TY - JOUR
T1 - Effects of age and size in the ears of gekkotan lizards
T2 - Auditory sensitivity, its determinants, and new insights into tetrapod middle-ear function
AU - Werner, Yehudah L.
AU - Montgomery, Lynda G.
AU - Seifan, Merav
AU - Saunders, James C.
N1 - Funding Information:
We thank Ken Aplin and the staff of the Western Australian Museum (WAM), and Aaron Bauer, for advice on collecting geckos in Australia (1993); the Department of Conservation and Land Management (CALM) of Western Australia for permit (SF001105) to collect; Nurit Werner for help in collecting; Patrick Berry (WAM) for mediating the export permit (PWS-P935483) from the Australian Nature Conservation Agency, Canberra; Jens V. Vindum and the staff of the California Academy of Sciences, San Francisco, for hosting the animals en route to Philadelphia; Ron Tremper, Center for Reptile and Amphibian Propagation, Boerne, Texas, USA, for the generous supply of eublepharid geckos; Ygern Martin, Alan Roberts, Rachel Kurian, Amy Lieberman for assorted assistance; and especially Mark Coleman, Bill Peake, and John Rosowski for enlightening help with literature and discussions, Zhongmin (John) Lu for helpful meticulous criticism of an earlier version of the MS, and two anonymous reviewers for significantly improving the final MS. YLW gratefully acknowledges the hospitality of Ken Aplin and the WAM, and MS—that of Katja Tielbörger and the Plant Ecology Department, Tübingen University. This work was supported in part by a research award (DC-000510) from the National Institute for Deafness and Other Communications Disorders (NIDCD) and the Pennsylvania Lions Hearing Research Foundation to JCS.
PY - 2008/8/1
Y1 - 2008/8/1
N2 - Do related, differently sized species differ in size-related structural or functional traits merely because they mature at different points of a uniform allometric ontogenetic growth curve, or do they evolutionarily diverge? We tested ears of gekkotan lizards through experiments distinguishing the two. Auditory sensitivity was assessed by compound action potential (CAP) thresholds in eight species. The best thresholds characterizing species ranged 22-72 dB sound pressure level at 0.5-1.0 kHz. Direct acoustic stimulation of the columella footplate elevated thresholds by 25-50 dB. Intraspecific CAP sensitivity was primarily affected by body length in Eublepharis macularius, but by tympanic-membrane velocity in Oedura marmorata. The chief factor determining middle-ear function (difference in CAP sensitivity before and after middle-ear ablation) was body length in both species. A secondary factor was the middle-ear hydraulic lever ratio in E. macularius, but the mechanical lever in O. marmorata. When intra- and interspecific data were compared, the relation of CAP thresholds to body size in E. macularius resembled the interspecific regression. The intraspecific regression of auditory sensitivity over tympanic membrane velocity in O. marmorata differed from that calculated interspecifically. Hence, the evolutionary contribution to size effects on CAP sensitivity exceeds the ontogenetic contribution. Putatively, body length affects CAP sensitivity through absolute sizes of tympanic membrane and columella footplate. These newly discovered effects join those of the hydraulic lever and (interspecifically) hair-cell number to improve the hearing of larger species that vocally communicate across wider spaces, apparently throughout the Tetrapoda.
AB - Do related, differently sized species differ in size-related structural or functional traits merely because they mature at different points of a uniform allometric ontogenetic growth curve, or do they evolutionarily diverge? We tested ears of gekkotan lizards through experiments distinguishing the two. Auditory sensitivity was assessed by compound action potential (CAP) thresholds in eight species. The best thresholds characterizing species ranged 22-72 dB sound pressure level at 0.5-1.0 kHz. Direct acoustic stimulation of the columella footplate elevated thresholds by 25-50 dB. Intraspecific CAP sensitivity was primarily affected by body length in Eublepharis macularius, but by tympanic-membrane velocity in Oedura marmorata. The chief factor determining middle-ear function (difference in CAP sensitivity before and after middle-ear ablation) was body length in both species. A secondary factor was the middle-ear hydraulic lever ratio in E. macularius, but the mechanical lever in O. marmorata. When intra- and interspecific data were compared, the relation of CAP thresholds to body size in E. macularius resembled the interspecific regression. The intraspecific regression of auditory sensitivity over tympanic membrane velocity in O. marmorata differed from that calculated interspecifically. Hence, the evolutionary contribution to size effects on CAP sensitivity exceeds the ontogenetic contribution. Putatively, body length affects CAP sensitivity through absolute sizes of tympanic membrane and columella footplate. These newly discovered effects join those of the hydraulic lever and (interspecifically) hair-cell number to improve the hearing of larger species that vocally communicate across wider spaces, apparently throughout the Tetrapoda.
KW - Columella footplate
KW - Compound action potential
KW - Gecko
KW - Ontogeny
KW - Phylogeny
KW - Tympanic membrane
UR - http://www.scopus.com/inward/record.url?scp=45649084927&partnerID=8YFLogxK
U2 - 10.1007/s00424-008-0462-0
DO - 10.1007/s00424-008-0462-0
M3 - Article
AN - SCOPUS:45649084927
SN - 0031-6768
VL - 456
SP - 951
EP - 967
JO - Pflugers Archiv European Journal of Physiology
JF - Pflugers Archiv European Journal of Physiology
IS - 5
ER -