Muller's ratchet and mutational meltdowns

We extend our earlier work on the role of deleterious mutations in the extinction of obligately asexual populations. First, we develop analytical models for mutation accumulation that obviate the need for time-consuming computer simulations in certain ranges of the parameter space. When the number of mutations entering the population each generation is fairly high, the number of mutations per individual and the mean time to extinction can be predicted using classical approaches in quantitative genetics. However, when the mutation rate is very low, a fixation-probability approach is quite effective. Second, we show that an intermediate selection coefficient (s) minimizes the time to extinction. The critical value of s can be quite low, and we discuss the evolutionary implications of this, showing that increased sensitivity to mutation and loss of capacity for DNA repair can be selectively advantageous in asexual organisms. Finally, we consider the consequences of the mutational meltdown for the extinction of mitochondrial lineages in sexual species

The mutational meltdown in asexual populations

Loss of fitness due to the accumulation of deleterious mutations appears to be inevitable in small, obligately asexual populations, as these are incapable of reconstituting highly fit genotypes by recombination or back mutation. The cumulative buildup of such mutations is expected to lead to an eventual reduction in population size, and this facilitates the chance accumulation of future mutations. This synergistic interaction between population size reduction and mutation accumulation leads to an extinction process known as the mutational meltdown, and provides a powerful explanation for the rarity of obligate asexuality. We give an overview of the theory of the mutational meltdown, showing how the process depends on the demographic properties of a population, the properties of mutations, and the relationship between fitness and number of mutations incurred

Freely forming groups: trying to be rare

A simple weakly frequency dependent model for the dynamics of a population with a finite number of types is proposed, based upon an advantage of being rare. In the infinite population limit, this model gives rise to a non-smooth dynamical system that reaches its globally stable equilibrium in finite time. This dynamical system is sufficiently simple to permit an explicit solution, built piecewise from solutions of the logistic equation in continuous time. It displays an interesting tree-like structure of coalescing components

Review on String Breaking - the Query in Quest of the Evidence

Considerable progress has been achieved recently in the observation of string breaking within non-Abelian Higgs models, by use of multi-channel methods allowing for broken string states. Similarly, in pure gauge theory this approach has been shown to reveal string breaking for color charges in the adjoint represaentation. For QCD with dynmical fermions, one needs substantial progress in noise reduction, however, to render such techniques viable.Comment: June 1999, 6 pages, 11 figures. Plenary talk presented at the 17th Int. Symposium on Lattice Field Theory (Lattice 99), Pisa, Italy 29 Jun - 3 Jul, 199

Thinking dimensional : prevalence of DSM-5 early adolescent full syndrome, partial and subthreshold eating disorders in a cross-sectional survey in German schools

OBJECTIVES: Investigating for the first time in Germany Diagnostic and Statistical Manual Fifth Edition (DSM-5) prevalences of adolescent full syndrome, Other Specified Feeding or Eating Disorder (OSFED), partial and subthreshold anorexia nervosa (AN), bulimia nervosa (BN) and binge eating disorder (BED). METHOD: A national school-based cross-sectional survey with nine schools in Germany was undertaken that was aimed at students from grades 7 and 8. Of the 1775 students who were contacted to participate in the study, 1654 participated (participation rate: 93.2%). The sample consisted of 873 female and 781 male adolescents (mean age=13.4 years). Prevalence rates were established using direct symptom criteria with a structured inventory (SIAB-S) and an additional self-report questionnaire (Eating Disorder Inventory 2 (EDI-2)). RESULTS: Prevalences for full syndrome were 0.3% for AN, 0.4% for BN, 0.5% for BED and 3.6% for OSFED-atypical AN, 0% for BN (low frequency/limited duration), 0% for BED (low frequency/limited duration) and 1.9% for purging disorder (PD). Prevalences of partial syndrome were 10.9% for AN (7.1% established with cognitive symptoms only, excluding weight criteria), 0.2% for BN and 2.1% for BED, and of subthreshold syndrome were 0.8% for AN, 0.3% for BN and 0.2% for BED. Cases on EDI-2 scales were much more pronounced with 12.6-21.1% of the participants with significant sex differences. CONCLUSIONS: The findings were in accordance with corresponding international studies but were in contrast to other German studies showing much higher prevalence rates. The study provides, for the first time, estimates for DSM-5 prevalences of eating disorders in adolescents for Germany, and evidence in favour of using valid measures for improving prevalence estimates

Kulturgutschutz und Notfallverbünde: Herausforderungen und neue Initiativen nach dem Hochwasser

