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At least 667 records · Page 37Linked to original sources
PubMed1999

Bat-associated histoplasmosis in returning travelers: case presentation and description of a cluster.

Histoplasma capsulatum is a dimorphic fungus with the mycelial form producing spores that are readily airborne and able to reach small bronchi and alveoli. Isolation of the mycelial form of H. capsulatum in nature shows a striking correlation with moist, acidic soils, frequently contaminated with bird or bat excreta. Bats, but not birds, may be infected by H. capsulatum and may excrete the fungus in their feces. Skin test surveys show that the infectious agent is present worldwide in the areas between 45 degrees north and 30 degrees south of the equator. Clusters of cases may occur because of the disturbance of soil contaminated with H. capsulatum, or by visiting bat caves. Cave-associated histoplasmosis has been reported from the Americas, Africa, Oceania, and Africa. Recently, cave-associated histoplasmosis has been reported in travelers returning from Costa Rica and Peru. We report a cluster of cave-associated acute histoplasmosis that occurred in college students returning from Ecuador. Advice regarding histoplasmosis prevention should be given to travelers planning to visit bat-infested caves, and histoplasmosis should be considered in the differential diagnosis of febrile illness in returning travelers with a history of epidemiologic or geographic exposure.

Acute Disease↗
PubMed2002

Pathogenesis studies with Australian bat lyssavirus in grey-headed flying foxes (Pteropus poliocephalus).

OBJECTIVE: To examine the susceptibility of the grey-headed flying fox (Pteropus poliocephalus) to Australian bat lyssavirus (ABL), and to provide preliminary observations on the pathogenesis of the disease in flying foxes. PROCEDURE: Ten flying foxes were inoculated intramuscularly with ABL, and four with a bat-associated rabies virus. Inoculated animals were observed daily, and clinical samples collected every 9 to 14 days. Animals with abnormal clinical signs were euthanased, and samples collected for histological, serological, virological and immunohistological examinations. At 3 months post inoculation (PI), all survivors were euthanased, and each submitted to a similar examination. RESULTS: Three ABL-inoculated flying foxes, and two rabies-inoculated animals developed abnormal clinical signs between 15 and 24 days PI. All three ABL-inoculated animals had histological lesions consistent with a lyssavirus infection, and lyssaviral antigen was identified in the central nervous system (CNS) of each. Virus was isolated from the brain of two affected animals. Of the rabies-inoculated flying foxes, both had histological lesions and viral antigen in the CNS. Virus was recovered from the brain of only one. None of the five affected flying foxes developed anti-lyssavirus antibodies, but, by 3 months PI, five of the seven ABL-inoculated survivors, and one of the two rabies virus-inoculated survivors, had seroconverted. The dynamics of the immune responses were quite variable. CONCLUSIONS: The response of flying foxes to ABL, administered by a peripheral route of inoculation, was similar to that of bats inoculated peripherally with bat-derived rabies viruses.

Animals↗
PubMed1982

Measurements of atmospheric attenuation at ultrasonic frequencies and the significance for echolocation by bats.

The absorption of sound propagating through the atmosphere under laboratory conditions of 25 degrees C and 50% relative humidity was measured at frequencies from 30 to 200 kHz. The attenuating effect on the passage of ultrasonic sounds through air ranged from 0.7 dB/m at 30 kHz. These measurements confirm theoretical expectations and earlier observations that atmospheric attenuation is progressively more severe at higher frequencies and that the atmosphere acts as a low-pass filter for conducting sounds in the frequency range used for echolocation by bats. Different species of bats use different portions of this range of frequencies, and bats emitting sonar signals predominantly above 100 kHz encounter especially severe attenuation of over 3 dB/m. With the greatly restricted operating distances for echolocation at such high frequencies, bats using these higher frequencies must be under compelling ecological pressures of a higher priority than long-range detection of targets.

Animals↗
PubMed1990

Range resolution and the possible use of spectral information in the echolocating bat, Eptesicus fuscus.

