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Acoustic deterrence has been proven instrumental in preventing fish invasions and safeguarding against fish ingress into hydro-turbines, with the systems often employing broadband sounds, such as boat noises or predator vocalizations. However, within these broadband sounds, the specific frequencies that elicit negative phonotaxis (avoidance behavior) in fish remain to be identified. The present study investigated the avoidance behavior of grass carp shoal in sound playback experiments conducted using pure tones within the frequency range of 100–1500 Hz and two broadband sounds. The alligator roar sounds, a known deterrent, were used as broadband sound 1, which was also manipulated to remove high-sound-pressure-level components, creating a novel broadband sound 2. Grass carp exhibited significant overt avoidance behavior and increased swimming speed in response to the 100 Hz pure tone. Under the effect of this tone, the number of avoidance responses over a 10-min experimental duration (8.14 ± 1.44 min) was significantly higher than that recorded in the control group (H = 34.929, P  < 0.05). These findings suggested that the low-frequency components in broadband sounds are essential to eliciting avoidance behaviors in fish. The present research offers novel insights into the strategic selection of sound frequencies in acoustic deterrence systems, facilitating the development of further precisely targeted and effective fish management strategies.

The use of acoustic attractants may have the potential to guide native migratory species towards safe passage. Flower fish Ptychobarbus kaznakovi, a short-distance migratory fish whose population is in decline in the past decades, was exposed to three acoustic stimuli (feeding sound, ambient riverine noise and the pure tone 1000 Hz) to examine the phonotaxic responses using playbacks approaches in a fibreglass tank. The results showed that the flower fish showed significantly greater positive phonotaxis and swam towards the sound sources significantly faster in response to the feeding sounds than to ambient riverine noise and the pure tone during the 5-min exposure. Distribution experiments were conducted to study the preference of flower fish to the three sounds stimuli. The results showed that the experimental fish in feeding sound trials spent significant more time in areas closer to the sound sources than that in the pure tone and the ambient riverine noise trials, respectively. This study indicates that the feeding sounds may serve as potential acoustic attractants to guide flower fish to safe passage routes.

Songbird vocal learning has interesting behavioural and neural parallels with speech acquisition in human infants. Zebra finch males sing one unique song that they imitate from conspecific males, and both sexes learn to recognize their father's song. Although males copy the stereotyped syllable sequence of their father's song, the role of sequential information in recognition remains unclear. Here, we investigated father's song recognition after changing the serial order of syllables (switching the middle syllables, first and last syllables, or playing all syllables in inverse order). Behavioural approach and call responses of adult male and female zebra finches to their father's versus unfamiliar songs in playback tests demonstrated significant recognition of father's song with all syllable-order manipulations. We then measured behavioural responses to normal versus inversed-order father's song. In line with our first results, the subjects did not differentiate between the two. Interestingly, when males' strength of song learning was taken into account, we found a significant correlation between song imitation scores and the approach responses to the father's song. These findings suggest that syllable sequence is not essential for recognition of father's song in zebra finches, but that it does affect responsiveness of males in proportion to the strength of vocal learning. This article is part of the theme issue 'Vocal learning in animals and humans'.

Invasive bigheaded carps ( Hypophthalmichthys molitrix and H. nobilis ) have caused substantial ecological and economic damage throughout the Mississippi River Basin and expanded their range threatening the Laurentian Great Lakes. Broadband acoustic deterrents have shown promise in repelling carp and are currently being assessed in navigational lock chambers on the Mississippi River. These nonphysical deterrents permit vessel navigation while reducing carp passage. However, no single deterrent is 100% effective and fish may habituate to the sound after repeated playback. Carp exhibit aversive behaviors to carbon dioxide, which suggests combining these two stimuli into one deterrent system could extend the effective duration of sound and reduce the frequency of carbon dioxide ( C O 2 ) application. We conditioned bigheaded carps to associate broadband sound from outboard boat motors (0.06–5 kHz, ~ 150 dB re. 1 μ Pa) with C O 2 application ( ~ 35,000 ppm) in small (80 L) and large (3475 L) two-choice shuttle tanks. We compared negative phonotaxis responses over one to four weeks between fish conditioned with sound and C O 2 , sound and air, or sound alone. Similar C O 2 avoidance thresholds were found across tank sizes and species. Conditioning treatment did not affect time to leave the sound chamber, confirming sound alone remains a deterrent for all fish. Carp conditioned with C O 2 took longer to return to the sound chamber than control treatments. Control fish were closer to the speaker during playback than during the pre-sound period, while fish conditioned with C O 2 were not significantly closer. Conditioning paradigms may extend the effective duration of nonphysical deterrents for bigheaded carps. Conditioning with C O 2 may also increase proactive flight-responses over reactive freeze-responses. Findings could be applied to increase nonphysical barrier effectiveness at locks along the Mississippi River and help protect the Laurentian Great Lakes from invasion.

