Anomalous fluctuations and selective extinction in primordial replicators: a ‘struggle for life’ at the origin of biological homochirality

2020 ◽  
Vol 19 (5) ◽  
pp. 386-392
Author(s):  
Savino Longo ◽  
Miriana Carmela Chincoli ◽  
Gaia Micca Longo
Keyword(s):  
Weak Interactions ◽  
Molecular Form ◽  
Selective Advantage ◽  
Chemical Energy ◽  
Key Points ◽  
Large Fluctuations ◽  
Autocatalytic Process ◽  
Extinction Events ◽  
Number Of Individuals ◽  
Selective Extinction

AbstractThe prevalent presence of a single chiral variant of molecules in live organisms is one of the most distinctive signs of life as a global phenomenon. One of the greatest ambitions of biochemistry and astrobiology is to provide an explanation of this predominance. Several mechanisms were proposed in the past, from the propagation of chirality from a homo-chiral substrate to the amplification of effects associated with electro-weak interactions. Here, a different scenario is proposed: anomalous fluctuations associated with a self-replication scenario can lead to the selective extinction of primordial organisms using one of two enantiomers as an enzyme. These fluctuations arise spontaneously under very general conditions. The idea is based on three key points: (a) the simulation of early biological processes as a ‘board game’; (b) the presence of large fluctuations during an autocatalytic process; (c) the presence of a limited source of chemical energy, inducing a form of competition in a primordial replicator population. In order to demonstrate this mechanism, a computational model is developed, describing the ‘struggle for life’ of two different kinds of primordial replicators on a ‘chessboard’ with periodic boundary conditions; each replicator employs enzymes of different chirality on a non-chiral substrate, thereby with no selective advantage. The replication occurs randomly and with a fixed probability, providing that a sufficient amount of chemical energy is locally available. For the first time, our model includes the local balance of chemical energy in a molecular form on the substrate. The correlation between the chemical energy and the local populations is shown. Results clearly show that strong fluctuations in the number of individuals of each species and subsequent selective extinction events of one of the two species are observed. These studies may contribute to shed light on the most mysterious phase transition that occurred during the biochemical evolution of our planet.

A possible method of evolution of the migratory habit in butterflies

1968 ◽  
Vol 253 (787) ◽  
pp. 309-341 ◽  
Keyword(s):  
Pieris Rapae ◽  
Selective Pressure ◽  
Selective Advantage ◽  
The Sun ◽  
Flight Direction ◽  
Movement Function ◽  
Effects Of Temperature ◽  
One Year ◽  
Vanessa Atalanta ◽  
Number Of Individuals

A new theory of migration in butterflies is outlined and present concepts are examined. During the course of evolution many butterflies have become adapted in the larval stage to foodplants that occur in small and scattered localities, the distribution of which changes constantly. It is argued that whenever this happens selection might be expected to produce a butterfly which flies from one foodplant site to another. Further it is argued that while they were crossing areas devoid of foodplants selection would have favoured those individuals that flew at a constant angle to the sun. At first all angles to the sun would be represented equally in the population but each individual would pass on to its offspring a bias towards its own particular angle. It is suggested that the temperature gradient experienced by a butterfly dispersing in this way would constitute a marked selective pressure. This selective pressure would cause an increase in the number of individuals flying at certain angles and a decrease in the number flying at others. The effects of temperature on rate of development and fecundity were demonstrated for Pieris rapae and P. brassicae in the laboratory. The effects of seasonal and geographical temperature variations on these two species in the field were also demonstrated. Based on these results the relative selective advantage of each flight direction was calculated for different times of the year. As a result of these calculations it was predicted that P. rapae should fly at 159° to the sun until 27 August, when it should fly at 0°. For P. brassicae it was predicted that the first brood should fly at 159° and the second brood at 339°. Observations of flight direction of these two species from August of one year to October of the following year agreed well with these predictions. The observations of flight direction also showed that P. rapae , and probably also P. brassicae and Vanessa atalanta , were using the sun as the environmental clue by which they were orientating themselves. There was no compensation for the sun’s movement during the day or season. Experiments showed that P. rapae is sensitive to photoperiod during the adult stage. It is by this means that the same individuals can change their flight direction from 159° to 0° at the most selectively advantageous time. A calculation based on the results of this investigation suggested that a return flight would be a selective disadvantage to both P. rapae and P. brassicae . Observation of these two species suggested that in neither does the southward movement function as a return flight, i.e. is equal in distance to the northward movement.

