Olfactory responses of blowflies to aliphatic aldehydes

The response of the blowfly Phormia regina to stimulation by aldehydes in the vapor phase has been studied by means of a specially designed olfactometer. The median rejection threshold and the maximum acceptance threshold were selected as criteria of response. For both acceptance and rejection the distribution of thresholds in the population is normal with respect to the logarithm of concentration. When thresholds are expressed as molar concentrations, the values decrease progressively as chain length is increased. There is no attraction beyond decanal and no rejection beyond dodecanal. When thresholds are expressed as activities, most members of the aldehyde series are approximately equally stimulating at rejection and equally stimulating at acceptance. The relationship is most exact over the middle range of chain lengths. There is a tendency for the terminal members to stimulate at higher activities. These relationships are in close agreement with those which were found earlier to apply to the normal aliphatic alcohols. The similarity between the relative actions of the members of the two series suggests that the relation of equal olfactory stimulation at equal thermodynamic activities by homologous aliphatic compounds at least for homologues of intermediate chain length may be of rather general application in olfaction.     

REJECTION THRESHOLDS OF THE BLOWFLY FOR A SERIES OF ALIPHATIC ALCOHOLS

Series of concentrations of 15 aliphatic alcohols were presented in 0.1 M sucrose to the tarsi of antennectomized-labellectomized blowflies (Phormia regina Meigen). With the pri-n-alcohols the mean concentrations at rejection formed a Traube series. When the rejection thresholds for all the alcohols tested were compared with their boiling points, vapor pressures, molecular surface areas) molecular moments, water-cottonseed oil distribution coefficients, standard free energies, and activity coefficients, a very high degree of correlation was found in each case. It is concluded that the limiting process which was measured is concerned with the receptor cells rather than with some other element in the complex response. Stimulative power was evidently not dependent on osmotic pressure nor on rate of molecular diffusion in solution, and the correlation with vapor pressure was inverse. It is judged that surface energy relationships are concerned in stimulation, but the exact mechanism cannot be defined until more is known about the structure of the sensory surface and about the process of excitation. The physiological activity of the alcohols is related more closely to the ease with which they gain access to the cell than to their chemical interaction with cellular constituents.     

The limiting mechanism in tarsal chemoreception

Rejection thresholds of eight primary alcohols applied to the tarsal chemoreceptors of the blowfly Phormia regina Meigen and the ovipositor of Gryllus assimilis Fab. have been determined. Three different solvents for the alcohols have been used: water, ethylene glycol, and mineral oil. The comparative stimulating effectiveness of the alcohols assumes a different aspect with each different solvent. In oil the range of thresholds from methanol to octanol extends over less than one log unit as compared with the corresponding thresholds in water which extend over four log units. In glycol the thresholds extend over two and one half log units only. When water is employed as a solvent, the line which describes the relationship between threshold concentration and chain length of the compound exhibits a sharp break at or near butanol. No such discontinuity is evident when glycol or oil is employed as solvent. This is offered as evidence supporting the hypothesis that the limiting mechanism in tarsal chemoreception involves a two phase system whereby highly water-soluble compounds gain access to the receptor through an aqueous phase and the larger lipoid-soluble molecules chiefly through a lipoid phase. Additional facts which support this idea are gained from data which show that the inflection in the curve occurs at different points with different species of insects and is conspicuously absent in the case of man. When thresholds in aqueous solutions are converted from molar concentrations to activities, it is clear that the relation of equal physiological effect at equal thermodynamic activities does not apply here. The lower members of the series stimulate at progressively increasing activities up to pentanol and then at progressively decreasing activities. Furthermore, the ratio of water threshold to oil threshold exhibits no obvious agreement with the water/oil partition coefficients determined experimentally. These results indicate either that the limiting process of chemoreception in these insects does not depend upon the establishment of an equilibrium or that some kinetic effect is obscuring an underlying relationship which does so depend.     

