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PubMed1989

Ultrastructural and functional characteristics of anterior pituitary cells in the Indian fruit bat, Rousettus leschenaulti (Desmarest).

The pituitary glands of normal and experimental male and female bats were examined by light and electron microscopy. Six cell types were identified in the anterior pituitary by differential staining techniques, ultrastructural characteristics and changes brought about during the different phases of the sexual cycle. Conventional methods like removal of thyroids, testes and adrenals, and animals in lactation withdrawal and treatment with propylthio-uracil, cyproterone acetate and metyrapone were employed. A marked predominance of somatotrophin and luteotrophin (LTH) cells were present in the intact adult female bat pituitary gland. LTH cells were also observed in milk retention experiments. The two gonadotrophic cell types were randomly distributed throughout the gland. Hypertrophy of two gonadotroph cells was observed in response to the physiological conditions of the animals, gonadectomy and administration of the male antifertility drug cyproterone acetate. Thyrotrophin and adrenocorticotrophin cells were identified by ablation of the respective target organs, thyroids and adrenals, and after treatment with propylthio-uracil and metyrapone. On the basis of the pathological conditions of the bats, the possible functional significance of the different cell types is also discussed.

Animals↗
PubMed1983

Early microvascular pathology during hyperglycemia in bats.

The microvascular changes in the wing of bats, Myoitis lucifugus, were observed during 3 weeks of normal life and 5 weeks of streptozotocin induced hyperglycemia (300-400 mg/dl, plasma). During normal life, week-to-week variations in diameter and blood flow in the same set of vessels were minor. After hyperglycemia was induced, the major initial response was dilation of all microvessels except the smallest arterioles which constricted. The dilation phase was followed by progressive constriction of all vessels. Blood flow was near normal during the dilation phase, but flow gradually decreased as hyperglycemia continued and vasoconstriction occurred. The ability to repeatedly observe the same set of microvessels on a week-to-week basis and the absence of anesthesia may make the diabetic bat a useful model in which to study the early phases of microvascular pathology during chronic hyperglycemia, which begins abruptly in adult life. In addition, the sequence of microvascular changes during chronic hyperglycemia in the bat are qualitatively similar to those in other diabetic mammals, including man.

Aging↗
PubMed2003

Seasonality and synchrony of reproduction in three species of nectarivorous Philippines bats.

BACKGROUND: Differences among species and among years in reproductive seasonality (the tendency for clusters of events to fall at approximately the same point in each year) and synchrony (amount of clustering of events within a year) have been intensively studied in bats, but are difficult to assess. Here, we use randomization methods with circular statistics to test for synchrony and seasonality of reproduction in three species of nectarivorous megachiropteran bats on Negros Island in the central Philippines. RESULTS: In Rousettus amplexicaudatus, estimated dates of birth were both highly synchronous and highly seasonal. In Macroglossus minimus, estimated births were seasonal and significantly clustered within years, but within each year births occurred over a broad period, indicating a low level of synchrony. In Eonycteris spelaea, estimated births were also seasonal and had statistically significant synchrony, with birth periods within years intermediate in synchrony between R. amplexicaudatus and M. minimus. All three species had a similar seasonal pattern, with two birth periods in each year, centered on March or April and August or September. In one species, R. amplexicaudatus, primigravid females (in their first pregnancy) produced their young in June and July, a birth period significantly different in timing from the two birth periods of older adult females. This more conservative pattern of young females may allow higher survival of parents and offspring at cost of a lost reproductive opportunity. There was weak evidence that in some years primigravid females of M. minimus might differ in timing from older adults. There were few significant differences in reproductive timing among different years, and those differences were generally less than two weeks, even during a severe drought in the severe el Niño of 1983. CONCLUSION: The results suggest that these species follow an obligately seasonal pattern of reproductive timing with very little phenotypic plasticity. The resampling methods were sensitive to differences in timing of under two weeks, in some cases, suggesting that these are useful methods for analyses of seasonality in wild populations of bats.

Age Factors↗
PubMed2003

Prey-capture success revealed by echolocation signals in pipistrelle bats (Pipistrellus pygmaeus).

