Adaptive suppression of subordinate reproduction in cooperative mammals.

Attempts to account for observed variation in the degree of reproductive skew among cooperative breeders have usually assumed that subordinate breeding has fitness costs to dominant females. They argue that dominant females concede reproductive opportunities to subordinates to retain them in the group or to dissuade them from challenging for the dominant position or that subordinate females breed where dominants are incapable of controlling them. However, an alternative possibility is that suppressing subordinate reproduction has substantive costs to the fitness of dominant females and that variation in these costs generates differences in the net benefits of suppression to dominants which are responsible for variation in the frequency of subordinate breeding that is not a consequence of either reproductive concessions or limitations in dominant control. Here, we show that, in wild Kalahari meerkats (Suricata suricatta), the frequency with which dominants evict subordinates or kill their pups varies with the costs and benefits to dominants of suppressing subordinate breeding, including the dominants' reproductive status, the size of their group, and the relatedness of subordinates. We review evidence from other studies that the suppression of reproduction by subordinates varies with the likely costs of subordinate breeding to dominants.