Combinational vocal usage for emotional expression in common marmoset (Callithrix jacchus).

Contrary to the thorough understanding of birdsong studies, understanding of vocal communication in primate still fall behind in the experimental investigations. Wild common marmosets (Callithrix jacchus) have thirteen call repertoires described by using configuration of spectrogram and observation of behavioral context (e.g., Egg call associated with vigilance behavior), suggesting their depending on rich vocal communications (Bezerra and Souto 2008). Studies using captive marmosets reported that Tsik calls were induced when they faced predator of fearful object (e.g., Clara et al. 2008). These previous studies described vocal repertoires based on mono-categorical syllables. However, we found that multi-syllabic elements, compounds of Tsik and Egg calls (named Twiggy), were vocalized when marmosets were isolated in a novel, isolated cage without predatory context. Twiggy was commonly observed from all marmosets tested, and clearly distinguished from Tsik by spectrum analysis. These suggest the separate usage of combinational element (i.e., Twiggy) and solitary element (i.e., Tsik) for different contexts. In this study, we aimed to experimentally differentiate the vocal usages by presentation of visual stimuli. We presented neutral or predatory photographs to six subjects to test they respond with different vocalizations. Tsik vocalizations significantly increased during the predatory stimuli than neutral stimuli (Generalized Linear Mixed Model, vocalizations = stimuli (neutoral or predator), cluster = subject, family = poisson, p < 0.001*). Twiggy was also vocalized, however the numbers of which were not significantly different between the stimulus contexts (Generalized Linear Mixed Model, vocalizations = stimuli (neutral or predator), cluster = subject, family = poisson, p = 0.53). Tsik were vocalized specifically in the predatory context, whereas Twiggy was used in both of the contexts. To identify the physiological background of Twiggy, we measured vocalizations under pharmacologically induced anxiety state by injecting FG-7142, a partial inverse agonist of the benzodiazepine receptor. FG-7142 is considered as anxiogenic drug, since it increased anxiety behavior in rodents and primates (Belzung and Griebel 2001, Carey et. al. 1991). Through the habituation to the isolated cage, the marmosets decrease their Twiggy vocalization. However, injection of FG-7142 reincreased Twiggy calls. Our results suggested that Twiggy is associated with anxiety rather than fear. Although the functional difference between the Tsik and Twiggy has to be tested by comparison of reactions to these calls, these experimental investigations would illuminate the understanding for semantic difference expressed by combination of multiple elements.Evolang