Ontogenetic Changes in Turtle Vocal Behavior

Widespread sound production across turtle taxa raises questions about its possible function. Although most acoustic communication has been observed in adults, acoustic behavior may play different roles across ontogeny, developing over the protracted lifespan of chelonians. Little is known about the changes in the acoustic repertoires across ontogeny or whether the extent of change varies among lineages. Such knowledge would provide the fundamental natural history information needed to better understand the behavioral evolution of this group of reptiles. Here we investigate if turtles' acoustic repertoires undergo ontogenetic changes, and if such changes are similar throughout the turtle phylogeny. If ontogenetic changes in vocalizations simply reflect predictable, morphological changes that occur with growth, then we predict dominant frequency will decrease across ontogeny in all chelonian species, and vocal complexity will remain constant. If, however, ontogenetic changes represent functional changes in acoustic communication, then both dominant frequency and vocal complexity will vary across ontogeny in a species-specific manner. Here we collected and compared sound recordings from 6 species in different life stages and found that the acoustic repertoire of some species does not grow in a simple manner across ontogeny, challenging the hypothesis that mean peak frequency decreases with body size. We discuss the possibility that changes in habitat use during ontogeny has driven concomitant changes in vocal repertoire, whereas continuity in habitat leads to a relatively stable repertoire across life, especially in species that socialize among individuals of all ages.