A commitment model of reproductive inhibition in cooperatively breeding groups

Cooperatively breeding groups include individuals that give up some current reproductive opportunities while remaining in a group. In some cases, these individuals are physiologically or morphologically unable to reproduce. Empirical and theoretical evidence suggest that this inability often does not result from stress or manipulation by dominants against the interests of subordinates. I argue that such reproductive inhibition can represent a commitment not to reproduce in exchange for a reduction in costs imposed by dominants. I present a model that allows subordinates to choose whether to inhibit their own reproduction (self-inhibition) and accept no direct reproduction while in the group or to remain flexible and attempt to take a share of group productivity. If dominants assess the reproductive status of subordinates and punish those that reproduce, this model predicts self-inhibition when group members are closely related, opportunities for independent breeding are poor, assessment of reproductive status and eviction are costly, and the chance of being detected when cheating is high. However, dominants are less likely to assess the reproductive status of subordinates that are closely related, resulting in a narrow window of relatedness in which self-inhibition is favored. Counterintuitively, this window is wider when flexible subordinates would be able to take a large share of group production. Although the model assumes that dominants are able to reliably detect commitment, it is generally robust against mistakes in the form of dominants failing to assess uncommitted subordinates, or even low frequencies of deception by flexible subordinates.