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PubMed2000

Moth hearing in response to bat echolocation calls manipulated independently in time and frequency.

We measured the auditory responses of the noctuid moth Noctua pronuba to bat echolocation calls which were manipulated independently in time and frequency. Such manipulations are important in understanding how insect hearing influences the evolution of echolocation call characteristics. We manipulated the calls of three bat species (Rhinolophus hipposideros, Myotis nattereri and Pipistrellus pipistrellus) that use different echolocation call features by doubling their duration or reducing their frequency, and measured the auditory thresholds from the A1 cells of the moths. Knowing the auditory responses of the moth we tested three predictions. (i) The ranking of the audibility of unmanipulated calls to the moths should be predictable from their temporal and/or frequency structure. This was supported. (ii) Doubling the duration of the calls should increase their audibility by ca. 3 dB for all species. Their audibility did indeed increase by 2.1-3.5 dB. (iii) Reducing the frequency of the calls would increase their audibility for all species. Reducing the frequency had small effects for the two bat species which used short duration (2.7-3.6 ms) calls. However, the relatively long-duration (50 ms), largely constant-frequency calls of R. hipposideros increased in audibility by 21.6 dB when their frequency was halved. Time and frequency changes influence the audibility of calls to tympanate moths in different ways according to call design. Large changes in frequency and time had relatively small changes on the audibility of calls for short, largely broadband calls. Channelling energy into the second harmonic of the call substantially decreased the audibility of calls for bats which use long-duration, constant-frequency components in echolocation calls. We discuss our findings in the contexts of the evolution of both bat echolocation call design and the potential responses of insects which hear ultrasound.

Animals↗
PubMed2000

Day-flying butterflies remain day-flying in a Polynesian, bat-free habitat.

To test the theory that insectivorous bats have selected for diurnality in earless butterflies I compared the nocturnal flight patterns of three species of nymphalid butterflies on the bat-free Pacific island of Moorea with those of three nymphalids in the bat-inhabited habitat of Queensland, Australia. Nocturnal flight, measured as the ratio of deep night (1 h following sunset to 1 h preceding sunrise) to twilight night (1 h before sunset to 30 min after sunrise) activity did not differ significantly between the two locations, nor did the percentage of individuals active and I conclude that living in a bat-released habitat has not produced nocturnal flight in these insects. This result is surprising considering the potential advantages of escaping diurnally active predators and suggests that physiological adaptations (e.g. thermoregulation and/or vision) currently constrain these insects to diurnal flight. Since taxonomic records suggest that gene flow does not exist with bat-exposed conspecifics, I suggest that insufficient time has elapsed since these species migrated to Moorea to have resulted in major phenotypic changes such as diel flight preferences.

Animals↗
PubMed2002

Ecomorphological analysis of trophic niche partitioning in a tropical savannah bat community.

The exceptional diversity of neotropical bat communities is sustained by an intricate partitioning of available resources among the member species. Trophical specialization is considered an important evolutionary avenue towards niche partitioning in neotropical phyllostomid bats. From an ancestral insectivorous condition, phyllostomids evolved into highly specialized frugivorous, carnivorous, nectarivorous, piscivorous and even sanguivorous species. Previously, correlations between cranial morphology and trophic ecology within this group have been documented. Here, we examine the evolutionary relationships between bite force and head shape in over 20 species of bats from a single tropical savannah bat community. The results show that bite force increases exponentially with body size across all species examined. Despite the significant differences between large dietary groups using traditional analysis (i.e. non-phylogenetic) and the strong evolutionary correlations between body mass and bite force, phylogenetic analyses indicated no differences in bite performance between insectivorous, omnivorous and frugivorous bats. Comparisons of three species with highly specialized feeding habits (nectarivory, piscivory and sanguivory) with the rest of the species in the community indicate that specialization into these niches comes at the expense of bite performance and, hence, may result in a reduction of the trophic niche breadth.

Animals↗
PubMed2003

Echolocation range and wingbeat period match in aerial-hawking bats.