1. Sexual signals may be acquired or lost over evolutionary time, and are tempered in their exaggeration by natural selection. 2. In the Pacific cricket, Teleogryllus oceanicus, a mutation (\"flatwing\") causing loss of the sexual signal, the song, spread in <20 generations in two of three Hawaiian islands where the crickets have been introduced. Flatwing (as well as some normal-wing) males behave as satellites, moving towards and settling near calling males to intercept phonotactic females. 3. From 2005 to 2012, we surveyed crickets and their responses to conspecific song, noting the morph and number of males and females before and after experimental playbacks. The three Hawaiian islands consistently contained different proportions of flatwing crickets, ranging from about 90% of males on Kauai to 50% on Oahu to rare on the Big Island of Hawaii. 4. Flatwing and normal-wing males do not appear to differ in responsiveness to playback, a behaviour that should influence the likelihood of a male encountering a phonotactic female. Instead, male and female crickets from populations in which little to no calling song is perceptible during development tended to seek out callers more readily than crickets that developed in noisier environments. Such increased phonotaxis makes females more likely to find either the caller to which they are responding or to encounter a flatwing (or normal male satellite) that has also been attracted to the song. 5. Our evidence suggests that pre-existing behavioural plasticity (manifest as flexible responses to social—particularly acoustic—information in the environment) is associated with the rapid spread of the flatwing trait. Different social environments select for differential success of flatwing or normal-wing males, which in turn alters the social environment itself.

Finding effective ways to direct native fish away from anthropogenic hazards and limit the spread of invasive species, without physical intervention, harming non-target fishes or interrupting aquatic commerce is a major challenge for fisheries management. One option is to target fish sensory systems to manipulate behavior using attractive or repulsive cues. Many, if not all species of fish, use sound as part of their behavioral repertoire and display varying degrees of phonotaxis. Sound has inherent advantages over other sensory stimuli such as light or odor as underwater sound attenuates slowly, is highly directional and is unimpeded by low light or water turbidity. This review details the use of acoustics to deter and guide fish movements for a wide variety of fishes, before critically assessing the benefits and limitations of the technology. No single method of fish deterrence is a “one size fits all”, and therefore this review will assist both managers and researchers attempting to use acoustic deterrents for different fish orders.

Animal signals are complex, comprising multiple components that receivers may use to inform their decisions. Components may carry information of differing value to receivers, and selection on one component could modulate or reverse selection on another, necessitating a multivariate approach to estimating selection gradients. However, surprisingly few empirical studies have estimated the strength of phenotypic selection on complex signals with appropriate design and adequate power to detect nonlinear selection. We used phonotaxis assays to measure sexual selection on the advertisement signal of Cope’s gray tree frog, hyla chrysoscelis. Female preferences were assessed for five signal components using single-and two-stimulus behavioral assays. Linear, quadratic, and correlational selection gradients were estimated from the single-stimulus data. Significant directional selection is acting on call duration, call rate, pulse rate, and relative amplitude; stabilizing selection is acting on call duration and call rate. Under the twostimulus paradigm, conclusions were qualitatively different, revealing nonlinear selection on all components except call duration. For individual subjects, the outcomes of single-and two-stimulus trials were frequently discordant, suggesting that the choice of testing paradigm may affect conclusions drawn from experiments.

