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Abstract Detail


Thornhill, Andrew [1], Ho, Simon [2], Külheim, Carsten [3], Crisp, Michael [4].

Interpreting the biogeographic history of Myrtaceae using a fossil-calibrated dated molecular phylogeny.

The angiosperm family Myrtaceae has extant and fossil taxa recorded from all southern continents and many groups have trans-oceanic distribution patterns that can be interpreted as a result of either vicariance or long-distance dispersal and establishment (LDDE). We tested these alternative hypotheses by estimating divergence times using a three-gene phylogeny of 88 genera and 202 species, representing both subfamilies and all tribes of Myrtaceae, with application of a relaxed molecular clock calibrated with 12 fossils. The phylogenetic program BEAST was used to develop the molecular dated phylogeny.
The application of reliable fossil calibrations represents a key component of many molecular studies of evolutionary timescales. In studies of plants, most paleontological calibrations are associated with macrofossils. However, the pollen record can also inform age calibrations if fossils matching extant pollen groups are found. Recent work has shown that Myrtaceae pollen can be classified into a number of morphological groups that are synapomorphic for clades discovered with molecular data. By assembling a data matrix of pollen morphological characters from extant and fossil Myrtaceae, we were able to measure the fit of 26 pollen fossils to the molecular phylogenetic tree using parsimony optimisation of characters. We identified eight Myrtaceidites fossils as appropriate for calibration based on the most parsimonious placements of these fossils on the tree. The other 18 fossils were not included because they were parsimoniously placed on nodes that had an older fossil already assigned to it.
To test conflicting biogeography hypotheses we mapped extant distribution ranges onto the dated phylogeny. Of the 22 disjunct sister-group in our study, up to five could possibly be explained by vicariance and 13 were inferred to be LDDE events, most of which have occurred since the Miocene. Estimated ages of some Myrtaceae groups were pulled deeper into time than results of previous studies through the use of fossil pollen which highlights its potential to compliment the use of macrofossils in molecular studies. With a more concentrated effort on extant and fossil pollen types and their 'phylogenetic signal', our current time calibrations could be greatly expanded and improved.

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1 - University of California, Berkeley, University and Jepson Herbaria, 1001 Valley Life Sciences Building # 2465 , Berkeley, CA, 94720-2465, USA
2 - The University of Sydney, Molecular Ecology, Evolution, and Phylogenetics, Sydney, NSW, 2006, Australia
3 - The Australian National University, Research School of Biology, Canberra, ACT, 2601, Australia
4 - The Australian National University, Daley Rd, Building 116, ANU, Canberra, N/A, 0200, Australia

fossil calibrations
molecular dating

Presentation Type: Oral Paper:Papers for Topics
Session: 59
Location: Salon 3/The Shaw Conference Centre
Date: Wednesday, July 29th, 2015
Time: 9:00 AM
Number: 59005
Abstract ID:287
Candidate for Awards:None

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