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

Abstract

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.