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We studied the acoustic and reproductive behaviour of the clawed frog, Xenopus laevis, in a pond with clear water in South Africa over a period of two months. It contained 21 adult males and female...

The ability to locate and discriminate water surface waves that impinge simultaneously from multiple directions was studied in the clawed frog, Xenopus laevis. Monofrequency waves of 5-30 Hz were presented from point sources at a distance of 10 cm from the frog, unless stated otherwise, and the animal's response turn towards the wave origin examined. Two-choice conditioning with two simultaneous frontal waves at a 90-degree inter-wave angle revealed discrimination thresholds lower than 1 Hz for 10- to 20-Hz source wave frequencies. Smaller inter-wave angles resulted in larger thresholds, and no discrimination was found below 40°. If a third wave was added from behind, the frequency discrimination of the two frontal waves deteriorated, with 18 Hz being discriminated from waves differing by at least 2.75 Hz. Subjects also discriminated between two simultaneous waves of equal frequency presented from differing distances. At a distance of 10 cm, the discrimination threshold was 0.95 cm. Thus, X. laevis is capable of discriminating source distances in an overlap on the basis of wave curvatures. The detection of source directions among four, six or eight waves of equal frequency and distance was investigated by measuring the angular distribution of the response turns. Turns were significantly more closely oriented towards sources than to intermediate directions. The orientation accuracy did not degrade with the number of waves.

Comparative studies of vocal repertoires over the geographical range of a species can improve our understanding of the function and evolution of animal vocalizations. They may also help to elucidate relationships between populations, where genetic studies are missing or difficult to perform. We recorded male bearded seal vocalizations from four sites throughout their Arctic distribution. We measured 16 parameters for each vocalization and examined variability using classification tree analyses. There were four major call categories: trill, ascent, sweep and moan. Trills divided further into three subcategories: trills with ascent/plume, long trills and short trills. Not all call categories were present at all sites: the ascent occurred only in Alaska and western Canada, the sweep occurred only in Svalbard and in the High Canadian Arctic, and the trill with ascent/plume occurred at all sites except Svalbard. Geographical differences between sites were apparent in repertoire size as well as in vocal structure. Furthermore, an east–west gradient in structural similarities between call types was apparent. The vocal repertoire of bearded seals seemed to be relatively stable; for example, over a period of 16 years no calls were lost or added to the Alaskan repertoire. The most likely explanation for the observed vocal differences between sites is the geographical isolation of populations by physical distance. Other factors, such as varying ecological influences (e.g. adaptation to varying ice habitats) or sexual selection, may also contribute to vocal variability and result in the observed geographical variation.

The ability to locate and discriminate water surface waves that impinge simultaneously from multiple directions was studied in the clawed frog, Xenopus laevis. Monofrequency waves of 5-30 Hz were presented from point sources at a distance of 10 cm from the frog, unless stated otherwise, and the animal's response turn towards the wave origin examined. Two-choice conditioning with two simultaneous frontal waves at a 90-degree inter-wave angle revealed discrimination thresholds lower than 1 Hz for 10- to 20-Hz source wave frequencies. Smaller inter-wave angles resulted in larger thresholds, and no discrimination was found below 40°. If a third wave was added from behind, the frequency discrimination of the two frontal waves deteriorated, with 18 Hz being discriminated from waves differing by at least 2.75 Hz. Subjects also discriminated between two simultaneous waves of equal frequency presented from differing distances. At a distance of 10 cm, the discrimination threshold was 0.95 cm. Thus, X. laevis is capable of discriminating source distances in an overlap on the basis of wave curvatures. The detection of source directions among four, six or eight waves of equal frequency and distance was investigated by measuring the angular distribution of the response turns. Turns were significantly more closely oriented towards sources than to intermediate directions. The orientation accuracy did not degrade with the number of waves.

