在不同状态和生境复杂度中大蹄蝠回声定位叫声的可塑性

蝙蝠回声定位声波的可塑性对其适应不同状态、生境以及捕食和社会交流具有重要的作用。为进一步研究大蹄蝠的回声定位声波在不同状态和生境下的可塑性,通过室内行为实验,对大蹄蝠在4 种不同状态(室内飞行、静息、布袋内和手持)和4 种不同生境复杂度(室外、室内0 棵树、室内1 棵树、室内5 棵树)条件下飞行的回声定位声波特征进行研究。结果表明:大蹄蝠的回声定位声波为CF - FM 型,通常连续发出2 - 4 个脉冲组成一个脉冲组。对比大蹄蝠在4 种不同状态下的回声定位叫声发现,主频按静息、布袋内、手持、飞行的顺序依次降低,后端FM 频宽则按手持、布袋内、飞行和静息的顺序依次变短;而脉冲间隔和脉冲时程则均按静 息、飞行、布袋内、手持的顺序依次增加。对比大蹄蝠在4 种不同生境复杂度中飞行的回声定位叫声发现,主频按室外、室内0 棵树、室内1 棵树、室内5 棵树依次提高,而脉冲时程及脉冲间隔则依次缩短;室外放飞条件下的后端FM 频宽比室内飞行的短。研究结果说明,大蹄蝠在不同状态、不同生境复杂度条件下的回声定位叫声具有明显的可塑性和生境适应性。     

普氏蹄蝠(Hipposideros pratti)回声定位声波、形态及捕食策略

研究了普氏蹄蝠(Hipposideros pratti)不同状态(飞行、悬挂)下的回声定位声波特征、形态特征和生态特征(捕食策略、捕食地和食物类型).结果表明,普氏蹄蝠的回声定位声波为CFFM型,在不同状态下,主频率有一定的差异,飞行状态的主频率略低于悬挂状态,表明普氏蹄蝠是利用多谱勒补偿效应来适应飞行速度引起的主频率变化,以进行准确的定位和有效的捕食;同时飞行状态下声脉冲时间、声脉冲间隔时间及FM带宽略低于悬挂状态,而声脉冲重复率和能率环略高于悬挂状态,表明普氏蹄蝠在不同状态下利用不同特征的声波进行捕食.由回声定位声波推断和野外观察可知,普氏蹄蝠可能在树冠周围以盘旋方式(在昆虫高峰期)或以捕蝇器式(在昆虫高峰期之后)捕食中等偏大的振翅昆虫(如甲虫).     

普氏蹄蝠(Hipposideros pratti)回声定位声波、形态及捕食策略

研究了普氏蹄蝠（Hipposideros pratti)不同状态（飞行,悬挂）下的回声定位声波特征,形态特征和生态特征（捕食策略,捕食地和食物类型）。结果表明,普氏蹄蝠的回声定位声波为CF－FM型,在不同状态下,主频率有一定的差异,飞行状态的主频率略低于悬挂状态,表明普氏蹄蝠是利用多谱勒补偿效应来适应飞行速度引起的主频率变化,以进行准确的定位和有效的捕食;同时飞行状态下声脉冲时间,声脉冲间隔时间及FM带宽略低于悬挂状态,而声脉冲重复率和能率环略主于悬挂状态,表明普氏蹄蝠在不同状态下利用不同特征的声波进行捕食,由回声定位声波推断和野外观察可知,普氏蹄蝠可能在树冠周围以盘旋方式（在昆虫高峰期）或以捕蝇器式（在昆虫高峰期这后）捕食中等偏大的振翅昆虫（如甲虫）。     

