Variation In Acoustic Signals Research Articles

Relation of the forest fragment matrix and the variation of acoustic signals of three species of Arremon (Passeriformes: Oscines)

Species communication systems are sensitive to habitat and act as indicators of anthropogenic environmental degradation, as they function as an early warning of the effects of fragmentation on avifauna in short periods. In this way, the study of vocal patterns helps in understanding geographic variations and cultural evolution of populations. In this study we evaluated 270 recordings of three species belonging to the genus Arremon, which occur in the Brazilian Atlantic Forest: Arremon flavirostris, Arremon semitorquatus and Arremon taciturnus; with the aim of identifying changes in vocal characteristics between populations of the same species and verifying the relationship with the type of matrix surrounding the forest fragment. We found significant intraspecific differences in the vocal parameters of the three analyzed species. Thus, this study contributes to the taxonomic knowledge of the Arremon complex and provides information about the diversity of vocal signals of Brazilian species.

Testing drivers of acoustic divergence in cicadas (Cicadidae: Tettigettalna).

Divergence in acoustic signals may have a crucial role in the speciation process of animals that rely on sound for intra-specific recognition and mate attraction. The acoustic adaptation hypothesis (AAH) postulates that signals should diverge according to the physical properties of the signalling environment. To be efficient, signals should maximize transmission and decrease degradation. To test which drivers of divergence exert the most influence in a speciose group of insects, we used a phylogenetic approach to the evolution of acoustic signals in the cicada genus Tettigettalna, investigating the relationship between acoustic traits (and their mode of evolution) and body size, climate and micro-/macro-habitat usage. Different traits showed different evolutionary paths. While acoustic divergence was generally independent of phylogenetic history, some temporal variables' divergence was associated with genetic drift. We found support for ecological adaptation at the temporal but not the spectral level. Temporal patterns are correlated with micro- and macro-habitat usage and temperature stochasticity in ways that run against the AAH predictions, degrading signals more easily. These traits are likely to have evolved as an anti-predator strategy in conspicuous environments and low-density populations. Our results support a role of ecological selection, not excluding a likely role of sexual selection in the evolution of Tettigettalna calling songs, which should be further investigated in an integrative approach.

Geographical variation of social calls and vocal discrimination in male Himalayan leaf-nosed bats

Like birds and many other animals, bats produce diverse acoustic calls for social communication. Geographical variation in social acoustic signals and perceptual discrimination abilities are well studied in birds but largely unexplored in bats. In this study, we recorded male territorial calls of the great Himalayan leaf-nosed bat, Hipposideros armiger, from nine colonies at a large geographical scale and investigated the patterns and causes of geographical variation in acoustic signals. We also performed habituation−dishabituation playbacks to investigate whether males could discriminate between territorial calls of their own versus a foreign colony. Overall, our results showed significant geographical variation in calls across colonies. Neither climatic differences, morphological differences, geographical distances nor genetic distances between colonies explained the observed acoustic variation between colonies. A playback experiment indicated that males from eastern China were able to discriminate between calls of males from their own colony and those of males from a colony in southwestern China. This study provides the first experimental evidence that bats can discriminate geographical variation in social calls.

Geographic variation in marmots’ alarm calls causes different responses

Geographic variation in acoustic signals has been investigated for five decades to better understand the evolution of communication. When receivers are able to discriminate among signals and to react accordingly, geographic variation can have major impacts on the ability of conspecifics to communicate. Surprisingly, geographic variation in alarm calls and its consequences for the communication process have been so far neglected despite their crucial role on individual survival. Working with four wild populations of Alpine marmots (Marmota marmota), we found differences in the acoustic structure of their alarm calls. These differences cannot be explained by geographic or genetic distances but more likely by other mechanisms including random processes. Moreover, playback experiments provided evidence that receivers discriminate between alarm calls from their own versus other populations, with responses at lower intensity when the alarm calls played back originated from their own population. Research on the mechanistic causes of geographic variation and on the relationship between alarm call variation, familiarity, and intelligibility of signal and behavioral responses is now required to better understand how predation pressure, and more widely natural selection, could drive the evolution of communication. Dialects (i.e., geographic variation) can have major impacts on the ability of conspecifics to communicate. Surprisingly, dialects in alarm calls have been neglected despite their crucial role on survival of individuals. Alpine marmots have dialects in alarm calls and discriminate their own dialects from others, being more frightened by alarm calls from another population than by those from their own. Confronted with an unknown dialect, marmots may adopt a self-preserving strategy and choose to run away before assessing the danger.

