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.