普氏蹄蝠下丘谐波内外神经元处理多普勒频移补偿信息的差异

为了探讨普氏蹄蝠下丘神经元在处理多普勒频移补偿后回声定位信号中的作用,实验采用双声刺激模式模拟蝙蝠不同飞行状态下产生多普勒频移补偿后的脉冲-回声对,即发声频率改变,回声频率维持恒定的情况下,研究下丘神经元对不同补偿值下的回声反应恢复率.结果发现:根据神经元在某一补偿值下对回声信号反应的恢复率是否超过70%,可将其分为具有选择性(S)和无选择性(NS)的两类神经元.且谐波内S神经元所占比例(68%)远超过非谐波内S神经元(39%).分析神经元的发放模式发现谐波内S神经元中相位型发放模式比例(44.3%)明显高于其他三种类型神经元.另外,虽然S和NS神经元的强度-潜伏期函数类型均以饱和型为主,但谐波内S神经元强度-潜伏期函数的最佳强度(best amplitude,BA)(95.3±14.0)dB SPL低于NS神经元的BA(104.1±10.2)d B SPL(P0.01),同时也低于非谐波内S神经元的BA(109.7±7.9)dB SPL(P0.01).以上实验结果表明,在下丘水平,神经元就已对多普勒频移补偿后回声定位信号的处理有了分工,集中在谐波内的S神经元通过提高对某一补偿值下回声信号反应的恢复率实现,对回声信息的精确编码,避免其他杂波干扰信息.同时,谐波内S神经元的发放模式和强度-潜伏期函数特点也满足其在复杂环境中精确声学成像的需求.     

大蹄蝠回声定位信号特征与下丘神经元频率调谐

采用超声监测仪录制超声信号和细胞外电生理记录下丘神经元的频率调谐曲线(frequency tuningcurqes,FTCs)的方法,探讨了大蹄蝠(Hipposideros armiger)回声定位信号与下丘(inferior colliculus,IC)神经元频率调谐之间的相关性.结果发现,大蹄蝠回声定位叫声为恒频-调频(consrant frequency-frequenevmodulated,CF-FM)信号,一般含有2-3个谐波,第二谐波为其主频,cF成分频率(Mean±SD,n=18)依次为:(33.3 4±0.2)、(66.5±0.3)、(99.4 4±0.5)kHz;电生理实验共获得72个神经元的频率调谐曲线,Q10-dB值的范围是0.5-95.4(9.2±14.6,rg=72),最佳频率(best frequency,BF)在回声定位主频附近的神经元具有尖锐的频率调谐特性.结果表明,大蹄蝠回声定位信号与下丘神经元频率调谐存在相关性,表现为最佳频率在回声定位信号主频附近的神经元频率调谐曲线的Q10-dB值较大,具有很强的频率分析能力.     

两种同域分布蹄蝠在开阔度不同的环境中回声定位声波的可塑性

在广西桂林研究了同域分布的大蹄蝠(Hipposideros armiger)和中蹄蝠(H.larvatus)在不同开阔度环境中回声定位声波信号的变化。用超声波仪录制自由悬挂和分别释放于人工"大棚"和"小棚"内飞行的蝙蝠的回声定位声波,使用超声分析软件分析声脉冲时程、主频率及声脉冲间隔,通过重复测量方差分析比较不同状态下的声波参数。结果表明:中蹄蝠声波的主频在悬挂状态下最高,小棚内飞行时次之,大棚内飞行最低;两种蹄蝠声波的脉冲时程和脉冲间隔在悬挂状态下最长,大棚内飞行次之,小棚内飞行最低。总之,这两种蹄蝠的回声定位声波能够随所处状态的变化而变化,可根据生境的复杂度调节声讯号,具有明显的声波可塑性。     

