Evolutionary rescue can be impeded by temporary environmental amelioration

Rapid evolutionary adaptation has the potential to rescue from extinction populations experiencing environmental changes. Little is known, however, about the impact of short‐term environmental fluctuations during long‐term environmental deterioration, an intrinsic property of realistic environmental changes. Temporary environmental amelioration arising from such fluctuations could either facilitate evolutionary rescue by allowing population recovery (a positive demographic effect) or impede it by relaxing selection for beneficial mutations required for future survival (a negative population genetic effect). We address this uncertainty in an experiment with populations of a bacteriophage virus that evolved under deteriorating conditions (gradually increasing temperature). Periodic environmental amelioration (short periods of reduced temperature) caused demographic recovery during the early phase of the experiment, but ultimately reduced the frequency of evolutionary rescue. These experimental results suggest that environmental fluctuations could reduce the potential of evolutionary rescue.     

The microenvironment of naked mole‐rat burrows in East Africa

Naked mole‐rats (Heterocephalus glaber) can be extremely long‐lived and are resistant to cancer. Hence, they have been proposed as a model organism for delayed ageing. Adaptation to a constant hypoxic and hypercapnic environment has been suggested as reason for their apparent ability to tolerate oxidative stress. Nevertheless, little is known about the natural habitat to which the species evolved. Naked mole‐rat burrow environments were assessed in Ethiopia and Kenya. Despite reported thermolability of naked mole‐rats, skin temperature upon capture varied (23.7–35.4°C), mostly within the species’ thermoneutral zone, demonstrating their ability to maintain homoiothermy even under wide fluctuations of burrow temperature (24.6–48.8°C) and humidity (31.2%–92.8%), which are far greater than previously reported. Burrow temperature regularly alternates during the daytime and night‐time, driving convective currents that circulate air in the tunnels. Consequently, concentrations of CO₂ and O₂ in burrows only slightly deviated from surface atmosphere. This contradicts the assumption of constant hypoxia/hypercapnia in subterranean burrows. In addition to diffusion, animal movement and occasional wind‐driven ventilation, our data support the temperature‐driven convective model of circulation. The naked mole‐rat burrow is a relatively normoxic subterranean microenvironment with considerable fluctuations in temperature and humidity.     

Experimental study on convective heat transfer coefficient of the human body

1. 1. The convective heat transfer coefficient of the human body is essential to predict convective heat loss from the body.

2. 2. The object of this paper is to calculate the convective heat transfer coefficient of the human body using heat flow meters and to estimate the thermally equivalent sphere and cylinder to the human body.

3. 3. The experimental formulae of the convective heat transfer coefficient for the whole body were obtained by regression analysis for natural, forced and mixed convection.

4. 4. Diameters of the thermally equivalent sphere and cylinder of the human body were calculated as 12.9 and 12.2 cm, respectively.

Resonance of plankton communities with temperature fluctuations

The interplay between intrinsic population dynamics and environmental variation is still poorly understood. It is known, however, that even mild environmental noise may induce large fluctuations in population abundances. This is due to a resonance effect that occurs in communities on the edge of stability. Here, we use a simple predator-prey model to explore the sensitivity of plankton communities to stochastic environmental fluctuations. Our results show that the magnitude of resonance depends on the timescale of intrinsic population dynamics relative to the characteristic timescale of the environmental fluctuations. Predator-prey communities with an intrinsic tendency to oscillate at a period T are particularly responsive to red noise characterized by a timescale of τ = T/2π. We compare these theoretical predictions with the timescales of temperature fluctuations measured in lakes and oceans. This reveals that plankton communities will be highly sensitive to natural temperature fluctuations. More specifically, we demonstrate that the relatively fast temperature fluctuations in shallow lakes fall largely within the range to which rotifers and cladocerans are most sensitive, while marine copepods and krill will tend to resonate more strongly with the slower temperature variability of the open ocean.     

