Some factors governing prey selection by the 15-spined stickleback, Spinachia spinachia (L.)

Using mysids as prey, the relative importance of four characters governing prey selection by Spinachia spinachia (L.) were examined. Moving prey were taken in preference to stationary prey of equal length and when the fish were hungry they could be induced to take moving non-optimum sized prey in preference to optimum sized stationary ones. A comparison of the frequency of attack on portions of the prey showed that heads were preferred to tails and darkened mysids to light ones. The order of preference was dark colour > head > light colour > tail and there was some indication that the stimuli presented by these characters were additive. It is concluded that the fish attacked the head of the prey because of its shape (greater thickness and presence of appendages) and darker colour. The colour of the prey did not affect the size (length) of prey taken. In general, the stimuli presented by the four characters could be ranked in the order movement ? length > colour > shape.     

Movement learning of free flying honeybees

Summary Free flying honeybees were conditioned to moving black and white stripe patterns. Bees learn rapidly to distinguish the direction of movement in the vertical and horizontal plane.After being trained to a moving pattern bees do not discriminate the moving alternative from a stationary one. There is no significant velocity discrimination for patterns moving in the same direction.For vertical movements there are clear asymmetries in the spontaneous choice preference and in the learning curves for patterns moving upward or downward.After bees are trained to a stationary pattern they can discriminate it from an upward moving alternative. Learning curves involving movement are generally biphasic, suggesting different adaptive systems depending on the number of rewards.The flight pattern of bees which are trained to movement changes during the process of learning. At the beginning of the learning procedure bees reveal an optokinetic response to the moving patterns, this response is strongly reduced after a number of rewards on a moving pattern.     

The precedence effect in the horizontal and vertical planes in experiments with a moving lagging signal

The precedence effect in the localization of a moving lagging sound source was studied in experiments on humans under the free field conditions in the presence of a stationary (lead) sound source. Broad-band noise (5–18 kHz) bursts 1 s in duration presented in the horizontal and vertical planes were used as signals. The lead-lag delays ranged from 1 to 40 ms. The results showed that, if the signals were presented in the horizontal plane, the probability of correct localization of the moving lagging signal was decreased for delays shorter than 25 ms; if the signals were presented in the vertical plane, it was decreased for delays shorter than 40 ms. If the delays were shorter than 8–10 ms, the subjects could not localize the moving lagging signal at all. In this interval of delays, the subjects could localize only the lead signal. The mean echo threshold for signals presented in the horizontal plane was smaller than for signals presented in the vertical plane (7.3 and 10.1 ms, respectively). However, comparison of these values across the sample of subject did not show significant differences [F(1, 5) = 5.52, p = 0.07]. The results of the study suggest that the precedence effect causes a tendency towards a stronger suppression of a moving lagging signal in the vertical plane than in the horizontal plane.     

Chlorophylls and carotenoids states in vivo I - A linear dichroism study of pigments orientation in spinach chloroplasts

Using a spectropolarimeter for measuring the linear dichroism of pigments in oriented spinach chloroplasts we found a composite signal that could be interpreted neither as textural dichroism nor as a sample birefringence. We detected a fairly good orientation of pigments with respect to the normal at the plane of chloroplast lamellae. We failed to show any orientation axe in this plane. We found that all the Ca 683 is oriented, its Y direction being parallel to, or lying in the lamellae plane. Ca 673 is either unoriented or is oriented with its Y direction making an angle of 55° with the normal. If Ca 673 is unoriented, then the X direction of Ca 683 could be space positionned at about 45° of the lamellae plane. Carotenoids are oriented in the lamellar plane or close to it. Cb is equally oriented.     

Motor Responses to Polarized Light and Gravity Sensing in Euglena gracilis*†

SYNOPSIS. Euglena gracilis strain Z has a motor response which results in orientation with respect to the polarization of a light stimulus. Cells swim preferentially in a direction perpendicular to the plane of polarization of the stimulus. If 2 polarized stimuli are given from opposite directions, the preferred direction is, under certain circumstances, at right angles to the directions of both stimuli. Euglena also preferentially assumes an orientation that is at right angles to the force of gravity. The relationships between these responses and phototactic movements oriented with respect to the direction of the stimulus are discussed.     

