WEBB, J.F.; HERMAN, J.L.; KETTEN, D.R.; Villanova University; Villanova University; Woods Hole Oceanographic Institution: Ear and Otolith Morphology in a Prominent Group of Coral Reef Fishes with a Putative Specialization for Enhanced Sound Reception

Specialized ear morphology is correlated with enhanced hearing in fishes with otophysic connections (ear-swim bladder linkages). Butterflyfishes of the genus Chaetodon (Family Chaetodontidae) have a unique swim bladder � lateral line connection (the laterophysic connection), which is thought to enhance the reception of acoustic stimuli by converting pressure flucutations in the swim bladder into fluid flow in the lateral line system. Proximity of anterior swim bladder extensions to not only the lateral line canals of the head, but to the inner ear, suggests that the ears of these fishes may demonstrate enhanced sensitivity to sound. Several species of Chaetodon are known to make sounds in the context of social and territorial interactions emphasizing the importance of sound reception in these fishes, which inhabit noisy coral reef habitats. SEM and CT imaging were used to determine if the ears of four Chaetodon species have the specialized features of the ears of fishes with otophysic connections, thus providing morphological evidence for enhanced auditory capabilities in these fishes. Analysis of the shape of the sensory maculae (utriculus, sacculus, lagena) and otoliths, hair cell orientation pattern, and hair cell morphology and density revealed unremarkable morphology similar to that found in percomorphs that are hearing non-specialists. Our results suggest that modifications in ear morphology are not required for enhancement of auditory capabilities, or alternatively, that reception of sound by the ears is not enhanced in these fishes. These results refocus our attention on the evolution of the laterophysic connection as a strategy for enhancing reception of behaviorally-important acoustic stimuli in noisy coral reef environments. Supported by NSF grant IBN-0132607 to JFW.