Michael Smotherman

Michael Smotherman
Texas A&M University | TAMU · Department of Biology

Professor

About

59
Publications
11,760
Reads
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982
Citations
Introduction
The bat lab at Texas A&M studies the wonderful world of sensory ecology . We are investigating the neural basis of echolocation behavior as well as how bats perform echolocation behaviors in different social and environmental contexts. We explore the social lives of bats and how they communicate with each other. We also investigate how other senses like olfaction are integrated with echolocation to guide behaviors.
Additional affiliations
January 2007 - December 2011
Texas A&M University
January 2000 - December 2002
University of California, Riverside
Position
  • PostDoc Position
January 1998 - December 2006
University of California, Los Angeles
Position
  • PhD Student
Education
August 1992 - May 1998

Publications

Publications (59)
Presentation
Spectrotemporal modulations are a prominent feature of natural sounds including animal vocalizations and human speech. Echolocating bats must process spectrotemporal cues such as echo delays and spectrum properties to navigate their environment; however, the neuronal networks in the primary auditory cortex (A1) that process features of natural soun...
Article
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Acoustic communication allows animals to coordinate and optimize resource utilization in space. Cardioderma cor, the heart‐nosed bat, is one of the few species of bats known to sing during nighttime foraging. Previous research found that heart‐nosed bats react aggressively to song playback, supporting the territorial defense hypothesis of singing i...
Article
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There is consensus that primary auditory cortex (A1) utilizes a combination of rate codes and temporally precise population codes to represent discreet auditory objects. During the response to auditory streams, forward suppression constrains cortical rate coding strategies, but it may also be well positioned to enhance temporal coding strategies th...
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Olfactory tracking generally sacrifices speed for sensitivity, but some fast-moving animals appear surprisingly efficient at foraging by smell. Here, we analysed the olfactory tracking strategies of flying bats foraging for fruit. Fruit- and nectar-feeding bats use odour cues to find food despite the sensory challenges derived from fast flight spee...
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Many studies have characterized olfactory-tracking behaviors in animals, and it has been proposed that search strategies may be generalizable across a wide range of species. Olfaction is important for fruit and nectar feeding bats, but it is uncertain if existing olfactory search models can predict the strategies of flying mammals that emit echoloc...
Chapter
Echolocating bats use sounds for both perceiving their surroundings and social communication, which makes bats vulnerable to environmental and anthropogenic noise. Whether a particular noise source affects bats depends upon the acoustic properties of the noise and those of the bat’s pulses as well as whether the bat is roosting, commuting or foragi...
Presentation
No PDF available ABSTRACT Surface texture is an integral cue used by echolocating mammals for characterizing and forming a mental representation of an ensonified target. Bats need to be able to recognize and discriminate between different target surface textures. Previous work showed that bats rely on spectral cues embedded in echoes to resolve tex...
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Echolocating bats rely upon spectral interference patterns in echoes to reconstruct fine details of a reflecting object's shape. However, the acoustic modulations required to do this are extremely brief, raising questions about how their auditory cortex encodes and processes such rapid and fine spectrotemporal details. Here, we tested the hypothesi...
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The Mexican free-tailed bat, Tadarida brasiliensis, is a fast-flying bat that hunts by biosonar at high altitudes in open space. The auditory periphery and ascending auditory pathways have been described in great detail for this species, but nothing is yet known about its auditory cortex. Here we describe the topographical organization of response...
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Many animals display morphological adaptations of the nose that improve their ability to detect and track odors. Bilateral odor sampling improves an animals’ ability to navigate using olfaction and increased separation of the nostrils facilitates olfactory source localization. Many bats use odors to find food and mates and bats display an elaborate...
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We studied the columnar and layer-specific response properties of neurons in the primary auditory cortex (A1) of six (four females, two males) anesthetized free-tailed bats, Tadarida brasiliensis, in response to pure tones and down and upward frequency modulated (FM; 50 kHz bandwidth) sweeps. In addition, we calculated current source density (CSD)...