Visual control of cursorial prey pursuit by tiger beetles (Cicindelidae)

Target detection poses problems for moving animals, such as tiger beetles, that track targets visually. The pursuer's movements degrade target image contrast and induce reafferent image movement that confounds continuous detection of prey. In nature, beetles pursue prey discontinuously with several iterations of stop-and-go running. The beetle's dynamics were analyzed by filming pursuits of prey or experimenter-controlled dummies. Durations of stops are inversely related to prey visual angular velocity; as the prey image moves between neighboring ommatidial fields, the beetle relocalizes it and renews running. During subsequent runs, translation and rotation depend upon prey visual angular velocity and position, respectively, seen during the previous stop. The beetle runs, then stops, while prey continues moving. After two to three iterations of stop-and-go the beetle catches its prey, suggesting open-loop control of running. Computational model simulations produce good qualitative spatio-temporal fit with actual pursuits. However, when pursuing prey dummies, beetles track continuously and quickly follow changes in target position, suggesting closed-loop control using a position-sensitive servo mechanism. Differences between these types of pursuit control system are discussed with respect to limitations in signal detection, particularly spatio-temporal contrast, that may force beetles to use an open-loop system. Accepted: 7 April 1997     

Responses of salamanders to stationary visual patterns

Summary The fire salamanderSalamandra salamandra (L.) exhibits prey-catching responses to stationary visual patterns if it has previously been stimulated by a moved dummy prey. When presented with two stationary objects, salamanders choose circular patterns over rectangles, regardless of the orientation of the latter. By contrast, when the pattern is moved horizontally, horizontally-oriented rectangles are preferred (Fig. 2). If an odor stimulus is associated with a stationary visual pattern the choice behavior may be altered, but visual stimuli play the greater role. Visual detection of stationary patterns can be explained by involuntary tremor-like eye movements.     

Precedence effect at horizontal and vertical plane and moving lagging signal

The precedence effect refers to the fact that humans are able to localize sound sources in reverberant environments. In this study, sound localization was studied with dual sound source: stationary (lead) and moving (lag) for two planes: horizontal and vertical. Duration of lead and lag signals was 1s. Lead-lag delays ranged from 1-40 ms. Testing was conducted in free field, with broadband noise busts (5-18 kHz). The listeners indicated the perceived location of the lag signal. Results suggest that at delays above to 25 ms in horizontal plane and 40 ms in vertical plane subjects localized correctly the moving signal. At short delays (up to 8-10 ms), regardless of the instructions, all subjects pointed to the trajectory near the lead. The echo threshold varied dramatically across listeners. Mean echo thresholds were 7.3 ms in horizontal plane and 10.1 ms in vertical plane. Statistically significant differences were not observed for two planes [F(1, 5) = 5.52; p = 0.07].     

Adaptation effects in the analyzer of movement direction

A prolonged observation of a point-like stimulus moving in a given direction influences the perception of movement direction of subsequent stimuli. The prolonged observation of the same stimulus results in a subjective drift of the perceived movement towards horizontal or vertical direction depending on which of these directions is nearer to the stimulus trajectory. If, however, the stimulus moves in vertical, diagonal and horizontal directions its perception does not change under prolonged observation.     

Fruit or aposematic insect? Context-dependent colour preferences in domestic chicks.

Colours are common stimuli in signalling systems. Requirements to function well as a signal sometimes conflict between different signallers, and the same colour stimulus is used to convey completely different messages to the same receiver. Fruits and aposematic insects both use red coloration as a signal, in the former case to signal profitability and in the latter case as a warning signal. In two experiments, we investigated whether the domestic chick, an omnivorous predator, differed in its unconditioned preference or avoidance of red and green stimuli depending on whether or not the stimulus was an insect. The experiments were designed as preference tests between red and green painted prey. The prey were live insects and artificial fruits (experiment 1), and, to investigate the effect of movement, live and dead insects (experiment 2). The chicks did not show any difference in pecking preference between red and green when fruit-like stimuli were used, but when the prey were insects, green prey were strongly preferred to red prey, and prey movement did not affect this bias. Thus, young chicks may recognize prey as insects and then discriminate between different prey colorations, or one type of food may elicit an unlearned colour preference-avoidance response that is absent with another type of food.     

