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1.
The ability to resist desiccation is an important component of biological fitness for terrestrial organisms. Several water balance characteristics have been studied for a strain of laboratory-reared Drosophila mimica and for four populations of D. mimica collected at sites differing in altitude and wetness. In the absence of drinking water, D. mimica are unable to maintain a water balance, even in nearly saturated environments. However, as av () decreases, transpiration does not increase as rapidly as expected and absorption remains nearly constant. The size of the fly is not correlated with its water loss characteristics, but some differences in regulation between the sexes are suggested. 相似文献
2.
Summary Four populations of Drosophila mimica and 1 population of D. kambysellisi collected at sites which differed in wetness were examined for several water balance characteristics. Net water loss per hour increased as av (relative humidity/100) decreased in all populations, but the rate of increase was lower in populations from dry sites. When exposed to 0.70 av, D. kambysellisi, which were from a rain forest, lost water faster and died sooner than did D. mimica. Two D. mimica collecting sites were divided into smaller units based on substrate type at one site and on litter wettness at the other site. The D. mimica at the first site were homogeneous with respect to the water balance properties studied here, but in the second site, there was evidence of population differentiation associated with litter wettness.Supported by research grant NSF DEB77-23370, training grants NIH 5 TO1 GM 00337-16 and NIH 5 T32 GM 07126-02 and a Grant-in-Aid from the Sigma Xi Society 相似文献
3.
Challenge from the simple: some caveats in linearization of the Boyle-van't Hoff and Arrhenius plots
Katkov II 《Cryobiology》2008,57(2):142-149
Some aspects of proper linearization of the Boyle-van’t Hoff (BVH) relationship for calculation of the osmotically inactive volume vb, and Arrhenius plot (AP) for the activation energy Ea are discussed. It is shown that the commonly used determination of the slope and the intercept (vb), which are presumed to be independent from each other, is invalid if the initial intracellular molality m0 is known. Instead, the linear regression with only one independent parameter (vb) or the Least Square Method (LSM) with vb as the only fitting LSM parameter must be applied. The slope can then be calculated from the BVH relationship as the function of vb. In case of unknown m0 (for example, if cells are preloaded with trehalose, or electroporation caused ion leakage, etc.), it is considered as the second independent statistical parameter to be found. In this (and only) scenario, all three methods give the same results for vb and m0. AP can be linearized only for water hydraulic conductivity (Lp) and solute mobility (ωs) while water and solute permeabilities Pw ≡ LpRT and Ps ≡ ωsRT cannot be linearized because they have pre-exponential factor (RT) that depends on the temperature T. 相似文献
4.
The temporal dependence of water exchange between an arthropod and its surroundings fits a mathematical model based on diffusion theory. The model requires that the mass change rate of L. echidnina results from a zeroorder component consisting primarily of water sorption and a first-order component made up largely of water loss. Tentatively, transpiration of water is associated with primarily the tracheal system, and sorption of water primarily with other surfaces. Placing mites in a CO2 atmosphere greatly increased their water loss, but had little effect on sorption of water. The effect of increase in temperature on the sorption rate () and transpiration rate constant (kT) was to increase them. The influence of the activity of the water in the vapour phase in the ambient air (av) was primarily on sorption. 相似文献
5.
K. Gaede 《Experimental & applied acarology》1992,15(3):181-198
The net water vapour exchange ofPhytoseiulus persimilis A.-H. is described. Water loss by transpiration increases progressively with ambient temperature. The transpiration rate is directly proportional to the saturation deficit of the air (15 to 30° C) and at constant temperature linearly dependent on the water vapour activity: mT=–0.81 av+0.91 (for av 0.0 to 0.85 at 20°C).