Three Pipistrellus pygmaeus bats were trained to capture prey on the wing while flying in the laboratory. The bats' capture behaviour and capture success were determined and correlated with acoustic analyses of post-buzz echolocation signals. Three acoustic parameters revealed capture success: in case of success, post-buzz pauses (pbP) were longer, interpulse intervals (IPI) of the post-buzz signals were longer and, most notably, the spectra of the echolocation signals showed a number of notches that were absent after unsuccessful attempts. If the bats touched the prey without seizing it, pbP was significantly increased, but by less than was seen following a successful capture. Thus, acoustic recordings can be used to determine the outcome of a capture attempt with 72-75% correct using IPI or pbP, and with 78% correct using notches. Even more trials (>85%) were classified correctly by using the first canonical discriminant factor from principal component analysis combining the three parameters. Four types of prey were used, of 7-22 mm length and 7-240 mg mass. After successful captures, interpulse intervals, post-buzz pause and notches all depended on prey type, but not in a way that was systematically related to size, indicating that acoustic parameters cannot reveal prey size.

Acoustics↗
PubMed2005

Functional and structural optimization of the respiratory system of the bat Tadarida brasiliensis (Chiroptera, Molossidae): does airway geometry matter?

We studied structure and function of the respiratory system in the bat Tadarida brasiliensis and compared it with those of two species of rodents, Abrothrix andinus and A. olivaceus. Tadarida brasiliensis had lower resting oxygen consumption, but higher maximum oxygen consumption and aerobic scope, than the rodents. The blood-gas barrier of the bat was thinner and its relative lung size was larger; however, alveolar surface density was similar among the three species. In consequence, T. brasiliensis has an oxygen diffusion capacity two or three times higher than that of the rodents. In Tadarida brasiliensis the characteristics of the lung were accompanied by geometrical changes in the proximal airway, such as high physical optimization as a consequence of small variations in the symmetry and the scaling ratio of the bronchial diameters. These may constitute an efficient way to save energy in respiratory mechanics and are the first report of airway adjustments to decrease entropy generation in bats.

Animals↗
PubMed2006

The absence of spatial echo suppression in the echolocating bats Megaderma lyra and Phyllostomus discolor.

Acoustic orientation most often takes place in echoic environments. The mammalian auditory system shows a variety of specializations to suppress misleading spatial information mediated by echoes. Psychophysically these specializations are summarized as the precedence effect. This study investigates how echolocating bats deal with multiple reflections of their sonar emissions from different spatial positions. In a two-alternative, forced choice paradigm, a study was made of the extent to which the echolocating bats Megaderma lyra and Phyllostomus discolor spontaneously suppress the spatial information of a second reflection of their sonar emission. The delay between the first and the second reflection ranged between 0 and 12.8 ms. In general, M. lyra (five individuals) and P. discolor (two individuals) did not suppress the spatial information of the second reflection of their sonar emission, whatever the delay. Only one M. lyra showed significant suppression for delays between 0.8 and 3.2 ms. However, this suppression could not be confirmed in an exact repetition of the experiment. The current data indicate that although bats may be able to suppress the spatial information of a second reflection, this is not their default mode of auditory processing. The reason for this exceptional absence of spatial echo suppression may lie in the shorter time constants of cochlear processing in the ultrasonic frequency range and the strong influence of cognitive components associated with the ;precedence effect'.

Animals↗
PubMed1992

Ultrasonic vocalizations of flying bats monitored by radiotelemetry.

Ultrasonic vocalizations of flying bats were effectively monitored with radiotelemetry. We describe a device light enough to be carried by an 11 g bat for periods of up to 1 h. It transmitted signals adequate for fine frequency analysis within a range of approximately 3 m. Telemetry permitted the recording of constant-frequency pulses free from flight-induced Doppler shifts and without time delays. The difference in frequency between telemetered signals and the same signals detected by a remote microphone was used to calculate velocity and Doppler shifts. Pulse emission behavior of Pteronotus parnellii in flight was compared with simulated flight on a pendulum. The data showed significant differences in echo bandwidths, constant-frequency pulse durations and interpulse intervals. In flight, pulses and interpulse intervals tended to be shorter and bats maintained echo frequencies within a significantly narrower band. Phases of echolocation that characterized the approach to a target were clearly evident in flight, but not during pendulum swings. Differences in pulse durations and interpulse intervals may be correlated with the integration of wingbeat, respiration and vocalization. The absence of wing motion in simulated flight changes this integration.

