Rhythm coordination in animal species, including humans: Entrainment from bushcricket chorusing to the philharmonic orchestra.

Michael Greenfield

ENES Bioacoustics Research Lab, CRNL, University of Saint-Etienne, CNRS

Department of Ecology and Evolutionary Biology, University of Kansas

Repetitive cycles of an activity or state, generally known as rhythm, are ubiquitous in living organisms, occurring in all branches of the tree of life.  In animal species rhythms play prominent roles in physiology and behavior, and they are commonly expressed as long-term (period > 12 h) cycles, entrained to recurring astronomical phenomena, at one end of the temporal spectrum, or as very short (< 10 s) ultradian cycles at the other.  In behavior, ultradian rhythms often involve movement or the broadcast of communication signals, and in some species neighboring individuals coordinate their rhythms in time.  Such coordination fascinates us because of its flawless precision and complexity, the horde of individuals that may participate, and the resulting crescendo of the communal display.  But aesthetic sensibilities aside, coordinated rhythms pose major questions concerning mechanisms and evolution :  How is coordination achieved, which individuals in a local population participate, why do neighbors bother to coordinate their activity and what is the phylogenetic distribution of these displays among animal taxa?

This seminar covers the diverse ways in which animals coordinate relatively fast behavioral rhythms.  We concentrate on the coordination of rhythms expressed in sexual advertisement and social communication, as these tend to be conspicuous to observers and their parameters can normally be measured unambiguously.  We begin with the various timing schemes found in rhythm coordination, noting the relative timing of the signaling by individual participants, how those participants tend to be arranged in space, and the signaling modalities used.  From the receiver’s perspective, we ask who perceives the signals, where these potential receivers are located (whether within or outside of the coordinated group), and how receivers may respond to the group display.  Because of moderate to extreme precision found in coordinated group displays, we pay special attention to the mechanisms with which individual signaling rhythms are aligned in different animal species.  We show how an understanding of mechanism is critical for the next step : evaluating adaptive explanations for synchrony and other group coordinations.  Although our survey of rhythm coordination among animals is certainly incomplete and probably reflects sampling bias favouring signals and species that are readily observed and that have been studied traditionally, some striking patterns emerge.  Rhythm coordination of both moderate and high precision appears mostly among certain arthropods and ‘lower’ vertebrates in the chordates, but also in humans where synchronous coordination is central in music, dance and other group activities.  We consider this curious, disjunct phylogenetic distribution, and specifically ask how and why strictly timed rhythmic synchrony operates in these very different organisms.  Importantly, this comparative approach holds promise for unraveling the origins of human musicality.