scholarly journals The effects of sex on extinction dynamics and evolutionary rescue of Chlamydomonas reinhardtii depend on the rate of environmental change

2019 ◽  
Author(s):  
Nikola Petkovic ◽  
Nick Colegrave
Keyword(s):  
Environmental Change ◽  
Sexual Reproduction ◽  
Chlamydomonas Reinhardtii ◽  
Population Size ◽  
Experimental Studies ◽  
High Rate ◽  
Extinction Rate ◽  
Mode Of Reproduction ◽  
Environmental Deterioration ◽  
Evolutionary Rescue

AbstractThe continued existence of sex despite many costs it entails still lacks an adequate explanation. Previous experimental studies demonstrated that sex enhances the rate of adaptation in changing environments. To the best of our knowledge, no experimental study that investigated the effects of sex on adaptation has manipulated the rate of environmental change, which is negatively correlated with the probability of population survival. Since the patterns of adaptation (adaptive walk) depend on the rate of environmental change, the overall effects of sex may also be altered by this factor.To investigate the interplay of sex and the rate of environmental deterioration, we carried out a long-term selection experiment with a unicellular alga (Chlamydomonas reinhardtii), by manipulating mode of reproduction (asexual or sexual populations) and the rate of environmental deterioration (an increase of salt concentration). We monitored both the population size and extinction dynamics and estimated the probability of evolutionary rescue.We detected a faster decline of population size in the asexual group relative to both the obligate sexual and facultative sexual group, irrespective of the rate of environmental deterioration. The results revealed significant interaction between mode of reproduction and the rate of environmental deterioration on extinction rate of experimental populations. Obligate sexual reproduction was advantageous under the intermediate rate of environmental deterioration, while facultative sexuality was favoured under the high rate of environmental deterioration. The populations within the obligate sexual group were most likely to adapt to grow in conditions lethal for the ancestral populations, irrespective of the rate of environmental deterioration.To the best of our knowledge, this is the first study which indicates that different modes of sexual reproduction will be beneficial (slower extinction rate) at different rates of environmental deterioration and that obligate sexuality maximizes the probability of adaptation irrespective of the rate of environmental deterioration.

scholarly journals Environmental fluctuations can promote evolutionary rescue in high-extinction-risk scenarios

2020 ◽  
Vol 287 (1932) ◽  
pp. 20201144
Author(s):  
James H. Peniston ◽  
Michael Barfield ◽  
Andrew Gonzalez ◽  
Robert D. Holt
Keyword(s):  
High Risk ◽  
Environmental Change ◽  
Population Size ◽  
Extinction Risk ◽  
Environmental Variation ◽  
Stochastic Simulations ◽  
Initial Population ◽  
Risk Scenarios ◽  
Evolutionary Rescue ◽  
Environmental Fluctuations

Substantial environmental change can force a population onto a path towards extinction, but under some conditions, adaptation by natural selection can rescue the population and allow it to persist. This process, known as evolutionary rescue, is believed to be less likely to occur with greater magnitudes of random environmental fluctuations because environmental variation decreases expected population size, increases variance in population size and increases evolutionary lag. However, previous studies of evolutionary rescue in fluctuating environments have only considered scenarios in which evolutionary rescue was likely to occur. We extend these studies to assess how baseline extinction risk (which we manipulated via changes in the initial population size, degree of environmental change or mutation rate) influences the effects of environmental variation on evolutionary rescue following an abrupt environmental change. Using a combination of analytical models and stochastic simulations, we show that autocorrelated environmental variation hinders evolutionary rescue in low-extinction-risk scenarios but facilitates rescue in high-risk scenarios. In these high-risk cases, the chance of a run of good years counteracts the otherwise negative effects of environmental variation on evolutionary demography. These findings can inform the development of effective conservation practices that consider evolutionary responses to abrupt environmental changes.

