scholarly journals A Flux-Limited Model for Glioma Patterning with Hypoxia-Induced Angiogenesis

Symmetry ◽  
2020 ◽  
Vol 12 (11) ◽  
pp. 1870
Author(s):  
Pawan Kumar ◽  
Christina Surulescu
Keyword(s):  
Brain Cancer ◽  
Reaction Diffusion ◽  
Population Level ◽  
Tumor Vascularization ◽  
Population Densities ◽  
Self Diffusion ◽  
Tumor Environment ◽  
Tissue Anisotropy ◽  
Flux Limitation ◽  
Model Scenarios

We propose a model for glioma patterns in a microlocal tumor environment under the influence of acidity, angiogenesis, and tissue anisotropy. The bottom-up model deduction eventually leads to a system of reaction–diffusion–taxis equations for glioma and endothelial cell population densities, of which the former infers flux limitation both in the self-diffusion and taxis terms. The model extends a recently introduced (Kumar, Li and Surulescu, 2020) description of glioma pseudopalisade formation with the aim of studying the effect of hypoxia-induced tumor vascularization on the establishment and maintenance of these histological patterns which are typical for high-grade brain cancer. Numerical simulations of the population level dynamics are performed to investigate several model scenarios containing this and further effects.

scholarly journals The shape of density dependence and the relationship between population growth, intraspecific competition and equilibrium population density

2018 ◽  
Author(s):  
Emanuel A. Fronhofer ◽  
Lynn Govaert ◽  
Mary I. O’Connor ◽  
Sebastian J. Schreiber ◽  
Florian Altermatt
Keyword(s):  
Population Growth ◽  
Growth Models ◽  
Population Level ◽  
Logistic Growth ◽  
Population Densities ◽  
Density Regulation ◽  
Logistic Growth Model ◽  
Regulation Functions ◽  
Consumer Resource ◽  
Population Growth Models

AbstractThe logistic growth model is one of the most frequently used formalizations of density dependence affecting population growth, persistence and evolution. Ecological and evolutionary theory and applications to understand population change over time often include this model. However, the assumptions and limitations of this popular model are often not well appreciated.Here, we briefly review past use of the logistic growth model and highlight limitations by deriving population growth models from underlying consumer-resource dynamics. We show that the logistic equation likely is not applicable to many biological systems. Rather, density-regulation functions are usually non-linear and may exhibit convex or both concave and convex curvatures depending on the biology of resources and consumers. In simple cases, the dynamics can be fully described by the continuous-time Beverton-Holt model. More complex consumer dynamics show similarities to a Maynard Smith-Slatkin model.Importantly, we show how population-level parameters, such as intrinsic rates of increase and equilibrium population densities are not independent, as often assumed. Rather, they are functions of the same underlying parameters. The commonly assumed positive relationship between equilibrium population density and competitive ability is typically invalid. As a solution, we propose simple and general relationships between intrinsic rates of increase and equilibrium population densities that capture the essence of different consumer-resource systems.Relating population level models to underlying mechanisms allows us to discuss applications to evolutionary outcomes and how these models depend on environmental conditions, like temperature via metabolic scaling. Finally, we use time-series from microbial food chains to fit population growth models and validate theoretical predictions.Our results show that density-regulation functions need to be chosen carefully as their shapes will depend on the study system’s biology. Importantly, we provide a mechanistic understanding of relationships between model parameters, which has implications for theory and for formulating biologically sound and empirically testable predictions.

scholarly journals Hermaphroditism and Gonochorism

2020 ◽  
pp. 197-241
Author(s):  
Chiara Benvenuto ◽  
Stephen C. Weeks
Keyword(s):  
Reproductive System ◽  
Reproductive Strategies ◽  
Population Level ◽  
Population Densities ◽  
Ecological Constraints ◽  
Evolutionary Transitions ◽  
Colonizing Species ◽  
Sexual Systems ◽  
Theoretical Perspectives ◽  
Successful Group

This chapter compares two sexual systems: hermaphroditism (each individual can produce gametes of either sex) and gonochorism (each individual produces gametes of only one of the two distinct sexes) in crustaceans. These two main sexual systems contain a variety of alternative modes of reproduction, which are of great interest from applied and theoretical perspectives. The chapter focuses on the description, prevalence, analysis, and interpretation of these sexual systems, centering on their evolutionary transitions. The ecological correlates of each reproductive system are also explored. In particular, the prevalence of “unusual” (non-gonochoristic) reproductive strategies has been identified under low population densities and in unpredictable/unstable environments, often linked to specific habitats or lifestyles (such as parasitism) and in colonizing species. Finally, population-level consequences of some sexual systems are considered, especially in terms of sex ratios. The chapter aims to provide a broad and extensive overview of the evolution, adaptation, ecological constraints, and implications of the various reproductive modes in this extraordinarily successful group of organisms.