Individuals of the echolocating bat Eptesicus fuscus were trained to discriminate simulated two-wave-front targets with internal time delays of 0 to 100 microns between the wave fronts from a one-wave-front target. The ability of bats to discriminate between such targets can be referred to as range resolution. In Eptesicus fuscus, this ability is limited to distinct internal time delays (12, 32-40, and 52-100 microns) between the two wave fronts of a double-wave-front target. Analysis of the simulated two-wave-front echoes reveals periodic frequency minima in the spectrum. Position and separation of these spectral minima depend on the time delay between the two wave fronts. The occurrence of spectral minima within the frequency range of the first harmonic in the echo of the bats' echolocation call correlates to the bats' ability to discriminate a one-wave-front echo from two-wave-front echoes, suggesting that Eptesicus fuscus uses spectral differences within the first harmonic in echoes for range resolution.

Animals↗
PubMed1992

Sonar gain control and echo detection thresholds in the echolocating bat, Eptesicus fuscus.

The echolocating bat, Eptesicus fuscus, detects sonar echoes with a sensitivity that changes according to the time elapsed between broadcasting of each sonar signal and reception of echoes. When tested in an electronic target simulator on a two-choice echo-detection task, the bat's threshold improved by 11.5 dB as echo delay changed from 2.3 to 4.6 ms (target ranges of 40 and 80 cm). Earlier experiments measured the change in detection threshold for delays from 1 to 6.4 ms (target ranges from about 17 to 110 cm) and obtained about 11 dB of improvement per doubling of delay. The new experiments used electronic delay lines to simulate echo delay, thus avoiding movement of loudspeakers to different distances and the possible creation of delay-dependent backward masking between stimulus echoes and cluttering echoes from the loudspeaker surfaces. The slope of the threshold shift defines an echo gain control that keeps echoes from point targets at a fixed sensation level--reducing sensitivity by 11 to 12 dB as echo amplitude increases by 12 dB per halving of range during the bat's approach to the target. A recent experiment using loudness discrimination of echoes at 70 to 80 dB SPL (roughly 50 dB above threshold) found a slope of about 6 dB per halving of range, so the gain-control effect may be level dependent. The observed effect is operationally equivalent to forward masking of echoes by the transmission, but any events correlated with vocalization which impair hearing sensitivity for a short interval following transmissions could cause a decline in sensitivity to echoes. Contractions of the bat's middle-ear muscles synchronized to transmissions may account for the observed threshold shift, at least for a span of echo delays associated with the most critical portion of the approach stage of pursuit. Forward masking by the sonar transmissions may contribute to the threshold shift, too, but middle-ear muscle contractions do occur and must be a significant part of the cause.

Animals↗
PubMed1992

Perception of structured phantom targets in the echolocating bat, Megaderma lyra.

Bats can discriminate among objects with different texture using echolocation. The mechanisms involved in texture discrimination are unknown. In real echoes reflected from three-dimensional objects, the spatial structure of the target creates a specific temporal and spectral pattern. In the experiments described here, simply structured phantom targets mimicking echoes reflected from an object with two parallel planes were generated by adding two differentially delayed copies of the bat's vocalizations. The discrimination performance of Megaderma lyra was studied in a two-alternative, forced-choice experiment using phantom targets with different internal delays and relative amplitudes of the two copies. When the reference target to which the bats were trained was presented, targets differing in internal delay by about 1 microseconds were discriminated. However, discrimination performance was not a globally monotonic function of the internal delay of the unrewarded target. When both targets presented in a trial differed from the reference, the bats still preferred one of them. Changes in overall level of the phantom target echo had little effect on performance; however, performance dropped considerably if only one of the two copies in an echo was attenuated. A model framework is introduced to account for these results. Models based on frequency processing yield better approximations than does a model based on time differences. The model based on spectral correlation gives a unified description of all the data. Although time domain models for texture discrimination cannot be generally refuted, the results presented here show that the discrimination of target surface structure can be explained as a discrimination of echo spectra.

