Renal function in the neotropical bat, Artibeus jamaicensis

1. When feeding on figs (Ficus insipida), the bat Artibeus jamaicensis increases dietary sodium density while decreasing potassium density by primarily extracting and ingesting pulp juices rather than other parts of the fruit. 2. Based on urine osmotic pressure, these bats are uniformly dehydrated when they leave day roosts and become rapidly rehydrated (0.5-1 hr) after initiation of feeding. 3. After 2000 hr, and throughout the night there is no difference in urine concentration of free-flying bats compared with bats held in the laboratory without food or water for the same time interval. 4. Mean maximum urine concentration in this species is 972 mOsm/kg.     

Echo SPL influences the ranging performance of the big brown bat,Eptesicus fuscus

Four bats of the species Eptesicus fuscus were trained in a two-alternative forced-choice procedure to discriminate between two phantom targets that differed in range. The rewarded stimulus was located at a distance of 52.7 cm, while the other unrewarded stimulus was further away. Only one target was presented at a time.In the first experiment we measured the range discrimination performance at an echo SPL of –28 dB relative to the bat's sonar transmission. A 75% correct performance level was arbitrarily defined as threshold and was obtained at a delay difference of 80 s, corresponding to a range difference of 13.8 mm.In the second experiment the delay difference was fixed at 150 s and the echo SPL varied between –8 and –48 dB relative to sonar emissions. The performance of the bats depended on the relative echo SPL. At –28 dB the bats showed the best performance. It deteriorated at an increase of the relative echo SPL to –18 dB and –8 dB. The performance also deteriorated when the relative echo SPL was reduced to –38 dB and –48 dB. Only at low relative echo SPLs did the bats partially compensate for the reduction in echo SPL and increased the SPL of their emitted signals by a few dB.Our results support the hypothesis that neurons exhibiting paradoxical latency shift may be involved in encoding target range. This hypothesis predicts a decrease in performance at high echo SPLs as we found it in our experiments. The observed reduction in performance at very low echo SPLs may be due to a decrease in S/N ratio.     

Detection of jitter in intertarget spacing by the big brown bat Eptesicus fuscus

We trained bats to detect intertarget jitter, i.e., relative motion between two virtual (electronically synthesized) targets. Both targets were themselves moving with respect to nearby objects (e.g., the microphone and speaker used to create the virtual targets) so that the only reliable cue available to the bats was variation in intertarget spacing. Given a target at 80 cm and another at 95, 110 or 125 cm, the threshold for intertarget jitter (ITJ) of the two bats tested was <10 μs, corresponding to <1.7 mm of range. When, for one bat, we increased the range instability of the targets by adding varying amounts of random range shift to the target complex (while preserving the correct intertarget spacing), ITJ threshold worsened. When we presented three targets, one of which was jittering, the bat's threshold improved to 0.9 μs (equivalent to 0.16 mm). If no second target was presented, i.e., if the task was to detect jitter added to a single moving target, then bats' jitter threshold was very high (>200 μs). Eptesicus fuscus appears to be very good at detecting changes in intertarget spacing, which might prove valuable for detecting targets moving relative to the background or for constructing a spatial image of a complex environment. Accepted: 7 April 1997     

Encoding repetition rate and duration in the inferior colliculus of the big brown bat,Eptesicus fuscus

1. Encoding of temporal stimulus parameters by inferior collicular (IC) neurons of Eptesicus fuscus was studied by recording their responses to a wide range of repetition rates (RRs) and durations at several stimulus intensities under free field stimulus conditions. 2. The response properties of 424 IC neurons recorded were similar to those reported in previous studies of this species. 3. IC neurons were classified as low-pass, band-pass, and high-pass according to their preference for RRs and/or durations characteristic of, respectively, search, approach, or terminal phases of echolocation. These neurons selectively process stimuli characteristic of the various phases of hunting. 4. Best RRs and best durations were not correlated with either the BFs or recording depths This suggests that each isofrequency lamina is capable of processing RRs and durations of all hunting phases. 5. Responses of one half of IC neurons studied were correlated with the stimulus duty cycle. These neurons may preferentially process terminal phase information when the bat's pulse emission duty cycle increases. 6. While the stimulus RR affected the dynamic range and overall profile of the intensity rate function, only little effect was observed with different stimulus durations.     

Terrestrial locomotor behaviors of the big brown bat (Vespertilionidae: Eptesicus fuscus)

Mammal Research - Although living bats (Mammalia: Chiroptera) demonstrate a wide variety of terrestrial behaviors and abilities, most research on terrestrial locomotor behaviors of bats has focused...     

