How Body Size Affects Middle-Ear Structure and Function and Auditory Sensitivity in Gekkonoid Lizards

Abstract

Gekkonoid lizards increase in body size throughout life, and the present study investigates whether changes in auditory function accompany these increases. Middle-ear structures in four groups of animals, adults and juveniles of two gekkonoid species (Eublepharis macularius and Oedura marmorata), were examined. Tympanic membrane velocity and phase were also measured in all four groups. An indication of peripheral auditory function was obtained for each group by measuring compound action potentials (CAPs) from the round window membrane. The middle-ear contribution to CAP thresholds was obtained by comparing threshold levels of the CAP response with and without an intact middle-ear system. The results from these studies indicated that significant changes occurred in middle-ear structure, tympanic membrane velocity and CAP threshold between the younger and older animals. In addition, the adults of both species exhibited better auditory function when the acoustic stimulus was delivered to the tympanic membrane than when it was delivered to the columella footplate. The findings show clearly that increased body size (or age) is accompanied by functional changes in the auditory periphery.

Geographic variation in the matching between call characteristics and tympanic sensitivity in the Weeping lizard

“…These values are within the lower limit of those reported for other lizard species at different stimulus levels (e.g., between 0.2 and 6.9 mm/s; dB SPL: 100, Saunders et al, 2000; Werner et al, 2002; dB SPL: 94, Christensen‐Dalsgaard & Manley, 2005; dB SPL: 70, Han & Young, 2018). We cannot rule out, however, that higher velocities could have been recorded for these populations if the laser beam had been aimed at locations other than the insertion point of the extracolumella, considering that the eardrum stiffness varies across its surface (Han & Young, 2018; Werner et al, 1998) and that the eardrum exhibits frequency‐dependent vibration modes (Bergevin et al, 2015).…”

Investigation of Age and Gender Effects on the Middle Ear With Wideband Tympanometry in Adults

“…It has been suggested that a possible increase in middle ear volume may increase the permeability of lower frequencies by reducing the stiffness of the air in this cavity (Relkin 1988). In addition, increased body size has been associated with increases in the size of middle ear structures such as the eardrum, ossicles, and base of the stapes in animal models (Werner et al 1998; Werner & Igić 2002). An increase in mass can disrupt the transmission of high frequencies through the middle ear (Werner & Igić 2002).…”