Morphological plasticity of a spreading aquatic macrophyte,Ranunculus peltatus,in response to environmental variables

Ranunculus peltatus Schrank is an aquatic macrophyte spreading in northeastern France. As with other Ranunculus species, its growth demonstrates considerable plasticity. A preliminary understanding of its development and precise adaptive strategy is possible through functional ecology. The present study took morphological traits into account in order to analyse R. peltatus' development and morphological plasticity in relation to environmental parameters. During the five-month growing season, field measurements of ten different morphological traits were performed monthly at twelve sampling sites presenting various physical and chemical characteristics. Three overall growth stages occurred between April and August 2000: a stage of elongation of the main stem, a stage of branching and flowering and a stage of decline associated with vegetative dispersion. The sampling sites were defined according to environmental parameters and divided into three groups corresponding to three morphologically different R. peltatus populations. Plants in upstream, nutrient-poor, undisturbed sites were small and achieved little sexual reproduction. Plants in nutrient-rich, undisturbed sites had long shoots and were branched. Plants in weakly shaded, disturbed sites were small but produced many flowers. Correlations between morphological traits and environmental parameters showed significant relationships between chemical parameters and some characteristic vegetative growth traits. Physical environmental parameters were found to be less well correlated with morphological traits than the chemical parameters. The phenology and morphological plasticity of R. peltatus confer competitive advantages that could explain its ability to spread in some circumstances. Finally, the previous classification of R. peltatus as a Grime CSR species is discussed in relation to its plasticity. According to its morphological characteristics, R. peltatus tended indeed to adopt a C-strategy in nutrient-rich undisturbed sites, a S-strategy in nutrient-poor undisturbed sites and a R-strategy in disturbed sites.     

Rule-Based Model of Vein Graft Remodeling

When vein segments are implanted into the arterial system for use in arterial bypass grafting, adaptation to the higher pressure and flow of the arterial system is accomplished thorough wall thickening and expansion. These early remodeling events have been found to be closely coupled to the local hemodynamic forces, such as shear stress and wall tension, and are believed to be the foundation for later vein graft failure. To further our mechanistic understanding of the cellular and extracellular interactions that lead to global changes in tissue architecture, a rule-based modeling method is developed through the application of basic rules of behaviors for these molecular and cellular activities. In the current method, smooth muscle cell (SMC), extracellular matrix (ECM), and monocytes are selected as the three components that occupy the elements of a grid system that comprise the developing vein graft intima. The probabilities of the cellular behaviors are developed based on data extracted from in vivo experiments. At each time step, the various probabilities are computed and applied to the SMC and ECM elements to determine their next physical state and behavior. One- and two-dimensional models are developed to test and validate the computational approach. The importance of monocyte infiltration, and the associated effect in augmenting extracellular matrix deposition, was evaluated and found to be an important component in model development. Final model validation is performed using an independent set of experiments, where model predictions of intimal growth are evaluated against experimental data obtained from the complex geometry and shear stress patterns offered by a mid-graft focal stenosis, where simulation results show good agreements with the experimental data.     

A versatile hybrid agent-based,particle and partial differential equations method to analyze vascular adaptation

