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 Holoth yrida) using 18S rRNA sequences. In our analyses, we included sequences fro m 36 taxa. Sequences for 13 hard ticks (Family Ixodidae), 5 soft ticks (Fam ily Argasidae), and 2 mesostigmatid mites were obtained from the GenBank da tabase 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 M esostigmata, the group used as outgroup in earlier molecular studies. This finding is consistent with Lehtinen's (1991) hypothesis that the Holothyrid a rather than the Mesostigmata is the sister-group to the Ixodida. Within t he hard ticks the genus Aponomma and thus the family Amblyomminae were para phyletic. Taxonomic revision of these taxa is needed. The genus Amblyomma w as paraphyletic without the inclusion of "typical" Aponomma species (Ap. la tum and Ap. fimbriatum). There was a basal divergence between endemic Austr alian and other species in both the Metastriata and the Prostriata division s of the hard ticks. (C) 1999 Academic Press.