Animals↗
PubMed1995

Respiratory muscle activity in relation to vocalization in flying bats.

The structure of the thoracic and abdominal walls of Pteronotus parnellii (Microchiroptera: Mormoopidae) was described with respect to their function in respiration and vocalization. We monitored electromyographic activity of respiratory and flight muscles in relation to echolocative vocalization. In flight, signals were telemetered with a small FM transmitter modified to summate the low-frequency myopotentials with biosonar signals from a ceramic-crystal microphone. Recordings were also made from the same bats confined to a small cage. Vocalizations were used as the parameter by which all muscle activities were correlated. A discrete burst of activity in the lateral abdominal wall muscles accompanied each vocalization. Diaphragmatic myopotentials occurred between groups of calls and did not coincide with activity of the abdominal wall or with vocalizations. Flight muscles were not active in resting bats. During flight, vocalizations and the abdominal muscle activity that accompanied them coincided with myopotentials of the pectoralis and serratus ventralis muscles. We propose that contractions of the lateral abdominal wall provide the primary power for the production of intense biosonar vocalization in flying and in stationary bats. In flight, synchronization of vocalization with activity of the pectoralis and serratus ventralis jointly contribute to the pressurization of the thoraco-abdominal cavity. This utilization of pressure that is normally generated in flight facilitates respiration and allows for the production of intense vocalizations with little additional energetic expenditure.

Abdominal Muscles↗
PubMed1995

Echolocation call structure and intensity in five species of insectivorous bats.

Echolocation call intensity was measured in the laboratory for five species of British insectivorous bats in free flight and in the hand. All species showed similar call intensities of between 80 and 90 dB peSPL (peak equivalent SPL) at 1 m during flight except Plecotus auritus, whose call intensity was between 68 and 77 dB peSPL at 1 m. Calls from stationary bats were about 13 dB less intense than calls during flight. A method is proposed to measure the root mean square (rms) amplitude of echolocation calls and, hence, to calculate the energy flux density of the call. The constant-frequency calls of Rhinolophus hipposideros have energy flux densities approximately ten times higher than those of bats using frequency-modulated calls as a result of their longer durations and lower crest factors. It is argued that the low-intensity calls of P. auritus allow it to approach tympanate moths more closely before triggering their escape response.

Animals↗
PubMed1998

Gas exchange during hovering flight in a nectar-feeding bat Glossophaga soricina.

Glossophagine nectar-feeding bats exploit flowers while hovering in front of them. Aerodynamic theory predicts that power output for hovering flight in Glossophaga soricina is 2.6 times higher than during horizontal flight. We tested this prediction by measuring rates of gas exchange during hover-feeding. Five individuals of Glossophaga soricina (mean mass 11.7 g) were trained to feed from a nectar dispenser designed as a flow-through respirometry mask. Single hover-feeding events lasted for up to 4.5 s. Measured rates of gas exchange varied as a function of hovering duration. O2 and CO2 during short hovering events (up to 1 s) were 20.5+/-6.7 ml g-1 h-1 (N=55) and 21.6+/-5.6 ml g-1 h-1 (N=39) (means +/- S.D.), respectively. These values are in the range of a previous estimate of the metabolic power input for level forward flight (23.8 ml O2 g-1 h-1). However, during hovering events lasting longer than 3 s, oxygen uptake was only 16.7+/-3.5 ml g-1 h-1 (N=73), which is only 70 % of the value expected for forward flight. Thus, bats reduced their rate of oxygen uptake during longer periods of hovering compared with level forward flight. This result is in contrast to the predicted hovering cost derived from aerodynamic theory. The exact metabolic power input during hovering remains uncertain. During longer hovering events, bats were probably not in respiratory steady state, as indicated by the deviation of the respiratory exchange ratio from the expected value of 1 (oxidization of nectar sugar) to the measured value of 0.8.

Animals↗
PubMed1999

Echolocation behaviour and prey-capture success in foraging bats: laboratory and field experiments on Myotis daubentonii.

