Constant Population Research Articles

Counteracting increased heat-related mortality through adaptation: a quantitative assessment in a multi-country multi-city setting.

Background & aims: Climate change is exacerbating the current heat-related health burden and will continue to do so at a higher speed in the coming decades if no adaptation occurs. Although previous studies have suggested potential paths of adaptation, there is little quantitative evidence on the degree of adaptation needed to counteract the increased heat-related mortality under different climate change scenarios. Methods: We performed a health impact projection analysis using observed data on 451 locations in 23 countries included in the MCC database and modelled temperature from 3 global circulation models (CMIP5 - ISMIP2b). For each city, we combined present-time risk functions, represented by the exposure-response association obtained from a two-stage time series analysis of the observed temperature-mortality data, with projected daily temperature in 20-year warming scenarios consistent with an increase in global mean temperature of 2, 3 and 4ºC from the preindustrial period. Using a novel optimization method, we estimated a risk reduction factor to be applied to the present-time exposure-response association representing the level of adaptation needed to counteract the increased heat-mortality burden under each warming target. Results: Assuming constant vulnerability and population, climate change would progressively amplify heat-related mortality reaching 3.9% (95%CI:0.6;0.9) of all-cause mortality due to heat at 4ºC warming scenario (vs. 0.4% (0.2-0.6) in baseline 1986-2005). To counteract the impact of the progressive increase of temperatures, present-time heat-related risks should reduce on average by 70% (35;104), 84% (60;104) and 91% (80;103) under the 2, 3 and 4ºC scenarios, respectively. Conclusions: Our preliminary findings show that substantial reductions in vulnerability would be required to counteract the increase in heat-mortality burden driven by climate change. Further steps will aim to extend the current analysis over a larger sample of locations and consider scenarios of population development. Keywords: climate change, adaptation, heat, mortality, projections, methods.

A Mathematical Model for a Transmissible Disease with a Variant

The outbreak of the Coronavirus (COVID-19) pandemic around the world has caused many health and socioeconomic problems, and the identification of variants like Delta and Omicron with similar and often even more transmissible modes of transmission has motivated us to do this study. In this article, we have proposed and analyzed a mathematical model in order to study the effect of health precautions and treatment for a disease transmitted by contact in a constant population. We determined the four equilibria of the system of ordinary differential equations representing the model and characterized their existence using exact methods of algebraic geometry and computer algebra. The model is studied using the stability theory for systems of differential equations and the basic reproduction number R 0 . The stability of the equilibria is analyzed using the Lienard-Chipart criterion and Lyapunov functions. The asymptotic or global stability of endemic equilibria is established, and the disease-free equilibrium is globally asymptotically stable if R 0 < 1 . Model simulation is done with Python software to study the effects of health precautions and treatment, and the results are analyzed. It is observed that if the rate of treatment and compliance with health precautions are high, the number of infections decreases in the classes of infectious and is canceled out over time. It is concluded that the high treatment rate accompanied by a suitable rate of compliance with health precautions allows for the control the disease.

How Do Long Term Crop Rotations Influence Weed Populations: Exploring the Impacts of More than 50 Years of Crop Management in Serbia

Crop rotation is known as an eco-friendlier approach, as provides diversification in crop management systems, modifies intensive pressure on the agricultural ecosystem, utilizes various soil horizons, and prevents the establishment of specific pests and weeds. We set out here a study on the farms that have been managed over 50 years of specific continuous crop management programs. The experimental treatments were in a different management system: monoculture of maize, winter wheat, and soybean, 2-year crop rotation (winter wheat–maize) with and without chemical fertilizer, and 3-year crop rotation (winter wheat–soybean–maize) with and without chemical fertilizer and manure. We took soil samples six times from 2014 to 2017 prior to sowing and after harvesting each year. Weed seeds were extracted from soils and identified and counted by species. We, upon the data of a long term experiment of crop rotation, could conclude that crop rotations with more crops in the sequence are significantly effective in maintaining weed populations, a low-input crop production could reach a constant low population below an important damaging density, and therefore will be a more sustainable crop production while chemical fertilizers would change the soil’s chemical and structure and imbalance the plant population diversity and manures with high weed seed infestations have the potential to totally eradicate crop rotation effects, Therefore, clean manures or compost are highly recommended.

