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In many taxa, breeding success depends heavily on reliable vocal recognition between parents and offspring. Although the acoustic basis of this recognition has been explored in several species, few studies have examined the evolution of acoustic cues to identity across development. Here, in a captive breeding program, we investigated for the first time the acoustic signals produced by North African houbara bustard Chlamydotis undulata undulata chicks. Two call types (contact and distress) were recorded from 15 chicks in 4 age classes. Acoustic analyses showed that the acoustic parameters of the calls varied systematically with age in both contact and distress calls. However, both call types remained highly stereotyped and individualized between chicks at every tested age, indicating that calls encode reliable information about individual identity throughout development, thus potentially enabling the mother to distinguish her own chicks through their development up to fledging. Playback experiments are now needed to verify such parent-chick recognition in houbara bustards and its efficiency across chick ontogeny.

International audience; In several species of non-human primates, non-agonistic vocal exchanges can be seen as a primitive form of conversation, as they respect basic temporal rules (i.e. turn-taking, overlap avoidance), the same as those that guide human conversations. Conversational rules have recently been suggested in captive great ape species, yet the only study investigating vocal turn-taking in wild great apes did not find any evidence of such vocal roles. Whether the environmental conditions (captivity versus free ranging) or the social organisation of a given species shape temporally ruled vocal exchanges remain open questions. Here, we investigated general calling patterns of peaceful vocal exchanges in a wild bonobo community. This pilot study revealed that wild bonobos respect the fundamental temporal rules of vocal turn-taking, namely the avoidance of overlapping and the presence of short call-intervals between interlocutors on the order of 2 sec, corroborating findings from captive bonobos. Despite the limited sample size, our finding suggests that vocal exchanges appear context-dependent but neither age nor sex seem to influence their occurrence. While further studies are needed to confirm these observations, this study helps to fill a major gap in research on the vocal communication of wild great apes, paving the way for more extensive comparative studies, representing a further step towards a better understanding of how vocal turn-taking arose in humans.

People across the world and throughout history have gone to great lengths to enhance their physical appearance. Evolutionary psychologists and ethologists have largely attempted to explain this phenomenon via mating preferences and strategies. Here, we test one of the most popular evolutionary hypotheses for beauty-enhancing behaviors, drawn from mating market and parasite stress perspectives, in a large cross-cultural sample. We also test hypotheses drawn from other influential and non-mutually exclusive theoretical frameworks, from biosocial role theory to a cultural media perspective. Survey data from 93,158 human participants across 93 countries provide evidence that behaviors such as applying makeup or using other cosmetics, hair grooming, clothing style, caring for body hygiene, and exercising or following a specific diet for the specific purpose of improving ones physical attractiveness, are universal. Indeed, 99% of participants reported spending >10 min a day performing beauty-enhancing behaviors. The results largely support evolutionary hypotheses: more time was spent enhancing beauty by women (almost 4 h a day, on average) than by men (3.6 h a day), by the youngest participants (and contrary to predictions, also the oldest), by those with a relatively more severe history of infectious diseases, and by participants currently dating compared to those in established relationships. The strongest predictor of attractiveness-enhancing behaviors was social media usage. Other predictors, in order of effect size, included adhering to traditional gender roles, residing in countries with less gender equality, considering oneself as highly attractive or, conversely, highly unattractive, TV watching time, higher socioeconomic status, right-wing political beliefs, a lower level of education, and personal individualistic attitudes. This study provides novel insight into universal beauty-enhancing behaviors by unifying evolutionary theory with several other complementary perspectives., National Science Center, Poland [2019/33/N/HS6/00054]; Basic Research Program at the National Research University Higher School of Economics (HSE University); Basic Research Program at HSE University, RF; FCT [UID/PSI/03125/2021, SFRH/BD/126304/2016]; UTAR Research Centre Excellence Award; Universiti Tunku Abdul Rahman [2019 -CAP (6401/0019)], This work is the result of the research project funded by the National Science Center, Poland (2019/33/N/HS6/00054). Dmitry Grigoryev was supported by the Basic Research Program at the National Research University Higher School of Economics (HSE University).; Dmitrii Dubrov was supported by the Basic Research Program at HSE University, RF.; Patricia Arriaga was supported by the FCT through funds from the research center UID/PSI/03125/2021. Anabela C. Santos was supported by the FCT through funds from a PhD grant SFRH/BD/126304/2016. Kavitha Nalla Muthu and Chee-Seng Tan were supported by the UTAR Research Centre Excellence Award 2019 -CAP (6401/0019) from the Universiti Tunku Abdul Rahman.