Geographic variation in the duets of the Rufous-naped Wren (Campylorhynchus rufinucha) complex

Abstract Acoustic signals used in animal communication play a key role in mate attraction, species recognition, and territory defense. Variation in acoustic signals may reflect population structure, lack of gene flow, and phylogenetic relationships. In birds, the study of geographic variation in acoustic signals has been useful for elucidating potential factors involved in phenotypic divergence and for establishing species limits. However, most of the studies on geographic variation have focused on calls and solo songs, with few studies focusing on complex behaviors such as duets. In this study, we investigated the variation in the duets of the Rufous-naped Wren (Campylorhynchus rufinucha). Our results suggest that duets vary across the distribution range of the species complex, matching the 3 taxonomic groups previously suggested (rufinucha, humilis, and capistratus). We also found a marked song sexual dimorphism in 2 groups, rufinucha and humilis, that is lacking in capistratus. At the local level, we found that duets also vary among sites within groups, but less than between groups. Our results suggest that groups rufinucha and humilis sing the most similar duets, whereas capistratus performs the most divergent duets of the 3 groups. Further, when comparing duet variation across geography, we found that birds living closer to each other sing more similar duets. We suggest that the existence of 3 vocal lineages is probably the result of historical geographic isolation followed by other selective (i.e. sexual selection, social selection, habitat structure) and/or non-selective factors (i.e. drift, isolation by distance), and that variation found within groups may be the result of cultural drift or social selection.

Geographic variation in vocalisations of the Military Macaw in western Mexico

ABSTRACT Geographic variation in acoustic signals may arise in vocal learning species due to processes of cultural evolution and population dynamics, but few studies have evaluated geographic vocal variation for large-bodied non-oscine species such as parrots. We evaluated similarity in a contact call of the Military Macaw (Ara militaris) among three populations along the coast of Jalisco, Mexico. We compared contact calls among sites using two approaches i) analysis of specific acoustic parameter measures using GLMM on Principal Components; and ii) evaluation of spectrogram similarity using cross-correlation with a Mantel test to evaluate site and distance effects. Acoustic parameter analysis found that incorporating the site where recordings were obtained significantly explained variation in call features, for both the complete and reduced, balanced dataset. The spectrogram cross-correlations similarity analysis indicated an association with site in spectral similarity of calls, and that call similarity decreased with distance. Our results demonstrated the accumulation of small, fine-scale changes in Military Macaw calls with distance, suggesting that large-bodied non-oscines such as macaws may be able to maintain connectivity among sites by dispersal, facilitating call diffusion, while limited movements among some populations may account for the differentiation among sites in call features.

Multi-scale characteristics and gas-solid interaction among multiple beds in a dual circulating fluidized bed reactor system

To investigate the gas-solid mixing and interaction among reactors of Dual Circulating Fluidized Bed Reactor (DCFBR), the detecting methods of acoustic emission and pressure fluctuation are employed to study the effects of operating parameters including riser gas velocity, bubbling bed gas velocity and pot-seal gas velocity on the gas-solid behavior and multi-scale characteristics of the DCFBR system. The experimental results demonstrate that gas disturbance makes bed particles fully mixed and the intensity of inter-particle mixing increases as gas disturbance intensifies. Meanwhile, inter-particle mixing can also cause changes in voidage. Therefore, gas and solid phases in the reactor have a mutual effect on each other. In addition, the particle circulation rate varies as the operating gas velocity changes, which in turn causes variations in both particle and bubble behaviors in the riser and the bubbling bed with particles and bubbles interacting with each other. By combining the methods of Hurst and fractal dimension analysis, the multi-scale variation of acoustic signals in the upper and lower parts of the riser under fast fluidization is obtained. As the results reveal, there are certain differences in particle clusters and bubble phase behaviors between the upper and lower parts of the riser. The larger the particle cluster size, the more uneven the flow inside the bed, indicating an intensified effect of the inter-granular particle cluster. Moreover, the size of particle cluster, which is related to particle concentration, increases as the concentration intensifies.