Anal cancers attributed to human papillomavirus are more common in areas in Victoria, Australia, with higher HIV notifications

Sexual Health ◽  
2013 ◽  
Vol 10 (3) ◽  
pp. 220
Author(s):  
Lenka A. Vodstrcil ◽  
Jane Hocking ◽  
Tim R. H. Read ◽  
Andrew E. Grulich ◽  
Christopher K. Fairley
Keyword(s):  
Colon Cancer ◽  
Anal Cancer ◽  
Brain Cancer ◽  
Incidence Rate Ratio ◽  
Population Level ◽  
Incidence Rates ◽  
Notification Rate ◽  
Anal Squamous Cell Carcinoma ◽  
Male Age ◽  
Sex With Men

Background Anal cancer is more common in men who have sex with men with HIV. We aimed to determine if there was an association between anal squamous cell carcinoma (SCC) and HIV notifications in men in Victoria, Australia, at a population level. Methods: We calculated the male age-standardised incidence rates for anal SCC, brain cancer and colon cancer for each local government area (LGA) in Victoria from 1982 to 31 December 2010 using the Victorian Cancer Registry. Male HIV rates in each LGA were calculated using the Victorian HIV Registry. Results: There were 288 men diagnosed with anal SCC, 8793 with brain cancer and 23 938 with colon cancer in 57 LGAs. There were 3163 men notified with HIV during the same period in the same LGAs (range: 4–435 per LGA). There was a significant positive correlation (r = 0.45, P < 0.001, r2 = 0.20) between the age-standardised rate of anal SCC and the rate of HIV notifications in men in each LGA but no correlation between the male age-standardised rate of colon (Pearson’s r = –0.11, P = 0.40) or brain (r = –0.05, P = 0.71) cancers, and the rate of HIV. The rate of anal cancer was ~50% higher in LGAs with the highest HIV notification rate (incidence rate ratio = 1.47; 95% confidence interval: 1.10–1.97). Conclusions: At a population level, about one in five cases (r2 = 0.20) of anal SCCs in men are explained by the rate of HIV notifications in that LGA.

Subsistence ecology and carrying capacity in two Papua New Guinea populations

1994 ◽  
Vol 26 (3) ◽  
pp. 395-407 ◽  
Author(s):  
Ryutaro Ohtsuka
Keyword(s):  
Land Use ◽  
Resource Management ◽  
Papua New Guinea ◽  
Carrying Capacity ◽  
Food Production ◽  
Population Level ◽  
New Guinea ◽  
Population Densities ◽  
Sustainable Food ◽  
Sustainable Food Production

SummaryThis article examines the mechanisms of subsistence adaptation of two Papua New Guinea populations, the Metroxylon sago-depending lowland Gidra and the taro-monoculture Mountain Ok, surviving in low population densities of 0·5 and 1·4 persons per km2. Observation of the groups' land use systems strongly suggests that their population densities have not been far below the carrying capacity, although the territory of each population is markedly heterogeneous. Both groups have maintained their sustainable food production not only for resource management but also for survival at a population level, either expanding their territory or changing the sustainable level in tandem with changes of subsistence system.

scholarly journals A survey and assessment of grasshoppers’ population in various sugarcane growing areas of Harion municipality in Sarlahi district, Nepal

2020 ◽  
Vol 3 (2) ◽  
pp. 314-320
Author(s):  
Kapil Paudel ◽  
Naresh Dangi ◽  
Anisur Rahman Ansari ◽  
Rashmi Regmi
Keyword(s):  
Natural Enemies ◽  
Population Level ◽  
Small Scale ◽  
Risk Category ◽  
First Year ◽  
Population Densities ◽  
Nymphal Stage ◽  
Weather Parameters ◽  
Second Year ◽  
The Relationship

