Abstract:
Rhipicephalus microplus belongs to the Ixodidae, the largest family of ticks, which are of great
economic importance due to their negative socio-economic impact on agriculture (BROUQUI 2011;
PORTO NETOA et al. 2011; SONENSHINE 1991). Acaricides have been the first choice in tick control for
cattle farmers, but R. microplus rapidly acquires resistance to these chemicals. Replication slippage
and recombination drive genetic diversity in tick populations (BAFFI et al. 2007; GUERRERO et al. 2007;
LI et al. 2007); generating point mutations and frame shifts within the genes targeted by acaricides,
resulting in resistance (BAFFI et al. 2007; HERNANDEZ et al. 2002; HERNANDEZ et al. 2000; JONSSON et
al. 2010; MORGAN et al. 2009). In addition, resistance can quickly accumulate in a population due to the
pangamy mating structure of ticks (CHEVILLON et al. 2007b; CUTULLÉ et al. 2010) and their ability to
produce multiple generations within one season (BUDELI et al. 2009; LI et al. 2007).
Vaccines have become increasingly important to control ticks, as acaricide resistance can be acquired
by field tick populations within two years (RODRIGUEZ-VIVAS et al. 2011). Although Bm86 has been
successful against multiple-acaricide resistant ticks, recent reports indicate that the Bm86 vaccine has
become ineffective, possibly due to resistance (PARIZI et al. 2009). Also, Bm86 vaccines display great
variability in terms of their efficacy against ticks isolated across Argentina (GARCIA-GARCIA et al. 2000;
PARIZI et al. 2009). This is hypothesised to be due to the genetic variability between R. micoplus
populations.
The majority of phylogenetic studies on ticks have been based on slow evolving sequences, such as
18S or 28S rRNA, which provide genus-level resolution. The COI, D3, ANT and ITS2 genes have the
potential to resolve intra-specific and interspecies variation, and may assist with the identification of
cryptic speciation within R. microplus of South Africa (ANSTEAD et al. 2011; BARKER 1998; CAREW et al.
2009; MURRELL et al. 2000; SONGA et al. 2011). Phylogeography is a multidisciplinary field that utilises
phylogenetic (molecular evidence of speciation) and population genetic principles (coalescence theory),
in combination with additional data (such as geography and population history), to determine the
genetic relationships of populations within a species (AVISE 2009) and was one of the main aspects of
this study. The phylogenetic and population genetic structure of R. microplus will provide valuable
information to geneticists, farmers and acaricide/vaccine suppliers about the different R. microplus tick
populations of South Africa. The information will facilitate more efficient and targeted tick control
whether acaricide or vaccine based as opposed to the inefficient approaches generally adopted to tick
control.
