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Abstract Detail


Systematics Section

Fishbein, Mark [3], Chuba, David [1], Weitemier, Kevin [2], Ovchinnikov, Sergey [2], Saadoun, Basma [2], Kilhoffer, Kevin [3], Watson, Linda E. [3], Fathepure, Shakuntala [3].

Detecting incomplete lineage sorting and past hybridization in American Asclepias (Apocynaceae).

Discordance between cytoplasmic and nuclear gene trees had long been attributed primarily to introgressive hybridzation until insights from population genetics raised awareness of the confounding effects of incomplete lineage sorting. Techniques for distinguishing between these causes of gene tree discordance, as well as discordance arising from systematic error in phylogeny estimation, have been developing rapidly. Similarly, powerful new techniques for inferring species phylogenies while accounting for these processes are also blossoming. Phylogenies of the well-known genus of American milkweeds (Asclepias, Apocynaceae) exhibit substantial discordance across plastid, nuclear ribosomal, and nuclear intronic loci. Species of Asclepias are notable for apparently sharp morphological demarcation and few documented instances of interspecific hybridization. Thus, high levels of introgression leading to "chloroplast capture" might not be expected in these plants. However, the plastidic phylogeny of Asclepias (based on five non-coding regions) contains numerous instances of morphologically puzzling, yet strongly supported relationships, suggesting either a poor understanding of relationships inferred from morphology, numerous instances of past chloroplast capture, extensive incomplete lineage sorting, or likely some combination of the preceding explanations. We analyzed sources of discordance among three putatively independent phylogenetic estimates (concatenated plastid loci, nuclear ribosomal ITS, nuclear pgiC introns) by 1) assessing the probability that these estimates support statistically incongruent phylogenies, 2) identifying regions of the phylogenies responsible for discordance, 3) assessing whether past hybridization makes sense given current species distributions and the putative timing of hybridization events, and 4) evaluating whether discordance among the estimated phylogenies can be accounted for solely by differential lineage sorting. We also provide a best estimate of the species tree for Asclepias considering the multispecies coalescent.

Broader Impacts:


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1 - University of Zambia, Biological Sciences Department, PO Box 32379, Lusaka, Zambia
2 - Portland State University, Biology Department, PO Box 751, Portland, OR, 97207, USA
3 - Oklahoma State University, Botany Department, 104 Life Sciences East, Stillwater, OK, 74078, USA

Keywords:
Apocynaceae
Asclepias
cpDNA
gene tree
hybridization
incomplete lineage sorting
ITS
milkweed
nuclear intron
pgiC
phylogeny
species tree.

Presentation Type: Oral Paper:Papers for Sections
Session: 49
Location: 552B/Convention Center
Date: Wednesday, August 4th, 2010
Time: 9:15 AM
Number: 49006
Abstract ID:670


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