Location: Subtropical Horticulture ResearchTitle: Hard Incongruence Between ITS and Plastid Phylogenetic Trees in Amaryllidaceae Tribe Hippeastreae (Asparagales)) Author
Submitted to: Meeting Abstract
Publication Type: Abstract only
Publication Acceptance Date: 6/15/2012
Publication Date: N/A
Citation: Interpretive Summary: Amaryllidaceae tribe Hippeastreae constitutes a horticulturally valuable group of American genera, with a diversity of chromosome numbers that may be descended in part from an ancient hybridization event. Its taxonomy at the generic level has been controversial, mainly due to a lack of clear cut distinguishing characters. We used both nuclear and chloroplast gene sequences to estimate the relationships among the generea and create a tree of life for the group. All markers agree that the tribe comprises two major groups. The trees derived from chloroplast and nuclear genes do not agree in their resolution. The resulting framework will serve as a basis for reclassification of the group.
Technical Abstract: Amaryllidaceae tribe Hippeastreae constitutes a horticulturally valuable group of American endemics, characterized by disploidy and polyploidy (x = 5, 6, 8, 9, 10, 11, 12; 2n = 10-150). It is a clade putatively descended (in part) from an ancient hybridization event. Its taxonomy at the generic level has been controversial, mainly due to the lack of unequivocal morphological characters. We sequenced ITS/5.8S and four plastid loci, 3'ycf1, ndhF, trnL intron, and trnL-F spacer, for 80 ingroup taxa (representing 44% of the tribe's species richness) and 10 outgroup taxa. No evidence of positive selection was found in plastid protein-coding loci, which suggests that they are suitable neutral markers for phylogenetic analysis. Separate analyses of each locus and of plastid vs. ITS sequences were conducted under Maximum Parsimony and Maximum Likelihood frameworks. All markers agree that the tribe comprises two major clades: a) Traubia, Placea, Phycella, Rhodolirium, and Famatina maulensis, characterized by x = 8, scarce polyploidy, and a capitate stigma, and b) Eithea, Habranthus, Hippeastrum, Rhodophiala, Sprekelia, Zephyranthes, and Famatina p.p., characterized by several basic chromosome numbers ranging between x = 5-12 and very frequent polyploidy and aneuploidy. No clear morphological features diagnose the latter clade; however, it contains ca. 90% of the tribe's species diversity. Phylogenetic analyses question the monophyly of all genera in the tribe and show hard incongruence in 10 out 13 ITS subclades in relation to the plastid- tree topology especially in the more diverse major clade, further supporting the proposed ancient reticulation in this portion of the tribal phylogeny. Network analyses were applied to visualize conflicting signals among data sets and putative scenarios of reticulate evolution. Additional analyses based on single-copy nuclear genes will facilitate several tests of the deep reticulation hypothesis in Hippeastreae. The resulting phylogenetic framework will serve as a basis for reclassification of the group and for study of chromosomal evolution.