During prey-capture attempts, many echolocating bats emit a 'terminal buzz', when pulse repetition rate is increased and pulse duration and interpulse interval are shortened. The buzz is followed by a silent interval (the post-buzz pause). We investigated whether variation in the structure of the terminal buzz, and the calls and silent periods following it, may provide information about whether the capture attempt was successful and about the size of prey detected - detail that is valuable in studies of habitat use and energetics. We studied the trawling bat Myotis daubentonii. The time between the first call of the approach phase and the end of the terminal phase was not related to prey size in the laboratory. The last portion of the terminal buzz (buzz II) was shortened or omitted during aborted capture attempts. Both in the laboratory and in the field, the mean interpulse interval immediately after the terminal buzz (post-buzz interpulse interval) was longer in successful captures than in unsuccessful attempts. In the laboratory, the post-buzz pause was longer after successful captures than for unsuccessful attempts, and the minimum frequency of the first search-phase call emitted after the buzz (Fmin) was higher than that of the last such call prior to the buzz. These effects were not apparent in field data. Both in the laboratory (85%) and in the field (74%), significant discrimination between successful and unsuccessful capture attempts was possible when the duration of the post-buzz pause, post-buzz interpulse interval and Fmin were entered into a discriminant analysis. Thus, variation in the echolocation calls of bats during prey-capture attempts can reveal substantial information about capture success and prey size.

Animals↗
PubMed2000

Acoustic identification of twelve species of echolocating bat by discriminant function analysis and artificial neural networks.

We recorded echolocation calls from 14 sympatric species of bat in Britain. Once digitised, one temporal and four spectral features were measured from each call. The frequency-time course of each call was approximated by fitting eight mathematical functions, and the goodness of fit, represented by the mean-squared error, was calculated. Measurements were taken using an automated process that extracted a single call from background noise and measured all variables without intervention. Two species of Rhinolophus were easily identified from call duration and spectral measurements. For the remaining 12 species, discriminant function analysis and multilayer back-propagation perceptrons were used to classify calls to species level. Analyses were carried out with and without the inclusion of curve-fitting data to evaluate its usefulness in distinguishing among species. Discriminant function analysis achieved an overall correct classification rate of 79% with curve-fitting data included, while an artificial neural network achieved 87%. The removal of curve-fitting data improved the performance of the discriminant function analysis by 2 %, while the performance of a perceptron decreased by 2 %. However, an increase in correct identification rates when curve-fitting information was included was not found for all species. The use of a hierarchical classification system, whereby calls were first classified to genus level and then to species level, had little effect on correct classification rates by discriminant function analysis but did improve rates achieved by perceptrons. This is the first published study to use artificial neural networks to classify the echolocation calls of bats to species level. Our findings are discussed in terms of recent advances in recording and analysis technologies, and are related to factors causing convergence and divergence of echolocation call design in bats.

Acoustics↗
PubMed2002

Scaling bat wingbeat frequency and amplitude.

Wingbeat frequency (f(w)) and amplitude (theta;(w)) were measured for 23 species of Australian bat, representing two sub-orders and six families. Maximum values were between 4 and 13 Hz for f(w), and between 90 and 150 degrees for theta;(w), depending on the species. Wingbeat frequency for each species was found to vary only slightly with flight speed over the lower half of the speed range. At high speeds, frequency is almost independent of velocity. Wingbeat frequency (Hz) depends on bat mass (m, kg) and flight speed (V, ms(-1)) according to the equation: f(w)=5.54-3.068log10m-2.857log10V. This simple relationship applies to both sub-orders and to all six families of bats studied. For 21 of the 23 species, the empirical values were within 1 Hz of the model values. One species, a small molossid, also had a second mode of flight in which f(w) was up to 3 Hz lower for all flight speeds. The following relationship predicts wingbeat amplitude to within +/-15 degrees from flight speed and wing area (S(REF), m(2)) at all flight speeds: theta;(w)=56.92+5.18V+16.06log10S(REF). This equation is based on data up to and including speeds that require maximum wingbeat amplitude to be sustained. For most species, the maximum wingbeat amplitude was 140 degrees.

Animals↗
PubMed2002

Hovering flight mechanics of neotropical flower bats (Phyllostomidae: Glossophaginae) in normodense and hypodense gas mixtures.

