Conservation genetics of the Common Tern (Sterna hirundo) in the North Atlantic region; implications for the critically endangered population at Bermuda

Common Terns nesting at Bermuda are isolated by 1,000-4,000 km from other populations of the species around the North Atlantic Ocean. This population experienced a severe demographic bottleneck as a result of a hurricane in 2003 and was subsequently re-established by four males and four females. Using seven microsatellite loci, we compared the genetic diversity of the pre- and post-bottleneck populations, compared the genetic profile of the Bermuda population with those of other populations around the North Atlantic Ocean and mainland Europe, and assessed the potential contribution of immigration to genetic diversity. We found a loss of genetic diversity (number of alleles and heterozygosity) in the post-bottleneck Bermudian population (4.6-2.9 and 0.56-0.52, respectively). We also report significant differentiation among all sampled locations (global F-ST = 0.16) with no evidence for immigration into Bermuda. Common Terns from the Azores were genetically more similar to those from mainland North America than to those from Bermuda or mainland Europe. Our results suggest that the critically endangered population in Bermuda is genetically distinct and requires continued and enhanced conservation priority.