Recent Topics Posters
Hipp, Andrew L. , Roalson, Eric .
Dynamic genome size and chromosome number
evolution in Carex subgenus Vignea (Cyperaceae).
Carex, one of the most species-rich genera in flowering plants, has diffuse or non-localized centromeres (holocentric chromosomes). This has been hypothesized to facilitate exceptionally variable aneuploidy in the genus, with haploid counts ranging from n = 6 to n = 48. We investigated chromosome number and genome size variation in 77 species of Carex subgenus Vignea using traditional cytogenetic methods in combination with flow cytometry. Previous, non-phylogenetic analyses have reported a negative correlation between chromosome number and genome size that appeared to demand explanation. Using phylogenetic correction (generalized least squares), we find that the regression of genome size on chromosome number is nonsignificant for subg. Vignea. The rate of evolution of chromosome number exhibits a significant increase at the base of sect. Ovales, a species-rich clade within subg. Vignea, while genome size exhibits no change in evolutionary rate. Additionally, genome size exhibits much higher phylogenetic dependence than chromosome number in sect. Ovales and subg. Vignea outside of sect. Ovales. These results in combination suggest that (1) the relatively high lineage diversity of sect. Ovales is associated with an increase in the rate of karyotypic diversification; (2) the evolutionary dynamics of chromosome rearrangements may be more labile than those of genome size; and (3) chromosome fission, fusion, and / or translocation play a very large role in Carex karyotype evolution, as evidenced by the flat relationship between genome size and chromosome number across the majority of the genus. Rapid evolution of karyotype diversity in sect. Ovales may be accompanied by an increased contribution of chromosome duplication and deletion, as evidenced by the transition to a positive correlation at the base of the section, that may be invisible or lost at deeper phylogenetic scales. However, as this correlation becomes nonsignificant with phylogenetic correlation, and the pattern bears further study. Phylogenetic conservatism of genome size suggests a potential utility for the character in revising sectional classification in Vignea.
The impacts of chromosome evolution in the systematics and conservation of plants is not well understood. In this study, we demonstrate an increase in the rate of chromosome evolution at the base of a species-rich clade in sedges, and show that this increase in chromosome evolution is driven by fissions, fusions, and / or translocations rather than chromosome deletions and duplications. These processes may drive speciation and affect population genetic structure in the largest genus of the temperate zone, Carex, and consequently they bear study with respect to questions in ecological restoration and species conservation.
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1 - The Morton Arboretum, 4100 Illinois Route 53, Lisle, IL, 60532-1293, USA
2 - Washington State University, School of Biological Sciences, Po Box 644236, Pullman, Washington, 99164-4236, USA
Phylogenetic comparative methods
Presentation Type: Recent Topics Poster
Location: Hall A/Convention Center
Date: Monday, August 2nd, 2010
Time: 5:30 PM