Project Title

Variation in the Stylohyal-Tympanic Bone Articulation in Laryngeally Echolocating Bats and Its Implications Regarding Function

Authors' Affiliations

Chelsie C.G. Snipes, Department of Biological Sciences, College of Art and Sciences, East Tennessee State University, Johnson City, TN Richard T. Carter, Department of Biological Sciences, College of Art and Sciences, East Tennessee State University, Johnson City, TN

Location

Culp Room 303

Start Date

4-6-2022 2:00 PM

End Date

4-6-2022 3:00 PM

Faculty Sponsor’s Department

Biological Sciences

Name of Project's Faculty Sponsor

Richard Carter

Additional Sponsors

Richard T. Carter, Peter Newman, Scott Pedersen

Classification of First Author

Graduate Student-Master’s

Competition Type

Competitive

Type

Oral Presentation

Project's Category

Anatomy, Biological Adaptation, Evolutionary Biology, Morphology, Acoustics

Abstract or Artist's Statement

To avoid masking incoming echoes with outgoing calls, bats use a low duty cycle (LDC) or high duty cycle (HDC) echolocation strategy. LDC echolocation is the most common and involves short pulses of broadband sound followed by relatively long periods of silence. In contrast, HDC echolocators emit long, narrowband sounds with short periods of silence and use Doppler shifts to detect the relative speed of prey. HDC echolocators are almost exclusively found in the families Rhinolophidae and Hipposidaridae. However, there are two known exceptions that have evolved echolocation strategies independent of the families of which they reside: Pternotus parnelli is from an LDC family but uses HDC echolocation, and conversely, Coelops frithii is from an HDC family but uses LDC echolocation. In our previous work, we used engineering software to model sound transmission from the larynx to the auditory bulla via the stylohyal-tympanic bone articulation and found that sound transmitted through the bony chain during echolocation call emission is likely loud enough for bats to hear. We also noticed differences in the morphology of the stylohyal and its placement on the tympanic bulla that might correlate with echolocation strategy. Pteronotus parnelli and C. frithii, having evolved echolocation strategies that differ from the other species in their respective families, provide the opportunity to test whether these morphologies are simply “evolutionary baggage” or driven by a selective pressure associated with function. To test this, we used µCT image data to compare the morphology of the stylohyal bones from P. parnelli, C. frithii, and other LDC and HDC echolocators. Preliminary results show that HDC echolocators have a stylohyal that sits on the medial side of the bulla, while the stylohyal in LDC echolocators sits on the lateral side of the bulla. The stylohyal in P. parnelli and C. frithi appear to have characteristics of both HDC and LDC echolocators. Further analysis will include a Multivariant Functional Shape Analysis (MFSA) to determine if these morphological differences are statistically significant and identify what variant(s) are likely driving these differences. Lastly, digital 3D models from each bat species have been built from µCT data to test for functional differences via acoustic engineering simulations. Since bone conducted sound can reach the cochlea through direct stimulation or stimulation of the eardrum, we predict that an LDC echolocator, with its stylohyal sitting on the lateral side of the bulla, will transmit sound to the cochlea more effectively through the eardrum. And given the stylohyal in HDC echolocators sits on the medial side of the bulla, we expect to see better direct stimulation of the cochlea than that of a LDC echolocator. This research uses an integrative approach to address a long-held assumption concerning the function of the stylohyal-tympanic bone articulation in laryngeally echolocating bats.

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Apr 6th, 2:00 PM Apr 6th, 3:00 PM

Variation in the Stylohyal-Tympanic Bone Articulation in Laryngeally Echolocating Bats and Its Implications Regarding Function

Culp Room 303

To avoid masking incoming echoes with outgoing calls, bats use a low duty cycle (LDC) or high duty cycle (HDC) echolocation strategy. LDC echolocation is the most common and involves short pulses of broadband sound followed by relatively long periods of silence. In contrast, HDC echolocators emit long, narrowband sounds with short periods of silence and use Doppler shifts to detect the relative speed of prey. HDC echolocators are almost exclusively found in the families Rhinolophidae and Hipposidaridae. However, there are two known exceptions that have evolved echolocation strategies independent of the families of which they reside: Pternotus parnelli is from an LDC family but uses HDC echolocation, and conversely, Coelops frithii is from an HDC family but uses LDC echolocation. In our previous work, we used engineering software to model sound transmission from the larynx to the auditory bulla via the stylohyal-tympanic bone articulation and found that sound transmitted through the bony chain during echolocation call emission is likely loud enough for bats to hear. We also noticed differences in the morphology of the stylohyal and its placement on the tympanic bulla that might correlate with echolocation strategy. Pteronotus parnelli and C. frithii, having evolved echolocation strategies that differ from the other species in their respective families, provide the opportunity to test whether these morphologies are simply “evolutionary baggage” or driven by a selective pressure associated with function. To test this, we used µCT image data to compare the morphology of the stylohyal bones from P. parnelli, C. frithii, and other LDC and HDC echolocators. Preliminary results show that HDC echolocators have a stylohyal that sits on the medial side of the bulla, while the stylohyal in LDC echolocators sits on the lateral side of the bulla. The stylohyal in P. parnelli and C. frithi appear to have characteristics of both HDC and LDC echolocators. Further analysis will include a Multivariant Functional Shape Analysis (MFSA) to determine if these morphological differences are statistically significant and identify what variant(s) are likely driving these differences. Lastly, digital 3D models from each bat species have been built from µCT data to test for functional differences via acoustic engineering simulations. Since bone conducted sound can reach the cochlea through direct stimulation or stimulation of the eardrum, we predict that an LDC echolocator, with its stylohyal sitting on the lateral side of the bulla, will transmit sound to the cochlea more effectively through the eardrum. And given the stylohyal in HDC echolocators sits on the medial side of the bulla, we expect to see better direct stimulation of the cochlea than that of a LDC echolocator. This research uses an integrative approach to address a long-held assumption concerning the function of the stylohyal-tympanic bone articulation in laryngeally echolocating bats.