Plastic microfluidic chip for continuous-flow polymerase chain reaction: simulations and experiments

A continuous flow polymerase chain reaction (CF-PCR) device comprises a single fluidic channel that is heated differentially to create spatial temperature variations such that a sample flowing through it experiences the thermal cycling required to induce amplification. This type of device can provide an effective means to detect the presence of a small amount of nucleic acid in very small sample volumes. CF-PCR is attractive for global health applications due to its less stringent requirements for temperature control than for other designs. For mass production of inexpensive CF-PCR devices, fabrication via thermoplastic molding will likely be necessary. Here we study the optimization of a PCR assay in a polymeric CF-PCR device. Three channel designs, with varying residence time ratios for the three PCR steps (denaturation, annealing, and extension), were modeled, built, and tested. A standardized assay was run on the three different chips, and the PCR yields were compared. The temperature gradient profiles of the three designs and the residence times of simulated DNA molecules flowing through each temperature zone were predicted using computational methods. PCR performance predicted by simulation corresponded to experimental results. The effects of DNA template size and cycle time on PCR yield were also studied. The experiments and simulations presented here guided the CF-PCR chip design and provide a model for predicting the performance of new CF-PCR designs prior to actual chip manufacture, resulting in faster turn around time for new device and assay design. Taken together, this framework of combined simulation and experimental development has greatly reduced assay development time for CF-PCR in our lab.     

微流控振荡流PCR快速检测单增李斯特氏菌

一种高通量振荡流PCR微流控技术已被成功开发,借此来快速检测食品致病菌-单增李斯特氏菌(L.monocytogenes).该PCR微流控装置主要由基于LabView的温度控制与采集系统、三个铜加热块以及聚四氟乙烯(PTFE)毛细管等构成.在该微流控装置上,三个铜块维持PCR反应所需要的三个温度,而包埋在铜块沟槽中的PT...     

A Temperature-Monitoring Vaginal Ring for Measuring Adherence

BackgroundProduct adherence is a pivotal issue in the development of effective vaginal microbicides to reduce sexual transmission of HIV. To date, the six Phase III studies of vaginal gel products have relied primarily on self-reporting of adherence. Accurate and reliable methods for monitoring user adherence to microbicide-releasing vaginal rings have yet to be established.MethodsA silicone elastomer vaginal ring prototype containing an embedded, miniature temperature logger has been developed and tested in vitro and in cynomolgus macaques for its potential to continuously monitor environmental temperature and accurately determine episodes of ring insertion and removal.ResultsIn vitro studies demonstrated that DST nano-T temperature loggers encapsulated in medical grade silicone elastomer were able to accurately and continuously measure environmental temperature. The devices responded quickly to temperature changes despite being embedded in different thickness of silicone elastomer. Prototype vaginal rings measured higher temperatures compared with a subcutaneously implanted device, showed high sensitivity to diurnal fluctuations in vaginal temperature, and accurately detected periods of ring removal when tested in macaques.ConclusionsVaginal rings containing embedded temperature loggers may be useful in the assessment of product adherence in late-stage clinical trials.     

Heat transport by countercurrent blood vessels in the presence of an arbitrary temperature gradient

This paper presents a three-dimensional analysis of the temperature field around a pair of countercurrent arteries and veins embedded in an infinite tissue that has an arbitrary temperature gradient along the axes of the vessels. Asymptotic methods are used to show that such vessels are thermally similar to a highly conductive fiber in the same tissue. Expressions are developed for the effective radius and thermal conductivity of the fiber so that it conducts heat at the same rate that the artery and vein together convect heat and so that its local temperature equals the mean temperature of the vessels. This result allows vascular tissue to be viewed as a composite of conductive materials with highly conductive fibers replacing the convective effects of the vasculature. By characterizing the size and thermal conductivity of these fibers, well-established methods from the study of composites may be applied to determine when an effective conductive model is appropriate for the tissue and vasculature as a whole.     

Physiological mechanisms of thermoregulation in reptiles: a review

The thermal dependence of biochemical reaction rates means that many animals regulate their body temperature so that fluctuations in body temperature are small compared to environmental temperature fluctuations. Thermoregulation is a complex process that involves sensing of the environment, and subsequent processing of the environmental information. We suggest that the physiological mechanisms that facilitate thermoregulation transcend phylogenetic boundaries. Reptiles are primarily used as model organisms for ecological and evolutionary research and, unlike in mammals, the physiological basis of many aspects in thermoregulation remains obscure. Here, we review recent research on regulation of body temperature, thermoreception, body temperature set-points, and cardiovascular control of heating and cooling in reptiles. The aim of this review is to place physiological thermoregulation of reptiles in a wider phylogenetic context. Future research on reptilian thermoregulation should focus on the pathways that connect peripheral sensing to central processing which will ultimately lead to the thermoregulatory response.     

