Biological Consequences Of Pleistocene Glaciations In East African Afro-alpine Environment As Inferred From Molecular Data Of Some Key Plant Species

The afro-montane/-alpine regions representing biological 'sky islands' comprise the highrnmountains of Ethiopia and tropical East Africa. The vegetation of the regions is characterized byrnfragmentation among the various mountain massifs with numerous local endemic species. Mostrnplant species in these ‘sky islands’ are quite different from those occurring in their respectivernimmediate surrounding lowlands. However, some primarily arctic-alpine plants also occur in thernmountains, as Arabis alpina. It has been suggested that this plant elements are Tertiary relict, butrna recent range-wide study of A. alpina suggested that the species colonized the region twicernduring the Pleistocene period. In addition to such immigrant species, some other key plantrnspecies, as Salvia merjamie and Cerastium afromontanum are very common in sub-alpine andrnmontane forests of the ‘sky islands. In this study, two overlapping phases of investigations havernbeen carried out on these three species using two basic molecular biological techniques: in thernfirst phase, the detail colonization history of A. alpina was investigated in the afro-alpine regionsrnbased on chloroplast DNA (cpDNA) sequences, and in the second phase, the phylogeographicrnstructures and conservation status of the three species were studied using amplified fragmentrnlength polymorphic DNA data (AFLP fingerprinting) obtained from 11 mountain systems, wherernpresent-day populations are often limited to isolated mountain tops. In the first phase, the resultsrnconfirm the twice-into-Africa scenario. The Asian lineage is also confined to the mountainsrnclosest to the Arabian Peninsula, on opposite sides of the Great Rift Valley (GRV), suggestingrnlong-distance dispersal of the A. alpina lineage. The African lineage is divided into twornphylogeographic groups with distinct geographic distribution. The observed pattern is consistentrnwith isolation of the African lineage in at least two interglacial refugia, located on separatedrnhighlands, followed by range expansion in cooler period(s), when the afro-alpine habitatrnextended further down the mountains. Several long-distance dispersal events across the GRV arernalso suggested by haplotypes observed outside the area occupied by the phylogeographic groupsrnthey belonged to. In the second phase of the investigation, in the Ethiopian and tropical EastrnAfrican mountains, A. alpina showed high and clearly structured genetic variability. Thernfragmented structure in the mountains indicated that A. alpina disperses little among establishedrnpopulations. However, occasional long-distance dispersal events were also suggested in all partsrnof the ranges, similar to the cpDNA data findings. In S. merjamie and C. afromontanum whichrnmay consist of the subspecies complex, the diversity is so high for the former and very low forrnthe latter species in certain isolated mountain regions in Ethiopia (i.e. the Simen Mts and GararnMuleta). The present analyses did also reveal very complex geographical structuring andrnphylogeographic patterns among the study areas. Moreover, the AFLP data clearly indicated veryrndistinct and genetically highly divergent individuals, which might represent possible crypticrnsubspecies signifying the call for future detail morphological assessments of the species in thernregion.rnKey words: cpDNA, AFLP, Arabis alpina, Salvia merjamie, Cerastium afromontanum,rnphylogeography, genetic diversity, refugia, afro-alpine, afro-montane, East Africa, Pleistocene.

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