Saturday, December 26, 2015

New research on vocalizations, grooming, and social bonds

Lemur catta Photo: author
Both grooming and vocalizing are linked to social bonds and relationships. Increases in the vocal repertoire of primates is correlated with group size and amount of time spent grooming (McComb and Semple, 2005). Previous research has shown that pairs of baboons (Papio cynocephalus) spend more time grooming one another (allo-grooming) and allo-groom more frequently if they are bonded socially (Silk et al., 2006). Dunbar first suggested that vocalizations may serve to act as a way of socially bonding when larger group sizes make grooming every member more difficult (1993; 2003; 2004).

A study published this December provides further insight into the reasons why small talk may have evolved and how it relates to social relationships. Studying ring-tailed lemurs (Lemur catta), Kulahci and colleagues (2015) examined vocalizations and grooming.  Four troops of free-ranging and semi-freeranging lemurs at the Duke Lemur Center and on St. Catherine's Island were studied. Vocalization and grooming network outdegrees were calculated to determine who each individual initiated vocalizations and grooming towards. The grooming network outdegree was simply the number of individuals the individual in question groomed. The vocalization network outdegree was   the number of individuals that the individual in question produced a vocal response towards upon hearing a call.

Kulahci and colleagues (2015) found that ring-tailed lemurs were more selective in who they vocalized to than who they chose to groom: as troop size increased, lemurs groomed more individuals but they did not vocalize directly towards more individuals. Regardless of troop size, vocalization network outdegrees were lower than grooming network outdegrees, showing that lemur are picky about who they vocalize to but less so about who they groom. Individuals responded to the vocalizations of lemurs they groomed more frequently than they did lemurs they groomed less often.

When audio playbacks were used, the same selectivity in vocalization responses was displayed. Thus, this selectivity in vocalizations is not due to olfactory or visual cues.

While this study agrees with previous work highlighting the connection between grooming and vocalizations, it does not align with Dunbar's hypothesis (1993; 2003; 2004) that vocalizations allow an individual to maintain more social bonds than grooming would. Whereas we would have expected to see vocalizations increase with group size, the opposite was true for this study. Rather than vocalize with more troop members as group size increases, L. catta selectively vocalize and groom all members. Thus, vocalizations may be a better indicator of social bonds than grooming, at least in L. catta.

Links of possible interest:
 Social grooming in primates
How the size of the neocortex and the size of grooming clusters relate
Derived vocal complexity of geladas


Dunbar, R. I. (1993). Coevolution of neocortical size, group size and language in humans. Behavioral and brain sciences, 16(04), 681-694.

Dunbar, R. I. (2003). The social brain: mind, language, and society in evolutionary perspective. Annual Review of Anthropology, 163-181.
Dunbar, R. I. (2004). Gossip in evolutionary perspective. Review of general psychology, 8(2), 100.
Kulahci, I. G., Rubenstein, D. I., & Ghazanfar, A. A. (2015). Lemurs groom-at-a-distance through vocal networks. Animal Behaviour, 110, 179-186.
Silk, J. B., Altmann, J., & Alberts, S. C. (2006). Social relationships among adult female baboons (Papio cynocephalus) I. Variation in the strength of social bonds. Behavioral Ecology and Sociobiology, 61(2), 183-195.

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