Philosophical Transactions of the Royal Society B: Biological Sciences最新文献

Nonlinear phenomena (NLP) are often associated with high arousal and function to grab attention and/or signal urgency in vocalizations such as distress calls. Although biomechanical models and in vivo/ex vivo experiments suggest that their occurrence reflects the destabilization of vocal fold vibration under intense subglottal pressure and muscle tension, comprehensive descriptions of the dynamics of NLP occurrence in natural vocal signals are critically lacking. Here, to plug this gap, we report the timing, type, extent and acoustic context of NLP in 12 011 whines produced by Beagle puppies (Canis familiaris) during a brief separation from their mothers. Within bouts of whines, we show that both the proportion of time vocalizing and the number of whines containing NLP, especially those with chaos, increase with time since separation, presumably reflecting heightened arousal. Within whines, we show that NLP are typically produced during the first half of the call, following the steepest rises in pitch (fundamental frequency, f_o) and amplitude. While our study reinforces the notion that NLP arise in calls due to instabilities in vocal production during high arousal, it also provides novel and efficient analytical tools for quantifying nonlinear acoustics in ecologically relevant mammal vocal communication contexts.This article is part of the theme issue 'Nonlinear phenomena in vertebrate vocalizations: mechanisms and communicative functions'.

As acoustic markers of emotional state, nonlinear phenomena (NLP) are commonly found in the calls that young mammals produce to solicit attention from their parents. However, data are lacking to assess the ontogeny of these NLP during early development, including the extent to which these acoustic cues vary with the age and sex of the emitter. In the present study, we evaluated the occurrence of NLP in the contact calls that northern elephant seal (Mirounga angustirostris) pups emit to solicit maternal care during the three-week period of maternal dependence. We found that five types of NLP are present at an early age. The relative occurrence of these NLP types varies with pup age, with more biphonation, chaos and subharmonics as pups get older, and fewer vibrato-like frequency-modulated components varying with both age and sex. Our results suggest that developmental changes-including body growth-facilitate increased flexibility in the vocal apparatus, which subsequently impacts the production of certain types of NLP. The production of nonlinear components within the calls of rapidly growing elephant seal pups is likely linked to their arousal state, which in turn is related to their high demand for maternal care. This can fluctuate throughout the lactation period and vary between male and female pups.This article is part of the theme issue 'Nonlinear phenomena in vertebrate vocalizations: mechanisms and communicative functions'.

Nonlinear phenomena (NLP) in animal vocalizations typically present as abrupt departures from normative controlled voicing. They occur most commonly in loud vocalizations, often in contexts of high arousal, including alarm, aggression, fear or distress, or in elaborate displays of territory or competitive ability. They therefore invite interpretation as 'mistakes' that evince loss of vocal control resulting from effortful, emotional 'over-driving' of the vocal system. However, vocal over-driving may be more flexible and purposeful, representing an alternative functional mode of voice control if NLP can benefit signallers in some contexts. The latter perspective is first elaborated with examples from non-human primates before turning to cases where NLP truly do evince loss of vocal control that may then 'leak' cues to signaller quality or condition. To support future frameworks to study and understand the different domains where NLP occur, a functional distinction is emphasized that turns on whether high-amplitude, effortful voicing-which inherently predisposes NLP-is at the discretion of the signaller such that the focus is on the adaptive production of NLP, or whether effortful voicing is effectively forced upon signallers by other dictates of the context itself, changing the focus to being the adaptive avoidance of NLP.This article is part of the theme issue 'Nonlinear phenomena in vertebrate vocalizations: mechanisms and communicative functions'.

