Individual differences show that only some bats can cope with noise-induced masking and distraction

Anthropogenic noise is a widespread pollutant that has received considerable recent attention. While alarming effects on wildlife have been documented, we have limited understanding of the perceptual mechanisms of noise disturbance, which are required to understand potential mitigation measures. Likewise, individual differences in response to noise (especially via perceptual mechanisms) are likely widespread, but lacking in empirical data. Here we use the echolocating bat Phyllostomus discolor, a trained discrimination task, and experimental noise playback to explicitly test perceptual mechanisms of noise disturbance. We demonstrate high individual variability in response to noise treatments and evidence for multiple perceptual mechanisms. Additionally, we highlight that only some individuals were able to cope with noise, while others were not. We tested for changes in echolocation call duration, amplitude, and peak frequency as possible ways of coping with noise. Although all bats strongly increased call amplitude and showed additional minor changes in call duration and frequency, these changes could not explain the differences in coping and non-coping individuals. Our understanding of noise disturbance needs to become more mechanistic and individualistic as research knowledge is transformed into policy changes and conservation action.

Cyto- and myeloarchitectural brain atlas of the pale spear-nosed bat (Phyllostomus discolor) in CT Aided Stereotaxic Coordinates

The pale spear-nosed bat Phyllostomus discolor, a microchiropteran bat, is well established as an animal model for research on the auditory system, echolocation and social communication of species-specific vocalizations. We have created a brain atlas of Phyllostomus discolor that provides high-quality histological material for identification of brain structures in reliable stereotaxic coordinates to strengthen neurobiological studies of this key species. The new atlas combines high-resolution images of frontal sections alternately stained for cell bodies (Nissl) and myelinated fibers (Gallyas) at 49 rostrocaudal levels, at intervals of 350 µm. To facilitate comparisons with other species, brain structures were named according to the widely accepted Paxinos nomenclature and previous neuroanatomical studies of other bat species. Outlines of auditory cortical fields, as defined in earlier studies, were mapped onto atlas sections and onto the brain surface, together with the architectonic subdivisions of the neocortex. X-ray computerized tomography (CT) of the bat’s head was used to establish the relationship between coordinates of brain structures and the skull. We used profile lines and the occipital crest as skull landmarks to line up skull and brain in standard atlas coordinates. An easily reproducible protocol allows sectioning of experimental brains in the standard frontal plane of the atlas. An electronic version of the atlas plates and supplementary material is available from 10.12751/g-node.8bbcxy

Biosonar spatial resolution along the distance axis: revisiting the clutter interference zone

ABSTRACTMany echolocating bats forage close to vegetation – a chaotic arrangement of prey and foliage where multiple targets are positioned behind one another. Bats excel at determining distance: they measure the delay between the outgoing call and the returning echo. In their auditory cortex, delay-sensitive neurons form a topographic map, suggesting that bats can resolve echoes of multiple targets along the distance axis – a skill crucial for the forage-amongst-foliage scenario. We tested this hypothesis combining an auditory virtual reality with formal psychophysics: we simulated a prey item embedded in two foliage elements, one in front of and one behind the prey. The simulated spacing between ‘prey’ (target) and ‘foliage’ (maskers) was defined by the inter-masker delay (IMD). We trained Phyllostomus discolor bats to detect the target in the presence of the maskers, systematically varying both loudness and spacing of the maskers. We show that target detection is impaired when maskers are closely spaced (IMD<1 ms), but remarkably improves when the spacing is increased: the release from masking is approximately 5 dB for intermediate IMDs (1–3 ms) and increases to over 15 dB for large IMDs (≥9 ms). These results are comparable to those from earlier work on the clutter interference zone of bats (Simmons et al., 1988). They suggest that prey would enjoy considerable acoustic protection from closely spaced foliage, but also that the range resolution of bats would let them ‘peek into gaps’. Our study puts target ranging into a meaningful context and highlights the limitations of computational topographic maps.