scholarly journals Prediction of rates of inbreeding in selected populations

1990 ◽  
Vol 55 (1) ◽  
pp. 41-54 ◽  
Author(s):  
Naomi R. Wray ◽  
Robin Thompson
Keyword(s):  
Selective Advantage ◽  
Mass Selection ◽  
Effective Population ◽  
The Matrix ◽  
Mean And Variance ◽  
Unselected Population ◽  
The Mean ◽  
Number Of Individuals ◽  
The Relationship

SummaryA method is presented for the prediction of rate of inbreeding for populations with discrete generations. The matrix of Wright's numerator relationships is partitioned into ‘contribution’ matrices which describe the contribution of the Mendelian sampling of genes of ancestors in a given generation to the relationship between individuals in later generations. These contributions stabilize with time and the value to which they stabilize is shown to be related to the asymptotic rate of inbreeding and therefore also the effective population size, where N is the number of individuals per generation and μr and are the mean and variance of long-term relationships or long-term contributions. These stabilized values are then predicted using a recursive equation via the concept of selective advantage for populations with hierarchical mating structures undergoing mass selection. Account is taken of the change in genetic parameters as a consequence of selection and also the increasing ‘competitiveness’ of contemporaries as selection proceeds. Examples are given and predicted rates of inbreeding are compared to those calculated in simulations. For populations of 20 males and 20, 40, 100 or 200 females the rate of inbreeding was found to increase by as much as 75% over the rate of inbreeding in an unselected population depending on mating ratio, selection intensity and heritability of the selected trait. The prediction presented here estimated the rate of inbreeding usually within 5% of that calculated from simulation.

scholarly journals INFLUENCE OF INTERSPECIFIC VARIATION ON TREE CARBON STOCK OF A BRAZILIAN CERRADO

2018 ◽  
Vol 41 (5) ◽  
Author(s):  
Sabina Cerruto Ribeiro ◽  
Laércio Antônio Gonçalves Jacovine ◽  
Carlos Moreira Miquelino Eleto Torres ◽  
Agostinho Lopes Souza
Keyword(s):  
Carbon Content ◽  
Carbon Balance ◽  
Carbon Stock ◽  
Interspecific Variation ◽  
Sensu Stricto ◽  
Allometric Equation ◽  
Average Value ◽  
Key Points ◽  
Dry Biomass ◽  
Number Of Individuals

ABSTRACT Cerrado is a biodiversity hotspot and possibly the most threatened tropical savanna in the world. Although Cerrado has an important role in the global carbon balance, studies about carbon stock in the biome are rare, especially with estimates per species. Thus, we estimated the carbon content and stock by species in a Cerrado area. We destructively sampled 120 trees from 18 species to determine tree aboveground biomass at a cerrado sensu stricto remnant. The carbon content in dry biomass was determined in laboratory and for the species not sampled an average value was used. The biomass of the remaining inventoried trees was estimated using an allometric equation. The carbon content in dry biomass had mean of 50.5 ± 0.20% and the carbon stock for the Cerrado remnant accounted for 22,385.46 kg ha-1. Results indicated that some species had higher carbon stock than others. The number of individuals, their size and wood density are key points that need to be considered in the evaluation of carbon stock in forests with large number of species. Maintaining species that contribute to higher carbon stock is essential to keep a positive carbon balance in Cerrado areas

scholarly journals Annual Migration Density and Stopover Patterns of Northern Saw-whet Owls (Aegolius acadicus)

The Auk ◽  
2002 ◽  
Vol 119 (4) ◽  
pp. 1154-1161
Author(s):  
David M. Whalen ◽  
Bryan D. Watts
Keyword(s):  
Body Condition ◽  
Good Condition ◽  
Condition Index ◽  
Annual Number ◽  
Eastern United States ◽  
Adult Age ◽  
Large Fluctuations ◽  
Aegolius Acadicus ◽  
Using Data ◽  
Number Of Individuals

