Scale effects and constraints for sound production in katydids (Orthoptera: Tettigoniidae): correlated evolution between morphology and signal parameters

Male katydids (Orthoptera: Tettigoniidae) produce mating calls by rubbing the wings together, using specialized structures in their forewings (stridulatory file, scraper and mirror). A large proportion of species (ca. 66%) reported in the literature produces ultrasonic signals as principal output. Relationships among body size, generator structures and the acoustic parameters carrier frequency (f_c) and pulse duration (p_d), were studied in 58 tropical species that use pure‐tone signals. A comparative analysis, based on the only available katydid phylogeny, shows how changes in sound generator form are related to changes in f_c and p_d. Anatomical changes of the sound generator that might have been selected via f_c and p_d are mirror size, file length and number of file teeth. Selection for structures of the stridulatory apparatus that enhance wing mechanics via file‐teeth and scraper morphology was crucial in the evolution of ultrasonic signals in the family Tettigoniidae.     

Variation among vocalizations of Taraba major (Aves: Thamnophilidae) subspecies

Geographical variation of bird vocalizations may be related to factors influencing sound production and sound propagation. If birds, e.g. the Great Antshrike (Taraba major), produce vocalizations that develop normally in the absence of learning, these variations may reflect evolutionary divergence within species. In this case, vocal variation could be influenced by habitat structure, since abiotic features and vegetal cover affect sound propagation through environment. Selective pressures may be acting on populations in different ways, which could culminate in a process of speciation. Thus, we searched for structural variation of Great Antshrike vocalizations between subspecies and sought for relationships between these vocal variation and environmental structure. We found variations in frequency and time features of vocalizations among subspecies, which are correlated to latitude, elevation and climate. We also observed an increase in vocal differences along with an increase in distances between individuals, which could reflect isolation of subspecies and the vocal adaptation to different environments.     

Spectral call features provide information about the aggression level of greater mouse-eared bats (Myotis myotis) during agonistic interactions

Bats rely heavily on acoustic signals in order to communicate with each other in a variety of social contexts. Among those, agonistic interactions and accompanying vocalizations have received comparatively little study. Here, we studied the communicational behaviour between male greater mouse-eared bats (Myotis myotis) during agonistic encounters. Two randomly paired adult males were placed in a box that allowed us to record video and sound synchronously. We describe their vocal repertoire and compare the acoustic structure of vocalizations between two aggression levels, which we quantified via the bats’ behaviour. By inspecting thirty, one-minute long encounters, we identified a rich variety of social calls that can be described as two basic call types: echolocation-like, low-frequency sweeps and long, broadband squawks. Squawks, the most common vocalization, were often noisy, i.e. exhibited a chaotic spectral structure. We further provide evidence for individual signatures and the presence of nonlinear phenomena in this species’ vocal repertoire. As the usage and acoustic structure of vocalizations is known to encode the internal state of the caller, we had predicted that the spectral structure of squawks would be affected by the caller’s aggression level. Confirming our hypothesis, we found that increased aggression positively correlated with an increase in call frequency and tonality. We hypothesize that the extreme spectral variability between and within squawks can be explained by small fluctuations in vocal control parameters (e.g. subglottal pressure) that are caused by the elevated arousal, which is in turn influenced by the aggression level.     

Quantification of total and particulate dimethylsulfoniopropionate (DMSP) in five Bermudian coral species across a depth gradient

