It's a warm Panamanian evening and male Physalaemus frogs are out crooning to their females. But with many other species serenading in the night's air, how do túngara females pick out their mates from the rest of the hullabaloo? Lisa Mangiamele and Sabrina Burmeister from the University of North Carolina at Chapel Hill explain that, `Sensory systems respond selectively to information in the environment – extracting some stimulus features while discarding others.' According to Burmeister, females respond to the drop in frequency as the male's whine glissandos from 900 to 400 Hz. They also respond equally well to a synthesised two-tone call that drops from 800 Hz to 500 Hz tone; the underlying two-tone signature is all that a túngara female needs to correctly select a mate of her own species. Knowing that a transcription factor, egr-1, is produced in brain tissue in response to stimulation, the duo decided to identify the regions of the female brain that are involved in processing the males' serenades by looking for evidence that the egr-1 gene had been activated in the brain after listening to natural and simulated mating calls ().
The duo found that one tiny region of the female's brain, the laminar nucleus of the torus semicircularis (Ltor), responded to both the males' whining glissando and the signature two-tone simulation, suggesting that Ltor is the `neural analyser for call recognition'. Other regions of the auditory brainstem and thalamus also responded to the males' full-spectrum call, but they failed to activate egr-1 in response to the two-tone signature, leading the duo to conclude, `Ltor activation is sufficient to explain species recognition decisions for female túngara frogs.'
