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Johannes-Gutenberg Universität in Mainz (2007)

Phylogeny and historical biogeography of the Australian Camphorosmeae (Chenopodiaceae)

Cabrera, Jonathan F.

Titre : Phylogeny and historical biogeography of the Australian Camphorosmeae (Chenopodiaceae)

Auteur : Cabrera, Jonathan F.

Université de soutenance : Johannes-Gutenberg Universität in Mainz

Grade : Doktor der Naturwissenschaften 2007

Molecular and morphological data were used to reconstruct the phylogeny and biogeographic history of the arid adapted plant group Camphorosmeae in Australia. Molecular phylogenies were constructed using Bayesian statistics and maximum likelihood. Nonparametric rate smoothing and penalized likelihood were employed to estimate divergence times within the Australian lineage. Morphological characters were parsimoniously mapped on the molecular-based phylogeny of Camphorosmeae. Primary Brooks parsimony analysis, cladistic analysis of distributions and endemism, dispersal-vicariance analysis, ancestral area analysis and weighted ancestral area analysis were performed to infer sequence and directionality of biogeographic pathways. From seven molecular markers tested, only the nuclear ETS and ITS provided enough variation for the successive analyses of the group ; the plastid markers trnL-trnF spacer, trnP-psaJ spacer, rpS16 intron, rpL16 intron and the trnS-trnG spacer showed degrees of variation unsuitable for phylogenetic studies in the Australian Camphorosmeae. Phylogenetic hypotheses inferred using the nuclear markers do not completely support the current taxonomy of the group. Neobassia, Threlkeldia, Osteocarpum and Enchylaena should be subsumed to the speciose genera Sclerolaena or Maireana. The results of the cladistic analyses of the fruiting perianth appendage characters support the taxonomic implications of the DNA-based phylogeny. However, indumentum character, which was reported to be of taxonomic significance in several groups in Chenopodiaceae, did not provide support for the phylogeny of Camphorosmeae in Australia. Ancestors of the present-day Camphorosmeae arrived in Australia during the Miocene (ca. 8-14 mya) via long-distance dispersal probably from continental Asia. Initial diversification of the group occurred during the Late Miocene until the Early Pliocene (ca. 4-7 mya), and by the end of the Pliocene 45% - 72% of the extant lineages were already present, indicating rapid diversification. This age coincides with previous hypotheses on the onset of aridification of the continent, suggesting that environmental evolution played a significant role in speciation in the group. Ancestors of the group appeared to have occupied the southern coastal regions of the continent prior to the aridity of the continent. They then “migrated” in multiple directions as aridity developed during the Late Tertiary and throughout the Quaternary. The success of the group in the then newly forming environment was determined by the adaptation of the ancestral lineages to arid conditions. The apparent absence of clear phylogenetic and generic boundaries among taxa in the Australian Camphorosmeae is believed to be the result of the young age of the group and its rapid diversification, therefore not allowing the accumulation of mutations and clear morphological distinctions.


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