Abstract Northern Saw-whet Owls (Aegolius acadicus) exhibit large fluctuations in annual number of individuals migrating in eastern United States. Underlying large differences in the magnitude of the migration may be important density-dependent effects on body condition and stopover patterns. We investigated such effects using data from saw-whet owls that were trapped and banded during autumn migration at the southern tip of the Delmarva Peninsula (near Cape Charles, Virginia) from 1994 to 2000. Irruptive migration events occurred in 1995 and 1999 when 1,002 and 700 owls were captured, respectively. Capture totals ranged from 22 to 105 owls during five nonirruptive years. Irruptive migration years were dominated by immature owls (82% of captures) and were characterized by low recapture rates (13%) and shorter minimum stopover lengths (median = 5 nights) for all owls. Body masses and body-condition index scores were significantly lower for both immature and adult age classes during years when owl density was very high. During such years, a smaller percentage of owls elected to stopover and, among those that did, individuals in good condition departed sooner than individuals in poor condition. Conversely, during nonirruptive years, adults constituted 67% of captures, recapture rates were nearly 3× higher (35%), and stopover lengths were twice as long (median = 10 nights). Recapture rates were significantly higher for adults (43%) than for immature owls (23%) and initial body condition of adults was positively correlated with their length of stopover. During light migration years, conditions may be conducive for extended residency, particularly for adult owls in good condition. Our results suggest that density-dependence is an important mechanism driving migration and stopover patterns of saw-whet owls.

Organic Syntheses During the Impact of a Comet with a Gaseous Planet

1997 ◽  
Vol 161 ◽  
pp. 189-195
Author(s):  
Cesare Guaita ◽  
Roberto Crippa ◽  
Federico Manzini
Keyword(s):  
Polymeric Material ◽  
Molecular Form ◽  
Parent Compound ◽  
Blue Filter ◽  
Organic Syntheses ◽  
The Impact

AbstractA large amount of CO has been detected above many SL9/Jupiter impacts. This gas was never detected before the collision. So, in our opinion, CO was released from a parent compound during the collision. We identify this compound as POM (polyoxymethylene), a formaldehyde (HCHO) polymer that, when suddenly heated, reformes monomeric HCHO. At temperatures higher than 1200°K HCHO cannot exist in molecular form and the most probable result of its decomposition is the formation of CO. At lower temperatures, HCHO can react with NH3 and/or HCN to form high UV-absorbing polymeric material. In our opinion, this kind of material has also to be taken in to account to explain the complex evolution of some SL9 impacts that we observed in CCD images taken with a blue filter.

Sustainable 2,5-furandicarboxylic synthesis by a direct 5-hydroxymethylfurfural fuel cell based on a bifunctional PtNiSx catalyst

2020 ◽  
Vol 56 (88) ◽  
pp. 13611-13614
Author(s):  
Jialu Wang ◽  
Xian Zhang ◽  
Guozhong Wang ◽  
Yunxia Zhang ◽  
Haimin Zhang
Keyword(s):  
Fuel Cell ◽  
Electric Energy ◽  
Value Added ◽  
Chemical Energy ◽  
New Type

A new type of direct 5-hydroxymethylfurfural (HMF) oxidation fuel cell based on a bifunctional PtNiSx/CB catalyst not only transformed chemical energy into electric energy but also converted HMF into value-added 2,5-furandicarboxylic (FDCA).

Two [Ln4] molecular rings folded as compact tetrahedra

2020 ◽  
Vol 49 (21) ◽  
pp. 7182-7188
Author(s):  
Jorge Salinas-Uber ◽  
Leoní A. Barrios ◽  
Olivier Roubeau ◽  
Guillem Aromí
Keyword(s):  
Weak Interactions ◽  
Molecular Rings

A new highly photo-switchable ligand furnishes supramolecular tetrahedral nanomagnets with Ln(iii) ions (Ln = Dy, Tb). Intramolecular weak interactions define the conformation of the ligand, quenching the photochromic activity.