Mating calls of three frog species abundant in northeast IndiaRana tigerina,Rana cyanophlyctis andRana limnocharis were recorded in the fields of Assam and Meghalaya during their breeding season (July-August, 1991). The calls were analysed for their temporal and spectral characters. They were species specific, with distinct call duration and call period, number of pulses per call and interpulse interval, and dominant frequency and frequency domain. A comparison of the mating calls ofRana cyanophlyctis with those of the siblingRana ehrenbergi from Yemen showed differences in their temporal and spectral characters, supporting the suggestion that these two species are distinct species, rather than subspecies of the same species. Differences in the temporal and spectral pattern were found in the mating calls of morphologically alike specimens ofRana limnocharis, indicating that the present morphotypeRana limnocharis in northeast India is composed of several species.

SUMMARYIn goldfish and other otophysans, the Weberian ossicles mechanically link the saccule of the inner ear to the anterior swimbladder chamber (ASB). These structures are correlated with enhanced sound-pressure sensitivity and greater sensitivity at high frequencies (600–2000 Hz). However, surprisingly little is known about the potential impact of the ASB on other otolithic organs and about how auditory responses are modulated by discrete sources that change their location or orientation with respect to the ASB. In this study, saccular and lagenar nerve fiber responses and conditioned behaviors of goldfish were measured to a small, low-frequency (50 Hz) vibrating sphere (dipole) source as a function of its location along the body and its orientation with respect to the ASB. Conditioned behaviors and saccular nerve fiber activity exhibited response characteristics nearly identical to those measured from a hydrophone in the same relative position as the ASB. By contrast, response patterns from lagena fibers could not be predicted by pressure inputs to the ASB. Deflation of the ASB abolished the characteristic spatial response pattern of saccular but not lagena fibers. These results show that: (1) the lagena is not driven by ASB-mediated pressure inputs to the ear; (2) the ASB–saccule pathway dominates behavioral responsiveness, operating effectively at frequencies as low as 50 Hz; and (3) behavioral and neural (saccular) responses are strongly modulated by the position and orientation of the dipole with respect to the ASB.

The state of our knowledge of wave analysis with the lateral line system in amphibians is reviewed. Knowledge is based largely on tests with the clawed frog, Xenopus laevis, and a few comparative studies in other species. In Xenopus, all lateral line organs have equal frequency tuning with maximal sensitivity at 25 Hz. Wave amplitude is encoded over 80 dB by synchronization and mean firing rate. Frequency discrimination has been demonstrated by conditioning, optimal discrimination is 4% at 14 Hz. Wave localization for all directions is very accurate, it depends on comparison of the inputs from neighbouring organs. Comparison between a few organs suffices for accurate localization, these may be located on various parts of the body or may even be unilateral. Centrally, a topological organization with regard to wave direction exists in the mid-brain. Xenopus can identify and localize component waves in a superposition of waves.

Several environmental pollutants have been identified as antiandrogenic endocrine disrupting chemicals (EDC), with flutamide (FLU) being a model compound for this type of action. Despite impacts of EDC interfering with sexual differentiation and reproduction in amphibians, established information about suggested effects on sexual behavior is still lacking. In this study adult male Xenopus laevis were injected with human chorionic gonadotropin (hCG) to initiate mate calling behavior. After one day hCG-stimulated frogs were treated via aqueous exposure over three days without and with FLU at concentrations of 10(-8) and 10(-6) M in comparison to untreated frogs. Androgen controlled mate calling behavior was recorded during the 12h dark period. At the end of exposure circulating levels of testosterone (T) and 17beta-estradiol (E2) were determined and furthermore gene expression was measured concerning reproductive biomarkers such as hypophysial luteinizing hormone (LH), follicle-stimulating hormone (FSH), testicular aromatase (ARO), 5alpha reductase type 1 (SRD5alpha1) and 5alpha reductase type 2 (SRD5alpha2). Both concentrations of FLU caused a significant decrease in calling activity starting at the second day of exposure. HCG injected positive controls had elevated levels of T compared to negative control frogs while in parallel treatment with FLU did not affect significantly the hCG elevated sex steroid levels. Furthermore, hCG treatment led to significantly decreased levels of gene expression for ARO and SRD5alpha2 but no impacts were detected on LH, FSH or SRD5alpha1 mRNA levels compared to negative controls. In summary, the behavioral parameter mate calling is the most sensitive biomarker detecting antiandrogenic modes of action in this challenge-experiment indicating that this non-invasive method could markedly contribute for sensitive assessment of antiandrogenic EDC.

