Seismic detection and communication in amphibians

To date, seismic communication has been demonstrated in a single amphibian, the frog Leptodactylus albilabris. Calling males produce both acoustic and seismic signals simultaneously. The inflating vocal sac not only aids in radiating the call into the air, but also strikes the wet substrate generating vertically polarized Rayleigh waves. These animals are highly sensitive to seismic signals (-122 dB rms re gravity) and they alter the timing of their calls in response to playbacks of the seismic component of conspecific calls. Several other frog behaviors have a potential seismic role, including thumping on the ground with the forelimbs and toe-twitching. Acute seismic sensitivities (-90 to -130 dB rms re gravity) have been reported in other amphibians including the frogs: Lithobates catesbeianus, Lithobates pipiens, and Rana temporaria, and the salamanders: Notophthalmus viridescens, Plethodon cinereus (adults), and Ambystoma macularum (larvae). While such sensitivity measurements bypassed the natural coupling of the inner ears to the substrate, amphibians posses an elaborate coupling solution, in which the opercularis muscle connects the Correspondence/Reprint request: Dr. Marcos Gridi-Papp, Department of Physiological Science, University of California, 621 Charles E. Young Dr. S., Los Angeles, CA 90095, USA. E-mail: [email protected] Marcos Gridi-Papp & Peter M. Narins 2 scapula to the oval window. Seismic vibrations that reach the shoulders through the forelimbs are, this way, transmitted directly into the inner ear. The embryos of amphibians are also responsive to seismic vibrations. Agalychnis callidryas and five other species of phyllomedusine treefrogs with arboreal egg clutches were shown to hatch immediately in response to seismic vibrations produced by predators. We compare the available data on seismic sensitivity in amphibians with data for other tetrapods, discuss the potential relevance of the substrate from which the animals call for seismic communication and identify questions for future research.