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

Ticks from mainland Australia (Victoria, New South Wales and Queensland) an d Tasmania, identified morphologically as either Ixodes holocyclus or Ixode s cornuatus, were compared genetically using 24 enzyme loci. The results sh owed 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, the re were fixed genetic differences at 0-60% of loci among I. holocyclus from different localities on the mainland. Ixodes holocyclus samples could be d ivided into four distinct clusters (with fixed genetic differences >15%), t hree of which were represented by one or two specimens. Nonetheless, these electrophoretic data suggest that I. holocyclus represents a species comple x. 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 iden tification, this study has demonstrated that I. cornuatus can be distinguis hed 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. cornunatus and the I. holocyclus complexes have a greater distribution than previously reported, with both occurring i n sympatry at Cape Patterson, on the southern coastline of Victoria. (C) 20 00 Australian Society for Parasitology Inc. Published by Elsevier Science L td. All rights reserved.