Minisatellite DNA detects sex, parentage, and adoption in the south polar skua

The south polar skua (Catharacta maccormicki) is a long-lived seabird. Adults of this species exhibit only a small degree of sexual dimorphism, while male and female juveniles and chicks are morphologically indistinguishable. Female-specific DNA fragments were detected in the minisatellite profiles of south polar skua with the multilocus probes 33.15 and pV47-2. Either one or two sex-specific fragments were present in each female and absent from each male. A significant difference was also detected in the mean number of bands recorded for each sex. South polar skua breed in pairs and often raise only a single chick, DNA profiles resulting from hybridization of the probe 33.15 were used to establish parentage of 14 chicks from 13 families. In all but two families the chicks were parented by the resident adults, in one of these families the chick was shown to be the product of extrapair paternity, while the chick in the other family was found to be the offspring of neither of the resident adults. We suggest the latter is an example of the adoption of a chick from a neighboring territory.