Acoustic Adaptation Hypothesis Research Articles

Sex and environment shape cochlear sensitivity in human populations worldwide

Hearing remains an underexplored aspect of human evolution. While the growing prevalence of hearing issues worldwide highlights the need to investigate factors beyond age, ototoxic substances, and recreational noise— factors affecting only a subset of the population —the role of environmental influences remains relatively unaddressed. In contrast, hearing and vocalizations have been extensively studied in many vertebrates through the Acoustic Adaptation Hypothesis, which suggests that acoustic communication adapts to the structure of the immediate environment. To explore how the environment shapes the ear’s ability to process sound, studying the cochlea is essential since it is responsible for capturing, amplifying, and converting sound waves into electrical signals. Cochlear sensitivity can be measured using Transient-Evoked Otoacoustic Emissions (TEOAE), which assess the cochlea’s ability to produce and transmit an acoustic response after sound stimulation. By analyzing TEOAE profiles, we gain valuable insights into how the cochlea responds to external auditory stimuli. We evaluated the influence of both endogenous (age, sex, ear side) and exogenous factors (ethnicity, environment, language) on cochlear sensitivity by collecting TEOAE data from 448 healthy individuals across 13 global populations in Ecuador, England, Gabon, South Africa, and Uzbekistan, living in diverse environments. For each individual, we derived six acoustic metrics from these TEOAE profiles to characterize the amplitude and frequency spectrum of cochlear sensitivity. Our results show that amplitude is primarily influenced by sex (up to 2 dB) and environment (up to 3.6 dB), followed by age and ear side. The frequency spectrum is determined exclusively by exogenous factors, with environment— particularly altitude, and urban versus rural settings —being the most significant. These findings challenge existing assumptions and highlight the need to consider both biological and environmental factors when studying auditory processes.

The adaptation and fitness costs to urban noise in the calls of the tree sparrow (Passer montanus)

Acoustic communication is one of the primary ways birds transmit and acquire important information. Birds living in urban environments are limited in the transmission and recognition of vocalizations due to intense low-frequency anthropogenic noise, but the Acoustic Adaptation Hypothesis (AAH) suggests that birds mitigate the masking effects of noise by modifying the structure and properties of their vocalizations. Although these adaptations can increase the efficiency of communication, they also impose potential fitness costs on the sender and receiver, which can negatively impact survival. The contact and alarm calls of tree sparrows have a frequency range of 1–10 kHz, which makes them likely to be partially masked by urban noise, limiting communication between individuals and interactions within populations. Thus, based on the AAH, we examined the modifications of contact and alarm calls in response to urban noise and confirmed the potential fitness costs of these modifications in tree sparrows. We recorded two contact calls and an alarm call at 80 sites with varying urban noise levels in Gwangju, Naju, and Damyang from March to April 2023. Both types of contact calls tended to have higher peak frequencies and shorter durations as urban noise increased. Alarm calls tended to increase in the number of notes and duration with increasing urban noise. These results indicate that tree sparrows respond to noisy environments through modifications of the spectral and temporal characteristics of their vocalizations. However, these adaptations impose potential fitness costs on both the sender and the receiver.

Acoustic ecology of anuran communities across Andean biomes: unveiling the soundscape of Northeastern Colombia

ABSTRACT Vocalisation acts as a primary communication mechanism in anurans, enabling the transmission of information between individuals in a community, facilitating mutual recognition, territorial dispute resolution, mate selection, and prevention of hybridisation. The interaction between habitat characteristics and species composition plays a significant role in shaping the acoustic structure of anuran communities. This study aims to characterise the advertisement calls of anuran species distributed in the Pamplonita River Basin, northeastern Colombia, and to examine how competition and habitat features affect their acoustic structure. It is proposed that environmental selection pressures, as outlined by the Acoustic Adaptation Hypothesis (AAH), and acoustic competition, as described by the Acoustic Niche Hypothesis (ANH), both influence the acoustic structure of communities. Descriptive and multivariate statistical analyses were employed to characterise the calls of species from five representative Andean biome localities, evaluating both hypotheses. A total of 23 species, representing 6 families and 13 genera, were recorded and described, including three candidate species and first-time descriptions for five species. The analyses revealed a clear separation among species based on their call characteristics, supporting the ANH. Furthermore, species’ vocalisations varied according to the specific environmental conditions of each habitat, lending support to the AAH.

