Gizaw, Abel Seid (2012) Plant Evolution in the African ‘Sky Islands’: Evidence from Fossil Calibrated Molecular Dating and Amplified Fragment Length Polymorphism. PhD thesis, Addis Ababa University.
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Abstract
The afro-alpine region in Eastern Africa encompasses the elevated plateaus and mountains in Ethiopia and the isolated high mountain peaks in Kenya, Tanzania, and Uganda, often referred to as biological 'sky islands'. The age of the flora on these mountains has been debated. Based on the high level of endemism, it has been suggested that the flora is old and might represent Tertiary relicts. Others have argued that some plant groups are young and have colonized these mountains during the Pleistocene. The impact of the glacial-interglacial oscillations of the Pleistocene on the origin and geographical structuring of the genetic diversity in many temperate plant species has been well documented, whereas only few studies for the afro-alpine plant speices have so far been conducted. Here we use a combination of molecular dating and phylogeographic analysis of selected plant species to provide insight into the evolution of plants in the afro-alpine region. A fossil calibrated multilocus species tree based on two nuclear and three plastid DNA regions was used to estimate the age of the afro-montane endemic Lychnis (Caryophyllaceae). Furthermore, Amplified Fragment Length Polymorphism (AFLP) fingerprinting was used to assess the genetic diversity and population genetic structure of seven plant species: two heather species from the ericaceous zone, Erica arborea, E. trimera (Ericaceae), and five species from the afro-alpine zone proper: Carex monostachya, C. runssoroensis (Cyperaceae), Lysimachia serpens (Primulaceae), Dicrocephala chrysanthemifolia and Haplocarpha rueppellii (Asteraceae). The multilocus species tree analysis have placed the mean age of the afro-montane Lychnis to 2.28-5.8 Myr (million years) corresponding to late Miocene to the late Pliocene and thus indicating a Tertiary relicts. The results from the AFLP analysis showed that all investigated species have very low levels of overall gene diversity, suggesting bottlenecks in small refugial populations during unfavourable climatic periods. The populations of E. trimera and H. rueppellii showed relatively distinct geographical structuring of the genetic variation, suggesting long-term isolation of the former in at least three separate places and of the latter in two refugial populations. The lack of common phylogeographic patterns indicates that different species have responded individually to the Pleistocene climatic oscillations.
| Item Type: | Thesis (PhD) |
|---|---|
| Uncontrolled Keywords: | AFLP, Afro-alpine, Afro-montane, Lychnis, Erica arborea, Erica trimera, Carex monostachya, Carex runssoroensis, Lysimachia serpens, Dicrocephala chrysanthemifolia, Haplocarpha rueppellii, Molecular dating, Phylogeography, Plio-Pleistocene, Tertiary-relicts. |
| Subjects: | Q Science > Q Science (General) Q Science > QE Geology Q Science > QH Natural history Q Science > QH Natural history > QH301 Biology Q Science > QK Botany |
| Divisions: | Africana |
| Depositing User: | Selom Ghislain |
| Date Deposited: | 25 Jun 2018 12:17 |
| Last Modified: | 25 Jun 2018 12:17 |
| URI: | http://thesisbank.jhia.ac.ke/id/eprint/4272 |
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