Predator kairomone triggers sexual reproduction of Daphnia population via increasing population density

Abstract Both predation risk and crowding can induce sexual reproduction in Daphnia, and predator kairomones can also cause population crowding. It is, however, unclear as to whether sexual reproduction is caused by kairomone per se or indirectly by kairomone‐induced crowding. In this study, we cultured Daphnia pulex in the presence of fish kairomone, with newborn offspring being retained (increasing population density) or removed (constant population density). The relationships among fish kairomone, population density, and indicators of sexual reproduction were assessed using structural equation models. The results showed that when offspring were retained in the population, the population density and sexual reproduction by Daphnia simultaneously increased in response to the presence of the fish kairomone, whereas sexual reproduction was not directly affected in the presence of fish kairomones alone. Conversely, when maintaining a constant population density, the number of ephippia and ratio of male to female of Daphnia increased with increasing population density, but the presence of fish kairomone did not promote sexual reproduction. Structural equation model analysis indicated that population density, rather than the fish kairomone, was the significant factor promoting sexual reproduction. The findings of this study indicate that population density directly triggers sexual reproduction in Daphnia populations. Our observations provide new insights into environmentally induced sexual reproduction, and on this basis, we suggest that a more thorough consideration of the interactions among environmental factors in determining sexual reproduction is necessary.

Assessment of the impact of conventional and organic agroecosystems management options and conservation tillage on soil fertility at the Montepaldi Long Term Experiment, Tuscany

Fertility is a characteristic of an agroecosystem which is usually and promptly identified with the crop yield. Nevertheless, it can be considered the result of many processes and factors such as climatic, edaphic and agronomic which cannot be extended and generalized to all systems and crops. This study evaluates the effects on soil fertility as influenced by organic (OR) and high-input (conventional, CO) management combined with three tillage systems, i.e., plowing (plw), chisel plowing (chp) and disk harrowing (dsh) at the Montepaldi Long Term Experiment (MoLTE), Tuscany, Italy. Fertility was evaluated through the following indicators: i) chemical (Olsen P, Kjeldahl N and, OM); ii) physical (bulk density on clods and cores, pore size distribution, penetrometry, aggregate stability, soil profile assessment, VESS, i.e. visual evaluation of soil structure); iii) biological (earthworm abundance and root distribution). As regards the effect of management, CO was higher in crop yields, available P2O5, bulk densities (clods), aggregate stability and soil penetration resistance, while OR was higher in bulk densities (cores). Nevertheless, the effect of management was observed for root distribution as a function of depth, where roots explored larger portions of soil in OR profiles. Regarding tillage, the order plw, chp, dsh was characterized by an increase in soil penetration resistance and number of earthworms. Moreover, a relationship with time was found for earthworm abundance, where the OR system exhibited a higher and constant population. Organic management seems to achieve a long-lasting soil fertility. In the MoLTE experiment results suggest that available P2O5, bulk density (clods), aggregate stability, soil penetration resistance, time-related earthworm abundance, root distribution and yields are the most informative on the impact of management and tillage options. Furthermore, results of physical and biological fertility indicators support the hypothesis that significant differences between OR and CO management, even if not observed in topsoil, might be detected in deeper soil layers, below 30cm.

Genomic Comparison and Genetic Marker Identification of the White-Spotted Bamboo Shark Chiloscyllium plagiosum