Phytoseiulus persimilis is able to absorb water vapour from the unsaturated atmosphere. This occurs above a certain threshold (critical equilibrium activity, CEA), which is av=0.9 at 15 to 25°C and increases to av=0.935 at 30°C.The environmental humidity conditions influencingP. persimilis on the leaf surface are described. The diurnal water vapour profile within the laminar layer at the leaf surface includes periods with water vapour values high enough for these mites to utilize their water vapour sorption capability and to restore a previously-suffered water deficit. In addition,P. persimilis shows a positive hygrotactic behaviour when in a state of water deficit.The survival time of starvingP. persimilis is at least doubled when a possibility to absorb water vapour is available. The water balance at limited food resources is discussed. With a food supply (one prey mite, containing about 5.5 g water) every 3 days and a water vapour activity of av=0.76 (20°C), water balance is achieved and the survival time is maximal (approximately 120 days). 相似文献
6.
Female North American house dust mites were found to exchange water with the ambient air from two compartments. At humidities above the critical equilibrium activity (CEA), transpiration out of a single large compartment was observed using HTO as a tracer for water. Total sorption into this compartment was also observed by following changes in the specific radioactivity. The sorption data required that an active process or pump be present. The water in this pump is the second compartment above the CEA. Below the CEA the large compartment could be identified as a compartment characterized by a small transpiration rate constant. The pump below the CEA becomes a rapidly transpiring fast compartment. By separating the water pool into two compartments, it was possible to relate av to k and . The major effect of av on k was related to its effect on the permeability of the cuticle. The influence of av on was different for active and passive sorption. Above the CEA the pump operated at full capacity and active was directly proportional to av. Passive sorption was influenced by av in two ways. The driving force for was further reduced below saturation by the effect of av on the permeability of the exchange surface. 相似文献
7.
In this work, photosystem II (PSII) photochemistry, leaf water potential, and pigment contents of male and female Pistacia lentiscus L. were investigated during a seasonal cycle at three different, arid locations: superior semiarid, inferior semiarid, and arid. The results showed that the gender, season, and the site conditions interacted to influence the quantum yield and pigment contents in P. lentiscus. Predawn leaf water status was determined only by the site and season. The annual patterns of PSII maximum quantum efficiency (Fv/Fm) were characterized by a suboptimal activity during the winter, especially, populations with the more negative water potential exhibited a lower chlorophyll (Chl) a content and chronic photoinhibition irrespective of a gender. We also demonstrated that both photochemical or nonphotochemical mechanisms were involved to avoid the photoinhibition and both of them depended on the season. This plasticity of photosynthetic machinery was accompanied by changes in carotenoids and Chl balance. In the spring, the female Fv/Fm ratio was significantly higher than in male individuals, when the sexual dimorphism occurred during the fruiting stage, regardless of site conditions. P. lentiscus sex-ratio in Mediterranean areas, where precipitations exceeded 500 mm, was potentially female-biased. Among the fluorescence parameters investigated, nonphotochemical quenching coefficient appeared as the most useful one and a correlation was found between Chl a content and Fv/Fm. These results suggest that functional ecology studies would be possible on a large scale through light reflectance analysis. 相似文献
8.
9.
Reduced Nav1.6 Sodium Channel Activity in Mice Increases In Vivo Sensitivity to Volatile Anesthetics
Dinesh Pal Julie M. Jones Stella Wisidagamage Miriam H. Meisler George A. Mashour 《PloS one》2015,10(8)
Nav1.6 is a major voltage-gated sodium channel in the central and peripheral nervous systems. Within neurons, the channel protein is concentrated at the axon initial segment and nodes of Ranvier, where it functions in initiation and propagation of action potentials. We examined the role of Nav1.6 in general anesthesia using two mouse mutants with reduced activity of Nav1.6, Scn8a
medJ/medJ and Scn8a
9J/9J. The mice were exposed to the general anesthetics isoflurane and sevoflurane in step-wise increments; the concentration required to produce loss of righting reflex, a surrogate for anesthetic-induced unconsciousness in rodents, was determined. Mice homozygous for these mutations exhibited increased sensitivity to both isoflurane and sevoflurane. The increased sensitivity was observed during induction of unconsciousness but not during the recovery phase, suggesting that the effect is not attributable to compromised systemic physiology. Electroencephalographic theta power during baseline waking was lower in mutants, suggesting decreased arousal and reduced neuronal excitability. This is the first report linking reduced activity of a specific voltage-gated sodium channel to increased sensitivity to general anesthetics in vivo. 相似文献
10.