Nonlinear phenomena (NLP) are widely observed in mammal vocalizations. One prominent, albeit rarely empirically tested, theory suggests that NLP serve to communicate individual emotional states. Here, we test this 'emotional hypothesis' by assessing NLP production in the vocalizations of chimpanzees and bonobos across various social contexts. These two species are relevant to test this hypothesis since bonobos are more socially opportunistic than chimpanzees. We found that both species produced, albeit at different frequencies, the same five distinct NLP types. Contextual valence influenced NLP production in both species with negative valence being associated with more frequent NLP production than positive and neutral valence. In contrast, using aggression severity and caller role as proxies for arousal, we found that in bonobos, but not in chimpanzees, vocalizations uttered during contact aggression or from victims and females contained more NLP. In contrast, the type of NLP produced was neither influenced by valence nor arousal in either species. Our study supports the emotional hypothesis regarding the occurrence of NLP production in mammals, particularly in opportunistics such as bonobos. This reinforces the hypothesis of an adaptative role of NLP in animal communication and prompts further investigations into their communicative functions.This article is part of the theme issue 'Nonlinear phenomena in vertebrate vocalizations: mechanisms and communicative functions'.

The recognition that nonlinear phenomena, including subharmonics, bifurcations and deterministic chaos, are present in human and animal vocalizations is a relatively recent one. I give a brief history of this revolution in our understanding of the voice, based on interviews with some of the key players and personal experience. Most of the key concepts and mathematical principles of nonlinear dynamics were already well worked out in the early 1980s. In the early 1990s, physicist Hanspeter Herzel and colleagues in Berlin recognized that these principles are applicable to the human voice, initially to baby cries. The physics and physiology underlying many of these nonlinear phenomena had remained mysterious up until then. This insight was later generalized to animal vocalizations. Nonlinear phenomena play a relatively peripheral role in most human vocal communication but are a common feature of many animal vocalizations. The broad recognition of the existence of nonlinear vocalizations, and the quantitative study of their production and perception, has now fuelled important and exciting advances in our understanding of animal communication. I concentrate on how the core concepts came into focus, and on their initial application to an ever-wider circle of call types and species, and end with a brief prospectus for the future.This article is part of the theme issue 'Nonlinear phenomena in vertebrate vocalizations: mechanisms and communicative functions'.

Nonlinear phenomena (NLP) are common elements of mammalian vocalizations. Resulting from irregular sound production, they contribute to perceived harshness and are often present in calls conveying urgency or arousal. Initially dismissed as by-products of vocal production, NLP are increasingly recognized for their adaptive potential. However, NLP have never been the subject of a comprehensive review across vertebrate taxa. Here, we introduce NLP and examine developments in NLP studies in mammals. We found 220 papers published between 1962 and 2023, with publication rates increasing with time. The studies covered a wide range of taxonomic groups but were dominated by artiodactyls, carnivores, bats, rodents and primates. Tinbergen's questions offer a framework for future investigations, highlighting that while much research has been conducted on adaptive function, our understanding is still lacking in terms of ontogeny, mechanisms and evolution. The existing literature is a testimony to the importance of NLP in animal vocalizations. With the use of novel tools for analysis and playback studies, NLP research can become more cohesive and impactful, fostering better understanding among researchers. We look forward to a new age of NLP research, which we anticipate will lead to a paradigm shift in our understanding of vocal communication in mammals.This article is part of the theme issue 'Nonlinear phenomena in vertebrate vocalizations: mechanisms and communicative functions'.

Among air-breathing tetrapods, the most common sound production mechanism is flow-induced self-sustained tissue oscillation, aka voiced sound production, driven by inherently nonlinear physical processes. Some signature features like deterministic chaos have received particular attention in bioacoustics as nonlinear phenomena (NLP). However, one type of NLP that extends frequency ranges and enriches timbres has received much less focus in comparative bioacoustics: vocal registers. Controlled by muscle activity, vocal registers constitute distinct periodic vibratory states of vocal tissues. Transitions between vocal registers often lead to abrupt fundamental frequency jumps, which are, e.g., deliberately used in human alpine yodelling, for example. Theoretical work suggests that register transitions are caused by saddle-node-in-limit-cycle bifurcations. Here, we review the biophysical underpinnings of vocal registers and what signatures they leave in vocal fold kinematics and acoustics in the best studied species: humans. Apart from human speech and song, registers have been described only in a few animal taxa, but the occurrence of signature features suggests that vocal registers could be much more common across vertebrates than currently appreciated. We suggest that registers are a fundamental trait of voice production and that they are favoured in selection because they vastly extend and diversify the acoustic signalling space. This article is part of the theme issue 'Nonlinear phenomena in vertebrate vocalizations: mechanisms and communicative functions.'