Stimulation of tarsal receptors of the blowfly by aliphatic aldehydes and ketones

Rejection of eight aldehydes, eight ketones, five secondary alcohols, and 3-pentanol has been studied in the blowfly Phormia regina Meigen. The data agree with results previously reported for normal alcohols and several series of glycols in showing a logarithmic increase in stimulating effect with increasing chain length. The order of increasing effectiveness among the different species of compounds thus far investigated is the following: polyglycols, diols, secondary alcohols, iso-alcohols, normal alcohols, ketones, iso-aldehydes, normal aldehydes. Curves relating the logarithms of threshold concentration to the logarithms of chain length for diols, alcohols, aldehydes, and ketones show inflections in the 3 to 6 carbon range. Above and below the region of inflection the curves are nearly rectilinear. The slopes for the upper limbs (smaller molecules) are of the order of -2; for the lower limbs, about -10. Comparisons of the threshold data with numerical values for molecular weights, molecular areas and volumes, oil-water distribution coefficients, activity coefficients, standard free energies, vapor pressures, boiling points, melting points, dipole moments, dielectric constants, and degree of association are discussed briefly, and it is concluded that none of the comparisons serves to bring the data from the several series and from the two portions of each series into a single homogeneous system. A qualitative comparison with water solubilities shows fewer discrepancies. It is suggested that the existence of a combination of aqueous and lipoid phases at the receptor surface would fit best with what is presently known about the relationship between chemical structure and stimulating effect in contact chemoreception. In this hypothesis the smaller and more highly water-soluble compounds are envisaged as gaining access to the receptors partly through the aqueous phase, the larger molecules predominantly through the lipoid phase.     

Two-Dimensional Continuum Percolation Threshold for Diffusing Particles of Nonzero Radius

Lateral diffusion in the plasma membrane is obstructed by proteins bound to the cytoskeleton. The most important parameter describing obstructed diffusion is the percolation threshold. The thresholds are well known for point tracers, but for tracers of nonzero radius, the threshold depends on the excluded area, not just the obstacle concentration. Here thresholds are obtained for circular obstacles on the continuum. Random obstacle configurations are generated by Brownian dynamics or Monte Carlo methods, the obstacles are immobilized, and the percolation threshold is obtained by solving a bond percolation problem on the Voronoi diagram of the obstacles. The percolation threshold is expressed as the diameter of the largest tracer that can cross a set of immobile obstacles at a prescribed number density. For random overlapping obstacles, the results agree with the known analytical solution quantitatively. When the obstacles are soft disks with a 1/r¹² repulsion, the percolating diameter is ∼20% lower than for overlapping obstacles. A percolation model predicts that the threshold is highly sensitive to the tracer radius. To our knowledge, such a strong dependence has so far not been reported for the plasma membrane, suggesting that percolation is not the factor controlling lateral diffusion. A definitive experiment is proposed.     

CHEMICAL STIMULATION BY ALCOHOLS IN THE BARNACLE,THE FROG AND PLANARIA

1. The stimulating efficiencies of some normal primary aliphatic alcohols have been determined for the barnacle, the frog, and Planaria, under conditions which do not involve narcosis or simultaneous stimulation by other agents. 2. Concentrations of the successive alcohols necessary to produce a given stimulatory effect vary according to the following geometrical series: 1: a ^–1: a ^–2: a ^–3: a ^–4: . . . ., where a represents some real number. 3. Within certain limits the relationship between the logarithm of the concentration necessary to produce a given effect and the reciprocal of the reaction time is linear in the frog and in Planaria. 4. The concentration effect may be expressed by an equation which contains one constant characteristic of the alcohol series, and another one characteristic of each member. The ratio of the latter constants for successive alcohols represents a in the above series. 5. The stimulation by alcohols in these animals is considered to be due to energy changes at the receptive surfaces, brought about by a definite orientation of the respective alcohol molecules. Increase in stimulating efficiency as the number of CH₂ groups increase must be due to the rôle of the non-polar portion of the alcohol molecule, since the polar group remains practically constant throughout the series. 6. In homologous series of organic compounds it is conceived that stimulating effects will be produced either by the polar group or the non-polar group, according to which one becomes dominant in effect, or to a combination of the two.     

The effect of tympanal position on the sound-sensitivity of the metathoracic scolopale organ of Corixa

Action potentials were recorded extracellularly from the receptor unit B2 of the metathoracic scolopale organ of Corixa punctata Ill. (Heteroptera, Corixidae). The background discharge rate is modulated by movement of the tympanal membrane, which under normal resting conditions is rhythmically pushed outward (strong excitation) and pulled inward (weak excitation).The receptor unit gives phasic-tonic responses to airborne sound. Threshold curves and intensity characteristics indicate that the sensitivity to sound depends on the position of the membrane at the time of stimulation. The thresholds to frequencies in the range 0.3–3.0 kHz measured with the membrane everted are as much as 20 dB lower than when it is inverted. In the frequency range where sensitivity is greatest (0.3–1.1 kHz), with membrane everted the threshold is ca. 74 dB RMS re 20 μPa.     