A Study on the Effects of Strain Rates on Characteristics of Brain Tissue

2017 ◽  
Author(s):  
Mohammad Hosseini Farid ◽  
Ashkan Eslaminejad ◽  
Mariusz Ziejewski ◽  
Ghodrat Karami
Keyword(s):  
Strain Rate ◽  
Brain Tissue ◽  
Mechanical Load ◽  
Experimental Studies ◽  
High Rate ◽  
Dynamic Strain ◽  
Strain Rates ◽  
Compression Tests ◽  
Static Strain ◽  
The Brain

Traumatic brain injury (TBI) often happens when the brain tissue undergoes a high rate mechanical load. Although numerous research works have been carried out to study the mechanical characterization of brain matter under quasi-static (strain rate ≤ 100 S−1) loading but a limited amount of experimental studies are available for brain tissue behavior under dynamic strain rates (strain rate ≥ 100 S−1). In this paper, the results of a study on mechanical properties of ovine brain tissue under unconfined compression tests are to be presented. The samples were compressed under uniaxial strain rates of 0.0667, 3.33, 6.667, 33.33, 66.667 and 200 S−1. The brain tissue presents a stiffer response with increasing strain rate, showing a time-dependent behavior. So the hyperelastic-only models are not adequate to exhibit the brain viscoelasticity. Therefore, two hyper-viscoelastic constitutive equations based on power function model and Mooney-Rivlin energy function are applied to the results with quasi-static strain rate (≤ 100 S−1). Good agreement of experimental and theoretical has been achieved for results of the low strain rates. It is concluded that the obtained material parameters from quasi-static tests are not appropriate enough to fit the result with the high strain rate of 200 S−1. The study will further provide new insight into a better understanding of the rate-dependency behavior of the brain tissue under dynamic conditions. This is essential in the development of constitutive material characteristics for an efficient human brain finite element models to predict TBI under impact condition or high motion.

Effects of perfusate buffer capacity on capillary CO2-HCO3(-)-H+ reactions: theory

1991 ◽  
Vol 71 (4) ◽  
pp. 1460-1468 ◽  
Author(s):  
A. Bidani ◽  
T. A. Heming
Keyword(s):  
Carbonic Anhydrase ◽  
Buffer Capacity ◽  
Experimental Studies ◽  
Nonlinear Effects ◽  
Co2 Exchange ◽  
High Rate ◽  
Pulmonary Capillaries ◽  
Sequential Combination ◽  
Time Courses

The importance of perfusate nonbicarbonate buffer capacity (beta nonHCO3) to intracapillary CO2-HCO3(-)-H+ reactions was assessed by theoretical analysis of CO2 exchange in saline-perfused pulmonary capillaries. Time courses for perfusate PCO2, [HCO3-], and [H+] were computed for capillaries containing different activities of luminal vascular carbonic anhydrase and different amounts of perfusate nonbicarbonate buffers. Mobilization of perfusate HCO3- toward CO2 during capillary transit is determined by the availability of HCO3- and H+. A supply of protons from the nonbicarbonate buffer pool is necessary to maintain a high rate of HCO3- dehydration. The analyses indicate that beta nonHCO3 has marked nonlinear effects on transcapillary CO2 exchange and intravascular pH equilibration. These nonlinear effects differ from those previously computed for CO2 reactions in an open system because the present model system consists of a sequential combination of open (within capillary proper) and closed (within postcapillary vasculature) systems. The role of luminal vascular carbonic anhydrase in capillary CO2 reactions is strongly dependent on beta nonHCO3. Perfusate nonbicarbonate buffer capacity must be considered when the results of experimental studies of transcapillary CO2 exchange and/or intravascular pH equilibration are interpreted.

scholarly journals Avoiding extinction under nonlinear environmental change: models of evolutionary rescue with plasticity

2021 ◽  
Vol 17 (12) ◽  
Author(s):  
Philip B. Greenspoon ◽  
Hamish G. Spencer
Keyword(s):  
Phenotypic Plasticity ◽  
Environmental Change ◽  
Environmental Changes ◽  
Extinction Risk ◽  
Current Theory ◽  
Species At Risk ◽  
Adaptive Genetic Variation ◽  
Change Models ◽  
Numerous Species ◽  
Evolutionary Rescue