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How bats mitigate mutual interference is a long-standing question that has ecological and technological implications as biosonar systems continue to outperform artificial sonar systems in noisy, cluttered environments. Echolocating bats display a mutual suppression response, slowing their pulse emission rates when flying in groups to gain a net imp...
Presentation
High bat mortalities at wind turbines have emerged as an unexpectedly severe environmental impact of developing wind farms all over the world, motivating an urgent need to develop effect deterrent strategies that can be implemented efficiently on a large scale. Echolocating bats use ultrasonic sonar to navigate, and some studies have shown that bro...
Article
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Forward masking is a widespread auditory phenomenon in which the response to one sound transiently reduces the response to a succeeding sound. This study used auditory brainstem responses to measure temporal masking effects in the free-tailed bat, Tadarida brasiliensis. A digital subtraction protocol was used to isolate responses to the second of a...
Article
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Singing to create and defend territory boundaries is common among birds but rare in mammals. The African heart-nosed bat, Cardioderma cor, is hypothesized to use loud, low-frequency songs to reestablish foraging territories nightly. Territoriality can be defined ecologically, whereby an individual exclusively uses an area repeatedly, and behavioral...
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Echolocating bats face the challenge of actively sensing their environment through their own emissions, while also hearing calls and echoes of nearby conspecifics. How bats mitigate interference is a long-standing question that has both ecological and technological implications, as biosonar systems continue to outperform man-made sonar systems in n...
Presentation
Echolocating bats may be able to manipulate the acoustic projection pattern of their sonar pulse emissions, but the mechanism(s) for this and potential constraints are unexplored. The Mexican free-tailed bat (Tadarida brasiliensis) appears to achieve this by finely adjusting the shape of its mouth cavity (beam-forming) in a behavior akin to suprala...
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Bats (Order Chiroptera) are an abundant group of mammals with tremendous ecological value as insectivores and plant dispersers, but their role as reservoirs of zoonotic diseases has received more attention in the last decade. With the goal of managing disease in free-ranging bats, we tested modified vaccinia Ankara (MVA) and raccoon poxvirus (RCN)...
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Singing plays an important role in the social lives of several disparate bat species, but just how significant the behavior may be among bats generally is unknown. Recent discoveries suggest singing by bats might be surprisingly more diverse and widespread than anticipated, but if true then two questions must be addressed: firstly why has singing b...
Chapter
Singing is a specialized vocal behavior that supports courtship and territoriality but costs energy and time. Singing behaviors are well documented in the Mexican free-tailed bat, Tadarida brasiliensis, but many important questions about the functional significance of singing in this species remain unanswered. To better understand how singing benef...
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The yellow-winged bat, Lavia frons, and the heart-nosed bat, Cardioderma cor, are sympatric species of the family Megadermatidae resident to East Africa. Cardioderma cor roost in groups and disperse to individual foraging areas at night, whereas L. frons roost in male-female pairs in Acacia trees within a foraging territory. Nightly foraging areas...
Conference Paper
Echolocating bats are social animals and must be able to use their biosonar capabilities in a wide range of social contexts. Bats roosting or flying in groups routinely adapt their pulse emissions to accommodate sharing the acoustic space with potentially many bats. In this regard, echolocation may be bound by the same rules and constraints governi...
Article
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The diversity of song repertoires and functions of singing in mammals are not well known. In bats, singing in the roost to court and defend mates has been studied; however, the concept of territorial behaviors and the role of singing outside of the roost is poorly understood. The heart-nosed bat, Cardioderma cor, roosts in mixed-sex and age groups...
Conference Paper
An important aspect of auditory scene analysis is the specialized neurocircuitry required for vocal production. in a dynamic acoustic environment. Although often taken for granted, enhanced audio-vocal feedback is relatively uncommon in animals and yet an important precursor to vocal learning. We argue that vocal complexity in bats is an exaptation...
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This paper describes the application of nanoparticle bombardment with time-of-flight secondary ion mass spectrometry (NP-ToF-SIMS) for the analysis of native biological surfaces for the case of sagittal sections of mammalian brain tissue. The use of high energy, single nanoparticle impacts (e.g. 520 keV Au400) permits desorption of intact lipid mol...
