Physiological consequences of intermittent exercise during compensable and uncompensable heat stress.

Time-weighted averaging is a traditional method used in heat stress analyses to approximate, in terms of a single continuous level of heat production, the rate of heat production from complex intermittent exercise patterns. Physiological responses during intermittent and continuous exercise were studied in four subjects exposed to heat stress in which evaporation was either free or severely restricted. Intermittent work consisted of repeated 10-min exercise-rest patterns. Continuous work was at the time-weighted average of intermittent exercise: 3.3 mets. When heat stress was uncompensable, intermittent work induced more physiological strain than continuous work: endurance time was 14 min less (P less than 0.05); core temperature at 60 min was 0.40 degrees C higher (P less than 0.05); and, after 30 min of exposure, the rate of core temperature rise was 33% greater. The difference in the rate of heat storage was not satisfactorily explained by a discrepancy in the average rate of heat production or in the calculated rate of surface heat loss. Alternatively, the results may be partially explained by interruptions in the usual rate of heat transport via the cutaneous circulation. These interruptions may be caused by nonthermal factors associated with postural and work load transitions. Although the mechanisms are not totally understood, it is clear that application of the time-weighted averaging method can lead to erroneous overprediction of endurance time and should be applied with discretion.     

Migrating Montagu's harriers frequently interrupt daily flights in both Europe and Africa

Time budgets are a powerful but hitherto seldom used way to study how migrants organise their bi‐annual travels. We studied daily time budgets of travelling Montagu's harriers Circus pygargus, based on GPS tracking data, in which we were particularly interested in how time budgets differ between regions and seasons, and are affected by wind. We found that Montagu's harriers used a relatively broad daily time window for travelling by starting daily travels just after sunrise and ending daily travels just before sunset. Occasionally, flights were extended into the night. Montagu's harriers frequently interrupted their daily flights for on average 1.5 h d^–1. These interruptions occurred in all regions and seasons. The tracking data during interruptions suggested two different behaviours: in 41% of all interruptions the birds were moving (presumed foraging,) and in 32% they were stationary (presumed resting; the remaining interruptions could not be classified). The interruptions for foraging indicate that Montagu's harriers have a fly‐and‐forage migration strategy (i.e. combine travelling and foraging on the same day), but the interruptions for resting illustrate that their travels comprise of more than fly‐and‐forage behaviour alone. The large number of interruptions for foraging in the Sahara Desert indicates that this region is less hostile for a migrating raptor than presumed previously. Importantly, harriers spent more time on interruptions for resting on days with stronger headwinds, suggesting that interruptions for resting serve a function of waiting for more favourable weather conditions. Daily variation in time budgets was largely explained by wind; harriers flew more hours per day, and interrupted their flights fewer hours per day, on days they experienced stronger tailwinds. In contrast, time budgets were similar between regions and seasons, suggesting that wind rather than landscape and season shape travel routines of Montagu's harriers.     

EXPERIMENTAL CONTROL OF FLOWERING IN LEMNA I. GENERAL METHODS. PHOTOPERIODISM IN L. PEPUSILLA 6746

Hillman , William S. (Yale U., New Haven, Conn.) Experimental control of flowering in Lemna. I. General methods. Photoperiodism in L. perpusilla 6746. Amer. Jour. Bot. 46(6): 466–473. Illus. 1959.—Lemna perpusilla strain 6746 flowers as a typical short-day plant when grown aseptically in Hutner's medium (containing ethylenediaminetetraacetic acid, [EDTA]) at 26–28°C. A method is described for quantitatively assaying the degree of flowering in a culture. Maximal flowering takes place under photoperiods of 6–11 hr., and none under photoperiods exceeding 15 hr. The flower-promoting effects of long nights are inhibited by brief interruptions with red light, such interruptions being most effective in the middle of the dark period. A single long night will cause the subsequent production of flowering fronds, but vegetative growth in the culture is resumed after a time. Only frond primordia at a very early stage of development appear to be sensitive to induction. Quantitative flowering experiments lasting a week or less can easily be performed with this plant; it is ideally suited for studies of the effects of light, darkness, temperature, organic compounds and other factors under highly controlled conditions.     

Floral Inhibition of Biloxi Soybean During a 72-hour Cycle

The inhibitory effect of light interruptions given during the photophobe phases of a 72-hour cycle was studied with Biloxi soybean [Glycine max (L.) Merr.]. The basic 72-hour cycle consisted of 8 hours of light followed by 64 hours of darkness and was repeated 7 times. Supplementary white light treatments given at the twenty-fourth and/or forty-eighth hour of the cycle (photophil phases) promoted the flowering levels of the controls and kept light treatments given at the most inhibitory points from inhibiting flowering completely. Such supplementary light treatments did not affect the time of maximum sensitivity to light interruptions. When 30-minute light breaks were used, maximum inhibition occurred at the 16-, 43-, and 63-hour points. The duration of the light breaks affected the time of maximum inhibition when given during the second photophobe phase. The time of maximum inhibition occurred earlier with 4-hour light breaks than with either 3-minute or 2-hour light interruptions.

