Parentage assignment and extra-group paternity in a cooperative breeder: the Seychelles warbler (Acrocephalus sechellensis)

We describe the development and initial application of a semiautomated pare ntage testing system in the Seychelles warbler (Acrocephalus sechellensis). This system used fluorescently labelled primers for 14 polymorphic microsa tellite loci in two multiplex loading groups to genotype efficiently over 9 6% of the warbler population on Cousin island. When used in conjunction wit h the program cervus, this system provided sufficient power to assign mater nity and paternity within the Seychelles warbler, despite the complications associated with its cooperative breeding system and a relatively low level of genetic variation. Parentage analyses showed that subordinate 'helper' females as well as the dominant 'primary' females laid eggs in communal nes ts, indicating that the Seychelles warbler has an intermediate level of fem ale reproductive skew, in between the alternative extremes of helper-at-the -nest and joint nesting systems. Forty-four per cent of helpers bred succes sfully, accounting for 15% of all offspring. Forty per cent of young result ed from extra-group paternity.