Conference Paper
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of a paper presented at Microscopy and Microanalysis 2013 in Indianapolis, Indiana, USA, August 4 – August 8, 2013.
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of a paper presented at Microscopy and Microanalysis 2013 in Indianapolis, Indiana, USA, August 4 – August 8, 2013.
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How bats adapt their sonar behavior to accommodate the noisiness of a crowded day roost is a mystery. Some bats change their pulse acoustics to enhance the distinction between theirs and another bat's echoes, but additional mechanisms are needed to explain the bat sonar system's exceptional resilience to jamming by conspecifics. Variable pulse repe...
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The capacity to modify vocal syntax to changes in social context is an important component of vocal plasticity and complexity in adult vertebrates, especially in human speech. The ecological significance of this behaviour has been well established in some avian species but not in mammals where complex, multisyllabic vocalizations are rare. The Braz...
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Recent studies of spontaneously vocalizing primates, cetaceans, bats and rodents suggest these animals possess a limited but meaningful capacity to manipulate the timing and acoustic structure of their vocalizations, yet the neural substrate for even the simplest forms of vocal modulation in mammals remains unknown. Echolocating bats rapidly and ro...
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The ability to control the bandwidth, amplitude and duration of echolocation pulses is a crucial aspect of echolocation performance but few details are known about the neural mechanisms underlying the control of these voice parameters in any mammal. The basal ganglia (BG) are a suite of forebrain nuclei centrally involved in sensory-motor control a...
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Bats are highly social and spend much of their lives echolocating in the presence of other bats. To reduce the effects of acoustic interferences from other bats' echolocation calls, we hypothesized that bats might shift the timing of their pulse emissions to minimize temporal overlap with another bat's echolocation pulses. To test this hypothesis w...
Article
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Background noise evokes a similar suite of adaptations in the acoustic structure of communication calls across a diverse range of vertebrates. Echolocating bats may have evolved specialized vocal strategies for echolocating in noise, but also seem to exhibit generic vertebrate responses such as the ubiquitous Lombard response. We wondered how bats...
Data
Time waveforms normalized to a maximum of 1 volt, of the four bats presented in Figure 2. (0.31 MB TIF)
Data
Song of College Station Bat 2 slowed eight times (0.34 MB WAV)
Data
Song of Austin Bat 2 slowed eight times (0.72 MB WAV)
Data
A slowed version of Movie S1 showing a male display and song. (1.13 MB MOV)
Data
Song of Austin Bat 1 slowed eight times. (0.72 MB WAV)
Data
Song of College Station Bat 1 slowed eight times (0.60 MB WAV)
Data
A male bat sings while performing a wing flapping display in front of his territory, a cloth pouch, where some females are roosting. (2.48 MB MOV)
Article
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The neurohormone melatonin is an important signal for both time of day and time of year in many seasonally breeding animals. High densities of melatonin receptors have been found in the suprachiasmatic nucleus, median eminence, and the pituitary gland in almost all mammals investigated so far, and lower densities of melatonin receptors have also be...
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In mammals, complex songs are uncommon and few studies have examined song composition or the order of elements in songs, particularly with respect to regional and individual variation. In this study we examine how syllables and phrases are ordered and combined, ie "syntax", of the song of Tadarida brasiliensis, the Brazilian free-tailed bat. Specif...
Article
Vocal motor patterning in mammals depends on a network of midbrain and brainstem sensory-motor integration centers that coordinate activity in facial, laryngeal and respiratory muscles. The temporary subjugation of respiratory drive for vocalizing and the entrainment of vocal timing to respiratory rhythms are achieved by a combination of descending...
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Doppler-shift compensation behavior (DSC) is a highly specialized vocal response displayed by bats that emit pulses with a prominent constant frequency (CF) component and adjust the frequency of their CF component to compensate for flight-speed induced Doppler shifts in the frequency of the returning echoes. DSC has only been observed in one member...
Article
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Somatosensory and auditory feedback mechanisms are dynamic components of the vocal motor pattern generator in mammals. This review explores how sensory cues arising from central auditory and somatosensory pathways actively guide the production of both simple sounds and complex phrases in mammals. While human speech is a uniquely sophisticated examp...