Three-minute red light interruptions produced essentially the same effect as 3-minute white light interruptions. Such treatments inhibited flowering completely in the first photophobe phase, inhibited flowering to only a small degree in the second photophobe phase, and inhibited flowering to an intermediate degree in the third photophobe phase. Far-red light interruptions strongly inhibited flowering in the first photophobe phase, especially when given early in the dark period. Three minutes of supplementary white light given at the twenty-fourth or forty-eighth hour of the cycle partially overcame the inhibitory effect of far-red light. Four hours of supplementary white light at these times completely overcame the far-red inhibition.

     

A Semidian Rhythm in the Flowering Response of Pharbitis nil to Far-Red Light: II. The Involvement of Phytochrome

The semidian (~12 h) periodicity in the effect of far-red (FR) interruptions of the light period preceding inductive darkness on flowering in Pharbitis nil appears to be mediated by phytochrome: (a) promotion by interruptions 2 hours before inductive darkness (−2 hours) and inhibition at −8 hours are greater the higher the proportion of FR/R+FR during the interruption; (b) brief FR exposures followed by darkness are even more effective than FR throughout; (c) the effect of brief FR is reversed by subsequent R; (d) R interruptions of an FR background are most promotive at −8 hours, when FR is most inhibitory. Promotive FR interruptions at −2 or −14 hours shorten the critical dark period whereas inhibitory FR interruptions at −8 hours lengthen it. We conclude that the semidian rhythm is controlled by a `timing pool' of phytochrome FR absorbing form (Pfr) which disappears rapidly in darkness: four different estimates from our experiments indicate that Pfr was reduced to the level set by FR within 20 to 45 minutes in darkness. However, flowering may also be influenced by a `metabolic pool' of Pfr with a delayed loss in darkness, the time of which can be advanced or retarded by shifting the semidian rhythm.     

Management of interruptions in radiotherapy treatments: Adaptive implementation in high workload sites

Owing to predictable or unpredictable causes, interruptions may arise during therapy. On average, the extension of fractionated radiotherapy treatments is prone to be delayed by several weeks and interruptions can come up extending overall treatment time (OTT). Clonogenic cells of aggressive tumors might benefit from this situation, modifying local control (LC).Preserving treatment quality in radiotherapy is an essential issue for the treatment outcome, and our institution is increasingly concerned about this line of work.Establishing some objective criteria to schedule patients that have suffered interruptions along their treatments is of capital importance and not a trivial issue. Publications strongly encourage departments to minimize the effect of lag periods during treatments. Therefore, in July 2017, our facility implemented the so called ‘Protocol to Manage Interruptions in Radiotherapy’, based on a scoring system for patient categorization that considers not only histology but also associated comorbidity and sequence of the therapy.     

Interruptions to foraging and learning in a changing environment

Many resources are both stochastic and variable in their average profitability. Animals have to sample them to track their current states, but whether it is economic to attempt this depends on many factors. Furthermore, there are many interruptions and distractions from foraging (e.g. escape from predators, bad weather, displacement by competitors) which interfere with the acquisition of information. We present a dynamic model of foraging in a stochastic and varying environment, under the constant threat of interruption, to investigate this very general problem. A forager faces two foraging options, one of which provides a known and constant reward, the other providing a reward that is not only stochastic, but whose mean payoff varies in time. The forager has to learn which option has the highest current payoff by sampling. However, interruptions to foraging can occur at any time, the timing and duration of which are beyond the animal's control. When there is a small probability of foraging being interrupted, the forager should forage extensively on the unknown option, but as the probability of interruptions is increased, there is a sudden transition to foraging only on the known option. This occurs because interruptions affect both the level of information required to make exploitation of the unknown option profitable, and the ability to acquire and maintain that information. At what probability of being interrupted this threshold emerges is affected by the value of learning about the unknown option and the duration of interruptions. We discuss the generality of our results with reference to the pervasive problem of updating information in the face of different types of interruption. Copyright 1999 The Association for the Study of Animal Behaviour.     