Sensory Basis of Food Detection in Wild <Emphasis Type="BoldItalic">Microcebus murinus</Emphasis>

Very little is known about how nocturnal primates find their food. Here we studied the sensory basis of food perception in wild-caught gray mouse lemurs (Microcebus murinus) in Madagascar. Mouse lemurs feed primarily on fruit and arthropods. We established a set of behavioral experiments to assess food detection in wild-born, field-experienced mouse lemurs in short-term captivity. Specifically, we investigated whether they use visual, auditory, and motion cues to find and to localize prey arthropods and further whether olfactory cues are sufficient for finding fruit. Visual cues from motionless arthropod dummies were not sufficient to allow reliable detection of prey in choice experiments, nor did they trigger prey capture behavior when presented on the feeding platform. In contrast, visual motion cues from moving prey dummies attracted their attention. Behavioral observations and experiments with live and recorded insect rustling sounds indicated that the lemurs make use of prey-generated acoustic cues for foraging. Both visual motion cues and acoustic prey stimuli on their own were sufficient to trigger approach and capture behavior in the mouse lemurs. For the detection of fruit, choice experiments showed that olfactory information was sufficient for mouse lemurs to find a piece of banana. Our study provides the first experimental data on the sensory ecology of food detection in mouse lemurs. Further research is necessary to address the role of sensory ecology for food selection and possibly for niche differentiation between sympatric Microcebus species.     

Auditory motion aftereffects of approaching and withdrawing sound sources

Auditory motion aftereffects of approaching and withdrawing sound sources were investigated in the free field. The approaching and withdrawing of a sound source were simulated by means of differently directed changes in the amplitude of impulses of broadband noise (from 20 Hz to 20 kHz) through two loudspeakers placed 1.1 and 4.5 m away from the listener. Presentation of the adapting approaching and withdrawing stimuli changed the perception of test signals following them: a stationary test signal was perceived by listeners as moving in the direction opposite to one of the movement of the adapting stimulus, whereas a test stimulus slowly moving in same direction as the adapting signal was perceived as stationary. The specific features of the auditory aftereffect of signals moving in a radial direction were similar to those of sound sources moving in a horizontal plane.     

The effects of capture spiral composition and orb-web orientation on prey interception

Cribellar prey capture threads found in primitive, horizontal orb-webs reflect more light, including ultraviolet wavelengths, than viscous threads found in more derived, vertical orb-webs. Low web visibility and vertical orientation are each thought to increase prey interception and may represent key innovations that contributed to the greater diversity of modern, araneoid orb-weaving spiders. This study compares prey interception rates of cribellate orb-webs constructed by Uloborus glomosus (Uloboridae) with viscous orb-webs constructed by Leucauge venusta (Tetragnathidae) and Micrathena gracilis (Araneidae). We placed sectors of cribellar and viscous threads side by side in frames that were oriented either horizontally or vertically. The webs of both U. glomosus and L. venusta intercepted more prey when vertically oriented. In each orientation L. venusta webs intercepted more insects than did U. glomosus. Although this is consistent with the greater visibility of cribellar threads, the more closely spaced capture spirals of L. venusta may have contributed to this difference. Micrathena gracilis webs intercepted more prey than did U. glomosus webs, although web orientation did not affect the performance of this araneoid species. The stickier and more closely spaced capture spirals of M. gracilis may have enhanced the interception rates of this species and accounted for the greater number of smaller dipterans retained in its webs. The tendency for these slow, weak flight insects to be blown into both horizontal and vertical webs may account for similar interception rates of horizontal and vertical M. gracilis webs. These observations support the enhanced prey interception of vertically oriented orb-webs, but offer only qualified support for the contributions of lower visibility viscous capture threads.     