Auditory evoked potentials (AEPs) to clicks and tonal pulses were recorded from medulla and midbrain in Xenopus laevis laevis . They comprise three components: an initial peak ( I ) at 2.2–3 ms latency, a fast series of peaks ( F ) at 5–15 ms latency, and a slow negative wave ( S ) at 20–40 ms latency. In medullary recordings, the initial peak was largest, whereas in midbrain recordings typically the two other components prevailed. For all components and animals, response threshold at 4 clicks/s was approximately 69 dB SPL. In response to tonal stimuli, AEP amplitudes were maximal at 1.3–2.0 and 3.5 kHz. Raising the click rate to 100/s gradually reduced the amplitude of the I and the first F peaks, whereas later F peaks and the S wave virtually disappeared at 20–40 clicks/s. On the other hand, extending the plateau duration of tonal stimuli from 4 to 10 ms hardly affected the I and F peaks but doubled the S amplitude. This suggests two systems for stimulus processing, a fast system capable to follow clicks up to high repetition rates and a slow system with longer integration time.

The clawed frog Xenopus is an aquatic predator catching prey at night by detecting water movements caused by its prey. We present a general method, a "minimal model" based on a minimum-variance estimator, to explain prey detection through the frog's many lateral-line organs, even in case several of them are defunct. We show how waveform reconstruction allows Xenopus' neuronal system to determine both the direction and the character of the prey and even to distinguish two simultaneous wave sources. The results can be applied to many aquatic amphibians, fish, or reptiles such as crocodiles.

Hearing threshold and frequency discrimination for underwater sound were measured in the clawed frog Xenopus laevis by means of conditioning. A go/no go discrimination procedure was used in which the test tone was presented concurrently with a wave on the surface of the water. The tone signalled whether or not the frog should respond to the wave. The hearing range of X. laevis was 200–4000 Hz. Similar thresholds of 92–96 dB re 1 μPa were found at 600 Hz, 1400–1800 Hz and 3200–3600 Hz. A high threshold at 1000–1300 Hz suggested that this was the frequency range between the sensitivities of the amphibian and basilar papillae. Relative frequency discrimination was approximately 5 % at 400–800 Hz, 45 % at 1000 Hz and 2.4–6 % at 1600–2500 Hz. This last range encompasses the dominant frequencies of the advertisement call of this species. High discrimination acuity at these frequencies may be used in distinguishing between calling males. The threshold for a one-third-octave bandpass noise centred at 600 Hz was 27.6 dB lower than that for a pure tone of 600 Hz, suggesting that sound intensity was integrated within this bandwidth, possibly by a critical-band mechanism.

Mammalian-like 'sensory neglect' phenomena were elicited in Xenopus laevis by unilateral telencephalic lesion: after damage of the caudal striatum response rate to contralateral water waves was significantly lower than to ipsilateral ones. Response accuracy, however, was not affected. Within 6-8 weeks, animals recovered from neglect of unilateral stimuli; but simultaneous bilateral stimulation revealed an enduring neglect of contralateral stimuli. Latencies during acute neglect were significantly higher than after recovery. These results suggest that the neural mechanisms of selective attention might have evolved earlier than thought so far.

