Acoustic Communication in Butterflyfishes: Anatomical Novelties, Physiology, Evolution, and Behavioral Ecology

Soundscapes as heard by invertebrates and fishes: Particle motion measurements on coral reefs

Coral reef soundscapes are increasingly studied for their ecological uses by invertebrates and fishes, for monitoring habitat quality, and to investigate effects of anthropogenic noise pollution. Few examinations of aquatic soundscapes have reported particle motion levels and variability, despite their relevance to invertebrates and fishes. In this study, ambient particle acceleration was quantified from orthogonal hydrophone arrays over several months at four coral reef sites, which varied in benthic habitat and fish communities. Time-averaged particle acceleration magnitudes were similar across axes, within 3 dB. Temporal trends of particle acceleration corresponded with those of sound pressure, and the strength of diel trends in both metrics significantly correlated with percent coral cover. Higher magnitude particle accelerations diverged further from pressure values, potentially representing sounds recorded in the near field. Particle acceleration levels were also reported for boat and example fish sounds. Comparisons with particle acceleration derived audiograms suggest the greatest capacity of invertebrates and fishes to detect soundscape components below 100 Hz, and poorer detectability of soundscapes by invertebrates compared to fishes. Based on these results, research foci are discussed for which reporting of particle motion is essential, versus those for which sound pressure may suffice.

Auditory evoked potentials of utricular hair cells in the plainfin midshipman, Porichthys notatus

The plainfin midshipman, Porichthys notatus, is a soniferous marine teleost fish that generates acoustic signals for intraspecific social communication. Nocturnally active males and females rely on their auditory sense to detect and locate vocally active conspecifics during social behaviors. Previous work showed that the midshipman inner ear saccule and lagena are highly adapted to detect and encode socially relevant acoustic stimuli, but the auditory sensitivity and function of the midshipman utricle remain largely unknown. Here, we characterized the auditory evoked potentials from hair cells in the utricle of non-reproductive type I males and tested the hypothesis that the midshipman utricle is sensitive to behaviorally relevant acoustic stimuli. Hair cell potentials were recorded from the rostral, medial and caudal regions of the utricle in response to pure tone stimuli presented by an underwater speaker. We show that the utricle is highly sensitive to particle motion stimuli produced by an underwater speaker positioned in the horizontal plane. Utricular potentials were recorded across a broad range of frequencies with lowest particle acceleration (dB re. 1 m s-2) thresholds occurring at 105 Hz (lowest frequency tested; mean threshold -32 dB re. 1 m s-2) and highest thresholds at 605-1005 Hz (mean threshold range -5 to -4 dB re. 1 m s-2). The high gain and broadband frequency sensitivity of the utricle suggest that it likely serves a primary auditory function and is well suited to detect conspecific vocalizations including broadband agonistic signals and the multiharmonic advertisement calls produced by reproductive type I males.

Sexually dimorphic swim bladder extensions enhance the auditory sensitivity of female plainfin midshipman fish, Porichthys notatus

The plainfin midshipman fish, Porichthys notatus, is a seasonally breeding, nocturnal marine teleost fish that produces acoustic signals for intraspecific social communication. Females rely on audition to detect and locate 'singing' males that produce multiharmonic advertisement calls in the shallow-water, intertidal breeding environments. Previous work showed that females possess sexually dimorphic, horn-like rostral swim bladder extensions that extend toward the primary auditory end organs, the saccule and lagena. Here, we tested the hypothesis that the rostral swim bladder extensions in females increase auditory sensitivity to sound pressure and higher frequencies, which potentially could enhance mate detection and localization in shallow-water habitats. We recorded the auditory evoked potentials that originated from hair cell receptors in the saccule of control females with intact swim bladders and compared them with those from treated females (swim bladders removed) and type I males (intact swim bladders lacking rostral extensions). Saccular potentials were recorded from hair cell populations in vivo while behaviorally relevant pure-tone stimuli (75-1005 Hz) were presented by an underwater speaker. The results indicate that control females were approximately 5-11 dB re. 1 µPa more sensitive to sound pressure than treated females and type I males at the frequencies tested. A higher percentage of the evoked saccular potentials were recorded from control females at frequencies >305 Hz than from treated females and type I males. This enhanced sensitivity in females to sound pressure and higher frequencies may facilitate the acquisition of auditory information needed for conspecific localization and mate choice decisions during the breeding season.

Underwater Soundscape Monitoring and Fish Bioacoustics: A Review

Soundscape ecology is a rapidly growing field with approximately 93% of all scientific articles on this topic having been published since 2010 (total about 610 publications since 1985). Current acoustic technology is also advancing rapidly, enabling new devices with voluminous data storage and automatic signal detection to define sounds. Future uses of passive acoustic monitoring (PAM) include biodiversity assessments, monitoring habitat health, and locating spawning fishes. This paper provides a review of ambient sound and soundscape ecology, fish acoustic monitoring, current recording and sampling methods used in long-term PAM, and parameters/metrics used in acoustic data analysis.

Intra- and Intersexual swim bladder dimorphisms in the plainfin midshipman fish (Porichthys notatus): Implications of swim bladder proximity to the inner ear for sound pressure detection

The plainfin midshipman fish, Porichthys notatus, is a nocturnal marine teleost that uses social acoustic signals for communication during the breeding season. Nesting type I males produce multiharmonic advertisement calls by contracting their swim bladder sonic muscles to attract females for courtship and spawning while subsequently attracting cuckholding type II males. Here, we report intra- and intersexual dimorphisms of the swim bladder in a vocal teleost fish and detail the swim bladder dimorphisms in the three sexual phenotypes (females, type I and II males) of plainfin midshipman fish. Micro-computerized tomography revealed that females and type II males have prominent, horn-like rostral swim bladder extensions that project toward the inner ear end organs (saccule, lagena, and utricle). The rostral swim bladder extensions were longer, and the distance between these swim bladder extensions and each inner-ear end organ type was significantly shorter in both females and type II males compared to that in type I males. Our results revealed that the normalized swim bladder length of females and type II males was longer than that in type I males while there was no difference in normalized swim bladder width among the three sexual phenotypes. We predict that these intrasexual and intersexual differences in swim bladder morphology among midshipman sexual phenotypes will afford greater sound pressure sensitivity and higher frequency detection in females and type II males and facilitate the detection and localization of conspecifics in shallow water environments, like those in which midshipman breed and nest.

Interspecific variation of warning calls in piranhas: a comparative analysis

Fish sounds are known to be species-specific, possessing unique temporal and spectral features. We have recorded and compared sounds in eight piranha species to evaluate the potential role of acoustic communication as a driving force in clade diversification. All piranha species showed the same kind of sound-producing mechanism: sonic muscles originate on vertebrae and attach to a tendon surrounding the bladder ventrally. Contractions of the sound-producing muscles force swimbladder vibration and dictate the fundamental frequency. It results the calling features of the eight piranha species logically share many common characteristics. In all the species, the calls are harmonic sounds composed of multiple continuous cycles. However, the sounds of Serrasalmus elongatus (higher number of cycles and high fundamental frequency) and S. manueli (long cycle periods and low fundamental frequency) are clearly distinguishable from the other species. The sonic mechanism being largely conserved throughout piranha evolution, acoustic communication can hardly be considered as the main driving force in the diversification process. However, sounds of some species are clearly distinguishable despite the short space for variations supporting the need for specific communication. Behavioural studies are needed to clearly understand the eventual role of the calls during spawning events.