Niche-related processes explain phylogenetic structure of acoustic bird communities in Mexico.

Acoustic communities are acoustically active species aggregations within a habitat, where vocal interactions between species can interfere their communication. The acoustic adaptation hypothesis (AAH) explains how the habitat favors the transmission of acoustic signals. To understand how bird acoustic communities are structured, we tested the effect of habitat structure on the phylogenetic structure, and on the phylogenetic and vocal diversity of acoustic communities in a semi-arid zone of Mexico. From autonomous recordings in three types of vegetation (crop fields, tetecheras, and mesquiteras), which differ in terms of complexity and canopy openness, we evaluated sound attenuation, and estimated metrics of phylogenetic structure and diversity as well as acoustic diversity with the use of two indices. Mesquiteras showed greater vegetation density, more attenuation, more vocal diversity, as well as a phylogenetic structure that tended towards overdispersion, in contrast to crop fields that showed less vegetation density, less attenuation, less vocal diversity and more phylogenetic relatedness, while tetecheras showed intermediate patterns. Phylogenetic structure was explained by vegetation density and excess attenuation. The higher vocal diversity, phylogenetic structure tended towards overdispersion. These results suggest a role for environmental filters in the crop fields, where more closely related species with similar vocal characteristics coexist (supporting AAH), and probably competitive exclusion in the mesquiteras, where more distantly related species coexist, promoting vocal diversity. This study offers information about the influence of habitat on the acoustic community structure, which could inform our understanding of the distribution of species from acoustic perspective.

Innovative microphone transmitter reveals differences in acoustic structure between broadcast and whisper songs of Myadestes obscurus (ʻŌmaʻo)

Abstract Low-amplitude “whisper songs” are a taxonomically broad phenomenon in birds that could play an important role in the suite of behaviors birds use to communicate. Due to its cryptic nature, there are inherent difficulties in capturing high-quality whisper song recordings without interrupting natural behaviors. Thus, whisper song acoustic structure is poorly understood and its potential function remains the subject of debate. Here, we present one of the first quantitative assessments of the acoustic structure of whisper song in birds. Using an innovative microphone transmitter, we collected high-quality recordings of broadcast and whisper songs from the Myadestes obscurus (ʻŌmaʻo), a thrush species endemic to the Island of Hawai‘i. The transmitter was attached to the birds and broadcasted radio-signals of all vocalizations produced by the individual to distances over 100 m away that minimized disruption of the birds’ normal behavior while recording. We demonstrate that M. obscurus whisper songs are a distinct class of vocalization that differ from broadcast songs in acoustic characteristics beyond amplitude, such as song length, frequency, and length of silent intervals between notes. These findings, in conjunction with habitat-associated variation in the rate at which M. obscurus emit these vocalization classes, indicate broadcast and whisper songs likely serve separate functions. This work provides evidence supporting the acoustic adaptation hypothesis that posits that densely vegetated habitats promote the evolution of songs with specific acoustic features that maintain signal integrity as the sound propagates through the environment.

Allometric Constraint Predominates Over the Acoustic Adaptation Hypothesis in a Radiation of Neotropical Treefrogs.

Male frogs emit stereotypical advertisement calls to attract mates and deter conspecific rivals. The evolution of these calls is thought to be linked to anatomical constraints and the acoustic characteristics of their surroundings. The acoustic adaptation hypothesis (AAH) posits that species evolve calls that maximize propagation distance and reduce signal degradation in the environment where they are emitted. We applied phylogenetic comparative analyses to study the association of body size, vegetation density, type of aquatic ecosystem, and calling site on the evolution of acoustic traits in Cophomantini, a large radiation of Neotropical treefrogs (Hylidae). We obtained and analyzed body size, acoustic, and habitat data from a total of 112 species (58% of Cophomantini), using the most inclusive available phylogeny. We found a significant negative correlation between peak frequency, body size, and calling site, but contrary to the predictions of the AAH, we did not find support for associations among call traits and environmental characteristics. Although spectral allometry is explained by an anatomical constraint, it could also be maintained by female choice. We recommend that future studies strive to incorporate factors such as female mate preferences, eavesdropping by predators or parasites, and genetic drift.

