Alexander Mielke

A method for automated individual, species and call type recognition in free-ranging animals

The ability to identify individuals reliably is often a key prerequisite for animal behaviour studies in the wild. In primates, recognition of other group members can be based on individual differences in the voice, but these cues are typically too subtle for human observers. We applied a combined mechanism consisting of a call feature extraction (mel frequency cepstral coefficients) and pattern recognition algorithm (artificial neural networks) to investigate whether automated caller identification is possible in free-ranging primates. The mechanism was tested for its accuracy in recognizing species, call type and caller identity in a large population of free-ranging blue monkeys, Cercopithecus mitis stuhlmanni, in Budongo Forest, Uganda. Classification was highly accurate with 96% at the species, 98% at the call type and 73% at the caller level. It also outperformed conventional discriminant function analysis in the individual recognition task. We conclude that software based on this method will make a powerful tool for future animal behaviour research, as it allows for automatic, fast and objective classifications in different animal species.

Vocal fold control beyond the species-specific repertoire in an orang-utan.

Vocal fold control was critical to the evolution of spoken language, much as it today allows us to learn vowel systems. It has, however, never been demonstrated directly in a non-human primate, leading to the suggestion that it evolved in the human lineage after divergence from great apes. Here, we provide the first evidence for real-time, dynamic and interactive vocal fold control in a great ape during an imitation “do-as-I-do” game with a human demonstrator. Notably, the orang-utan subject skilfully produced “wookies” – an idiosyncratic vocalization exhibiting a unique spectral profile among the orang-utan vocal repertoire. The subject instantaneously matched human-produced wookies as they were randomly modulated in pitch, adjusting his voice frequency up or down when the human demonstrator did so, readily generating distinct low vs. high frequency sub-variants. These sub-variants were significantly different from spontaneous ones (not produced in matching trials). Results indicate a latent capacity for vocal fold exercise in a great ape (i) in real-time, (ii) up and down the frequency spectrum, (iii) across a register range beyond the species-repertoire and, (iv) in a co-operative turn-taking social setup. Such ancestral capacity likely provided the neuro-behavioural basis of the more fine-tuned vocal fold control that is a human hallmark.

Bystanders intervene to impede grooming in Western chimpanzees and sooty mangabeys

Grooming interactions benefit groomers, but may have negative consequences for bystanders. Grooming limits bystanders grooming access and ensuing alliances could threaten the bystanders hierarchy rank or their previous investment in the groomers. To gain a competitive advantage, bystanders could intervene into a grooming bout to increase their own grooming access or to prevent the negative impact of others grooming. We tested the impact of dominance rank and social relationships on grooming intervention likelihood and outcome in two sympatric primate species, Western chimpanzees (Pan troglodytes verus) and sooty mangabeys (Cercocebus atys atys). In both species, rather than increasing their own access to preferred partners, bystanders intervened mainly when an alliance between groomers could have a negative impact on them: when the lower-ranking groomer was close to the bystander in rank, when either groomer was an affiliation partner whose services they could lose, or the groomers were not yet strongly affiliated with each other. Thus, bystanders in both species appear to monitor grooming interactions and intervene based on their own dominance rank and social relationships, as well as triadic awareness of the relationship between groomers. While the motivation to intervene did not differ between species, mangabeys appeared to be more constrained by dominance rank than chimpanzees.

Factors influencing bacterial microbiome composition in a wild non-human primate community in Taï National Park, Côte d’Ivoire

Microbiomes impact a variety of processes including a host’s ability to access nutrients and maintain health. While host species differences in microbiomes have been described across ecosystems, little is known about how microbiomes assemble, particularly in the ecological and social contexts in which they evolved. We examined gut microbiome composition in nine sympatric wild non-human primate (NHP) species. Despite sharing an environment and interspecific interactions, individuals harbored unique and persistent microbiomes influenced by host species, social group, and parentage, but surprisingly not by social relationships among members of a social group. We found a branching order of host-species networks constructed using the composition of their microbiomes as characters, which was incongruent with known NHP phylogenetic relationships, with chimpanzees (Pan troglodytes verus) sister to colobines, upon which they regularly prey. In contrast to phylogenetic clustering found in all monkey microbiomes, chimpanzee microbiomes were unique in that they exhibited patterns of phylogenetic overdispersion. This reflects unique ecological processes impacting microbiome composition in chimpanzees and future studies will elucidate the aspects of chimpanzee ecology, life history, and physiology that explain their unique microbiome community structure. Our study of contemporaneous microbiomes of all sympatric diurnal NHP in an ecosystem highlights the diverse dispersal routes shaping these complex communities.

