An electrophoretic comparison of the Australian paralysis tick, Ixodes holocyclus Neumann, 1899, with I. cornuatus Roberts, 1960 (Acari : Ixodidae)

Abstract

An electrophoretic study was conducted on ticks morphologically identified as either Ixodes cornuatus or I. holocyclus from Tasmania and several localities on mainland Australia. Ticks were characterised genetically at 27 enzyme loci encoding 24 enzymes. The extent of genetic divergence (52–69% fixed differences) between ticks from Tasmania and those from the mainland was equivalent to that found between these two groups and two morphologically distinct species, I. hirsti and I. fecialis. The Tasmanian ticks therefore represent a different species from the specimens from the mainland and the electrophoretic data show that the morphological characters currently used to distinguish I. holocyclus from I. cornuatus are inadequate. Genetic heterogeneity was detected in samples from different localities on the mainland. This could represent either population variation, or the existence of cryptic species, but more ticks from these mainland localities need to be examined electrophoretically to resolve this.

Clinical presentation and treatment of tick paralysis in dogs and cats in Sydney (2001–2010)

“…It has been suggested that ticks from different geographic regions secrete toxin at different rates and volumes . Genetic variation among individual ticks, which was assessed using electrophoresis of multiple enzyme loci, is so marked that some authors have suggested that I. holocyclus could be a complex of several species and this could underscore differential rates of toxin production.…”

Asymmetrical focal neurological deficits in dogs and cats with naturally occurring tick paralysis (Ixodes holocyclus): 27 cases (1999–2006)

“…Conversely, differences in toxin production or toxin content, possibly related to genetic variation within I. holocyclus might offer an alternative explanation 30 . Three neurotoxins (holocyclotoxins: HT‐1, HT‐2, HT‐3) have been recently isolated from I. holocyclus 31 and genetic studies using multilocus enzyme electrophoresis suggest that I. holocyclus is not a single species, but represents a complex of two or more species that can coexist in the same geographic location 32,33 . Hence, different subspecies of I. holocyclus , existing in sympatry, might secrete a different battery of neurotoxins with varying local and general effects, thereby providing a plausible explanation as to why some ticks which cause TP produce unilateral facial paralysis and others at similar sites of attachment do not.…”

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

“…Jackson et al (1998) also found substantial differences between I. holocyclus and I. cornuatus: variation at 52-69% of allozyme loci studied. More recently, Jackson et al (2000) found that up to 80% of allozyme loci studied varied between I. holocyclus and I. cornuatus.…”

“…However, Penglis (1987) was unable to find differences in oviposition period, egg-incubation time or in other aspects of reproduction of I. holocyclus between highland and lowland areas of south-east Queensland. Jackson et al (1998; studied variation in I. holocyclus and I. cornuatus at 24-27 allozyme loci and found that the two species were genetically distinct. In addition, Jackson et al (2000) found preliminary evidence that I. holocyclus may represent a species complex.…”