OPTIMAL TEMPERATURES FOR INNER-EAR PERFORMANCE IN GEKKONOID LIZARDS

Temperature effects on the cochlear alternating potentials were described in lizards of the Eublepharidae (4 spp. and sspp.), Diplodactylinae (2 spp.), Gekkoninae (7 spp. and sspp.) and Sphaerodactylidae (1 sp.). Pure tones (50-15,000 Hz) were applied to the anesthetized gecko''s external ear. Sound intensity needed for a standard response was plotted (dB vs. frequency). A total of 249 such sensitivity functions were obtained from 50 animals, at temperatures of 15-40.degree. C. For each species, an optimal sensitivity function was definable by its extreme sensitivity and relative smoothness. This was obtained throughout a specific optimal temperature range. At lower temperatures the function was less sensitive and its best sensitivity was at a lower frequency. The specific optimal cochlear temperature range resembled the specific ecological temperature perferendum were known. Both were broader in gekkonoid than in iguanid lizards. The temperature effects on the sensitivity function occurred even with aerial or mechanical stimulation at the oval window after middle ear extirpation. Hence they arise in the inner ear. Their magnitude (dB/.degree. C) was 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.