A small-scale study of grasshopper populations was undertaken in Harion municipality of Sarlahi district to ascertain whether grasshopper population in sugarcane growing areas is changing in consecutive years 2014 and 2015. The regular sugarcane growing areas were randomly selected and the survey was conducted to estimate the population in those consecutive years in 14 different locations where outbreak of Hieroglyphus banian (Fabricius) has occurred. The per square meter population was estimated using a ‘T’ shape which was made by tying 1m long two sticks to estimate one square meter area. The population of two consecutive years was compared to study the relationship between two years populations. The grasshopper infestation by risk category indicated that infestation warranted rating of severe in ward seven, eight and nine for 2015 from the population of 2014 AD. For 2016 AD, the risk was found low as most of the areas was categorized as moderate to light category as the population was found low in 2015 AD. Grasshopper population densities were found higher in some areas of Sarlahi district in the first year as compared to the second year. The population level in the first year was not found to induce population in next year as the population decreased in the second year. The trend of grasshopper population was not so threatening as the population was not found increasing in these years so was risk for next year. This might be due to the management of grasshoppers in nymphal stage in previous year, weather parameters, location, inter-cultural operations, decreasing of the rationing crops or presence of natural enemies. These findings provide guidance for the farmers in relation to grasshopper management and for future survey programs in relation to targeting regions of the district at risk from grasshoppers.

scholarly journals Quorum Sensing but Not Autoinduction of Ti Plasmid Conjugal Transfer Requires Control by the Opine Regulon and the Antiactivator TraM

2000 ◽  
Vol 182 (4) ◽  
pp. 1080-1088 ◽  
Author(s):  
Kevin R. Piper ◽  
Stephen K. Farrand
Keyword(s):  
Quorum Sensing ◽  
Control Process ◽  
Population Level ◽  
Homoserine Lactone ◽  
Ti Plasmid ◽  
Conjugal Transfer ◽  
Population Densities ◽  
Independent Manner ◽  
Ti Plasmids ◽  
Donor Population

ABSTRACT Conjugal transfer of the Ti plasmids from Agrobacterium tumefaciens is controlled by autoinduction via the transcriptional activator TraR and the acyl-homoserine lactone ligand,Agrobacterium autoinducer (AAI). This control process is itself regulated by opines, which are small carbon compounds produced by the crown gall tumors that are induced by the bacteria. Opines control autoinduction by regulating the expression of traR. Transfer of pTiC58 from donors grown with agrocinopines A and B, the conjugal opines for this Ti plasmid, was detected only after the donors had reached a population level of 107 cells per cm2. Donors incubated with the opines and AAI transferred their Ti plasmids at population levels about 10-fold lower than those incubated with opines only. Transcription of the traregulon, as assessed by monitoring atraA::lacZ reporter, showed a similar dependence on the density of the donor population. However, even in cultures at low population densities that were induced with opines and AAI, there was a temporal lag of between 15 and 20 h in the development of conjugal competence. Moreover, even after this latent period, maximal transfer frequencies required several hours to develop. This lag period was independent of the population density of the donors but could be reduced somewhat by addition of exogenous AAI. Quorum-dependent development of conjugal competence required control by the opine regulon; donors harboring a mutant of pTiC58 deleted for the master opine responsive repressor accR transferred the Ti plasmid at maximum frequencies at very low population densities. Similarly, an otherwise wild-type derivative of pTiC58 lackingtraM, which codes for an antiactivator that inhibits TraR activity, transferred at high frequency in a population-independent manner in the absence of the conjugal opines. Thus, while quorum sensing is dependent upon autoinduction, the two phenomena are not synonymous. We conclude that conjugal transfer of pTiC58 is regulated in a quorum-dependent fashion but that supercontrol of the TraR-AAI system by opines and by TraM results in a complex control process that requires not only the accumulation of AAI but also the expression of TraR and the synthesis of this protein at levels that overcome the inhibitory activity of TraM.

Study of Diffusion and Reaction Diffusion in the Fe-C-Nb System

2007 ◽  
Vol 264 ◽  
pp. 163-169
Author(s):  
Rodolfo A. Pérez ◽  
Patrick Gas ◽  
Philippe Maugis
Keyword(s):  
Diffusion Coefficient ◽  
Diffusion Process ◽  
Pure Iron ◽  
Infinite Dilution ◽  
Reaction Diffusion ◽  
The Self ◽  
Carbon Vacancy ◽  
Self Diffusion ◽  
System A ◽  
Proportional Decrease

