Pattern-generating circuitry underlying the vocal basis for acoustic communication in fishes and tetrapods evolved from an ancestrally shared hindbrain, rh8-spinal compartment. This compartment also gave rise to premotor-motor circuitry for pectoral appendages that serve locomotion and nonvocal, sonic–acoustic signaling functions in fishes. These shared developmental origins suggest that the functional coupling between more highly derived vocal and pectoral mechanisms that have evolved for acoustic and gestural signaling in tetrapods originated in fishes.
More broadly, we propose that, among vertebrates in general, rh8-spinal networks include anatomically separate premotor nuclei, each of which has a distinct suite of intrinsic and network properties determining specific behavioral attributes (Fig. 10.5). Each network’s ensemble of premotor nuclei configures the spatiotemporal activity of one or more neuromuscular systems underlying entire behaviors such as vocalization [also see Llinás and Paré (1994)]. By comparing rh8-spinal networks across vertebrate lineages, we can identify ancestral characters contributing to evolutionarily derived networks, for example, the anatomical and neurophysiological properties of sonic–vocal networks in fishes found in the sonic–vocal networks of birds and mammals. This includes phylogenetically deep homologies, that is, “molecular and cellular components . . . contributing to phenotypic novelties” that “enable us to reconstruct how a phenotype was built over evolutionary time” (McCune and Schimenti, 2012).
We thank R. Baker, D. Deitcher, L.-H. Ma, R. G. Northcutt, K. Rohmann, N. Segil, and the reviewers for helpful discussions and comments on earlier versions of the manuscript; R. Baker, E. Gilland, and L.-H. Ma for collaborations on research reviewed here; M. Nelson and M. Marchaterre for drawings in Fig. 10.1; M. Marchaterre for movies used in analysis; E. Adkins-Regan, K. Bostwick, F. Ladich, U. Jürgens, and M. Marchaterre for sound recordings; John Avise, Francisco Ayala, and Georg Striedter for the invitation to participate in the Sackler Colloquium. This work was supported by National Institutes of Health Grant DC00092 and National Science Foundation Grant IOS1120925.