Cytosystematics of five North American Dermacentor (Acari: Ixodidae) species

The karyotypes of five species of Dermacentor ticks found in North America were examined for the presence and location of constitutive heterochromatin (C-bands) and the location of the nucleolar organizing regions (NORs). All specimens examined had 20 autosomes and an XX:XO sex-determining system; the X was the largest element in the karyotype. Except as noted, the autosomes of all species were acrocentric, and heterochromatin was restricted to the centromeric region. The one-host species D. nitens and D. albipictus were distinguished from the three-host species by a lack of additional bands of heterochromatin and by having a subtelocentric X chromosome. However, some individuals of D. albipictus were observed to have acrocentric X chromosomes. D. nitens differed from D. albipictus in having two subtelocentric autosomal pairs (pairs 1 and 8). A single pair of NORs was noted for the one-host species; however, heterochromatin was not associated with the NORs. Among the three-host species, D. occidentalis showed a band of heterochromatin proximal to the centromere in autosomal pairs 1 and 8, and D. andersoni had similar bands in autosomal pairs 1, 3, 7, and 9. D. variabilis displayed heterochromatic bands in autosomal pairs 3, 7, and 9. All three-host species displayed a single pair of NORs, which was associated with the band of heterochromatin on pair 9. Indications of some genetic incompatibility between the two recognized forms of D. albipictus are discussed.