The symbiotic dinoflagellate microalgae of corals (Symbiodinium spp.) contain high concentrations of dimethylsulfoniopropionate (DMSP), a multifunctional metabolite commonly found in many species of marine algae and dinoflagellates. A photoprotective antioxidant function for DMSP and its breakdown products has often been inferred in algae, but its role(s) in the coral–algal symbiosis remains elusive. To examine potential correlations between environmental and physiological parameters and DMSP, total DMSP (DMSP_t, from the host coral and zooxanthellae), particulate DMSP (DMSP_p, from the zooxanthellae only), coral surface area, and total protein, as well as zooxanthellae density, chlorophyll concentration, cell volume and genotype (i.e., clade) were measured in five coral species from the Diploria-Montastraea-Porites species complex in Bermuda along a depth gradient of 4, 12, 18, and 24 m. DMSP_t concentrations were consistently greater than DMSP_p concentrations in all species suggesting the possible translocation of DMSP from symbiont to host. D. labyrinthiformis was notably different from the other corals examined, showing DMSP_p and DMSP_t increases (per coral surface area or tissue biomass) with increasing water depth. However, overall, there were no consistent depth-related patterns in DMSP_p and DMSP_t concentrations. Further research, investigating dimethylsulfide (DMS), dimethylsulfoxide, and acrylate levels and DMSP-lyase activity in correlation with other biomarker endpoints that have been shown to be depth (i.e., temperature and light) responsive are needed to substantiate the significance of these findings.     

Vocal Tract Morphology Determines Species-Specific Features in Vocal Signals of Lemurs (Eulemur)

The source-filter theory describes vocal production as a two-stage process involving the generation of a sound source, with its own spectral structure, which is then filtered by the resonant properties of the vocal tract. This theory has been successfully applied to the study of animal vocal signals since the 1990s. As an extension, models reproducing vocal tract resonance can be used to reproduce formant patterns and to understand the role of vocal tract filtering in nonhuman vocalizations. We studied three congeneric lemur species —Eulemur fulvus, E. macaco, E. rubriventer— using morphological measurements to build computational models of the vocal tract to estimate formants, and acoustic analysis to measure formants from natural calls. We focused on call types emitted through the nose, without apparent articulation. On the basis of anatomical measurements, we modeled the vocal tract of each species as a series of concatenated tubes, with a cross-sectional area that changed along the tract to approximate the morphology of the larynx, the nasopharyngeal cavity, the nasal chambers, and the nostrils. For each species, we calculated the resonance frequencies in 2500 randomly generated vocal tracts, in which we simulated intraspecific length and size variation. Formant location and spacing showed significant species-specific differences determined by the length of the vocal tract. We then measured formants of a set of nasal vocalizations (“grunts”) recorded from captive lemurs of the same species. We found species-specific differences in the natural calls. This is the first evidence that morphology of the vocal tract is relevant in generating filter-related acoustic cues that potentially provide receivers with information about the species of the emitter.     

Low-frequency distortion product otoacoustic emissions in two species of kangaroo rats: implications for auditory sensitivity

Low-frequency distortion-product otoacoustic emissions were measured in two species of kangaroo rats to test the prediction that a large footdrumming species (e.g., Dipodomys spectabilis) would have greater distortion-product otoacoustic emission amplitude than a small non-footdrumming species (e.g., Dipodomys merriami), indicating better hearing sensitivity at low frequencies. Equal-level (65 dB SPL) stimulus tones (f ₁, f ₂), presented over a (f ₁) range of 200–1000 Hz, were used to evoke the 2f ₁–f ₂ distortion-product otoacoustic emission. Mean 2f ₁–f ₂ levels for D. merriami showed good correspondence to previously published audiograms for that species. Mean 2f ₁–f ₂ levels and 95% confidence intervals indicated species differences below 400 Hz, supporting the theory that low-frequency hearing sensitivity is better in large kangaroo rat species. These results suggest that the size-related divergence in footdrumming behavior may be related to differential auditory sensitivity.Abbreviations DPOAE distortion-product otoacoustic emission - OAE otoacoustic emission - PVC polyvinyl chloride     

The function of loud calls (Hoot Series) in wild western gorillas (Gorilla gorilla)