Aerial-hawking bats searching the sky for prey face the problem that flight and echolocation exert independent and possibly conflicting influences on call intervals. These bats can only exploit their full echolocation range unambiguously if they emit their next call when all echoes from the preceding call would have arrived. However, not every call interval is equally available. The need to reduce the high energetic costs of echolocation forces aerial-hawking bats to couple call emission to their wingbeat. We compared the wingbeat periods of 11 aerial-hawking bat species with the delays of the last-expected echoes. Acoustic flight-path tracking was employed to measure the source levels (SLs) of echolocation calls in the field. SLs were very high, extending the known range to 133 dB peak equivalent sound pressure level. We calculated the maximum detection distances for insects, larger flying objects and background targets. Wingbeat periods were derived from call intervals. Small and medium-sized bats in fact matched their maximum detection range for insects and larger flying targets to their wingbeat period. The tendency to skip calls correlated with the species' detection range for background targets. We argue that a species' call frequency is at such a pitch that the resulting detection range matches their wingbeat period.

Animals↗
PubMed2006

A new phylogenetic lineage of rabies virus associated with western pipistrelle bats (Pipistrellus hesperus).

Bats represent the major source of human rabies cases in the New World. In the USA, most cases are associated with species that are not commonly found or reported rabid. To understand better the epidemiology and public health significance of potentially important bat species, a molecular study was performed on samples collected from naturally infected rabid western pipistrelle (Pipistrellus hesperus), eastern pipistrelle (Pipistrellus subflavus) and silver-haired bats (Lasionycteris noctivagans) from different regions of their geographical distribution in the USA. A 264 bp fragment at the 5' end of the N gene coding region was sequenced and analysed in comparison with rabies virus variants circulating within other North American mammals. Phylogenetic analysis demonstrated that P. hesperus bats maintain a unique rabies virus variant. Preliminary data also suggest that P. subflavus and Lasionycteris noctivagans may harbour two different rabies virus variants (Ps and Ln) that are likely to be maintained independently by each bat species, which recently appear to have emerged as major vectors of human disease.

Amino Acid Sequence↗
PubMed2006

Full-length genome sequences of two SARS-like coronaviruses in horseshoe bats and genetic variation analysis.

Bats were recently identified as natural reservoirs of SARS-like coronavirus (SL-CoV) or SARS coronavirus-like virus. These viruses, together with SARS coronaviruses (SARS-CoV) isolated from human and palm civet, form a distinctive cluster within the group 2 coronaviruses of the genus Coronavirus, tentatively named group 2b (G2b). In this study, complete genome sequences of two additional group 2b coronaviruses (G2b-CoVs) were determined from horseshoe bat Rhinolophus ferrumequinum (G2b-CoV Rf1) and Rhinolophus macrotis (G2b-CoV Rm1). The bat G2b-CoV isolates have an identical genome organization and share an overall genome sequence identity of 88-92 % among themselves and between them and the human/civet isolates. The most variable regions are located in the genes encoding nsp3, ORF3a, spike protein and ORF8 when bat and human/civet G2b-CoV isolates are compared. Genetic analysis demonstrated that a diverse G2b-CoV population exists in the bat habitat and has evolved from a common ancestor of SARS-CoV.

Animals↗
PubMedDate not supplied

Toward a global bat-signal database.

We propose a scheme for a new database using standardized protocol for recording and analysis of bat calls. The proposed database will describe and archive echolocation signals to create a reference library of bat calls. This information should be accessible to the public, thus encouraging continuous feedback from a broad audience. Because it is essential to evaluate the quality and reliability of such data, detailed information of recording and analysis procedures as well as the resulting species identification is required. A standardized and growing database on bat calls would be a potentially invaluable tool for global species identification, comparison, and distribution of microchiropterans. Currently, apart from a few websites with local call libraries, there is no "global" database established yet. We hope that researchers, amateurs, and wildlife and management authorities will adopt and further modify our suggestions for a standardized database for bat calls. We also hope that this database will stimulate new directions in bat research.

Animals↗
PubMed2005

Neorickettsia risticii is vertically transmitted in the trematode Acanthatrium oregonense and horizontally transmitted to bats.

