Effects of surgery and other experimental factors on the evaluation of middle ear function in gekkonoid lizards

This study examines three artificial factors likely to cause variation betw een results from different investigations of auditory function, at least in lizards. Controlled tests were performed on gecko lizards, by external las er interferometry of the middle ear transfer function at the tympanic membr ane (TM). In conclusion, studies of middle ear function should examine moti on both at the insertion of the columella-extracolumella shaft onto the TM, and at the tip of the extracolumellar pars inferior, because the internal proportions and function of the extracolumellar lever vary among species. A t least in scansorial geckos, auditory experiments may be conducted with th e animal on its back, as this posture introduces no acoustic artifacts. Pos itioning the subject on its belly, with the throat resting on the substrate , imposes small but significant artifacts on middle ear function. Similar a rtifacts occur with the belly up but the throat loaded with a modeling clay plate. The surgical fenestration of the ventral throat wall, common in aud itory studies on lizards, causes (at least in Eublepharis) artificial enhan cement of sensitivity at low frequencies and erratic responses at high freq uencies. (C) 2001 Elsevier Science B.V. All rights reserved.