The structure of the anode space charge sheath of a vacuum arc is studied with allowance for the dependence of the negative anode fall on the ratio of the directed electron velocity v 0 to the electron thermal velocity v T for different values of the flux density of atoms evaporated from the anode. Poisson’s equation for the sheath potential is solved taking into account the electron space charge, fast cathode ions, and slow ions produced due to the ionization of atoms evaporated from the anode. The kinetic equation for atoms and slow anode ions is solved with allowance for ionization in the collision integral. Analytic solutions for the velocity distribution functions of atoms and slow ions and the density of slow ions are obtained. It is shown that the flux of slow ions substantially affects the spatial distribution of the electric field E(z) in the sheath. As the flux density increases, the nonmonotonic dependence E(z) transforms into a monotonic one and the sheath narrows. For a given flux of evaporated atoms Πa, the increase in the ratio of the directed electron velocity to the electron thermal velocity leads again to a nonmonotonic dependence E(z). As z increases, the electric field first increases, passes through the maximum, decreases, passes through the minimum E min, and then again increases toward the anode. There is a limiting value of the ratio (v 0/v T )* at which E min(z) vanishes. At v 0/v T > (v 0/V T )*, the condition for the existence of a steady-state sheath is violated and the profiles of the field and potential in the sheath become oscillating. The dependence of (v 0/v T )* on the flux density of evaporated atoms Π a is obtained. It is shown that the domain of existence of steady-state solutions in the sheath broadens with increasing Π a . 相似文献
11.
Su–Su Xia An–Wei Yu Li–Dan Zhao Hui–Ying Zhang Wei–Hong Zheng Jin–Song Liu 《Journal of thermal biology》2013
Basal metabolic rate (BMR) is thought to be a major hub in the network of physiological mechanisms connecting life history traits. Evaporative water loss (EWL) is a physiological indicator that is widely used to measure water relations in inter- or intraspecific studies of birds in different environments. In this study, we examined the physiological responses of summer-acclimatized Hwamei Garrulax canorus to temperature by measuring their body temperature (Tb), metabolic rate (MR) and EWL at ambient temperatures (Ta) between 5 and 40 °C. Overall, we found that mean body temperature was 42.4 °C and average minimum thermal conductance (C) was 0.15 ml O2 g−1 h−1 °C−1 measured between 5 and 20 °C. The thermal neutral zone (TNZ) was 31.8–35.3 °C and BMR was 181.83 ml O2 h−1. Below the lower critical temperature, MR increased linearly with decreasing Ta according to the relationship: MR (ml O2 h−1)=266.59–2.66 Ta. At Tas above the upper critical temperature, MR increased with Ta according to the relationship: MR (ml O2 h−1)=−271.26+12.85 Ta. EWL increased with Ta according to the relationship: EWL (mg H2O h−1)=−19.16+12.64 Ta and exceeded metabolic water production at Ta>14.0 °C. The high Tb and thermal conductance, low BMR, narrow TNZ, and high evaporative water production/metabolic water production (EWP/MWP) ratio in the Hwamei are consistent with the idea that this species is adapted to warm, mesic climates, where metabolic thermogenesis and water conservation are not strong selective pressures. 相似文献
12.
《International Biodeterioration》1990,26(6):381-396
The relationship between moisture content and water activity (aw) in cured tobacco was significantly influenced by sugar content. Overall, high sugar tobaccos such as Oriental and Virginia had a higher moisture content at any given water activity compared to low sugar tobaccos such as Burley. Virginia and Burley were both predominantly colonised by Aspergillus and Penicillium spp. Of these, about 80% of isolates could germinate at between 0·75 and 0·85 aw, equivalent to moisture contents of between 18% and 24% in Burley and between 22% and 31% in Virginia. Growth of the dominant Aspergillus and Penicillium spp. was much slower on Virginia and Burley tobacco extract than on malt extract agars over the range 0.85 to 0.98 aw. For some species the optimum aw for growth on tobacco extract medium was altered from that on the richer malt extract agar and for some there was also a significant difference in growth between Virginia and Burley extract agars. The mould-free storage periods for five different tobacco types was influenced by aw. Visible moulding occurred within 7–14 days at 0.85–0.90 aw but only after about six months at 0.70–0.75 aw. There were some differences in rate of moulding between tobacco types as well as in the range of fungi isolated at different aw storage levels. 相似文献
13.
