TAXONOMIC STATUS OF IXODES NEOTOMAE AND I-SPINIPALPIS (ACARI, IXODIDAE) BASED ON MITOCHONDRIAL-DNA EVIDENCE

Ixodes spinipalpis Hadwen & Nuttall and I. neotomae Cooley are enzooti c 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 mitoch ondrial 16S ribosomal DNA gene was amplified in 28 specimens of I. neo tomae and 149 specimens of I. spinipalpis. These products were screene d 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 ha plotypes characterized either one. Phylogenetic analysis of 18 sequenc es, representing a replicate of each of the 9 haplotypes, was performe d with Ixodes pacificus Cooley & Kohls and Ixodes jellisoni Cooley & K ohls as outgroups. Strong monophyletic support was found for a clade c ontaining I. neotomae and I. spinipalpis and within this clade no line ages comprised exclusively either taxon. These results argue against t reatment of I. neotomae and I. spinipalpis as distinct species.