Low intraspecific variation in the rRNA internal transcribed spacer 2 (ITS2) of the Australian paralysis tick, Ixodes holocyclus.

Ixodes holocyclus has a narrow, discontinuous distribution along the east coast of Australia. We studied ticks from 17 localities throughout the geographic range of this tick. The ITS2 of I. holocyclus is 793 bp long. We found nucleotide variation at eight of the 588 nucleotide positions (1.4%) that were compared for all ticks. There were eight different nucleotide sequences. Most sequences were not restricted to a particular geographic region. However, sequences F, G and H, which had an adenine at position 197, were found only in the far north of Queensland--all other ticks had a guanine at this position. The low level of intraspecific variation in this tick (0.7%) contrasts with the sequence divergence between I. holocyclus and its close relative, I. cornuatus (13.1%). These data indicate that I. holocyclus does not contain cryptic species despite possible geographic isolation of some populations. We conclude that variation in the ITS2 is likely to be informative about the phylogeny of the group.