Discovery of an acoustically locating parasitoid with a potential role in divergence of song types among sympatric populations of the bush cricket Mecopoda elongata

The bush cricket Mecopoda elongata provides a striking example of sympatric intraspecific divergence in mating signals. Five completely distinct song types are found in various parapatric and sympatric locations in South India. While there is convincing evidence that population divergence in M. elongata is being maintained as a result of divergence in acoustic signals, cuticular chemical profiles, and genital characters, the causes of the evolution of such divergence in the first place are unknown. We describe the discovery of a tachinid parasitoid with an orthopteroid hearing mechanism affecting M. elongata. This parasitoid may have a role in driving the extraordinary divergence that had occurred among M. elongata song types. Over two years we sampled individuals of three sympatric song types in the wild and retained individuals in captivity to reveal rates of parasitization. We found that all three song types were infected with the parasitoid but that there were significant differences among song types in their probability of being infected. The probability of tachinid parasitization also differed between the two sampling periods. Therefore, it is possible that parasitoid infection plays a role in song type divergence among sympatric bush cricket populations.

Characteristics of acoustic signals from lightning using a microphone array observation system

The acoustic signals of thunder provide information on the lightning channel, such as frequency, power spectra density, and images. In this study, to analyze the frequency variation in acoustic signals of thunder and to reconstruct the 3D lightning channel imaging, the short time Fourier transform (STFT) and differential time of arrival (DTOA) methods were used. The results showed that the frequency for four microphones varied from 4.88 Hz to 175.78 Hz. Furthermore, the range of power spectra density values for the four microphones was between -0.59 dB/Hz and -28.31 dB/Hz. This system can reconstruct 3D lightning channel imaging.

Understanding sources of variance and correlation among features of Bornean gibbon (Hylobates muelleri) female calls

Acoustic signals serve important functions in mate choice, resource defense, and species recognition. Quantifying patterns and sources of variation in acoustic signals can advance understanding of the evolutionary processes that shape behavioral diversity more broadly. Animal vocalization datasets are inherently multivariate and hierarchical, wherein multiple features are estimated from calls of many individuals across different recording locations. Patterns of variation within different hierarchical levels-notwithstanding the challenges they present for modeling and inference-can provide insight into processes shaping vocal variation. The current work presents a multivariate, variance components model to investigate three levels of variance (within-female, between-female, and between-site) in Bornean gibbon calls. For six of the eight features estimated from call spectrograms, between-female variance was the most important contributor to total variance. For one feature, trill rate, there were site-level differences, which may be related to geographic isolation of certain gibbon populations. There was also a negative relationship between trill rate and duration of the introduction, suggesting trade-offs in the production of gibbon calls. Given substantial inter-individual variation in gibbon calls, it seems likely that there has been selection to confer information regarding caller identity, but mechanisms leading to site-level variation in trill rate remain to be determined.

