MITOCHONDRIAL DNA REVEALS POPULATION GENETIC STRUCTURE WITHIN ATLANTIC BUT NOT PACIFIC POPULATIONS OF A HOLARCTIC SEABIRD

To predict evolutionary processes, such as speciation and local adaptation, we need to understand the mechanisms causing genetic differentiation of populations. We used mitochondrial control region sequence variation to investigate the genetic structure within and between Atlantic and Pacific populations of Black-legged Kittiwake (Rissa t. tridactyla and R. t. pollicaris, respectively). We predicted that genetic divergence of these populations, as in other northern hemisphere seabird species. might have been caused by glacial vicariance in the late Pleistocene. Further, because of regional differences in the morphology of kittiwakes. and the hypothesized historical vicariance, we predicted that genetic structure would exist within Atlantic but not Pacific populations. Population genetic and phylogenetic analyses of 756 base pairs of control region sequence for 398 kittiwakes indicated that Atlantic and Pacific populations are genetically differentiated from one another. Phylogenetic analyses indicated historical divergence of two mtDNA clades within the Pacific population and four mtDNA clades within the Atlantic population. Population genetic analyses indicated that colonies within the Atlantic were strongly differentiated from one another, which could be explained by restrictions in contemporary gene flow and historical fragmentation in historical refugia. Population genetic analyses provided little evidence for genetic structure in the Pacific population, which we attributed to longer time since vicariance, allowing more migration between colonies. Our results agree with current subspecies designations of Atlantic and Pacific populations.