Am 5. November 2010 hat der Beauftragte für Kultur und Medien der Bundesregierung, Staatsminister Bernd Neumann, zusätzliche 500.000 EUR für den Schutz schriftlichen Kulturguts in Deutschland bewilligt. In Sachsen erhalten u.a. das Kloster Marienthal und das Schumann-Haus in Zwickau Fördermittel. Die Koordinierung für Sachsen hat die Landesstelle für Bestandserhaltung an der SLUB Dresden übernommen. Das erneute Hochwasser an Oder und Neiße im August 2010 hat gezeigt, dass die Notfallvorsorge ganz oben auf der Tagesordnung stehen muss

Numerical Investigations of a Counter-Current Moving Bed Reactor for Thermochemical Energy Storage at High Temperatures

High temperature storage is a key factor for compensating the fluctuating energy supply of solar thermal power plants, and thus enables renewable base load power. In thermochemical energy storage, the thermal energy is stored as the reaction enthalpy of a chemically reversible gas-solid reaction. Metal oxides are suitable candidates for thermochemical energy storage for solar thermal power plants, due to their high reaction temperatures and use of oxygen as a gaseous reaction partner. However, it is crucial to extract both sensible and thermochemical energy at these elevated temperatures to boost the overall system efficiency. Therefore, this study focuses on the combined extraction of thermochemical and sensible energy from a metal oxide and its effects on thermal power and energy density during discharging. A counter-current moving bed, based on manganese-iron-oxide, was investigated with a transient, one-dimensional model using the finite element method. A nearly isothermal temperature distribution along the bed height was formed, as long as the gas flow did not exceed a tipping point. A maximal energy density of 933 kJ/kg was achieved, when (Mn,Fe)3O4 was oxidized and cooled from 1050 °C to 300 °C. However, reaction kinetics can limit the thermal power and energy density. To avoid this drawback, a moving bed reactor based on the investigated manganese-iron oxide should combine direct and indirect heat transfer to overcome kinetic limitations

Originator Dynamics

We study the origin of evolution. Evolution is based on replication, mutation, and selection. But how does evolution begin? When do chemical kinetics turn into evolutionary dynamics? We propose “prelife” and “prevolution” as the logical precursors of life and evolution. Prelife generates sequences of variable length. Prelife is a generative chemistry that proliferates information and produces diversity without replication. The resulting “prevolutionary dynamics” have mutation and selection. We propose an equation that allows us to investigate the origin of evolution. In one limit, this “originator equation” gives the classical selection equation. In the other limit, we obtain “prelife.” There is competition between life and prelife and there can be selection for or against replication. Simple prelife equations with uniform rate constants have the property that longer sequences are exponentially less frequent than shorter ones. But replication can reverse such an ordering. As the replication rate increases, some longer sequences can become more frequent than shorter ones. Thus, replication can lead to “reversals” in the equilibrium portraits. We study these reversals, which mark the transition from prelife to life in our model. If the replication potential exceeds a critical value, then life replicates into existence.MathematicsOrganismic and Evolutionary Biolog

Aversive tension in female adolescents with Anorexia Nervosa : a controlled ecological momentary assessment using smartphones

BACKGROUND: Current models of Anorexia Nervosa (AN) emphasize the role of emotion regulation. Aversive tension, described as a state of intense arousal and negative valence, is considered to be a link between emotional events and disordered eating. Recent research focused only on adult patients, and mainly general emotion regulation traits were studied. However, the momentary occurrence of aversive tension, particularly in adolescents with AN, has not been previously studied. METHOD: 20 female adolescents with AN in outpatient treatment and 20 healthy adolescents aged 12 to 19years participated in an ecological momentary assessment using their smartphones. Current states of aversive tension and events were assessed hourly for two consecutive weekdays. Mean and maximum values of aversive tension were compared. Multilevel analyses were computed to test the influence of time and reported events on aversive tension. The effect of reported events on subsequent changes of aversive tension in patients with AN were additionally tested in a multilevel model. RESULTS: AN patients showed higher mean and maximum levels of aversive tension. In a multilevel model, reported food intake was associated with higher levels of aversive tension in the AN group, whereas reported school or sport-related events were not linked to specific states of aversive tension. After food intake, subsequent increases of aversive tension were diminished and decreases of aversive tension were induced in adolescents with AN. CONCLUSIONS: Aversive tension may play a substantial role in the psychopathology of AN, particular in relation with food intake. Therefore, treatment should consider aversive tension as a possible intervening variable during refeeding. Our findings encourage further research on aversive tension and its link to disordered eating. TRIAL REGISTRATION: German register of clinical trials (DRKS): DRKS00005228 (Date of registration: September 2, 2013)