Meeting Abstract
To identify mechanisms underlying the divergent evolution of motor behaviors, we investigated a hindbrain circuit that controls vocal patterns in two frog species that diverged ~17 mya: Xenopus borealis and Xenopus laevis. Male advertisement calls differ: X. laevis calls consist of many rapid sound pulses with a ~1000 ms period, while X. borealis calls consist of a single sound pulse with a 200-500 ms period. Sound pulses in both species are activated by bilateral bursts of laryngeal nerve activity called compound action potentials (CAPs). To investigate premotor mechanisms of species-typical call production, we used electrophysiological recordings in fictively calling isolated brains that generate CAPs with species-typical temporal patterns. In X. borealis CAPs are long (~50 ms), while X. laevis CAPs are brief (~5 ms). Vocal premotor neuron activity matched species-typical CAP durations: X. borealis neurons produced long spike bursts during each CAP, while X. laevis neurons generated only 1-2 spikes during each CAP. We also investigated the neural basis of distinct call periods. Extracellular recordings in the premotor nucleus revealed a slow wave of activity that corresponds to each call period, and this wave persists when the premotor nucleus is isolated from other vocal areas. Further, both X. laevis and X. borealis premotor neurons intrinsically produce oscillations that may correspond to call periods. In sum, these findings reveal that distinct premotor circuit properties underlie the evolution of divergent vocal behaviors.
