Meeting Abstract
The motor circuits of closely related species are well suited for examining proximate mechanisms that underlie divergent behaviors. Vocalization is a stereotyped motor behavior essential to successful courtship in many species. Males of extant species of the Xenopus genus produce a unique advertisement call to attract female mates of their own species. Two species, X. laevis› and X. petersii, diverged ~8.5 million years ago and produce calls consisting of two alternating trains of sound pulses: fast (~60 Hz pulses) and slow (~30 Hz) trill. Despite similar trill rates, their calls differ substantially in duration and period; X. laevis trills are longer and slower than those of X. petersii. In a fictively calling isolated brain preparation, in which nerve activity patterns resemble sound pulse patterns of advertisement calls, we use whole-cell recordings to identify premotor cells in the central pattern generators of both species. These cells typically produce spikes time-locked to nerve activity. In both species, most premotor neurons display a long-lasting depolarization (LLD) that coincides with each fictive fast trill. In each species, the LLD duration and period are strongly correlated with the duration and period of the fictive fast trill, respectively, and are significantly shorter in X. petersii than X. laevis. In the presence of tetrodotoxin, which blocks network activity, premotor neurons oscillate in response to NMDA in a species-specific manner. X. laevis neurons respond to increasing NMDA doses with a lengthening of the oscillation duration and period, while neuronal oscillations in X. petersii remain relatively short and rapid. We propose that unique cellular properties of these putatively homologous neuronal populations underlie vocal differences between X. laevis and X. petersii.
