Reproductive suppression and inbreeding avoidance in wild populations of co operatively breeding meerkats (Suricata suricatta)

Meerkats live in co-operatively breeding familial groups in which reproduct ion is monopolised by a dominant pair of breeders. Offspring of the breeder s are behaviourally subordinate, and typically remain in their natal group as sexually mature, non-breeding helpers. In this study, we investigated th e proximate factors limiting subordinate reproduction. Evidence for reprodu ctive suppression by dominants was investigated by comparing life history, behaviour and hormonal profiles of dominants and subordinates. Baseline lev els of plasma luteinising hormone (LH) were significantly higher in dominan t than in subordinate females. However, following an exogenous injection of gonadotrophin-releasing hormone (GnRH), both categories had comparable con centrations of circulating LH. There were no significant differences in pre - or post-GnRH challenge LH levels in dominant or subordinate males. Reprod uction in both dominant and subordinate females rarely occurred in the abse nce of unrelated males. Given that groups typically comprise parents and of fspring, lack of suitable mates emerged as the primary constraint on subord inate reproduction. When this constraint was removed, subordinates typicall y bred but at a lower rate than dominants. This difference in reproduction may be attributed to intrasexual competition manifested through direct inte rference by dominant females through subordinate evictions, infanticide and the abandoning of subordinate litters. We argue that differences in reprod uctive regulation within mammalian co-operative breeding systems may be exp lained by differences in the mating strategy (inbreeding versus outbreeding ) and the probability that subordinates in obligate outbreeding species wil l encounter unrelated opposite-sex partners.