Genetic variability and isolation of Cory's Shearwater colonies in the Northeast Atlantic

DNA fingerprinting was used to compare levels of genetic variability within and among eight colonies of Gory's Shearwater (Calonectris diomedea boreal is) in the Madeira, Azores, Canarias, and Berlenga archipelagoes in the Nor theast Atlantic. Fingerprint diversity, as measured by one probe and two re striction enzymes, showed very little correlation with population size, sug gesting that genetic diversity reflects historical rather than current popu lation sizes. Mean band sharing between pairs of colonies did not show any relation with between-population geographic distance. However, all between- population similarity indexes were lower than the corresponding within-popu lation similarity index, a trend that suggests a small degree of population structure across the breeding range of this subspecies. Despite banding re cords suggesting high levels of philopatry,gene flow seems sufficient to pr event considerable divergence at these loci. Alternative and equally plausi ble explanations for the results also are discussed.