemies of P. xylostella, which could be adapted for the study of other phytophagous pests.