Potomac horse fever is known to be transmitted through the ingestion of caddisflies parasitized with Neorickettsia (formerly Ehrlichia) risticii-infected metacercaria. However, the species of trematode involved and how N. risticii is maintained in nature are unknown. In this study, gravid trematodes were recovered from the intestines of 12 out of 15 Eptesicus fuscus big brown bats and eight out of nine Myotis lucifugus little brown bats from various sites in Pennsylvania, USA. Trematode specimens isolated from six E. fuscus bats contained N. risticii DNA. The trematode was identified as Acanthatrium oregonense. N. risticii was detected within individual trematode eggs by polymerase chain reaction as well as by immunofluorescence labelling with an anti-N. risticii antibody, indicating that N. risticii is vertically transmitted (from adult to egg) in A. oregonense. Furthermore, N. risticii DNA was detected in the blood, liver or spleen of 23 out of 53 E. fuscus and M. lucifugus bats, suggesting that N. risticii can also be transmitted horizontally from trematode to bat. These results indicate that A. oregonense is a natural reservoir and probably a vector of N. risticii.

Anaplasmataceae Infections↗
PubMed2006

Site-specific conjugation of bifunctional chelator BAT to mouse IgG1 Fab' fragment.

AIM: To perform a site-specific conjugation of Fab' fragments of a mouse monoclonal antibody(MoAb) B43(of IgG1 subtype) to a bifunctional chelator 6-[p-(bromoacetamido)benzyl]-1,4,8,11-tetraazacyclotetradecane-N,N',N' 'N' ' '-tetraacetic acid (BAT) via the thiol groups in the hinge distal to the antigen-binding site of the Fab'. METHODS: B43 was cleaved using a simple 2-step method. First, stable F(ab')(2) was produced by pepsin treatment. Fab' with free thiol in the hinge region was then obtained by cysteine reduction of F(ab')2. Second, a site-specific conjugation of Fab' to thiol-specific BAT was performed in a one-step reaction. RESULTS: The Fab' fragment had approximately 1.8 free thiol groups per molecule after cysteine reduction. The conjugation efficiency and the chemical yield were approximately 1.28 moles chelator/Fab' and 74% of the initial concentration of Fab', respectively. The F(ab')2, Fab' and Fab'-BAT all maintained reasonable antigen-binding properties. (67)Cu labeling of the conjugate under standard conditions did not impair the immunoreactivity of Fab'-BAT. CONCLUSION: This is a simple and efficient method for producing immunoreactive conjugates of Fab'-BAT, which can be used to make radiometal-labeled conjugates for further diagnostic and therapeutic applications.

Acetamides↗
PubMed1999

Veterinary surgeon's guide to Australian bat lyssavirus.

Veterinary surgeons in Australia must be aware of the emerging viral diseases and their potential effects on public health generally and, more specifically, on the veterinary profession. Australian bat lyssavirus was identified in 1996 and causes rabies-like disease in bats and humans. Two humans from Queensland have died of Australian bat lyssavirus encephalitis. Surveillance has shown that all Australian bats must be considered carriers of this new virus, therefore protective apparel should be used when handling bats. The pre-exposure regimen of inactivated rabies vaccine (Pasteur Mérieux) provides protection against infection. As part of the preventive regimen, at risk groups, such as veterinary surgeons, should seriously consider pre-exposure rabies vaccination. The post-exposure protocol involves administration of human rabies immunoglobulins and five intramuscular injections of the inactivated rabies vaccine.

Animals↗
PubMed2001

Evidence for an analytic perception of multiharmonic sounds in the bat, Megaderma lyra, and its possible role for echo spectral analysis.

For echolocation, the gleaning bat Megaderma lyra relies on short and broadband calls consisting of multiple harmonic components, each of which is downward frequency modulated. The harmonic components in M. lyra's calls have a relatively small frequency excursion and do not overlap spectrally. Broadband calls of other bat species, on the other hand, often consist of only a few harmonics which are modulated over broad and sometimes overlapping frequency ranges. A call consisting of narrow and nonoverlapping harmonic components may provide a less complete representation of target structure than a call which consists of broadly modulated components. However, a multiharmonic call may help the bats to perceive local spectral changes in the echo from shifts in the peak frequencies of single harmonics, and thereby to extract additional information about the target. To assess this hypothesis, the accuracy with which M. lyra can analyze frequency shifts of single partials in multiharmonic complex tones was investigated. A two-alternative, forced-choice behavioral task was used to measure M. lyra's frequency discrimination threshold for the third partial in complex tones whose spectral composition resembled that of the bat's sonar calls. The discrimination threshold for the third partial in a 21.5-kHz harmonic tone amounted to about 2% and was similar to the bat's pure-tone discrimination threshold at 64.5 kHz. Discrimination performance was essentially unaffected by random frequency changes of the other partials and by reducing stimulus duration from 50.5 to 1.5 ms. Both findings are in accordance with predictions made on the basis of the shape of M. Ivra's cochlear filters. The comparison between the observed frequency discrimination performance and a computational estimate of the expected frequency shift in the third harmonic of an echo reflected by a simple, two-front target showed that M. lyra's frequency resolution is sufficient for analyzing the target-specific information conveyed by shifts in the peak frequency of single echo components.

