Cross-modal integration in a dart-poison frog.

The mechanisms by which the brain binds together inputs from separate sensory modalities to effect a unified percept of events are poorly understood. This phenomenon was studied in males of the dart-poison frog Epipedobates femoralis. These animals physically and vigorously defend their territories against conspecific calling intruders. In prior field studies with an electromechanical model frog, we were able to experimentally evoke this aggressive behavior only when an auditory cue (advertisement call) was presented simultaneously with a visual cue (vocal-sac pulsations). In the present field experiments, we used a modified version of the electromechanical model frog to present territorial males with visual and auditory cues separated by experimentally introduced temporal delays or spatial disparities to probe temporal and spatial integration in this animal. In temporal integration experiments, bimodal stimuli with temporal overlap during calling bouts consistently evoked aggressive behavior; stimuli lacking bimodal temporal overlap were relatively ineffective at the same task. In spatial integration studies, despite presenting the components of the bimodal stimulus with an initial spatial disparity of up to 12 cm, fighting behavior persisted. These results demonstrate that temporal and spatial integration may be reliably estimated in a freely behaving animal in its natural habitat and that we can use aggressive behavior in this species as an index of cross-modal integration in the field.