Flexible decision-making in grooming partner choice in sooty mangabeys and chimpanzees

Living in permanent social groups forces animals to make decisions about when, how and with whom to interact, requiring decisions to be made that integrate multiple sources of information. Changing social environments can influence this decision-making process by constraining choice or altering the likelihood of a positive outcome. Here, we conceptualized grooming as a choice situation where an individual chooses one of a number of potential partners. Studying two wild populations of sympatric primate species, sooty mangabeys (Cercocebus atys atys) and western chimpanzees (Pan troglodytes verus), we tested what properties of potential partners influenced grooming decisions, including their relative value based on available alternatives and the social relationships of potential partners with bystanders who could observe the outcome of the decision. Across 1529 decision events, multiple partner attributes (e.g. dominance ranks, social relationship quality, reproductive state, partner sex) influenced choice. Individuals preferred to initiate grooming with partners of similar global rank, but this effect was driven by a bias towards partners with a high rank compared to other locally available options. Individuals also avoided grooming partners who had strong social relationships with at least one bystander. Results indicated flexible decision-making in grooming interactions in both species, based on a partners value given the local social environment. Viewing partner choice as a value-based decision-making process allows researchers to compare how different species solve similar social problems.

Social bonds facilitate cooperative resource sharing in wild chimpanzees

Why share when access to benefits is uncertain is crucial to our understanding of the evolution of humans extensive cooperation. Here, we investigated some of the different human sharing hypotheses and potential neuroendocrine mechanisms, in one of our closest living relatives, chimpanzees. The strongest predictor of sharing across food types was the presence of enduring and mutually preferred grooming partners, more than harassment, direct signalling, or trade. Moreover, urinary oxytocin levels were higher after the sharing of both individually and jointly acquired resources compared with controls. We conclude that the emotional connection inherent in social bonds was a key factor determining sharing patterns, with the oxytocinergic system potentially facilitating long-term cooperative exchanges. Testing for the role of social bonds in increasing predictability of sharing behaviour, a feature frequently overlooked, may help us to identify the evolutionary drivers of resource sharing and mechanisms that sustain delayed reciprocity between non-kin.

Urinary oxytocin levels in relation to post-conflict affiliations in wild male chimpanzees (Pan troglodytes verus)

ABSTRACT Many animals living in social groups have evolved behaviors to resolve conflicts between group members, behaviors thought crucial for maintaining stable group life. Several hypotheses, based mainly on observational data, aim to explain how post‐conflict (PC) affiliations, such as reconciliation and consolation, resolve conflicts by restoring relationships and/or alleviating anxiety. To examine a potential endocrinological mechanism of PC affiliations, we used an experimental‐like procedure to investigate whether the oxytocinergic system is activated during naturally observed reconciliations, receiving bystander PC affiliations and aggressions not followed by PC affiliations in wild male chimpanzees. We compared urinary oxytocin (uOT) levels after reconciliations, receiving bystander PC affiliations or aggressions without affiliations with two control conditions: affiliations without previous aggression and after time periods without social interactions. We furthermore tested the ‘valuable relationship’ hypothesis of reconciliation, as well as the influence of relationship quality between individuals engaged in each of the three behavioral conditions involving aggression on uOT levels. We found that the probability to reconcile a conflict increased with increasing relationship quality between opponents, thus our results support the ‘valuable relationship’ hypothesis. However, relationship quality did not influence uOT levels, while behavioral condition had a significant effect on uOT levels. uOT levels after reconciliations, receiving bystander PC affiliations and affiliations not related to conflicts were higher than after aggressions alone and time periods without social interactions. Overall, our results indicate that the oxytocinergic system is activated during affiliative interactions, whether occurring as reconciliation, bystander PC affiliation or affiliation alone. We conclude that the oxytocinergic system, in addition to building and maintaining social relationships, also takes part in repairing them. HIGHLIGHTSuOT levels after reconciliation and bystander PC affiliation were higher than uOT levels after aggression alone.uOT levels were higher after any condition involving affiliation than uOT levels after a non‐social control condition.Aggressions alone did not elevate uOT levels.Relationship quality did not have a significant effect on uOT levels.