Black Swans Cygnus atratus adopt related cygnets

摘要

In many species of bird with precocial young, breeding pairs occasionally adopt conspecific young into their broods or are the subject of 'eggdumping'. Here I test the hypothesis that kin selection may play a role in such alloparental behaviour in a wild population of Black Swan Cygnus atratus in which closely related individuals of both sexes occur in the breeding population. A set of eight polymorphic microsatellite loci was used to determine the genetic relatedness between 11 alien cygnets and their foster parents. The mean relatedness between alien cygnets and their foster parents was significantly higher than expected by chance. Alien cygnets were also more likely to be cared for by high-quality pairs than by low-quality pairs. I therefore suggest that cygnets move from low-quality to related, high-quality pairs. In principle, all par-ties can derive fitness benefits from alloparental care in this system: the cygnet and its true parents from its higher survival and the foster family from kin selection.