Abstract Detail

Systematics Section/ASPT

Little, Damon [1], Hansen, Kimberley [2], Lam, Vivienne K.Y. [3], Ross, Gregory [4], Rai, Hardeep [5], Raubeson, Linda [6], Graham, Sean W. [3], Straub, Shannon [7], Liston, Aaron [8], Stevenson, Dennis [9], Mathews, Sarah [10].

Plastid phylogenomics resolves relationships among cycad genera.

The 300 living species of cycads are distributed between two families, Cycadaceae and Zamiaceae, which are estimated to have diverged from one another from 150 to 250 million years ago (Ma). Cycadaceae comprises a single genus, Cycas, while Zamiaceae comprises nine genera, Bowenia, Ceratozamia, Dioon, Encephalartos, Lepidozamia, Macrozamia, Microcycas, Stangeria, and Zamia. Phylogenetic structure within Zamiaceae has been challenging to resolve, with the positions of the Australian genus, Bowenia (2 species), and the African genus, Stangeria (1 species) being particularly uncertain. Based on cladistic analyses of morphological data they had been placed in a third family, Stangeriaceae, but molecular data have not supported this consistently. Dioon also has been differently placed in trees from molecular data. These difficulties may result from the ages of splits among genera, which range from 50-100 Ma, from high rates of extinction in the Mesozoic, leading to the loss of at least 16 genera, and/or from extinction of species in the five depauperate or monotypic genera, which include Dioon. To address relationships among cycad genera, we sampled whole plastid genomes from 50 species. Data from the coding sequences were analyzed separately and in a supermatrix that included an additional 220 species, represented by data from just matK and/or rbcL. Analyses of the 50-taxon complete matrix and the 270-taxon supermatrix resolve all nodes in Zamiaceae with strong bootstrap support, yielding the same relationships as analyses of a smaller number of characters in a nuclear multigene matrix. The first split in the family is between Dioon and the rest, followed by a deep split into two clades with four genera each. In one clade, Bowenia is sister to (Macrozamia(Encephalartos,Lepidozamia)) and in the other, Stangeria is sister to (Ceratozamia(Microcycas,Zamia)). This topology conflicts with some of the individual gene trees, resulting in low internode certainty values for some nodes. We are exploring this further with topology tests. This degree of resolution provides a solid framework for further analyses we will discuss in this talk, including the reconstruction of cycad biogeography and analyses that combine molecular data with a morphological matrix that includes fossils.

1 - New York Botanical Garden, Bronx, NY, USA
2 - Northern Arizona University, Biological Sciences Department, 617 S. Beaver St., P.O. Box 5640, Flagstaff, AZ, 86011, USA
3 - University of British Columbia, Department of Botany, Vancouver, BC, Canada
4 - University Of British Columbia, Botany, 3529 - 6270 University Boulevard, Vancouver, BC, V6T 1Z4, Canada
5 - University of Alberta, Edmonton, AL, Canada
6 - Central Washington University, Ellensburg, WA, USA
7 - Hobart and William Smith Colleges, Department of Biology, 300 Pulteney St., Geneva, NY, 14456, United States
8 - Oregon State University, Department Of Botany & Plant Pathology, 2082 Cordley Hall, Corvallis, OR, 97331-2902, USA, 541/737-5301
9 - The NY Botanical Garden, 2900 Southern Blvd, Bronx, NY, 10458-5126, USA
10 - CSIRO National Research Collections Australia, The Australian National Herbarium, Canberra, ACT, 2601, Australia

Keywords:
cycads
phylogenomics
plastid genes.

Presentation Type: Oral Paper:Papers for Sections
Session: 33
Location: Salon 10/The Shaw Conference Centre
Date: Tuesday, July 28th, 2015
Time: 8:30 AM
Number: 33003
Abstract ID:711
Candidate for Awards:None