The use of loud vocal signals to reduce distance among separated social partners is well documented in many species; however, the underlying mechanisms by which the reduction of spacing occurs and how they differ across species remain unclear. Western gorillas (Gorilla gorilla) offer an opportunity to investigate these issues because their vocal repertoire includes a loud, long‐distance call (i.e., hoot series) that is potentially used in within‐group communication, whereas mountain gorillas use an identical call exclusively during intergroup encounters. First, we tested whether the hoot series functions as a contact/separation call. Second, we examined which individuals were more likely to reply and which party was more responsible for decreasing distance to identify the underlying mechanisms and cognitive implications of hoot series. We collected behavioral, spatial, and acoustic data on five adult gorillas over 15 months at the Mondika Research Center (Republic of Congo and CAR). Hoot series are individually distinct calls and given by both male and female gorillas when separated from each other. Following hooting, the distance between separated group members decreased significantly; thus we concluded that western gorillas use this call to reestablish group cohesion. The way in which proximity was achieved depended upon listeners replying or not to the caller. Replies may indicate a conflict between callers about intended travel direction, with vocal interchanges serving to negotiate a consensus. Although the acoustic features of vocal signals are highly constrained in closely related species, our results demonstrate that the function and usage of particular calls can be flexible. Am J Phys Anthropol 155:379–391, 2014. © 2014 Wiley Periodicals, Inc.     

Ecoacoustics can detect ecosystem responses to environmental water allocations

1. Globally, water abstraction for human consumption and irrigated agriculture leads to significant changes in aquatic ecosystems. To counter these detrimental effects, water releases—often termed environmental water allocations—restore overbank flow or are delivered to artificially disconnected wetlands. While a suite of monitoring methods is available, few programmes track continuous change in biota, mainly because repeated remote site visits can be prohibitively expensive.
2. In this paper, we propose a new approach to environmental flow monitoring, using ecoacoustic methods. We test acoustic monitoring of frog and waterbird responses to environmental water deliveries in the Goulburn Broken, a valley in the southern Murray–Darling river system. Response to three major environmental water deliveries within 2 years was monitored at four sites along Reedy swamp. Every 2 weeks, 30 s were recorded every 30 min, for a total of 24 hr.
3. We used two analysis strategies—manual counts of bird calls, as well as ecoacoustic indices, which describe the sonic properties of the acoustic spectrum at a site. Manual counts demonstrated that water-dependent birds were clearly responding to environmental water deliveries, whereas non-water-dependent species did not show any increases in activity. After restricting the analysis to the dawn chorus of birds and frogs, two acoustic indices (the median amplitude and the acoustic complexity index) showed responses to watering events.
4. Ecoacoustic methods show promise for continuous response monitoring to environmental water allocations. However, the first strategy—manual annotation of calls—might be too labour intensive for standard monitoring programmes. The second strategy—index-based approaches—can also detect ecological responses, although further investigation using control sites is needed. Automated call classifiers are an alternative that is currently being developed for endangered species. We also encourage simultaneous monitoring of the soundscape above and under water.

     

Vocal communication of wild bonnet macaques (Macaca radiata)

Field observations and spectrographic analyses of sound recordings of South Indian bonnet macaques revealed a vocal repertoire of at least 25 basic patterns. The repertoire consists of well separated sound classes and acoustic categories connected by structural intergradation. Besides structural variations within and between different elements of the repertoire, the vocal system ofMacaca radiata is characterized by regular combinations of particular basic patterns. These combinations occurred not only between calls of similar structure and function but also between calls usually emitted in entirely different social contexts. According to the qualitative analysis, sex-specific asymmetries of the vocal behaviour were less pronounced than age-dependent characteristics. The comparison of clear call vocalizations ofMacaca radiata andM. fuscata revealed significant species-specific differences on the structural and the behavioural level. Evaluations of the structural features of alarm calls of various macaque species imply marked differences between members of thefascicularis group andsinica group on one hand and thesilenus group andarctoides group on the other.     