The white-spotted bamboo shark (Chiloscyllium plagiosum) is an ecologically and commercially important marine cartilaginous fish in the Indo-Western Pacific. However, the resources of this species are declining in recent years due to habitat degradation and overfishing. Studies on genomics and genetic markers can provide valuable information for sound management and conservation of C. plagiosum. In this study, genome resequencing data of a domesticated C. plagiosum individual were generated for genomic comparison between wild and domesticated samples. Based on 281.17 Gb of clean sequencing data, the genome size of the domesticated sample was estimated as 4.99 Gb, with heterozygosity of 0.51% and repeat ratio of 74.67%, which is about 1 Gb larger than that of the wild sample (3.85 Gb with a repeat ratio of 63.53%). By using a reference-based approach, we assembled a nearly 3.45 Gb genome sequence of the domesticated sample, with the scaffold N50 of 69.45 Mb. Subsequent identification of genome-wide microsatellite markers confirmed the different abundance of repeat elements in wild and domesticated C. plagiosum. Additionally, a total of 8,703,211 single-nucleotide polymorphisms (SNPs) were detected and annotated. The demographic analysis based on identified SNPs revealed a large and constant effective population size of C. plagiosum after the last population expansion (~0.3 million years ago). The genomic data and identified genetic markers in this study can provide fundamental and useful information for further comparative genomics, evolutionary biology, and conservation genetics of C. plagiosum.

Mathematical Modeling: Global Stability Analysis of Super Spreading Transmission of Respiratory Syncytial Virus (RSV) Disease

In this paper, a model for the transmission of respiratory syncytial virus (RSV) in a constant human population in which there exist super spreading infected individuals (who infect many people during a single encounter) is considered. It has been observed in the epidemiological data for the diseases caused by this virus that there are cases where some individuals are super-spreaders of the virus. We formulate a simply SEIrIsR (susceptible–exposed–regular infected–super-spreading infected–recovered) mathematical model to describe the dynamics of the transmission of this disease. The proposed model is analyzed using the standard stability method by using Routh-Hurwitz criteria. We obtain the basic reproductive number (R0) using the next generation method. We establish that when R0<1, the disease-free state is locally asymptotically stable and the disease endemic state is unstable. The reverse is true when R0>1, the disease endemic state becomes the locally asymptotically stable state and the disease-free state becomes unstable. It is also established that the two equilibrium states are globally asymptotically stable. The numerical simulations show how the dynamics of the disease change as values of the parameters in the SEIrIsR are varied.

Population-genomic analyses reveal bottlenecks and asymmetric introgression from Persian into iron walnut during domestication

BackgroundPersian walnut, Juglans regia, occurs naturally from Greece to western China, while its closest relative, the iron walnut, Juglans sigillata, is endemic in southwest China; both species are cultivated for their nuts and wood. Here, we infer their demographic histories and the time and direction of possible hybridization and introgression between them.ResultsWe use whole-genome resequencing data, different population-genetic approaches (PSMC and GONE), and isolation-with-migration models (IMa3) on individuals from Europe, Iran, Kazakhstan, Pakistan, and China. IMa3 analyses indicate that the two species diverged from each other by 0.85 million years ago, with unidirectional gene flow from eastern J. regia and its ancestor into J. sigillata, including the shell-thickness gene. Within J. regia, a western group, located from Europe to Iran, and an eastern group with individuals from northern China, experienced dramatically declining population sizes about 80 generations ago (roughly 2400 to 4000 years), followed by an expansion at about 40 generations, while J. sigillata had a constant population size from about 100 to 20 generations ago, followed by a rapid decline.ConclusionsBoth J. regia and J. sigillata appear to have suffered sudden population declines during their domestication, suggesting that the bottleneck scenario of plant domestication may well apply in at least some perennial crop species. Introgression from introduced J. regia appears to have played a role in the domestication of J. sigillata.

Characterizing outbreak vulnerability in a stochastic SIS model with an external disease reservoir.

In this article, we take a mathematical approach to the study of population-level disease spread, performing a quantitative and qualitative investigation of an SISκ model which is a susceptible-infectious-susceptible (SIS) model with exposure to an external disease reservoir. The external reservoir is non-dynamic, and exposure from the external reservoir is assumed to be proportional to the size of the susceptible population. The full stochastic system is modelled using a master equation formalism. A constant population size assumption allows us to solve for the stationary probability distribution, which is then used to investigate the predicted disease prevalence under a variety of conditions. By using this approach, we quantify outbreak vulnerability by performing the sensitivity analysis of disease prevalence to changing population characteristics. In addition, the shape of the probability density function is used to understand where, in parameter space, there is a transition from disease free, to disease present, and to a disease endemic system state. Finally, we use Kullback-Leibler divergence to compare our semi-analytical results for the SISκ model with more complex susceptible-infectious-recovered (SIR) and susceptible-exposed-infectious-recovered (SEIR) models.

