Plant Biology and Biodiversity Management

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Browsing Plant Biology and Biodiversity Management by Subject "afro-montane"

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    Biological Consequences of Pleistocene Glaciations in East African Afro-Alpine Environment As Inferred From Molecular Data of Some Key Plant Species
    (Addis Ababa University, 2007-07) Assefa, Adane; Nemomissa, Sileshi (Professor)
    The afro-montane/-alpine regions representing biological 'sky islands' comprise the high mountains of Ethiopia and tropical East Africa. The vegetation of the regions is characterized by fragmentation among the various mountain massifs with numerous local endemic species. Most plant species in these ‘sky islands’ are quite different from those occurring in their respective immediate surrounding lowlands. However, some primarily arctic-alpine plants also occur in the mountains, as Arabis alpina. It has been suggested that this plant elements are Tertiary relict, but a recent range-wide study of A. alpina suggested that the species colonized the region twice during the Pleistocene period. In addition to such immigrant species, some other key plant species, as Salvia merjamie and Cerastium afromontanum are very common in sub-alpine and montane forests of the ‘sky islands. In this study, two overlapping phases of investigations have been carried out on these three species using two basic molecular biological techniques: in the first phase, the detail colonization history of A. alpina was investigated in the afro-alpine regions based on chloroplast DNA (cpDNA) sequences, and in the second phase, the phylogeographic structures and conservation status of the three species were studied using amplified fragment length polymorphic DNA data (AFLP fingerprinting) obtained from 11 mountain systems, where present-day populations are often limited to isolated mountain tops. In the first phase, the results confirm the twice-into-Africa scenario. The Asian lineage is also confined to the mountains closest to the Arabian Peninsula, on opposite sides of the Great Rift Valley (GRV), suggesting long-distance dispersal of the A. alpina lineage. The African lineage is divided into two phylogeographic groups with distinct geographic distribution. The observed pattern is consistent with isolation of the African lineage in at least two interglacial refugia, located on separated highlands, followed by range expansion in cooler period(s), when the afro-alpine habitat extended further down the mountains. Several long-distance dispersal events across the GRV are also suggested by haplotypes observed outside the area occupied by the phylogeographic groups they belonged to. In the second phase of the investigation, in the Ethiopian and tropical East African mountains, A. alpina showed high and clearly structured genetic variability. The fragmented structure in the mountains indicated that A. alpina disperses little among established populations. However, occasional long-distance dispersal events were also suggested in all parts of the ranges, similar to the cpDNA data findings. In S. merjamie and C. afromontanum which may consist of the subspecies complex, the diversity is so high for the former and very low for the latter species in certain isolated mountain regions in Ethiopia (i.e. the Simen Mts and Gara Muleta). The present analyses did also reveal very complex geographical structuring and phylogeographic patterns among the study areas. Moreover, the AFLP data clearly indicated very distinct and genetically highly divergent individuals, which might represent possible cryptic subspecies signifying the call for future detail morphological assessments of the species in the region. Key words: cpDNA, AFLP, Arabis alpina, Salvia merjamie, Cerastium afromontanum, phylogeography, genetic diversity, refugia, afro-alpine, afro-montane, East Africa, Pleistocene.