| dc.description.abstracteng | When studying the evolution of animal communication it is important to consider both, the signaller (i.e. signal structure and signal usage) and the receiver (i.e. signal response). While in primates the structure of sounds is supposed to be largely innate, the usage of calls is more malleable and modifiable by experience. The perception and response to calls is highly flexible in primates and, in contrast to signal production, depend strongly on developmental and cognitive mechanisms. Accordingly, the three aspects are expected to be differently affected by evolutionary constrains and selective pressures.
The major goal of my thesis was to investigate primate vocal communication from an evolutionary perspective. I examined the vocal communication of free ranging Guinea baboons (Papio papio) and assessed how the characteristics of their social relationships might have contributed to the specifics of their vocal behaviour. To clarify the impact of the Guinea baboons’ social system on their vocal communication, I separately studied the structure and usage of their vocal signals as well as their response behaviour, and compared my results to studies conducted on other closely related baboon taxa. Guinea baboons differ in their social system from the well-known savannah baboons (i.e. chacma baboons (P. ursinus), olive baboons (P. anubis), yellow baboons (P. cynocephalus)), which makes them ideal candidates to study the social impact on the characteristics of vocal communication, in general. While savannah baboons live in stable multi-male, multi-female groups with rather hostile male-male relationships, Guinea baboons live in a complex multi-level society with a much less competitive and more tolerant social style among males.
To assess the reliability and validity of acoustic parameters, firstly, I conducted sound transmission experiments, before I used them for acoustic analysis. By re-recording different baboon vocalizations under various broadcasting conditions (i.e. various heights, distances and habitat types) I investigated which parameters where particularly susceptible to degradation. Acoustic parameters, such as start- or end- parameters, where not reliable; i.e. they were highly variable even when recorded under the same conditions. Almost all measured parameters were strongly affected by degradation over distance, which could mainly be attributed to amplitude based attenuation effects. Tonal parameters were only marginally affected by different broadcasting conditions and remained highly valid even when calls were recorded from larger distances. Based on the outcomes of my transmission experiments, I adjusted the recording conditions in the field. Furthermore, I could systematically justify the parameter selection for the following acoustic analyses of the Guinea baboons’ vocal repertoire.
In the second part of my project I examined the vocal repertoire of Guinea baboons and analysed their call structure as well as their call usage. I found important differences and similarities of the Guinea baboons’ vocal behaviour in comparison to other taxa. While the structure of their vocal repertoire largely coincided with call structures found in other baboons, i.e. the same call types occurred; the usage of calls differed and corresponded to the less competitive and rather affiliative social style of Guinea baboons. Males showed only a diminished usage of contest or display vocalizations (a common vocal pattern observed in the competitive chacma baboons), while they frequently used vocal signals during affiliative and greeting interactions. My results suggest that the use of calls is adapted to the requirements of the specific social system and that competition and cooperation affect animal signalling behaviour to regulate social interactions.
Finally, I conducted playback experiments to investigate how the response behaviour of male Guinea baboons was influenced by the characteristics of their social relationships. Specifically, I played back male calls from individuals of different social units (i.e. their own social unit, a neighbouring unit or a stranger unit) and examined how subjects differentiated among their conspecifics. In correspondence with their highly tolerant social style, males largely ignored any male outside their own unit, irrespective whether the caller was a neighbour or a complete stranger, a response pattern that stands in stark contrast to numerous group living primates. On the other hand, males responded strongly to calls of their own unit members, with whom they are socially related, which indicates that they are strongly motivated to monitor the social manoeuvres of their associates. My findings suggest that the quality and consistency of social interactions appear to be important for the response behaviour in primates and that the allocation of social attention is tuned to the specifics of a species’ social organization.
In sum, the evolution of primate vocal communication appears to be driven by a species’ social system, although the different aspects of communication (i.e. structure, usage and response) are differentially affected. While phylogenetic constrains play an important role by limiting the variation in the structure of nonhuman primate vocalizations, the use of calls as well as the way primates respond, can be flexibly adapted to the requirements of the specific social structure and social organisation. Hence, to understand the overall influence of the determining factors (i.e. phylogeny, social system) on the evolution of animal communication it is important to elucidate the differences and similarities of both, signal production and receivers’ responses. | de |