Phylogeny of Ameronothroidea in the south polar region and the phylogeography of selected species on sub-antarctic Marion Island

[摘要] ENGLISH ABSTRACT: Sub-Antarctic islands represent the only mid to high latitude terrestrial biomes in the Southern Hemisphere. Theseislands have various geological origins and histories, well-preserved terrestrial ecosystems and high levels ofspecies endemism. In an attempt to understand the evolution and biogeography of terrestrial taxa in the SouthPolar Region, the first broad-scale molecular phylogeny was constructed for the unique terrestrial group, theameronothroid mites (genus Halozetes (Oribatida)), collected from sub-Antarctic and Maritime Antarctic localities.Phylogenetic analyses based on a combined mitochondrial (cytochrome oxidase subunit I (COI)) and nuclear(histone-3 (H3)) sequence dataset indicated that the evolution of these mites were habitat specific (i.e. intertidal,supralittoral and terrestrial). Notwithstanding criticisms levelled against a molecular clock, the mites wereevolutionary young (<10myo), contrary to their status as an ancient group predating Gondwana fragmentation.Biogeographic analyses indicated a complex pattern mainly sculpted by multiple independent dispersal eventsacross the Antarctic Polar Frontal Zone similar to previous findings for other marine and terrestrial taxa. Also, themolecular phylogeny displayed considerable discourse with contemporary taxonomy suggesting the need fortaxonomic revisions and reassessment of morphological characters. Sub-Antarctic Marion Island, the larger of thetwo islands comprising the Prince Edward Island archipelago (PEI), has experienced extensive glaciation andvolcanism. To assess the impact of historical events (volcanism (including recent eruptions) and glaciation) andcontemporary mechanisms (gene flow) on the genetic spatial distribution of species from Marion Island, two mitespecies namely Eupodes minutus (Prostigmata) and Halozetes fulvus (Oribatida) as well as a single plant species,Azorella selago (Apiaceae), were selected as model organisms. For independent phylogeographic analyses,mitochondrial sequence data (COI) were obtained for both mite species, while chloroplast sequence (trnH-psbA)and amplified fragment length polymorphism (AFLP) data were generated for the cushion plant, A. selago. SinceA. selago is typified by two growth forms namely discrete cushions and continuous mats, it was essential toexamine the growth dynamics prior to phylogeographic analyses. The sequence and fragment data indicated thatboth mite and plant species were significantly substructured across Marion Island. Manual comparisons indicatedunique populations on the western (Kaalkoppie for H. fulvus, La Grange Kop for E. minutus and Mixed Pickle forA. selago), eastern (Bullard Beach for H. fulvus and Kildalkey Bay for E. minutus), northern (Middelman and LongRidge for H. fulvus) and southern side (Grey Headed for H. fulvus and Watertunnel for A. selago) of the island.Importantly, the western side had unique localities for all species. Interestingly, based on the H. fulvus data, thewestern populations were relatively young, characterized by high migration rates, small effective (female)population sizes with no isolation-by-distance. The opposite scenario was found for the eastern populations. Thisspatial genetic structure described for species on Marion Island can be ascribed to both historical events andenvironmental conditions. These areas with their unique genetic composition are of special conservationalconcern; consequently this research will contribute to an active management plan for PEI, South Africa's onlySpecial Nature Reserve.

[发布机构] Stellenbosch University