Cytogenetics of Ticks (Acari: Ixodoidea). 10. Chromosomes of the Winter Tick, Dermacentor albipictus (Ixodidae)

Abstract

Karyotype, sex determination, and meiosis were studied in the one-host tick, Dermacentor albipictus. Males possess 20 autosomes plus 1 sex chromosome. Ten autosomal bivalents and 1 sex univalent are present at diplonemma, diakinesis, and metaphase I; reduction division, at least for the sex chromosome, occurs at anaphase I. Centromeres probably occur terminally or nearly so in all chromosomes, but this is not certain. The sex chromosome is one of the longest and sometimes the longest chromosome at diplonemma, diakinesis, and metaphase I. It frequently migrates precociously to one pole and is the largest dyad present from anaphase I through anaphase II. No major chromosomal differences are noted in this species when compared to other Dermacentor species. Of the approximately 30 species of Dermacentor described, seven are endemic to the United States. Dermacentor species are vectors and reservoirs of several species of microorganisms. They are annoying pests and sometimes produce tick paralysis in man and animals. Oliver et al. (1972) attempted hybridization of three species of Dermacentor and Oliver (1972) reviewed the published results on chromosomes, sex determination, and spermatogenesis of Dermacentor species including new data on five North American species. Homsher and Sonenshine (1972) further studied spermatogenesis in D. variabilis in relation to host attachment. Oliver (1972) noted the scarcity of cytogenetic data on species in this genus and that published data still do not exist for D. halli and D. albipictus, the other two species found in the United States. The former occurs in southern Texas and Mexico and parasitizes the peccary and skunk. The latter species is a one-host tick and occurs on many species of wild and domesticated ungulates. It is one of the most widely distributed ticks in North America. In nature, moose and deer appear to be preferred hosts and among domestic animals, horses often become severely infested. Attacks on man are rare, but do occur (Gregson, 1956). D. albipictus is a vector of the bacillus, Klebsiella paralytica, anaplasmosis, and is a possible Received for publication 18 July 1972. * This work was supported in part by grant No. 09556 from the NIAID (NIH). vector of Rocky Mountain spotted fever. Diamant and Strickland (1965) experimentally demonstrated hereditary transmission of Corynebacterium ovis, causative agent of caseous lymphadenitis. This paper provides data on chromosomes and spermatogenesis in the winter tick, D. albipictus. MATERIALS AND METHODS Ticks were collected from elk near Hamilton, Montana, and placed in Carnoy's fixative through the cooperation of Dr. Lyle Brinton, Rocky Mountain Laboratory, Hamilton. Tick testes were subsequently removed, subdivided, placed in a drop of lacto-aceto-orcein on a slide, and squashed. These temporary slide preparations were studied and photographed.