No 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.

No abstract

Acoustic signals are critical for inter-and intraspecific communication in many animals. In bony fishes, sound production is widespread and is used in a variety of speciesspecific behaviors such as agonistic interactions and reproduction (see Lobel, 1992;Zelick et al., 1999;Myrberg and Fuiman, 2002). Acoustic cues can provide information on mate location, reproductive readiness to synchronize gamete release, size, aggression level, territory quality, fitness, and species or individual identity (Myrberg and Riggio, 1985;Myrberg et al., 1986;Myrberg et al., 1993;Kenyon, 1994;Lobel and Mann, 1995;Myrberg, 1997;Lobel, 2001;Myrberg and Stadler, 2002). Thus, identification and characterization of both biologically relevant acoustic signals and the response properties of the auditory system are important to understand the function and evolution of acoustic communication in fishes.Acoustic communication involves the transmission of information by a sender to a receiver with potential benefits to both individuals (Bradbury and Vehrencamp, 1998). In this case, natural selection should favor the production of sounds with frequency spectra and energy content that match the hearing abilities of the intended receiver, and vice versa. This sensory drive model of signal evolution assumes that sender and receiver coevolve within specific constraints of the environment (e.g. background noise and transmission properties) (Endler, 1992). However, few studies on fishes examine both sound production and hearing ability within a single species to test for adaptive coupling of sender signal production and receiver signal reception. Hearing sensitivity was found to match the characteristics of sounds produced in the frequency domain in some species, but a mismatch was observed in others (Cohen and Winn, 1967;Myrberg and Spires, 1980;Fine, 1981;Schellart and Popper, 1992;Ladich and Yan, 1998;Yan et al., 2000;Ladich, 2000). As a result, enhanced intraspecific acoustic communication may not be the main driving force for the evolution of accessory hearing structures because there is no clear relationship between frequency spectra of fish sounds and auditory sensitivity among species with Weberian ossicles, suprabranchial chambers and auditory bullae that serve to increase or modify hearing ability (Ladich, 1999; Ladich, 2000).Sounds provide important signals for inter-and intraspecific communication in fishes, but few studies examine fish acoustic behavior in the context of coevolution of sound production and hearing ability within a species. This study characterizes the acoustic behavior in a reproductive population of the Hawaiian sergeant fish, Abudefduf abdominalis, and compares acoustic features to hearing ability, measured by the auditory evoked potential (AEP) technique. Sergeant fish produce sounds at close distances to the intended receiver (р1-2 body lengths), with different pulse characteristics that are associated primarily with aggression, nest preparation and courtship-female-visit behaviors. Energy peaks of all sounds were be...

Elucidating the origins of complex biological structures has been one of the major challenges of evolutionary studies. Within vertebrates, the capacity to produce regular coordinated electric organ discharges (EODs) has evolved independently in different fish lineages. Intermediate stages, however, are not known. We show that, within a single catfish genus, some species are able to produce sounds, electric discharges or both signals (though not simultaneously). We highlight that both acoustic and electric communication result from actions of the same muscle. In parallel to their abilities, the studied species show different degrees of myofibril development in the sonic and electric muscle. The lowest myofibril density was observed in Synodontis nigriventris , which produced EODs but no swim bladder sounds, whereas the greatest myofibril density was observed in Synodontis grandiops , the species that produced the longest sound trains but did not emit EODs. Additionally, S. grandiops exhibited the lowest auditory thresholds. Swim bladder sounds were similar among species, while EODs were distinctive at the species level. We hypothesize that communication with conspecifics favoured the development of species-specific EOD signals and suggest an evolutionary explanation for the transition from a fast sonic muscle to electrocytes.