Moisture requirements were evaluated for female adults of spider beetles Mezium affine Boieldieu and Gibbium aequinoctiale Boieldieu to determine how they are differentially adapted for life in a dry environment. Features showing extreme desiccation resistance of M. affine were an impermeable cuticle wherein activation energies (43 kJ/mol) were suppressed, daily water losses as little as 0.3%/day with an associated group effect, a low 64% water content and an impressive ability to survive nearly 3 months with no food and water. Behaviorally, the extended period of water stress and fasting was marked by long intervals of physical inactivity (quiescence), as though dead. These characteristics emphasizing water retention rather than gain are shared by G. aequinoctiale and reflect a typical xerophilic water balance profile. Water uptake was restricted to imbibing liquid, as evidenced by uptake of dye-stained droplets of free water and a critical equilibrium activity of 1.00av, where the inability to absorb water vapor from the air fails to equilibrate declining water levels (gain≠loss) except at saturation. Four-fold reduction in survival time within dry air and accelerated water loss rates with high activation energies for female adults of the closely related winged Prostephanus truncatus (Say) suggest that the enhanced water conservation of spider beetles is due, in part, to fusion of their elytra supplemented by entering into quiescence. 相似文献
14.
Lars Chresten Lund-Hansen 《Hydrobiologia》2011,673(1):105-118
The aims of the study were to analyse the relations between the physics of a water column and the location of the subsurface chlorophyll maximum (SCM) peaks in a strongly stratified estuary. Could extension and depth location of the SCM be explained by the physical conditions in terms of water column stratification and density interface? Questions were addressed by obtaining data on water column density (CTD), chlorophyll a (Chl a), nutrients, (F v/F m), σPSII and K d(PAR) at 15 positions along a 575 km transect in the Kattegat estuary. Results showed that the estuary was strongly stratified with mixed surface and bottom layers intercepted by a layer where density increased with depth. The SCM occurred only in this density interface, and widths of SCM and density interface were highly correlated. The surface waters were nearly depleted of inorganic nitrogen, phosphate and silicate though with significant higher concentrations in the waters below the interface. The Chl a concentration was comparatively higher in the SCM peak as well as maximum quantum efficiency (F v/F m) and functional cross sectional area (σPSII). The SCM was maintained at very low light levels and by a diapycnal nitrogen flux, with a stratified water column and nutrient depleted surface waters as predecessors. It was concluded that the depth location and vertical extension of the SCM in the estuary were closely linked to the physical structure of the water column in terms of density interface and stratification. 相似文献
15.
Understanding the dynamics of upwelling systems, especially the interactions between nutrients and light, has benefited from the application of models of varying complexity. Validation of such models using unialgal cultures or field observations has often proven difficult, but short-term incubations of contained natural assemblages and use of instantaneous physiological indicators offer an alternative approach. In May and June 1996, phytoplankton communities deep in the euphotic zone were sampled from nearly identical physical environments. Replicate samples (20 l volume) were incubated on deck at 50% surface irradiance with either no nutrient additions (Controls) or additions of 20 μM nitrate (Enrichments). Over 24 h, variable fluorescence (F v:F m), nitrate reductase activity (NR), nutrients, chlorophyll a and particulate C and N were monitored. Initial chlorophyll a (~3 μg l?1), phosphate (~0.2 μM), nitrate (~1.5 μM) and silicate (~3 μM) were similar in both months. Changes in NR and F v:F m indicated clear physiological responses to changes in irradiance and added nitrate that differed between months. In May, Controls and Enrichments responded in the same way. F v:F m stayed constant (0.5), chlorophyll a increased slightly, and NR activity increased markedly in all samples. In contrast, in June, treatments responded quite differently. F v:F m was near the theoretical maximum (0.7–0.8) initially and remained constant in Enrichments, but fell sharply in Controls. Declines in controls were also seen for chlorophyll a, and NR activity. Thus, the addition of 20 μM nitrate had a significant effect even though ambient levels of nitrate (>1 μM) should not have been limiting. Small (<20 μm) flagellates predominated in the May samples, but in June large and chain-forming centric diatoms constituted a significant proportion of the phytoplankton community. We conclude that the response of a phytoplankton community to environmental changes can depend on factors that are poorly represented by bulk measurements of chlorophyll, nutrients and particulate elements. 相似文献
16.
