Phase transition in a mean-field model for sympatric speciation

We introduce an analytical model for population dynamics with intra-specific competition, mutation and assortative mating as basic ingredients. The set of equations that describes the time evolution of population size in a mean-field approximation may be decoupled. We find a phase transition leading to sympatric speciation as a parameter that quantifies competition strength is varied. This transition, previously found in a computational model, occurs to be of first order.Comment: accepted for Physica

Simulations of a mortality plateau in the sexual Penna model for biological ageing

The Penna model is a strategy to simulate the genetic dynamics of age-structured populations, in which the individuals genomes are represented by bit-strings. It provides a simple metaphor for the evolutionary process in terms of the mutation accumulation theory. In its original version, an individual dies due to inherited diseases when its current number of accumulated mutations, n, reaches a threshold value, T. Since the number of accumulated diseases increases with age, the probability to die is zero for very young ages (n = T). Here, instead of using a step function to determine the genetic death age, we test several other functions that may or may not slightly increase the death probability at young ages (n < T), but that decreases this probability at old ones. Our purpose is to study the oldest old effect, that is, a plateau in the mortality curves at advanced ages. Imposing certain conditions, it has been possible to obtain a clear plateau using the Penna model. However, a more realistic one appears when a modified version, that keeps the population size fixed without fluctuations, is used. We also find a relation between the birth rate, the age-structure of the population and the death probability.Comment: submitted to Phys. Rev.

Computer simulations of sympatric speciation in a simple food web

Galapagos finches, have motivated much theoretical research aimed at understanding the processes associated with the formation of the species. Inspired by them, in this paper we investigate the process of sympatric speciation in a simple food web model. For that we modify the individual-based Penna model that has been widely used to study aging as well as other evolutionary processes. Initially, our web consists of a primary food source and a single herbivore species that feeds on this resource. Subsequently we introduce a predator that feeds on the herbivore. In both instances we manipulate directly a basal resource distribution and monitor the changes in the populations. Sympatric speciation is obtained for the top species in both cases, and our results suggest that the speciation velocity depends on how far up, in the food chain, the focus population is feeding. Simulations are done with three different sexual imprintinglike mechanisms, in order to discuss adaptation by natural selection

Health- and Vision-Related Quality of Life in a Randomized Controlled Trial Comparing Methotrexate and Mycophenolate Mofetil for&nbsp;Uveitis

PurposeTo evaluate changes in health-related and vision-related quality of life (VRQoL) among patients with noninfectious uveitis who were treated with antimetabolites.DesignSecondary analysis of a randomized controlled trial.ParticipantsPatients with noninfectious uveitis from India, the United States, Australia, Saudi Arabia, and Mexico.MethodsFrom 2013 through 2017, 216 participants were randomized to receive 25 mg weekly oral methotrexate or 1.5 g twice daily oral mycophenolate mofetil. Median changes in quality of life (QoL) were measured using Wilcoxon signed-rank tests, and differences between treatment groups were measured using linear mixed models, adjusting for baseline QoL score, age, gender, and site. Among Indian patients, VRQoL scores from a general scale (the National Eye Institute Visual Function Questionnaire [NEI-VFQ]) and a culturally specific scale (the Indian Visual Function Questionnaire [IND-VFQ]) were compared using Pearson correlation tests.Main outcome measuresVision-related QoL (NEI-VFQ and IND-VFQ) and health-related QoL (HRQoL; physical component score [PCS] and mental component score [MCS] of the Medical Outcomes Study 36-Item Short Form Survey [SF-36v2]) were measured at baseline, the primary end point (6 months or treatment failure before 6 months), and the secondary end point (12 months or treatment failure between 6 and 12 months).ResultsAmong 193 participants who reached the primary end point, VRQoL increased from baseline by a median of 12.0 points (interquartile range [IQR], 1.0-26.1, NEI-VFQ scale), physical HRQoL increased by a median of 3.6 points (IQR, -1.4 to 14.9, PCS SF-36v2), and mental HRQoL increased by a median of 3.0 points (IQR, -3.7 to 11.9, MCS SF-36v2). These improvements in NEI-VFQ, SF-36v2 PCS, and SF-36v2 MCS scores all were significant (P &lt; 0.01). The linear mixed models showed that QoL did not differ between treatment groups for each QoL assessment (NEI-VFQ, IND-VFQ, PCS SF-36v2, and MCS SF-36v2; P &gt; 0.05 for all). The NEI-VFQ and IND-VFQ scores for Indian participants were correlated highly at baseline and the primary and secondary end points (correlation coefficients, 0.87, 0.80, and 0.90, respectively).ConclusionsAmong patients treated with methotrexate or mycophenolate mofetil for uveitis, VRQoL and HRQoL improved significantly over the course of 1 year and did not differ by treatment allocation. These findings suggest that antimetabolites could improve overall patient well-being and daily functioning