Vocal divergence between two disjunct populations of Giant Antshrike (Batara cinerea) is related to environmental conditions

Variation in the avian vocal signals emitted may have a significant impact on species evolution. Vocal divergence in suboscine species like Giant Antshrike (Batara cinerea) may be associated with selective adaptation, since learning has little influence on vocal development and variation in acoustic structure cannot be attributed to learning deviation. Consequently, tracheophone suboscine species are ideal subjects to explore vocal variation, since cultural evolution does not seem to influence vocal variation in this group. Environmental conditions may determine the selection of vocal features because acoustic transmission could be attenuated under certain conditions of temperature, humidity and vegetation cover. Here, we examined vocalizations of Giant Antshrike and assessed possible acoustic variations between two disjunct groups (Andean and Atlantic), correlating the differences to the environmental structure. Univariate and multivariate analysis show temporal and spectral differences between both groups. Andean individuals produce vocalizations with longer duration, faster trill rates, shorter syllable duration and higher frequencies. Environmental features are different between the two populations, and they are correlated to the acoustic structure of vocalizations. Temporal variations arise directly from climatic influence, while spectral divergence could be a secondary effect of morphological adaptation to habitat structure.     

FishSounds Version 1.0: A website for the compilation of fish sound production information and recordings

Many fish species use active sound production for communication in numerous behaviors. Additionally, likely all fish can make passive or incidental sounds that may also serve some signal functions. Despite the ecological importance of fish sounds, their evident passive acoustic monitoring applications, and extensive endeavors to document soniferous fish diversity, the fields of bioacoustics and ichthyology have historically lacked an easily accessible, global inventory of known fish sound production. To alleviate this limitation, we developed http://FishSounds.net, a website that compiles and disseminates fish sound production information and recordings. FishSounds Version 1.0 launched in 2021, cataloging documented examinations for active and passive sound production for 1185 fish species from 837 references as well as 239 exemplary audio recordings. FishSounds allows users to search by taxa (e.g., family or common name), geographical distribution (e.g., region or water body), sound type, or reference. We have also made available the code used to create the website, so that it may be used in other data-sharing efforts—acoustic or otherwise. Subsequent versions of the website will update the data and improve the website functionality. FishSounds will advance research into fish behavior, passive acoustic monitoring, and human impacts on underwater soundscapes; serve as a resource for public outreach; and provide the foundation needed to investigate more of the 96% of fish species that lack published examinations of sound production. We further hope the FishSounds design, implementation, and engagement strategies will serve as a model for future data management and sharing efforts.     

Manipulations of sensory experiences during development reveal mechanisms underlying vocal learning biases in zebra finches

Biological predispositions in learning can bias and constrain the cultural evolution of social and communicative behaviors (e.g., speech and birdsong), and lead to the emergence of behavioral and cultural “universals.” For example, surveys of laboratory and wild populations of zebra finches (Taeniopygia guttata) document consistent patterning of vocal elements (“syllables”) with respect to their acoustic properties (e.g., duration, mean frequency). Furthermore, such universal patterns are also produced by birds that are experimentally tutored with songs containing randomly sequenced syllables (“tutored birds”). Despite extensive demonstrations of learning biases, much remains to be uncovered about the nature of biological predispositions that bias song learning and production in songbirds. Here, we examined the degree to which “innate” auditory templates and/or biases in vocal motor production contribute to vocal learning biases and production in zebra finches. Such contributions can be revealed by examining acoustic patterns in the songs of birds raised without sensory exposure to song (“untutored birds”) or of birds that are unable to hear from early in development (“early‐deafened birds”). We observed that untutored zebra finches and early‐deafened zebra finches produce songs with positional variation in some acoustic features (e.g., mean frequency) that resemble universal patterns observed in tutored birds. Similar to tutored birds, early‐deafened birds also produced song motifs with alternation in acoustic features across adjacent syllables. That universal acoustic patterns are observed in the songs of both untutored and early‐deafened birds highlights the contribution motor production biases to the emergence of universals in culturally transmitted behaviors.     

