An electrophysiological study of sound sensitive neurons in the ‘Primitive ear’ of Acheta domesticus

Crickets have two types of mechanisms for the reception of environmental sounds: (1) the tympanal organs in the two forelegs and (2) the freely articulated setal receptors on the abdominal ceri. The cercal setal receptors have hitherto received much less experimental attention as decoders of biologically significant sounds than have the tympano-receptors. In the present study the cercal auditory system of Acheta domesticus was examined electrophysiologically to determine its auditory frequency sensitivity, the tuning characteristics of individual units, and the synchronization between nerve impulses and stimulus frequency. Both pre- and postsynaptic units were examined in the fifth abdominal ganglion; several of the observed response patterns were compared with those of homologous cercal sensory neurons in Periplaneta americana. The results show that (1) A. domesticus possesses an elaborate array of cercal receptors which are highly sensitive to sounds, (2) the cercal setal receptors are more sensitive and numerous in the cricket than in the cockroach, and (3) the cercal auditory system can decode stimulus information by narrow tuning in individual cells and by synchronous discharge patterns; firing frequencies range up to 300 Hz in presynaptic sensory units and 60 Hz in the postsynaptic giants. The response patterns were related to the structure of the receptor and the behavioural adaptations of the insect.     

Can spectral cues contribute to species separation in closely related grasshoppers?

 The acridid grasshoppers Chorthippus biguttulus and Ch. mollis, which are closely related and often sympatric species, were compared intra- and interspecifically with regard to the spectra of their calling and courtship songs and of the sound-induced vibrations of the tympanal membrane, as well as the threshold curves of the tympanal nerve. In the low-frequency range but not in the ultrasound region, the maxima of these various curves fall at distinctly different frequencies in the two species. It is shown that the low-frequency sensitivity of the auditory system in both species, especially in females, is well matched to the conspecific song spectra but not to those of the heterospecific songs. Whether these characteristics actually contribute to species discrimination remains to be determined by behavioural tests. Accepted: 23 August 1996     

Directional characteristics of the auditory system of cicadas: is the sound producing tymbal an integral part of directional hearing?

Abstract. Directional hearing is investigated in males of two species of cicadas, Tympanistalna gastrica (Stål) and Tettigetta josei Boulard, that are similar in size but show different calling song spectra. The vibrational response of the ears is measured with laser vibrometry and compared with thresholds determined from auditory nerve recordings. The data are used to investigate to what extent the directional characteristic of the tympanal vibrations is encoded by the activity of auditory receptors. Laser measurements show complex vibrations of the tympanum, and reveal that directional differences are rather high (>15 dB) in characteristic but limited frequency ranges. At low frequencies, both species show a large directional difference at the same frequency (3–5 kHz) whereas, above 10 kHz, the directional differences correspond to the different resonant frequencies of the respective tymbals. Consequently, due to the mechanical resonance of the tymbal, the frequency range at which directional differences are high differs between the two species that otherwise show similar dimensions of the acoustic system. The directional differences observed in the tympanal vibrations are also observed in the auditory nerve activity. These recordings confirm that the biophysically determined directional differences are available within the nervous system for further processing. Despite considerable intra as well as interindividual variability, the ears of the cicadas investigated here exhibit profound directional characteristics, because the thresholds determined from recordings of the auditory nerve at 30° to the right and left of the longitudinal axis differ by more than 5 dB.     

Correlated Electrophysiological and Ultrastructural Studies of a Crustacean Motor Unit

