Phylogenetic relationships among tick subfamilies (Ixodida: Ixodidae: Argasidae) based on the 18S nuclear rDNA gene.

Phylogenetic relationships among tick subfamilies have been estimated using morphological and molecular characters. However, the phylogeny based on a portion of the 16S mitochondrial rDNA gene differed from the morphologically based phylogeny in a number of important respects. The entire 18S rDNA gene was examined in 18 taxa from all tick subfamilies to test the 16S rDNA based phylogeny. The 18S phylogeny supports the earlier 16S based phylogeny in placing members of Hyalomminae on a common branch with members of the Rhipicephalinae and in indicating long branch lengths among soft tick taxa. However, unlike the 16S phylogeny, Amblyomminae was monophyletic and members of Haemaphysalinae did not arise within Amblyomminae. Argasinae formed a monophyletic group within Argasidae and was not a sister taxon of the hard ticks. In most respects, the phylogeny based on the 18S rDNA gene resembles the morphologically based phylogeny.

Black WC 4th ，Klompen JS ，Keirans JE 《MOLECULAR PHYLOGENETICS AND EVOLUTION》

Phylogeny of the hard ticks (Ixodidae) inferred from 18S rRNA indicates that the genus Aponomma is paraphyletic.

We examined the phylogeny of ticks (Acari:Parasitiformes:Ixodida) and their closest known mite relatives (Acari:Parasitiformes:Mesostigmata and Holothyrida) using 18S rRNA sequences. In our analyses, we included sequences from 36 taxa. Sequences for 13 hard ticks (Family Ixodidae), 5 soft ticks (Family Argasidae), and 2 mesostigmatid mites were obtained from the GenBank database and we generated sequences for 15 hard ticks and 1 holothyrid mite. Ten of these tick species were endemic to Australia. Our analyses indicated that the suborder Holothyrida is more closely related to Ixodida than to Mesostigmata, the group used as outgroup in earlier molecular studies. This finding is consistent with Lehtinen's (1991) hypothesis that the Holothyrida rather than the Mesostigmata is the sister-group to the Ixodida. Within the hard ticks the genus Aponomma and thus the family Amblyomminae were paraphyletic. Taxonomic revision of these taxa is needed. The genus Amblyomma was paraphyletic without the inclusion of "typical" Aponomma species (Ap. latum and Ap. fimbriatum). There was a basal divergence between endemic Australian and other species in both the Metastriata and the Prostriata divisions of the hard ticks.

Dobson SJ ，Barker SC 《MOLECULAR PHYLOGENETICS AND EVOLUTION》

Phylogeny of hard- and soft-tick taxa (Acari: Ixodida) based on mitochondrial 16S rDNA sequences.

Ticks are parasitiform mites that are obligate hematophagous ectoparasites of amphibians, reptiles, birds, and mammals. A phylogeny for tick families, subfamilies, and genera has been described based on morphological characters, life histories, and host associations. To test the existing phylogeny, we sequenced approximately 460 bp from the 3' end of the mitochondrial 16S rRNA gene (rDNA) in 36 hard- and soft-tick species; a mesostigmatid mite, Dermanyssus gallinae, was used as an outgroup. Phylogenies derived using distance, maximum-parsimony, or maximum-likelihood methods were congruent. The existing phylogeny was largely supported with four exceptions. In hard ticks (Ixodidae), members of Haemaphysalinae were monophyletic with the primitive Amblyomminae and members of Hyalomminae grouped within the Rhipicephalinae. In soft ticks (Argasidae), the derived phylogeny failed to support a monophyletic relationship among members of Ornithodorinae and supported placement of Argasinae as basal to the Ixodidae, suggesting that hard ticks may have originated from an Argas-like ancestor. Because most Argas species are obligate bird octoparasites, this result supports earlier suggestions that hard ticks did not evolve until the late Cretaceous.

Black WC 4th ，Piesman J 《-》

18S rRNA gene sequences and phylogenetic relationships of European hard-tick species (Acari: Ixodidae).

The complete 18S rRNA gene sequences of the following six European hard-tick species were obtained by direct PCR cycle sequencing and silver-staining methods: Rhipicephalus pusillus, Boophilus annulatus, Dermacentor marginatus, Hyalomma lusitanicum, Haemaphysalis punctata, and Ixodes ricinus. Differences observed in the sequence alignment of these six species together with the 18S rRNA gene sequences of 13 other hard-tick species demonstrate that this gene is a good marker for supraspecific differentiation as well as genus grouping among hard ticks. Phylogenetic analyses strongly support that Hyalomma species share a common ancestor with Rhipicephalinae and, consequently, Hyalomminae should no longer be considered an independent subfamily. However, no definitive conclusion could be reached to support or oppose the separation of the subfamilies Haemaphysalinae and Amblyomminae.

Mangold AJ ，Bargues MD ，Mas-Coma S 《PARASITOLOGY RESEARCH》

Phylogeny of ticks (Ixodida) inferred from nuclear ribosomal DNA.

Phylogenetic relationships of 9 species of ticks were inferred from nucleotide sequences of the D1 domain of large subunit ribosomal DNA (rDNA), the V4 region of small subunit rDNA and sequences immediately adjacent to these regions. Six of the 7 subfamilies in the Argasidae and Ixodidae were represented: Ornithodorinae and Argasinae from the Argasidae (soft ticks); and Ixodinae, Amblyomminae, Haemaphysalinae and Rhipicephalinae from the Ixodidae (hard ticks). A mite, Phytoseiulus persimilis, from the Mesostigmata, the putative sister group of the Ixodida, was used for out-group reference. Our sequence alignment, which contained the D1, V4 and adjacent sequences, comprised 503 sites; 209 of these varied among the species studied and 77 were phylogenetically informative, i.e. at least 2 different nucleotides were represented at least 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) monophyly of the 2 species of Amblyomma (93-99%); (iii) monophyly of the 6 species of Metastriata (96-99%); (iv) a sister-group relationship between Ixodes pilosus and the 6 species of Metastriata (98-100%); and (v) a sister-group relationship between Ornithodoros capensis (Ornithodorinae) and the 7 species of Ixodidae (94-99% support). The last result may be preliminary evidence that the Argasidae family (soft ticks) is paraphyletic since the 2 argasid species did not form a monophyletic group. The paraphyletic status of the Argasidae has been previously suggested by Black & Piesman (1994; Proceedings of the National Academy of Sciences U.S.A. 91: 10034). Our study indicates that the D1, V4 and adjacent sequences may be used to answer long-standing questions about the phylogeny of the Ixodida.

Crampton A ，McKay I ，Barker SC 《INTERNATIONAL JOURNAL FOR PARASITOLOGY》