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Ticks Tick Borne Dis. 2019 Jan;10(1):219-240. doi: 10.1016/j.ttbdis.2018.09.010. Epub 2018 Oct 1.

Argasid and ixodid systematics: Implications for soft tick evolution and systematics, with a new argasid species list.

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Epidemiology, Parasites and Vectors, Agricultural Research Council-Onderstepoort Veterinary Research, Onderstepoort 0110, South Africa; Department of Life and Consumer Sciences, University of South Africa, South Africa. Electronic address:
The Biotechnology Platform, Agricultural Research Council-Biotechnology Platform, Onderstepoort 0110, South Africa.
Epidemiology, Parasites and Vectors, Agricultural Research Council-Onderstepoort Veterinary Research, Onderstepoort 0110, South Africa.
Laboratory of Bacteriology, Rocky Mountain Laboratories, National Institute of Allergy and Infectious Diseases, Hamilton, MT, United States.
Department of Paediatrics, National School of Tropical Medicine, Paediatric Tropical Medicine, Baylor College of Medicine, Houston, TX, United States.
Department of Entomology, Texas A&M AgriLife Research, Texas A&M University, College Station, TX, United States.
USDA-ARS Knipling-Bushland U.S. Livestock Insects Research Laboratory and Veterinary Pest Genomics Center, Kerrville, TX, United States.
Department of Biological Sciences, Old Dominion University, Norfolk, VA, United States; Vector Biology Section, Laboratory of Malaria and Vector Research, National Institute of Allergy and Infectious Diseases (NIH), Rockville, MD, United States.
Agricultural Research Service, United States Department of Agriculture, Washington, D.C., United States.
Department of Biochemistry, School of Medicine, University of Nairobi, P.O BOX 30197, 00100, Nairobi, Kenya.
Döhne Agricultural Development Institute, Private Bag X15, Stutterheim, 4930, South Africa.
Laboratoire d'Entomologie, Institut Pasteur de Tunis, Tunis, Tunisia.
School of Life Sciences, University of KwaZulu-Natal, Durban, Westville, South Africa.


The systematics of the genera and subgenera within the soft tick family Argasidae is not adequately resolved. Different classification schemes, reflecting diverse schools of scientific thought that elevated or downgraded groups to genera or subgenera, have been proposed. In the most recent classification scheme, Argas and Ornithodoros are paraphyletic and the placement of various subgenera remains uncertain because molecular data are lacking. Thus, reclassification of the Argasidae is required. This will enable an understanding of soft tick systematics within an evolutionary context. This study addressed that knowledge gap using mitochondrial genome and nuclear (18S and 28S ribosomal RNA) sequence data for representatives of the subgenera Alectorobius, Argas, Chiropterargas, Ogadenus, Ornamentum, Ornithodoros, Navis (subgen. nov.), Pavlovskyella, Persicargas, Proknekalia, Reticulinasus and Secretargas, from the Afrotropical, Nearctic and Palearctic regions. Hard tick species (Ixodidae) and a new representative of Nuttalliella namaqua (Nuttalliellidae), were also sequenced with a total of 83 whole mitochondrial genomes, 18S rRNA and 28S rRNA genes generated. The study confirmed the utility of next-generation sequencing to retrieve systematic markers. Paraphyly of Argas and Ornithodoros was resolved by systematic analysis and a new species list is proposed. This corresponds broadly with the morphological cladistic analysis of Klompen and Oliver (1993). Estimation of divergence times using molecular dating allowed dissection of phylogeographic patterns for argasid evolution. The discovery of cryptic species in the subgenera Chiropterargas, Ogadenus and Ornithodoros, suggests that cryptic speciation is common within the Argasidae. Cryptic speciation has implications for past biological studies of soft ticks. These are discussed in particular for the Ornithodoros (Ornithodoros) moubata and Ornithodoros (Ornithodoros) savignyi groups.


18S rRNA; 28S rRNA; Argasidae; Evolution; Mitochondrial genome; Molecular dating; Systematics

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