When can embryos learn? A test of the timing of learning in embryonic amphibians

Learning is crucial to the survival of organisms across their life span, including during embryonic development. We set out to determine when learning becomes possible in amphibian development by exposing spotted salamander (Ambystoma maculatum) embryos to chemical stimuli from a predator (Ambystoma opacum), nonpredator (Lithobates clamitans), or control at developmental stages 16–21 or 36–38 (Harrison 1969 ). Once exposures were completed and embryos hatched, we recorded the number of movements and time spent moving of individuals in both groups and all treatments. There was no significant difference in number of movements or time spent moving among any of the treatments. The groups that were exposed to predator stimuli and a blank control at stages 36–38 were also tested to determine whether there was a difference in refuge preference or difference in survivorship when exposed to a predator (marbled salamander). There was no difference in survival or refuge preference between individuals; however, all individuals preferred vegetated over open areas regardless of treatment type. We discuss hypotheses for the absence of embryonic learning in this species and suggest it may be the result of the intensity of the predator–prey interaction between the predator, large marbled salamander larvae, and the prey, spotted salamander larvae.     

Wind-sensitive interneurones in the spider CNS (Cupiennius salei ): directional information processing of sensory inputs from trichobothria on the walking legs

Spiders can use air particle movements to localize moving prey. We studied the responses of 32 wind-sensitive interneurones in the hunting spider Cupiennius salei to prey stimuli. Stimulation with a tethered flying fly or with artificial air pulses activated plurisegmental interneurones that responded to changes in air movement velocity and were thus well suited to represent the highly fluctuating air stream typical of prey stimuli. In most interneurones (n = 18) the responses to the stimulation of different legs were not significantly different from each other. Different interneurones had different response characteristics and their latencies largely overlapped suggesting that there is parallel processing of the signals by populations of interneurones with different response characteristics. In two interneurones the number of spikes and the spiking pattern elicited by stimulation of each of the eight legs markedly differed depending on the leg stimulated. These neurones may play an important role in directional information processing. Stimulation of the adjacent legs from front to back or from back to front revealed two interneurones sensitive to the direction of successive stimulation of the legs. These neurones may be able to detect the motion of an air movement source in a preferred direction and thus act as nearfield motion detectors to localize a moving prey item. Accepted: 28 September 1996     

Female Preferences for Sailfin and Body Size in the Sailfin Molly, Poecilia latipinna

We tested the mating preference of female sailfin mollies (Poecilia latipinna) by presenting them with pairs of dummy males differing in: (I) sailfin and body size together (holding sailfin : body size ratio constant); (II) body size alone (holding sailfin size constant); (III) sailfin size alone (holding body size constant); and (IV) sailfin : body size ratio (holding total lateral projection area constant). Females spent more time near dummies of greater sailfin or greater body size. The preference functions based on the first three sets of stimuli showed a similar pattern: the preference between any two simultaneously presented dummies increased with the magnitude of the discrepancy in lateral projection area (LPA) between them. However, when LPA was held constant in expt (IV), neither body size, sailfin size, nor any particular dummy (i.e. any particular sailfin + body size combination) was preferred. These findings suggest that increased LPA is more stimulating to sexually receptive females and that females consequently prefer larger males. The sailfin may therefore have evolved as a way for males to exploit this sensory bias and appear larger to prospective mates.     

