African Clawed Frog swimming underwater

The characteristic trill of male Xenopus laevis frogs is rooted in the firing patterns of particular brain cells. Credit: Heidi & Hans-Juergen Koch/Minden/Getty

Neuroscience

The brain waves that make frogs pitch perfect

A subset of neurons helped two species to evolve distinct courting trills.

Many frog species utter distinctive calls to lure mates. One group of neurons could help to explain the difference between two species.

Erik Zornik at Reed College in Portland, Oregon, and his colleagues studied the brains of two closely related species of African clawed frog: Xenopus laevis and Xenopus petersii. Males of both species emit fast trills while courting, but X. laevis produces longer, lower-pitched trills than X. petersii.

After dissecting the frogs’ brains, the researchers identified two subtypes of neuron involved in the frogs’ calls. When the scientists isolated and triggered these cells, one subtype, called ‘fast-trill neurons’, exhibited longer-lasting and slower responses in X. laevis than in X. petersii. Bathing the brains in serotonin evoked electrical activity with a pattern that resembled that seen during courtship calls. Again, the fast-trill neurons responded more slowly and for longer in X. laevis than in X. petersii.

Changes to these neurons probably contributed to the evolution of the two species’ distinctive courtship calls.