Gernot Wendler

Cricket phonotaxis: localization depends on recognition of the calling song pattern

SummaryCalling song with a carrier frequency of 5 kHz evokes positive phonotaxis in female crickets,Gryllus bimaculatus, when presented at an azimuth. In contrast, a continuous tone of 4.7 kHz in the same position when paired with calling song from above leads to negative phonotaxis. Under open-loop conditions, when a tethered animal runs on a paired tread wheel, characteristic curves are produced with the stable equilibrium point towards or away from the stimulus, respectively (Fig. 3).In order to understand this sign reversal at the neuronal level, directional characteristics of the ascending acoustic inter neurons AN1 and AN2 were measured using extracellular recordings from the cervical connectives.Taking the mean spike rate of the interneurons as a measure for their excitation, the function relating response magnitude to stimulus direction for calling song corresponds well to the behavioural characteristic curve (Fig. 5). The response function obtained using a continuous tone with simultaneous presentation of calling song from above is similar (Fig. 5) and hence does not correspond to the inverse behavioural characteristic curve.However, consideration of the extent to which the temporal parameters of the calling song (syllables and chirps) are reflected in the neuronal response (amplitudes of the Fourier components) leads to characteristic curves for AN1 and AN2 which are in good agreement with the behaviour for stimulation with calling song as well as for the continuous tone experiment (Fig. 8). In addition, the neural response curves correspond to the behaviour in showing smaller amplitudes when a continuous tone rather than the calling song is presented on the horizon (Fig. 8).From these data we conclude that the activity in interneurons AN1 and AN2 does not directly guide orientation in mating behaviour but first is filtered by a mechanism tuned to the frequency of syllables and/or chirps. According to this hypothesis recognition of conspecific song and localization proceed sequentially inGryllus.

The Phasic Influence of Self-Generated Air Current Modulations on the Locust Flight Motor*

Summary1.Using high speed film analysis (500 frames/s) to investigate the head nodding movement during tethered flight inLocusta shows that the position of the wind-sensitive head hairs with respect to the flight direction is altered by 5.5° in the rhythm of the wing beat (Fig. 2).2.Wind measurements in the region of the hair fields demonstrate that the wind reaching the hairs during flight is modulated by the animals own wing beat. The modulation has a peak-to-peak value of 0.6–1.0 m/s (Fig. 3).3.An airstream with its speed modulated by these values was used to stimulate the wind-sensitive hairs to analyse the steady-state response during tethered flight in animals with the antennae removed (Fig. 1). In these entrainment experiments absolute coordination (a relation of locked phase) between the wind modulation and the flight oscillator is found in a range of about 3 Hz around the intrinsic flight frequency. At frequencies both above and below this range, relative coordination (a relation of preferred phase) is obtained (Figs. 4–7).4.The dynamic response to step changes in the modulation frequency was tested. There is an immediate reaction, but it takes several wing beats to reach the new steady-state (Fig. 8).5.When flight was elicited while a modulated wind stream was already blowing, the first wing beat occurred in a preferred phase with respect to the stimulus modulation (Figs. 10 and 11).6.To understand the generation of the flight pattern, the whole flight oscillator must be considered as a cooperative system of central neuronal, sensory (proprioceptive) and mechanical components (Fig. 12).

Stick insects walking on a wheel: Perturbations induced by obstruction of leg protraction

SummaryStick insects (Carausius morosus) walking on a wheel were perturbed by restricting the forward protraction of individual legs. A barrier placed before a single middle or rear leg prevented that leg from reaching its normal protraction endpoint but allowed it unimpeded retraction. Upon striking the barrier, the protracting leg attempted to get past it and thereby prolonged protraction. This prolongation increased with the extent to which the obstruction infringed upon the legs normal step range. Barriers placed near the midpoint of this range elicited large perturbations: the blocked leg often continued its protraction throughout many step cycles of the other legs (Fig. 1 E, F). For the most part walking was irregular and smooth forward progression was disrupted. Nevertheless, the infrequent steps by the affected leg usually were coordinated with those of the adjacent ipsilateral legs.More rostral barrier positions elicited smaller perturbations: the blocked leg usually made one step in each step cycle of the other legs (Fig. 1 B, C, D, G). Measurements for these regular step sequences showed quantitatively that protraction duration increased in proportion to the severity of the infringement on normal leg movement (Figs. 3, 4). The fraction of the step period occupied by protraction increased from ca. 10% for normal walking to ca. 50% for caudal barrier positions. This proportionality is interpreted to show the importance of spatial components of the walking program.When one leg was obstructed, its extended protraction influenced the stepping of the three adjacent legs as follows. First, the ipsilateral rostral leg showed the largest change: its protraction onset was regularly delayed for the duration of the extended protraction (Figs. 4, 7, 8), demonstrating a strong, centrally mediated inhibition. The presence of a further delay of up to 100 to 140 ms suggests that peripheral input from the protracting leg may be important for releasing this inhibition. Second, steps by an adjacent caudal leg were not measurably affected. However, the method may not have sufficed to reveal such effects because during regular walking middle leg protractions rarely lasted long enough to conflict with subsequent steps by the ipsilateral rear leg. Third, contralateral effects differed between middle and rear leg obstructions. If the obstructed leg was a middle leg, its extended protraction had little effect upon stepping by the contralateral middle leg: the latter leg frequently protracted while the blocked leg continued its protraction and there was no consistent change in the phase relation of these two legs (Table 1). In contrast, if the obstructed leg was a rear leg, protractions by the contralateral rear leg tended to be delayed (Table 1).