Geographic variation of contact calls suggest distinct modes of vocal transmission in a leaf-roosting bat

Populations that have historically been isolated from each other are expected to differ in some heritable features. This divergence could be due to drift (and other mechanisms of neutral evolution) or differential adaptation of populations to local conditions. Discriminating between these two evolutionary trajectories can be difficult, but when possible, such data provides critical insight into the evolutionary history of a species. Here, we examine the patterns of geographic variation of two contact signals regularly produced by disc-winged bats, Thyroptera tricolor, and discuss possible processes leading to the observed patterns of differentiation. We compared allopatric populations separated by an elevational barrier, and estimated genetic distance using nuclear microsatellite loci. Our findings revealed that the mountain ridge is permeable to gene flow. Acoustic divergence was significantly explained by genetic and spatial factors, supporting the notion that stochastic factors are the main drivers of signal divergence. Yet, we found different patterns of geographic variation between the two types of calls. We examine how this variability in the patterns of acoustic divergence may suggest distinct modes of signal transmission within and between populations (i.e., social vs genetic transmission). This work provides further support of the role of random change shaping communication systems in mammals, and highlights the importance of studying multiple elements of a species repertoire to evaluate the underlying processes driving signal evolution. Despite increasing interest in studying patterns of acoustic divergence, the relative contribution of adaptive and stochastic processes underlying variation of acoustic signals remain poorly understood, particularly in mammals. Our study examines signal divergence in Spix’s disc-winged bats, Thyoptera tricolor, with the goal of understanding the underlying processes driving signal evolution. Specifically, we studied whether the patterns of geographic variation of two social signals regularly emitted by T. tricolor are congruent with patterns of genetic distance among populations separated by a geographic barrier. We demonstrate that genetic and spatial distance explains acoustic variation, which points to stochastic processes as major drivers of signal divergence in T. tricolor. Notably, we found that the patterns of geographic variation differ between the two types of calls studied. We suggest that this variation results from distinct modes of vocal transmission within populations. Comparison of different signal types provides additional insight of social pressures shaping call design.

The ‘hot male’ hypothesis: do female crickets prefer males with increased body temperature in mate choice scenarios?

Insects have been extensively used as model systems to study mating preferences based on variation in acoustic signals. In many species, females perform phonotaxis towards attractive, long-range acoustic signals produced by males, whereas the final mating decision is based on an assessment of additional, multimodal, close-range cues. The production of acoustic signals is costly, because invested energy is inefficiently converted into acoustic power. Here, we investigated whether heat released as a by-product during song generation might serve as an additional cue during mate choice decisions. Males that broadcast highly energetic calling songs increased their thoracic temperature considerably above ambient temperatures. The use of this additional cue would turn the acoustic signal into an inherently bimodal one, indirectly indicating the quality of the sender. To test this hot male hypothesis, we performed trackball and Y-maze experiments with Anurogryllus muticus. For comparison, additional trackball experiments were conducted with Gryllus bimaculatus females. In all paradigms, females of both species showed no evidence of a preference for hot males and, therefore, we conclude that increases in thoracic temperature do not seem to play a role as a multimodal component in mate choice decisions in A. muticus.

Geographic variation in call structure, likelihood, and call-song associations across subspecies boundaries, migratory patterns, and habitat types in the Marsh Wren (Cistothorus palustris)

ABSTRACT Geographic variation in acoustic signals can be important in species divergence, especially the maintenance of prezygotic barriers to gene flow. Furthermore, selective pressures on acoustic signals likely vary both across geographic distances and among vocalizations used in different behavioral contexts. We described the call repertoire of 5 subspecies of Marsh Wren (Cistothorus palustris) in eastern North America and tested for variation in both the acoustic structure and likelihood of production of each call type at 3 functional–ecological levels: subspecies identity, migratory pattern, and habitat type. Three of the 7 described call types exhibited acoustic variation best explained by either migratory pattern or habitat type. These calls were used principally in courtship–territorial patrol contexts, whereas 4 calls that did not exhibit geographic variation were used in agonistic interactions. How often a call is used in a population may be indicative of the behavior or breeding phenology asso...