La voz humana transmite información sobre la fuerza física de un vocalizador que los oyentes pueden percibir y que puede influir en la elección de pareja y la competencia intrasexual. Sin embargo, los correlatos acústicos confiables de la fuerza en el habla humana siguen sin estar claros. En comparación con el habla, las vocalizaciones no verbales agresivas (rugidos) pueden funcionar para maximizar la fuerza percibida, lo que sugiere que su estructura acústica ha sido seleccionada para comunicar formidable, similar a las demostraciones vocales de amenaza de otros animales. Aquí, probamos esta predicción en dos muestras africanas NO EXTRAÑAS: una comunidad urbana de cameruneses y cazadores-recolectores nómadas rurales hadza en los matorrales de Tanzania. Los participantes produjeron un habla estandarizada y rugidos voluntarios y proporcionaron medidas de fuerza de agarre. Usando análisis acústico y técnicas de promediación e inferencia multimodelo de teoría de la información, mostramos que la fuerza se puede medir tanto a partir del habla como de los rugidos, y como se predijo, la fuerza se mide de manera más confiable a partir de los rugidos que de las vocales, las palabras o los saludos. La estructura acústica de los rugidos explica entre el 40 y el 70 % de la variación de la fuerza real en adultos de ambos sexos. Sin embargo, la fuerza se predice mediante múltiples parámetros acústicos cuyas combinaciones varían según el sexo, la muestra y el tipo vocal. Por lo tanto, si bien los rugidos pueden indicar una fuerza máxima, se necesita más investigación para descubrir correlatos acústicos consistentes y probablemente interactivos de la fuerza en la voz humana. Este artículo forma parte del número temático 'Modulación de la voz: desde el origen y el mecanismo hasta el impacto social (Parte I)'. The human voice carries information about a vocalizer's physical strength that listeners can perceive and that may influence mate choice and intrasexual competition. Yet, reliable acoustic correlates of strength in human speech remain unclear. Compared to speech, aggressive nonverbal vocalizations (roars) may function to maximize perceived strength, suggesting that their acoustic structure has been selected to communicate formidability, similar to the vocal threat displays of other animals. Here, we test this prediction in two non-WEIRD African samples: an urban community of Cameroonians and rural nomadic Hadza hunter-gatherers in the Tanzanian bushlands. Participants produced standardized speech and volitional roars and provided handgrip strength measures. Using acoustic analysis and information-theoretic multi-model inference and averaging techniques, we show that strength can be measured from both speech and roars, and as predicted, strength is more reliably gauged from roars than vowels, words or greetings. The acoustic structure of roars explains 40-70% of the variance in actual strength within adults of either sex. However, strength is predicted by multiple acoustic parameters whose combinations vary by sex, sample and vocal type. Thus, while roars may maximally signal strength, more research is needed to uncover consistent and likely interacting acoustic correlates of strength in the human voice. This article is part of the theme issue 'Voice modulation: from origin and mechanism to social impact (Part I)'.

International audience; Reproductive success can improve with experience, which increases with age in many long-lived species. Signals that provide reliable information about age are therefore of importance for mate choice and consequently are under sexual selection. In birds, these are often vocal signals as well as visual signals in the form of plumage coloration. King penguins, Aptenodytes patagonicus, are sexually monomorphically ornamented seabirds that perform a complex visual and acoustic courtship display. Coloured beak spots and ear patches contain information about the condition and physiological status of adult males and females, but their role as a signal of age has previously only been studied in young birds. Vocalizations have mainly been studied as signals of individuality and not in the context of courtship. We investigated two multicomponent signals in the context of mate choice by analysing beak spot, ear patch and call parameters of wild king penguins. We explored the relation between these signals and age as well as age classes (chicks, juveniles, adults). Ornament parameters were weakly correlated with in males, but not in females, while acoustic parameters were highly correlated with age in both sexes. The calls' fundamental frequency and energy parameters and all the beak spot parameters reliably classified individuals into their age class. Since age class was redundantly encoded in both acoustic and colour parameters, we hypothesize that calls and ornaments function as back-up signals that increase the chance of accurately conveying the age class of the sender to receivers. King penguins might sequentially analyse age class signals during courtship, where acoustic signals serve as long-range communication when sender and receiver are out of sight, and ornamentation signals become important at close range. We show the importance of considering bimodal, multicomponent signals when studying complex behaviour and discuss how signalling environment, the species' life history and mating system influence the evolution of communication signals.

