QUICK SEARCH:   [advanced] Author: Keyword(s):
Home     Help     Feedback     Subscriptions     Archive     Search     Table of Contents

First published online July 26, 2004
Journal of Experimental Biology 207, 3067-3072 (2004)
Published by The Company of Biologists 2004
doi: 10.1242/jeb.01153

This Article Figures Only Full Text Full Text (PDF) Alert me when this article is cited Alert me if a correction is posted Services Email this article to a friend Similar articles in this journal Similar articles in PubMed Alert me to new issues of the journal Download to citation manager Citing Articles Citing Articles via Google Scholar Google Scholar Articles by Ott, M. Articles by Sherbrooke, W. C. Search for Related Content PubMed PubMed Citation Articles by Ott, M. Articles by Sherbrooke, W. C.

Prey snapping and visual distance estimation in Texas horned lizards, Phrynosoma cornutum

Matthias Ott¹, Joachim Ostheim^2,* and Wade C. Sherbrooke³

¹ Institute for Anatomy, University of Tübingen, Österbergstrasse 3, 72074 Tübingen, Germany
² Allgemeine Psychologie, University of Konstanz, Postfach 5560 C36, 78457 Konstanz, Germany
³ Southwestern Research Station, American Museum of Natural History, Portal, AZ 85632, USA

^* Author for correspondence (e-mail: ott{at}anatu.uni-tuebingen.de)

Accepted 18 June 2004

Captive Texas horned lizards were high-speed videotaped while feeding on ants in order to study the role of vision in facilitating tongue-protrusion capture of prey. Analysis of tongue movements revealed that prey snapping in these lizards is not a typical fixed-action pattern. By contrast, it is variable in performance and duration. Lizards adjusted head and tongue direction during the strike, within a few milliseconds, in response to movements of the prey. The duration of a typical tongue strike was 100-150 ms. The strike duration was prolonged after ophthalmic lenses were placed in front of one or both eyes. These lenses were used to investigate whether horned lizards use accommodation to judge prey distance. Focal changes of negatively powered ophthalmic lenses (employed monocularly) induced a clear underestimation of prey distance by the lizards, confirming the hypothesized expectation that accommodation is used for depth perception. The effect of the lenses was different in the two animals tested with monocular restriction. This, together with the lack of difference in responses by the lizards when untreated and when both eyes were lens covered (binocular treatment of equal power, -9 D), illustrates that horned lizards also use other visual parameters for depth perception.

Key words: visual depth perception, accommodation, horned lizard, tongue protrusion, fixed-action pattern