Animals↗
PubMed1994

Stroboscopic hearing as a mechanism for prey discrimination in frequency-modulated bats?

A hypothesis was proposed that bats employing frequency-modulated (FM) echolocation pulses could utilize dynamic information of a flying insect to discriminate prey on the basis of "stroboscopic hearing." To test this hypothesis, single unit recordings were made from the inferior colliculus (IC) of the little brown bat, Myotis lucifugus. Response characteristics of IC units to trains of modulated and unmodulated sound pulses were analyzed at various pulse repetition rates that corresponded to a bat's pulse emission rates during the different stages of its target directed flight. The results show that amplitude modulation (AM) across a train of sound pulses was faithfully encoded in the units' discharge pattern when the pulse repetition rate was different from the AM frequency. When the AM frequency was integer multiples of the pulse repetition rate, the stimulus amplitude was reduced drastically under these conditions. Consequently, the discharge of an IC unit diminished precipitously, or if there was a phase delay between the pulse onset and the modulating sinusoidal waveform the unit fired to each modulation cycle with more or less the same vigor as if the modulation was absent. These data indicate that the across-pulse amplitude modulation becomes undetectable when the AM frequency is integer multiples of the pulse repetition rate. It is interpreted that FM bats can potentially employ a "stroboscopic hearing" strategy for discriminating insects on the basis of the wing-beat frequency of the prey.

Acoustic Stimulation↗
PubMed1994

Acoustic information available to bats using frequency-modulated sounds for the perception of insect prey.

Through the present study, the acoustic information available to an echolocating bat that uses brief frequency-modulated (FM) sonar sounds for the pursuit and capture of insect prey has been characterized. Computer-generated sonar pulses were broadcast at tethered insects, and the returning echoes were recorded on analog tape at high speed for off-line analyses. Echoes from stationary and fluttering insects were displayed using time waveform, spectrogram, power spectrum, and cross-correlation representations. The results show echo signatures for the different insect species studied, which change with the angle of incident sound. Sequences of echoes from fluttering insects show irregular changes in sound amplitude and time-frequency structure, reflecting a random temporal relation between the changing wing position and the arrival of incident sound. A set of recordings that controlled the temporal relation between incident sound and insect wing position suggests that information about the spatial profile of a flying insect could be enhanced if the bat were to produce a sequence of sounds that synchronized briefly with the moving target's wing-beat cycle. From this study, it has been proposed that the FM bat receives stroboscopic-like glimpses of fluttering prey whose spatial representation depends on the operation of the bat's sonar receiver.

Animals↗
PubMed1995

Spatially dependent acoustic cues generated by the external ear of the big brown bat, Eptesicus fuscus.

To measure the directionality of the external ear of the echolocating bat, Eptesicus fuscus, the left or right eardrum of a dead bat was replaced by a microphone which recorded signals received from a sound source that was moved around the stationary head. The test signal was a 0.5-ms FM sweep from 100 kHz to 10 kHz (covering all frequencies in the bat's biosonar sounds). Notches and peaks in transfer functions for 7 tested ears varied systematically with changes in elevation. For the most prominent notch, center frequency decreased from about 50 kHz for elevations at or near the horizontal to 30-40 kHz for elevations 30 degrees-40 degrees below the horizontal. A second notch shifted from about 85 kHz to 70 kHz over these same elevations. Above the horizontal, a peak that flanks these notches changed in amplitude by 15 dB with changes in elevation. Removal of the tragus from the external ear disrupted the systematic movement of notch frequencies with elevation but did not disrupt changes in the peak's amplitude. Smaller changes in notch frequency also occurred with changes in azimuth, so monaural notch information alone cannot determine the position of sound sources away from the median plane. However, because bats routinely keep the head pointed at the target's azimuth, median-plane localization occurs with monaural cues delivered to the two ears. Corresponding changes with elevation occurred in the impulse-response, which consists of a series of 3-6 peaks spaced 10-20 microseconds apart. The time separation of two prominent impulse peaks systematically increased from 22-26 microseconds above the horizontal to about 36-40 microseconds below the horizontal, and removal of the tragus disrupted this time shift below the horizontal.