Structural and functional interrelationships between the pre- and postsynaptic elements of a singly motor innervated crab muscle (stretcher of Hyas araneus L.) were examined using electrophysiological and electron microscopic techniques. Excitatory postsynaptic potential (EPSP) amplitude at 1 Hz was found to be inversely related to the extent of facilitation, and directly related both to the amount of transmitter released at 1 Hz and the muscle fiber input resistance (R_in). The extent of facilitation (F_e), taken as the ratio of the EPSP amplitude at 10 Hz to that 1 Hz, was inversely related to muscle fiber R_in, τ_m, and sarcomere length. Sarcomere length was directly related to R_in and τ_m. The excitatory nerve terminals of low F_e muscle fibers had larger neuromuscular synapses than did those of high F_e fibers. Inhibitory axo-axonal synapses were more often found in low F_e muscle fibers. These structural features may account for the greater release of transmitter at low frequencies from the low F_e nerve terminals as well as provide for a greater amount of presynaptic inhibition of low F_e muscle fibers. The implications of these findings for the development and physiological performance of the crustacean motor unit are discussed. It is proposed that both nerve and muscle fiber properties may be determined by the developmental pattern of nerve growth.     

Recognition of conspecific song by the rufous-sided towhee

Dual-speaker experiments conducted with rufous-sided towhees (Pipilo erythrophthalmus) demonstrated that they do not respond to song of three other species and that the sequence and diversity of phrases within a song, and the time interval between syllables of the note-complex phrase, may be important in species recognition. These results are compared with results of song recognition studies done with species that are extensively sympatric with towhees in eastern North America.     

TEMPERATURE AND CRITICAL ILLUMINATION FOR REACTION TO FLICKERING LIGHT : V. XIPHOPHORUS,PLATYPOECILIUS, AND THEIR HYBRIDS

For the teleosts Xiphophorus montezuma, Platypoecilius maculatus, and their F ₁ hybrids the temperature characteristics (µ in Arrhenius'' equation) are the same for the shift of the low intensity and the high intensity segments of the respective and different flicker response contours (critical intensity I as a function of flash frequency F, with light time fraction constant, at 50 per cent). The value of µ is 12,500 calories or a very little less, over the range 12.5 to 36°. This shows that 1/I can be understood as a measure of excitability, with F fixed, and that the excitability is governed by the velocity of a chemical process common to both the classes of elements represented in the duplex performance curve (rods and cones). It is accordingly illegitimate to assume that the different shapes of the rod and cone branches of the curves are determined by differences in the chemical mechanisms of excitability. It is also forbidden to assume that the differing form constants for the homologous segments in the curves for two forms (X. and P.) are the reflections of a difference in the chemical factors of primary excitability. These differences are determined by statistical factors of the distribution of excitabilities among the elements implicated in the sensory effect vs. intensity function, and are independent of temperature and of the temperature characteristic. It must be concluded that the physicochemical nature of the excitatory process cannot be deduced from the shape of the performance contour. The form constants (σ''_{log I} and F_max.) for F vs. log I are specifically heritable in F ₁, although µ is here the same as for X. and P. In an intergeneric cross one cannot in general expect Mendelian simplicity of segregation in subsequent generations, and in the present case we find that F ₂ individuals are indistinguishable from F ₁, both as regards F vs. log I and as regards the variation of I within a group of 17 individuals. The result in F ₂ definitely shows, however, that certain specific statistical form constants for the F-log I contour are transmissible in inheritance. It is pointed out that there thus is provided an instance in which statistical (distribution) factors in performance characteristics involving the summating properties of assemblages of cellular units are heritable in a simple manner without the implication of detectable differences in chemical organization of the units involved. This has an important bearing upon the logic of the theory of the gene.     