The stationary and quasi-stationary properties of neutral multi-type branching process diffusions

The stationary asymptotic properties of the diffusion limit of a multi-type branching process with neutral mutations are studied. For the critical and subcritical processes the interesting limits are those of quasi-stationary distributions conditioned on non-extinction. Pedagogical derivations are given for known results that the limiting distributions for supercritical and critical processes are found to collapse onto rays aligned with stationary eigenvectors of the mutation rate matrix, in agreement with discrete multi-type branching processes. For the sub-critical process the previously unsolved quasi-stationary distribution is obtained to first order in the overall mutation rate, which is assumed to be small. The sampling distribution over allele types for a sample of given finite size is found to agree to first order in mutation rates with the analogous sampling distribution for a Wright-Fisher diffusion with constant population size.

Growing threat of unempolyment and indian perspective

Unemployment as growing threat, every year more youth are entering into the competition world for jobs and better life. But constant population growth, improper skills set deceases the chances of employment in youth not only economy of state affects but also social and harmony of society affects.

The impact of genetic modifiers on variation in germline mutation rates within and among human populations.

Mutation rates and spectra differ among human populations. Here, we examine whether this variation could be explained by evolution at mutation modifiers. To this end, we consider genetic modifier sites at which mutations, "mutator alleles," increase genome-wide mutation rates and model their evolution under purifying selection due to the additional deleterious mutations that they cause, genetic drift, and demographic processes. We solve the model analytically for a constant population size and characterize how evolution at modifier sites impacts variation in mutation rates within and among populations. We then use simulations to study the effects of modifier sites under a plausible demographic model for Africans and Europeans. When comparing populations that evolve independently, weakly selected modifier sites (2Nes≈1), which evolve slowly, contribute the most to variation in mutation rates. In contrast, when populations recently split from a common ancestral population, strongly selected modifier sites (2Nes≫1), which evolve rapidly, contribute the most to variation between them. Moreover, a modest number of modifier sites (e.g. 10 per mutation type in the standard classification into 96 types) subject to moderate to strong selection (2Nes>1)could account for the variation in mutation rates observed among human populations. If such modifier sites indeed underlie differences among populations, they should also cause variation in mutation rates within populations and their effects should be detectable in pedigree studies.

Clonal dynamics of haematopoiesis across the human lifespan

Age-related change in human haematopoiesis causes reduced regenerative capacity1, cytopenias2, immune dysfunction3 and increased risk of blood cancer4–6, but the reason for such abrupt functional decline after 70 years of age remains unclear. Here we sequenced 3,579 genomes from single cell-derived colonies of haematopoietic cells across 10 human subjects from 0 to 81 years of age. Haematopoietic stem cells or multipotent progenitors (HSC/MPPs) accumulated a mean of 17 mutations per year after birth and lost 30 base pairs per year of telomere length. Haematopoiesis in adults less than 65 years of age was massively polyclonal, with high clonal diversity and a stable population of 20,000–200,000 HSC/MPPs contributing evenly to blood production. By contrast, haematopoiesis in individuals aged over 75 showed profoundly decreased clonal diversity. In each of the older subjects, 30–60% of haematopoiesis was accounted for by 12–18 independent clones, each contributing 1–34% of blood production. Most clones had begun their expansion before the subject was 40 years old, but only 22% had known driver mutations. Genome-wide selection analysis estimated that between 1 in 34 and 1 in 12 non-synonymous mutations were drivers, accruing at constant rates throughout life, affecting more genes than identified in blood cancers. Loss of the Y chromosome conferred selective benefits in males. Simulations of haematopoiesis, with constant stem cell population size and constant acquisition of driver mutations conferring moderate fitness benefits, entirely explained the abrupt change in clonal structure in the elderly. Rapidly decreasing clonal diversity is a universal feature of haematopoiesis in aged humans, underpinned by pervasive positive selection acting on many more genes than currently identified.

