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|Title: ||Taxonomic and Demographic Studies on Three Species Compexes within the Genus Aloe L. (Aloaceae) in Ethiopia|
|Authors: ||Fikre, Dessalegn|
|Date Added: ||31-Aug-2007 |
|Abstract: ||Taxonomic and demographic studies were conducted on three species complexes within
the genus Aloe L. (Aloaceae) in Ethiopia. The studies aimed to contribute new additional
knowledge necessary to delineate the Aloe species and their conservation in the Flora of
Ethiopia and Eritrea (FEE).
In the taxonomic study, the status of 11 species was evaluated using morphological and
molecular (AFLP) data. Morphological data were collected from herbarium specimens,
fresh materials and literature. Data matrices were constructed for qualitative, quantitative
and combined morphological data sets. Molecular (AFLP) data were obtained from
leaves of randomly selected germinated seedlings. Total genomic DNA was extracted
using a modified 2 x CTAB method described by Doyle and Doyle (1990). AFLP
analysis was performed following a protocol modified from Vos et al. (1995). Fragments
produced by each primer combination were analyzed and scored for the presence (1) or
absence (0) of selected markers/fragments. Binary data matrices were constructed for
each of the primer combinations and also for the combined data set. Each of the data
matrices constructed for morphological and molecular (AFLP) data sets was subjected to
multivariate analyses: cluster analysis (UPGMA) and principal coordinate analysis
The results from the analyses of both morphological and AFLP data supported the
present status of nine out of the eleven species: A. harlana Reynolds, A. monticola
Reynolds, A. debrana Christian, A. percrassa Tod., A. yavellana Reynolds, A.
megalacantha Baker, A. gilbertii Sebsebe & Brandham, A. calidophila Reynolds and A.
sinana Reynolds. The boundary between the two caulescent species from the northern
part of the FEE area: A. camperi Schweinf. and A. adigratana Reynolds was not very
clear and particularly the genetic delimitation displayed close relationship. The neighborjoining
tree constructed from combined AFLP data revealed thus weak support for A.
camperi (51%) and A. adigratana (62%) but kept them together with high bootstrap
In the PCO plot they constituted one single cluster. It is accordingly suggested that the
two species should be recognized at subspecies level as A. camperi Schweinf. subsp.
camperi and A. camperi subsp. adigratana (Reynolds) Fikre comb. et stat. nov.
In the demographic study, population structure and dynamics of three endemic species: A.
gilbertii, A. debrana and A. harlana, representing the three complexes and different
centers of endemism were analyzed. Nine permanent plots of 5 x 20 m², three plots per
species, were established in selected sites. Each individual clone consisting of one genet
and one or more ramet(s) were marked, mapped and recorded. For every genet, stem
length and stem diameter were measured (when present) and for every ramet, rosette
diameter, rosette height and number of inflorescence(s) were measured and counted.
These measurements were undertaken in successive seasons (2003-2005) following their
phenology. Recruitments and mortalities of genets and ramets were recorded in the
second season. Based on the data recorded, population structure was described by the
clone size and rosette diameter of ramets using descriptive and inferential statistics.
Dynamics at the ramet and genet levels were analyzed using matrix model developed by
The results showed that the three species displayed different population structures. The
population of A. debrana had the highest number of genets (221) as compared to A.
gilbertii (208) and A. harlana (102). Including seedlings, 83.3% in A. debrana, 69.6% in
A. harlana, and 54.3% in A. gilbertii of the genets were represented by a single
ramet/genet. The A. gilbertii population was composed of a relatively greater proportion
(45.7%) of multi-rameted genets (2-25). Thus, the three species vary significantly in the
extent of clone size/formation (P < 0.09), and also in the size class distribution of the
rosette diameter of ramets (P < 0.20). The number of ramets ‘born’ between seasons was
not correlated (r = 0.15) with the number of ramets died. Dynamics (growth rate)
analysed at ramet-level indicated that A. gilbertii (l = 1. 30) and A. debrana (l = 1.28)
populations were expanding whereas A. harlana (l = 1.08) population was nearly stable
or slightly increasing for the period of study.
A total of 83, 69 and 15 seedlings were recruited; and a total of 9, 4 and 5 genets died in
A. gilbertii, A. debrana and A. harlana populations respectively. The number of seedlings
recruited between seasons was not correlated (r = 0.42) to the number of genets died. The
dynamics at genet-level was more apparent in A. gilbertii (l = 1.38) with relatively high
rejuvenation as compared to A. debrana (l = 1.24) and A. harlana (l = 1.16) populations
even if mortality of genet is less pronounced in both species.
Isoenzyme data of six populations and 78 individuals representing the three species
analysed demographically were generated. Genetic variation within and among the
populations was analysed using the computer package GENEPOP (ver. 3.4) (Raymond
and Rouset, 2003). Average levels of polymorphism (P = 60.9) and allelic richness (Na =
2.18) were higher than that has been previously observed for other Aloe species.
Observed heterozygosity (mean Ho = 4.5) was higher than expected under Hardy-
Weinberg equilibrium (mean He = 4.2) resulted in negative fixation coefficient (mean Fis
= -0.06), suggesting absence of inbreeding and an excess of heterozygosities. Since Fst
values within populations of species are rather high (upto 25% in A. gilbertii and 18% in
A. debrana, it is recommended that several populations of a species must be conserved in
their natural habitat to keep the genetic diversity.
The germination success of field-collected seeds in the greenhouse was assessed and
observations were made in the field to identify threats to aloes in the flora area. The
percentage of germination was highest for A. yavellana (86%) and surprisingly very low
success record was for A. megalacantha (18%). Despite variation in the success, the
germination experiments indicated that most species are tolerant of the many soil types to
be found in gardens and potting mixtures. Hence the cultivation of aloes in ex-situ
conditions can be applied as effective conservation strategy. Clearing natural habitats for
agricultural lands, due to development construction such as roads and urbanization were
found to be the major threats to aloes in the flora area. Urgent in-situ conservation
measures to protect habitats inhabited by aloes, particularly the narrow endemics where
their habitats cleared at alarming pace, are highly needed in Ethiopia.|
|Description: ||A Thesis Submitted to the School of Graduate Studies, Addis Ababa University in partial Flulfillment of PhD Dgree in Biology (Botanical Sciences)|
|Appears in:||Thesis - Biology|
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