Prior research on cooperative breeders has considered correlations between group reproductive output (GRO) and the number of individuals in each age-sex class, but without controlling for uneven sampling efforts, the underlying effects of group size, and pseudoreplication at the group and species levels. Among callitrichids, age-sex classes do not provide meaningful categories, as individuals within an age-sex class can demonstrate varying reproductive development due to reproductive dominance of a few individuals per group. This study re-assesses the drivers of GRO in callitrichids by a) conducting a meta-analysis of published studies of callitrichid group composition; b) determining a novel method to assign developmental class based on reproductive morphology; and c) utilizing a multistep modelling approach to assess whether any sex-based developmental class predicts both the presence and the numbers of surviving offspring among free-ranging saddleback (Leontocebus weddelli) and emperor tamarins (Saguinus imperator) in Peru. The meta-analysis utilizing a historical dataset revealed that adult females and group size, but not the number of adult males is significantly correlated with GRO. Statistical models of the new dataset revealed that only mature males predicted if groups had any infants at all, but that the number of surviving infants was predicted by mature females and group size. Thus mature males appear to be necessary for groups to raise any infants, but mature females and a larger group size increase group reproductive output overall..

Primate long calls are high-amplitude vocalizations that can be critical in maintaining intragroup contact and intergroup spacing, and can encode abundant information about a call's producer, such as age, sex, and individual identity. Long calls of the wild emperor (Saguinus imperator) and saddleback (Leontocebus weddelli) tamarins were tested for these identity signals using artificial neural networks, machine-learning models that reduce subjectivity in vocalization classification. To assess whether modelling could be streamlined by using only factors which were responsible for the majority of variation within networks, each series of networks was re-trained after implementing two methods of feature selection. First, networks were trained and run using only the subset of variables whose weights accounted for ≥50% of each original network's variation, as identified by the networks themselves. In the second, only variables implemented by decision trees in predicting outcomes were used. Networks predicted dependent variables above chance (≥58.7% for sex, ≥69.2 for age class, and ≥38.8% for seven to eight individuals), but classification accuracy was not markedly improved by feature selection. Findings are discussed with regard to implications for future studies on identity signaling in vocalizations and streamlining of data analysis.

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.

Prior research on cooperative breeders has considered correlations between group reproductive output (GRO) and the number of individuals in each age-sex class, but without controlling for uneven sampling efforts, the underlying effects of group size, and pseudoreplication at the group and species levels. Among callitrichids, age-sex classes do not provide meaningful categories, as individuals within an age-sex class can demonstrate varying reproductive development due to reproductive dominance of a few individuals per group. This study re-assesses the drivers of GRO in callitrichids by a) conducting a meta-analysis of published studies of callitrichid group composition; b) determining a novel method to assign developmental class based on reproductive morphology; and c) utilizing a multistep modelling approach to assess whether any sex-based developmental class predicts both the presence and the numbers of surviving offspring among free-ranging saddleback (Leontocebus weddelli) and emperor tamarins (Saguinus imperator) in Peru. The meta-analysis utilizing a historical dataset revealed that adult females and group size, but not the number of adult males is significantly correlated with GRO. Statistical models of the new dataset revealed that only mature males predicted if groups had any infants at all, but that the number of surviving infants was predicted by mature females and group size. Thus mature males appear to be necessary for groups to raise any infants, but mature females and a larger group size increase group reproductive output overall.