I review a case study of marmots that contributed to the empirical basis of the nonlinearity and fear hypothesis, which explains why certain nonlinear acoustic phenomena (NLP) are produced in extremely high-risk situations and communicate high urgency. In response to detecting predatory threats, yellow-bellied marmots (Marmota flaviventer) emit alarm calls and, in some situations, emit fear screams. Prior work on marmots has shown that call production is associated with the degree of risk the caller experiences and that they are individually distinctive. Receivers respond to calls and are sensitive to variation in caller reliability. Calls also contain nonlinear acoustic phenomena. Work has shown that socially isolated animals and those infected with Eimeria, an intestinal parasite, produced 'noisier' calls. However, animals that were likely under greater stress (as measured with faecal glucocorticoid metabolites) produced more structured and less noisy calls. The addition of NLP increases responsiveness in receivers. NLP in alarm calls have modest heritability. Taken together, the study of NLP in marmots has enhanced our understanding of the potential information encoded in alarm calls and is consistent with the hypothesis that variation in NLP production communicates fear, which stimulates work with other species, including humans.This article is part of the theme issue 'Nonlinear phenomena in vertebrate vocalizations: mechanisms and communicative functions'.

The Brazilian Cerrado is a heterogeneous region of open ecosystems adapted to fire intermingled with patches of woody growth-forms, with high levels of biodiversity and endemism. In recent decades, land conversion and human activities have proliferated across the Cerrado, losing about half of its original area. These changes, coupled with climate change, are altering its fire regimes with uncertain, but possibly adverse, consequences for Cerrado ecosystems. Here, we used burned area data to characterize the fire regimes of each cell on a 30 km grid over the Cerrado, and used a spatially constrained hierarchical clustering approach to delineate the regions with different fire regimes in four consecutive 9-year periods between 1985 and 2020. Comparing the periods 1985-1993 and 2012-2020, we found substantial changes in the number and shape of the fire regime regions, and in their fire characteristics. The main factor differentiating these regions was their level of fire activity: some showed large, numerous and frequent fires, while others showed small, few and infrequent fires. We also identified a region in the north with a later peak of the fire season, characterized by small but numerous fires. Finally, we found that while the fire activity of the southern areas of the Cerrado substantially decreased, fire activity levels in the centre and north increased or remained high over time.This article is part of the theme issue 'Novel fire regimes under climate changes and human influences: impacts, ecosystem responses and feedbacks'.

Persistent positive anomalies (PPAs) in 500 hPa geopotential height are upper-air circulation patterns associated with surface heatwaves, drought and fuel aridity. We examined the association between PPA events and surface fire weather and burned area at a pan-European level. Europe-wide, extreme fire weather and wildfires were on average 3.5 and 2.3 times more likely to occur concurrently with a PPA, respectively. PPAs were associated with 45% of pan-European area burned between March and October 2001-2021, and there was a latitudinal increase of up to 63% in the percentage of area burned during or up to 7 days following PPAs over Northern Europe. The burned area was highest up to one week following PPA presence, and fuel moisture indices from the Canadian Fire Weather Index System lagged behind peak PPA strength, demonstrating the role of PPAs in pre-drying fuels. Our findings highlight opportunities for developing early warning systems of wildfire danger, having implications for wildfire awareness and preparedness, informing policy and wildfire management decisions like early mobilization and resource sharing initiatives across Europe.This article is part of the theme issue 'Novel fire regimes under climate changes and human influences: impacts, ecosystem responses and feedbacks'.