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ABSTRACT: The study of non‐human animals, in particular primates, can provide essential insights into language evolution. A critical element of language is vocal production learning, i.e. learning how to produce calls. In contrast to other lineages such as songbirds, vocal production learning of completely new signals is strikingly rare in non‐human primates. An increasing body of research, however, suggests that various species of non‐human primates engage in vocal accommodation and adjust the structure of their calls in response to environmental noise or conspecific vocalizations. To date it is unclear what role vocal accommodation may have played in language evolution, in particular because it summarizes a variety of heterogeneous phenomena which are potentially achieved by different mechanisms. In contrast to non‐human primates, accommodation research in humans has a long tradition in psychology and linguistics. Based on theoretical models from these research traditions, we provide a new framework which allows comparing instances of accommodation across species, and studying them according to their underlying mechanism and ultimate biological function. We found that at the mechanistic level, many cases of accommodation can be explained with an automatic perception–production link, but some instances arguably require higher levels of vocal control. Functionally, both human and non‐human primates use social accommodation to signal social closeness or social distance to a partner or social group. Together, this indicates that not only some vocal control, but also the communicative function of vocal accommodation to signal social closeness and distance must have evolved prior to the emergence of language, rather than being the result of it. Vocal accommodation as found in other primates has thus endowed our ancestors with pre‐adaptations that may have paved the way for language evolution. [ABSTRACT FROM AUTHOR]

Language is a cognitively demanding human trait, but it is also a fundamentally cooperative enterprise that rests on the motivation to share information. Great apes possess many of the cognitive prerequisites for language, but largely lack the motivation to share information. Callitrichids (including marmosets and tamarins) are highly vocal monkeys that are more distantly related to humans than great apes are, but like humans, they are cooperative breeders and all group members help raising offspring. Among primates, this rearing system is correlated with proactive prosociality, which can be expressed as motivation to share information. We therefore propose that the unique coincidence of these two components in humans set the stage for language evolution: The cognitive component inherited from our great ape-like ancestors, and the motivational one added convergently as a result of cooperative breeding. We evaluate this scenario based on a review of callitrichd vocal communication and show that furthermore, they possess many of the mechanistic elements emphasized by the mirror system hypothesis of language evolution. We end by highlighting how more systematic phylogenetic comparisons will enable us to further promote our understanding of the role of cooperative breeding during language evolution. [ABSTRACT FROM AUTHOR]

Individuals often show consistent differences in behavioural traits that may belong to a behavioural syndrome. Aggressive propensity is usually an important component of consistent behavioural types, potentially generating benefits in resource competition with conspecifics that may be traded off against costs in other contexts (e.g. acquisition of mates or coexistence with group members). Such trade-offs have not yet been studied in highly social species. We investigated how aggressive propensity influences competition for dominance, shelters and mates in the cooperatively breeding cichlid Neolamprologus pulcher. Following an established protocol we compared growth trajectories of groups of four fish either matched or unmatched for aggressive type. Furthermore, we analysed social interactions, the acquisition of shelter and possible mating partners (by proximity to shelters and prospective mates) according to aggressive type, showing either high or low aggression levels. Contrary to prediction we found that differences in behavioural idiosyncrasies affected the likelihood of obtaining the dominant position and high-quality territories only marginally. Social interactions, growth rates and body reserve accumulation were affected by behavioural differences. However, the patterns observed in this experiment differed from previous studies and suggest a modulating effect of the social environment on the link between behavioural types and life history decisions. Hence, we suggest that in future studies this relationship should be thoroughly investigated under varying social contexts, especially in highly social species. [ABSTRACT FROM AUTHOR]

With their highly social nature and complex vocal communication system, marmosets are important models for comparative studies of vocal communication and, eventually, language evolution. However, our knowledge about marmoset vocalizations predominantly originates from playback studies or vocal interactions between dyads, and there is a need to move towards studying group-level communication dynamics. Efficient source identification from marmoset vocalizations is essential for this challenge, and machine learning algorithms (MLAs) can aid it. Here we built a pipeline capable of plentiful feature extraction, meaningful feature selection, and supervised classification of vocalizations of up to 18 marmosets. We optimized the classifier by building a hierarchical MLA that first learned to determine the sex of the source, narrowed down the possible source individuals based on their sex and then determined the source identity. We were able to correctly identify the source individual with high precisions (87.21%-94.42%, depending on call type, and up to 97.79% after the removal of twins from the dataset). We also examine the robustness of identification across varying sample sizes. Our pipeline is a promising tool not only for source identification from marmoset vocalizations but also for analysing vocalizations of other species.

The acoustic properties of vocalizations in common marmosets differ between populations. These differences may be the result of social vocal learning, but they can also result from environmental or genetic differences between populations. We performed translocation experiments to separately quantify the influence of a change in the physical environment (experiment 1), and a change in the social environment (experiment 2) on the acoustic properties of calls from individual captive common marmosets. If population differences were due to genetic differences, we expected no change in the vocalizations of the translocated marmosets. If differences were due to environmental factors, we expected vocalizations to permanently change contingent with environmental changes. If social learning was involved, we expected that the vocalizations of animals translocated to a new population with a different dialect would become more similar to the new population. In experiment 1, we translocated marmosets to a different physical environment without changing the social composition of the groups or their neighbours. Immediately after the translocation to the new facility, one out of three call types showed a significant change in call structure, but 5-6 weeks later, the calls were no longer different from before the translocation. Thus, the novel physical environment did not induce long lasting changes in the vocalizations of the marmosets. In experiment 2, we translocated marmosets to a new population with a different dialect. Importantly, our previous work had shown that these two populations differed significantly in vocalization structure. The translocated marmosets were still housed in their original social group, but after translocation they were surrounded by the vocalizations from neighbouring groups of the new population. The vocal distance between the translocated individuals and the new population decreased for two out of three call types over 16 weeks. Thus, even without direct social contact or interaction, the vocalizations of the translocated animals converged towards the new population, indicating that common marmosets can modify their calls due to acoustic input from conspecifics alone, via crowd vocal learning. To our knowledge, this is the first study able to distinguish between different explanations for vocal dialects as well as to show crowd vocal learning in a primate species., Competing Interests: The authors have declared that no competing interests exist.