Genotypic diversity and environmental variability affect the invasibility of experimental plant populations

The world is experiencing increasing climatic variability, an ongoing loss of biodiversity and a growing spread of invasive species. Previous experimental studies demonstrated that the invasibility of plant populations is reduced with increasing resident genetic diversity and is promoted by environmental fluctuations, but their combined effect has so far not been considered. In a growth chamber experiment, we tested whether the genotypic diversity of experimental populations of Arabidopsis thaliana (1, 3 or 6 genotypes) and temperature fluctuations affect population invasion by Senecio vulgaris, and how these factors interact. We found that genotypic diversity tended to increase the invasion resistance of experimental plant populations in terms of the biomass ratio between the species, and that temperature fluctuations strongly favoured Arabidopsis (biomass: +49%) over Senecio (–28%). However, there were no interactions between environmental fluctuations and genotypic diversity. Nevertheless, the magnitude of net diversity effects and transgressive overyielding depended on temperature conditions, indicating that increased environmental variability can influence diversity mechanisms. Our study shows that, although genotypic diversity and environmental variability did not interact, these two factors independently affected the invasibility of plant populations.     

Periodic variation in Sr/Ca ratios in statoliths of the Japanese Common Squid Todarodes pacificus Steenstrup, 1880 (Cephalopoda: Ommastrephidae) maintained under constant water temperature

The Japanese Common Squid, Todarodes pacificus Steenstrup, 1880, moves vertically in the water column in time with the natural day-night cycle and this exposes the animal to considerable temperature changes throughout the 24-h period. We considered that this behavior could result in daily fluctuations of the statolith strontium/calcium ratio (Sr/Ca ratio), if this ratio is thermally sensitive, as is found for coral skeletons. To investigate this hypothesis, Japanese Common Squid were reared under constant temperature (15 °C) for 64 days and their statolith Sr/Ca ratios, in the area that had been deposited while in captivity, measured by wavelength dispersive spectrometer. Small repetitive fluctuations were observed in the statolith Sr/Ca ratios of the captive squid (N=5, 2.7-day cycle) but similar fluctuations were also observed in the statoliths of Japanese Common Squid collected from the wild (N=5, 2.4-day cycle). These results imply that the daily vertical movements in the water column are not reflected in the statolith Sr/Ca ratios in the Japanese Common Squid. The observed small repetitive fluctuations are discussed in relation to the periodic feeding activity of the captive squid (1.9-day cycle).     

Jensen’s Inequality and the Impact of Short-Term Environmental Variability on Long-Term Population Growth Rates

It is well established in theory that short-term environmental fluctuations could affect the long-term growth rates of wildlife populations, but this theory has rarely been tested and there remains little empirical evidence that the effect is actually important in practice. Here we develop models to quantify the effects of daily, seasonal, and yearly temperature fluctuations on the average population growth rates, and we apply them to long-term data on the endangered Black-faced Spoonbill (Platalea minor); an endothermic species whose population growth rates follow a concave relationship with temperature. We demonstrate for the first time that the current levels of temperature variability, particularly seasonal variability, are already large enough to substantially reduce long-term population growth rates. As the climate changes, our results highlight the importance of considering the ecological effects of climate variability and not just average conditions.     

Selection in a fluctuating environment leads to decreased genetic variation and facilitates the evolution of phenotypic plasticity

Changes in the environment are expected to induce changes in the quantitative genetic variation, which influences the ability of a population to adapt to environmental change. Furthermore, environmental changes are not constant in time, but fluctuate. Here, we investigate the effect of rapid, continuous and/or fluctuating temperature changes in the seed beetle Callosobruchus maculatus, using an evolution experiment followed by a split-brood experiment. In line with expectations, individuals responded in a plastic way and had an overall higher potential to respond to selection after a rapid change in the environment. After selection in an environment with increasing temperature, plasticity remained unchanged (or decreased) and environmental variation decreased, especially when fluctuations were added; these results were unexpected. As expected, the genetic variation decreased after fluctuating selection. Our results suggest that fluctuations in the environment have major impact on the response of a population to environmental change; in a highly variable environment with low predictability, a plastic response might not be beneficial and the response is genetically and environmentally canalized resulting in a low potential to respond to selection and low environmental sensitivity. Interestingly, we found greater variation for phenotypic plasticity after selection, suggesting that the potential for plasticity to evolve is facilitated after exposure to environmental fluctuations. Our study highlights that environmental fluctuations should be considered when investigating the response of a population to environmental change.     

