Analyses of mitochondrial genes reveal two sympatric but genetically divergent lineages of Rhipicephalus appendiculatus in Kenya
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Date
2016
Authors
Kanduma, E.G.
Mwacharo, J.M.
Githaka, N.W.
Kinyanjui, P.W.
Njuguna, J.N.
Kamau, L.C.
Kariuki, E.
Mwaura, S.
Skilton, R.A.
Bishop, R.P.
Journal Title
Journal ISSN
Volume Title
Publisher
BioMed Central
Abstract
Background: The ixodid tick Rhipicephalus appendiculatus transmits the apicomplexan protozoan parasite Theileria
parva, which causes East coast fever (ECF), the most economically important cattle disease in eastern and southern
Africa. Recent analysis of micro- and minisatellite markers showed an absence of geographical and host-associated
genetic sub-structuring amongst field populations of R. appendiculatus in Kenya. To assess further the phylogenetic
relationships between field and laboratory R. appendiculatus tick isolates, this study examined sequence variations at
two mitochondrial genes, cytochrome c oxidase subunit I (COI) and 12S ribosomal RNA (rRNA), and the nuclear
encoded ribosomal internal transcribed spacer 2 (ITS2) of the rRNA gene, respectively.
Results: The analysis of 332 COI sequences revealed 30 polymorphic sites, which defined 28 haplotypes that were
separated into two distinct haplogroups (A and B). Inclusion of previously published haplotypes in our analysis
revealed a high degree of phylogenetic complexity never reported before in haplogroup A. Neither haplogroup
however, showed any clustering pattern related to either the geographical sampling location, the type of tick
sampled (laboratory stocks vs field populations) or the mammalian host species. This finding was supported by the
results obtained from the analysis of 12S rDNA sequences. Analysis of molecular variance (AMOVA) indicated that
90.8 % of the total genetic variation was explained by the two haplogroups, providing further support for their
genetic divergence. These results were, however, not replicated by the nuclear transcribed ITS2 sequences likely
because of recombination between the nuclear genomes maintaining a high level of genetic sequence
conservation.
Conclusions: COI and 12S rDNA are better markers than ITS2 for studying intraspecific diversity. Based on these
genes, two major genetic groups of R. appendiculatus that have gone through a demographic expansion exist in
Kenya. The two groups show no phylogeographic structure or correlation with the type of host species from which
the ticks were collected, nor to the evolutionary and breeding history of the species. The two lineages may have a
wide geographic distribution range in eastern and southern Africa. The findings of this study may have implications
for the spread and control of R. appendiculatus, and indirectly, on the transmission dynamics of ECF
Description
Research Article
Keywords
Ticks, COI, 12S rRNA, ITS2, Phylogeography, Population genetics, Genetic differentiation, Genetic markers, East coast fever
Citation
Parasites & Vectors (2016) 9:353; DOI 10.1186/s13071-016-1631-1