Phonotaxis inGryllus campestris L. (Orthoptera, Gryllidae)

SummaryPhonotaxis of receptive female field crickets (Gryllus campestris L.) towards a taped model of the species-specific calling song (Fig. 1) presented azimuthally at 12 different sound pressure levels, ranging from 39 to 106.5 dB, is investigated using a locomotion compensator. The orientational performance of the crickets is analysed in the intact state (1.), as well as after occlusion of both prothoracic spiracles (2.), both posterior tympana (3.), both prothoracic spiracles and both posterior tympana (4.), one posterior tympanum and one prothoracic spiracle at a time (5.).1.In intact female crickets acoustic orientation on average starts at 44 dB. The orientational performance improves steadily up to 79.5 dB, deteriorates slightly at 86 and 91.5 dB and remarkably at 106.5 dB calling song intensity (Figs. 3, 4 and 11).2.Following wax occlusion of both prothoracic spiracles (Figs. 5 and 6) behavioural threshold of phonotaxis is raised by on average 5 dB to 49 dB. The course of the intensity curve is similar to that evaluated for intact crickets, the orientational performance at a given intensity being merely slightly reduced (Fig. 11).3.Occlusion of both posterior tympana (Figs. 7 and 8) does not abolish the capability of acoustic orientation. Compared to intact animals the behavioural threshold is only raised by on average 17.5 dB to 61.5 dB (Fig. 11). Orientational performance at suprathreshold intensities improves with increasing song intensity, but remains inferior to that of intact crickets unless a 106.5 dB calling song is presented.4.Phonotaxis is even evident after occlusion of the posterior tympana and the prothoracic spiracles with wax (Figs. 9 and 10). This operation results in an effective attenuation of on average 30 dB, the behavioural threshold being raised to 74 dB (Fig. 11). At suprathreshold intensities orientational performance is further reduced compared to that of crickets after occlusion of the posterior tympana only.5.Occlusion of a posterior tympanum and a prothoracic spiracle on opposite sides results in a stable course deviation of on average 49 ° towards the side of the intact posterior tympanum at 61.5 to 91.5 dB (Figs. 13, 14A and B). This demonstrates that the effect of an occluded posterior tympanum overrides that of an occluded prothoracic spiracle. Occlusion of these sound entrances on the same side results in strong turning tendencies towards the intact side, which increase with calling song intensity (Fig. 14C and D). Except in a single crickets run performed at 106.5 dB, stable courses are no longer found (Fig. 15). Thus, phonotaxis is more strongly impaired than after occlusion of these sound entrances on opposite sides.

Pattern Recognition and Localization in Cricket Phonotaxis

Males of the cricket species Gryllus campestris and Gryllus bimaculatus produce a calling song which consists of groups (=chirps) of 3 to 4 syllables. Receptive females approach the male (phonotaxis), guided by the calling song. The females solve two problems: 1) They recognize the conspecific calling song and distinguish it from noise and from heterospecific sounds. 2) They find the correct direction towards the male. The following contribution will deal with the interdependence between these two processes.