New Results and Open Questions for SIR-PH Epidemic Models with Linear Birth Rate, Loss of Immunity, Vaccination, and Disease and Vaccination Fatalities

Our paper presents three new classes of models: SIR-PH, SIR-PH-FA, and SIR-PH-IA, and states two problems we would like to solve about them. Recall that deterministic mathematical epidemiology has one basic general law, the “R0 alternative” of Van den Driessche and Watmough, which states that the local stability condition of the disease-free equilibrium may be expressed as R0<1, where R0 is the famous basic reproduction number, which also plays a major role in the theory of branching processes. The literature suggests that it is impossible to find general laws concerning the endemic points. However, it is quite common that 1. When R0>1, there exists a unique fixed endemic point, and 2. the endemic point is locally stable when R0>1. One would like to establish these properties for a large class of realistic epidemic models (and we do not include here epidemics without casualties). We have introduced recently a “simple” but broad class of “SIR-PH models” with varying populations, with the express purpose of establishing for these processes the two properties above. Since that seemed still hard, we have introduced a further class of “SIR-PH-FA” models, which may be interpreted as approximations for the SIR-PH models, and which include simpler models typically studied in the literature (with constant population, without loss of immunity, etc.). For this class, the first “endemic law” above is “almost established”, as explicit formulas for a unique endemic point are available, independently of the number of infectious compartments, and it only remains to check its belonging to the invariant domain. This may yet turn out to be always verified, but we have not been able to establish that. However, the second property, the sufficiency of R0>1 for the local stability of an endemic point, remains open even for SIR-PH-FA models, despite the numerous particular cases in which it was checked to hold (via Routh–Hurwitz time-onerous computations, or Lyapunov functions). The goal of our paper is to draw attention to the two open problems above, for the SIR-PH and SIR-PH-FA, and also for a second, more refined “intermediate approximation” SIR-PH-IA. We illustrate the current status-quo by presenting new results on a generalization of the SAIRS epidemic model.

Molecular insights into the population structure and haplotype network of Theileria annulata based on the small-subunit ribosomal RNA (18S rRNA) gene.

The present study was conducted to elucidate the population genetic diversity and haplotype network of Theileria annulata based on all available nearly complete 18S rRNA gene sequences in the GenBank™. In total, 52 sequences of the nuclear 18S rRNA gene used to assess the relationship of T. annulata with their country of origin identified 34 haplotypes. Haplotype 4 was widespread, occurring in India, China, Turkey and Iran, while the remaining haplotypes were singleton and unique to one country. Haplotype 4 displayed numerous single haplotypes around it and the stellate shape of the network suggested a rapid population expansion. India exhibited the largest number of haplotypes (h=25) followed by Turkey (h=6), China (h=4), and Iran and Italy (h=1). No geographical clustering of haplotypes was recorded. Nucleotide diversity was the highest in the Turkish followed by the Indian and Chinese populations. Similarly, haplotype diversity was the highest in China followed by Turkey, and the lowest in India. The overall dataset exhibited a low nucleotide diversity (0.00253±0.00035), but high haplotype diversity (0.917±0.034). It suggested the presence of only minor differences (01-11 nucleotide) between haplotypes which was also evident from the haplotype network. A high level of genetic diversity was documented within the Indian, Chinese and Turkish populations of T. annulata, whereas little genetic differentiation was noticed among these populations with a very high level of gene flow. Analysis of molecular variance (AMOVA) of T. annulata sequences revealed higher genetic variation within countries (83.58%) as compared to the variation among countries (16.42%). Neutrality indices, viz., Tajima's D, Fu and Li's F, Fu's Fs, and R2, along with the unimodal mismatch distributions demonstrated a recent population expansion of T. annulata in India and the overall dataset. However, the non-significant values of Tajima's D, Fu and Li's F, and Fu's Fs for the Chinese population along with a bimodal mismatch distribution signified a constant population size. For the Turkish population, the neutrality and mismatch distribution tests either indicated a constant or a slight increase in population size. The present study provides novel insights into the population genetics and haplotype network of T. annulata based on the 18S rRNA gene for the first time.

Projecting National-Level Prevalence of General Obesity and Abdominal Obesity Among Chinese Adults With Aging Effects.