Animals↗
PubMed2005

A molecular phylogeny for bats illuminates biogeography and the fossil record.

Bats make up more than 20% of extant mammals, yet their evolutionary history is largely unknown because of a limited fossil record and conflicting or incomplete phylogenies. Here, we present a highly resolved molecular phylogeny for all extant bat families. Our results support the hypothesis that megabats are nested among four major microbat lineages, which originated in the early Eocene [52 to 50 million years ago (Mya)], coincident with a significant global rise in temperature, increase in plant diversity and abundance, and the zenith of Tertiary insect diversity. Our data suggest that bats originated in Laurasia, possibly in North America, and that three of the major microbat lineages are Laurasian in origin, whereas the fourth is Gondwanan. Combining principles of ghost lineage analysis with molecular divergence dates, we estimate that the bat fossil record underestimates (unrepresented basal branch length, UBBL) first occurrences by, on average, 73% and that the sum of missing fossil history is 61%.

Africa↗
PubMed1964

BATS: SENSITIVITY TO DDT.

Big brown bats, Eptesicus fuscus, were fed single doses of varying amounts of DDT in corn oil injected into meal worms. All the doses of DDT fed to the bats, 40 milligrams or more per kilogram of body weight, were lethal. Within a few hours to 13 days after being dosed, the animals developed convulsions; some bats survived up to 3 days after the oniset of the symptoms of poisoning. Bats appear to be far more sensitive to DDT than any other mammal yet tested.

Animals↗
PubMed1991

Distinctive cranial and cervical innervation of wing muscles: new evidence for bat monophyly.

The traditional view that Old World fruit bats (Megachiroptera) and insect bats (Microchiroptera) are closely related has been challenged by claims that Megachiroptera are the sister group to flying lemurs (Dermoptera) or Primates. We found that the specialized muscles of the rostral part of the wing in Microchiroptera and Megachiroptera receive double innervation by both the facial nerve and cervical spinal nerves, suggesting that bats are monophyletic. Innervation by the facial nerve also occurs in Dermoptera and suggests that bats and Dermoptera share a common ancestor that had wings.

Animals↗
PubMed1985

Sonar tracking of horizontally moving targets by the big brown bat Eptesicus fuscus.

When following a moving target, echolocating bats (Eptesicus fuscus) keep their heads aimed at the target's position. This tracking behavior seems not to involve predicting the target's trajectory, but is achieved by the bat's pointing its head at the target's last known position. The bat obtains frequent position updates by emitting sonar signals at a high rate. After the lag between head and target positions and the nonunity tracking gain were corrected for, bats' tracking accuracy in the horizontal plane was +/- 1.6 degree.

Animals↗
PubMed1978

Dieldrin-induced mortality in an endangered species, the gray bat (Myotis grisescens).

Brains of juvenile gray bats, Myotis grisescens, found dead beneath maternity roosts in two Missouri caves contained lethal concentrations of dieldrin. One colony appeared to be abnormally small, and more dead bats were found a year after the juvenile bats had been collected. This is the first report to link the field mortality of bats directly to insecticide residues acquired through the food chain.

Aldrin↗
PubMed1979

Target range-sensitive neurons in the auditory cortex of the mustache bat.

