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ARS Home » Pacific West Area » Davis, California » Nat'l Clonal Germplasm Rep - Tree Fruit & Nut Crops & Grapes » Research » Publications at this Location » Publication #169106
Title: ORIGIN, EVOLUTION, AND BIOGEOGRAPHY OF JUGLANS L: A PHYLOGENETIC PERSPECTIVE

Author
item Aradhya, Mallikarjuna
item Simon, Charles
item POTTER, DANIEL - UNIV. CALIF, DAVIS

Submitted to: Acta Horticulture Proceedings
Publication Type: Popular Publication
Publication Acceptance Date: 11/11/2004
Publication Date: 3/1/2006
Citation: Aradhya, M.K., Simon, C.J., Potter, D. Origin, evolution, and biogeography of juglans l: a phylogenetic perspective. Acta Horticulture Proceedings.

Interpretive Summary: Phylogenetic relationship within the genus Juglans was analyzed using five cpDNA intergenic spacer sequences. In general pairwise divergence was extremely low within and between the sections. The cladograms from all the three analyses namely maximum parsimony, minimum evolution, and maximum likelihood were concordent with each other and contained three well-supported monophyletic clades corresponding to the section Juglans, Cardiocaryon, and Rhysocrayon. The single North American butternut, J. cinerea representing the section Trachycaryon was placed within the Rhysocaryon clade sharing four unique synapomrophies. The results suggest that: (1) the IGS sequence divergence levels observed within and between different sections of Juglans are low; (2) basal placement of the section Juglans in all the three analyses suggests its ancient origin in contrast to fossil evidence, which suggests the earliest divergence of sections Rhysocaryon and Cardiocaryon; (3) the Persian walnuts and butternuts have evolved at different rates as compared to black walnuts; and finally (4) the extant taxa may not represent the entire evolutionary history of the genus.

Technical Abstract: Phylogenetic analyses of extant Juglans (Juglandaceae) using five cpDNA intergenic spacer (IGS) sequences (trnT-trnF, psbA-trnH, atpB-rbcL, trnV-16S rRNA, and trnS-trnfM) were performed to elucidate the origin, diversification, historical biogeography, and evolutionary relationships within the genus. Overall, 3834 characters were sampled, yielding 112 (2.9%) variable sites, of which, 41 (1.06%) were potentially parsimony informative. In all, seventeen in-group (Juglans) and two out-group (Carya and Pterocarya) taxa were analyzed using the parsimony, likelihood, and minimum evolution methods, which produced concordant trees with three well supported clades corresponding to the sections Juglans, Cardiocrayon (butternuts), and Rhysocaryon (black walnuts). Juglans cinerea from the section Trachycaryon was placed within the black walnut clade, probably suggesting historical introgression of black walnut chloroplast during its evolution in North America. Black walnuts were not well resolved perhaps suggestive of their relatively recent origin and diversification or reticulate evolution within the section. Within butternuts, J. hopeiensis is moderately supported as a sister to J. ailantifolia, J. cathayensis, and J. mandshurica, which were well supported as a clade in all three analyses. The Persian walnut, J. regia and its sister taxon, J. sigillata formed a distinct clade sister to both butternuts and black walnuts. The cladogenesis within the genus Juglans appears to deviate from the evolutionary hypothesis based on the fossil history and biogeographic evidence. The results suggest that: (1) the IGS sequence divergence levels observed within and between different sections of Juglans are low; (2) basal placement of the section Juglans in all the three analyses suggests its ancient origin in contrast to fossil evidence, which suggests the earliest divergence of sections Rhysocaryon and Cardiocaryon; (3) the Persian walnuts and butternuts have evolved at different rates as compared to black walnuts; and finally (4) the extant taxa may not represent the entire evolutionary history of the genus.