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Distinct Geographic Structure as Evidenced by Chloroplast DNA Haplotypes and Ploidy Level in Japanese Aucuba (Aucubaceae)
Tetsuo Ohi, Tadashi Kajita and Jin Murata
American Journal of Botany
Vol. 90, No. 11 (Nov., 2003), pp. 1645-1652
Published by: Botanical Society of America, Inc.
Stable URL: http://www.jstor.org/stable/4123721
Page Count: 8
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The geographic distribution of diploid and tetraploid cytotypes and cpDNA haplotypes throughout the entire range of Aucuba japonica was investigated. We measured relative genome size using flow cytometry and sequenced two cpDNA intergenic regions, atpB-rbcL and psbA-trnH (GUG). Two haplotypes include both diploids and tetraploids; four others are all tetraploids. Based on the combination of these haplotypes and cytotypes, eight "haplo-cytotypes" can be defined, which show a distinct geographic structure. Two diploid haplo-cytotypes are distributed in the southwestern part and six tetraploid ones in the northeastern part of the Japanese archipelago. Diploid and tetraploid haplo-cytotypes with the same haplotype are, in one case, disjunctively distributed, and in another case, in contact. The phylogenetic relationships of haplo-cytotypes indicate that the traditional circumscription of A. japonica is paraphyletic. One lineage consists of four tetraploid haplo-cytotypes and another of diploid and tetraploid haplo-cytotypes plus A. chinensis. Tetraploidization occurred independently at least three times, once at the base of the former lineage and twice in the latter. Taking the geographic, cytological, and phylogenetic evidence into account, the formation of the present geographic differentiation pattern of haplo-cytotypes through postglacial expansion from glacial refugia is discussed.
American Journal of Botany © 2003 Botanical Society of America, Inc.