Motivation before Meaning: Motivational Information Encoded in Meerkat Alarm Calls Develops Earlier than Referential Information

University of Zurich, Zürich, Zurich, Switzerland
The American Naturalist (Impact Factor: 3.83). 07/2007; 169(6):758-67. DOI: 10.1086/516719
Source: PubMed


In contrast to historical assumptions about the affective nature of animal vocalizations, it is now clear that many vertebrates are capable of producing specific alarm calls in response to different predators, calls that provide information that goes beyond the motivational state of a caller. However, although these calls function referentially, it does not mean that they are devoid of motivational content. Studies on meerkats (Suricata suricatta) directly support this conclusion. The acoustic structure of their alarm calls simultaneously encodes information that is both motivational (level of urgency) and referential (predator specific). In this study, we investigated whether alarm calls of young meerkats undergo developmental modification and whether the motivational or the referential aspect of calls changes more over time. We found that, based on their acoustic structure, calls of young showed a high correct assignment to low- and high-urgency contexts but, in contrast to adults, low assignment to specific predator types. However, the discrimination among predator types was better in high-urgency than in low-urgency contexts. Our results suggest that acoustic features related to level of urgency are expressed earlier than those related to predator-specific information and may support the idea that referential calls evolve from motivational signals.

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Available from: Linda I Hollén
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    • "Interestingly, young meerkats tend to respond with an appropriate level of urgency, even while producing inappropriate calls more often than adults, suggesting that the ability to respond appropriately to predation risk develops earlier than functional reference (Holl en & Manser 2007). Age-related changes may reflect differences in innate responses to alarm calls by particular age classes or may reflect learning through accumulation of experiences required before young animals adopt appropriate reactions to referential signals (Lea & Blumstein 2011). "
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    ABSTRACT: A long-standing question in animal communication is whether signals reveal intrinsic properties of the signaller or extrinsic properties of its environment. Alarm calls, one of the most conspicuous components of antipredator behaviour, intuitively would appear to reflect internal states of the signaller. Pioneering research in primates and fowl, however, demonstrated that signallers may produce unique alarm calls during encounters with different types of predators, suggesting that signallers through selective production of alarm calls provide to conspecific receivers information about predators in the environment. In this article, we review evidence for such functional reference' in the alarm calls of birds based on explicit tests of two criteria proposed in Macedonia & Evans' (Ethology 93, 1993, 177) influential conceptual framework: (1) that unique alarm calls are given to specific predator categories, and (2) that alarm calls isolated from contextual information elicit antipredator responses from receivers similar to those produced during actual predator encounters. Despite the importance of research on birds in development of the conceptual framework and the ubiquity of alarm calls in birds, evidence for functionally referential alarm calls in this clade is limited to six species. In these species, alarm calls are associated with the type of predator encountered as well as variation in hunting behaviour; with defence of reproductive effort in addition to predators of adults; with age-related changes in predation risk; and with strong fitness benefits. Our review likely underestimates the occurrence of functional reference in avian alarm calls, as incomplete application and testing of the conceptual framework has limited our understanding. Throughout, therefore, we suggest avian taxa for future studies, as well as additional questions and experimental approaches that would strengthen our understanding of the meaning of functional reference in avian alarm calls.
    Full-text · Article · Jun 2013 · Ethology
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    • "Due to the success of these ventures, however, there is a bias in what we know about the development of communication systems. Most studies have focused on the ontogeny of signal production rather than receiver decoding, and similar emphasis has been given to learning over nonlearning [17–21]. But receivers are a key part of a communication network, and it might be that nonlearned mechanisms are more ubiquitous than learned ones in the communication systems of most animals [22–30]. "
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    ABSTRACT: Most studies addressing the development of animal communication have focused on signal production rather than receiver decoding, and similar emphasis has been given to learning over nonlearning. But receivers are an integral part of a communication network, and nonlearned mechanisms appear to be more ubiquitous than learned ones in the communication systems of most animals. Here we review the results of recent experiments and outline future directions for integrative studies on the development of a primarily nonlearned behaviour-recognition of communication signals during ontogeny in a tropical frog. The results suggest that antecedents to adult behaviours might be a common feature of developing organisms. Given the essential role that acoustic communication serves in reproduction for many organisms and that receivers can exert strong influence on the evolution of signals, understanding the evolutionary developmental basis of mate recognition will provide new insights into the evolution of communication systems.
    Full-text · Article · May 2012 · The Scientific World Journal
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    • "Furthermore, even calls with presumably high motivational content (as may be the case for food discovery) are still able to inform receivers about the external world. This has been demonstrated by studies showing that, regardless of the signaller's motivational state during call production, calls can provide listeners with representational information about external objects and events, in way that can be studied experimentally [1], [27], [41], [43]–[45]. Recent work on the alarm call responses of meerkats (Suricata suricata) for example, has demonstrated that both emotional and referential information are encoded into the same signal and develop on different ontogenetic time scales [45]. Meaningful progress will focus more specifically on the motivational experience of the caller and how this influences signal production. "
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    ABSTRACT: Studies on language-trained bonobos have revealed their remarkable abilities in representational and communication tasks. Surprisingly, however, corresponding research into their natural communication has largely been neglected. We address this issue with a first playback study on the natural vocal behaviour of bonobos. Bonobos produce five acoustically distinct call types when finding food, which they regularly mix together into longer call sequences. We found that individual call types were relatively poor indicators of food quality, while context specificity was much greater at the call sequence level. We therefore investigated whether receivers could extract meaning about the quality of food encountered by the caller by integrating across different call sequences. We first trained four captive individuals to find two types of foods, kiwi (preferred) and apples (less preferred) at two different locations. We then conducted naturalistic playback experiments during which we broadcasted sequences of four calls, originally produced by a familiar individual responding to either kiwi or apples. All sequences contained the same number of calls but varied in the composition of call types. Following playbacks, we found that subjects devoted significantly more search effort to the field indicated by the call sequence. Rather than attending to individual calls, bonobos attended to the entire sequences to make inferences about the food encountered by a caller. These results provide the first empirical evidence that bonobos are able to extract information about external events by attending to vocal sequences of other individuals and highlight the importance of call combinations in their natural communication system.
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