ON SEX-SPECIFIC DISPERSAL AND MATING TACTICS IN THE COMMON EIDER SOMATERIA MOLLISSIMA AS INFERRED FROM THE GENETIC STRUCTURE OF BREEDING COLONIES

The common eider is a colony breeding seaduck with extreme female philopatry. Molecular genctic techniques (mt:DNA sequencing and microsatellite analysis) were applied on Baltic eiders lo infer sex-specific dispersal and mating tacties among breeding colonies with different seasonal migration behaviour, i.e. sedentary, short distance migratory, and long distance migratory. MtDNA patterns show pronounced differentiation among colonies in maternally inherited trails. The estimated number of exchanged females per generation was 1.0-1.4. Smaller colonies showed a lower level of genetic variation in mtDNA, Microsatellite patterns suggest male-mediated gene flow to be sufficient for preventing inbreeding even in smaller colonies. However, though eiders of different geographic origin mix on wintering grounds, where mating occurs, male choice is not random: The bias towards males of similar geographic origin might reflect a different time of arrival at the wintering ground for eiders of different origin, together with the adaptive signiticance of early pair formation.