Rapid environmental changes are putting numerous species at risk of extinction. For migration-limited species, persistence depends on either phenotypic plasticity or evolutionary adaptation (evolutionary rescue). Current theory on evolutionary rescue typically assumes linear environmental change. Yet accelerating environmental change may pose a bigger threat. Here, we present a model of a species encountering an environment with accelerating or decelerating change, to which it can adapt through evolution or phenotypic plasticity (within-generational or transgenerational). We show that unless either form of plasticity is sufficiently strong or adaptive genetic variation is sufficiently plentiful, accelerating or decelerating environmental change increases extinction risk compared to linear environmental change for the same mean rate of environmental change.

scholarly journals Population size mediates the contribution of high-rate and large-benefit mutations to parallel evolution

2021 ◽  
Author(s):  
Martijn F. Schenk ◽  
Mark P. Zwart ◽  
Sungmin Hwang ◽  
Philip Ruelens ◽  
Edouard Severing ◽  
...  
Keyword(s):  
Population Size ◽  
Parallel Evolution ◽  
Point Mutations ◽  
High Rate ◽  
Structural Variants ◽  
Bacterial Populations ◽  
Fitness Effects ◽  
Different Types ◽  
Large Benefit

Both mutations with large benefits and mutations occurring at high rates may cause parallel evolution, but their contribution is expected to depend on population size. We show that small and large bacterial populations adapt to a novel antibiotic using similar numbers, but different types of mutations. Small populations repeatedly substitute similar high-rate structural variants, including the deletion of a nonfunctional β-lactamase, and evolve modest resistance levels. Hundred-fold larger populations more frequently use the same low-rate, large-benefit point mutations, including those activating the β-lactamase, and reach 50-fold higher resistance levels. Our results demonstrate a key role of clonal interference in mediating the contribution of high-rate and large-benefit mutations in populations of different size, facilitated by a tradeoff between rates and fitness effects of different mutation classes.

scholarly journals Hypertension, a Moving Target in COVID-19

2021 ◽  
Vol 128 (7) ◽  
pp. 1062-1079
Author(s):  
Carmine Savoia ◽  
Massimo Volpe ◽  
Reinhold Kreutz
Keyword(s):  
Global Health ◽  
Angiotensin Receptor Blockers ◽  
Experimental Studies ◽  
Renin Angiotensin System ◽  
Host Cells ◽  
High Rate ◽  
Direct Role ◽  
Pressure Lowering ◽  
Ras Blockers

Coronavirus disease 2019 (COVID-19) caused by severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) associates with a considerable high rate of mortality and represents currently the most important concern in global health. The risk of more severe clinical manifestation of COVID-19 is higher in males and steeply raised with age but also increased by the presence of chronic comorbidities. Among the latter, early reports suggested that arterial hypertension associates with higher susceptibility to SARS-CoV-2 infection, more severe course and increased COVID-19–related deaths. Furthermore, experimental studies suggested that key pathophysiological hypertension mechanisms, such as activation of the renin-angiotensin system (RAS), may play a role in COVID-19. In fact, ACE2 (angiotensin-converting-enzyme 2) is the pivotal receptor for SARS-CoV-2 to enter host cells and provides thus a link between COVID-19 and RAS. It was thus anticipated that drugs modulating the RAS including an upregulation of ACE2 may increase the risk for infection with SARS-CoV-2 and poorer outcomes in COVID-19. Since the use of RAS-blockers, ACE inhibitors or angiotensin receptor blockers, represents the backbone of recommended antihypertensive therapy and intense debate about their use in the COVID-19 pandemic has developed. Currently, a direct role of hypertension, independent of age and other comorbidities, as a risk factor for the SARS-COV-2 infection and COVID-19 outcome, particularly death, has not been established. Similarly, both current experimental and clinical studies do not support an unfavorable effect of RAS-blockers or other classes of first line blood pressure lowering drugs in COVID-19. Here, we review available data on the role of hypertension and its management on COVID-19. Conversely, some aspects as to how the COVID-19 affects hypertension management and impacts on future developments are also briefly discussed. COVID-19 has and continues to proof the critical importance of hypertension research to address questions that are important for global health.

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