Harrington, Mark (2008) Phylogeny and evolutionary history of Sapindaceae and Dodonaea. PhD thesis, James Cook University.

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Abstract

The Sapindaceae (soapberry family) is a large family of trees, shrubs and lianas comprising 133 genera (49 monotypic) and ca.1450 species, most with a tropical to subtropical distribution. The circumscription of Sapindaceae has varied, particularly with regard to inclusion of genera from the closely related, predominantly temperate families Aceraceae and Hippocastanaceae. Sequence data from two plastid genes, analysed separately and together using parsimony and Bayesian analysis support a broadly defined Sapindaceae incorporating Aceraceae, Hippocastanaceae and Xanthoceras. A division into four subfamilies is proposed: Sapindoideae, Hippocastanoideae, Dodonaeoideae, and Xanthoceroideae. Tribal groupings are critically evaluated in light of the analyses.

The evolutionary history of Sapindaceae is evaluated using a variety of Bayesian relaxed clock molecular estimates of divergence times, which either incorporate the dates implied by the fossil record, fossil constraints from outside Sapindaceae, and no fossil constraints. Analyses with fossil constraints from outside Sapindaceae imply a Pliocene-Miocene (6-28 Mya) origin for Acer and Aesculus rather than a Paleocene (ca 64 Mya) origin implied by the earliest attributed fossils of these genera, and an evolutionary rate for Acer and Aesculus consistent with the majority of other genera of Sapindaceae sampled. Including the fossil dated Paleocene origin of Acer and Aesculus as hard bound priors and using four constraints from outside Sapindaceae result in a potentially biologically implausible rapid change in the mean evolutionary rate on the stem branch leading to the split between Acer and Aesculus and their respective sister genera. These conflicting scenarios suggest the need for a substantial re-evaluation of our understanding of the tempo and mode of evolution of these lineages.

Intergeneric relationships within Dodonaeoideae, Hippcastanoideae and Xanthoceroideae were also assessed by firstly, generating secondary structure predictions for ITS and partial ETS sequences, and then using these predictions to assist alignment of the sequences. Secondly, the alignment was analysed using RNA specific models of sequence evolution that account for the variation in nucleotide evolution in the independent loops and covariating stems regions of the ribosomal spacers. The phylogeny drawn from the analyses was compared with that from analyses using ‘traditional’ 4-state models and the plastid analyses.

To further our understanding of the origins of the Australian flora, and in particular plant adaptation and evolution in increasingly arid environments, the phylogeny and evolutionary history of Hopbushes (Dodonaea – Sapindaceae) and Pepperflowers (Diplopeltis – Sapindaceae) were evaluated based on nuclear ITS and partial ETS sequences and models of nucleotide evolution that incorporate secondary structure. The tempo and mode of evolution of these sister genera were evaluated using Bayesian relaxed clock molecular estimates of divergence times, Bayesian relative rates test, lineage through time plots and estimations of diversification rates (speciation minus extinction). The dry and temperate adapted genera of Sapindaceae (Diplopeltis species and Dodonaea including Distichostemon species) are relatively recent radiations in the Australian flora, and are most likely to be in response to increased aridity and seasonality from the late Miocene14 Mya to Recent. There is evidence of long distance dispersal from northern Australia to Madagascar in the early Pliocene.

The cosmopolitan, polymorphic species Dodonaea viscosa (hop bush, varnish tree) has been the subject of taxonomic and ecological enquiry for over 150 years. ITS and partial ETS sequences for 50 samples from across its worldwide distribution were used to evaluate the evolutionary and biogeographic history of this species complex. Dodonaea viscosa is not an old lineage as has often been speculated based primarily on it vast distribution, but diverged from its most recent common ancestor and subsequently dispersed around the world within the last two million years. Results also indicate that there are at least two evolutionary lineages within D. viscosa.

Item ID:	7893
Item Type:	Thesis (PhD)
Keywords:	soapberry genera, Sapindaceae genus, Dodonaea genus, genetic evolution, Australian flora, evolutionary adaption, climate adaptation, dispersal,plant phylogeny
Date Deposited:	22 Dec 2009 06:12
FoR Codes:	06 BIOLOGICAL SCIENCES > 0603 Evolutionary Biology > 060309 Phylogeny and Comparative Analysis @ 33% 06 BIOLOGICAL SCIENCES > 0607 Plant Biology > 060703 Plant Developmental and Reproductive Biology @ 34% 06 BIOLOGICAL SCIENCES > 0603 Evolutionary Biology > 060303 Biological Adaptation @ 33%
SEO Codes:	97 EXPANDING KNOWLEDGE > 970106 Expanding Knowledge in the Biological Sciences @ 100%
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