Anesthetized clawed frogs (Xenopus laevis) were stimulated with underwater sound and the tympanic disk vibrations were studied using laser vibrometry. The tympanic disk velocities ranged from 0.01 to 0.5 mm/s (at a sound pressure of 2 Pa) in the frequency range of 0.4-4 kHz and were 20-40 dB higher than those of the surrounding tissue. The frequency response of the disk had two peaks, in the range of 0.6-1.1 kHz and 1.6-2.2 kHz, respectively. The first peak corresponded to the peak vibrations of the body wall overlying the lung. The second peak matched model predictions of the pulsations of the air bubble in the middle ear cavity. Filling the middle ear cavity with water lowered the disk vibrations by 10-30 dB in the frequency range of 0.5-3 kHz. Inflating the lungs shifted the low-frequency peak downwards, but did not change the high-frequency peak. Thus, the disk vibrations in the frequency range of the mating call (main energy at 1.7-1.9 kHz) were mainly caused by pulsations of the air in the middle ear cavity; sound transmission via the lungs was more important at low frequencies (below 1 kHz). Furthermore, the low-frequency peak could be reversibly reduced in amplitude by loading the larynx with metal or tissue glue. This shows that the sound-induced vibrations of the lungs are probably coupled to the middle ear cavities via the larynx. Also, anatomical observations show that the two middle ear cavities and the larynx are connected in an air-filled recess in submerged animals.(ABSTRACT TRUNCATED AT 250 WORDS) Udgivelsesdato: 1995-Mar

The acuity of frequency discrimination was tested in the clawed frog, xenopus l. laevis by means of conditioning. xenopus is completely aquatic and communicates acoustically on the bottom of ponds. For conditioning, a tank was built in which pure tones could be presented to the animal. The paradigm was discrimination of water surface waves contingent upon the underwater tone presented simultaneously, i.e., distinguishing a wave presented with tone A from a wave with tone B. Frequency discrimination was best in the range 1600–2000 Hz, where relative discrimination up to 2% was found. This range matches the range of the dominant frequency in the frog’s advertisement call. Whereas there is considerable variation between individuals, the dominant frequency of a given individual is very constant, varying by less than 10–20 Hz even when the hormonal status of the animal or the temperature of the water is changed. Thus the animals can distinguish between calling males on the basis of the dominant frequency. In the field, males establish territories whose location may remain constant for weeks up to years, so that stable neighbor relationships are formed. In such a situation, recognition of the neighbor’s call may be advantageous.

Auditory interneurone responses in the mesothoracic ganglion of the cricket Gryllus bimaculatus were investigated with special regard to temporal features of the calling song. Units representing five response types were found. One type codes verse syllables and intensity. The second codes syllables of highfrequency verses. The third responds as a pulse marker. The fourth shows adaptation and the response pattern depends on the verse frequency. The fifth fires a burst at verse onset. Responses of mesothoracic units recorded in two other cricket species do not differ markedly from those of Gryllus bimaculatus. Particularly, no tuning is found to species-specific differences in their calling songs. The stimulus direction can affect the threshold in different ways: dependence at all frequencies, dependence only between 3 and 6 kHz, and independence are found. The dependence is mainly expressed by a higher threshold for contralateral sounds. The mesothoracic branching of a few neurones was demonstrated by extracellular CoS-staining. These cells pass through the ganglion as connective fibres giving off small branches into the ventro-medial and dorso-medial neuropiles.

1. The role of the ventral lateral line organs in water surface wave localization in the clawed toad,Xenopus laevis Daudin, was tested in blinded animals with various lesions of lateral line organs. 2. After destruction of all its dorsal lateral line organs, but with all its ventral organs intact,Xenopus shows normal responsiveness and full response accuracy to waves from any direction (Fig. 2). 3. Additional partial destruction of ventral organs seriously impairs wave localization (Fig. 2). Determination of the stimulus side, however, is mostly not affected by these lesions (Table 1). Thus, information about the side to which to turn, and the angle through which to turn are obtained differently from lateral line input. 4. Xenopus with only one side's dorsal receptors intact responds to waves as accurately as animals with intact dorsal and ventral receptors on that side (Fig. 2). Thus, ventral input does not improve accuracy of localization in the horizontal plane beyond that provided already by the dorsal receptors alone. 5. Xenopus with only its ventral receptors intact shows a significant increase in turning down, which is specific for this type of lesion (Table 2). Thus, comparison between dorsal and ventral inputs is involved in vertical localization. 6. InXenopus with only its ventral receptors on one head side intact, turn angles to given stimulus angles vary more than in specimens with total lateral line destruction. This suggests a hierarchy inXenopus' reliance on its sense organs for wave localization in that even indistinct lateral line input is taken as more relevant than the information from the frog's other wave localizing organ(s).