Extent of adaptation is not limited by unpredictability of the environment in laboratory populations of Escherichia coli

Environmental variability is on the rise in different parts of the earth, and the survival of many species depends on how well they cope with these fluctuations. Our current understanding of how organisms adapt to unpredictably fluctuating environments is almost entirely based on studies that investigate fluctuations among different values of a single environmental stressor such as temperature or pH . How would unpredictability affect adaptation when the environment fluctuates between qualitatively very different kinds of stresses? To answer this question, we subjected laboratory populations of Escherichia coli to selection over ~ 260 generations. The populations faced predictable and unpredictable environmental fluctuations across qualitatively different selection environments, namely, salt and acidic pH . We show that predictability of environmental fluctuations does not play a role in determining the extent of adaptation, although the extent of ancestral adaptation to the chosen selection environments is of key importance.     

Stochastic environmental fluctuations drive epidemiology in experimental host–parasite metapopulations

Environmental fluctuations are important for parasite spread and persistence. However, the effects of the spatial and temporal structure of environmental fluctuations on host–parasite dynamics are not well understood. Temporal fluctuations can be random but positively autocorrelated, such that the environment is similar to the recent past (red noise), or random and uncorrelated with the past (white noise). We imposed red or white temporal temperature fluctuations on experimental metapopulations of Paramecium caudatum, experiencing an epidemic of the bacterial parasite Holospora undulata. Metapopulations (two subpopulations linked by migration) experienced fluctuations between stressful (5°C) and permissive (23°C) conditions following red or white temporal sequences. Spatial variation in temperature fluctuations was implemented by exposing subpopulations to the same (synchronous temperatures) or different (asynchronous temperatures) temporal sequences. Red noise, compared with white noise, enhanced parasite persistence. Despite this, red noise coupled with asynchronous temperatures allowed infected host populations to maintain sizes equivalent to uninfected populations. It is likely that this occurs because subpopulations in permissive conditions rescue declining subpopulations in stressful conditions. We show how patterns of temporal and spatial environmental fluctuations can impact parasite spread and host population abundance. We conclude that accurate prediction of parasite epidemics may require realistic models of environmental noise.     

Membrane fluidity and its roles in the perception of environmental signals

Poikilothermic organisms are exposed to frequent changes in environmental conditions and their survival depends on their ability to acclimate to such changes. Changes in ambient temperature and osmolarity cause fluctuations in the fluidity of cell membranes. Such fluctuations are considered to be critical to the initiation of the regulatory reactions that ultimately lead to acclimation. The mechanisms responsible for the perception of changes in membrane fluidity have not been fully characterized. However, the analysis of genome-wide gene expression using DNA microarrays has provided a powerful new approach to studies of the contribution of membrane fluidity to gene expression and to the identification of environmental sensors. In this review, we focus on the mechanisms that regulate membrane fluidity, on putative sensors that perceive changes in membrane fluidity, and on the subsequent expression of genes that ensures acclimation to a new set of environmental conditions.     

Bioluminescent monitoring of turbulent bioconvection.