Peripheral arterial occlusive disease is a chronic pathology affecting at least 8–12 million people in the USA, typically treated with a vein graft bypass or through the deployment of a stent in order to restore the physiological circulation. Failure of peripheral endovascular interventions occurs at the intersection of vascular biology, biomechanics, and clinical decision making. It is our hypothesis that the majority of endovascular treatment approaches share the same driving mechanisms and that a deep understanding of the adaptation process is pivotal in order to improve the current outcome of the procedure. The postsurgical adaptation of vein graft bypasses offers the perfect example of how the balance between intimal hyperplasia and wall remodeling determines the failure or the success of the intervention. Accordingly, this work presents a versatile computational model able to capture the feedback loop that describes the interaction between events at cellular/tissue level and mechano-environmental conditions. The work here presented is a generalization and an improvement of a previous work by our group of investigators, where an agent-based model uses a cellular automata principle on a fixed hexagonal grid to reproduce the leading events of the graft’s restenosis. The new hybrid model here presented allows a more realistic simulation both of the biological laws that drive the cellular behavior and of the active role of the membranes that separate the various layers of the vein. The novel feature is to use an immersed boundary implementation of a highly viscous flow to represent SMC motility and matrix reorganization in response to graft adaptation. Our implementation is modular, and this makes us able to choose the right compromise between closeness to the physiological reality and complexity of the model. The focus of this paper is to offer a new modular implementation that combines the best features of an agent-based model, continuum mechanics, and particle-tracking methods to cope with the multiscale nature of the adaptation phenomena. This hybrid method allows us to quickly test various hypotheses with a particular attention to cellular motility, a process that we demonstrated should be driven by mechanical homeostasis in order to maintain the right balance between cells and extracellular matrix in order to reproduce a distribution similar to histological experimental data from vein grafts.

     

Structural blueprint and ontogeny determine the adaptive value of the plastic response to competition in clonal plants: a modelling approach

Local competitive interactions strongly influence plant community dynamics. To maintain their performance under competition, clonal plants may plastically modify their network architecture to grow in the direction of least interference. The adaptive value of this plastic avoidance response may depend, however, on traits linked with the plant’s structural blueprint and ontogeny. We tested this hypothesis using virtual populations. We used an Individual Based Model to simulate competitive interactions among clones within a plant population. Clonal growth was studied under three competition intensities in plastic and non-plastic individuals. Plasticity buffered the negative impacts of competition at intermediate densities of competitors by promoting clone clumping. Success despite competition was promoted by traits linked with (1) the plant’s structural blueprint (weak apical dominance and sympodial growth) and (2) ontogenetic processes, with an increasing or a decreasing dependence of the elongation process on the branch generation level or length along the competition intensity gradient respectively. The adaptive value of the plastic avoidance response depended on the same traits. This response only modulated their importance for clone success. Our results show that structural blueprint and ontogeny can be primary filters of plasticity and can have strong implications for evolutionary ecology, as they may explain why clonal plants have developed many species-specific plastic avoidance behaviours.     

Interrogating a Multifactorial Model of Breast Conserving Therapy with Clinical Data

Most women with early stage breast cancer do not require removal of the entire breast to treat their cancer; instead, up to 70% of women can be effectively and safely treated by breast conserving therapy (BCT) with surgical removal of the tumor only (lumpectomy) followed by radiation treatment of the remaining breast tissue. Unfortunately, the final contour and cosmesis of the treated breast is suboptimal in approximately 30% of patients. The ability to accurately predict breast contour after BCT for breast cancer could significantly improve patient decision-making regarding the choice of surgery for breast cancer. Our overall hypothesis is that the complex interplay among mechanical forces due to gravity, breast tissue constitutive law distribution, inflammation induced by radiotherapy and internal stress generated by the healing process play a dominant role in determining the success or failure of lumpectomy in preserving the breast contour and cosmesis. We have shown here from a first patient study that even in the idealistic situation of excellent cosmetic outcome this problem requires multiscale modeling. We propose a method to decide which component of the model works best for each phase of healing and what parameters should be considered dominant and patient specific. This patient study is part of a clinical trial registered on ClinicalTrial.gov, identifier NCT02310711.     

An experimental study of the plastic responses of Ranunculus peltatus Schrank to four environmental parameters

The impact of four environmental parameters (water depth, type of substratum, current velocity and light intensity), on Ranunculus peltatus morphology and reproduction was tested in four 1 month semi- controlled experiments. Four development stages were underlined from April to August 2001 in R. peltatus: an elongation stage (April–June), a flowering stage (May–June), a fragmentation stage (June–July) and a potential regenerative stage (July–August). Water depth was therefore tested on R. peltatus elongation, type of substratum on R. peltatus elongation and flowering, current velocity on R. peltatus fragmentation and light intensity on its possible regeneration. The maximum development was measured for a 32 cm water depth. Current velocity did not have a significant effect on R. peltatus fragmentation. Regeneration depended strongly on light availability. This stage occurred only for unshaded or 50% shaded plants. Darkness prevented plants from regrowing.     

