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Abstract Detail

Systematics Section/ASPT


Calibrated chronograms, fossils, outgroup relationships, and root priors: re-examining the historical biogeography of Geraniales.

We re-examined the recent study by Palazzesi et al. (2012) published in the Biological Journal of the Linnean Society (107: 67–85) that presented the historical diversification of Geraniales using BEAST analysis of the plastid spacer trnL-F and the non-coding nuclear ribosomal ITS. Their study presented a set of new fossils within the order, generated a chronogram for Geraniales and other rosid orders using fossil-based priors on five nodes, demonstrated an Eocene radiation of Geraniales (and other rosid orders), and argued for more recent (Pliocene - Pleistocene) and climate linked diversification of genera in the five recognized families relative to previous studies. Due to very young ages for the crown of Geraniales and other rosid orders, unusual relationships of Geraniales to other rosids, and apparent nucleotide substitution saturation of the two gene regions, we conducted a broad series of BEAST analyses that either incorporated additional rosid fossil priors, used more accepted rosid ordinal topologies, or altered the placement of one fossil Geraniales prior. Our results indicate that their ages are 20-50% too young due to a combination of (1) strong nucleotide saturation of the DNA regions starting at 65 Mya, (2) lack of a root (rosid-stem) or other rosid ordinal stem fossil-based priors, (3) inability of the two DNA regions (with alignment issues) to obtain a monophyletic Geraniales as well as reasonable relationships of Geraniales to other rosid orders, and (4) apparent issues with the nodal placement of a Pelargonium fossil. The Geraniales crown is much older (Campanian of Cretaceous, 86 Mya), the posterior age distribution on all but two fossil nodes are well older than the priors, the placement of a Pelargonium-like fossil is more likely at the crown rather than the stem, but their models of diversification within several clades linked to climatic and orogeny appear supported. We discuss a number of the inherent issues of relaxed clock dating and outline some "best practice" approaches for such studies.

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1 - University Of Wisconsin, Department Of Botany, Birge Hall, 430 Lincoln Drive, Madison, WI, 53706, USA
2 - St. John's University, 8000 Utopia Parkway, Queens, NY, 11439, USA

molecular clock
substitution saturation
historical biogeography.

Presentation Type: Oral Paper:Papers for Sections
Session: 14
Location: Cottonwoods North/Boise Centre
Date: Monday, July 28th, 2014
Time: 4:00 PM
Number: 14010
Abstract ID:363
Candidate for Awards:None

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