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

Authors: MANS, BEN - Onderstepoort Veterinary Institute; FEATHERSTON, J - Onderstepoort Veterinary Institute; KVAS, MARIJA - Onderstepoort Veterinary Institute; PILLAY, KERRY-ANNE - Onderstepoort Veterinary Institute; DE KLERK, DANIEL - Onderstepoort Veterinary Institute; PIENAAR, RONEL - Onderstepoort Veterinary Institute; DE CASTRO, MINIQUE - Onderstepoort Veterinary Institute; SCHWAN, TOM - Rocky Mountain Laboratory; LOPEZ, JOB - Baylor College Of Medicine; TEEL, PETE - Texas A&M University; Perez De Leon, Adalberto - Beto; SONENSHINE, DANIEL - Old Dominion University; Egekwu, Noble; BAKKES, DEON - Onderstepoort Veterinary Institute; HEYNE, HELOISE - Onderstepoort Veterinary Institute; KANDUMA, ESTHER - University Of Nairobi; NYANGIWE, NKULULEKO - Non ARS Employee; BOUATTOUR, ALI - Non ARS Employee; LATIF, ABDALLA - University Of Kwazulu-Natal

Submitted to: Ticks and Tick Borne Diseases
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 9/22/2018
Publication Date: N/A
Citation: N/A

Interpretive Summary: This study addressed the need to revise aspects related to the classification of soft ticks in the family called Argasidae. Genetic research was conducted to reclassify these organisms. The identification of molecular markers was enhanced by applying next-generation sequencing to obtain gene data from different structures within tick cells. The approach allowed the integration of genetic and morphologic data and provided evolutionary context to the reclassification exercise. A new species list is proposed for some members of the Argasidae family. Estimation of divergence times using molecular dating increased our understanding of evolutionary relationships within the Argasidae according to the geographic region under consideration. The evolution of species that are difficult to distinguish based on their visual appearance, a process technically known as cryptic speciation, appears to be common in the Argasidae. Cryptic speciation must be taken into consideration when conducting soft tick research.

Technical Abstract: The systematics of the genera and subgenera within the soft tick family Argasidae is not adqueately resolved. Different classification schemes, reflecting diverse schools of scientific thought that elevated or downgraded groups to genera of 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 and evolutionary context. This study addressed that knowledge gap using mitochondrail 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 (Nutelliellidae), were also sequenced with a total of 83 whole mitochondrial genomes, 18S rRNA and 28S rRNA genesgenerated. 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, suggest 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.