(American Journal of Botany. 2000;87:1066-1067.)
© 2000 Botanical Society of
America, Inc.
Origin of Livistona chinensis var. subglobosa (Arecaceae) on the "islet of the gods": Aoshima, Japan1
Naoto Yoshida4,2,
Rika Nobe2,
Kihachiro Ogawa2 and
Yoshikatsu Murooka3
2 Department of Biological Resource Sciences, Faculty of Agriculture, Miyazaki University, 1-1 Gakuen Kibanadai Nishi, Miyazaki-shi, Miyazaki 889-2192, Japan; and
3 Department of Biotechnology, Graduate School of Engineering, Osaka University, 2-1 Yamadaoka, Suita-shi, Osaka 565-0871, Japan
Received for publication November 29, 1999.
Accepted for publication April 6, 2000.
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ABSTRACT
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RAPD analysis was performed to discuss the origin of Livistona chinensis var. subglobosa using samples from eight localities, Iriomotejima, Ishigakijima, Okinawa, Yakushima, Tanegashima, Cape Sata, Tsukishima, and Aoshima, in Japan. Random amplified polymorphic DNA (RAPD) markers were obtained using five random primers and analyzed by the unweighted pair group method arithmetic (UPGMA). Data from Iriomotejima clustered with data from Aoshima, suggesting the possibility that seeds or green woods were carried by the tidal current from the southern fields of Iriomotejima to Aoshima.
Key Words: Arecaceae • evolution • haplotype • Livistona chinensis var. subglobosa • RAPD
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INTRODUCTION
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The genus Livistona consist of ~28 species, occurring from the Horn of Africa and Arabia, to the Himalayas and Ryukyu Islands south through Indochina and Malaysia to New Guinea, the Solomon Islands, and Australia which has the most species (Uhl and Dransfield, 1987
). One species, Livistona chinensis R. Br. var. subglobosa Becc. (fan palm) (Fig. 1A), is distributed from Taiwan through the islands of Okinawa as far north as Kyushu, Japan, where it grows along shores washed by the warm Kuroshio current. However, virgin L. chinensis forest is now found only on the islets of Aoshima and Tsukishima in the Miyazaki prefecture, Kyushu. Aoshima is the extreme northern limit of the Arecaceae plant community. The vegetation of the islet (4.4 ha) consists mostly of L. chinensis palms, ~4000 individuals, giving it the appearance of a subtropical jungle. According to legend, Aoshima has been conserved in this state because it was the home of a mythical God-family, the ancestors of the Emperor of Japan. Livistona chinensis has become a symbol of Miyazaki, giving visitors to Aoshima the impression that they have travelled to a tropical island. Stands of L. chinensis are rare, even though the species is widely distributed throughout the region, including the Okinawan islands.
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Fig. 1. (A) Livistona chinensis R. Br. var. subglobosa Becc. on Aoshima islet, Miyazaki prefecture. The main trunk is stout, with a wavy, circular pattern. (B) Map of the region south of Japan showing the eight locations where L. chinensis leaves were collected. The dark gray area on the island of Kyushu depicts the Miyazaki prefecture. (C) Phylogenetic tree based on haplotypes of L. chinensis samples obtained from eight locations. The bar shows the genetic distance
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Because there is little natural L. chinensis forest remaining elsewhere, it is of interest to know why this species grows primarily only on Aoshima. There are two hypotheses as to the origin of L. chinensis on Aoshima. One hypothesis is that seeds or green wood of L. chinensis were carried by the Kuroshio ocean current northwards from Taiwan or Okinawa to Aoshima, where the plant established itself, became naturalized, and eventually grew into a thick forest (Honda, 1918
). The other hypothesis is that the plant flourished throughout the region when the climate was warm, but after the Tertiary period changes in the climatic zones led to its gradually dying out, remaining only on islets washed by a moderately warm sea (Nakano, 1925
). Although the former hypothesis seems to have more credence among the general public, this opinion is not based on rigorous scientific evidence. The two papers referred to above were published in the early 1900s and the authors relied on a combination of guess work, well-known facts, and old observation records. Using new scientific techniques and DNA analysis, we offer our interpretation of the origin and dispersal of L. chinensis. Our findings are based on analysis of the polymorphism of its DNA using random amplified polymorphic DNA (RAPD) markers (Williams et al., 1990
).
