Mitochondrial DNA sequence variation in Ixodes pacificus (Acari: Ixodidae)

Abstract

The western black-legged tick, Ixodes paci®cus, is a primary vector of the spirochaete, Borrelia burgdorferi, that causes Lyme disease. We used variation in a 355-bp DNA portion of the mitochondrial cytochrome oxidase III gene to assess the population structure of the tick across its range from British Columbia to southern California and east to Utah. Ixodes paci®cus showed considerable haplotype diversity despite low nucleotide diversity. Maximum parsimony and isolationby-distance analyses revealed little genetic structure except between a geographically isolated Utah locality and all other localities. Loss of mtDNA polymorphism in Utah ticks is consistent with a postPleistocene founder event. The pattern of genetic di erentiation in the continuous part of the range of Ixodes paci®cus reinforces recent recognition of the di culties involved in using genetic frequency data to infer gene¯ow and migration.

Assessment of intraspecific mtDNA variability of European Ixodes ricinus sensu stricto (Acari: Ixodidae)

“…The suggested lack of phylogeography structure observed in Europe within I. ricinus s.s. ticks contrasts with the geographic genetic differentiation recorded in North America for other tick species of the I. ricinus complex (Norris et al, 1996;Kain et al, 1999;Qiu et al, 2002). Norris et al (1996), using mitochondrial DNA markers (12S and 16S rDNA) and the single strand conformation polymorphism assay (SSCP), analysed the phylogeography of I. scapularis ticks originating from north-east America (Norris et al, 1996).…”

“…These results were confirmed by Qiu et al (2002), who analysed the mitochondrial 16S rDNA with SSCP and reported that I. scapularis is geographically structured across the East Coast: the northern (''American clade'') and southern (''Southern clade'') populations are genetically separated and present different evolutionary and demographic histories with an effective increase of the Northern tick population size (Qiu et al, 2002). However, allozyme analysis of the mitochondrial COIII gene of another north American tick species, I. pacificus, suggested weak differentiation and the tree generated from these data revealed little geographic structure for the coastal ticks, but a separation of the Utah samples (an inland state) (Kain et al, 1999). To summarise, in North-America I. scapularis seems to have a geographic structure more marked than I. pacificus, while the variability of the genetic markers analysed is approximately the same, 12.6% (53/420, 12S rDNA, (Norris et al, 1996)) and 10.1% (36/355, COIII, (Kain et al, 1999)), respectively.…”

“…However, allozyme analysis of the mitochondrial COIII gene of another north American tick species, I. pacificus, suggested weak differentiation and the tree generated from these data revealed little geographic structure for the coastal ticks, but a separation of the Utah samples (an inland state) (Kain et al, 1999). To summarise, in North-America I. scapularis seems to have a geographic structure more marked than I. pacificus, while the variability of the genetic markers analysed is approximately the same, 12.6% (53/420, 12S rDNA, (Norris et al, 1996)) and 10.1% (36/355, COIII, (Kain et al, 1999)), respectively. Thus, the two American Ixodes species mentioned above show a more pronounced phylogeography structure and variability (especially I. scapularis) than that observed for I. ricinus s.s. in Europe.…”

“…The consequence of the glaciation period is the extinction and the loss of genetic variation of the living populations in the affected regions (Hewitt, 1996). The deep structure of I. scapularis and the weak structure of I. pacificus may reflect the past presence of different refugia populations in north-east (Qiu et al, 2002) and in north-west America, precisely in Utah (Kain et al, 1999), and on the west coast, which were not affected by the ice, with the consequent independent evolution of the enclaves (Hewitt, 1996). In contrast, the recent expansion of I. ricinus population northward from the South appears associated with a low degree of genetic diversity and the concomitant absence of deep genetic structure (McLain et al, 2001).…”

Sex-Biased Genetic Structure in the Vector of Lyme Disease, Ixodes Ricinus

“…Mitochondrial DNA also suggested weak differentiation at a large scale in a related species, I. pacificus (Kain et al 1999). The development of other microsatellites may be a difficult task because such loci are rare in the I. ricinus species complex (Delaye et al 1998;Fagerberg et al 2001) and because the primers developed for I. uriae did not amplify I. ricinus DNA (McCoy and Tirard 2000).…”