I. Giladi B. Pinshow 《Journal of comparative physiology. B, Biochemical, systemic, and environmental physiology》1999,169(4-5):311-318
Body water conservation is important in flying birds because the very high metabolic demands and heat dissipation requirements
during flight depend on plasma-volume integrity. Wind tunnel experiments and theoretical model predictions show that evaporative
water loss (EWL) depends on air temperature (T
a) and water vapor density (ρa), but these relationships have not been examined in free-flying birds. The contribution of excretory water loss to the total
water loss of a flying bird is thought to be negligible but this assumption is untested. To study the dependence of water
losses on environmental conditions in free-flying birds and to quantify the contribution of excretory water loss to total
water loss, we estimated evaporative and excretory water losses in 16 trained, free-flying tippler pigeons (Columba livia, 250–340 g). We collected excreta by attaching a light latex, water-impermeable receptacle around each bird's vent. By gravimetry,
we measured evaporative and excretory water losses of birds for eight flights at different T
as and compared flying to resting (control) birds for two of these flights. EWL was constant with respect to T
a when less than 15 °C, and increased with increasing T
a above 19 °C, indicating that evaporative cooling was invoked when the heat load increased. EWL increased with increasing
ρa, possibly due to the strong correlation between ρa and T
a. Excretory water loss was independent of ρa or T
a and averaged almost 10% of the total water loss. Measurements of EWL made on pigeons during wind tunnel experiments and previous
free-flight studies are consistent with our free-flight measurements made at similar T
a
s.
Accepted: 13 April 1999 相似文献
17.
Luisa Brito Paiva Jurandi Gonçalves de Oliveira Ricardo A. Azevedo Douglas Rodrigues Ribeiro Marcelo Gomes da Silva Angela P. Vitória 《Environmental and Experimental Botany》2009,65(2-3):403-409
Due to its wide industrial use, chromium (Cr) is considered a serious environmental pollutant of aquatic bodies. In order to investigate the ecophysiological responses of water hyacinth [Eichhornia crassipes (Mart.) Solms] to Cr treatment, plants were exposed to 1 and 10 mM Cr2O3 (Cr3+) and K2Cr2O7 (Cr6+) concentrations for two or 4 days in a hydroponic system. Plants exposed to the higher concentration of Cr6+ for 4 days did not survive, whereas a 2 days treatment with 1 mM Cr3+ apparently stimulated growth. Analysis of Cr uptake indicated that most of the Cr accumulated in the roots, but some was also translocated and accumulated in the leaves. However, in plants exposed to Cr6+ (1 mM), a higher translocation of Cr from roots to shoots was observed. It is possible that the conversion from Cr6+ to Cr3+, which immobilizes Cr in roots, was not total due to the presence of Cr6+, causing deleterious effects on gas exchange, chlorophyll a fluorescence and photosynthetic pigment contents. Chlorophyll a was more sensitive to Cr than chlorophyll b. Cr3+ was shown to be less toxic than Cr6+ and, in some cases even increased photosynthesis and chlorophyll content. This result indicated that the Fv/F0 ratio was more effective than the Fv/Fm ratio in monitoring the development of stress by Cr6+. There was a linear relationship between qP and Fv/Fm. No statistical differences were observed in NPQ and chlorophyll a/b ratio, but there was a tendency to decrease these values with Cr exposure. This suggests that there were alterations in thylakoid stacking, which might explain the data obtained for gas exchanges and other chlorophyll a fluorescence parameters. 相似文献
18.