NUEVO REGISTRO DE HISTIOSTRONGYLUS CORONATUS (NEMATODA, MOLINEIDAE) PARASITANDO MURCIÉLAGOS (MAMMALIA, CHIROPTERA) EN BRASIL

Registramos Histiostrongylus coronatus Molin, 1861 no intestino delgado de Phyllostomus discolor Wagner, 1843 (Phyllostomidae). O helminto foi descrito baseado apenas em uma fêmea adulta, porém esta apresentou caraterísticas morfológicas compatíveis com descrições prévias da espécie. O presente trabalho amplia a ocorrência geográfica do parasito para o Estado de Minas Gerais e constitui o segundo relato da espécie do helminto no Brasil.

Vocal production learning in the pale spear-nosed bat, Phyllostomus discolor

Vocal production learning (VPL), or the ability to modify vocalizations through the imitation of sounds, is a rare trait in the animal kingdom. While humans are exceptional vocal learners, few other mammalian species share this trait. Owing to their singular ecology and lifestyle, bats are highly specialized for the precise emission and reception of acoustic signals. This specialization makes them ideal candidates for the study of vocal learning, and several bat species have previously shown evidence supportive of vocal learning. Here we use a sophisticated automated set-up and a contingency training paradigm to explore the vocal learning capacity of pale spear-nosed bats. We show that these bats are capable of directional change of the fundamental frequency of their calls according to an auditory target. With this study, we further highlight the importance of bats for the study of vocal learning and provide evidence for the VPL capacity of the pale spear-nosed bat.

Biosonar spatial resolution along the distance axis: revisiting the clutter interference zone

Unlike all other remote senses like vision or hearing, echolocation allows estimating the distance of an object. Not only have echolocating bats and toothed whales been shown to measure distance by echolocation extremely precisely, distance information is even topographically represented by a neuro-computational map in bats’ auditory cortex. This topographic representation and the corresponding tuning of cortical cells to object distance suggests the bats may be able to perceptually resolve multiple, simultaneously present objects along the distance axis. Here we use a novel psychophysical paradigm with complex phantom targets to quantity spatial resolution along the distance axis in the echolocating bat Phyllostomus discolor. We show that our bats can indeed perceptually resolve objects along the distance axis when they are separated by about 40 cm (around a reference distance of 108 cm) along the distance axis. These results are well comparable to earlier work on bats’ clutter interference zone (Simmons et al., 1988) and confirm those results with a more robust psychophysical paradigm.Summary statementEcholocating bats perceive absolute distance to objects by measuring the time delay between call and echo. In addition, they possess spatial resolution along the distance axis.

Processing of fast amplitude modulations in bat auditory cortex matches communication call-specific sound features

Bats use a large repertoire of calls for social communication. In the bat Phyllostomus discolor, social communication calls are often characterized by sinusoidal amplitude and frequency modulations with modulation frequencies in the range of 100–130 Hz. However, peaks in mammalian auditory cortical modulation transfer functions are typically limited to modulation frequencies below 100 Hz. We investigated the coding of sinusoidally amplitude modulated sounds in auditory cortical neurons in P. discolor by constructing rate and temporal modulation transfer functions. Neuronal responses to playbacks of various communication calls were additionally recorded and compared with the neurons’ responses to sinusoidally amplitude-modulated sounds. Cortical neurons in the posterior dorsal field of the auditory cortex were tuned to unusually high modulation frequencies: rate modulation transfer functions often peaked around 130 Hz (median: 87 Hz), and the median of the highest modulation frequency that evoked significant phase-locking was also 130 Hz. Both values are much higher than reported from the auditory cortex of other mammals, with more than 51% of the units preferring modulation frequencies exceeding 100 Hz. Conspicuously, the fast modulations preferred by the neurons match the fast amplitude and frequency modulations of prosocial, and mostly of aggressive, communication calls in P. discolor. We suggest that the preference for fast amplitude modulations in the P. discolor dorsal auditory cortex serves to reliably encode the fast modulations seen in their communication calls. NEW & NOTEWORTHY Neural processing of temporal sound features is crucial for the analysis of communication calls. In bats, these calls are often characterized by fast temporal envelope modulations. Because auditory cortex neurons typically encode only low modulation frequencies, it is unclear how species-specific vocalizations are cortically processed. We show that auditory cortex neurons in the bat Phyllostomus discolor encode fast temporal envelope modulations. This property improves response specificity to communication calls and thus might support species-specific communication.