Onuxodon species are well known for living inside pearl oysters. As in other carapids, their anatomy highlights their ability to make sounds but sound production has never been documented in Onuxodon. This paper describes sound production in Onuxodon fowleri as well as the anatomy of the sound production apparatus. Single-pulsed sounds and multiple-pulsed sounds that sometimes last more than 3 s were recorded in the field and in captivity (Makemo Island, French Polynesia). These pulses are characterized by a broadband frequency spectrum from 100 to 1000 Hz. Onuxodon fowleri is mainly characterized by its ability to modulate the pulse period, meaning that this species can produce pulsed sounds and tonal-like sounds using the same mechanism. In addition, the sound can be remarkably amplified by the shell cavity (peak gain can exceed 10 dB for some frequencies). The sonic apparatus of O. fowleri is characterized by a rocker bone in front of the swimbladder, modified vertebrae and epineurals, and two pairs of sonic muscles, one of which (primary sonic muscle) inserts on the rocker bone. The latter structure, which is absent in other carapid genera, appears to be sexually dimorphic suggesting differences in sound production in males and females. Sound production in O. fowleri could be an example of adaptation where an animal exploits features of its environment to enhance communication.
L.K., O.C., M.L. and E.P. conceived and designed the experiments. L.K., O.C., F.L., D.L. and E.P. collected the fish and performed field recordings. M.L. performed the ‘oyster shell cavity’ experiment. A.H. performed the μCT-scans. K.L. studied the muscle histology, analyzed the data and wrote the manuscript. O.C., M.L., F.L., D.L., A.H. and E.P. revised the manuscript. E.P. gave final approval for submission.
The authors declare no competing financial interests.
This study was supported by the Belgian National Fund for Scientific Research (F.R.S.-FNRS) [grant numbers.F.R.F.C. 2.4.535.10.F and P.D.R. T.0056.13].
Supplementary material available online at http://jeb.biologists.org/lookup/suppl/doi:10.1242/jeb.109363/-/DC1
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