Phylogeography of the rodent mites Laelaps giganteus and Laelaps muricola using mitochondrial and nuclear DNA markers: an evolutionary approach to host-parasite interactions

Engelbrecht, Adriaan (2016-03)

Thesis (PhD)--Stellenbosch University, 2016.

Thesis

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.

AFRIKAANSE OPSOMMING: Die parasitiese myte, Laelaps giganteus en Laelaps muricola (Mesostigmata; Laelapidae) is wydverspreid en volop op klein soogdiere in suider Afrika. Die groot gasheer spektrum en komplekse lewensgeskiedenis van hierdie ektoparasiete mag aandui dat daar moontlike intraspesifieke kriptiese diversiteit in hierdie taxa is. Die meganismes verantwoordelik vir hierdie patrone en spesiasie met die klem op ko-diversifikasie in parasiet-gasheer stelsels is egter onduidelik op die oomblik. Hoe prosesse soos biogeografie, parasiet lewensgeskiedenis en gasheer verspreiding evolusionêre ko-diversifikasie beinvloed is ook tans heeltemal onbekend in myt biologiesie stelsels in Suid-Afrika. Hier word „n vergelykbare filogeografiese benadering tussen die twee mytspesies en hulle bekende gasheerspesies gevolg. Die hoof doelstellings van die studie was om: (1) die evolusionêre geskiedenis en taksonomiese status van twee suider-Afrikaanse Mesostigmata myte, L. giganteus en L. muricola, te ondersoek deur gebruik te maak van „n multi-dissiplinêre benadering wat „n kombinasie van mitokondriale DNS (mtDNS), kernDNS merkers en uitgesoekte morfologiese karakters insluit (2) „n vergelykbare filogenetise raamwerk tussen L. giganteus en Rhabdomys te gebruik in „n poging om meer duidelikheid te kry oor hoe parasiete met hul gashere op filogeografie vlak ko-diversifiseer, en (3) te bepaal of die ruimtelike genetiese struktuur van L. muricola, „n myt met „n weier gasheerspektrum, ooreenstem met die van L. giganteus, „n spesie met „n nouer gasheerspektrum, in suider Afrika. Om die genetiese en morfologiese diversiteit in L. giganteus en L. muricola te bepaal is 228 klein soögdiere van agt lokaliteite in Suid-Afrika versamel. Hier was nege van die voorheen geidentifiseerde gashere versamel. Laelaps muricola was waargeneem op Mastomys natalensis en Micaelamys namaquensis terwyl L. giganteus slegs op Rhabdomys dilectus en Lemniscomys rosalia gevind was. Filogenetise analises van die mtDNS (COI) en kernDNS (ITS1) data het oorweldigende ondersteuning aangedui dat L. giganteus en L. muricola as twee aparte spesies beskryf moet word terwyl die TropoM kernDNS interon dit deels ondersteun het. Sterk ondersteuning is ook verleen dat twee nuwe afstammelinge binne L. giganteus voorkom: L. giganteus lyn 1 kom slegs voor op R. dilectus terwyl die L. giganteus lyn 2 slegs op L. rosalia voorkom. Hierdie gasheer spesifieke monofiletiese lyne is ook geskei deur 9.84% mtDNS volgorde bepaling divergensie en 3.44% kernDNS volgorde bepaling divergensie. Siende dat kwantitatiewe morfometriese ontledings nie die genetiese onderskeiding ondersteun het nie verteenwoordig die twee heel waarskynlik kriptiese spesies. Verdere versameling van gashere om die patroon te bevestig het getoon dat L. giganteus op vier ander spesies binne die genus Rhabdomys voorkom. Sitochroom Oxidase I parsimoniese haplotiepe netwerke wat gebaseer is op 262 gasheer en 278 parasiet individue het aangedui op duidelike filogeografiese ooreenkomste, wat deels bevestig was deur analises van die TropoM intron. Alhoewel afstand-gebaseerde ko-filogenetiese ontledings in AXPARAFIT nie ko-diversifikasie ondersteun nie (P > 0.02), het gebeurtenis-gebaseerde ontledings getoon dat beduidende ko-filogenie tussen Rhabdomys en L. giganteus afstammelinge (CORE-PA: P = 0.046 and JANE: P = 0.00) bestaan. Hierdie bevindinge en die swak kongruensie wat voorheen vir die permanente ekto-parasitiese luis Polyplax op Rhabdomys genoteer was is teenstrydig met die voorspelling dat gasheer-parasiet intimiteit (tyd gespandeer op die gasheer) die hoof dryfkrag is van beduidende ko-diversifikasie. Hier stel die bevindinge ook voor dat die filogeografiese sein afgegee deur „n parasiet bevolking behou word na nuwe individue aansluit by die lokale bevolking. Hierdie verskynsel word beskryf as die parasiet “verdrink by aankoms”. Nuwe inligting oor die gasheerspektrum van L. muricola in suider Afrika is ook gevind. Bewyse word hier gelewer oor „n moonlike kriptiese parasiet wat op die indringer bruin rot, Rattus norvegicus, voorkom in Suid-Afrika. Verdere resultate dui daarop dat waneer na die natuurlike geshere van L. muricola gekyk word, geen filogeografiese stuktuur voorkom nie. Die patroon mag dalk veroorsaak word deur die feit dat L. muricola se gashere in verskeie habitatte kan oorleef en vinnig kan aanteel en versprei wanneer goeie toestande aanbreek.

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