Experience-based plasticity of acoustically evoked aggression in a territorial frog

Territorial male bullfrogs (Rana catesbeiana) display lower levels of aggression toward familiar territorial neighbors compared to unfamiliar individuals based on the perception of individual differences in vocalizations. Stimulus-specific habituation elicited by repeated exposures to a neighbor's vocalizations is believed to play a role in mediating the low levels of aggression between neighbors. The present study describes habituation in multiple components of the bullfrog territorial aggressive response and examines whether these separate response components habituate at similar or different rates. In response to repeated broadcasts of synthetic bullfrog advertisement calls in a field playback experiment, the numbers of aggressive calls and movements, the latency to the first aggressive call, and the distance approached toward the playback speaker exhibited significant response decrements that developed at nearly identical rates. All four responses exhibited recovery upon subsequent broadcasts of a novel stimulus simulating a different individual. In contrast, the number of advertisement calls did not exhibit significant decrements with repeated playbacks. The patterns of stimulus-specific response decrement were inconsistent with explanations such as sensory adaptation, effector fatigue, non-specific changes in motivation, and a simple form of auditory habituation. Possible mechanisms for the observed plasticity in aggression are discussed in the context of anuran communication.