Abstract
Social complexity may drive complexity in communicative systems due to an individual's need to navigate unpredictable interactions with multiple conspecifics. Cooperative breeding primates (marmosets and tamarins; family: Callitrichidae) live in groups with moderate to high reproductive skew, particularly in females, whereby sexually mature individuals are frequently prevented from breeding. Remarkably, dispersal from natal groups is not stereotyped upon reaching reproductive maturity. Individuals are often observed remaining in their natal groups until the same-sex breeder in their group or a neighboring group dies, experiencing hormonal reproductive suppression, aggression, and limited access to potential mates. Here we examined whether emperor tamarins (Saguinus imperator) might use vocal signals to reduce dispersal risks and maximize the likelihood of attaining a breeding position. Using six consecutive years of mark-recapture data, we showed that sexually mature non-breeders (herein "secondary breeders") are more likely to leave their groups from one year to the next than sexually mature breeders ("primary breeders"). This confirmed that, unlike primary breeders who do not need to disperse in order to reproduce, secondary breeders are choosing to accept the risks associated with dispersal and emigrating from their natal groups. We used neural networks to classify vocalizations according to individual breeding status, and conducted a series of playback experiments which demonstrated that tamarins discriminated between the calls of primary and secondary breeders. Our data support the hypotheses that secondary breeders disperse to increase mating opportunities and use vocalizations to signal their availability to potential mates. This species of cooperative breeder appears to use vocalization to navigate its social and reproductive systems, minimizing risks of dispersal and in turn increasing the likelihood of reproductive success. This research has important implications for our understanding of sexual signaling, partner choice, and reproductive success in cooperative breeders.
