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The plainfin midshipman fish, Porichthys notatus, is a seasonally breeding species of marine teleost fish that generates acoustic signals for intraspecific social and reproductive-related communication. Female midshipman use the inner ear saccule as the main acoustic endorgan for hearing to detect and locate vocalizing males that produce multiharmonic advertisement calls during the breeding season. Previous work showed that the frequency sensitivity of midshipman auditory saccular afferents changed seasonally with female reproductive state such that summer reproductive females became better suited than winter nonreproductive females to encode the dominant higher harmonics of the male advertisement calls. The focus of this study was to test the hypothesis that seasonal reproductive-dependent changes in saccular afferent tuning is paralleled by similar changes in saccular sensitivity at the level of the hair-cell receptor. Here, I examined the evoked response properties of midshipman saccular hair cells from winter nonreproductive and summer reproductive females to determine if reproductive state affects the frequency response and threshold of the saccule to behaviorally relevant single tone stimuli. Saccular potentials were recorded from populations of hair cells in vivo while sound was presented by an underwater speaker. Results indicate that saccular hair cells from reproductive females had thresholds that were ∼8 to 13 dB lower than nonreproductive females across a broad range of frequencies that included the dominant higher harmonic components and the fundamental frequency of the male''s advertisement call. These seasonal-reproductive-dependent changes in thresholds varied differentially across the three (rostral, middle, and caudal) regions of the saccule. Such reproductive-dependent changes in saccule sensitivity may represent an adaptive plasticity of the midshipman auditory sense to enhance mate detection, recognition, and localization during the breeding season. [ABSTRACT FROM AUTHOR]

This article describes a novel and interdisciplinary context for learning about real-world sound waves. The ‘song’ of the plainfin midshipman fish consists of an acoustical wave that is periodic but not sinusoidal. This acoustical signal is the focus of active research in sound source localization by fishes, the effects of hormones on hearing systems and the elucidation of neural mechanisms involved in social acoustic communication. In this paper, we introduce the reproductive biology and bioacoustics of the midshipman fish. We describe the use of the advertisement ‘song’ of the male fish to visualize and interpret the dramatically different displacement, velocity and acceleration waveforms, to explore the roles of pressure and particle motion in production and detection of acoustical waves and to apply Fourier analysis to understand the implications of the frequency spectrum in the production, transmission and reception of sound in an aquatic environment. [ABSTRACT FROM AUTHOR]