Echo delay versus spectral cues for temporal hyperacuity in the big brown bat,Eptesicus fuscus

Big brown bats can discriminate between echoes that alternate in delay (jitter) by as little as 10–15 ns and echoes that are stationary in delay. This delay hyperacuity seems so extreme that it has been rejected in favor of an explanation in terms of artifacts in echoes, most likely spectral in nature, that presumably are correlated with delay. Using different combinations of digital, analog, and cable delays, we dissociated the overall delay of jittering echoes from the size of the analog component of delay, which alone is presumed to determine the strength of the apparatus artifact. The bats' performance remains invariant with respect to the overall delay of the jittering echoes, not with respect to the amount of analog delay. This result is not consistent with the possible use of delay-related artifacts produced by the analog delay devices. Moreover, both electronic and acoustic measurements disclose no spectral cues or impedance-mismatch reflections in delayed signals, just time-delays. The absence of artifacts from the apparatus and the failure of overlap and interference from reverberation to account for the 10-ns result means that closing the gap between the level of temporal accuracy plausibly explained from physiology and the level observed in behavior may require a better understanding of the physiology.Abbreviations FM frequency-modulated - XCR cross-correlation function     

在背景干扰条件下大棕蝠对静止及移动目标的探测

采用“双选”的心理物理学方法 ,研究了训练后的大棕蝠 (Eptesicusfuscus)在背景干扰的条件下探测半圆形目标的能力。半圆形目标系以静止、旋转、摆动或不同组合的旋转与摆动呈现于蝙蝠。在测试室 ,蝙蝠-目标间距从 3 0cm开始 ,依次递增 10cm直至 110cm为止。当蝙蝠 -目标间距小于 80cm时 ,目标回声的强度总是大于背景干扰声。由旋转目标反射的回声强度则依正弦波调制。结果发现 :蝙蝠对目标的正确探测率随蝙蝠 -目标间距的增加而降低 ;在每一特定间距 ,对移动目标的正确探测率均高于对静止目标的正确探测率     

Preference of a revolving target to a stationary one by the big brown bat, Eptesicus fuscus

Utilizing a three-ramp platform, we studied the detection of a revolving and a stationary target in the presence of background clutter by trained Eptesicus fuscus. During the test, the mean amplitude of echo from either target was always larger than that of the background echoes at the bat-to-target distance of 30, 70 and 100 cm. The amplitude of the echo reflected back from a revolving target was modulated between a maximum and a minimum value. An electric motor was used to revolve a target. The frequency contents of the motor noise were mostly below 1 kHz. While the total percent response of approaching either target is always more than 90% at every bat-to-target distance tested, the bats approach a revolving target more frequently than a stationary one. Echolocation pulses emitted by the bats during the test were recorded and analyzed. The bats shortened their pulse durations and interpulse intervals and lowered the frequency contents as they entered into the crawling phase from the searching phase. Potential interference of background echoes and ambient noise with the performance of the bats is discussed. The preference of a revolving target to a stationary one by the bats is perhaps due to the fact that a revolving target has a higher releasing value than a stationary one does.     

Direction-dependent corticofugal modulation of frequency-tuning curves of inferior collicular neurons in the big brown bat, Eptesicus fuscus

This study examined if corticofugal modulation of subcortical frequency-tuning curves varied with sound direction. Both excitatory and inhibitory frequency tuning curves of inferior collicular neurons of the big brown bat, Eptesicus fuscus were plotted before and during electrical stimulation in the auditory cortex at two sound directions (contra-40 degrees and ipsi-40 degrees). Most collicular neurons had broader excitatory frequency-tuning curves at contra-40 degrees but had broader inhibitory frequency-tuning curves at ipsi-40 degrees. Cortical electrical stimulation changed the excitatory minimum thresholds of most collicular neurons at a greater degree at ipsi-40 degrees than at contra-40 degrees. However, cortical electrical stimulation produced a greater increase in the sharpness of excitatory frequency-tuning curves of most corticofugally inhibited collicular neurons at contra-40 degrees but produced a greater decrease in the sharpness of excitatory frequency-tuning curves of most corticofugally facilitated collicular neurons at ipsi-40 degrees. Cortical electrical stimulation also produced a greater change in the sharpness of inhibitory frequency-tuning curves of most corticofugally inhibited collicular neurons at contra-40 degrees than at ipsi-40 degrees. Possible mechanisms for this direction-dependent corticofugal modulation of frequency-tuning curves of collicular neurons are discussed.     

Extended incubation period of rabies virus in a captive big brown bat (Eptesicus fuscus)

Rabies virus incubation in bats is typically less than 180 days, yet longer incubation periods have been described. We report a 267-day incubation in a big brown bat (Eptesicus fuscus) exposed to rabies virus before entering our captive colony.     

Echo SPL, training experience, and experimental procedure influence the ranging performance in the big brown bat, Eptesicus fuscus

Four Eptesicus fuscus were trained in a range discrimination experiment to choose the closer of two phantom targets. Echo attenuation was roving between trials returning echoes ranging from −10 dB to −50 dB SPL (sound pressure level) relative to emission SPL. Discrimination thresholds were determined. After sufficient training, ranging performance was stable and about the same in the range between −20 dB and −50 dB with range difference thresholds around 300 μs. At −10 dB, performance was poor even after long training. After additional training at a constant relative echo SPL of −30 dB and a delay difference of 300 μs the performance measured with roving echo SPL improved at all relative echo SPL between −20 dB and −50 dB but not at −10 dB. The new experimental procedure improved the performance by additional learning, and the bats generalized over a wide range of relative echo SPL. Threshold improved to 100 μs when measured at a constant relative echo SPL of −30 dB, again indicating the influence of the experimental procedure. In correspondence to neurophysiological data the ranging performance deteriorates if the echo SPL is close to the emission SPL. Signal duration and emission SPL were variable during range discrimination. Accepted: 7 March 1998     

