Systematics/Phytogeography / Taxonomie/ Section
Morgan, David R. , Korn, Randi-Lynn , Mugleston, Spencer L. .
5S ribosomal RNA spacer variation in Machaerantherinae (Asteraceae: Astereae): Resolution of relationships and clarification of reticulate evolution processes.
The 5S ribosomal RNA (rRNA) spacer was investigated to characterize its structure, variation, and phylogenetic usefulness in Machaerantherinae. Spacers from 32 members of the subtribe were cloned, sequenced, and subjected to phylogenetic analysis. The spacers were 322-389 bp long in all species except four species of Xanthisma, in which they were 543-557 bp long. Regardless of length, all spacers consisted of two well defined regions: an upstream region with considerable intraspecific and interspecific variation in sequence and length, and a much more conserved downstream region that was about 200 bp long in most species. Phylogenetic analysis of the downstream region supported relationships that in most cases were the same as those supported by ITS and ETS sequence data. Combined analysis of 5S and ITS/ETS datasets produced well-resolved phylogenies in which many clades were well supported, resolving many interspecific and intergeneric relationships. The results also permitted some resolution of reticulate evolution processes in Machaerantherinae. For most lineages with a history of reticulate evolution, 5S and ITS/ETS evidence supported the same or similar relationships, indicating that these two regions of the nuclear genome were descended from the same ancestor or from two closely related ancestors in these lineages. Although in most cases 5S and ITS/ETS evidence supported the same relationships, they disagreed on the relationships of Arida riparia. This disagreement suggests that this species has experienced some kind of reticulate evolution during its history, such as nuclear introgression or hybrid speciation.
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1 - University of West Georgia, Biology, Carrollton, Georgia, 30118, U.S.A.
2 - United States Department of Agriculture, Bothell, Washington, 98021, U.S.A.
5S ribosomal RNA
Presentation Type: Oral Paper:Papers for Sections
Date: Wednesday, July 30th, 2008
Time: 4:15 PM