THEORY AND MEASUREMENT OF VISUAL MECHANISMS : VI. WAVE-LENGTH AND FLASH DURATION IN FLICKER

For spectral regions associated with violet, blue, green, and red the relation between mean critical flash intensity I_m for visual flicker and the flash frequency F is modified as already found with white light when the light time fraction t_L in the flash cycle is changed. For a square image 6.13° on a side, foveally fixated, the "rod" and "cone" contributions to the duplex contour are analyzed in the way already used for white. It is pointed out that several customary qualitative criteria for cone functioning do not necessarily give concordant results. The analysis shows that the three parameters of the probability summations giving the "rod" and "cone" curves are changed independently as a function of wave-length composition of the light, and of the light time fraction. The correlation of these changes, and of those found in the associated variability functions, can be understood in terms of differences in (1) the numbers of neural units potentially excitable and (2) in the numbers of elements of neural effect obtained from them. In a multivariate situation of this kind it is necessary to compare intensities of luminous flux required to activate half the total population of potentially available elements when this total size is held constant for the different conditions. The results of this comparison, for the filtered lights used, are discussed in relation to certain aspects of excitation vs. wave-length. The problem is a general one, arising where the effects produced as a function of a particular variable are concerned. In the distinction between (1) units excited and (2) the actions they produce may be found the clue for the curious fact that with certain wave-lengths the critical intensities are lower than for white. The extension of the observations to other parts of the retina may be expected to further this analysis.     

Regeneration of axotomized tympanal nerve fibres in the adult grasshopper Chorthippus biguttulus (L.) (Orthoptera: Acrididae) correlates with regaining the localization ability

Adult males of the grasshopper Chorthippus biguttulus exhibit a stereotyped turning behaviour towards the direction of the female song. This behaviour has been used to study the regeneration of synaptic connections used for pattern recognition and sound localization. Unilaterally deafened animals are not able to localize the sound direction and turn exclusively towards the intact side, regardless of the speaker position. This behaviour does not change with postoperative time. After an axotomy of the tympanic nerve fibres the sensory axons regrow and regenerate their synaptic contacts which is deduced from the recovery of the ability to localize sound. The behavioural threshold for stimulation from the operated side is increased by approx. 5 dB SPL. The probability of correct turning towards the operated side increases with postoperative time. The ability for lateralization improves with postoperative time and may reach values of intact animals (discrimination of 1–2 dB SPL difference. Animals with two operations (axotomy of one tympanal nerve and blocking of the other ear) do not react to the female song, which suggests that recognition of the species-specific song pattern is not possible with the regenerated fibres and their synaptic connections alone. Neuroanatomical studies show that the regeneration of localization ability is correlated with an ingrowth of sensory fibres into the frontal auditory neuropil of the metathoracic ganglion.     

Hybrid immune response to parental liver tissue grafts

Parental-to-F₁-hybrid liver tissue grafts in like-sex donor-recipient combinations survive indefinitely, although several F₁ recipients demonstrate an immunological response to the parental graft. Female F₁ recipients, particularly those carrying theH-2 ^b haplotype, respond vigorously to male parental liver grafts. However F₁ female responses to male parental liver tissue grafts differ substantively from the responses of parental females to syngeneic male grafts. C3H male liver grafts are rejected vigorously by F₁ females as long as the F₁ carries theH-2 ^b haplotype. These findings support previous reports of strong immunological responses to C3H H-Y antigen in female F₁ and C3H.SW animals, a response which is absent in C3H females. Female F₁ hybrids carrying theH-2 ^b haplotype do not reject grafts of B10 or B6 male liver as rapidly as do B10 or B6 parental females. This reduced F₁ response may be related to the formation of hybrid antigens and consequent alteration of the anti-H-Y response. Alternatively, cells that specifically suppress the anti-H-Y response may be present in F₁ hybrids. Factors responsible for suppression appear to be controlled by non-MHC antigens, at least in (OH x B6 or B10) F₁ hybrids.     