Asymptotic analysis of an epidemic model with primary and secondary infection

For many biological systems, the behavior of interest is contained in the evolution of transients rather than in the stability of equilibria. These include systems in which perturbations and interruptions occur on a time scale much shorter than the equilibration time, and those in which any final equilibrium is sensitive to initial conditions. In this article, we examine a model of fungal root disease in a crop involving primary and secondary infection mechanisms. This system is subject to regular interruptions in the form of harvesting and sowing. Using an asymptotic approach in which certain parameter values are assumed to be small, the model can be broken down into a set of simpler subsystems respresenting recognizable biological mechanisms. These linear models can be solved to give closed-form analytical solutions for transient evolution. From this information, it is possible to construct an annual map of disease severity in the crop, and determine the parameter values under which the infection will bulk up or fade out.     

Interruption-deficient mutants of bacteriophage T5 I. Isolation and general properties.

Mutations of bacteriophage T5 were isolated which lack one or more of the natural single-chain interruptions that occur in the mature DNA of this virus. Interruption-deficient mutants were detected by screening survivors of hydroxylamine mutagenesis for altered DNA structure by electrophoresis in agarose slab gels. Over 60 independent mutants were isolated from a survey of approximately 800 phages particles. All of the mutants were viable and could be grouped into two classes. Mutants in one class lacked one of the localized sites where interruptions occur in T5 DNA. To date, mutants that affect five different sites have been obtained. Mutants in the other class were essentially free from interruptions or had a reduced frequency of interruptions throughout the genome. The members of this class included several amber mutants. Complementation tests indicated that at least two genes are required for the presence of interruptions in mature T5 DNA.     

Physical map of bacteriophage BF23 DNA: terminal redundancy and localization of single-chain interruptions.

The DNA of bacteriophage BF23 possesses two structural features, localized single-chain interruptions and a large terminal repetition, previously described for T5, a closely related virus. As is the case for T5, single-chain interruptions occur with variable frequencies at a small number of fixed sites within one strand of the double-stranded BF23 genome. The sites where interruptions occur with the highest frequencies were napped by an electrophoretic analysis of the single-stranded fragments produced by denaturation of BF23 DNA. The positions of these fragments were determined by degrading BF23 DNA to various extents with lambda exonuclease and observing the relative order with which they were (i) degraded or (ii) released intact from the undenatured duplex. The exact locations of the interruptions were determined from analysis of analogous duplex fragments produced by degrading exonuclease III-treated BF23 DNA with a single-strand-specific endonuclease. BF23 has five principal sites (located at 7.9, 18.7, 32.4, 65.8, and 99.6% from the left end of the DNA) where interruptions occur in most molecules. The principal interruptions in T5 DNA occur at similar positions. The locations of eight secondary interruptions in BF23 DNA were also determined. In general, BF23 DNA has fewer secondary interruptions than t5 dna, although there is at least one location where an interruption occurs with a greater frequency in BF23. The presence of a terminal repetition in BF23 DNA was demonstrated by annealing ligase-repaired molecules that had been partially digested with lambda exonuclease. If the complementary sequences at both ends of the DNA were exposed by exonuclease treatment, the duplex segment that resulted from annealing could be released by digestion with a single-strand-specific endonuclease. This segment was analyzed by agarose gel electrophoresis and found to represent 8.4% of BF23 DNA.     

A general framework for understanding the effects of variability and interruptions on foraging behaviour

A general framework for analysing the effects of variability and the effects of interruptions on foraging is presented. The animal is characterised by its level of energetic reserves, x. We consider behaviour over a period of time [0,T]. A terminal reward function R(x) determines the expected future reproductive success of an animal with reserves x at time T. For any state x at a time in the period, we give the animal a choice between various options and then constrain it to follow a background strategy. The best option is the one that maximizes expected future reproductive success. Using this framework, we show that sensitivity to variability in amount of energy gained is logically distinct from sensitivity to variability in the time at which food is obtained. We also show that incorporating interruptions results in both a preference for variability in time and a preference for a reward followed by a delay as opposed to the same delay before the reward.     

Daphnia magna shows reduced infection upon secondary exposure to a pathogen

Previous pathogen exposure is an important predictor of the probability of becoming infected. This is deeply understood for vertebrate hosts, and increasingly so for invertebrate hosts. Here, we test if an initial pathogen exposure changes the infection outcome to a secondary pathogen exposure in the natural host–pathogen system Daphnia magna and Pasteuria ramosa. Hosts were initially exposed to an infective pathogen strain, a non-infective pathogen strain or a control. The same hosts underwent a second exposure, this time to an infective pathogen strain, either immediately after the initial encounter or 48 h later. We observed that an initial encounter with a pathogen always conferred protection against infection compared with controls.     