1. The ability of adultXenopus laevis to discriminate water waves of different frequencies was tested by go/no-go conditioning. 2. In the range 5–30 Hz,Xenopus can distinguish waves on the basis of frequency. In this range, the relative discrimination limen DL had an optimum of 0.04 at 14 Hz and increased to 0.15 one octave above and below (Fig. 3). When the relative difficulty of the conditioning paradigm is taken into account, this discrimination acuity is in the range of vertebrate auditory discrimination. 3. Frequency discrimination was not limited to surface waves, but was also performed when the frog was sitting on the bottom of the basin.

The central nervous organization of water wave localization in the clawed frog Xenopus laevis was investigated by performing behavioral tests on frogs that had various brain ablations. The criterion of localization was the orientation of response turns toward the origin of stimulus waves. After complete midbrain ablation, Xenopus still detected impinging waves but could not localize them. After thalamopretectal ablation, however, Xenopus localized waves with normal accuracy. Thus, wave localization can be accomplished in the brainstem, and the midbrain is necessary for it. After forebrain ablation, the frogs no longer responded to water waves, which shows that higher brain centers modulate localization. Tectal lesions that spared the ventrolateral tectum did not abolish localization. After unilateral extirpation of tectum and torus, all ipsilateral waves were localized, but contralateral waves were not. This indicates a functional chiasm for the determination of wave directions in the midbrain. Total localization failure after unilateral midbrain destruction demonstrates that wave localization also requires the ipsilateral motorial tegmentum. When wave localization was abolished, a residual correlation between stimulus directions and response angles remained.

The ability of adultXenopus laevis to identify water wave frequencies was demonstrated by go/no-go conditioning. The acuity of frequency recognition is of absolute-pitch quality.

1. The accuracy of taxis response in blinded adult clawed toads (Xenopus laevis Daudin) to water surface waves was measured in animals with an intact lateral line system and in animals with either total or one of 12 different partial lesions of the system. 2. Animals with an intact lateral line system are able to locate wave directions at least to within ±5 ° (Fig. 2A). 3. In response to stimuli coming from behind,Xenopus tend to turn through less than the stimulus angle. This tendency varies substantially even in the same animal and apparently reflects the frog's motivational state rather than sensory inaccuracy of the system (Fig. 2). It can be affected by the type of food the animals are given (Table 1). 4. Shallow water (3–4 cm) decreases the angle through which the animals turn by 5–15% irrespective of the stimulus direction (Table 1). 5. Xenopus with all of their lateral line organs destroyed are still able to respond to surface waves in an oriented fashion. Compared to animals with an intact system they respond somewhat less accurately to anterior stimuli and much less accurately to stimuli from behind (Fig. 3). 6. Elimination of fewer than half of the receptors has no effect on response accuracy. In some lesions even after destruction of 70–95% of the receptors response accuracy does not differ from that of animals with an intact system (Fig. 3). 7. After certain lesions involving unilateral destruction of the head receptors differences in the responses to right- and left-side stimulation are found (Fig. 3). 8. Several lesions resulted in an increased tendency to turn contralateral to the stimulus. The average size of these contralateral rotations increases with increasing stimulus angle (Table 2). 9. The following conclusions can be drawn about spatial analysis by the lateral line system: Wave directions are not located by evaluating their intensity gradient along the animal. The animal does not orient according to the direction of maximum sensitivity of its activated receptors. Temporal comparison of receptor activation seems to be involved in the location of wave directions. Multiple representation with full accuracy of all stimulus angles is present in several subsets of the lateral line receptors. Decisions about the size and the side of the response are, at least in part, made independently.