CRITICAL ILLUMINATION AND CRITICAL FREQUENCY FOR RESPONSE TO FLICKERED LIGHT,IN DRAGONFLY LARVAE

Curves relating flicker frequency (F) to mean critical illumination (I_m) for threshold response to flickered light, with equal durations of light and no light intervals, and relating illumination (I) to mean critical flicker frequency (F_m) for the same response, have been obtained from homogeneous data based upon the reactions of dragonfly larvae (Anax junius). These curves exhibit the properties already described in the case of the fish Lepomis. The curve for F_m lies above the curve of I_m by an amount which, as a function of I, can be predicted from a knowledge either of the variation of I_m or of F_m. The law of the observable connection between F and I is properly expressed as a band, not as a simple curve. The variation of I_m (and of F_m) is not due to "experimental error," but is an expression of the variable character of the organism''s capacity to exhibit the reaction which is the basis of the measurements. As in other series of measurements, P.E. _I is a rectilinear function of I_m; P.E. _F passes through a maximum as F (or I) increases. The form of P.E. _F as a function of I can be predicted from the measurements of P.E. _I. It is pointed out that the equations which have been proposed for the interpretation of curves of critical flicker frequency as a function of intensity, based upon the balance of light adaptation and dark adaptation, have in fact the character of "population curves;" and that their contained constants do not have the properties requisite for the consistent application of the view that the shape of the F - I curve is governed by the steady state condition of adaptation. These curves can, however, be understood as resulting from the achievement of a certain level of difference between the average effect of a light flash and its average after effect during the dark interval.     

Individual increase in inbreeding allows estimating effective sizes from pedigrees

We present here a simple approach to obtain reliable estimates of the effective population size in real world populations via the computation of the increase in inbreeding for each individual (delta F_i) in a given population. The values of delta F_i are computed as t-root of 1 - (1 - F_i) where F_i is the inbreeding coefficient and t is the equivalent complete generations for each individual. The values of delta F computed for a pre-defined reference subset can be averaged and used to estimate effective size. A standard error of this estimate of N_e can be further computed from the standard deviation of the individual increase in inbreeding. The methodology is demonstrated by applying it to several simulated examples and to a real pedigree in which other methodologies fail when considering reference subpopulations. The main characteristics of the approach and its possible use are discussed both for predictive purposes and for analyzing genealogies.     

Reversible unfolding of the β2 subunit of Escherichia coli tryptophan synthetase and its proteolytic fragments

The guanidine hydrochloride-induced reversible unfolding transitions at 4 °C of the β₂ subunit of tryptophan synthetase (l-serine hydrolyase (adding indole) EC. 4.2.1.20) and of its two proteolytic fragments, F₁ and F₂, are compared. The unfolding of the β₂ subunit shows a multistate behaviour, as judged by circular dichroism and fluorescence measurements. When isolated, the two fragments have different stabilities. Within β₂, the region corresponding to the large fragment, F₁ behaves as the corresponding isolated fragment, and no stabilization arising from the interaction with the complementary fragment can be detected. The same behaviour is suggested for the small fragment, F₂. These results lead to the apparent conclusion that, at least under these experimental conditions, the interactions between domains do not contribute greatly to the energetics of the folding process of the large β₂ protein.     

Sequential assembly of photosynthetic units in Rhodobacter sphaeroides as revealed by fast repetition rate analysis of variable bacteriochlorophyll a fluorescence

The development of functional photosynthetic units in Rhodobacter sphaeroides was followed by near infra-red fast repetition rate (IRFRR) fluorescence measurements that were correlated to absorption spectroscopy, electron microscopy and pigment analyses. To induce the formation of intracytoplasmic membranes (ICM) (greening), cells grown aerobically both in batch culture and in a carbon-limited chemostat were transferred to semiaerobic conditions. In both aerobic cultures, a low level of photosynthetic complexes was observed, which were composed of the reaction center and the LH1 core antenna. Interestingly, in the batch cultures the reaction centers were essentially inactive in forward electron transfer and exhibited low photochemical yields F_V/F_M, whereas the chemostat culture displayed functional reaction centers with a rather rapid (1-2 ms) electron transfer turnover, as well as a high F_V/F_M of ∼0.8. In both cases, the transfer to semiaerobiosis resulted in rapid induction of bacteriochlorophyll a synthesis that was reflected by both an increase in the number of LH1-reaction center and peripheral LH2 antenna complexes. These studies establish that photosynthetic units are assembled in a sequential manner, where the appearance of the LH1-reaction center cores is followed by the activation of functional electron transfer, and finally by the accumulation of the LH2 complexes.     