Perceptual Learning of Vocoded Speech With and Without Contralateral Hearing: Implications for Cochlear Implant Rehabilitation

2020 ◽  
pp. 1-10
Author(s):  
Martin Chavant ◽  
Alexis Hervais-Adelman ◽  
Olivier Macherey
Keyword(s):  
Cochlear Implant ◽  
Perceptual Learning ◽  
Speech Signal ◽  
Training Phase ◽  
Monosyllabic Words ◽  
Low Pass ◽  
Contralateral Ear ◽  
Number Of Individuals ◽  
Insight Into ◽  
Vocoded Speech

Purpose An increasing number of individuals with residual or even normal contralateral hearing are being considered for cochlear implantation. It remains unknown whether the presence of contralateral hearing is beneficial or detrimental to their perceptual learning of cochlear implant (CI)–processed speech. The aim of this experiment was to provide a first insight into this question using acoustic simulations of CI processing. Method Sixty normal-hearing listeners took part in an auditory perceptual learning experiment. Each subject was randomly assigned to one of three groups of 20 referred to as NORMAL, LOWPASS, and NOTHING. The experiment consisted of two test phases separated by a training phase. In the test phases, all subjects were tested on recognition of monosyllabic words passed through a six-channel “PSHC” vocoder presented to a single ear. In the training phase, which consisted of listening to a 25-min audio book, all subjects were also presented with the same vocoded speech in one ear but the signal they received in their other ear differed across groups. The NORMAL group was presented with the unprocessed speech signal, the LOWPASS group with a low-pass filtered version of the speech signal, and the NOTHING group with no sound at all. Results The improvement in speech scores following training was significantly smaller for the NORMAL than for the LOWPASS and NOTHING groups. Conclusions This study suggests that the presentation of normal speech in the contralateral ear reduces or slows down perceptual learning of vocoded speech but that an unintelligible low-pass filtered contralateral signal does not have this effect. Potential implications for the rehabilitation of CI patients with partial or full contralateral hearing are discussed.

Autism and Neurodiversity: Addressing Concerns and Offering Implications for the School-Based Speech-Language Pathologist

2020 ◽  
pp. 1-7
Author(s):  
Laura S. DeThorne ◽  
Kelly Searsmith
Keyword(s):  
Service Provision ◽  
Individualized Education Program ◽  
Institutional Constraints ◽  
Individualized Education ◽  
Existing Structures ◽  
Eligibility Determination ◽  
Speech Language Pathologist ◽  
School Based ◽  
Key Points ◽  
C Center

Purpose The purpose of this article is to address some common concerns associated with the neurodiversity paradigm and to offer related implications for service provision to school-age autistic students. In particular, we highlight the need to (a) view first-person autistic perspectives as an integral component of evidence-based practice, (b) use the individualized education plan as a means to actively address environmental contributions to communicative competence, and (c) center intervention around respect for autistic sociality and self-expression. We support these points with cross-disciplinary scholarship and writings from autistic individuals. Conclusions We recognize that school-based speech-language pathologists are bound by institutional constraints, such as eligibility determination and Individualized Education Program processes that are not inherently consistent with the neurodiversity paradigm. Consequently, we offer examples for implementing the neurodiversity paradigm while working within these existing structures. In sum, this article addresses key points of tension related to the neurodiversity paradigm in a way that we hope will directly translate into improved service provision for autistic students. Supplemental Material https://doi.org/10.23641/asha.13345727

Optimal Experimental Design With Nesting of Persons in Organizations

2013 ◽  
Vol 221 (3) ◽  
pp. 145-159 ◽  
Author(s):  
Gerard J. P. van Breukelen
Keyword(s):  
Repeated Measures ◽  
Optimal Number ◽  
Health Centers ◽  
Randomized Experiments ◽  
Optimal Sample ◽  
Treatment Conditions ◽  
Sampling Cost ◽  
Nested Designs ◽  
Simple Equations ◽  
Number Of Individuals

This paper introduces optimal design of randomized experiments where individuals are nested within organizations, such as schools, health centers, or companies. The focus is on nested designs with two levels (organization, individual) and two treatment conditions (treated, control), with treatment assignment to organizations, or to individuals within organizations. For each type of assignment, a multilevel model is first presented for the analysis of a quantitative dependent variable or outcome. Simple equations are then given for the optimal sample size per level (number of organizations, number of individuals) as a function of the sampling cost and outcome variance at each level, with realistic examples. Next, it is explained how the equations can be applied if the dependent variable is dichotomous, or if there are covariates in the model, or if the effects of two treatment factors are studied in a factorial nested design, or if the dependent variable is repeatedly measured. Designs with three levels of nesting and the optimal number of repeated measures are briefly discussed, and the paper ends with a short discussion of robust design.

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