Population Genetic Structure of Ixodes pacificus (Acari: Ixodidae) Using Allozymes

Abstract

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.

Thirty years of tick population genetics: A comprehensive review

“…pacificus is responsible for the transmission of B. burgdorferi in the western US. Low to moderate gene flow has been observed in this tick vector using eight polymorphic allozymes against 20 populations sampled along the species range (Kain et al, 1997). A possible differentiation between northern and southern regions was particularly strong at one locus.…”

“…Two major mitochondrial lineages, possibly from mtDNA introgression from D. nitens; microsatellites predict three recently diverged genetic groups in Alberta Crosbie et al (1998), Leo et al (2010Leo et al ( , 2012Leo et al ( , 2014 Dermacentor andersoni Variable structure depending on scale and markers used; high structure observed among host-specific races; also sex-biased dispersal is known Casati et al (2008), De Meeûs et al (2002, Delaye et al (1997Delaye et al ( , 1998, Dinnis et al (2014), Healy (1979a,b), Kempf et al (2009b), Noureddine et al (2011 Ixodes pacificus DNA sequence (COIII), allozymes High structure on highly mobile hosts Kain et al (1997Kain et al ( , 1999, McLain et al (1995), Wesson et al (1993) Ixodes scapularis Microsatellites, DNA sequence (16S/cytc) High structure on highly mobile hosts Humphrey et al (2010), Kempf et al (2009bKempf et al ( , 2010Kempf et al ( , 2011, Krakowetz et al (2011), McLain et al (1995, Norris et al (1996), Qiu et al (2002), Rich et al (1995), Wesson et al (1993) …”

Lyme borreliosis in Europe and North America

“…Although the populations of I. pacificus are principally coastal, isolated inland populations have been described in such arid overall climates as Mohave County, Arizona (Olson et al 1992) and the southwestern corner of Utah (Kain et al 1997). There is no evidence of genetic isolation among these diverse populations of I. pacificus (Kain et al 1999).…”

Population Genetics and Phylogeography ofIxodes scapularis1from Canines and Deer in Arkansas

“…However, the ITS-2 region is not useful for assessing phylogenetic relationships among ticks because the region is variable and ticks evolved relatively recently (Rich et al 1997). Other genetic studies using allozymes for I. pacificus Cooley (Kain et al 1997) and I. ricinus (L.) (de Laye et al 1997) found a lack of differentiation among the populations between nearby localities and high rates of gene flow, indicating a rapid expansion of each population. Those allozyme studies concluded that the dispersal and population size of the host as well as use by ticks of a broad host range contributes to the great amounts of gene flow.…”