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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 (PCO). 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 support (94%). 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 (Caswell, 1998). 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)
URI: http://hdl.handle.net/123456789/36
Appears in:Thesis - Biology

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