Recolonization of Ethiopia by Hagenia after the LGM from the south of Ethiopia
by IBC ~ December 4th, 2009. Filed under: Evolution.Taye Bekele (PhD)
Published scientific article (Part of a PhD research) on “Chloroplast DNA haplotype diversity and postglacial recolonization of Hagenia abyssinica (Bruce) J.F. Gmel. in Ethiopia” revealed that recolonization of Ethiopia by Hagenia after the Last Glacial Maximum (LGM) was from the south of Ethiopia and possibly south western Ethiopia
Graceful tree of Hagenia abyssinica
The chloroplast haplotypes found in Hagenia showed a clear pattern of congruence between their geographical distribution and genealogical relationships. Very low haplotype diversity within populations and a very high population differentiation was observed, reflecting very low mixing between recolonizing lineages. Restricted gene flow through seeds, rare long-distance dispersal, contiguous range expansion and mutation shaped the genetic structure of Hagenia. Fossil pollen records suggested that the trend of postglacial recolonization of Hagenia was first in the south and latter went to the north in Ethiopia.
Dr. Taye Bekele writes, “The joint interpretation of genealogical relationships among the chloroplast haplotypes and the fossil pollen evidences allowed us to accept the hypothesis predicting recolonization of Ethiopia by Hagenia after the LGM from the south of Ethiopia and possibly south western Ethiopia…”
“…The first is supported by palynological information whereas the second is by molecular and current climate information. There was no indication of past fragmentation of Hagenia populations from our results, pointing to the effect of random long distance seed dispersal. It is most likely that populations were established from few parent seed trees. Given the mountainous topography of the country that is intermittently dissected by wide valleys, Hagenia did not have a continuous distribution.”
According to this finding, the cpDNA assay detected sufficient variation for a phylogeographic study of H. abyssinica in Ethiopia. A remarkable subdivision of cpDNA diversity in the species was found, as indicated by a high level of genetic differentiation. The chloroplast haplotypes of H. abyssinica demonstrated a pattern of isolation-by-distance. Unlike most of the wind-dispersed tree species, the chloroplast haplotypes found in Hagenia showed a clear pattern of congruence between their geographical distribution and genealogical relationships, allowing to accept the prediction on geographic structuring.
The study recommends that analysis of cpDNA types and palynological inventories, including all countries where the species is known to grow, would fully resolve the genealogical relationships and help to identify the glacial refugia of Hagenia in Africa. The analysis of pollen records from different sites and altitudes in Ethiopia where Hagenia is growing would help to fully understand the recolonization route of the species within the country.
Download/View Full Article Chloroplast DNA haplotype diversity and postglacial recolonization of Hagenia abyssinica (Bruce) J.F. Gmel. in Ethiopia (201)
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