Optimal temperatures for inner-ear performance in gekkonoid lizards

Temperature effects on the cochlear alternating potentials are described in lizards of the Eublepharidae (4 spp. and subspp.), Diplodactylinae (2 spp.), Gekkoninae (7 spp. and subspp.) and Sphaerodactylidae (1 sp.). Pure tones (50-15,000 Hz) were applied to the anaesthetized gecko's external ear. Sound intensity needed for a standard response was plotted (db versus frequency). A total of 249 such sensitivity functions were obtained from 50 animals, at temperatures of 15-40 degrees C. For each species, an optimal sensitivity function is definable by its extreme sensitivity and relative smoothness. This is obtained throughout a specific optimal temperature range. At lower temperatures, the function is less sensitive and its best sensitivity is at a lower frequency. The specific optimal cochlear temperature range resembles the specific ecological temperature preferendum where known. Both are broader in gekkonoid than in iguanid lizards. The temperature effects on the sensitivity function occur even with aerial or mechanical stimulation at the oval window after middle ear extirpation. Hence they arise in the inner ear. Their magnitude (db/ degrees C) is half that known from auditory nerve potentials. When accurate auditory data are desired, the specific optimal temperature and its possible seasonal variation require consideration. This increases the need for proper identification of subjects by name and origin, and for monitoring experimental thermal parameters, including pre-experimental acclimation.