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Title: Phylogenetics of the genus Echium L. (Boraginaceae)
Author: Silva, Dylan De
ISNI:       0000 0001 3410 4658
Awarding Body: University of Reading
Current Institution: University of Reading
Date of Award: 2005
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Maximum parsimony and Bayesian analysis of the ITS 1&2, tm T-F and 5s rDNA spacer regions was performed for a selection ofmainland and island taxa from the genus Eehium. ITS and tm datasets reveal that both mainland and island taxa separate into two distinct clades. All but two of the island taxa show the characteristic of insular woodiness, suggesting that the evolution of this character may have been a 'key innovation' assisting the diversity ofthe genus on the Macaronesian islands. Lack of basal resolution in the trees generated from the ITS dataset meant that the relative ancestral vs. derived status of these two clades was unclear. Analysis of tm T-F data confirmed the split between mainland and island taxa with the latter being in a derived position in the tree. This is concordant with the results of a number of other studies undertaken for island taxa such as Aeonium, So'!ehus and Argyranthemum. Conflicts ~n the data meant that the combined ITS 1&2 and tm T-F tree was not basally resolved and the question of (', evolutionary polarity was again unclear. Both datasets showed a paucity of characters and lack of I teirninal resolution in the island clade. Hybridisation and long generations time is rejected as a possible cause of this genetic homogeneity and it is concluded that the island EeMa have instead undergone a recent and rapid radiative speciation. Relationships amongst island taxa were similarly unresolved following analysis of clones of the 5s NTS. Given that the 5s region is one of the most rapidly mutating regions of the plant genome, it is concluded that robust cladistic resolution is unlikely to be achievable with single or groups of genes in instances of rapid species radiations. It has been suggested that morphological characters, as direct manifestations of the evolutionary process, are better suited to the study of rapid species radiations. A morphological data matrix for a suite of 25 characters was constructed for Eehium and analysed using maximum parsimony. The perennial difficulty of recognising between convergence and true synapomorphy in morphological characters was highlighted by the paraphyletic nature of the resulting tree in which the mainland/island disjunction defined by molecular analyses was distorted and several outgroup taxa were placed deep within the ingroup. The validity of defming taxic relationships based on morphology in Eehium is therefore considered questionable. The implication associated with the lack of genetic variation in many island plant groups is discuSsed in the context of recognising conservation priorities. Should this minimal genetic diversity be a cause to reassess the conservation importance of island floras?
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available