Meta-analysis of the acoustic adaptation hypothesis reveals no support for the effect of vegetation structure on acoustic signalling across terrestrial vertebrates.

Acoustic communication plays a prominent role in various ecological and evolutionary processes involving social interactions. The properties of acoustic signals are thought to be influenced not only by the interaction between signaller and receiver but also by the acoustic characteristics of the environment through which the signal is transmitted. This conjecture forms the core of the so-called "acoustic adaptation hypothesis" (AAH), which posits that vegetation structure affects frequency and temporal parameters of acoustic signals emitted by a signaller as a function of their acoustic degradation properties. Specifically, animals in densely vegetated "closed habitats" are expected to produce longer acoustic signals with lower repetition rates and lower frequencies (minimum, mean, maximum, and peak) compared to those inhabiting less-vegetated "open habitats". To date, this hypothesis has received mixed results, with the level of support depending on the taxonomic group and the methodology used. We conducted a systematic literature search of empirical studies testing for an effect of vegetation structure on acoustic signalling and assessed the generality of the AAH using a meta-analytic approach based on 371 effect sizes from 75 studies and 57 taxa encompassing birds, mammals and amphibians. Overall, our results do not provide consistent support for the AAH, neither in within-species comparisons (suggesting no overall phenotypically plastic response of acoustic signalling to vegetation structure) nor in among-species comparisons (suggesting no overall evolutionary response). However, when considering birds only, we found weak support for the AAH in within-species comparisons, which was mainly driven by studies that measured frequency bandwidth, suggesting that this variable may exhibit a phenotypically plastic response to vegetation structure. For among-species comparisons in birds, we also found support for the AAH, but this effect was not significant after excluding comparative studies that did not account for phylogenetic non-independence. Collectively, our synthesis does not support a universal role of vegetation structure in the evolution of acoustic communication. We highlight the need for more empirical work on currently under-studied taxa such as amphibians, mammals, and insects. Furthermore, we propose a framework for future research on the AAH. We specifically advocate for a more detailed and quantitative characterisation of habitats to identify frequencies with the highest detection probability and to determine if frequencies with greater detection distances are preferentially used. Finally, we stress that empirical tests of the AAH should focus on signals that are selected for increased transmission distance.

The Acoustic adaptation hypothesis does not support the occurrence of common songs in a neotropical urban bird species

ABSTRACT The Acoustic Adaptation Hypothesis indicates that vocalisations will have acoustic characteristics that maximise their transmission within the habitat where they are produced. Therefore, vocalisations of the same species are expected to vary between habitats if the habitats vary in structure. We conducted a sound transmission experiment to analyse if the common songs of the White-eared ground sparrow, Melozone leucotis, an urban bird species, differ between populations because they are adapted to the characteristics of each habitat to maximise their transmission. The experiment was conducted in four isolated populations within the urban areas of Costa Rica with different habitats: secondary forests, coffee plantations, gardens and thickets. In each population, we reproduced the three common songs of each population, and we compared four song degradation measures (excess attenuation, blur ratio, signal-to-noise ratio, and tail-to-signal ratio). Contrary to our expectations, our results contradicted the Acoustic Adaptation Hypothesis, since the common songs of each population did not transmit better in their own habitat, but the songs are adapted to transmit better in the original habitat. We suggest that common songs of this bird may be selected and maintained in each population by female selection.

Body size shapes song in honeyeaters.

