Taxonomic status of Ixodes neotomae and I. spinipalpis (Acari: Ixodidae) based on mitochondrial DNA evidence

Ixodes spinipalpis Hadwen & Nuttall and I. neotomae Cooley are enzootic vectors of Borrelia burgdorferi Johnson, Schmid, Hyde, Steigerwalt & Brenner in western North America. The taxa overlap in host preference, habitat, and morphology. Mitochondrial DNA was compared between the taxa to test for reproductive isolation. A 300-bp region of the mitochondrial 16S ribosomal DNA gene was amplified in 28 specimens of I. neotomae and 149 specimens of I. spinipalpis. These products were screened for sequence variation using single-strand conformation polymorphism analysis, and 9 haplotypes were detected. Haplotype frequencies varied between taxa; however, Shannon diversity analysis indicated that most variation arose among collections within each taxon, and no unique haplotypes characterized either one. Phylogenetic analysis of 18 sequences, representing a replicate of each of the 9 haplotypes, was performed with Ixodes pacificus Cooley & Kohls and Ixodes jellisoni Cooley & Kohls as outgroups. Strong monophyletic support was found for a clade containing I. neotomae and I spinipalpis and within this clade no lineages comprised exclusively either taxon. These results argue against treatment of I. neotomae and I. spinipalpis as distinct species.