Under adjusted experimental conditions, open-to-air cultures of lux gene-engineered Ralstonia eutropha (wholecell biosensors of copper) exhibit bioconvection, which accounts for fluctuating bioluminescence. The power spectrum of bioluminescence intensity fluctuations recorded from a cylindrical sample 9 mm in diameter and approximately 10 mm in height is characterized by a dominant low-frequency oscillation (with a characteristic period of approximately 8-12 min), which is occasionally accompanied by a few weaker oscillations. The corresponding spectral peaks emerge on a high-noise background. The spectra of bioluminescence intensity fluctuations qualitatively resemble the spectra of temperature or fluid velocity fluctuations in an appropriate turbulent thermal convection system. It has been suggested that in a bioconvective system, like in thermal convection systems, the emergence of oscillation reflects the large-scale convective circulation that spans the height of the cylindrical cell. The velocity of large-scale bioconvective circulation was estimated to be 37-48 microm/s. The occasional emergence of weaker-than-dominant oscillations was explained through the coexistence and interaction of the large-scale circulation with, presumably, a gene-expression-related cyclic process (with a characteristic period of approximately 25-50 min).     

Testing a biological mechanism of the insurance hypothesis in experimental aquatic communities

1.  The insurance hypothesis predicts a stabilizing effect of increasing species richness on community and ecosystem properties. Difference among species' responses to environmental fluctuations provides a general mechanism for the hypothesis. Previous experimental investigations of the insurance hypothesis have not examined this mechanism directly.
2.  First, responses to temperature of four protist species were measured in laboratory microcosms. For each species, we measured the response of intrinsic rate of increase ( r ) and carrying capacity ( K ) to temperature.
3.  Next, communities containing pairs of species were exposed to temperature fluctuations. Community biomass varied less when correlation in K between species (but not r ) was more negative, and this resulted from more negative covariances in population sizes, as predicted. Results were contingent on species identity, with findings differing between analyses including or not including communities containing one particular species.
4.  These findings provide the clearest support to date for this mechanism of the insurance hypothesis. Biodiversity, in terms of differences in species' responses to environmental fluctuations (i.e. functional response diversity) stabilizes community dynamics.     

Application of Taylor''s hypothesis to an unsteady convective field for the spectral analysis of turbulence in the aorta

Two types of unsteadiness must be considered when spectral analysis is applied to unsteady turbulence such as that found in the aorta. Firstly, the statistical properties of the turbulence itself change in time and so the definition of spectral density must be reconsidered. Secondly, the turbulent velocity fluctuations, whether they are steady or unsteady, are carried by an unsteady convective velocity which alters their properties as seen by a stationary observer.

In the present study, unsteadiness of turbulence in the latter sense is discussed by applying Taylor's hypothesis of ‘frozen turbulence’ to turbulence with an unsteady convective velocity. If both a ‘frozen’ pattern of turbulence and a constant convective velocity are assumed, measured frequency spectra can be easily transformed into wavenumber (spatial) spectra, usually as a trivial part of normalisation. In the case of unsteady turbulence, however, the convection velocity is no longer constant and the conventional method can not be used. A new method of estimating the spatial properties of unsteady turbulence is proposed in which the temporal fluctuations of the turbulent velocity are transformed into spatial fluctuations using a nonlinear transformation based upon the unsteady convective velocity. The transformed data are then Fourier analysed to yield a wavenumber spectrum directly.

The proposed method is applied to data obtained in the canine ascending aorta. Spectra calculated by the proposed method differ significantly from those obtained by the conventional method, particularly in the high wavenumber (or frequency) range. This difference is discussed as an ‘aliasing’ phenomenon that has also been known in steady turbulence.     

Biodiversity enhancement induced by environmental noise

Recent research in ecology has concentrated on the effect of environmental changes on ecosystem structure and function. In most cases the focus has been on how ecosystems respond to changes in the mean values of environmental parameters, while the impact of changes in the variance has seldom been studied. However, changes in environmental variability may be important. For example, recent climate change predictions indicate that, in addition to trends in the mean values of climate variables, an increase in interannual variability is expected to occur in the near future. How will this increase in the variance of environmental parameters affect the dynamics of terrestrial and aquatic ecosystems? Environmental fluctuations are usually believed to play a "destructive role" in ecosystem dynamics and to act as a source of disturbance, which perturbs the state of a system. However, noise is also known for its "constructive role", i.e., for the ability to create new ordered states in dynamical systems. Here we show that environmental noise may also enhance biodiversity. To this end we develop a conceptual model to show how random environmental fluctuations may favor biodiversity. Noise-induced biodiversity is observed for moderate levels of noise intensity, while it disappears with stronger environmental fluctuations, consistently with the notion underlying the "intermediate disturbance hypothesis".