ObjectivesTo explore the impact of population aging on the projected prevalence of obesity among Chinese adults in 2030.MethodsIn total, 71450 observations were extracted from the China Health and Nutrition Survey between 1991 and 2015.Population was projected to 2030 using a Bayesian hierarchical modeling method. Two different approaches were adopted to estimate and project the national prevalence of overweight/obesity from 1991 to 2030. One method assumed a constant population at the base year, while the other allowed the age and gender distributions vary in each year.ResultsOur projection indicated that approximately two-thirds of Chinese adults would be affected by overweight/general obesity in 2030, and more than 60% of Chinese adults will suffer from abdominal obesity in 2030. Ignoring population aging led to an underestimation of overweight, general obesity and abdominal obesity for women by 3.81, 0.06, and 3.16 percentage points (pp), and overweight and abdominal obesity among men by 1.67 and 0.53 pp, respectively; but the prevalence of general obesity among men will be overestimated by 2.11 pp. Similar underestimations were detected in the estimation from 1991 to 2015.ConclusionsEstimating and projecting the national prevalence of obesity using a constant population structure at the base line would cause significant underestimation if countries are undergoing rapid population aging.

Extinction threshold and large population limit of a plant metapopulation model with recurrent extinction events and a seed bank component

We introduce a new model for plant metapopulations with a seed bank component, living in a fragmented environment in which local extinction events are frequent. This model is an intermediate between population dynamics models with a seed bank component, based on the classical Wright–Fisher model, and Stochastic Patch Occupancy Models (SPOMs) used in metapopulation ecology. Its main feature is the use of “ghost” individuals, which can reproduce but with a very strong selective disadvantage against “real” individuals, to artificially ensure a constant population size. We show the existence of an extinction threshold above which persistence of the subpopulation of “real” individuals is not possible, and investigate how the seed bank characteristics affect this extinction threshold. We also show the convergence of the model to a SPOM under an appropriate scaling, bridging the gap between individual-based models and occupancy models.

Simple model of epidemic dynamics with memory effects

We introduce a compartment model with memory for the dynamics of epidemic spreading in a constant population of individuals. Each individual is in one of the states S=susceptible, I=infected, or R=recovered (SIR model). In state R an individual is assumed to stay immune within a finite-time interval. In the first part, we introduce a random lifetime or duration of immunity which is drawn from a certain probability density function. Once the time of immunity is elapsed an individual makes an instantaneous transition to the susceptible state. By introducing a random duration of immunity a memory effect is introduced into the process which crucially determines the epidemic dynamics. In the second part, we investigate the influence of the memory effect on the space-time dynamics of the epidemic spreading by implementing this approach into computer simulations and employ a multiple random walker's model. If a susceptible walker meets an infectious one on the same site, then the susceptible one gets infected with a certain probability. The computer experiments allow us to identify relevant parameters for spread or extinction of an epidemic. In both parts, the finite duration of immunity causes persistent oscillations in the number of infected individuals with ongoing epidemic activity preventing the system from relaxation to a steady state solution. Such oscillatory behavior is supported by real-life observations and not captured by the classical standard SIR model.

The Impact of Media Coverage on Obesity

In this paper, we develop a deterministic compartmental model for the obesity dynamics. Contrary to other contributions on this subject we explore the impact of the media on the spreading of this phenomenon in a constant population. Stability analysis shows that the disease-free equilibrium point is globally asymptotically stable when the number of reproduction is less than unity. We also show that the endemic equilibrium point when it exists is globally asymptotically stable under some conditions.

Sparse Moments of Univariate Step Functions and Allele Frequency Spectra

We study the univariate moment problem of piecewise-constant density functions on the interval [0,1] and its consequences for an inference problem in population genetics. We show that, up to closure, any collection of n moments is achieved by a step function with at most n − 1 breakpoints and that this bound is tight. We use this to show that any point in the n th coalescence manifold in population genetics can be attained by a piecewise constant population history with at most n − 2 changes. Both the moment cones and the coalescence manifold are projected spectrahedra and we describe the problem of finding a nearest point on them as a semidefinite program.