Recognition of individuals within the social group: signature vocalizations

Recognising the key role of individual recognition in social networks

Many aspects of sociality rely on individuals recognising one another. Understanding how, when, and if individuals recognise others can yield insights into the foundations of social relationships and behaviours. Through synthesising individual recognition research in different sensory and social domains, and doing so across various related social contexts, we propose that a social network perspective can help to uncover how individual recognition may vary across different settings, species, and populations. Specifically, combining individual recognition with social networks has unrecognised potential for determining the level and relative importance of individual recognition complexity. This will provide insights not only on the ecology and evolution of individual recognition itself, but also on social structure, social transmission, and social interactions such as cooperation.

An intra-population analysis of the indris' song dissimilarity in the light of genetic distance

The increasing interest in the evolution of human language has led several fields of research to focus on primate vocal communication. The 'singing primates', which produce elaborated and complex sequences of vocalizations, are of particular interest for this topic. Indris (Indri indri) are the only singing lemurs and emit songs whose most distinctive portions are "descending phrases" consisting of 2-5 units. We examined how the structure of the indris' phrases varied with genetic relatedness among individuals. We tested whether the acoustic structure could provide conspecifics with information about individual identity and group membership. When analyzing phrase dissimilarity and genetic distance of both sexes, we found significant results for males but not for females. We found that similarity of male song-phrases correlates with kin in both time and frequency parameters, while, for females, this information is encoded only in the frequency of a single type. Song phrases have consistent individual-specific features, but we did not find any potential for advertising group membership. We emphasize the fact that genetic and social factors may play a role in the acoustic plasticity of female indris. Altogether, these findings open a new perspective for future research on the possibility of vocal production learning in these primates.

Segmental concatenation of individual signatures and context cues in banded mongoose (Mungos mungo) close calls

BACKGROUND

All animals are anatomically constrained in the number of discrete call types they can produce. Recent studies suggest that by combining existing calls into meaningful sequences, animals can increase the information content of their vocal repertoire despite these constraints. Additionally, signalers can use vocal signatures or cues correlated to other individual traits or contexts to increase the information encoded in their vocalizations. However, encoding multiple vocal signatures or cues using the same components of vocalizations usually reduces the signals' reliability. Segregation of information could effectively circumvent this trade-off. In this study we investigate how banded mongooses (Mungos mungo) encode multiple vocal signatures or cues in their frequently emitted graded single syllable close calls.

RESULTS

The data for this study were collected on a wild, but habituated, population of banded mongooses. Using behavioral observations and acoustical analysis we found that close calls contain two acoustically different segments. The first being stable and individually distinct, and the second being graded and correlating with the current behavior of the individual, whether it is digging, searching or moving. This provides evidence of Marler's hypothesis on temporal segregation of information within a single syllable call type. Additionally, our work represents an example of an identity cue integrated as a discrete segment within a single call that is independent from context. This likely functions to avoid ambiguity between individuals or receivers having to keep track of several context-specific identity cues.

CONCLUSIONS

Our study provides the first evidence of segmental concatenation of information within a single syllable in non-human vocalizations. By reviewing descriptions of call structures in the literature, we suggest a general application of this mechanism. Our study indicates that temporal segregation and segmental concatenation of vocal signatures or cues is likely a common, but so far neglected, dimension of information coding in animal vocal communication. We argue that temporal segregation of vocal signatures and cues evolves in species where communication of multiple unambiguous signals is crucial, but is limited by the number of call types produced.