Genetic variation within the ticks Ixodes holocyclus and Ixodes cornuatus from south-eastern Australia

Ticks from mainland Australia (Victoria, New South Wales and Queensland) and Tasmania, identified morphologically as either Ixodes holocyclus or Ixodes cornuatus, were compared genetically using 24 enzyme loci. The results showed that ticks from three localities in Victoria were genetically similar to I. cornuatus in Tasmania, but both groups had fixed genetic differences at >45% of loci compared with other ticks on the mainland. In addition, there were fixed genetic differences at 0-60% of loci among I. holocyclus from different localities on the mainland. Ixodes holocyclus samples could be divided into four distinct clusters (with fixed genetic differences >15%), three of which were represented by one or two specimens. Nonetheless, these electrophoretic data suggest that I. holocyclus represents a species complex. The results also showed that the morphological criteria used to identify specimens were not always accurate because several specimens had been mis-identified morphologically. Despite limitations with the morphological identification, this study has demonstrated that I. cornuatus can be distinguished from the I. holocyclus species complex using six enzyme loci, providing the foundation for a re-examination of morphological characteristics. The present study has shown that I. cornuatus and the I. holocyclus complexes have a greater distribution than previously reported, with both occurring in sympatry at Cape Patterson, on the southern coastline of Victoria.