Molecular phylogeny of Juglans (Juglandaceae): a biogeographic perspective |
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Authors: | Mallikarjuna K Aradhya Daniel Potter Fangyou Gao Charles J Simon |
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Institution: | (1) USDA Germplasm Repository, University of California, One Shields Avenue, Davis, CA 95616, USA;(2) Department of Plant Sciences, University of California, One Shields Avenue, Davis, CA 95616, USA;(3) Plant Genetic Resources Unit, USDA-ARS, Cornell University, Geneva, NY 14456-0462, USA |
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Abstract: | The eastern Asian and eastern North American disjunction in Juglans offers an opportunity to estimate the time since divergence of the Eurasian and American lineages and to compare it with
paleobotanical evidence. Five chloroplast DNA noncoding spacer (NCS) sequences: trnT−trnF, psbA−trnH, atpB−rbcL, trnV-16S rRNA, and trnS-trnfM and data from earlier studies (matK, ITS, and nuclear RFLP) were used to reconstruct phylogeny and to estimate the divergence time of major lineages. Seventeen
taxa from four sections of Juglans and two outgroup taxa, Pterocarya stenoptera and Carya illinoiensis were included. NCS data was congruent only with matK data. Both maximum parsimony (MP) and maximum likelihood (ML) cladograms were concordant at the sectional level and revealed
three well-supported monophyletic clades corresponding to sections Juglans, Cardiocaryon, and Rhysocaryon in both NCS and combined analyses. The single extant American butternut, Juglans cinerea was placed within the poorly resolved, but well-supported Rhysocaryon. Placement of taxa within Rhysocaryon and Cardiocaryon were inconsistent between NCS and combined analyses. Overall, the results suggest that: (1) the NCS sequence divergence observed
within and between sections of Juglans is low and the addition of matK data only marginally improved resolution within Rhysocaryon; (2) the early divergence of section Juglans in both MP and ML analyses of NCS and combined data implies its ancient origin in contrast to fossil evidence, which suggests
the earliest divergence of sections Rhysocaryon and Cardiocaryon; and (3) the extant taxa may not hold the footprints to unravel the evolutionary history of the genus. |
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Keywords: | Biogeography Chloroplast DNA Cladogenesis Disjunction Juglandaceae Juglans Noncoding spacer sequence Phylogeny Walnut |
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