© 2001 by The Society for Integrative and Comparative Biology
Do Male White-Lipped Frogs Use Seismic Signals for Intraspecific Communication?1
1 Department of EECS, University of California, Berkeley, California 94720-1771
2 Department of Physiological Science, UCLA, Los Angeles, California 90095-1606
3 Graduate group in Bioengineering, University of California, Berkeley, CA 94720-1708
4 Graduate group in Neuroscience, University of California, Berkeley, CA 94720-3200
Modern frogs and toads possess a structurally unique saccule, endowing them with seismic sensitivity greater than that observed so far in any other group of terrestrial vertebrates. In synchrony with their advertisement calls, approximately half of the calling males of one frog species, the Puerto-Rican white-lipped frog (Leptodactylus albilabris), produce impulsive seismic signals (thumps). The spectral distribution of power in these seismic signals matches precisely the spectral sensitivity of the frog's saccule. The signals have sufficient amplitude to be sensed easily by the frog's saccule up to several meters from the source—well beyond the typical spacing when these frogs are calling in a group. This circumstantial evidence suggests that white-lipped frogs may use the seismic channel in intraspecific communication, possibly as an alternative to the airborne channel, which often is cluttered with noise and interference. Using the frog's vocalizations as our assay, we set out to test that proposition. In response to playback calls, the male white-lipped frog adjusts several of its own calling parameters. The most conspicuous of these involves call timing—specifically the tendency for a gap in the distribution of call onsets, precisely timed with respect to the onsets of the playback calls. When the airborne component is unavailable (e.g., masked by noise), approximately one in five animals produces the calling gap in response to the seismic signals alone.