Birdsongs are among the most distinctive animal signals. Their evolution is thought to be shaped simultaneously by habitat structure and by the constraints of morphology. Habitat structure affects song transmission and detectability, thus influencing song (the acoustic adaptation hypothesis), while body size and beak size and shape necessarily constrain song characteristics (the morphological constraint hypothesis). Yet, support for the acoustic adaptation and morphological constraint hypotheses remains equivocal, and their simultaneous examination is infrequent. Using a phenotypically diverse Australasian bird clade, the honeyeaters (Aves: Meliphagidae), we compile a dataset consisting of song, environmental, and morphological variables for 163 species and jointly examine predictions of these two hypotheses. Overall, we find that body size constrains song frequency and pace in honeyeaters. Although habitat type and environmental temperature influence aspects of song, that influence is indirect, likely via effects of environmental variation on body size, with some evidence that elevation constrains the evolution of song peak frequency. Our results demonstrate that morphology has an overwhelming influence on birdsong, in support of the morphological constraint hypothesis, with the environment playing a secondary role generally via body size rather than habitat structure. These results suggest that changing body size (a consequence of both global effects such as climate change and local effects such as habitat transformation) will substantially influence the nature of birdsong.

Changes in the acoustic structure of Australian bird communities along a habitat complexity gradient

Abstract Avian vocalizations have evolved in response to a variety of abiotic and biotic selective pressures. While there is some support for signal convergence in similar habitats that are attributed to adaptation to the acoustic properties of the environment (the “acoustic adaptation hypothesis,” AAH), there is also evidence for character displacement as a result of competition for signal space among coexisting species (the “acoustic niche partitioning hypothesis”). We explored the acoustic space of avian assemblages distributed along six different habitat types (from herbaceous habitats to warm rainforests) in southeastern Queensland, Australia. We employed three acoustic diversity indices (acoustic richness, evenness, and divergence) to characterize the signal space. In addition, we quantified the phylogenetic and morphological structure (in terms of both body mass and beak size) of each community. Acoustic parameters showed a moderately low phylogenetic signal, indicating labile evolution. Although we did not find meaningful differences in acoustic diversity indices among habitat categories, there was a significant relationship between the regularity component (evenness) and vegetation height, indicating that acoustic signals are more evenly distributed in dense habitats. After accounting for differences in species richness, the volume of acoustic space (i.e., acoustic richness) decreased as the level of phylogenetic and morphological resemblance among species in a given community increased. Additionally, we found a significantly negative relationship between acoustic divergence and divergence in body mass indicating that the less different species are in their body mass, the more different their songs are likely to be. This implies the existence of acoustic niche partitioning at a community level. Overall, while we found mixed support for the AAH, our results suggest that community-level effects may play a role in structuring acoustic signals within avian communities in this region. This study shows that signal diversity estimated by diversity metrics of community ecology based on basic acoustic parameters can provide additional insight into the structure of animal vocalizations.

Ecological factors drive the divergence of morphological, colour and behavioural traits in cactus wrens (Aves, Troglodytidae).

The study of ecological mechanisms influencing organisms' phenotypic variation is a central subject of evolutionary biology. In this study, we characterized morphological, plumage colour and acoustic variation in cactus wrens Campylorhynchus brunneicapillus throughout its distribution. We assessed whether Gloger's, Allen's and Bergmann's ecogeographical rules, and the acoustic adaptation hypothesis relate to geographical trait variation. We analysed specimen coloration in belly and crown plumage, beak shape and structural song characteristics. We tested whether the subspecific classification or the peninsular/mainland groups mirrored the geographical variation in phenotypes and whether ecological factors were associated with patterns of trait variation. Our results suggest that colour, beak shape and acoustic traits varied across the range, in agreement with two lineages described by genetics. The simple versions of Gloger's and Allen's rules are related to variations in colour traits and morphology. Conversely, patterns of phenotypic variation did not support Bergmann's rule. The acoustic adaptation hypothesis supported song divergence for frequency-related traits. Phenotypic variation supports the hypothesis of two taxa: C. affinis in the Baja California peninsula and C. brunneicapillus in the mainland. The ecological factors are associated with phenotypic trait adaptations, suggesting that divergence between lineages could result from ecological divergence.