The hypothesis of ecological and morphological convergence of the taxonomically distinct intertidal fish assemblages from central California, USA, and central Chile was tested by comparing the feeding guild structures and the morphologies associated with food capture and processing of guild members from each region. We determined the diets of the most abundant intertidal fishes from 3 central California sites by examining gut contents. A matrix of dietary overlap among species within the Californian and Chilean assemblages (diets of Chilean fishes determined in another study) was constructed, and statistically significant guilds were determined using a bootstrapping procedure. Ten morphological features were examined for species in each region, and the relationship between diet and consumer morphology was evaluated. Three feeding guilds, omnivore, microcarnivore, and carnivore, were common to both regions, but a fourth guild, polychaete feeders, was unique to California. Feeding guild structure was not associated with phylogenetic relatedness within either assemblage. An assemblage-wide relationship between diet and morphology was found in each assemblage, but only a few associations between diet and morphology were common to both regions. In both California and Chile, omnivores tended to have longer digestive tracts and closer-set gill rakers, microcarnivores tended to have larger relative mouth heights, and all carnivorous fishes tended to have shorter guts and more widely spaced gill rakers. Overall, interregional morphological patterns were associated with phylogenetic relatedness, rather than with dietary similarities.

The microtides, wave regimes, and relative isolation of the Hawaiian archipelago may provide unique environmental and biogeographic effects that shape the structure of tidepool fishes. We sampled fishes across a narrow gradient at low tide from 6 sites on the island of O`ahu. We tested predictions of the hypotheses that environmental conditions (pool depth, volume, macroalgal cover, temperature, and salinity) would result in a vertically structured tidepool fish assemblage unique to basalt or limestone rocky shores. 343 fish were recorded from 40 pools, and 19 species from 10 families were identified. Tidepool fish diversity (H': O`ahu=2.4; Sites Average=0.0-0.9) was typical for tropical islands, with members from Gobiidae (5 species), Blenniidae (4 species), Pomacentridae (3 species), Acanthuridae (2 species) and Kuhliidae (2 species) among the most common. Endemism (32%) was higher than other well studied assemblages yet similar to Hawaiian reef fishes (25%). Assemblage abundance varied among shores with basalt or limestone substrate, among sites, and vertically among high, mid, and low pools. In general, blenniids occurred at higher proportions on limestone shores and gobiids were more common on basalt shores. High pools were characterized by an abundance of a small sized (29.0 mm median standard length) blenniid Istiblennius zebra, while the blenniid Entomacrodus marmoratus and wrasses Thalassoma spp. were more common in low pools. Temperature was the best environmental predictor of assemblages and this relationship warrants further investigation. Our findings indicate that assemblages can vary across a narrow geographical range and intertidal shore.

Acoustic behaviors are widespread among diverse fish taxa but mechanisms of sound production are known from relatively few species, vary widely and convergent mechanisms are poorly known. We examined the sound production mechanism in the pyramid butterflyfish, Hemitaurichthys polylepis, a member of the socially and ecologically diverse reef fish family Chaetodontidae. In the field, fish produce pulse trains at dusk during social interactions that are probably related to mate attraction and courtship. In laboratory experiments, sound production was synchronized to high-speed video to determine body movement associated with sound generation. In addition, electromyography (EMG) recordings tested the activity of six candidate muscles. Fish produced individual pulses with a mean peak frequency of 97 Hz in rapid succession. EMG experiments show that anterior hypaxial muscles contract at high bilaterally synchronous rates (up to 120 Hz) in near perfect association with rapid inward buckling visible outside the body over the anterior swim bladder. Muscle activity often showed EMG doublets that occurred within the time of a single sound pulse but was not sustained. Buckling and sound pulse rates correlated strongly (R(2)≈1.00) and sound pulse rate measured over two successive pulses (maximum of 38 pulses s(-1)) was lower than muscle firing rate. These results show that the extrinsic swim bladder muscles of pyramid butterflyfish involve single contractions that produce pulses in a manner similar to distantly related teleosts, but involve a novel doublet motor-neuron firing pattern. Thus, the sound production mechanism in pyramid butterflyfish is likely convergent with several percomorph taxa and divergent from the related chaetodontid genus Forcipiger.