Abstract Detail

Systematics Section/ASPT

Ickert-Bond, Stefanie [1], Pellicer, Jaume [2], Souza, Aretuza [3], Metzgar, Jordan [4], Leitch, Ilia [2].

Ephedra – the gymnosperm genus with the largest and most diverse genome sizes driven by a high frequency of recently-derived polyploid taxa and a lack of genome downsizing.

The Gnetalean gymnosperm genus Ephedra (Ephedraceae) is chromosomally highly variable. In contrast to the relatively small genomes of most angiosperms (mean 1C = 5.6 pg), gymnosperm genomes are typically large (mean 1C = 18.1 pg), exhibit relatively low chromosome numbers (range 2n = 14 - 66), and show a remarkable consistency of chromosome number and karyotype within genera, with few reports of polyploidy. In contrast to this uniformity, Ephedra, a genus with ca. 50 species, is chromosomally highly variable – with numbers spanning nearly the whole range encountered in gymnosperms as a whole (i.e. 2n = 14 – 56). Genome sizes were assessed using flow cytometry in 166 samples representing 48 species spanning the entire phylogenetic tree and new chromosome numbers for 4 species (E. californica, 2n = 42; E. foeminea 2n = 14; E. pseudodistachya 2n = 28; and E. rhytidosperma 2n = 14) were obtained and published chromosome numbers for 31 species were recorded. We employed maximum likelihood and Bayesian phylogenetic inferences to estimate the ancestral haploid chromosome numbers and genome size using ChromEvol v. 1.3 and Bayes Traits. Ephedra is the most diverse gymnosperm based on genome size, with 1C-values ranging nearly 5-fold from 8.09-38.34 pg and it includes the largest genome size so far reported for any gymnosperm (E. antisyphilitica, 2n = 8x = 56). Chromosome counts as well as C-value estimation revealed that 69.3% of the species were polyploid, with tetraploidy being the most common (53.9 % are tetraploid, 1.9 % are pentaploid, 9.6 % are hexaploid and 3.9 % are octaploid). The monoploid (1Cx) values at different ploidy levels are relatively uniform (mean 1Cx for 2x = 9.38 pg; 4x = 9.17 pg; 5x = 10.15 pg; 6x = 9.46 pg; 8x = 9.27 pg) suggesting that polyploidy is not accompanied by significant genome downsizing, as commonly reported in angiosperms. It is unclear if the large genome of Ephedra is dominated by low abundance of highly diverged repeats, as reported for Pinus taeda, but epigenetic mechanisms constraining repeat amplification have been reported to differ between angiosperms and gymnosperms. The frequency of polyploid formation observed across all clades of Ephedra might point to polyploidization as a successful mechanism to diversify in arid regions of the world. Species boundaries in North American Ephedra appear to have been obscured by hybridization and polyploidization.

1 - University Of Alaska Museum Of The North, Herbarium (ALA) And Dept. Of Biology And Wildlife, University Of Alaska Fairbanks, 907 Yukon Dr., Fairbanks, AK, 99775, USA
2 - Royal Botanic Gardens, Kew, Jodrell Laboratory, Richmond, Surrey, TW9 3 AB, UK
3 - Ludwig-Maximilians-Universität München, Department of Biology, Systematic Botany and Mycology , Menzinger Straße 67, München, 80638, Germany
4 - University Of Alaska Fairbanks, Museum Of The North, 907 Yukon Drive, Fairbanks, AK, 99775, USA

Keywords:
Ephedra
Chromosomes
C-value
molecular phylogeny
ancestral state reconstruction
Polyploidy
Bayes traits.

Presentation Type: Oral Paper:Papers for Sections
Session: 33
Location: Salon 10/The Shaw Conference Centre
Date: Tuesday, July 28th, 2015
Time: 9:00 AM
Number: 33005
Abstract ID:862
Candidate for Awards:None