1. The responses of free-standing lateral-line organs to water surface waves were examined in the clawed frog,Xenopus laevis, by recording from the organs' afferent fibers. 2. Responses to waves consisted of modulations of the fiber's spontaneous discharge frequency. Typically, the modulation followed the wave frequency, but occasionally transients or harmonic or subharmonic modulations were observed (Figs. 3, 10). 3. Stimulus intensity was encoded by the degree of spike synchronization with the excitatory phase of the wave cycle and by the organ's maximal firing rate (Figs. 3, 4). Synchronization reached saturation at about 29 dB above threshold, but maximal firing increased linearly with the logarithm of the stimulus amplitude up to 80 dB above threshold. 4. The sensitivity of the organs could fluctuate with time; such changes were correlated with shifts in the spontaneous firing rate of the organ (Fig. 5). 5. Stimulus intensity did not affect the phase of the response period, but within that period the mean phase of firing shifted slightly with stimulus intensity (Fig. 6). 6. The data demonstrate an asymmetry between the inhibitory and excitatory transduction processes. Inhibition saturated at about 29 dB above threshold, but excitation continued to increase with stimulus intensity through all amplitudes applied. On the other hand, inhibition was strong enough to completely suppress firing for up to 70% of the wave cycle (Fig. 4). 7. The responses of the organs were maximal at 5 Hz, the lowest frequency tested in our equipment. With higher wave frequencies, response threshold increased, and the upper frequency response limit was mostly below 20 Hz (Fig. 7). It is suggested that this shift of responsiveness toward lower frequencies is due to characteristics of the surface wave. 8. From the thresholds for surface waves, the minimal threshold amplitude for water movementsat the cupula was calculated to be 0.01 μm (Table 1). 9. Stimulus direction affected considerably the response latencies and thresholds of the organs (Figs. 8, 9). The main determining factor for the response threshold was the animal's wave shadow, which could be as high as 30–40 dB.

The organization of water surface wave analysis with the lateral-line system has been investigated by electrophysiological recording and behavioral testing in the clawed frog, Xenopus laevis. In the afferent fibers, wave frequency is encoded by phase coupling of the discharges, while stimulus intensity is encoded over a range of 80 dB by phase coupling and mean firing rate. Additionally, cardioid directional sensitivity is found. Behavioral tests after partial lesions show that small groups of the animal’s lateral-line organs are sufficient for localizing waves from any direction; this suggests that the high number of lateral-line organs in Xenopus may serve more complex wave analyses. The capability for complex analysis is demonstrated in the animal’s ability to detect the direction and the frequency of component waves in wave superpositions. In the midbrain, a topological organization with regard to wave direction is found that does not reflect the topology of the organs on the body. Wave frequency discrimination is found: its accuracy is comparable to that in hearing, and wave frequency memory is of absolute pitch quality. The results correspond to stimulus processing in the auditory system and give new support to the octavolateralis hypothesis of a common evolutionary origin of the lateral-line and eighth-nerve sensory systems.

Perception of water movement on the body by means of lateral line organs is lacking in humans. Therefore, to understand stimulus analysis with the lateral line system, behavioral analyses that reveal the system’s sensory capacities are particularly important. The results of psychophysical testing provide insight into what kind of information about the aquatic environment can be obtained with the system. They are further prerequisites for adequate electrophysiological and theoretical analyses of how the system’s properties are accomplished. In this chapter, the results of behavioral analyses of the mechanoreceptive lateral line system (subsequently referred to as lateral line system) in amphibians are reviewed, and some parallels to stimulus analysis in the electroreceptive lateral line and auditory systems are pointed out.