Abstract Detail

Recent Topics Posters

Ickert-Bond, Stefanie [1], Sousa, Aretuza [2], Min, Ya [2], Leitch, Ilia J. [3], Pellicer, Jaume  [4].

The evolution of genome size in the gymnosperm genus Ephedra: Flow cytometry and new chromosome counts support high levels of polyploidy.

While the incidence of chromosomal change is well documented, its impact on speciation is less understood, particularly in gymnosperms. Compared with angiosperms, gymnosperms are characterized by a large genome (mean 1C = 18.1 pg), relatively low chromosome numbers (range 2n = 14 - 66), a remarkable consistency of number and karyotype within genera and generally few polyploids. In contrast to this uniformity, Ephedra, a genus with ca. 50 species, is chromosomally highly variable. As documented sequence divergence in Ephedra is low, chromosome analyses and genome size estimations might represent the most appropriate and informative approaches for investigating sibling species. To assess this we performed 1) flow cytometry 2) chromosome counts and 3) phylogenetic modeling of chromosome number change to determine if Ephedra have been influenced by polyploidy. Here, we report the genome size for 36 taxa of Ephedra (with multiple accessions for many of the species) spanning the entire phylogenic tree. This assessment includes 17 taxa that have never been assessed cytogenetically and hence chromosome counts are lacking. In addition, we also provide new chromosome counts for 5 taxa, these were based on the same accessions as those used for flow cytometry. Our results have considerably increased the range of genome sizes encountered in Ephedra such that Ephedraceae is now the most variable of all gymnosperm families, with 1C-values ranging nearly 5-fold from 8.09-38.03 pg, and it includes the largest genome size so far reported for any gymnosperm (E. antisyphilitica, 2n = 8x = 56). Chromosome numbers range from 2n = 14, to 2n = 56 with 28 taxa (77%) showing polyploid genomes. Of these polyploids, most (i.e. 78.6%) were tetraploid. 1Cx-values at different ploidy levels are relatively uniform (mean 1Cx for 2x = 9.13 pg; 4x = 9.14 pg; 5x = 10.17 pg; 6x = 9.51 pg; 8x = 9.38 pg) suggesting that polyploidy is not accompanied by significant genome downsizing, as commonly reported in angiosperms. The ancestral chromosome number reconstructed using a maximum likelihood model of chromosome number change in Ephedra was a = 7, which was inferred and statistically supported at all nodes of the phylogenetic tree, except for three clades close to the tips with a = 14. Duplication is the predominant inferred event in the karyotype evolution of Ephedra, whereas chromosome losses are inferred less frequently. Chromosome counts and C-value data support the model-based inference of the importance of polyploidization in Ephedra.

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 - University of Munich (LMU), Department of Biology, Munich, D-80638 , Germany
3 - Royal Botanic Gardens, Kew, Jodrell Laboratory, Richmond, Surrey, TW9 3 AB, UK
4 - Royal Botanic Gardens, Kew, Jodrell Laboratory, Richmond, Surrey, TW9 3 AB, UK

Keywords:
gymnosperms
polyploidy
C-values
ancestral chromosome number
Ephedra.

Presentation Type: Recent Topics Poster
Session: P
Location: /
Date: Monday, July 28th, 2014
Time: 5:30 PM
Number: PRT015
Abstract ID:1253
Candidate for Awards:None