The common eider is a colony breeding seaduck with extreme female philopatry. Molecular genetic techniques (mtDNA sequencing and microsatellite analysis) were applied on Baltic eiders to infer sex-specific dispersal and mating tactics 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 traits. 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, mate choice is not random: The bias towards mates of similar geographic origin might reflect a different time of arrival at the wintering ground for eiders of different origin, together with the adaptive significance of early pair formation.
Rates of multiple paternities were investigated in the sailfin molly (Poecilialatipinna), using eight microsatellite loci. Genotyping was performed for offspring and mothers in 40 broods from four allopatric populations from the south-eastern U.S.A. along a geographic stretch of 1200 km in west-east direction and approximately 200 km from north to south. No significant differences regarding rates of multiple paternities were found between populations despite sample populations stemming from ecologically divergent habitats. Even the most conservative statistical approach revealed a minimum of 70% of the broods being sired by at least two males, with an average of 1.80-2.95 putative fathers per brood. Within broods, one male typically sired far more offspring than would be expected under an assumed equal probability of all detected males siring offspring.