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MATERIALS AND METHODS
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Leaves from five fronds of L. chinensises were collected from several locations on the islands of Iriomotejima, Ishigakijima, Okinawa, Yakushima, Tanegashima, Tsukishima, and Aoshima, and from Cape Sata (see Fig. 1B). Natural L. chinensis stands no longer exist in Taiwan. Chromosomal DNA was purified from the leaves collected from each area. Five polymerase chain reactions were performed using five kinds of random primers consisting of 12 mers and Taq DNA polymerase, and the haplotype was determined from the band pattern of the DNA amplified by each primer. The gene frequency in each population was determined from the haplotype. The genetic distance was calculated from these values in the same manner as that used to calculate genetic distance from the degree of heterozygosity or genetic diversity by studying protein polymorphism (Nei and Li, 1979
). A phylogenetic tree was drawn from the genetic distance values by the unweighted pair group method arithmetic (UPGMA) (Sokal and Michener, 1959
).
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RESULTS
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When haplotypes from the amplified DNA band patterns were compared, the haplotypic diversity of the population in each area was found to have a very high value, with a mean of 43.4%. Judging from the phylogenetic tree prepared from the genetic distances (Fig. 1C), the earliest individual differentiation occurred in the area around the islands of Ishigakijima and Okinawa. In other words, the results suggest that this area was the cradle of L. chinensis. Furthermore, it is assumed from the phylogenetic tree that L. chinensis spread from Okinawa and Ishigakijima northward to Tanegashima and Yakushima, and southward to Iriomotejima. The fact that L. chinensis on Aoshima is proximal in genetic distance with that on Iriomotejima may suggest that seeds or green tissue of the plant happened to be washed to Aoshima by the Kuroshio current, where it gradually became established and flourished. Our findings thus lead us to support the hypothesis that the plant drifted ashore on Aoshima and became naturalized. The value of a genetic distance of 1 is estimated at ~5 million years. If this estimate is correct, the origin of L. chinensis should be placed in the Quarternary period at least ~1.25 million years ago, because the mean genetic distance between the populations of Okinawa and Ishigakijima and other populations is 0.2492. Livistona chinensis does not appear to have been on Aoshima since the warm Tertiary period. Though it seems to have originated on Aoshima during the ice age of the Quarternary period, the development of L. chinensis was not apparently unduly retarded. It is likely that L. chinensis originally had cold resistance; it is known to have occurred on Tsushima island (at latitude 34°N) located to the south of the Korean Peninsula as well, suggesting that it lived through the ice age. We are proud of the rare L. chinensis forest on Aoshima and hope that many people will have the opportunity to visit the "islet of the Gods."
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FOOTNOTES
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1 This work was supported by Grant-in-Aid for Research from the President of Miyazaki University, Dr. Koji Futagami. 
2 Author for correspondence (e-mail: a04109u{at}cc.miyazaki-u.ac.jp
).
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LITERATURE CITED
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Honda, S. 1918 The formation of Livistona forest in Aoshima and protection law. Shiseki-Meishou-Tennenkinenbutsu (in Japanese) 2: 36–38.
Nakano, H. 1925 Plants in Miyazaki and Kagoshima prefecture. Tennenkinenbutsu-chousahoukoku-shokubutsu (in Japanese) 2: 1–27.
Nei, M., and W. H. Li. 1979 Mathematical model for studying genetic variation on terms of restriction endonucleases. Proceedings of the National Academy of Sciences, USA 76: 5269–5273.[Abstract/Free Full Text]
Sokal, R. R., and C. D. Michener. 1959 A statistical method for evaluating systematic relationships. University of Kansas Science Bulletin 28: 1409–1438.
Uhl, N. W., and J. Dransfield. 1987 Genera Palmarum. Allen Press, Inc., Lawrence, Kansas, USA.
Williams, J. G. K., A. R. Kubelik, K. J. Livak, J. A. Rafalski, and S. V. Tingey. 1990 DNA polymorphisms amplified by arbitrary primers are useful as genetic markers. Nucleic Acids Research 18: 6531–6535.[Abstract/Free Full Text]
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