Browsing by Author "Engelbrecht, Adriaan"

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    Comparative phylogeography of parasitic Laelaps mites contribute new insights into the specialist-generalist variation hypothesis (SGVH)
    (BMC (part of Springer Nature), 2018-09-03) Matthee, Conrad A.; Engelbrecht, Adriaan; Matthee, Sonja
    Background: The specialist-generalist variation hypothesis (SGVH) in parasites suggests that, due to patchiness in habitat (host availability), specialist species will show more subdivided population structure when compared to generalist species. In addition, since specialist species are more prone to local stochastic extinction events with their hosts, they will show lower levels of intraspecific genetic diversity when compared to more generalist. Results: To test the wider applicability of the SGVH we compared 337 cytochrome oxidase I mitochondrial DNA and 268 nuclear tropomyosin DNA sequenced fragments derived from two co-distributed Laelaps mite species and compared the data to 294 COI mtDNA sequences derived from the respective hosts Rhabdomys dilectus, R. bechuanae, Mastomys coucha and M. natalensis. In support of the SGVH, the generalist L. muricola was characterized by a high mtDNA haplotypic diversity of 0.97 (±0.00) and a low level of population differentiation (mtDNA Fst= 0.56, p < 0.05; nuDNA Fst = 0.33, P < 0.05) while the specialist L. giganteus was overall characterized by a lower haplotypic diversity of 0.77 (±0.03) and comparatively higher levels of population differentiation (mtDNA Fst = 0.87, P < 0.05; nuDNA Fst = 0.48, P < 0.05). When the two specialist L. giganteus lineages, which occur on two different Rhabdomys species, are respectively compared to the generalist parasite, L. muricola, the SGVH is not fully supported. One of the specialist L. giganteus species occurring on R. dilectus shows similar low levels of population differentiation (mtDNA Fst= 0.53, P < 0. 05; nuDNA Fst= 0.12, P < 0.05) than that found for the generalist L. muricola. This finding can be correlated to differences in host dispersal: R. bechuanae populations are characterized by a differentiated mtDNA Fst of 0.79 (P < 0.05) while R. dilectus populations are less structured with a mtDNA Fst= 0.18 (P < 0.05). Conclusions: These findings suggest that in ectoparasites, host specificity and the vagility of the host are both important drivers for parasite dispersal. It is proposed that the SGHV hypothesis should also incorporate reference to host dispersal since in our case only the specialist species who occur on less mobile hosts showed more subdivided population structure when compared to generalist species.
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    Phylogeography of the rodent mites Laelaps giganteus and Laelaps muricola using mitochondrial and nuclear DNA markers: an evolutionary approach to host-parasite interactions
    (Stellenbosch : Stellenbosch University, 2016-03) Engelbrecht, Adriaan; Matthee, Sonja; Matthee, Conrad A.; Stellenbosch University. Faculty of Agrisciences. Dept. of Conservation Ecology and Entomology.
    ENGLISH ABSTRACT: Laelaps giganteus and Laelaps muricola (Mesostigmata; Laelapidae) are widespread and locally abundant mites on small mammals in southern Africa. The large host range and complex life history of these ectoparasites suggest possible intraspecific cryptic diversity in these taxa. The mechanisms responsible for speciation in response to codiversification in parasite-host systems are poorly understood. Similarly, how biogeography, parasite life history, and host vagility influence evolutionary codivergences is at present unknown in mite systems in southern Africa. A comparative phylogeography approach was followed to study the evolution and taxonomy of two mite species and their known host species. The main objectives of the study were to: (1) investigate the evolutionary history and taxonomic status of two southern African Mesotigmatid mites, L. giganteus and L. muricola, using a multidisciplinary approach including a combination of mitochondrial and nuclear DNA markers and selected morphological characters, (2) apply a comparative phylogenetic framework to L. giganteus which is only found on a single rodent genus, Rhabdomys, in an attempt to better understand codivergence between parasites and hosts, particularly at the phylogeographic level, and (3) determine whether L. muricola with a wide host range, yet similar life history, would show similar phylogeographic patterning to the host specialist L. giganteus across southern Africa. To assess the genetic and morphological diversity in L. giganteus and L. muricola, 228 rodents were collected from eight localities in southern Africa. This sample included nine previously recorded host species and on these, L. muricola was predominantly recorded from Mastomys natalensis and Micaelamys namaquensis while L. giganteus was found on Rhabdomys dilectus and Lemniscomys rosalia. Phylogenetic analyses of mtDNA cytochrome oxidase subunit I (COI) and nuclear ITS1 data strongly supported the recognition of L. giganteus and L. muricola as distinct species, a scenario partly supported by sequence data of the Tropomyosin intron. Strong support for evolutionarily distinct lineages within L. giganteus was found: L. giganteus lineage 1 was confined to R. dilectus and L. giganteus lineage 2 was confined to L. rosalia. These host-specific monophyletic lineages were separated by 9.84% mtDNA sequence divergence and 3.44% nuclear DNA sequence divergence. Since quantitative morphometric analyses were not congruent with these findings, these two lineages more than likely represent cryptic species. Further sampling across southern Africa indicated that L. giganteus occurs on four rodent species within the genus Rhabdomys. Cytochrome Oxidase I parsimony haplotype networks derived for 262 host and 278 parasite