The orientation of grain weevils (Sitophilus granarius): influence of spontaneous turning tendencies and of gravitational stimuli

SummaryThe paths followed by grain weevils (Sitophilus granarius) in a featureless environment are curved or circular. Animals walking in circles display average angular velocities that may exceed 10°/s. The circling is not due to any asymmetrical damage to the weevils limbs. Circling weevils walking on a sloping surface follow characteristic paths: on slight slopes the circles become cycloids, which in turn, become relatively straight paths on steep slopes. The mean direction of the cycloidal paths deviates from the direction of the straight paths. Left circlers deviate to the left and right circlers deviate to the right. These results can be explained by a feedback control loop with an additive interaction of internal and feedback signals. The cycloid paths thus result from an unstable state of the feedback loop in which the feedback signal from the gravity receptors is always smaller than the internal signal.

THE GIANT FIBER SYSTEM IN THE FORELEGS (WHIPS) OF THE WHIP SPIDER HETEROPHRYNUS ELAPHUS POCOCK (ARACHNIDA:AMBLYPYGI)

SummaryThe front legs of the whip spider H. elaphus are strongly modified to serve sensory functions. They contain several afferent nerve fibers which are so large that their action potentials can be recorded externally through the cuticle. In recordings from the tarsus 7 different types of afferent spikes were identified; 6 additional types of afferent spikes were discriminated in recordings from the tibia and femur. Most of the recorded potentials could be attributed to identifiable neurons serving different functions. These neurons include giant interneurons and giant fibers from diverse mechanoreceptors such as slit sense organs, trichobothria, and a joint receptor. In the present report these neurons are characterized using electrophysiological and histological methods. Their functions are discussed in the context of the animals behavior.

Aggregation Agents in German Cockroach Blattella germanica: Examination of Efficacy

Aggregation behavior and reduced locomotory activity in the German cockroach is known to be caused by chemical compounds in the feces. The attractive and/or arrestant efficacy of three relevant substances was tested in first instars by a two-choice aggregation test and in adults with a locomotion compensator apparatus that allows quantification of taste-directed orientation and walking speed as a function of antennal stimulation. The three substances tested were a feces crude extract; a mixture of six carboxylic acids (mix G) out of a total of 29 that were identified in the feces extract and tested as single compounds and in various combinations; and a steroid glucoside denoted as blattellastanoside A, which has been suggested as an aggregation arrestant pheromone in Blattella germanica. With both of our test methods, feces extract and mix G proved to be very attractive, whereas the effects of blattellastanoside A were, if anything, very poor. Possible reasons for discrepancies are discussed.

The activity of pleurodorsal muscles during flight and at rest in the moth Manduca sexta (L.)

In the moth Manduca sexta, the paired mesothoracic flight steering muscle II PD2m takes part in the generation of the flight rhythm and is spontaneously active in the non-flying animal. This spontaneous activity is modulated by optomotor stimuli and directionally selective. The directional response characteristics are analyzed. Another spontaneously active steering muscle pair, the III PD2c, is situated in the metathorax. The activities of this pair and of a third muscle pair, the III PD3 are also influenced by visual stimulation.The responses of all 6 muscles to optomotor stimuli which simulate the flight situations yaw, roll, thrust and lift are analyzed. Each situation elicits a unique pattern of activation/deactivation within this set of muscles. The activity pattern in non-flying animals allows the prediction of flight steering mechanisms such as changes of wing area in flight turns and provides a useful basis for the analysis of visuo-motor pathways.

Morphology and physiology of peripheral giant interneurons in the forelegs (whips) of the whip spider Heterophrynus elaphus Pocock (Arachnida: Amblypygi)

SummaryThe tarsi of the modified front legs (whips) of the whip spider Heterophrynus elaphus contain two afferent giant fibers, GN1 and GN2, with diameters at the tibia-tarsus joint of ca. 21 μm and 14 μm, respectively. The somata of these two neurons lie in the periphery, about 25 cm away from the CNS. These two neurons are interneurons which receive mechanoreceptive inputs from approximately 750 and 1500 bristles, respectively. The receptive fields of GN1 and GN2 overlap; they extend for 40 mm (GN1) and 90 mm (GN2) along the length of the tarsus. About 90% of the synapses onto the giant fibers are axo-axonic. Mechanical stimulation of a single bristle is sufficient to elicit action potentials in one or both interneurons. The response of the interneurons adapts quickly. Average conduction time from the soma to the CNS is 45 ms for GN1 and 55 ms for GN2. Mean conduction velocities are 5.5 and 4.2 m/s, respectively. Activity in the giant fibers does not elicit a motor response; hence the giant fibers do not mediate an escape response. Possible functions of these giant fibers are discussed and compared to those of giant fiber systems in other arthropods.