The effect of catchment urbanization on nutrient uptake and biofilm enzyme activity in Lake Superior (USA) tributary streams

We compared landscape, habitat, and chemistry variables with nutrient spiraling and biofilm extracellular enzyme activity (EEA), to assess the response of nine Lake Superior tributaries to the level of urbanization in their catchments. We found no significant correlation between uptake metrics for NH₄ ⁺ and PO₄ ^3? and the level of catchment urbanization. NH₄ ⁺ and PO₄ ^3– uptake velocities (V _f) were, however, positively correlated with biofilm EEA and with biofilm respiration (DHA). In general, biofilm EEA was negatively correlated with indicators of increased urbanization (e.g., % impervious surface cover and Cl^? concentration) and positively correlated with % forest cover. Biofilm respiration measured as dehydrogenase activity (DHA) decreased with indicators of increased urbanization (e.g., % ISC, storm sewer length, % of the stream channel shaded by the riparian canopy, and Cl^?) and increased with non-urban indicators (e.g., % forest, % wetland, and stream width and depth). Regression of V _f and uptake rate (U) versus ambient nutrient concentrations indicated phosphorus limitation in the study streams, a result supported by regression biofilm peptidase versus phosphatase activity. There was no evidence of NH₄ ⁺ saturation or limitation. This is the first study to demonstrate correlations between nutrient uptake and biofilm EEA in streams, with linkages to catchment-scale disturbances.     

Predicting Achievable Fundamental Frequency Ranges in Vocalization Across Species

Vocal folds are used as sound sources in various species, but it is unknown how vocal fold morphologies are optimized for different acoustic objectives. Here we identify two main variables affecting range of vocal fold vibration frequency, namely vocal fold elongation and tissue fiber stress. A simple vibrating string model is used to predict fundamental frequency ranges across species of different vocal fold sizes. While average fundamental frequency is predominantly determined by vocal fold length (larynx size), range of fundamental frequency is facilitated by (1) laryngeal muscles that control elongation and by (2) nonlinearity in tissue fiber tension. One adaptation that would increase fundamental frequency range is greater freedom in joint rotation or gliding of two cartilages (thyroid and cricoid), so that vocal fold length change is maximized. Alternatively, tissue layers can develop to bear a disproportionate fiber tension (i.e., a ligament with high density collagen fibers), increasing the fundamental frequency range and thereby vocal versatility. The range of fundamental frequency across species is thus not simply one-dimensional, but can be conceptualized as the dependent variable in a multi-dimensional morphospace. In humans, this could allow for variations that could be clinically important for voice therapy and vocal fold repair. Alternative solutions could also have importance in vocal training for singing and other highly-skilled vocalizations.     

Blue phosphorescent iridium complexes based on 2-(fluoro substituted phenyl)-4-methylpyridines: Synthesis, crystal structure, and photophysics

A series blue phosphorescent emitting materials based on 2-(fluoro substituted phenyl)-4-methylpyridine as the cyclometalated ligands have been synthesized and characterized. The complexes have the general structure (C^{^}N)₂Ir(pic), where C^{^}N is a monoanionic cyclometalating ligand (e.g., 2-(2,4-difluorophenyl)-4-methylpyridine (24f₂pmpyH), 2-(3,4-difluorophenyl)-4-methylpyridine (34f₂pmpyH), 2-(3,5-difluorophenyl)-4-methylpyridine (35f₂pmpyH), and 2-(3,4,5-trifluorophenyl)-4-methyl-pyridine (345f₃pmpyH)), pic is 2-picolinic acid. The absorption, emission, cyclic voltammetry and thermostability of the complexes were systematically investigated. The (46f₂pmpy)₂Ir(pic) has been characterized using X-ray crystallography and the electronic ground state calculated using B3LYP density functional theory. HOMO levels are a mixture of Ir and 2-(fluoro phenyl)-4-methylpyridine ligand orbitals, while the LUMO is predominantly pic ligand based. Introduction of fluorine atoms and methyl group into ppy ligand and changing in position of F substituents in phenyl ring can finely tune emission of the complexes, showing bright blue-to-green luminescence at a wavelength of 463-501 nm at room temperature in CH₂Cl₂.     