普氏蹄蝠下丘单反应和双反应神经元加工多普勒频移补偿信号的特点及生理机制

恒频-调频(constant frequency-frequency modulation,CF-FM)蝙蝠独特的多普勒频移补偿(Doppler-shift compensation,DSC)行为可保证其对回声信息的精确提取.那么听中枢加工DSC信号的适应性机制是什么?本实验模拟CF-FM蝙蝠DSC后的回声定位信号,研究下丘(inferior colliculus,IC)神经元加工DSC信号的特点及生理机制.实验共获得117个IC神经元,在CF-FM声刺激下,神经元表现为single-on(SO,n=83)和double-on(DO,n=34)两种反应模式.无论是在蝙蝠的正向还是负向补偿过程中,SO和DO神经元对回声反应恢复到50%时的双声刺激间隔(inter-pulse interval,IPI)值,均会随补偿条件的改变而发生变化.当双声刺激由无补偿转变为最佳补偿条件时,两类神经元的50%IPI显著缩短(P0.001),但SO神经元50%IPI缩短率超过70%的神经元数目较DO神经元多,且偏好正向补偿的IC神经元中,SO神经元的平均DSC范围也要显著宽于DO神经元(P0.05).该研究结果提示,IC中SO神经元可能较DO神经元更能充分利用蝙蝠DSC行为,来提高对回声反应的恢复能力,以最大程度地获取猎物信息并准确判断与猎物的相对速度.     

青藏高原东部高寒草甸群落生物量和补偿能力对施肥与刈割的响应

以青藏高原东部高寒草甸群落为研究对象,通过比较了不同施肥条件和不同刈割对群落地上生物量和多样性的影响。结果表明施肥可提高生物量且生物多样性降低,施肥和刈割处理后,施肥效应显著而刈割效应不显著,说明施肥是主效应。实验还发现施肥可提高群落的补偿能力;不同资源梯度的情况下植物群落对刈割处理后补偿作用也不相同,对刈割处理后植物群落补偿能力随资源的升高而增强。当未施肥和施肥30g/m^2时相同强度的1次刈割的补偿能力较相同强度的2次刈割的补偿能力大;当施肥60g/m^2和120g/m^2时相同强度的2次刈割的补偿能力较相同强度的1次刈割的补偿能力大。     

八种菊头蝠回声定位声波频率与体型的相关性

菊头蝠回声定位声波中含有强的恒频(con-stant frequency,CF)组分,通常在开始和结尾伴有短的FM组分(Schnitzler,1968).飞行状态能影响回音信号(张树义等,1999).在飞行中,蝙蝠发出的频率变低以补偿由飞行速度引起的多谱勒变化,返回的回声接近于蝙蝠停止时的声波频率(Schnitzler,1968).回声定位声波的频率随蝙蝠年龄和季节的变化会产生一些变动,但如果频率被身体结构制约,CF组分频率在蝙蝠静止时会保持相对恒定(Vater,1987;Heller et al.,1989;Joneset al.1994).Francis et al.(1998)对19种菊头蝠、Heller et al.(1989)对26种菊头蝠进行了体型测量和回声定位声波信号的测定,得出结论为:菊头蝠回声定位声波中CF组分的频率与体型大小成负相关.但Jones(1992)和Jones et al.(1993)认为体型大小对菊头蝠回声定位声波没有影响.     

莫扎特奏鸣曲K.448对脑电功率谱与重心频率的影响

采用脑电功率谱(power spectrum,PS)和重心频率(gravity frequency,GF)分析方法研究"莫扎特效应"代表音乐--Sonata K.448的神经电生理效应.在静息和播放不同音乐状态下记录16名非音乐专业大学生的脑电,通过平均周期图法计算脑电PS和GF.结果显示:3种音乐都显著升高了GF值,...     

Spectral and temporal gating mechanisms enhance the clutter rejection in the echolocating bat,Rhinolophus rouxi

