Watts David P
Department of Anthropology, Yale University, P.O. Box 208277, New Haven, CT, 06520-8277, USA.
Primates. 2016 Jan;57(1):61-72. doi: 10.1007/s10329-015-0497-8. Epub 2015 Nov 6.
Chimpanzees (Pan troglodytes) use some communicative signals flexibly and voluntarily, with use influenced by learning. These signals include some vocalizations and also sounds made using the lips, oral cavity, and/or teeth, but not the vocal tract, such as "attention-getting" sounds directed at humans by captive chimpanzees and lip smacking during social grooming. Chimpanzees at Ngogo, in Kibale National Park, Uganda, make four distinct sounds while grooming others. Here, I present data on two of these ("splutters" and "teeth chomps") and consider whether social learning contributes to variation in their production and whether they serve social functions. Higher congruence in the use of these two sounds between dyads of maternal relatives than dyads of non-relatives implies that social learning occurs and mostly involves vertical transmission, but the results are not conclusive and it is unclear which learning mechanisms may be involved. In grooming between adult males, tooth chomps and splutters were more likely in long than in short bouts; in bouts that were bidirectional rather than unidirectional; in grooming directed toward high-ranking males than toward low-ranking males; and in bouts between allies than in those between non-allies. Males were also more likely to make these sounds while they were grooming other males than while they were grooming females. These results are expected if the sounds promote social bonds and induce tolerance of proximity and of grooming by high-ranking males. However, the alternative hypothesis that the sounds are merely associated with motivation to groom, with no additional social function, cannot be ruled out. Limited data showing that bouts accompanied by teeth chomping or spluttering at their initiation were longer than bouts for which this was not the case point toward a social function, but more data are needed for a definitive test. Comparison to other research sites shows that the possible existence of grooming-specific sound dialects in chimpanzees deserves further investigation.
黑猩猩（Pan troglodytes）能灵活且自主地使用一些交流信号，其使用受到学习的影响。这些信号包括一些叫声，以及利用嘴唇、口腔和/或牙齿发出的声音，但不包括声道发出的声音，例如圈养黑猩猩对人类发出的“引起注意”的声音以及社交梳理时的咂嘴声。乌干达基巴莱国家公园恩戈戈的黑猩猩在梳理其他黑猩猩时会发出四种不同的声音。在此，我展示了其中两种声音（“噼啪声”和“咬牙声”）的数据，并探讨社会学习是否会导致它们在发声上的差异，以及它们是否具有社会功能。母系亲属二元组之间这两种声音的使用比非亲属二元组之间具有更高的一致性，这意味着社会学习确实存在，且主要涉及垂直传播，但结果并不确凿，也不清楚可能涉及哪些学习机制。在成年雄性之间的梳理行为中，长时间的梳理比短时间的梳理更有可能出现咬牙声和噼啪声；双向而非单向的梳理行为中更易出现；针对高等级雄性的梳理比针对低等级雄性的梳理更易出现；盟友之间的梳理比非盟友之间的梳理更易出现。雄性在梳理其他雄性时比梳理雌性时更有可能发出这些声音。如果这些声音能促进社会联系，并促使高等级雄性容忍接近和梳理行为，那么这些结果是可以预期的。然而，声音仅仅与梳理动机相关而没有额外社会功能的替代假设也不能被排除。有限的数据表明，开始时伴有咬牙声或噼啪声的梳理行为持续时间比没有这些声音的梳理行为更长，这指向了一种社会功能，但还需要更多数据进行确定性测试。与其他研究地点的比较表明，黑猩猩中可能存在特定于梳理行为的声音方言，这值得进一步研究。