Comparison of the physiology of the auditory receptor organs in Gryllus bimaculatus and Ephippiger ephippiger: CSD Recordings within the auditory neuropiles

The syllables of the song of the tettigoniid Ephippiger ephippiger consist of a series of short sound impulses with a broad-banded frequency spectrum. Syllables of the song of the gryllid species Gryllus bimaculatus are nearly pure tones with sharply tuned frequency maxima. A comparison of the physiology of the audiotory receptor organs of both species was carried out by using acoustical stimuli with different carrier frequencies and time-amplitude patterns. The neuronal ensemble activity of receptor cell groups of the tympanal organ was measured within the prothoracic ganglion using the CSD technique. In E. ephippiger, response maxima were found at carrier frequencies mirroring the broad frequency content of the conspecific song. The receptor cells of E. ephippiger are highly sensitive to transient sound impulses. In G. bimaculatus, the receptor cell population is more sharply tuned to the basic frequencies of the natural songs; pure tones represent more effective stimuli than transient sound signals. The causes for these speciesspecific differences are discussed with regard to probable adaptations of the receptor organs to the parameters of the conspecific songs. © 1993 John Wiley & Sons, Inc.     

Atypical Song Reveals Spontaneously Developing Coordination between Multi-Modal Signals in Brown-Headed Cowbirds (Molothrus ater)

The courtship and dominance behavior of brown-headed cowbirds (Molothrus ater) consists of a multi-modal display, including song as well as postural and wing movements. The temporal sequences of the acoustic and the visual display are coordinated. In adult male cowbirds the largest wing movements of the display are synchronized with silent periods of song, but it is unknown how this coordination emerges during song development. Here we investigate how visual display features are coordinated with song by using atypical song sequence structure of isolation-reared male cowbirds. In birds with atypical song, all components of the visual display were highly similar to those of “normal” song displays, but their timing was slightly different. The number of maximal wing movement cycles of isolation-reared males was linked to the number of sound units in the song, and was therefore reduced during the abbreviated song types of isolates. These data indicate that young cowbirds do not need to be exposed to a model of the visual display during ontogeny and that there is synchronization with the temporal structure of song. A physiological link between respiratory and syringeal control of silent periods between sound units and wing movement cycles may be driving this synchronization.     

Auditory interneurones in the mesothoracic ganglion of crickets

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.     

Song learning in domesticated canaries in a restricted acoustic environment

Many songbirds learn their songs early in life from a song model. In the absence of such a model, they develop an improvised song that often lacks the species-typical song structure. Open-ended learners, such as the domesticated canary, are able to modify their songs in adulthood, although the mechanisms that guide and time the song-learning process are still not fully understood. In a previous study, we showed that male domesticated canaries lacking an adult song model in their first year substantially change their song repertoire and composition when exposed to normally reared conspecifics in their second year. Here, we investigate song development in descendants of canaries that were raised and kept as a peer group without a song model. Such males represent tutors with abnormal song characteristics. Interestingly, the F₁ generation developed quite normal song structure, and when brought into an environment with normally raised canaries in their second year, they did not modify their songs substantially. These results suggest that contact with an adult song model early in life is crucial for song crystallization, but also that song development is at least partly guided by innate rules. They also question the existing classification of canaries as open-ended learners.     

Hearing in the crepuscular owl butterfly (Caligo eurilochus,Nymphalidae)

Tympanal organs are widespread in Nymphalidae butterflies, with a great deal of variability in the morphology of these ears. How this variation reflects differences in hearing physiology is not currently understood. This study provides the first examination of hearing organs in the crepuscular owl butterfly, Caligo eurilochus. We examined the tuning and sensitivity of the C. eurilochus hearing organ, called Vogel’s organ, using laser Doppler vibrometry and extracellular neurophysiology. We show that the C. eurilochus ear responds to sound and is most sensitive to frequencies between 1 and 4 kHz, as confirmed by both the vibration of the tympanal membrane and the physiological response of the associated nerve branches. In comparison to the hearing of its diurnally active relative, Morpho peleides, C. eurilochus has a narrower frequency range with higher auditory thresholds. Hypotheses explaining the function of hearing in this crepuscular butterfly are discussed.