A re-evaluation of relationships in the Metastriata (Acari: Parasitiformes: Ixodidae)

Abstract

A systematic analysis of generic/subgeneric relationships in the ixodid lineage Metastriata was conducted based on 82 structural and developmental characters, 15 of which have multiple states. Results of the analysis show considerable agreement with current classifications of the Ixodidae, including good support for monophyly of the Metastriata, the genera Ixodes and Haemaphysalis, and the grouping of Hoogstraal's Rhipicephalinae and Hyalomminae, and fair support for the genus Hyalomma. Our results differ from these classifications most notably by rejecting monophyly of the genera Aponomma and Amblyomma. Instead, the analysis provides weak support for a hypothesis in which the basal two to three lineages in the Metastriata are all composed of Aponomma species, and in which a fourth lineage within that genus, Aponomma elaphense, clusters with Amblyomma quadricavum to form a more derived lineage. Resolution is insufficient to support or reject monophyly of the genera Dermacentor and Rhipicephalus, or to resolve the position of the genus Haemaphysalis relative to the other Metastriata. Overall resolution within the Rhipicephalinae/Hyalomminae is quite good, but it is quite poor among the Amblyomminae and Haemaphysalinae. These results are similar to the results of recent 16S and 18S rDNA based molecular analyses. There are few indications of host specificity among the lineages analysed. The basal metastriate lineages contain a large number of squamate associates, but the pattern is not sufficiently clear to reject the hypothesis that these ticks will feed on all available vertebrate hosts. On the other hand, nearly all of the basal taxa are Australian. This suggests a possible origin of the Metastriata in Australia, with subsequent dispersal to other parts of the world.