Animals↗
PubMed2002

Transformation of external-ear spectral cues into perceived delays by the big brown bat, Eptesicus fuscus.

The external-ear transfer function for big brown bats (Eptesicus fuscus) contains two prominent notches that vary from 30 to 55 kHz and from 70 to 100 kHz, respectively, as sound-source elevation moves from -40 to +10 degrees. These notches resemble a higher-frequency version of external-ear cues for vertical localization in humans and other mammals. However, they also resemble interference notches created in echoes when reflected sounds overlap at short time separations of 30-50 micros. Psychophysical experiments have shown that bats actually perceive small time separations from interference notches, and here we used the same technique to test whether external-ear notches are recognized as a corresponding time separation, too. The bats' performance reveals the elevation dependence of a time-separation estimate at 25-45 micros in perceived delay. Convergence of target-shape and external-ear cues onto echo spectra creates ambiguity about whether a particular notch relates to the object or to its location, which the bat could resolve by ignoring the presence of notches at external-ear frequencies. Instead, the bat registers the frequencies of notches caused by the external ear along with notches caused by the target's structure and employs spectrogram correlation and transformation (SCAT) to convert them all into a family of delay estimates that includes elevation.

Animals↗
PubMed2003

The sonar beam pattern of a flying bat as it tracks tethered insects.

This paper describes measurements of the sonar beam pattern of flying echolocating bats, Eptesicus fuscus, performing various insect capture tasks in a large laboratory flight room. The beam pattern is deduced using the signal intensity across a linear array of microphones. The positions of the bat and insect prey are obtained by stereoscopic reconstruction from two camera views. Results are reported in the form of beam-pattern plots and estimated direction of the beam axis. The bat centers its beam axis on the selected target with a standard deviation (sigma) of 3 degrees. The experimental error is +/- 1.4 degrees. Trials conducted with two targets show that the bat consistently tracks one of the targets with its beam. These findings suggest that the axis of the bat sonar beam is a good index of selective tracking of targets, and in this respect is analogous to gaze in predominantly visual animals.

Animals↗
PubMed1986

Accuracy of distance measurement in the bat Eptesicus fuscus: theoretical aspects and computer simulations.

Behavioral experiments of Simmons [J. Acoust. Soc. Am. 54, 157-173 (1973) and Science 204, 1336-1338 (1979)] on the ranging accuracy in the bat Eptesicus fuscus have led to far-reaching postulates on the existence of optimal and phase-conserving processing mechanisms in the bat. In this paper, the results of computer simulations of these experiments are presented. Two receiver types are investigated: the fully coherent cross-correlation receiver and the cross-correlation receiver with envelope processing (semicoherent). It is shown that Simmons' experiments cannot be treated as a simple estimation of distance, but require at least two (range difference experiment; see Simmons, 1973) or four (range jitter experiment; see Simmons, 1979) echolocation sounds for one decision. The performance of the bat in both experiments is much worse than predicted for a coherent and a semicoherent receiver type. The bat's accuracy in Simmons' range difference experiment is at least 18 dB worse than predicted for an optimal receiver. The results of the jitter experiment cannot be interpreted in a simple way as proof that bats are able to evaluate phase information as in a fully coherent cross-correlation receiver.

Animals↗
PubMed1989

Range estimation by echolocation in the bat Eptesicus fuscus: trading of phase versus time cues.