Summary Doppler shift compensation behaviour in horseshoe bats, Rhinolophus rouxi, was used to test the interference of pure tones and narrow band noise with compensation performance. The distortions in Doppler shift compensation to sinusoidally frequency shifted echoes (modulation frequency: 0.1 Hz, maximum frequency shift: 3 kHz) consisted of a reduced compensation amplitude and/or a shift of the emitted frequency to lower frequencies (Fig. 1).Pure tones at frequencies between 200 and 900 Hz above the bat's resting frequency (RF) disturbed the Doppler shift compensation, with a maximum of intererence between 400 and 550 Hz (Fig. 2). Minimum duration of pure tones for interference was 20 ms and durations above 40 ms were most effective (Fig. 3). Interfering pure tones arriving later than about 10 ms after the onset of the echolocation call showed markedly reduced interference (Fig. 4). Doppler shift compensation was affected by pure tones at the optimum interfering frequency with sound pressure levels down to –48 dB rel the intensity level of the emitted call (Figs. 5, 6).Narrow bandwidth noise (bandwidth from ± 100 Hz to ± 800 Hz) disturbed Doppler shift compensation at carrier frequencies between –250 Hz below and 800 Hz above RF with a maximum of interference between 250 and 500 Hz above resting frequency (Fig. 7). The duration and delay of the noise had similar influences on interference with Doppler shift compensation as did pure tones (Figs. 8, 9). Intensity dependence for noise interference was more variable than for pure tones (-32 dB to -45 dB rel emitted sound pressure level, Fig. 10).The temporal and spectral gating in Doppler shift compensation behaviour is discussed as an effective mechanism for clutter rejection by improving the processing of frequency and amplitude transients in the echoes of horseshoe bats.Abbreviations CF constant frequency - FM frequency modulation - RF resting frequency - SPL sound pressure level     

Rapid jamming avoidance in biosonar

The sonar systems of bats and dolphins are in many ways superior to man-made sonar and radar systems, and considerable effort has been devoted to understanding the signal-processing strategies underlying these capabilities. A major feature determining the efficiency of sonar systems is the sensitivity to noise and jamming signals. Previous studies indicated that echolocating bats may adjust their signal structure to avoid jamming ('jamming avoidance response'; JAR). However, these studies relied on behavioural correlations and not controlled experiments. Here, we provide the first experimental evidence for JAR in bats. We presented bats (Tadarida brasiliensis) with 'playback stimuli' consisting of recorded echolocation calls at one of six frequencies. The bats exhibited a JAR by shifting their call frequency away from the presented playback frequency. When the approaching bats were challenged by an abrupt change in the playback stimulus, they responded by shifting their call frequencies upwards, away from the playback. Interestingly, even bats initially calling below the playback's frequency shifted their frequencies upwards, 'jumping' over the playback frequency. These spectral shifts in the bats' calls occurred often within less than 200 ms, in the first echolocation call emitted after the stimulus switch-suggesting that rapid jamming avoidance is important for the bat.     

Binaural influences on Doppler shift compensation of the horseshoe bat Rhinolophus rouxi

The flying horseshoe bat Rhinolophus rouxi compensates for Doppler shifts in echoes of their orientation pulses. By lowering the frequency of subsequent calls the echo's constant frequency is stabilized at the so-called reference frequency centered in a narrow and sensitive cochlear filter. This audio-vocal behaviour is known as Doppler shift compensation. To investigate whether the bats depend on binaural cues when compensating, three animals were tested for compensation on a swing before and after unilateral deafening. In each case compensation was severely impaired by unilateral deafening. Individual animals' compensation amplitude was reduced to 28–48% of the preoperational compensation of a +1.8 kHz shift. Doppler shift compensation performance did not recover to control levels during the observed period of 24 h after surgery. In contrast, unilateral middle ear removal which induces a unilateral auditory threshold increase of 9–14 dB does not impair compensation performance on the swing. To mimick Doppler shifts in a fixed setup, the frequencies of recorded echolocation calls were experimentally shifted between 0 and +2 kHz and played back via earphones to six animals. The bats completely compensated the experimental shifts only as long as the interaural intensity difference of the playback did not exceed 20 dB. No animal compensated with monaural playback. Accepted: 27 August 1999     

