Sound production inOnuxodon fowleri(Carapidae) and its amplification by the host shell

Abstract

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.

New insights into sound production in <I>Carapus mourlani</I> (Carapidae)

“…Staccatos are interesting because the same kind of long-duration sounds were also recorded in O. fowleri (Kéver et al 2014). In this species, sounds could be detected at 40 m from the emitter, which implies that these regular beats are made to attract conspecifics.…”

“…Parasite species feed on the internal tissues of their host, mainly the gonads (Arnold 1956, Trott 1970, Parmentier and Das 2004, Parmentier and Michel 2013. Another interesting aspect of this group of fishes is their ability to produce sounds (Parmentier et al 2003a,b, 2008, Kéver et al 2014. In captivity, series of pulsed sounds have been recorded for Carapus boraborensis (Kaup, 1856), Carapus homei (Richardson, 1846), and Encheliophis gracilis (Bleeker, 1856), only after an individual had entered a sea cucumber that was already occupied by a conspecific or a heterospecific organism (Parmentier et al 2003b, Lagardère et al 2005).…”

“…Because sound attenuation by the sea cucumber tegument is negligible at the frequencies emitted by carapids, they have the potential to call for mates from the safety of their hosts (Lagardère et al 2005). In the species Onuxodon fowleri (Smith, 1955), known to live inside pearl oysters, the sounds can be amplified by the shell cavity enhancing the communication distance (Kéver et al 2014). Therefore, the ability to communicate acoustically would be an advantage during host colonization, territory defense, or reproduction.…”

Symbiotic relationship between the carapid fish <em>Onuxodon fowleri</em> (Ophidiiformes: Carapidae) and the pearl oyster <em>Pinctada margaritifera</em> (Mollusca: Bivalvia: Pteriidae)

“…In addition, the high percentage of empty stomachs observed in O. fowleri might be related to the time of sampling (10:00 am -3:00 pm). Recently, Kéver et al (2014) reported that the majority of sounds produced by O. fowleri in the field were recorded between 5:00 PM and 12:00 AM, which implies a nocturnal activity in this species. Assuming that O. fowleri forages for food mainly at night, it is thus likely that most of the stomach contents were empty because they were opened during daytime.…”

“…Among this fish family, members of a third genus (Onuxodon) are also known to live inside bivalves, being located between the mantle and the shell (Fowler 1927, Trott 1970, Tyler 1970). Fowler's pearlfish, Onuxodon fowleri (Smith, 1955) (Carapinae: Echiodontini), lives inside representatives of the pearl oyster P. margaritifera (Fowler 1927, Parmentier et al 2000, Kéver et al 2014. Onuxodon fowleri is considered a commensal species that uses its host as a shelter and leaves it to feed on small benthic preys such as annelids and small crustaceans (Trott 1981, Parmentier et al 2000.…”