Deriving indicators for breast conserving surgery using finite element analysis

Breast conserving therapy (BCT), comprising a complete surgical excision of the tumour (partial mastectomy) with post-operative radiotherapy to the remaining breast tissue, is feasible for most women undergoing treatment for breast cancer. The goal of BCT is to achieve local control of the cancer, as well as to preserve a breast that satisfies a woman's cosmetic concerns. Although most women undergo partial mastectomy with satisfactory cosmetic results, in many patients the remaining breast is left with major cosmetic defects including concave deformities, distortion of the nipple–areolar complex, asymmetry and changes in tissue density characterised by excessive density associated with parenchymal scarring, as well as breast pain. There are currently no tools, other than surgical experience and judgement, which can predict the impact of partial mastectomy on the contour, the deformity of the treated breast and the mechanical stress that it induces. In this study, we use a finite element model to execute virtual surgery and carry out a sensitivity analysis on the resection location, the resection size, the breast tissue mechanical property and the different post-surgery recovery stage. We output the result in two different built-in indicators labelled as the cosmetic and the functional indicators. This study used the breast model for three women with breast cancer who have been elected to undergo BCT and are being treated at the Methodist Hospital in Houston, TX. The goal of this study was to propose a first glimpse of the key parameter leading to satisfactory post-BCT cosmetic results.     

Variation in P-content in aquatic plant tissues offers an efficient tool for determining plant growth strategies along a resource gradient

1. The application of functional ecology models to aquatic plants often relies on morphological and life‐history traits which may reflect, in part, the phenotypic plasticity displayed by aquatic plants. The present study was designed to evaluate the use of physiological traits, such as nutrition patterns, to describe aquatic plant strategies along a gradient of increasing resource availablity. 2. Taking phosphorus (P) as an example, nutrition‐use efficiencies were evaluated in five species, through the P‐content in plant tissues, the variations in P‐content according to nutrient availability and the perenniality of P‐storage. Plasticity in P‐storage was also investigated in Ranunculus peltatus, a morphologically highly plastic species. 3. In 2001, P‐content was analysed in Callitriche hamulata, C. obtusangula, C. platycarpa, Elodea nuttallii and R. peltatus tissue samples. These five species were sampled at nine different sites in streams along an increasing resource gradient in the Northern Vosges Biosphere Reserve (NE France). Variations of P‐content in the roots, stems and dissected and floating leaves of R. peltatus were also studied. 4. Only C. platycarpa and R. peltatus were found to occur in low nutrient availability conditions. Callitriche hamulata, C. obtusangula and E. nuttallii were restricted to mesotrophic and eutrophic sites. The highest nutrient‐use efficiency was found for E. nuttallii which was able to adapt its P‐storage to varying resource availabilities. Ranunculus peltatus was able to store high concentrations of P, but its P‐integration within the vegetative structure was less efficient under eutrophic conditions. Callitriche spp. appeared to have relatively low nutrient‐use efficiencies, although C. obtusangula displayed a high P‐content. While P was stored preferentially in roots in R. peltatus populations occurring in nutrient‐rich sites, there was no particular P‐storage organ for populations from nutrient‐poor sites. 5. On the basis of P‐usage, R. peltatus and E. nuttallii presented competitor traits, C. hamulata and C. platycarpa displayed stress‐tolerant nutrient signatures and for C. obtusangula, ruderal or competitor characteristics dominated. The use of physiological traits, such as nutrition patterns, may provide valuable, complementary information about aquatic plant strategies, independent from the influence of morphological trait plasticity often displayed by these plants.