Monogamous dominant pairs monopolize reproduction in the cooperatively breeding pied babbler

Abstract

Understanding how reproduction is partitioned between group members is essential in explaining the apparent reproductive altruism of cooperatively breeding systems. Here, we use genetic data from a population of cooperatively breeding pied babblers (<it>Turdoides bicolor</it>) to show that reproduction is highly skewed toward behaviorally dominant birds. Dominant birds monopolized reproduction, accounting for 95.2% of all chicks. Inbreeding avoidance appears to constrain subordinate reproduction because the rare incidences of subordinate reproduction occurred only with unrelated members of their groups. However, even when unrelated potential breeding partners were present in the group, subordinates rarely bred. Although half of chicks hatched into groups where subordinates could potentially breed, only 9.6% of these chicks had a subordinate parent, indicating that additional factors limit subordinate reproduction, such as reproductive conflict with dominants. Groups were highly kin structured and most subordinates were closely related to one another such that help was almost invariably directed toward close relatives. Consequently, helping in this species confers indirect fitness benefits on subordinates, which are likely to play an important role in the evolution and maintenance of cooperative helping behavior.