PHYLOGENY OF TICKS (IXODIDA) INFERRED FROM NUCLEAR RIBOSOMAL DNA

Phylogenetic relationships of 9 species of ticks were inferred from nu cleotide sequences of the D1 domain of large subunit ribosomal DNA (rD NA), the V4 region of small subunit rDNA and sequences immediately adj acent to these regions. Six of the 7 subfamilies in the Argasidae and Ixodidae were represented: Ornithodorinae and Argasinae from the Argas idae (soft ticks); and Ixodinae, Amblyomminae, Haemaphysalinae and Rhi picephalinae from the Ixodidae (hard ticks). A mite, Phytoseiulus pers imilis, from the Mesostigmata, the putative sister group of the Ixodid a, was used for out-group reference. Our sequence alignment, which con tained the D1, V4 and adjacent sequences, comprised 503 sites; 209 of these varied among the species studied and 77 were phylogenetically in formative, i.e. at least 2 different nucleotides were represented at l east twice. This alignment was subjected to maximum parsimony, genetic distance and maximum likelihood analyses. We found strong support in bootstrap resampling experiments for the following relationships: (i) monophyly of the 7 species of Ixodidae (98-100% support); (ii) monophy ly of the 2 species of Amblyomma (93-99%); (iii) monophyly of the 6 sp ecies of Metastriata (96-99%); (iv) a sister-group relationship betwee n Ixodes pilosus and the 6 species of Metastriata (98-100%); and (v) a sister-group relationship between Ornithodoros capensis (Ornithodorin ae) and the 7 species of Ixodidae (94-99% support). The last result ma y be preliminary evidence that the Argasidae family (soft ticks) is pa raphyletic since the 2 argasid species did not form a monophyletic gro up. The paraphyletic status of the Argasidae has been previously sugge sted by Black & Piesman (1994; Proceedings of the National Academy of Sciences U.S.A. 91: 10034). Our study indicates that the D1, V4 and ad jacent sequences may be used to answer long-standing questions about t he phylogeny of the Ixodida. Copyright (C) 1996 Australian Society for Parasitology. Published by Elsevier Science Ltd.