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Population genetic structure of Ixodes pacificus (Acari: Ixodidae) using allozymes

Kain, D.E., Sperling, F.A.H., Lane, R.S.
Journal of medical entomology 1997 v.34 no.4 pp. 441-450
Ixodes pacificus, population genetics, population structure, genetic variation, allozymes, loci, glucose-6-phosphate isomerase, alleles, gene frequency, genetic distance, gene flow, geographical variation, enzyme polymorphism, British Columbia, Oregon, California, Arizona, Utah
Genetic analysis of the population structure of the western blacklegged tick, Ixodes pacificus Cooley & Kohls, was conducted using allozymes. This vector tick transmits the Lyme disease spirochete, Borrelia burgdorferi Johnson, Schmid, Hyde, Steigerwalt & Brenner, in the far-western United States. It ranges from British Columbia to Baja California and disjunct populations are present in Oregon, Nevada, Utah, and Arizona. Host-seeking adult ticks were collected from vegetation across the range of the species and were partially fed on rabbits prior to analysis. Twelve putative loci were resolved using starch gel electrophoresis. One locus, glucose-6-phosphate isomerase, formed an apparent north/south latitudinal cline and showed significant geographic structure. None of the remaining loci exhibited much genetic differentiation. Estimates of gene flow were high relative to other arthropods. Isolation-by-distance analysis suggests a recent and rapid range expansion. We conclude that the overall lack of differentiation is due high rates of gene flow.