SRA

Population genetic structure can aide in developing conservation and management strategies by characterizing populations on local and regional scales. The Elegant Tern (Thalasseus elegans) has a restricted breeding range, with a majority of its nesting population historically found on Isla Rasa in the Gulf of California, Mexico. Northward expansion to southern California was noted in 1959; however, in recent years low marine productivity and warm oceanographic anomalies, such as El Nino events, have caused increased northward expansion of Elegant Tern breeding colonies into southern California, USA (San Diego Bay National Wildlife Refuge, Bolsa Chica Ecological Reserve, and Port of Los Angeles). We theorize there will be high gene flow between Gulf of California and southern California Elegant Tern breeding colonies due to northward movements of birds over the past half century. Restriction-site associated DNA sequencing (RADseq) was used to analyze 5,510 single nucleotide polymorphisms from 69 Elegant Terns sampled across four known breeding sites: 30 individuals from Isla Rasa (Mexico), 17 individuals from San Diego (USA), 11 individuals from Bolsa Chica Ecological Reserve (USA), and 11 individuals from the Port of Los Angeles (USA). Our analyses revealed little population structure, with non-significant genetic differentiation (FST) among sites. We also found no geographic association of individuals in a principal components analysis, and individual-based clustering failed to resolve any groups. Discriminant analysis of principal components suggested subtle clustering of individuals by breeding site; however, based on randomization analysis, the data indicate that this outcome may be a statistical artifact. These results suggest a strong degree of connectivity (gene flow) among the Gulf of California and southern California nesting colonies. Our findings indicate that Elegant Tern breeding colonies are highly fluid and move readily among sites.