Existing estimates of flight energetics in glossophagine flower bats, the heaviest hovering vertebrate taxon, suggest disproportionately high expenditure of mechanical power. We determined wingbeat kinematics and mechanical power expenditure for one of the largest flower bats (Leptonycteris curasoae Martinez and Villa) during hovering flight in normodense and hypodense gas mixtures. Additional experiments examined the effects of supplemental oxygen availability on maximum flight performance. Bats failed to sustain hovering flight at normoxic air densities averaging 63% that of normodense air. Kinematic responses to hypodense aerodynamic challenge involved increases in wing positional angles and in total stroke amplitude; wingbeat frequency was unchanged. At near-failure air densities, total power expenditure assuming perfect elastic energy storage was 17-42% greater than that for hovering in normodense air, depending on the assumed value for the profile drag coefficient. Assuming a flight muscle ratio of 26%, the associated muscle-mass-specific power output at the point of near-failure varied between 90.8 W kg(-1) (profile drag coefficient of 0.02) to 175.6 W kg(-1) (profile drag coefficient of 0.2). Hyperoxia did not enhance hovering performance in hypodense air, and, with the exception of a small increase (10%) in stroke plane angle, yielded no significant change in any of the kinematic parameters studied. Revised energetic estimates suggest that mechanical power expenditure of hovering glossophagines is comparable with that in slow forward flight.

Air↗
PubMed1986

The primary structure of a mouse-eared bat (Myotis velifer, Chiroptera) hemoglobin.

The hemoglobin of the Mouse-Eared Bat Myotis velifer consists of one component. We present the primary structures of the alpha- and beta-globin chains which have been separated by chromatography on carboxymethyl-cellulose CM-52. The sequences have been determined by Edman-degradation with the film technic or the gas phase method, using the native chains and the tryptic peptides, as well as the C-terminal prolyl-peptides obtained by acid hydrolysis of the Asp-Pro-bonds. Compared to the corresponding human chains we found only 13 substitutions in the alpha-chains, but 27 in the beta-chains. The amino-acid residues substituted in the alpha-chains are not involved in any contacts, whereas in the beta-chains, one exchange involves a heme contact, three alpha 1/beta 1- and one alpha 1/beta 2-contacts, the latter [beta 43(CD2)-Glu----Thr] brings for the first time threonine in this position of the beta-chains. Comparison with the Egyptian Fruit Bat (Rousettus aegyptiacus) shows 12 and 25 substitutions in the alpha- and beta-chains, respectively, suggesting a large phylogenetic distance between Micro- and Megachiroptera. We consider this primary structure as a contribution towards solving the problem of the origin of bats and their relation to primates.

Amino Acid Sequence↗
PubMed1984

Reproductive failure due to the entrapment of oocytes in luteinized follicles of the little bulldog bat (Noctilio albiventris).

The reproductive tracts of 112 female little bulldog bats collected around the onset of a breeding season in the Cauca Valley of Colombia were examined histologically. Of the 88 females with luteinizing/luteinized follicles or new CL, 72 carried tubal ova or uterine blastocysts and 16 were non-pregnant. In 14 of the latter follicle rupture had apparently failed to occur, and the oocyte or a collapsed zona pellucida was found within a luteinizing or luteinized follicle. These structures appeared to be functional because most of the affected bats demonstrated preferential stimulation of the ipsilateral oviduct and/or uterine horn. Two of these animals also had a second, older luteinized follicle which contained the remnants of an oocyte. None of these 14 bats exhibited the uterine modifications thought to be associated with a previous pregnancy or had prominent mammary glands. Such reproductive features were, in contrast, frequently demonstrated by other females in the population. These observations suggest that the luteinization of unruptured follicles may have occurred in prepubertal members of the population and reflect immaturity of the hypothalamo-pituitary -ovarian axis in these individuals.

Animals↗
PubMed1984

Effects of elevated temperatures on the embryonic development and corpus luteum activity in the Japanese long-fingered bat, Miniopterus schreibersii fuliginosus.

Gravid female Japanese long-fingered bats were kept in captivity without hibernation at elevated temperatures (23-25 degrees C) in winter. The embryonic growth rate was accelerated and consequently parturition was advanced by a period equivalent to that of exclusion from hibernation as compared with that in the wild population. The corpus luteum became active, as indicated by an increase in the 'light' lutein cells in an experimental bat pregnant with a 15-mm embryo, but was less active (more 'dark' cells) in 2 hibernating control bats with an implanting blastocyst.

Animals↗