Genetic Variation in Mitochondrial DNA of North American Herring Gulls,Larus argentatus

The herring gull (Larus argentatus), which is one of the most abundant gulls in temperate North America, is used as an important bioindicator species, but little is known about its patterns of genetic variation. This study examines DNA sequence diversity in the cytochrome b gene of mitochondrial DNA (mtDNA) from herring gull colonies in the Great Lakes basin and from a site in the Maritimes. A 307-bp fragment of the gene was analyzed using a rapid mutation screening procedure coupling directed termination PCR (DT-PCR) with single-stranded conformation polymorphism (SSCP). Seven mtDNA haplotypes were revealed in 224 specimens with a common haplotype dominating all populations. Direct sequencing of a 1063-bp fragment of the cytochrome b gene identified 8 additional haplotypes, but the sequence divergence among all 15 haplotypes was very low (average 0.24%). These data suggest that herring gulls experienced a bottleneck during the last glaciation that is now reflected in their low levels of genetic divergence. The geographic distribution of mtDNA haplotypes indicates that gene flow among herring gull populations is sufficient to ensure genetic homogeneity in the Great Lakes, but insufficient to homogenize genetic variation between the Great Lakes and the Maritimes. Meanwhile, a comparison analysis of frozen egg specimens suggests a possible shift in the genetic composition of the Great Lakes populations over the last 15 years.