Adaptive suppression of subordinate reproduction in cooperative mammals

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This project will investigate the evolutionary processes and physiological mechanisms underlying variation in reproductive success among females in mammals that breed cooperatively. Previous studies have either assumed that subordinate females breed where dominant females grant them reproductive concessions to ensure that they remain in the group and assist in rearing their offspring or that subordinates breed where dominants are incapable of preventing them from conceiving or rearing young. However, they have had limited success in explaining the distribution of subordinate reproduction within or across species. We shall test the alternative hypothesis that the frequency with which subordinate females breed varies because dominants adjust the extent to which they suppress subordinate reproduction in relation to variation in the likely costs and benefits of subordinate breeding to their own fitness. In an existing study population of Kalahari meerkats Suricata suricatta, where full life-history records are already available for large samples of individuals, the project will use a combination of novel experiments involving the manipulation of reproduction by subordinate and dominant females and quantitative analyses of existing data to (1) measure the costs of subordinate breeding to dominant females by preventing subordinates from breeding in a sample of groups and (2) determine whether the extent to which dominants tolerate the presence or breeding attempts of subordinates when the likely costs of subordinate reproduction to their own breeding success are low by preventing dominants from breeding and examining how this affects their treatment of subordinate females and their offspring (3) determine whether dominants monitor the growth of subordinates and suppress the growth of individuals close to them in weight or (4) attempt to manipulate the identity of their successors by selectively evicting distantly related females immediately below them in the hierarchy (beta females). Finally, we shall develop novel game-theoretical models based on realistic estimates of the costs and benefits of suppressing or evicting subordinates to dominants that can be used to predict the frequency of subordinate reproduction and the structure of groups in other cooperative breeders.