Department of Botany and Zoology

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Browsing Department of Botany and Zoology by browse.metadata.advisor "Apanaskevich, Dmitry A."

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    A molecular genetic perspective on the evolution of Hyalomma ticks with emphasis on the phylogeography of H. truncatum
    (Stellenbosch : Stellenbosch University, 2016-03) Sands, Arthur Francis; Matthee, Conrad A.; Apanaskevich, Dmitry A.; Matthee, Sonja; Stellenbosch University. Faculty of Science. Dept. of Botany and Zoology.
    ENGLISH ABSTRACT: The tick genus Hyalomma is spread throughout the old world and species in this genus are vectors of a number of harmful pathogens. This makes them of key veterinary and medical importance, yet their systematics, and the factors giving rise to their diversity, remain largely unknown. As different species, and even different lineages, can vary in vector potential and level of acaricide resistance, it is thus of particular importance to resolve the systematics of the genus. To resolve the systematics of the genus and to obtain better insights into the mechanisms that play a role in tick evolution, the present study used both a phylogeographic and phylogenetic approach. The aims of the study were: 1) to provide a phylogeographic perspective for H. truncatum using the mtDNA COI and nDNA H3 and CRT gene regions, and 2) to create a comprehensive phylogeny for all the described extant Hyalomma species by using morphological and molecular data, derived from multiple nuclear and mitochondrial genetic markers (COI, 16S, 28S, ITS II and H3). By making use of phylogeographic networks, AMOVA analyses and Bayesian analyses, 186 H. truncatum specimens could be divided into two lineages across Africa (with a northern and southern clade). Historical demographic population analyses suggest that the two clades have different evolutionary histories, and support the notion that they have been isolated for a prolonged period time. On a regional scale, the northern clade showed higher levels of substructure with five COI phylogroups over the sampled region. The geographical positioning of these phylogroups aligns with those seen in multiple species of ungulates, primates and rodents, and it is argued that they have formed as a result of glacial cycles that caused shifts in the distribution of host species. The southern clade lacked substructure (probably due to the lack of geographic barriers to gene flow in the region). A COI sequence distance of 9.88% (SD ± 0.40%) and significant population differentiation at nuclear DNA level suggest that the two continental lineages probably represent separate species. To gain further insights into the status of H. albiparmatum and H. nitidum, and the species status of the two H. truncatum clades, a higher level systematic study was conducted on 82 specimens inclusive of all recognised Hyalomma species. Three nDNA markers (ITS II, 28S and H3), two mtDNA markers (COI and 16S) and 47 morphological characters were used to resolve relationships among Hyalomma species. Parsimony and Bayesian analyses were performed and a dated phylogeny was also constructed using available fossil data. The data suggests that the first diversification within Hyalomma began around 36.25 Mya (95% HPD 34.75-39.80 Mya) and thereafter later divergences gave rise to five groups. Since Hyalomma have limited dispersal capabilities off the host, it is likely that mechanisms responsible for speciation events are more than likely coupled to vicariance events separating multiple hosts. Certainly several faunal exchanges between zoogeographic regions such as those associated with the African-Eurasian land bridge across the Arabian plate 16-20 Mya can be correlated to speciation in Hyalomma. Furthermore sea-level oscillations of the Mediterranean Sea degradation of the Paratethys Sea, and the development of the Himalayan mountainous belt and the East African Rift Valley have been proposed as mechanisms driving speciation in a number of host such as ungulates and rodents. Although these events likely played a role in early Hyalomma evolution, substantiating the mechanisms involved in the recent divergences of many extant Hyalomma species remains difficult. The latter is mainly due to the availability of limited knowledge on the exact ranges and host associations of several taxa. Nevertheless, the results documented in this thesis propose a number of changes to the current taxonomy of the genus: 1) Ticks recognized as H. truncatum comprised of two distinct species. Following conventional zoological nomenclature, we propose the southern clade of H. truncatum to likely represent a novel species (H. species nova). 2) Hyalomma marginatum and H. turanicum should be regarded as synonyms. 3) Hyalomma nitidum should be synonymized with the H. truncatum clade found in north Africa, while H. albiparmatum should remain a distinct species entity.