Biology subjects

Christensen-Dalsgaard, J.

Publications and source records attributed to Christensen-Dalsgaard, J..

5 recordsLinked to original sources

bioRxiv2025

Zebra finches produce intralaryngeal laminar flow whistles during panting

Birds and mammals converged upon the same physical mechanism of vocal fold vibration to produce their broad range of voiced sounds critical to communication1. The frequency range of vocal fold vibration is limited per species by biophysical constraints to 3-4 octaves2. However, recent work reported vocalizations in zebra finches with apparent fundamental frequencies of 7-11 kHz3 that far exceed the range of regular calls and song (0.5-1.5 kHz)4,5. These "heat" or "incubation" calls are suggested to have close-range communicative relevance in the global temperature rise context3,6, but their acoustics are poorly described and by what biophysical mechanism they are produced remains unknown. We recorded heat calls in adult zebra finches in vivo and show they are extremely soft, frequency-modulated calls with source levels of 13.9 {+/-} 3.3 dB SPL at one meter with dominant frequencies of 6.8 {+/-} 0.6 kHz. Through a series of in vitro experiments, we establish that these calls are aerodynamic whistles produced inside the avian larynx, not syrinx, during inspiration. Respiratory air flow during whistle production is an order of magnitude higher than song and consistent with thermal panting for evaporative cooling6,7. Laryngeal geometry and dimensional flow analysis suggest that these whistles are laminar flow whistles that occur when a flow boundary layer is in a transition phase from laminar to turbulent flows8,9. Birds, like some rodents10-12, are thus able to produce both voiced sounds and aerodynamical whistles in their vocal tract.

physiology↗

bioRxiv2024

Postnatal hearing development limits early parent-to-offspring vocal communication and gates sensorimotor learning in the zebra finch

Acoustic communication relies critically on the receivers ability to hear. In precocial birds, hearing can already be functional during embryonic stages in the egg, whereas in altricial species the limited available data indicate a gradual postnatal development with poor sensitivity in early hatchlings, implying even lower sensitivity in embryos. Recent research suggests that zebra fnnch embryos, despite being altricial, have functional hearing already in the egg to engage in parent-embryo acoustic communication and anthropogenic noise detection. However, their auditory sensitivity during early development remains unknown. Here, we measure auditory brainstem responses (ABR) over early postnatal development and show that zebra fnnch hatchlings have >54 dB lower threshold than adults to loud, broadband clicks. ABR responses emerge between 4-8 days after hatching. Auditory sensitivity develops progressively and reaches adult levels by day 20. Additionally, egg vibrations induced by sound remain far below detection thresholds of vibrotactile senses. Together these data contradict the notion of acoustic perception in embryos and early parent-to-embryo communication in zebra fnnches. The striking timing coincidence between maturation of the peripheral auditory system and the onset of song learning suggests that hearing functionality may gate the onset of vocal learning in zebra fnnches.

physiology↗

bioRxiv2022

A general mechanism of air-borne hearing in Recent and early non-tympanate tetrapods

Tetrapod tympanic hearing probably emerged in the Triassic with independent origins in each of the major groups, more than 120 Myr after the water-land transition. During this long period, any auditory sensitivity must have been based on non-tympanic, bone conduction mechanisms. However, bone conduction is a non-specific term describing several different modes of vibration that can stimulate the inner ear. To understand hearing in a non-tympanic ear, we focus on the simplest model: that sound translates the head, i.e., that the head is pushed and pulled by the sound wave, and that this vibration is transduced by the inner ear. Simple translation is the mode of human low-frequency bone conduction sensitivity and translation by underwater sound is also the mode of auditory stimulation for most fishes. It is therefore a straightforward assumption that this may have been the mechanism of hearing in the early tetrapods. According to acoustic theory, the efficiency of translation of an object by sound is determined by its density and ka, the product of the acoustic wavenumber (k) and the radius (a) of the head. Simple finite-element models of translation by sound show that vibration velocities only depend on ka and density (for objects of the same shape and composition) and are almost constant (between 4 and 5 {micro}m/s/Pa depending on shape) for objects with ka<1. We compare sensitivity to sound and to vibrations of the skull in animals lacking tympanic middle ears (snakes, salamanders, earless frogs, and lungfish) and show that the low-frequency air-borne sound sensitivity in these species is largely consistent with a translation mechanism. How translation of the head or body can stimulate the inner ear is most evident in an inertial system like the otolithic/otoconial ears of fish and early tetrapods, but fluid inertia in the inner ear may also generate hydrodynamic waves that can stimulate hair cells in the tetrapod inner ear, providing a mechanism for this simple mode of sound reception to confer hearing in earless animals.

animal behavior and cognition↗

bioRxiv2020

Lung-to-ear sound transmission does not improve directional hearing in green treefrogs (Hyla cinerea)

Amphibians are unique among extant vertebrates in having middle ear cavities that are internally coupled to each other and to the lungs. In frogs, the lung-to-ear sound transmission pathway can influence the tympanums inherent directionality, but what role such effects might play in directional hearing remain unclear. In this study of the American green treefrog (Hyla cinerea), we tested the hypothesis that the lung-to-ear sound transmission pathway functions to improve directional hearing, particularly in the context of interspecific sexual communication. Using laser vibrometry, we measured the tympanums vibration amplitude in females in response to a frequency modulated sweep presented from 12 sound incidence angles in azimuth. Tympanum directionality was determined across three states of lung inflation (inflated, deflated, reinflated) both for a single tympanum in the form of the vibration amplitude difference (VAD) and for binaural comparisons in the form of the interaural vibration amplitude difference (IVAD). The state of lung inflation had negligible effects (typically less than 0.5 dB) on both VADs and IVADs at frequencies emphasized in the advertisement calls produced by conspecific males (834 Hz and 2730 Hz). Directionality at the peak resonance frequency of the lungs (1558 Hz) was improved by {cong} 3 dB for a single tympanum when the lungs were inflated versus deflated, but IVADs were not impacted by the state of lung inflation. Based on these results, we reject the hypothesis that the lung-to-ear sound transmission pathway functions to improve directional hearing in frogs. SUMMARY STATEMENTContrary to prevailing views on the mechanisms of hearing in frogs, the lung-to-ear pathway for sound transmission does not improve directional hearing in these vociferous vertebrates.

zoology↗

bioRxiv2020

Lungs contribute to solving the frog's cocktail party problem by enhancing the spectral contrast of conspecific vocal signals

Noise impairs signal perception and is a major source of selection on animal communication. Identifying adaptations that enable receivers to cope with noise is critical to discovering how animal sensory and communication systems evolve. We integrated biophysical and bioacoustic measurements with physiological modeling to demonstrate that the lungs of frogs serve a heretofore unknown noise-control function in vocal communication. Lung resonance enhances the signal-to-noise ratio for communication by selectively reducing the tympanums sensitivity at critical frequencies where the tuning of two inner ear organs overlaps. Social network analysis of citizen-science data on frog calling behavior indicates the calls of other frog species in multi-species choruses are a prominent source of environmental noise attenuated by the lungs. These data reveal that an ancient adaptation for detecting sound via the lungs has been evolutionarily co-opted to create spectral contrast enhancement that contributes to solving a multi-species cocktail party problem.

zoology↗