Theoretical aspects of sexual selection: A generalized model of mating behaviour

A model of mate selection is described in which females mate preferentially according to their probability of encounter with the males they prefer. In this model, different thresholds of response to the courtship of different male phenotypes determine the female mating preferences. Females with a lower threshold toward particular males require fewer encounters before mating with these males and more encounters before mating with any of the others. Such females mate preferentially if they encounter a male they prefer before they have been stimulated to the level of the higher threshold. At the higher threshold they mate at random. The number of the extra encounters required to raise the females' level of stimulation from the lower to the higher threshold is a parameter of the model. The frequency of the preferred males then determines the probability that a female encounters and mates with one of them before she has been sufficiently stimulated to mate at random. Sexual selection by differences in male courtship can also be described in terms of this model.The preferred characters may be determined either by dominant and recessive alleles or by each different genotype. When only one extra encounter is required before the females mate at random, the preferred males only gain a slight frequency-dependent advantage: Stable polymorphisms can only be maintained if the heterozygotes have the greater preference in their favor. When more than one extra encounter is required before random mating, the males gain a negative frequency-dependent advantage: Stable polymorphisms are generally maintained.The models are fitted to published data on the mating success of male Drosophila at varying frequencies and provide an explanation of the “rare male” effect in which less common males gain a mating advantage.     

NATURE OF THE ACTION CURRENT IN NITELLA : V. PARTIAL RESPONSE AND THE ALL-OR-NONE LAW

When a stimulus arrives before recovery is complete there may be no response or only a partial response. A typical response appears to involve an immediate loss of potential at the inner protoplasmic surface but not at the outer surface. As long as recovery is incomplete only a part of the total potential is located at the inner protoplasmic surface and the loss of this part of the total potential can cause only a partial response; i.e., one of smaller magnitude than the normal. Even after the action curve has returned to the base line recovery may be incomplete and the response only a partial one. The return of the action curve to the base line means a recovery of total potential but if part of this is located at the outer protoplasmic surface and if this part is not lost when stimulation occurs the response can be only a partial one. During recovery there is a shift of potential from the outer to the inner protoplasmic surface. Not until this shift is completed can recovery be called complete. The response to stimulation then becomes normal because the loss of potential reaches the normal amount. In many cases the partial responses appear to conform to the all-or-none law. In other cases this is doubtful.     

Stimulus-response relationships of insect olfaction: Correlations among neurophysiological and behavioral measures of response

The inter-relationships among parameters of odorant concentration, the responses evoked in single olfactory receptor neurons, the whole-animal behavioral threshold, and the intensity of the behavioral response are examined for insect olfaction from the perspective of a new phenomenological model of the perceived intensity of single odorants. Electrophysiological and behavioral data compiled from diverse insect studies are analyzed in detail to determine the utility of the model for interpreting these studies and for designing new studies. The analysis of electrophysiological data indicates that the response of olfactory receptor neurons can be expressed as a power function of the odorant concentration. The behavioral thresholds to sex pheromone, predicted by the model from direct calculations using phenomenological parameters, are in good agreement with thresholds measured by bioassay. It is also shown that the interpretation of behavioral bioassay data in terms of concepts introduced by the model provides more information about the behavioral response than provided by the currently popular probit analysis. In addition, aspects of the physiological significance of power functions are discussed, and new methods are presented for distinguishing background activity from activity evoked in single olfactory neurons by an odor at threshold levels.     

Effects of cortical ablations on the turning response evoked by stimulation of the pulvinar-lateralis posterior nucleus complex in the cat

The role played by the cerebral cortex on turning responses elicited by electrical stimulation of P-LP was studied in 9 chronic cats. In three animals the sensorimotor cortex was bilaterally ablated and the threshold values for inducing a turning response were determined. None of the cats showed abnormal threshold values. In six cats the cerebral cortical area known to have reciprocal anatomical connections with P-LP was unilaterally removed. Seven days after surgery, 50% of the electrodes gave no responses; 25% evoked responses with high thresholds and 25% with normal thresholds. One month after surgery the percentages were: 14, 18 and 68 respectively. Histological findings show important fiber and neuronal degeneration in P-LP. It is postulated that this area of the cerebral cortex plays, a facilitatory role on the P-LP ability to induce turning response and that the recovery of this ability can be explained by the development of P-LP denervation supersensitivity.     