Effects of Prey Movement and Prey Odor on Feeding in Garter Snakes

The role of prey movement in feeding behavior was investigated in 10 garter snakes (Thamnophis sirtalis) repeatedly presented with paired stationary and continuously rotating sections of earthworm (Lumbricus terrestris). Additionally, prey odor intensity and source were varied and the performance of a tongueless snake was compared to normal animals. Experiment 1 showed that garter snakes will selectively attack rotating over nonmoving sections of earthworm across a wide range of speeds (1–2048 rpm) with an optimum between 16 and 256 rpm. However, blocking the odor from the sections and presentation of speeds greater than 500 rpm decreased response to moving sections. Experiment 2 showed that at 22–32 rpm moving sections were selected over stationary sections when odor from both was blocked. Experiment 3 assessed the effects of varying ambient odor conditions upon selection of artificial moving and stationary prey. Ambient earthworm odor resulted in a sustained high rate of tongue-flicking while, with no odor present, snakes showed a gradually increasing rate of tongue-flicking that declined within a few minutes. Experiments 4 and 5 studied the effects of tongue removal upon the selection of moving and nonmoving prey. Gross changes in the feeding sequence were noted. A long-term tongue-less adult fed by opening her mouth and thrashing about her cage when presented with earthworm odor and only preferred moving prey at 32 rpm; a control showed the normal stalk-and-strike sequence. The tongueless snake was less attracted to the moving earthworm at a distance than were normal snakes and the use of vision seemed less integrated rather than compensably improved. The results are discussed in reference to the critical flicker-fusion frequency, klepto-parasitism, and escape tactics of prey.     

Discrimination Contours for Moving Sounds Reveal Duration and Distance Cues Dominate Auditory Speed Perception

Evidence that the auditory system contains specialised motion detectors is mixed. Many psychophysical studies confound speed cues with distance and duration cues and present sound sources that do not appear to move in external space. Here we use the ‘discrimination contours’ technique to probe the probabilistic combination of speed, distance and duration for stimuli moving in a horizontal arc around the listener in virtual auditory space. The technique produces a set of motion discrimination thresholds that define a contour in the distance-duration plane for different combination of the three cues, based on a 3-interval oddity task. The orientation of the contour (typically elliptical in shape) reveals which cue or combination of cues dominates. If the auditory system contains specialised motion detectors, stimuli moving over different distances and durations but defining the same speed should be more difficult to discriminate. The resulting discrimination contours should therefore be oriented obliquely along iso-speed lines within the distance-duration plane. However, we found that over a wide range of speeds, distances and durations, the ellipses aligned with distance-duration axes and were stretched vertically, suggesting that listeners were most sensitive to duration. A second experiment showed that listeners were able to make speed judgements when distance and duration cues were degraded by noise, but that performance was worse. Our results therefore suggest that speed is not a primary cue to motion in the auditory system, but that listeners are able to use speed to make discrimination judgements when distance and duration cues are unreliable.     

Gating of ventilatory activity in the cave-cricket, Troglophilus cavicola

ABSTRACT. The rhythm of 'abdominal respiratory movements' (ARMs) in partly tethered cave-crickets was recorded via correlated hindleg movements associated with abdominal ventilation, and analysed with respect to postural changes (cricket placed horizontally or vertically) under the following stimulus regimes: touch stimuli of constant duration but varying rates were presented to the hind legs independently of the ARM rhythm; touch stimuli with constant delays were triggered by the previous ARM; and light stimuli were presented, preceding the touch stimuli. With constantly spaced touch stimuli, on- and off-effects are visible in the number of ARMs per time unit and this is more pronounced in the horizontal than in the vertical position. Continuous modulations of ARMs patterning (tonic effects) are revealed in free run cycles which are intercalated in rhythmic driving series: at intertouch lengths of 20 s such free run cycling is faster under vertical than under horizontal conditions. With the vertical stance it is delayed by additional light. Even the kind of vertical orientation causes tonic effects. Thus crickets that face downward exhibit a slower ARM rhythm than those facing upward. Under entrainment to constantly delayed touches, two parameters of ARM rhythm ('basic period' and 'consecutive period') were studied to elucidate the hypothetical cycling of the pacemaker under different stances. Under horizontal conditions the 'basic periods' are shortened if the delay of touch does not exceed 0.2 periods of free run cycling. However, in the vertical position, the 'basic periods' are prolonged. With delay times exceeding 0.5 periods of free run cycle, the 'consecutive periods' are lengthened if the cricket is oriented vertically, but remain unaffected under horizontal conditions. On the basis of these results, a model for resetting and sensory modulation of ARM control is presented.