Characterization of the advertisement call oscillator in the frogEleutherodactylus coqui

Summary

• 1. Eleutherodactylus coqui treefrogs spontaneously produce advertisement calls. Intercall intervals are typically between 2 and 3 s.

• 2. When periodic tone burst stimuli were broadcast to individual frogs in the wild, their calling became entrained such that each vocalization occurred in the silent interval between stimulus tones.

• 3. For stimulus repetition periods similar to the nominal call repetition period (2.5 s), the mode of the distribution of intercall intervals (preferred interval) matched the interstimulus interval (1∶1 locking or entrainment). The preferred interval continued to match the interstimulus interval when the latter was varied over a range of approximately 1 s, or 40% of the nominal spontaneous intercall interval. Faster stimulus rates (shorter interstimulus intervals) resulted in 1∶2 locking, in which calls were produced for every second tone burst.

• 4. For each frog, the transition between 1∶1 and 1∶2 locking appeared to positively co-vary with the spontaneous preferred interval.

• 5. The frogs were able to track a pseudorandom sequence of long and short duration tones. Long duration tones tended to be spanned by long intercall intervals while short duration tones were spanned with shorter intervals. Cueing to tone offset is the most parsimonious explanation for such tracking ability.

• 6. These findings suggest that calling behavior inE. coqui is driven by an internal oscillator, the period of which may be adjusted over a considerable range in order to entrain to an external acoustic stimulus. Furthermore, the period of the oscillator may be changed within a single call cycle in response to a pseudorandom sequence of stimuli.