Chris R. Feldman Edmund D. Brodie Jr Edmund D. Brodie III Michael E. Pfrender 《Proceedings. Biological sciences / The Royal Society》2010,277(1698):3317-3325
Detailing the genetic basis of adaptive variation in natural populations is a first step towards understanding the process of adaptive evolution, yet few ecologically relevant traits have been characterized at the genetic level in wild populations. Traits that mediate coevolutionary interactions between species are ideal for studying adaptation because of the intensity of selection and the well-characterized ecological context. We have previously described the ecological context, evolutionary history and partial genetic basis of tetrodotoxin (TTX) resistance in garter snakes (Thamnophis). Derived mutations in a voltage-gated sodium channel gene (Nav1.4) in three garter snake species are associated with resistance to TTX, the lethal neurotoxin found in their newt prey (Taricha). Here we evaluate the contribution of Nav1.4 alleles to TTX resistance in two of those species from central coastal California. We measured the phenotypes (TTX resistance) and genotypes (Nav1.4 and microsatellites) in a local sample of Thamnophis atratus and Thamnophis sirtalis. Allelic variation in Nav1.4 explains 23 per cent of the variation in TTX resistance in T. atratus while variation in a haphazard sample of the genome (neutral microsatellite markers) shows no association with the phenotype. Similarly, allelic variation in Nav1.4 correlates almost perfectly with TTX resistance in T. sirtalis, but neutral variation does not. These strong correlations suggest that Nav1.4 is a major effect locus. The simple genetic architecture of TTX resistance in garter snakes may significantly impact the dynamics of phenotypic coevolution. Fixation of a few alleles of major effect in some garter snake populations may have led to the evolution of extreme phenotypes and an ‘escape’ from the arms race with newts. 相似文献
19.
Continuous wave nuclear magnetic resonance (NMR) studies indicated that the line width of the water absorption peak (Δv½) from crowns of winter and spring wheat (Triticum aestivum L.) increased during cold acclimation. There was a negative correlation between Δv½ and crown water content, and both of these parameters were correlated with the lowest survival temperature at which 50% or more of the crowns were not killed by freezing (LT50). Regression analyses indicated that Δv½ and water content account for similar variability in LT50. Slow dehydration of unacclimated winter wheat crowns by artificial means resulted in similarly correlated changes in water content and Δv½. Rapid dehydration of unacclimated crowns reduced water content but did not influence Δv½. The incubation of unacclimated winter wheat crowns in a sucrose medium reduced water content and increased Δv½. The increase in Δv½ appears to be dependent in part on a reduction in water content and an increase in solutes. 相似文献
20.
As part of a program to select maritime pine (Pinus pinaster Ait.) genotypes for resistance to low winter temperatures, we examined variation in photosystem II activity by chlorophyll fluorescence. Populations and families within populations from contrasting climates were tested during two consecutive winters through two progeny trials, one located at a continental and xeric site and one at a mesic site with Atlantic influence. We also obtained the LT50, or the temperature that causes 50% damage, by controlled freezing and the subsequent analysis of chlorophyll fluorescence in needles and stems that were collected from populations at the continental trial site.
P. pinaster showed sensitivity to winter stress at the continental site, during the colder winter. The combination of low temperatures, high solar irradiation and low precipitation caused sustained decreases in maximal photochemical efficiency (Fv/Fm), quantum yield of non-cyclic electron transport (ΦPSII) and photochemical quenching (qP). The variation in photochemical parameters was larger among families than among populations, and population differences appeared only under the harshest conditions at the continental site. As expected, the environmental effects (winter and site) on the photochemical parameters were much larger than the genotypic effects (population or family). LT50 was closely related to the minimum winter temperatures of the population''s range. The dark-adapted Fv/Fm ratio discriminated clearly between interior and coastal populations.In conclusion, variations in Fv/Fm, ΦPSII, qP and non-photochemical quenching (NPQ) in response to winter stress were primarily due to the differences between the winter conditions and the sites and secondarily due to the differences among families and their interactions with the environment. Populations from continental climates showed higher frost tolerance (LT50) than coastal populations that typically experience mild winters. Therefore, LT50, as estimated by Fv/Fm, is a reliable indicator of frost tolerance among P. pinaster populations. 相似文献