Optimal temperatures for inner-ear performance in gekkonoid lizards.

Area of Science:

• Auditory Neuroscience
• Comparative Physiology
• Herpetology

Background:

• Cochlear potentials reflect auditory system function.
• Temperature significantly influences physiological processes in ectotherms like lizards.

Purpose of the Study:

• To investigate the impact of varying temperatures on the auditory sensitivity of geckos.
• To determine the optimal temperature ranges for gecko hearing.
• To localize the origin of temperature-dependent auditory changes within the inner ear.

Main Methods:

• Recorded cochlear alternating potentials in response to pure tones (50-15,000 Hz) across a temperature range of 15-40°C in 50 anesthetized lizards from four families.
• Generated 249 auditory sensitivity functions (dB vs. frequency).
• Performed experiments with middle ear extirpation to isolate inner ear responses.

Main Results:

• Auditory sensitivity functions varied with temperature, with lower temperatures reducing sensitivity and shifting optimal frequencies lower.
• Each species exhibited an optimal temperature range for maximal auditory sensitivity and function smoothness.
• Optimal cochlear temperature ranges correlated with known ecological temperature preferenda, being broader in gekkonoids than iguanids.
• Temperature effects persisted after middle ear removal, indicating an inner ear origin.
• The magnitude of temperature effects on cochlear potentials was approximately half that observed in auditory nerve potentials.

Conclusions:

• Temperature is a critical factor influencing gecko auditory sensitivity, originating within the inner ear.
• Accurate auditory data requires consideration of species-specific optimal temperatures and potential seasonal variations.
• Precise species identification and controlled thermal parameters are essential for reliable auditory research in lizards.