Effects of differential alcohol dehydrogenase activity on the developmental toxicity of ethanol in Drosophila melanogaster

The role of alcohol dehydrogenase (ADH) activity in ethanol toxicity was investigated in Drosophila melanogaster. Flies from three congenic Adh strains (high, medium, and low ADH activity) were allowed to deposit eggs on medium containing 0, 4, or 8% ethanol. The resulting larvae were allowed to complete their development in the medium, and emerging flies were examined for defects. Flies with high ADH activity had malformation incidences of 0.8, 2.4, and 5.2% at 0, 4, and 8% ethanol, respectively. The comparable incidences for the low ADH strain were 1.0, 4.1, and 8.4%, while those for the medium ADH strain were intermediate in value. These results indicate that ethanol teratogenesis may be inversely related to ADH activity. When larvae were treated with ethanol for different lengths of time during development, the incidence of defects in flies from the high ADH strain was 3.9% when exposure started at the first instar and 3.09% when exposure started at the third instar. Results of the same exposures for the intermediate ADH strain were 5.2 and 3.4%, respectively, while those for the low ADH strain were 6.9 and 5.5%, respectively. Thus, length of ethanol exposure was directly related to the increased incidence of malformations in all tested Drosophila strains. For all tested strains, defect incidences appeared to be dose-related as well, regardless of length of exposure. ADH in Drosophila has a dual function and thus can catalyze oxidation of both ethanol and its toxic metabolite, acetaldehyde. This suggests that ethanol is the proximate teratogen in Drosophila.     

Folding delay and structural perturbations caused by type IV collagen natural interruptions and nearby Gly missense mutations

The standard collagen triple helix requires Gly as every third residue in the amino acid sequence, yet all nonfibrillar collagens contain sites where this repeating pattern is interrupted. To explore the effects of such natural interruptions on the triple helix, a 4- or 15-residue sequence from human basement membrane type IV collagen was introduced between (Gly-Xaa-Yaa)(n) domains within a recombinant bacterial collagen. The interruptions had little effect on melting temperature, consistent with the high thermal stability reported for nonfibrillar collagens. Although the 4-residue interruption cannot be accommodated within a standard triple helix, trypsin and thermolysin resistance indicated a tightly packed structure. Central residues of the 15-residue interruption were protease-susceptible, whereas residues near the (Gly-Xaa-Yaa)(n) boundary were resistant, supporting a transition from an alternate conformation to a well packed triple helix. Both interruptions led to a delay in triple-helix folding, with the 15-residue interruption causing slower folding than the 4-residue interruption. These results suggest that propagation through interruptions represents a slow folding step. To clarify the relation between natural interruptions and pathological mutations, a Gly to Ser missense mutation was placed three triplets away from the 4-residue interruption. As a result of this mutation, the 4-residue interruption and nearby triple helix became susceptible to protease digestion, and an additional folding delay was observed. Because Gly missense mutations that cause disease are often located near natural interruptions, structural and folding perturbations arising from such proximity could be a factor in collagen genetic diseases.     

Multiple responses to increasing spring temperatures in the breeding cycle of blue and great tits (Cyanistes caeruleus,Parus major)

Many bird species start laying their eggs earlier in response to increasing spring temperatures, but the causes of variation between and within species have not been fully explained. Moreover, synchronization of the nestling period with the food supply not only depends on first‐egg dates but also on additional reproductive parameters including laying interruptions, incubation time and nestling growth rate. We studied the breeding cycle of two sympatric and closely related species, the blue tit Cyanistes caeruleus and the great tit Parus major in a rich oak‐beech forest, and found that both advanced their mean first‐egg dates by 11–12 days over the last three decades. In addition, the time from first egg to fledging has shortened by 2–3 days, through a decrease in laying interruptions, incubation time (not statistically significant) and nestling development time. This decrease is correlated with a gradual increase of temperatures during laying, suggesting a major effect of the reduction in laying interruptions. In both species, the occurrence of second clutches has strongly decreased over time. As a consequence, the average time of fledging (all broods combined) has advanced by 15.4 and 18.6 days for blue and great tits, respectively, and variance in fledging dates has decreased by 70–75%. Indirect estimates of the food peak suggest that both species have maintained synchronization with the food supply. We found consistent selection for large clutch size, early laying and short nest time (laying to fledging), but no consistent changes in selection over time. Analyses of within‐individual variation show that most of the change can be explained by individual plasticity in laying date, fledging date and nest time. This study highlights the importance of studying all components of the reproductive cycle, including second clutches, in order to assess how natural populations respond to climate change.     

Increased inactivation of Saccharomyces cerevisiae by protraction of UV irradiation.

