PATEK, Sheila: Squeaking with a sliding joint: the origin of sound production in spiny lobsters

The origin of arthropod sound producing morphology typically involves modification of two translating body surfaces, such as the legs and thorax. In an unusual structural rearrangement, one lineage of palinurid lobsters lost an antennal joint articulation, which transformed this joint from moving with one degree of freedom into a sliding joint with multiple degrees of freedom. With this sliding joint, “stick and slip” sounds are produced by rubbing the base of each antenna against the cephalothorax. To better understand the musculo-skeletal changes that occurred during the origin and evolutionary variation of this sound producing mechanism, I examined joint morphology and antennal muscle anatomy across sound producing and non-sound producing palinurids. Using phylogenetic comparative methods, I tested for correlations between sound producing structures and temporal signal features. Antennal muscle size and orientation changed dramatically across sound producing lobsters following the origin of the sliding joint. In addition, temporal acoustic features were correlated with the size of the sound producing mechanism, specifically the maximum distance translated by the sliding joint. Construction of a sliding joint appears to be the key modification in the origin of this sound producing mechanism, since the translational motion permitted by the sliding joint is necessary for sound production. However, this joint modification could have evolved either in concert with or prior to sound production, possibly to increase maneuverability during defensive antennal movements.