Research reportVocalizations associated with anxiety and fear in the common marmoset (Callithrix jacchus)

- Tsik-egg call was identified as a multisyllabic call type rather than a sequence of tsik and egg call.
- Marmosets vocalized tsik-egg calls without tsik calls under anxiety-related situations.
- Marmosets vocalized tsik and tsik-egg calls when they were exposed to predatory stimuli.
- Tsik-egg with/without tsik calls appear to be vocal indices for fear/anxiety in marmosets.

Vocalizations of common marmoset (Callithrix jacchus) were examined under experimental situations related to fear or anxiety. When marmosets were isolated in an unfamiliar environment, they frequently vocalized “tsik-egg” calls, which were the combination calls of 'tsik' followed by several 'egg'. Tsik-egg calls were also observed after treatment with the anxiogenic drug FG-7142 (20 mg/kg, sc). In contrast, when marmosets were exposed to predatory stimuli as fear-evoking situations, they frequently vocalized tsik solo calls as well as tsik-egg calls. These results suggest that marmosets dissociate the vocalization of tsik-egg and tsik calls under conditions related to fear/anxiety; tsik-egg solo vocalizations were emitted under anxiety-related conditions (e.g., isolation and anxiogenic drug treatment), whereas a mixed vocalization of tsik-egg and tsik was emitted when confronted with fear-provoking stimuli (i.e., threatening predatory stimuli). Tsik-egg call with/without tsik can be used as a specific vocal index of fear/anxiety in marmosets, which allows us to understand the neural mechanism of negative emotions in primate.