The principle of equi-effectivity of the product of intensity and exposure time (principle of Bunsen-Roscoe) of UV irradiation has been assumed to be valid for the inactivation of microorganisms in general. Earlier studies claimed higher survival of Escherichia coli B/r with fractionated irradiation compared with single-exposure survival. However, data on the inactivation effect of protraction of UV irradiation are not available. By means of a specially designed UV irradiation apparatus which secured absolute UV dose measurements throughout the experiments, the effects of variation of UV irradiation intensities (253.7 nm) and exposure times were tested on the inactivation of a bacterial virus (Staphylococcus aureus phage A994), a vegetative bacterial strain (E. coli ATCC 25922), and bacterial spores (Bacillus subtilis ATCC 6633) as well as three haploid laboratory strains (RC43a, YNN281, and YNN282) and two diploid strains (commercial bakery yeast strain and laboratory strain YNN281 x YNN282) or yeast (Saccharomyces cerevisiae) and spores of the latter diploid yeast strain. Each test organism was exposed to three UV intensities (0.02, 0.2, and 2 W/m2), with corresponding exposure times resulting in three dose levels for each intensity. Differences in inactivation rates were tested by analyses of variance and Newman-Keuls tests. Virus and bacteria showed no differences in inactivation rates by variation of intensities and exposure times within selected UV doses; hence, the principle of Bunsen-Roscoe could not be rejected for these strains. However, in the eukaryotic test strains of S. cerevisiae longer exposure times with lower intensities led to enhanced inactivation in both haploid and diploid strains, with a more pronounced effect in the diploid yeast strains, whereas in yeast spores in this dose rate effect could not be observed.     

Viral Dynamics during Structured Treatment Interruptions of Chronic Human Immunodeficiency Virus Type 1 Infection

Although antiviral agents which block human immunodeficiency virus (HIV) replication can result in long-term suppression of viral loads to undetectable levels in plasma, long-term therapy fails to eradicate virus, which generally rebounds after a single treatment interruption. Multiple structured treatment interruptions (STIs) have been suggested as a possible strategy that may boost HIV-specific immune responses and control viral replication. We analyze viral dynamics during four consecutive STI cycles in 12 chronically infected patients with a history (>2 years) of viral suppression under highly active antiretroviral therapy. We fitted a simple model of viral rebound to the viral load data from each patient by using a novel statistical approach that allows us to overcome problems of estimating viral dynamics parameters when there are many viral load measurements below the limit of detection. There is an approximate halving of the average viral growth rate between the first and fourth STI cycles, yet the average time between treatment interruption and detection of viral loads in the plasma is approximately the same in the first and fourth interruptions. We hypothesize that reseeding of viral reservoirs during treatment interruptions can account for this discrepancy, although factors such as stochastic effects and the strength of HIV-specific immune responses may also affect the time to viral rebound. We also demonstrate spontaneous drops in viral load in later STIs, which reflect fluctuations in the rates of viral production and/or clearance that may be caused by a complex interaction between virus and target cells and/or immune responses.     

赤拟谷盗的磷化氢敏感和抗性品系体内羧酸酯酶的活性比较

本文比较测定了赤拟谷盗Tribolium castaneum(Herbst)的磷化氢抗性(Rf=327)和敏感品系害虫的羧酸酯酶活性,研究了该害虫同一品系不同个体间羧酸酯酶的活性差异,比较了两品系害虫在系列磷化氢浓度下熏蒸24h和6.94×10-2mg/L磷化氢浓度下熏蒸不同时间的羧酸酯酶活性。主要结果为:未熏蒸的抗性害虫幼虫和蛹体内的羧酸酯酶活性分别高于敏感品系的1.37和1.16倍;敏感和抗性害虫同品系内不同个体间羧酸酯酶活性分布频率都存在明显差异,抗性害虫中酶活性大的个体数量占的比例较大;磷化氢浓度分别为0.69×10-2、2.78×10-2、5.56×10-2、8.33×10-2和11.11×10-2mg/L时都可导致敏感害虫羧酸酯酶的活性降低,但活性受抑制的程度不因浓度高低呈相应的增减。浓度分别为5.56×10-2、11.11×10-2、13.89×10-2、20.83×10-2和27.78×10-2mg/L的熏蒸中抗性害虫体内酶活性增加,且活性增高的程度与浓度增减也不呈对应变化。在6.94×10-2mg/L磷化氢浓度下熏蒸不同时间的结果中,敏感害虫的酶活性随时间延长而下降,抗性害虫的活性则随时间延长而增大。研究表明赤拟谷盗对磷化氢的抗性可能与羧酸酯酶的活性增加有关。