Calling at the highway: The spatiotemporal constraint of road noise on Pacific chorus frog communication

Loss of acoustic habitat due to anthropogenic noise is a key environmental stressor for vocal amphibian species, a taxonomic group that is experiencing global population declines. The Pacific chorus frog (Pseudacris regilla) is the most common vocal species of the Pacific Northwest and can occupy human‐dominated habitat types, including agricultural and urban wetlands. This species is exposed to anthropogenic noise, which can interfere with vocalizations during the breeding season. We hypothesized that Pacific chorus frogs would alter the spatial and temporal structure of their breeding vocalizations in response to road noise, a widespread anthropogenic stressor. We compared Pacific chorus frog call structure and ambient road noise levels along a gradient of road noise exposures in the Willamette Valley, Oregon, USA. We used both passive acoustic monitoring and directional recordings to determine source level (i.e., amplitude or volume), dominant frequency (i.e., pitch), call duration, and call rate of individual frogs and to quantify ambient road noise levels. Pacific chorus frogs were unable to change their vocalizations to compensate for road noise. A model of the active space and time (“spatiotemporal communication”) over which a Pacific chorus frog vocalization could be heard revealed that in high‐noise habitats, spatiotemporal communication was drastically reduced for an individual. This may have implications for the reproductive success of this species, which relies on specific call repertoires to portray relative fitness and attract mates. Using the acoustic call parameters defined by this study (frequency, source level, call rate, and call duration), we developed a simplified model of acoustic communication space–time for this species. This model can be used in combination with models that determine the insertion loss for various acoustic barriers to define the impact of anthropogenic noise on the radius of communication in threatened species. Additionally, this model can be applied to other vocal taxonomic groups provided the necessary acoustic parameters are determined, including the frequency parameters and perception thresholds. Reduction in acoustic habitat by anthropogenic noise may emerge as a compounding environmental stressor for an already sensitive taxonomic group.     

Extrapair paternity in chestnut-sided warblers is correlated with consistent vocal performance

The elaborateness of many bird songs is commonly presumed tohave evolved under the influence of sexual selection by femalemate choice. Thus, aspects of acoustic diversity, such as songrepertoire size, are seen as likely targets of female choice.In many songbird species with song repertoires, however, therepertoires are small. In such species, female choice mightbe based on song features other than, or in addition to, songdiversity. To investigate this conjecture, I assessed singingand paternity in a population of chestnut-sided warblers (Dendroicapensylvanica), a species in which song repertoires are of modestsize. Twenty-two song traits were evaluated to determine whichones best predicted male extrapair reproductive success. Thecandidate traits encompassed measures of song diversity (e.g.,song repertoire size), gross-scale song performance (e.g., singingrate), and fine-scale song performance (e.g., variability amongsongs in a bout). Regression analysis revealed that the bestpredictor of extrapair success was singing with little variability.In particular, the most successful males sang with consistentpitch and timing, as well as high pitch. The greater extrapairsuccess of males with more consistent vocal performance maybe due to female preference for such performance, which couldbe an indicator of male quality.     

Vocal-tract filtering by lingual articulation in a parrot

Human speech and bird vocalization are complex communicative behaviors with notable similarities in development and underlying mechanisms. However, there is an important difference between humans and birds in the way vocal complexity is generally produced. Human speech originates from independent modulatory actions of a sound source, e.g., the vibrating vocal folds, and an acoustic filter, formed by the resonances of the vocal tract (formants). Modulation in bird vocalization, in contrast, is thought to originate predominantly from the sound source, whereas the role of the resonance filter is only subsidiary in emphasizing the complex time-frequency patterns of the source (e.g., but see ). However, it has been suggested that, analogous to human speech production, tongue movements observed in parrot vocalizations modulate formant characteristics independently from the vocal source. As yet, direct evidence of such a causal relationship is lacking. In five Monk parakeets, Myiopsitta monachus, we replaced the vocal source, the syrinx, with a small speaker that generated a broad-band sound, and we measured the effects of tongue placement on the sound emitted from the beak. The results show that tongue movements cause significant frequency changes in two formants and cause amplitude changes in all four formants present between 0.5 and 10 kHz. We suggest that lingual articulation may thus in part explain the well-known ability of parrots to mimic human speech, and, even more intriguingly, may also underlie a speech-like formant system in natural parrot vocalizations.