Fine control of call frequency by horseshoe bats

The auditory system of horseshoe bats is narrowly tuned to the sound of their own echoes. During flight these bats continuously adjust the frequency of their echolocation calls to compensate for Doppler-effects in the returning echo. Horseshoe bats can accurately compensate for changes in echo frequency up to 5 kHz, but they do so through a sequence of small, temporally-independent, step changes in call frequency. The relationship between an echo's frequency and its subsequent impact on the frequency of the very next call is fundamental to how Doppler-shift compensation behavior works. We analyzed how horseshoe bats control call frequency by measuring the changes occurring between many successive pairs of calls during Doppler-shift compensation and relating the magnitude of these changes to the frequency of each intervening echo. The results indicate that Doppler-shift compensation is mediated by a pair of (echo)frequency-specific sigmoidal functions characterized by a threshold, a slope, and an upper limit to the maximum change in frequency that may occur between successive calls. The exact values of these parameters necessarily reflect properties of the underlying neural circuitry of Doppler-shift compensation and the motor control of vocalization, and provide insight into how neural feedback can accommodate the need for speed without sacrificing stability.     

Echolocation calls produced by Kuhl's pipistrelles in different flight situations

Flexibility in the echolocation call structure of bats can improve their performances, because, in some situations, some signal designs are better than others. Hence, at least some bats should adjust their echolocation calls according to the setting in which they are operating but also to the specific task at hand, that is their behavioral intention. We studied variation in the echolocation calls of Pipistrellus kuhlii emitted during four flight situations that were similar in setting but differed in behavioral context: emergence from a roost, commuting to and from foraging sites, foraging and returning to a roost. Echolocation calls produced by P. kuhlii differed significantly according to the flight situation. Call types differed most distinctly between foraging and commuting. We also found a high variance in the emergence calls we recorded, perhaps reflecting pre- and post-takeoff calls. Discriminant function analysis on calls emitted while foraging, commuting or returning to the roost classified the calls to the correct group 73.3% of the time. The differences between bats' echolocation calls in different flight situations might indicate an intrinsic change in the bat's behavior. Recognizing these differences could be crucial when using call variables to identify bat species.     

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.     

On-board telemetry of emitted sounds from free-flying bats: compensation for velocity and distance stabilizes echo frequency and amplitude

To understand complex sensory-motor behavior related to object perception by echolocating bats, precise measurements are needed for echoes that bats actually listen to during flight. Recordings of echolocation broadcasts were made from flying bats with a miniature light-weight microphone and radio transmitter (Telemike) set at the position of the bat's ears and carried during flights to a landing point on a wall. Telemike recordings confirm that flying horseshoe bats (Rhinolophus ferrumequinum nippon) adjust the frequency of their sonar broadcasts to compensate for echo Doppler shifts. Returning constant frequency echoes were maintained at the bat's reference frequency +/-83 Hz during flight, indicating that the bats compensated for frequency changes with an accuracy equivalent to that at rest. The flying bats simultaneously compensate for increases in echo amplitude as target range becomes shorter. Flying bats thus receive echoes with both stabilized frequencies and stabilized amplitudes. Although it is widely understood that Doppler-shift frequency compensation facilitates detection of fluttering insects, approaches to a landing do not involve fluttering objects. Combined frequency and amplitude compensation may instead be for optimization of successive frequency modulated echoes for target range estimation to control approach and landing.     

The evolution of echolocation in bats

Recent molecular phylogenies have changed our perspective on the evolution of echolocation in bats. These phylogenies suggest that certain bats with sophisticated echolocation (e.g. horseshoe bats) share a common ancestry with non-echolocating bats (e.g. Old World fruit bats). One interpretation of these trees presumes that laryngeal echolocation (calls produced in the larynx) probably evolved in the ancestor of all extant bats. Echolocation might have subsequently been lost in Old World fruit bats, only to evolve secondarily (by tongue clicking) in this family. Remarkable acoustic features such as Doppler shift compensation, whispering echolocation and nasal emission of sound each show multiple convergent origins in bats. The extensive adaptive radiation in echolocation call design is shaped largely by ecology, showing how perceptual challenges imposed by the environment can often override phylogenetic constraints.