Article
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Echolocating insectivorous bats consummate prey captures using a distinct vocal motor pattern commonly known as the terminal or feeding buzz, which is widely considered a fixed motor pattern executed independently of auditory feedback influences. The Mexican free-tailed bat, Tadarida brasiliensis, offers an opportunity to explore the role of sensor...
Article
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Mammalian vocalizations require the precise coordination of separate laryngeal and respiratory motor pathways. Precisely how and where in the brain vocal motor patterns interact with respiratory rhythm control is unknown. The parabrachial nucleus (PB) is known to mediate key respiratory reflexes and is also considered a principle component of the m...
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During flight, auditory feedback causes horseshoe bats to adjust the duration and repetition rate of their vocalizations in a context-dependent manner. As these bats approach a target, they make finely graded adjustments in call duration and interpulse interval (IPI), but their echolocation behavior is also characterized by abrupt transitions in ov...
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Most amphibians have within their ears the substrate to hear efficiently underwater, underground, and in air, a talent few if any other vertebrates can lay claim to. They have achieved this by being very conservative in the nature of novel addition s and specialized adaptations to their ears. Indeed, regressive events appear to be just as common as...
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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 sequenc...
Article
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Hearing one's own voice is essential for the production of correct vocalization patterns in many birds and mammals, including humans. Bats, for instance, adjust temporal, spectral, and intensity parameters of their echolocation calls by precisely monitoring the characteristics of the returning echo signals. However, neuronal substrates and mechanis...
Article
Full-text available
Echolocating horseshoe bats respond to flight-speed induced shifts in echo frequency by adjusting the frequency of subsequent calls. Under natural conditions, Doppler effects may force the frequency of a returning echo several kilohertz above the original emission frequency. By lowering subsequent call frequencies, the bat can return echo frequenci...
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Among mammals, echolocation in bats illustrates the vital role of proper audio-vocal feedback control particularly well. Bats adjust the temporal, spectral and intensity parameters of their echolocation calls depending on the characteristics of the returning echo signal. The mechanism of audio-vocal integration in both mammals and birds is, however...
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For more than four decades, hearing in frogs has been an important source of information for those interested in auditory neuroscience, neuroethology and the evolution of hearing. Individual features of the frog auditory system can be found represented in one or many of the other vertebrate classes, but collectively the frog inner ear represents a...
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The amphibian papilla (AP) is the principal auditory organ of the frog. Anatomical and neurophysiological evidence suggests that this hearing organ utilizes both mechanical and electrical (hair cell-based) frequency tuning mechanisms, yet relatively little is known about the electrophysiology of AP hair cells. Using the whole-cell patch-clamp techn...
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The whole-cell patch-clamp technique was used to identify and characterize ionic currents in isolated hair cells of the leopard frog basilar papilla (BP). This end organ is responsible for encoding the upper limits of a frog’s spectral sensitivity (1.25–2.0 kHz in the leopard frog). Isolated BP hair cells are the smallest hair cells in the frog aud...
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Leopard frog saccular hair cells exhibit an electrical resonance in response to a depolarizing stimulus that has been proposed to contribute to the tuning properties of the frog sacculus by acting as an electrical band-pass filter. With the whole cell patch-clamp technique, we have investigated the effect of temperature on electrical resonances in...

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Projects

Project (1)
Project
The goal of this project is to identify behavioral and neurophysiological adaptations that facilitate the classification and identification of obstacles and targets by biosonar. We utilize behavioral assays to test hypotheses about how bats interpret echoes while inspecting and making decisions about a target. We use neurophysiological tools to examine how important acoustic cues embedded within echoes are encoded in the auditory system and reunited to form a perception of the object.