Title: Phylogeny and evolutionary history of Sapindaceae and Dodonaea
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.
Publication Year: 2008
Publication Date: 2008-01-01
Language: en
Type: dissertation
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Cited By Count: 9
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