DO MELANOPHORE NERVES SHOW ANTIDROMIC RESPONSES?

1. In Fundulus heteroclitus the dispersing melanophore nerve fibers have a relatively high threshold for faradic stimulation and a low one for stimulation by cutting. When they are protected from the competing action of the concentrating fibers, they show through the responses of their melanophores well marked antidromic activities which can also be seen to a slight degree even where the concentrating fibers are active. 2. The concentrating melanophore nerve fibers in this fish have a relatively low threshold for faradic stimulation and a high one for stimulation by cutting. They also exhibit clear antidromic responses as shown by their associated melanophores.     

A model for generating aspects of zebra and other mammalian coat patterns

A model is put forward which is capable of generating chemical maps whose concentration contours are similar to the patterns seen on the flanks of zebras, cats and other mammals. The model derives from the reaction-diffusion kinetics invented by Turing (1952) and it is assumed that the necessary molecular apparatus is present in each cell of a two-dimensional array and that the cells are in diffusion contact. The model was expressed in differential equation form and solved digitally under a range of different initial, boundary and other conditions. The main forms of pattern that the model generated were spots of variable complexity, rings, and both vertical and horizontal stripes. If morphogen concentration levels are assumed to act as melanin-production switches, then a common basic mechanism is capable of generating a variety of skin patterns. Simple spots such as those found in the fallow deer or the serval, F. serval, are generated if the kinetics are initiated simultaneously in each cell and interpretation depends only on the presence or absence of morphogen, which is assumed for the deer to be an activator and for the cat a suppressor of pigment formation. The reticulated pattern of the giraffe is generated if there is a single high-value threshold. Complex spots typical of the leopards can be produced if there are different concentration thresholds for different colours. Rings of pattern typical of those found on cat tails are generated if the cellular array is a very narrow cylinder. Horizontal stripes are generated if the kinetics in each cell are initiated by a diffusion gradient whose source is the dorsal line of cells and these stripes may break up into spots to give a pattern very similar to that of, for example, the fishing cat, F. viverina. The vertical stripes of the caffre cat, F. caffra, or the zebras are formed if the kinetics are initiated by a vertically-moving constant-velocity wave which also allows morphogen diffusion between previously uncoupled cells. Thus far, the mechanism has generated neither the triradii that are commonly found on forelimbs nor the rings often observed on mammalian limbs. It does however incorporate the randomness that characterizes skin pattern, its operation is of the scale required in embryogenesis, it can be made stable to growth and it can explain certain degenerate patterns. Analysis of a spotted zebra in the light of the model provides evidence that zebra stripes arise from the inhibition rather than the stimulation of melanin; their pattern is thus of white stripes on a black background.     

The three isoforms of nitric oxide synthase distinctively affect mouse nocifensive behavior

Nitric oxide synthases (NOSs) have been shown to modulate thermal hyperalgesia and mechanical hypersensitivity in inflammatory and neuropathic pain. However, little is known about the effect of NOSs on baseline function of sensory nerve fibers. Using genetic deficiency and pharmacologic inhibition of NOSs, we examined the impact of the three isoforms NOS1, NOS2, and NOS3 on baseline nocifensive behavior by measuring current vocalization threshold in response to electrical stimulation at 5, 250, 2000 Hz that preferentially stimulate C, Aδ, and Aβ fibers. In response to 5, 250 and 2000 Hz, NOS1-deficient animals had significantly higher current vocalization thresholds compared with wild-type. Genetic deficiency of NOS2 was associated with higher current vocalization thresholds in response to 5 Hz (C-fiber) stimulation. In contrast, NOS3-deficient animals had an overall weak trend toward lower current vocalization thresholds at 5 Hz and significantly lower current vocalization threshold compared with wild-type animals at 250 and 2000 Hz. Therefore, NOSs distinctively affect baseline mouse current vocalization threshold and appear to play a role on nocifensive response to electrical stimulation of sensory nerve fibers.     