Temporally patterned pulse trains affect directional sensitivity of inferior collicular neurons of the big brown bat, Eptesicus fuscus

The directional sensitivity of inferior collicular neurons of the big brown bat, Eptesicus fuscus, was studied under free field stimulation conditions with 3 temporally patterned trains of sound pulses which differed in pulse repetition rate and duration. The directional sensitivity curves of 92 neurons studied can be described as hemifield, directionally-selective, or non-directional according to the variation in the number of impulses with pulse train direction. When these neurons were stimulated with all 3 pulse trains, the directional sensitivity curves of 50 neurons was unchanged but that of the other 42 neurons changed from one type into another. When these pulse trains were delivered at high pulse repetition rate and short pulse duration, they significantly sharpened the directional sensitivity of two thirds of the neurons examined by reducing the angular range and increasing the slope of their impulse directional sensitivity curves. These pulse trains also sharpened the slope of the threshold directional sensitivity curves of 25 neurons studied. However, when directional sensitivity of collicular neurons was determined with pulse trains that differed only in pulse repetition rate or in pulse duration, significant sharpening of directional sensitivity was rarely observed in all experimental conditions tested. Possible mechanisms underlying these findings are discussed.     

Mitochondrial DNA polymorphism in three Antillean island populations of the fruit bat, Artibeus jamaicensis

The Neotropical fruit bat, Artibeus jamaicensis, occurs throughout Latin America and on many islands in the Caribbean. Populations from Jamaica (in the Greater Antilles) to Barbados (in the Lesser Antilles) have been classified as a subspecies (A.j. jamaicensis) separate from that on the Lesser Antillean island of St. Vincent (A.j. schwartzi). Mitochondrial DNA (mtDNA) was isolated from 54 individuals collected on these islands, analyzed by digestion with restriction endonucleases, and the restriction sites were mapped. Three different mtDNA genotypes (16,000 +/- 200 bp) were identified: J-1 (16 animals from Jamaica, one from St. Vincent, 15 from Barbados), J-2 (two animals from Jamaica), and SV-1 (18 animals from St. Vincent, two from Barbados). The J-1 and J-2 genotypes were estimated to differ from each other by only 0.4%, but the SV-1 genotype differed from J-1 and J-2 by 8.1%-10.5%. The estimated sequence divergence between SV-1 and J-1 is unusually large for mammals that are regarded as conspecific. Restriction mapping showed that the differences among the genotypes (presence or absence of particular restriction sites) were located throughout the genome. The presence of the J-1 mtDNA genotype on Jamaica and on St. Vincent and Barbados (1,400 km away) demonstrates that maternal lineages in these bats are not necessarily confined to single islands or limited geographic regions. The presence of the J-1 mtDNA genotype within the A. j. schwartzi population on St. Vincent and the presence of the SV-1 genotype in two specimens of A. j. jamaicensis from Barbados document genetic exchange between subspecific populations on these islands, which are separated by 180 km of open water.     

后掩蔽效应对大棕蝠下丘神经元声反应的影响

以回声定位蝙蝠为模式动物,采用在体动物细胞外单位记录法,研究了后掩蔽效应对下丘神经元声反应的影响。结果显示,部分神经元(38％,12／31)对测试声刺激的反应明显受到掩蔽声的抑制,其后掩蔽效应强弱与掩蔽声和测试声的相对强度差(inter-stimulus level difference,SLD),以及测试声与掩蔽声之间的间隔时间(inter-stimulus onset asynchrony,SOA)有关：当掩蔽声强度升高或测试声强度降低时,后掩蔽效应增强;而SOA的缩短,亦可见后掩蔽效应增强。另外,相当数量的神经元(52%,16／31)对测试声刺激的反应并不受掩蔽声的影响,其中有的神经元只有在特定SLD和SOA时,才表现出后掩蔽效应。而少数下丘神经元(10％,3／31)在特定SLD和SOA时,掩蔽声对测试声反应有易化作用。上述结果表明,部分下丘神经元参与了声认知活动中的后掩蔽形成过程,推测下丘神经元在定型声反应特性中,对掩蔽声诱导的兴奋前抑制性输入与测试声诱导的兴奋性输入之间的时相性动态整合起关键作用。     

Target-detection by the echolocating bat,Eptesicus fuscus

Summary The long-range echo-detection capabilities of echolocating bats (Eptesicus fuscus) were studied in a two-choice psychophysical procedure.E. fuscus can detect 4.8 mm diameter spheres at a distance of 2.9 m, and 19.1 mm diameter spheres at a distance of 5.1 m. The threshold of echo-detection corresponds to the distance at which a target returns an echo amplitude in the region of 0 dB SPL. The results demonstrate that the maximum effective range of bat sonar is greater than previously indicated by obstacleavoidance and target-interception tasks.