Frogs are able to do Selective Hearing
TO a female frog, the mating season must sound like a cacophony of rock, rap, and country tunes. Males of all species croak and bellow for attention. So how does she find Mr. Right Species? It turns out that she doesn't evaluate each call but rather blocks those that are biologically meaningless to her.
Researchers already knew that female túngara frogs ready to lay eggs searching for mates pay more attention to the calls of their own species. Placed in a confined space and given a choice between a speaker emitting the “whine-chuck” of a túngara male or the call of another species, the females invariably hopped toward the túngara speaker. But male túngara frogs showed no such discrimination; they amped up their own calls whether they heard another túngara male or a male from another species. Kim Hoke, a neuroscientist at the University of Texas, Austin, suspected that males and females process the calls differently. To find out what part of the brain is involved, Hoke and colleagues tested 60 wild-caught túngara frogs that were ready for mating. Each frog listened for 30 minutes to either a recording of a male túngara calling, to a different species, or to silence. They were immediately euthanised and their brains frozen were treated with a radioactive marker to reveal neural activity.
The simple auditory regions of the lower brainstem looked the same in the males and females thus both sexes heard the calls of all species. But deeper in the brains in an area important for making behavioral decisions, the females' brain tissue showed activity only after listening to the calls of a túngara male. The males' neurons, meanwhile, were activated regardless of the species that made the calls. The females were blocking out the calls of the nontúngara males. Females needed to choose a mate carefully, as they produce fewer eggs than males producing sperm.