International audience; Until recently, human nonverbal vocalisations such as cries, laughs, screams, moans, and groans have received relatively little attention in the human behavioural sciences. Yet these vocal signals are ubiquitous in human social interactions across diverse cultures and may represent a missing link between relatively fixed nonhuman animal vocalisations and highly flexible human speech. Here, we review converging empirical evidence that the acoustic structure (“forms”) of these affective vocal sounds in humans reflect their evolved biological and social “functions”. Human nonverbal vocalisations thus largely parallel the form-function mapping found in the affective calls of other animals, such as play vocalisations, distress cries, and aggressive roars, pointing to a homologous nonverbal vocal communication system shared across mammals, including humans. We aim to illustrate how this form-function approach can provide a solid framework for making predictions, including about cross-species and cross-cultural universals or variations in the production and perception of nonverbal vocalisations. Despite preliminary evidence that key features of human vocalisations may indeed be universal and develop reliably across distinct cultures, including small-scale societies, we emphasise the important role of vocal control in their production among humans. Unlike most other terrestrial mammals including nonhuman primates, people can flexibly manipulate vocalisations, from conversational laughter and fake pleasure moans to exaggerated roar-like threat displays. We discuss how human vocalisations may thus represent the cradle of vocal control, a precursor of human speech articulation, providing important insight into the origins of speech. Finally, we describe how ground-breaking parametric synthesis technologies are now allowing researchers to create highly naturalistic, yet fully experimentally controlled vocal stimuli to directly test hypotheses about form and function in nonverbal vocalisations, opening the way for a new era of voice sciences.

International audience; Kinship and inbreeding are two major components involved in sexual selection and mating system evolution. However, the mechanisms underlying recognition and discrimination of genetically related or inbred individuals remain unclear. We investigated whether kinship and inbreeding information is related to low-frequency vocalizations, "booms," produced by males during their courtship in the lekking houbara bustard (Chlamydotis undulata undulata). Based on a captive breeding program where the pedigree of all males is known, we investigated the similarity of booms' acoustic parameters among captive males more or less individually inbred and therefore genetically related with each other. In the wild, we investigated the relationship between the spatial distribution of males within leks and the similarity of acoustic parameters of their booms. In the captive population, we found (a) a relationship between the individual inbreeding level of captive males and their vocalization parameters; (b) that kin share similar frequency and temporal characteristics of their vocalizations. In the wild, we found no evidence for spatial structuring of males based on their acoustic parameters, in agreement with previous genetic findings on the absence of kin association within houbara bustard leks. Overall, our results indicate that genetic information potentially related to both the identity and quality of males is contained in their vocalizations.

Selection pressures acting on both intrasexual competition and intersexual relationships may lead to the emphasis of individual variation and might thus lead to the expression of individual signature. This is particularly true in lek mating systems, where providing information on identity and/or quality to potential mates or congeners of the same sex can be essential for individuals to optimize their reproductive success. Visual and acoustic signals produced during the courtship of the lekking North African Houbara bustard (Chlamydotis undulata undulata), based on field data from wild birds, are investigated here for the first time. Results show that the vocal signals, called booms, are characterized by a very low frequency, a rare phenomenon in birds which should allow booms to propagate over long distances. Results also show that both visual and acoustic signals are individualized and stereotyped between males. Using three methods of analysis, we highlight the acoustic parameters likely to support vocal individual signature and show that such information mainly relies on frequency parameters.