specimens showed marked phylogeographic congruence, which was in part confirmed by analyses of the Tropomyosin (TropoM) intron. Although distance-based cophylogenetic analyses in AXPARAFIT failed to support significant mtDNA codivergences (P ≥ 0.020), event-based analyses revealed significant cophylogeny between Rhabdomys and L. giganteus lineages using CORE-PA (P = 0.046) and JANE (P = 0.000). These findings, in conjunction with the weak congruence previously reported among the permanent ectoparasitic lice Polyplax and Rhabdomys, suggest that parasite-host intimacy (time spent on the host) is not the main driver of significant codivergence in the study system. Instead the restricted dispersal ability of L. giganteus resulted in strong spatial structuring and when this was coupled to an intimate relationship with the host, significant codivergence emerged. Both event-based reconstruction methods also indicated host switching that in some instances could be linked to climate-induced range shifts in the host distribution. When host range shifts occur, the phylogeographic signature of L. giganteus is preserved, as the genetic contribution of the dispersing individuals is overwhelmed by the large number of individuals already present in nests within the new environment, a phenomenon described as a parasite “drowning on arrival”. Novel phylogeographic insights into the host range of L. muricola are also shown, expanding the contemporary information available on this species in southern Africa. Results show the first evidence of a putative cryptic L. muricola lineage on the brown rat, Rattus norvegicus, present in South Africa. On native hosts, L. muricola indicate a lack of phylogeographic structuring owing to its generalist life style and the unique life history of some of its hosts. Mastomys coucha and M. natalensis are able to survive in multiple refugia and rapidly expand once favourable conditions set in. The pattern we find in this host generalist confirms that host dispersal is driving the genetic structure in both L. muricola and L. giganteus.
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    Phylogeography of the southern African vlei rat, Otomys irroratus, inferred from chromosomal and DNA sequence data
    (Stellenbosch : University of Stellenbosch, 2010-12) Engelbrecht, Adriaan; Rambau, Ramugondo Victor; Daniels, Savel Reagan; University of Stellenbosch. Faculty of Science. Dept. of Botany and Zoology.
    ENGLISH ABSTRACT: This study examines the phylogeography of the southern African vlei rat, Otomys irroratus using the mtDNA cyt b gene and chromosomal data derived using G-, and C-banding, Ag-NOR staining and fluorescence in situ hybridization (FISH using flow sorts of Myotomys unisulcatus). A total of N = 102 specimens were used from the Western Cape, Eastern Cape, Northern Cape, Free State, Mpumalanga and KwaZulu-Natal provinces of South Africa. Of the N = 102, N = 55 comprised fresh material while N = 47 comprises museum material obtained from the Durban Natural Science Museum of South Africa. Cytogentic analysis of N = 55 specimens collected from seven localities in South Africa revealed intra-specific variation resulting from two rearrangements, namely pericentric inversions and heterochromatin variation. Of the 55 specimens that were analyzed 47% contained inversions or centromeric shifts on four autosomes (OIR1, OIR4, OIR6 and OIR10) which were present singly in specimens (i.e. none of the specimens contained all four inversions concurrently). These inversions were present in both homozygous and heterozygous state over a wide geographic range suggesting that they are floating polymorphisms. Given the potential role of inversions in post-mating isolation (through production of aneuploid gametes), the prevalence of inversions as floating polymorphisms in the vlei rats suggest that they are probably retained in the population through suppression of recombination in the inverted regions of the chromosomes. In addition, differences between populations is due to the presence or absence of heterochromatic arms (and not inversions), which cause variation in the NFa (40 – 49) and supernumerary B chromosomes, resulting in the variation in diploid number (2n = 28 – 32). Analysis of N = 55 specimens revealed Ag-NORs on 7 autosomal pairs 1, 2, 5, 7, 8 and 9 proximal to the centromere on the short arm of the chromosome. Pair 8 also displayed Ag-NOR at the distal end of the long arm of the chromosome in individuals from the Free State province. Pair 3 showed two Ag- NORs occurring proximal to the centromere on the short arm and on the terminal end of the long arm, respectively. I obtained 953bp of mtDNA cyt b from fresh material and 400bp from museum material. Using maximum parsimony and Bayesian inference two main clades were retrieved. Clade A specimens occur mainly in the Western and Eastern Cape provinces of South Africa. Clade B specimens occur in the Eastern Cape, Free State, KwaZulu-Natal, Northern Cape and Mpumalanga provinces of South Africa. The mean sequence divergence between the main clades (A and B) is 7.0% and between sub-clades comprising clade B is 4.8%, while within clade A the sequence divergence was 1.91%. Nested clade analysis revealed allopatric fragmentation within O. irroratus. Chromosomal characters also support the two evolutionary lineages as clade A has pericentric inversions which occur as floating polymorphisms which are absent in clade B. Clade B in turn is fixed for a complex tandem fusion rearrangement which is absent from clade A. Divergence date estimates indicate that the two clades separated around 1.1 MYA, which coincides with climate changes since the late Pliocene/Pleistocene epochs. Cladogenesis within this species complex could therefore have been influenced by habitat fragmentation. A full taxonomic review of O. irroratus is therefore warranted by this study.