Evolutionary diversification of new caledonian Araucaria

New Caledonia is a global biodiversity hotspot. Hypotheses for its biotic richness suggest either that the island is a ‘museum’ for an old Gondwana biota or alternatively it has developed following relatively recent long distance dispersal and in situ radiation. The conifer genus Araucaria (Araucariaceae) comprises 19 species globally with 13 endemic to this island. With a typically Gondwanan distribution, Araucaria is particularly well suited to testing alternative biogeographic hypotheses concerning the origins of New Caledonian biota. We derived phylogenetic estimates using 11 plastid and rDNA ITS2 sequence data for a complete sampling of Araucaria (including multiple accessions of each of the 13 New Caledonian Araucaria species). In addition, we developed a dataset comprising 4 plastid regions for a wider taxon sample to facilitate fossil based molecular dating. Following statistical analyses to identify a credible and internally consistent set of fossil constraints, divergence times estimated using a Bayesian relaxed clock approach were contrasted with geological scenarios to explore the biogeographic history of Araucaria. The phylogenetic data resolve relationships within Araucariaceae and among the main lineages in Araucaria, but provide limited resolution within the monophyletic New Caledonian species group. Divergence time estimates suggest a Late Cretaceous-Cenozoic radiation of extant Araucaria and a Neogene radiation of the New Caledonian lineage. A molecular timescale for the evolution of Araucariaceae supports a relatively recent radiation, and suggests that earlier (pre-Cenozoic) fossil types assigned to Araucaria may have affinities elsewhere in Araucariaceae. While additional data will be required to adequately resolve relationships among the New Caledonian species, their recent origin is consistent with overwater dispersal following Eocene emersion of New Caledonia but is too old to support a single dispersal from Australia to Norfolk Island for the radiation of the Pacific Araucaria sect. Eutacta clade.Mai Lan Kranitz, Edward Biffin, Alexandra Clark, Michelle L. Hollingsworth, Markus Ruhsam, Martin F. Gardner, Philip Thomas, Robert R. Mill, Richard A. Ennos, Myriam Gaudeul, Andrew J. Lowe, Peter M. Hollingswort

Araucariaceae phylogeny inferred from ITS2 DNA sequences using Bayesian optimisation criteria (50% majority rule topology).

<p>Support values are as detailed for <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0110308#pone-0110308-g002" target="_blank">Figure 2</a>.</p

Araucariaceae phylogeny inferred from plastid DNA sequences using Bayesian optimisation criteria (50% majority rule topology).

<p>Support values, below the branch, are: ML bootstrap/Bayesian posterior probability. Branches marked with an asterisk have a BS of 100% and a PP of 1.0. Detail of the relationships among New Caledonian <i>Araucaria</i> is shown at the bottom left. Branch lengths are proportional to the inferred number of substitutions along that branch.</p

Divergence time estimates for Araucariaceae.

<p>The topology presented is the maximum credibility tree (median node heights) obtained by pooling four separate runs under two constraint scenarios (see <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0110308#pone-0110308-t001" target="_blank">Table 1</a>, and text for details). Circles indicate nodes that were included in the assessment of candidate nodal constraints, and the dark shaded circles indicate nodes that were constrained for the BRC analyses (see <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0110308#pone-0110308-t001" target="_blank">Table 1</a> for details). Node bars (nodes with a posterior probability ≥0.75) indicate the 95% HPD of divergence times for the two prior scenarios: left, log normal prior mean  =  minimum fossil age +50%; right, log normal prior mean  =  minimum fossil age +10% (NC, New Caledonia; NI, Norfolk Island).</p

Araucariaceae phylogeny inferred from a combined plastid and ITS2 DNA data set using Bayesian optimisation criteria (50% majority rule).

<p>Support values are as detailed for <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0110308#pone-0110308-g002" target="_blank">Figure 2</a>.</p

Assessment of calibration constraints using empirical scaling factor (S<i>_i</i>) estimates.

<p>The mean (circle) and 95% highest posterior density interval (lines) of S<i>_i</i> is shown for each proposed calibration, including: (a) alternative nodal placements of fossil <i>Agathis</i> and <i>Araucaria</i> (vertical boxes). In (a), the S<i>_i</i> intervals are contrasted with the estimated age of conifers (c. 320 Ma; horizontal box). In (b), candidate fossils with S<i>_i</i> estimates that consistently exceeded the maximum age of conifers have been removed. The grey shading indicates the region of overlap in S<i>_i</i> intervals for the five retained calibrations.</p