Hearing of old world monkeys (Cercopithecinae)

The characteristics of normal hearing were examined in the laboratory for seven species of Old World monkeys. Operant conditioning procedures, coupled with standard audiometric testing methods, were used to assess thresholds of hearing, frequency range of hearing, and differential sensitivity to auditory intensity and frequency. To produce tonal stimulation, an animal was trained to touch and maintain manual contact with a contact-sensitive key and to report hearing the tone by lifting his hand from the key; this response was followed by food reinforcement. When the reporting response occurred without the auditory signal, the animal was punished by a short suspension from the experiment. Additional contingencies were added to ensure stable and reliable responding, and threshold and differential acuity determinations were then made. Threshold was defined as the stimulus value responded to correctly 50% of the time. The frequency range of hearing of all the cercopithecoids tested extended from 60 to 40,000 Hz, an octave above the upper bound of 20,000 Hz for man but well below the 60–70,000 Hz limit for some prosimians. Absolute sensitivity for tonal stimulation in the most sensitive frequency range (1–8 kHz) was about 2 × 10^?4 microbars, comparable to that of other primates tested, including man. Thus, the Old World monkey appears only slightly less sensitive than man to small changes in intensity and frequency of acoustic stimulation. At 1000 Hz at 60 dB above the threshold of audibility, his limit of resolution is about 5 Hz for frequency and 2 dB for intensity.     

Exploring the correlation between deltamethrin stress and Keap1-Nrf2-ARE pathway from Drosophila melanogaster RNASeq data

Deltamethrin (DM) is widely used in a variety of pest control, resulting in serious drug resistance. Keap1-Nrf2-ARE is the antioxidant stress pathway. We identified 268 genes differentially expressed (DEGs) in Drosophila Kc cells treated with DM, including up-regulated 180 genes and down-regulated 88 genes compared with the control group (fold-change≥2, qValue≤0.001) by RNA-seq, they are mainly linked to metabolic process, stimulation response, immune system process. When the cells are treated with DM in the case of overexpression of the Keap1 gene, the cytochrome P450 family genes were significantly down-regulated, and some diseases-related genes and non-coding genes also changed. Our data shown that Keap1-Nrf2-ARE pathway may play an important role in DM stress, which will provide a new direction for studying the mechanism of insect resistance.     

Reappraising Social Insect Behavior through Aversive Responsiveness and Learning

Background

The success of social insects can be in part attributed to their division of labor, which has been explained by a response threshold model. This model posits that individuals differ in their response thresholds to task-associated stimuli, so that individuals with lower thresholds specialize in this task. This model is at odds with findings on honeybee behavior as nectar and pollen foragers exhibit different responsiveness to sucrose, with nectar foragers having higher response thresholds to sucrose concentration. Moreover, it has been suggested that sucrose responsiveness correlates with responsiveness to most if not all other stimuli. If this is the case, explaining task specialization and the origins of division of labor on the basis of differences in response thresholds is difficult.

Methodology

To compare responsiveness to stimuli presenting clear-cut differences in hedonic value and behavioral contexts, we measured appetitive and aversive responsiveness in the same bees in the laboratory. We quantified proboscis extension responses to increasing sucrose concentrations and sting extension responses to electric shocks of increasing voltage. We analyzed the relationship between aversive responsiveness and aversive olfactory conditioning of the sting extension reflex, and determined how this relationship relates to division of labor.

Principal Findings

Sucrose and shock responsiveness measured in the same bees did not correlate, thus suggesting that they correspond to independent behavioral syndromes, a foraging and a defensive one. Bees which were more responsive to shock learned and memorized better aversive associations. Finally, guards were less responsive than nectar foragers to electric shocks, exhibiting higher tolerance to low voltage shocks. Consequently, foragers, which are more sensitive, were the ones learning and memorizing better in aversive conditioning.

Conclusions

Our results constitute the first integrative study on how aversive responsiveness affects learning, memory and social organization in honeybees. We suggest that parallel behavioral modules (e.g. appetitive, aversive) coexist within each individual bee and determine its tendency to adopt a given task. This conclusion, which is at odds with a simple threshold model, should open new opportunities for exploring the division of labor in social insects.     