Phenotypic differentiation in populations of a gladiator tree frog: environment, genetic drift and sexual selection

Abstract Phenotypic differentiation among animal populations is common, yet few studies have simultaneously examined the adaptive and neutral mechanisms behind it. Such evolutionary processes become more relevant in species with complex behaviours that undergo global and local selective pressures throughout their geographical range. Here we measured and compared morphological and acoustic variation across the distribution range of a Neotropical gladiator tree frog that shows elaborate reproduction (territoriality, complex courtship and female choice). We then incorporated molecular and landscape data to examine the roles of sexual selection, genetic drift and acoustic adaptation to the environment in call differentiation, i.e. the acoustic adaptation hypothesis (AAH). We found that calls varied more than morphology among populations, but differences in calls or morphological traits were not explained by genetic differentiation. We found no evidence for the AAH, but a significant relationship in the opposite direction regarding call frequencies suggests an indirect role of sexual selection. Differentiation on call traits that are associated with individual discrimination and/or female attraction also corroborated an important role of sexual selection. We show that multitrait and multimechanism approaches can elucidate intricate processes leading to phenotypic variation among individuals and populations. We emphasize that studies of species with complex reproductive behaviours across their range may provide insights into different selective pressures leading to phenotypic differentiation.

Assessment of the acoustic adaptation hypothesis in frogs using large‐scale citizen science data

AbstractAcoustic communication is vital to the survival and fitness of many vertebrates. While successful communication is reliant on acoustic signals reaching an intended receiver and maintaining content fidelity, propagating signals are attenuated by environmental factors such as habitat type. The acoustic adaptation hypothesis (AAH) predicts that the acoustic properties of signals are selected for optimal transmission in the habitats in which they propagate. To date, consistent evidence to support the theory is lacking, but studies have typically been primarily based on localized datasets with small sample sizes. Citizen science is emerging as a potential means to overcome the challenges associated with broad‐scale sampling, allowing us to assess the validity of the AAH in frogs on a continental scale. We analysed the male advertisement calls of 674 individual banjo frogs (Limnodynastes dorsalis, L. dumerilii, L. interioris and L. terraereginae) from across their range, pairing these citizen science data with remotely sensed measures of habitat complexity. While we detected considerable variation in acoustic structure within and among banjo frog species, this was not strongly correlated with habitat complexity. Thus, we found no support for the AAH. However, with our study spanning an area of over 1.7 million km2, we conducted the largest‐scale test of the AAH in frogs to date, contributing to the global understanding of acoustic signal evolution.

How do tree density and body size influence acoustic signals in Amazonian nurse frogs?

ABSTRACT The Acoustic Adaptation Hypothesis (AAH) predicts that acoustic signals emitted at sites with greater vegetation density should have spectral and temporal characteristics that increase signal transmission, but there is a pleiotropism related to body size: large animals produce signals with lower frequency. We used 238 advertisement calls of 34 populations of Amazonian nurse frogs from two Amazonian rainforests with different vegetation density to test if tree density influences the evolution of acoustic parameters. We used PGLS to test for relationships between acoustic traits and phenotypic, environmental and geographic predictors. Spectral and temporal features of calls have an allometric relationship with body size. We found a novel quadratic relationship between note duration and body size. The allometric relationship between dominant frequency and body size and a direct effect of tree density indicates that the evolutionary trajectories of Amazonian nurse frogs follow a general macro-evolutionary pattern as in birds. The temporal features of calls have opposite evolutionary trajectories to those predicted by AAH; frogs from lower tree density environments emit longer notes and have higher note rates than those from denser-tree environments. Subtle differences between Amazonian forest types can drive acoustic diversification of temporal and spectral features of calls at micro-evolutionary scales.

Landscape characteristics and predation risk influence spatial variation in auditory courtship of an upland game bird

ContextNumerous wildlife species use a polygynous mating system, where males use auditory courtship behaviors to secure breeding opportunities. The acoustic adaptation hypothesis, risk reward, and landscape of fear theories suggest spatial variation in male auditory courtship will be influenced by areas in landscapes where sound transmission is increased, and predation risk is reduced. However, it is often unclear what landscape features drive spatial variation in courtship behaviors.ObjectivesWe quantified the influence of predation risk, land cover type, and resource selection on spatial trends in the auditory courtship behavior (gobbling activity) of Eastern wild turkeys (Meleagris gallopavo silvestris).MethodsWe used 53,025 gobbles coupled with GPS locations from 111 turkeys and 36 coyotes (Canis latrans), and distance metrics associated with hunter activity and land cover type, to investigate influences of predation risk, resource selection, and land cover type on spatial variation in gobbling activity in Georgia, USA.ResultsDistance to public access during hunting was the most influential predictor of gobbling activity, wherein the expected number of daily gobbles increased by 40% for every 500 m farther from public access. Daily gobbles decreased by 22% for every 500 m farther away from private property during hunting. We failed to find significant effects of land cover type and coyote use but found limited evidence that areas with increased predicted probability of turkey use was associated with increased gobbling.ConclusionsPredation risk associated with increased anthropogenic disturbance had the greatest influence on gobbling activity. Our findings suggest that altering hunter access by closing roads to vehicle use, reducing hunter activity, or creating refuge areas on the landscape could positively influence gobbling activity.

