Meeting Abstract

P3.77  Wednesday, Jan. 6  Acoustic resonance of the middle-ear in Alligator—implications for behavioral correlations. DUFEAU, DL*; WITMER, LM; Ohio University; Ohio University dd299405@ohio.edu

The middle-ear space of crocodylians, and the pneumatic diverticula arising from it, are greatly expanded. This expanded sinus system invades the braincase to the extent that broad contralateral communications are created, resulting in a middle-ear volume that completely encircles the brain. This augmented middle-ear volume increases the compliance of the sound transduction mechanism, thereby optimizing the impedance matching performance to lower frequencies. Additionally, this increased paratympanic sinus volume also can act as a Helmholtz resonator, responding to particular frequencies as a function, in part, of its volume. Using CT scanning methods, we examined a growth series of American alligator ranging from perinatal to individuals approaching the growth asymptote. From these data we were able to characterize the acoustic properties of the middle ear. We gave particular attention to its resonance with the goal of discovering correlations between calculated resonant frequencies and particular performance parameters or behavioral auditory cues. A number of bony ostia were tested as candidate resonator openings—one particular bony opening, the subtympanic foramen, yielded resonant frequencies in the range of 950 to 1200 Hz between the specimens sampled. This range of frequencies represents a good fit to frequencies corresponding to both measured greatest cochlear sensitivities and greatest call intensities of hatchling alligators. It is not clear whether the morphological conformation required for this range of resonant frequencies is an adaptation in response to juvenile calling or is merely exapted such that juveniles call at frequencies that exploit this acoustic aspect of crocodylian anatomy. This correlation does, however, underscore the role of audition to parental care in crocodylians.