Do Male White-Lipped Frogs Use Seismic Signals for Intraspecific Communication?

Modern frogs and toads possess a structurally unique saccule,endowing them with seismic sensitivity greater than that observedso far in any other group of terrestrial vertebrates. In synchronywith their advertisement calls, approximately half of the callingmales of one frog species, the Puerto-Rican white-lipped frog(Leptodactylus albilabris), produce impulsive seismic signals(thumps). The spectral distribution of power in these seismicsignals matches precisely the spectral sensitivity of the frog'ssaccule. The signals have sufficient amplitude to be sensedeasily by the frog's saccule up to several meters from the source—wellbeyond the typical spacing when these frogs are calling in agroup. This circumstantial evidence suggests that white-lippedfrogs may use the seismic channel in intraspecific communication,possibly as an alternative to the airborne channel, which oftenis cluttered with noise and interference. Using the frog's vocalizationsas our assay, we set out to test that proposition. In responseto playback calls, the male white-lipped frog adjusts severalof its own calling parameters. The most conspicuous of theseinvolves call timing—specifically the tendency for a gapin the distribution of call onsets, precisely timed with respectto the onsets of the playback calls. When the airborne componentis unavailable (e.g., masked by noise), approximately one infive animals produces the calling gap in response to the seismicsignals alone.