Bats of the species Eptesicus fuscus have been trained to discriminate a stationary simulated target from a target with a virtual distance that jitters from sound to sound. Similar to Simmons [Science 207, 1336-1338 (1979)], a jitter-detection threshold below 1 microsecond was found. However, Simmons' decreased performance at a time delay jitter of 30 microseconds could not be replicated, a critical feature used to postulate the idea that bats employ a coherent cross-correlation receiver for ranging. Such a receiver uses all phase information in the signal for delay estimation and therefore will be biased by phase manipulations. To test for such a bias, a phase jitter of +/- 45 degrees and a time jitter in the echo were overlaid. It was not found that there was a combination of both where their effects canceled. Full phase information is thus not used in delay estimation. However, bats were able to detect a pure phase jitter, e.g., polarity inversion of the signal. Bats could also detect phase jitter in the presence of randomized time jitter and vice versa. Phase jitter and time jitter, therefore, are separable features for a bat. The underlying physiological mechanism is not clear.

Amplifiers, Electronic↗
PubMed1996

Sound source elevation and external ear cues influence the discrimination of spectral notches by the big brown bat, Eptesicus fuscus.

Measurements of external ear transfer functions in the echolocating bat Eptesicus fuscus have revealed a prominent spectral notch that decreases in center frequency (50 to 30-35 kHz) as elevation decreases [Wotton et al., J. Acoust. Soc. Am. 98, 1423-1445 (1995)]. To examine the influence of this notch, four Eptesicus were trained to discriminate between two sets of electronically generated artificial echoes. The negative (unrewarded) stimulus contained a test spectral notch at a specific frequency that varied from 30 to 50 kHz, while the positive (rewarded) stimulus contained no test notch. The vertical position of the loudspeakers delivering these simulated echoes was changed daily. When echoes were returned from an elevation at which the external ear introduced a spectral notch at the same frequency as the test notch, then the discrimination should have been difficult. The bats' performance conformed to this prediction: All bats discriminated the presence of a 35-kHz notch at all elevations except -10 degrees. As the frequency of the synthesized notch increased, the elevation at which bats could not perform the discrimination also increased. The movement of the bat's "blind spot" for the test notch of different frequencies followed the movement of the external ear notch at different elevations.

Animals↗
PubMed1998

Target flutter rate discrimination by bats using frequency-modulated sonar sounds: behavior and signal processing models.

This study utilized psychophysical data and acoustical measurements of sonar echoes from artificial fluttering targets to develop insights to the information used by FM bats to discriminate the wingbeat rate of flying insects. Fluttering targets were produced by rotating blades that moved towards the bat, and the animal learned to discriminate between two rates of movement, a reference rate (30 or 50 Hz) and a slower, variable rate. Threshold discrimination performance depended on the rotation rate of the reference target, with a difference value of 9 Hz for the reference rate of 30 Hz and 14 Hz for the reference rate of 50 Hz. Control experiments demonstrated that the bats used sonar echoes from the moving targets to perform the discrimination task. Acoustical measurements showed that the moving target produced a Doppler shift in the echo and a concomitant change in the arrival time of each frequency in the linear period FM sweep. The difference in delay between echoes from moving and stationary parts varied linearly with flutter rate and depended on the characteristics of the bat's sonar sounds. Simulations also showed a reduction in average echo bandwidth with increasing flutter rate, which may account for a higher delay discrimination threshold using the 50-Hz reference rate. This work suggests that Doppler-induced changes in echo delays produced by fluttering targets may contribute to the FM bat's perception of flying insect prey.

Acoustics↗
PubMed1999

Perception of complex tones and its analogy to echo spectral analysis in the bat, Megaderma lyra.

The gleaning bat Megaderma lyra emits broadband echolocation sounds consisting of multiple frequency components. The present study investigates into which perceptual qualities the spectral characteristics of echoes may be translated in the auditory system of M. lyra. Three bats were trained in a 2-AFC behavioral experiment to classify nine complex tones, which spectrally resembled M. lyra's sonar calls, into two perceptual categories. Then the bats' spontaneous responses to unknown complex tones were recorded. The results show that the animals based their classifications of the complex tones on a sound quality which was mediated by their broadband frequency spectra. The bats used the training stimuli as spectral templates and classified the test stimuli according to their broadband spectral similarity with the learned patterns. Assuming that passive hearing and echo processing are governed by similar perceptual qualities and subject to similar limitations, the perceptual mode which was used by the bats to compare the multicomponent spectral patterns in the reported experiments could serve as a powerful tool for the spectral analysis of M. lyra's multicomponent echoes. The analogy between the perception of complex tones and echo spectral analysis in M. lyra is theoretically elaborated in the "formant-mode" model.

Animals↗