The effects of cultural drift on geographic variation in echolocation calls of the Chinese rufous horseshoe bat (Rhinolophus sinicus)

AbstractDrift, selection, or their combined effects commonly drive geographic variation in traits. Clarifying the relative roles of each process is a long‐standing research goal in evolutionary biology. Acoustic signals of bats are a phenotypic characteristic that plays an important role in social organization and species recognition. We extensively sampled the Chinese rufous horseshoe bat (Rhinolophus sinicus) throughout China and Vietnam and reconstructed a species phylogeny to better understand the patterns and causes of the geographic variation of acoustic signals. Our results showed that the resting frequency (RF) of calls varied with latitude, sex, and distance among different colony locations. RF differences were not correlated with genetic distance (based on only one nuclear locus and the mitochondrial locus), climatic factors (mean annual temperature and mean annual precipitable water), or body size, although differences in calls increased with distance among various populations. This suggests that cultural drift may play more important roles than genetic drift and acoustic adaptation in shaping acoustic differences within regions in R. sinicus.

Bill morphology and neutral genetic structure both predict variation in acoustic signals within a bird population

Lay Summary Bills not only influence what birds eat – they can also influence what birds sound like. Island Scrub-Jays, which only occur on one island, have bills that are adapted to food in their local habitat. Here, we report that females with longer, shallower bills (characteristic of pine habitats) produce calls that differ from females with shorter, deeper bills (characteristic of oak habitats), an association that may have aided the evolution of different bills within the island.

Acoustic differentiation of Shiho- and Naisa-type short-finned pilot whales in the Pacific Ocean.

Divergence in acoustic signals used by different populations of marine mammals can be caused by a variety of environmental, hereditary, or social factors, and can indicate isolation between those populations. Two types of genetically and morphologically distinct short-finned pilot whales, called the Naisa- and Shiho-types when first described off Japan, have been identified in the Pacific Ocean. Acoustic differentiation between these types would support their designation as sub-species or species, and improve the understanding of their distribution in areas where genetic samples are difficult to obtain. Calls from two regions representing the two types were analyzed using 24 recordings from Hawai'i (Naisa-type) and 12 recordings from the eastern Pacific Ocean (Shiho-type). Calls from the two types were significantly differentiated in median start frequency, frequency range, and duration, and were significantly differentiated in the cumulative distribution of start frequency, frequency range, and duration. Gaussian mixture models were used to classify calls from the two different regions with 74% accuracy, which was significantly greater than chance. The results of these analyses indicate that the two types are acoustically distinct, which supports the hypothesis that the two types may be separate sub-species.

Decoupled Evolution between Senders and Receivers in the Neotropical Allobates femoralis Frog Complex.

During acoustic communication, an audible message is transmitted from a sender to a receiver, often producing changes in behavior. In a system where evolutionary changes of the sender do not result in a concomitant adjustment in the receiver, communication and species recognition could fail. However, the possibility of an evolutionary decoupling between sender and receiver has rarely been studied. Frog populations in the Allobates femoralis cryptic species complex are known for their extensive morphological, genetic and acoustic variation. We hypothesized that geographic variation in acoustic signals of A. femoralis was correlated with geographic changes in communication through changes in male-male recognition. To test this hypothesis, we quantified male call recognition using phonotactic responses to playback experiments of advertisement calls with two, three and four notes in eight localities of the Amazonian basin. Then, we reconstructed the ancestral states of call note number in a phylogenetic framework and evaluated whether the character state of the most recent common ancestor predicted current relative responses to two, three and four notes. The probability of a phonotactic response to advertisement calls of A. femoralis males was strongly influenced by the call mid-frequency and the number of notes in most populations. Positive phonotaxis was complete for calls from each individual's population, and in some populations, it was also partial for allotopic calls; however, in two populations, individuals equally recognized calls with two, three or four notes. This evidence, in conjunction with our results from phylogenetic comparative methods, supports the hypothesis of decoupled evolution between sender and receiver in the male-male communication system of the A. femoralis complex. Thus, signal recognition appears to evolve more slowly than the calls.