Recruitment of coral larvae on reefs is crucial for individual survival and ecosystem integrity alike. Coral larvae can detect and respond to a wide range of biotic and abiotic cues, including acoustic cues, to locate suitable sites for settlement and metamorphosis. However, the acoustic ecology of coral larvae, including how they perceive auditory cues, remains poorly understood. In this mini-review we consider both ex situ physiology and behavior, and in situ ecological and behavioral studies, to first provide an updated overview of the abiotic and biotic cues used by coral larvae to guide settlement. We then explore in detail the use of acoustic cues and the current literature on behavioral responses to acoustic stimuli. Finally, we discuss gaps in our understanding of the mechanisms by which coral larvae detect acoustic cues, highlighting a novel application of technology to explore these sensory capabilities. We also address how larval phonotaxis, i.e., the ability to orient to a sound cue, can be applied to coral reef conservation. Current research suggests that acoustic cues are likely used at small spatial scales, and that coral larvae may have directional acoustic sensitivity enabling phonotactic behavior. Recruitment of coral larvae on reefs is significantly influenced by habitat-specific soundscape variation and likely affected by anthropogenic disturbance. We propose a novel application of the remote sensing technology, micro-scanning laser Doppler vibrometry (LDV), to quantify the micromechanical responses of putative acoustically sensitive epidermal microstructures. We then highlight the potential for incorporation of acoustic enrichment techniques in coral reef conservation and restoration interventions.

In most anuran species, vocalizations often consist of different notes with various temporal and spectral acoustic attributes which play a crucial role in their survival and reproductive success. Although the first call note might be necessary for anuran communication, we know little about how different notes of the calls influence female choice. The present study used phonotaxis experiments to examine the effects of the notes on female choice in the Anhui tree frog (Rhacophorus zhoukaiyae). The stimulus pair consisted of the original male advertisement call (OC) and one of four revised versions, where the first (WN1), second (WN2), or fifth (WN5) notes were replaced by band-limited white noise (WN), and the second note was replaced by a period of silence (SN2), played back antiphonally. The results showed that (1) the females preferred OC compared with WN1, suggesting the first call note plays an important role in female choice, and (2) the females preferred WN2 and SN2 compared with OC. We discuss the possibility that the second note might be the result of the combined effects of physiological constraint and avoiding backward masking of the second note on the first one over evolutionary time. These results support the notion that the first two functionally antagonistic call notes may influence female choice in this species. Significance statementVocalizations consisting of different components are a prerequisite for acoustic communication. However, the effect of different notes in anuran advertisement calls on female choice is still unknown. We adapted different notes of the original male advertisement call of the Anhui tree frog (R. zhoukaiyae) and played them back to females in order to explore the effects of these modifications on female choice. We found that females preferred male advertisement calls that contained the first note, but not the second one. These results support the idea that the first call note may play an important role in female choice, while the second note might have resulted from the combined effects of physiological constraint and avoiding backward masking of the second note on the first one.

For complex communication signals, it is often difficult to identify the information-bearing elements and their parameters necessary to elicit functional behavior. Consequently, it may be difficult to design stimuli that test how neurons contribute to communicative processing. For túngara frogs ( Physalaemus pustulosus ), however, previous behavioral testing with numerous stimuli showed that a particular frequency modulated (FM) transition in the male call is required to elicit phonotaxis and vocal responses. Modeled on such behavioral experiments, we used awake in vivo recordings of single units in the midbrain to determine if their excitation was biased to behaviorally important FM parameters. Comparisons of stimulus driven action potentials revealed greatest excitation to the behaviorally important FM transition: a downward FM sweep or step that crosses ~600 Hz. Previous studies using long-duration acoustic exposure found immediate early gene expression in many midbrain neurons to be most sensitive to similar FM. However, those data could not determine if FM coding was accomplished by the population and/or individual neurons. Our data suggest both coding schemes could operate, as 1) individual neurons are more sensitive to the behaviorally significant FM transition and 2) when single unit recordings are analytically combined across cells, the combined code can produce high stimulus discrimination (FM vs. noise driven excitation), approaching that found in behavioral discrimination of call vs. noise.