Echolocating bats determine distance to targets by the time delay between their emitted biosonar pulses and the returning echoes. By varying the delay between synthetic pulses and echoes in stimulus pairs at various repetition rates and durations, neurons have been found in the auditory cortex of the mustache bat (Pteronotus parnellii rubiginosus) which are sensitive to target range during the search, approach, and terminal phases of prey capture or landing. Two classes of range-sensitive neurons were found: (i) tracking neurons, whose best delay for response to an echo following the emitted pulse becomes shorter and narrower as the bat closes in on the target, and (ii) range-tuned neurons, whose best delay is constant, and which respond to the target only when it is within a certain narrow fixed range. Range-tuned neurons are specialized for processing echoes only during a particular period of the search, approach, or terminal phases of echolocation, and they provide support for a theory of ranging in bats that incorporates groups of neurons with a spectrum of preferred echo delays to detect target distance.

Action Potentials↗
PubMed2005

Trichosporon species isolated from guano samples obtained from bat-inhabited caves in Japan.

Yeasts from caves have rarely been examined. We examined yeasts collected from bat guano samples from 20 bat-inhabited limestone and volcanic caves located in 11 prefectures in Japan. Of approximately 700 yeast-like colonies, nine Trichosporon species were recovered from 15 caves. Two of these were known species, and the remaining seven are potentially novel species, based on molecular phylogenetic analyses. In addition to Trichosporon species, identifiable strains of eight ascomycetous yeasts and one basidiomycetous yeast were recovered at frequencies of 5 to 35%. Our findings suggest that Trichosporon spp. are the major yeast species in bat guano in Japan and that bat guano is a potentially rich source of previously undescribed yeast species.

Animals↗
PubMed2000

First isolation of a rabies-related virus from a Daubenton's bat in the United Kingdom.

On May 30, 1996, a sick Daubenton's bat (Myotis daubentonii) was recovered from the cellar of a public house in Newhaven, East Sussex. Its condition deteriorated rapidly, and it was euthanased and examined. Positive results, establishing the presence of a rabies or rabies-related virus in its brain, were obtained from the fluorescent antibody test, the rabies tissue culture isolation test, and a hemi-nested reverse-transcription PCR. The complete sequence of the nucleoprotein gene was determined and a phylogenetic analysis, based on the 470 nucleotide bases of the amino terminus of the nucleoprotein, established the genotype of the virus as European bat lyssavirus 2. Bat rabies had not previously been recorded in the UK but does occur in mainland Europe. A study of the back-trajectories of the wind on May 29 and 30, established that the infected bat possibly came from near the Franco-Swiss border.

Amino Acid Sequence↗
PubMed1985

Mitochondrial thermogenin content is unchanged during atrophy of BAT of fasting mice.

The objectives of this study were to evaluate the rate at which brown adipose tissue (BAT) from mice atrophies when its thermogenic activity is suppressed during fasting or exposure to a thermoneutral environment (33 degrees C) and whether such atrophy is accompanied by loss from BAT mitochondria of "thermogenin," the GDP binding protein associated with the calorigenic proton conductance pathway. Atrophy of mouse BAT was characterized by rapid loss of protein but unchanged tissue DNA content. The rate of protein loss varied from 2 to 6 mg protein/day depending on the environmental and feeding status of the mice. In synchrony with tissue protein loss, there was a marked reduction in the tissue content of mitochondrial proteins and of thermogenin, measured by immunoassay. However, the concentration of thermogenin in isolated mitochondria was unchanged by fasting or exposure of the mice to 33 degrees C for 48 h. By contrast, marked reduction in [3H]GDP binding to isolated mitochondria were observed after exposure of the mice to 33 degrees C. Mice acclimated at 4 but not those acclimated at 21 degrees C showed reduction in GDP binding to isolated mitochondria during fasting. These results clearly indicate that changes in purine nucleotide binding to isolated mitochondria can occur in the absence of changes in the mitochondrial concentration of thermogenin. Thus rapid decrease in BAT thermogenic capacity (e.g., during fasting or 33 degrees C exposure) appears dependent on extensive loss of tissue protein, probably whole mitochondria, rather than rapid and selective removal of thermogenin from the mitochondria.

Acclimatization↗