Sexual dimorphism of sonic apparatus and extreme intersexual variation of sounds in Ophidion rochei (Ophidiidae): first evidence of a tight relationship between morphology and sound characteristics in Ophidiidae

Loïc Kéver,Branko Dragičević,Eric Parmentier,Jakov Dulčić,Kelly S Boyle,Margarida Casadevall

doi:10.1186/1742-9994-9-34

Loïc Kéver, Branko Dragičević + Show 4 more

Open Access

https://doi.org/10.1186/1742-9994-9-34

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Abstract

BackgroundMany Ophidiidae are active in dark environments and display complex sonic apparatus morphologies. However, sound recordings are scarce and little is known about acoustic communication in this family. This paper focuses on Ophidion rochei which is known to display an important sexual dimorphism in swimbladder and anterior skeleton. The aims of this study were to compare the sound producing morphology, and the resulting sounds in juveniles, females and males of O. rochei.ResultsMales, females, and juveniles possessed different morphotypes. Females and juveniles contrasted with males because they possessed dramatic differences in morphology of their sonic muscles, swimbladder, supraoccipital crest, and first vertebrae and associated ribs. Further, they lacked the ‘rocker bone’ typically found in males. Sounds from each morphotype were highly divergent. Males generally produced non harmonic, multiple-pulsed sounds that lasted for several seconds (3.5 ± 1.3 s) with a pulse period of ca. 100 ms. Juvenile and female sounds were recorded for the first time in ophidiids. Female sounds were harmonic, had shorter pulse period (±3.7 ms), and never exceeded a few dozen milliseconds (18 ± 11 ms). Moreover, unlike male sounds, female sounds did not have alternating long and short pulse periods. Juvenile sounds were weaker but appear to be similar to female sounds.ConclusionsAlthough it is not possible to distinguish externally male from female in O. rochei, they show a sonic apparatus and sounds that are dramatically different. This difference is likely due to their nocturnal habits that may have favored the evolution of internal secondary sexual characters that help to distinguish males from females and that could facilitate mate choice by females. Moreover, the comparison of different morphotypes in this study shows that these morphological differences result from a peramorphosis that takes place during the development of the gonads.

Highlights

Many Ophidiidae are active in dark environments and display complex sonic apparatus morphologies
Gross morphology of the sonic apparatus The sonic apparatus of male Ophidion rochei was described by Parmentier et al [9]
Anterior skeleton In Ophidion rochei, skeletal structures involved in sound production are located at the level of the head and the first five vertebrae (Figure 1)

Summary

Introduction

Many Ophidiidae are active in dark environments and display complex sonic apparatus morphologies. The sound-generating mechanism of many fishes, especially the sonic muscles, is sexually dimorphic [15]. In sciaenid species such as Micropogonias undulatus, the sonic muscles and associated swimbladder are larger in males [27,28]. Some fish species display a hypertrophy of sonic muscles during breeding season [33,34] In weakfish, this hypertrophy results in the emission of sounds with higher intensities, lower frequencies, and longer pulse durations [20]

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