Dialects in North American elk bugle calls: comparisons between source and translocated elk populations

AbstractIdentifying the factors shaping dialects can reveal selective pressures and cultural influences on acoustic signals. Translocations of species have been considered the “gold standard” for identifying population differences in vocalizations, including dialects. The North American elk (Cervus canadensis) is a species that has experienced numerous translocations, but no published studies exist on dialects in elk or any other ungulate species. Adult male North American elk utter an iconic vocalization during the breeding season, which is termed the bugle call due to the power, duration, and pitch of the sound. We investigated if dialect differences existed between three populations: a source population in Wyoming (N = 10 bulls, 132 calls) and translocated populations in Colorado (N = 13 bulls, 92 calls) and Pennsylvania (N = 20 bulls, 160 calls). Dialect differences existed between the populations in 9 of 10 measured variables, in both the frequency domain and time domain. Habitat factors (acoustic adaptation hypothesis) affecting sound transmission were inconsistently related to dialects in the populations. Genetic factors may be related to dialects, as the historically bottlenecked Pennsylvania population, with low heterozygosity and low allelic richness, exhibited the least variability in acoustic measures. Cultural transmission and vocal learning may also contribute to dialect development in this highly vocal, social ungulate species.

Habitat influence on the evolution of male mating vocalizations in subterranean and surface-dwelling rodents (Rodentia)

The acoustic adaptation hypothesis (AAH) is often tested between species from open and closed habitats. However, the acoustic differences are rather small and thus the evidence is ambiguous. We tested the AAH between subterranean and surface-dwelling species living in very different acoustic environments. Lower frequencies (<1 kHz) are transmitted best in subterranean burrows and there is a high-frequency cut off around 3 kHz. The other important factor influencing the frequencies of vocal signals is body size. Acoustic allometry – a negative relationship between body size and frequency of acoustic signals – indicates that larger species tend to produce sounds of lower frequencies than smaller species, due to their larger vocal apparatus. The present study shows, that acoustic allometry applies to subterranean as well as surface-dwelling rodents and that the environment influences the main frequency of their vocalization. Besides, the subterranean species tend to have lower vocal signals than surface-dwelling 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.

Environment rather than character displacement explains call evolution in glassfrogs.

The acoustic adaptation hypothesis (AAH) and ecological character displacement (ECD) are two potential mechanisms shaping call evolution that can predict opposite trends for the differentiation of signals. Under AAH, signals evolve to minimize environmental degradation and maximize detection against background noise, predicting call homogenization in similar habitats due to environmental constraints on signals. In contrast, ECD predicts greater differences in call traits of closely related taxa in sympatry because of selection against acoustic interference. We used comparative phylogenetic analyses to test the strength of these two selective mechanisms on the evolution of advertisement calls in glassfrogs, a highly diverse family of neotropical anurans. We found that, overall, acoustic adaptation to the environment may outweigh effects of species interactions. As expected under the AAH, temporal call parameters are correlated with vegetation density, but spectral call parameters had an unexpected inverse correlation with vegetation density, as well as an unexpected correlation with temperature. We detected call convergence among co-occurring species and also across multiple populations from the same species in different glassfrogs communities. Our results indicate that call convergence is common in glassfrogs, likely due to habitat filtering, while character displacement is relatively rare, suggesting that costs of signal similarity among related species may not drive divergent selection in all systems.

Testing the acoustic adaptation hypothesis with vocalizations from three mongoose species

Testing the acoustic adaptation hypothesis with vocalizations from three mongoose species