Molecular identification and phylogeny of one host Dermacentor ticks in North America

The genus Dermacentor is represented by 12 species in the New World. Of these, the winter tick (Dermacentor albipictus (Packard)) has the broadest geographic range, from Southern Canada to Mexico and Central America, and widely but disjunctly distributed throughout the contiguous U.S. (Furman and Loomis 1984, Yunker et al. 1986). The extensive but fragmented distribution seen in D. albipictus may result in the existence of isolated populations with disrupted gene flow, leading to population differentiation and eventual speciation (Nadler 1995). D. albipictus and D. nigrolineatus were described as separate species by Packard in 1869, but later grouped as a single species, namely D. albipictus, by Cooley in 1938. Nevertheless, some authors continued to recognize D. nigrolineatus as a distinct species  (Bishopp and Trembley, 1945; Camicas et al. 1998).  In a molecular phylogenetic study of all North American Dermacentor, Crosbie et al. (1998) found substantial intraspecific variation within D. albipictus and concluded that morphological and genetic evidence suggest that the winter tick may be a species complex, where some specimens were grouping more closely to another one-host tick, the tropical horse tick, D. nitens. Our preliminary data, based on sequences from 12S and 16S and including multiple specimens of D. albipictus from various areas of its range, also exhibit similar splitting of D. albipictus by D. nitens, and clearly show separate lineages within this species. Our molecular data are consistent with recent morphological findings in this species (Apanaskevich- in press). Our combined morphological and molecular data may lead to re-evaluation of taxonomic status of some morphological entities in the genus.