Experiments of niobium diffusion at infinite dilution and Nb reaction-diffusion in pure iron and in ferrites with different amounts of carbon were performed, for comparison, in order to understand the influence of carbon on the diffusion process in the Nb-Fe system. A proportional decrease of the diffusion coefficient with the increasing amount of carbon was found. This effect seems to be stronger than in the self-diffusion analyzing the literature; moreover SIMS measurements in niobium- implanted samples show a redistribution of carbon during the first steps of the diffusion process. For those reasons, a stronger effect of carbon-niobium interaction over the carbon-vacancy interaction seems to be responsible for the decrease in the diffusion coefficient.

scholarly journals Concentration dependence of lipopolymer self-diffusion in supported bilayer membranes

2010 ◽  
Vol 8 (54) ◽  
pp. 127-143 ◽  
Author(s):  
Huai-Ying Zhang ◽  
Reghan J. Hill
Keyword(s):  
Diffusion Coefficient ◽  
Ethylene Glycol ◽  
Reaction Diffusion ◽  
Poly Ethylene Glycol ◽  
Frictional Drag ◽  
Mole Percent ◽  
Self Diffusion ◽  
Reaction Diffusion Model ◽  
Poly Ethylene ◽  
Self Diffusion Coefficient

Self-diffusion coefficients of poly(ethylene glycol)2k-derivatized lipids (DSPE-PEG2k-CF) in glass-supported DOPC phospholipid bilayers are ascertained from quantitative fluorescence recovery after photobleaching (FRAP). We developed a first-order reaction–diffusion model to ascertain the bleaching constant, mobile fraction and lipopolymer self-diffusion coefficient D s at concentrations in the range c ≈ 0.5–5 mol%. In contrast to control experiments with 1,2-dioleoyl-sn-glycero-3-phosphoethanolamine-N-(7-nitro-2-1,3-benzoxadiazol-4-yl) (ammonium salt) (DOPE-NBD) in 1,2-dioleoyl-sn-glycero-3-phosphocholine (DOPC), the lipopolymer self-diffusion coefficient decreases monotonically with increasing concentration, without a distinguishing mushroom-to-brush transition. Our data yield a correlation D s = D 0 /(1 + α c ), where D 0 ≈ 3.36 µm 2 s −1 and α ≈ 0.56 (with c expressed as a mole percent). Interpreting the dilute limit with the Scalettar–Abney–Owicki statistical mechanical theory for transmembrane proteins yields an effective disc radius a e ≈ 2.41 nm. On the other hand, the Bussell–Koch–Hammer theory, which includes hydrodynamic interactions, yields a e ≈ 2.92 nm. As expected, both measures are smaller than the Flory radius of the 2 kDa poly(ethylene glycol) (PEG) chains, R F ≈ 3.83 nm, and significantly larger than the nominal radius of the phospholipid heads, a l ≈ 0.46 nm. The diffusion coefficient at infinite dilution D 0 was interpreted using the Evans–Sackmann theory, furnishing an inter-leaflet frictional drag coefficient b s ≈ 1.33 × 10 8 N s m −3 . Our results suggest that lipopolymer interactions are dominated by the excluded volume of the PEG-chain segments, with frictional drag dominated by the two-dimensional bilayer hydrodynamics.

scholarly journals Cooperation Enhances Robustness of Coexistence in Spatially Structured Consortia

2018 ◽  
Author(s):  
Xinying Ren ◽  
Richard M. Murray
Keyword(s):  
Reaction Diffusion ◽  
Population Level ◽  
Microbial Consortia ◽  
Interspecies Interactions ◽  
Major Goal ◽  
E Coli ◽  
Cooperative Interactions ◽  
Multiple Species ◽  
The Stability ◽  
Synthetic Microbial Consortia

AbstractDesigning synthetic microbial consortia is an emerging area in synthetic biology and a major goal is to realize stable and robust coexistence of multiple species. Co-operation and competition are fundamental intra/interspecies interactions that shape population level behaviors, yet it is not well-understood how these interactions affect the stability and robustness of coexistence. In this paper, we show that communities with cooperative interactions are more robust to population disturbance, e.g., depletion by antibiotics, by forming intermixed spatial patterns. Meanwhile, competition leads to population spatial heterogeneity and more fragile coexistence in communities. Using reaction-diffusion and nonlocal PDE models and simulations of a two-species E. coli consortium, we demonstrate that cooperation is more beneficial than competition in maintaining coexistence in spatially structured consortia, but not in well-mixed environments. This also suggests a trade-off between constructing heterogeneous communities with localized functions and maintaining robust coexistence. The results provide general strategies for engineering spatially structured consortia by designing interspecies interactions and suggest the importance of cooperation for biodiversity in microbial community.

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