A mathematical model for the kinetics of Methanobacterium bryantii M.o.H. considering hydrogen thresholds

We develop a kinetic model that builds on the foundation of classic Monod kinetics, but incorporates new phenomena such as substrate thresholds and survival mode observed in experiments with the H2-oxidizing methanogen Methanobacterium bryantii M.o.H. We apply our model to the experimental data presented in our companion paper on H2 thresholds. The model accurately describes H2 consumption, CH4 generation, biomass growth, substrate thresholds, and survival state during batch experiments. Methane formation stops when its Gibbs free energy is equal zero, although this does not interrupt H2 oxidation. The thermodynamic threshold for H2 oxidation occurs when the free energy for oxidizing H2 and transferring electrons to biomass is no longer negative, at approximately 0.4 nM. This threshold is not controlled by the Gibbs free energy equation of methanogenesis from H2 + HCO3- as we show in our companion paper. Beyond this threshold, the microorganisms shift to a low-maintenance metabolism called "the survival state" in response to extended H2 starvation; adding the starvation response as another new feature of the kinetic model. A kinetic threshold (or S (min)), a natural feature of the Monod kinetics, is also captured by the model at H2 concentration of around approximately 2,400 nM. S (min) is the minimum substrate concentration to maintain steady-state biomass concentration. Our model will be useful for interpreting threshold results and designing new studies to understand thresholds and their ecological implications.     

Visual Adaptation in the Retina of the Skate

The electroretinogram (ERG) and single-unit ganglion cell activity were recorded from the eyecup of the skate (Raja erinacea and R. oscellata), and the adaptation properties of both types of response compared with in situ rhodopsin measurements obtained by fundus reflectometry. Under all conditions tested, the b-wave of the ERG and the ganglion cell discharge showed identical adaptation properties. For example, after flash adaptation that bleached 80% of the rhodopsin, neither ganglion cell nor b-wave activity could be elicited for 10–15 min. Following this unresponsive period, thresholds fell rapidly; by 20 min after the flash, sensitivity was within 3 log units of the dark-adapted level. Further recovery of threshold was slow, requiring an additional 70–90 min to reach absolute threshold. Measurements of rhodopsin levels showed a close correlation with the slow recovery of threshold that occurred between 20 and 120 min of dark adaptation; there is a linear relation between rhodopsin concentration and log threshold. Other experiments dealt with the initial unresponsive period induced by light adaptation. The duration of this unresponsive period depended on the brightness of the adapting field; with bright backgrounds, suppression of retinal activity lasted 20–25 min, but sensitivity subsequently returned and thresholds fell to a steady-state value. At all background levels tested, increment thresholds were linearly related to background luminance.     

基于附石硅藻的三峡水库入库支流氮、磷阈值

为全面了解河流附石硅藻群落对水体氮、磷变化的响应规律,并找出氮、磷指示物种,本研究采用非参数突变点分析法(nCPA)及临界指示物种分析法(TITAN)探讨了三峡水库入库支流附石藻类叶绿素a、硅藻物种丰富度、Shannon多样性指数以及硅藻群落组成的总氮(TN)、总磷(TP)阈值.结果表明: 据nCPA得到的所有藻类参数的TP阈值均接近0.03 mg·L^-1;除硅藻群落组成外,其他参数的TN阈值也较接近(约为0.8 mg·L^-1).TITAN区分了群落中敏感种、耐受种对TN、TP变化的响应,且阈值范围涵盖了其他参数的阈值;还确定了9种TN指示种和10种TP指示种,其中TN敏感种1种,耐受种8种;TP敏感种5种,耐受种5种.因此,本研究以TITAN结果为依据确定河流的TN、TP阈值.即:当河流TN浓度低于0.382 mg·L^-1或TP浓度低于0.016 mg·L^-1时(负响应阈值),河流附石硅藻群落组成相对稳定;超过这一浓度阈值后,敏感种密度减少;当河流的TN浓度超过1.298 mg·L^-1或TP浓度超过0.065 mg·L^-1时(正响应阈值),耐受种也将受到明显影响,附石藻类的群落组成会发生显著变化.据此标准,调查样点中约87%的样点TN浓度超过TN负响应阈值,22%的样点超过正响应阈值;而超过TP负响应阈值的点占94%,超过TP正响应阈值的点占14%,说明三峡水库大部分入库河流虽受到了一定程度的干扰,但干扰程度并不严重.本研究结果可为三峡水库入库河流生态管理决策提供科学依据.