Sensory Drive Mediated by Climatic Gradients Partially Explains Divergence in Acoustic Signals in Two Horseshoe Bat Species, Rhinolophus swinnyi and Rhinolophus simulator

Geographic variation can be an indicator of still poorly understood evolutionary processes such as adaptation and drift. Sensory systems used in communication play a key role in mate choice and species recognition. Habitat-mediated (i.e. adaptive) differences in communication signals may therefore lead to diversification. We investigated geographic variation in echolocation calls of African horseshoe bats, Rhinolophus simulator and R. swinnyi in the context of two adaptive hypotheses: 1) James’ Rule and 2) the Sensory Drive Hypothesis. According to James’ Rule body-size should vary in response to relative humidity and temperature so that divergence in call frequency may therefore be the result of climate-mediated variation in body size because of the correlation between body size and call frequency. The Sensory Drive Hypothesis proposes that call frequency is a response to climate-induced differences in atmospheric attenuation and predicts that increases in atmospheric attenuation selects for calls of lower frequency. We measured the morphology and resting call frequency (RF) of 111 R. simulator and 126 R. swinnyi individuals across their distributional range to test the above hypotheses. Contrary to the prediction of James’ Rule, divergence in body size could not explain the variation in RF. Instead, acoustic divergence in RF was best predicted by latitude, geography and climate-induced differences in atmospheric attenuation, as predicted by the Sensory Drive Hypothesis. Although variation in RF was strongly influenced by temperature and humidity, other climatic variables (associated with latitude and altitude) as well as drift (as suggested by a positive correlation between call variation and geographic distance, especially in R. simulator) may also play an important role.

Insularization effects on acoustic signals of 2 suboscine Amazonian birds

Environmental change may alter the communication systems of birds by imposing shifts in their acoustic signals. In tropical forests, vocally active species usually avoid overlapping signals in acoustic space by calling within narrow frequency ranges, whereas in forest islands a less saturated acoustic space may allow variation in acoustic signals. Some signals are also adapted to optimize its propagation in the prevailing habitat. Despite a growing understanding of what drives acoustic variation, it is unclear if human-induced insularization of natural landscapes can unleash alterations in avian communication systems. We investigated the variability of acoustic signal properties in 2 suboscines birds (Lipaugus vociferans and Tyranneutes virescens) in islands within an artificial lake created by the damming of the Uatuma River, in Brazilian Amazonia. We tested if signal variability was related to variation in acoustic community proxies (island area and isolation), and vegetation structure by surveying 13 variable-sized forest sites and 2 mainland continuous forest sites. Bandwidth variation in L. vociferans songs was related to island area and isolation (N = 67 inds), but these relationships were not observed in T. virescens songs (N = 69 inds). Additionally, the lowest and peak frequencies of songs of both species were higher in islands with greater tree basal area. In both species, temporal properties of songs were not associated with variation in island characteristics. Our study suggests that land-use changes may lead to alterations in particular traits of acoustic signals for species for which songs are innate.

Geographic variation in the time-frequency characteristics of high-frequency whistles produced by killer whales (Orcinus orca)

Investigating intraspecific variation in acoustic signals can indicate the extent of isolation and divergence between populations and adaptations to local environments. Here we analyze the variation in killer whale high frequency (>17 kHz) whistles recorded off Norway, Iceland, and in the North Pacific. We used a combination of methods including multivariate comparisons of spectral and temporal parameters and categorization of contours to types. Our results show that spectral and temporal characteristics of high-frequency whistles recorded in the North Pacific show significant differences from whistles recorded in the Northeast Atlantic, being generally stereotyped, lower in frequency, and slightly longer in duration. Most high-frequency whistles from the North Pacific were downsweeps, whereas this was one of the least common types recorded in the Northeast Atlantic. The repertoire of whistles recorded in Norway was similar to Iceland, but whistles produced in Norway had significantly lower maximum frequency and frequency range. Most methods were able to discriminate between whistles of the North Pacific and the Northeast Atlantic, but were unable to consistently distinguish whistles from Iceland and Norway. This suggests that macro- and microgeographic differences in high-frequency whistles of killer whales may reflect historical geographic isolation between ocean basins and more recent divergence between adjacent populations.