The Evolution of Cooperative Breeding in Vertebrates

Abstract

Abstract Cooperative breeding – in which some sexually mature individuals forgo independent breeding, join a group as subordinate and help to raise the offspring of others – occurs in at least 3% (mammals) and 9% (birds) of vertebrates. Because helping others is costly, this behaviour contradicts the concept of ‘selfish’ natural selection. The intriguing evolutionary paradox of such seemingly altruistic behaviour has, therefore, been the focus of much study aiming to unravelling the evolutionary drivers underlying cooperative breeding. The benefits of group living, costs of dispersal and constraints of limited available independent breeding positions may persuade individuals to delay independent breeding and remain as subordinates within a group. However, it is the range of subsequent benefits (indirect benefits – such as improving reproduction and survival of related individuals or direct benefits – such as gaining breeding experience, benefits of future cooperation with raised recruits or gaining a share in reproduction) that favour the evolution of helping. Key Concepts The evolution of cooperative breeding is best understood by considering the benefits for helpers obtained from delayed dispersal and from helping, and the benefits helpers impose on breeders. Subordinate individuals are expected to stay when there are constraints on independent breeding and/or when they obtain benefits in their resident territory. Subordinates individuals can help related individuals and gain indirect (kin selected) fitness benefits, but in many species, helpers can also be unrelated; direct benefits of helping (like parentage, being allowed to stay) may thus be more important than commonly assumed. Breeders can benefit from helpers, either because these improve their reproductive success or because breeders can reduce their own investment in the offspring. The surplus of reproductive capable individuals and the effects of helpers on survival and reproduction can have important implications for population dynamics in cooperatively breeding species.