Population Genetics and Gene Flow of the Common Tern

Genetic analysis using isoelectric focusing of blood proteins indicated that Common Terns, Sterna hirundo, from four colonies in Minnesota and Wisconsin had an observed average heterozygosity (Ho) of 0.044 and had 12 polymorphic loci of the 34 loci examined (P = 0.353). These values suggest that Common Terns of Minnesota and Wisconsin have approximately average levels of genetic variation and diversity for avian species. Interpopulational Fst values, four genetic distance estimates and an overall Fst value of 0.0022 revealed that the four colonies (subpopulations) were not genetically differentiated. Indirect estimates of gene flow, using the method of conditional average allelic frequency, indicated high levels of gene flow. Using the method of private alleles (alleles found in only one subpopulation), the estimated number of immigrants per generation (Nm) into each subpopulation ranged from seven to 16, again demonstrating significant levels of movement of terns among colonies. Direct estimates of dispersal from band recovery data corroborated these findings. By extending these results, I suggest that other Common Tern colonies in North America have at least as much gene flow among regional breeding populations as do these disjunct inland colonies.