Recent Population Fluctuation of an Endangered Species Melastoma tetramerum (Melastomataceae) and Necessity of Genetic Assessment for Future Conservation

2008·7.1 MB·English

by  Tetsuo Ohi-Toma

植物研究雑誌 323
J.Jpn.Bot.
Originals
83:323–330(2008)
Recent Population Fluctuation of an Endangered Species
Melastoma tetramerum (Melastomataceae) and Necessity
of Genetic Assessment for Future Conservation
Tetsuo OHI-TOMA, Yoshiteru KOMAKI, Kazunori HIRAI and Jin MURATA
BotanicalGardens,GraduateSchoolofScience,theUniversityofTokyo
3-7-1,Hakusan,Bunkyo-ku,Tokyo,112-0001JAPAN
E-mail:[email protected]
(ReceivedonMay10,2008)
Melastoma tetramerum is one of the most seriously endangered of the the endemic
species of the Bonin (Ogasawara) Islands. Although only one wild tree remained in
Higashi-daira (HD) of Chichi-jima in the 1980s, a new population of over 200 trees was
found in Higashi-kaigan (HK) of Chichi-jima in 1993. This study reports gradual reduc-
tion of the number of adult trees in HK, which included the death of most adult trees in
2007.BotanicalGardensoftheUniversityofTokyoiskeepingthelast10treesincluding
the last one in HD and starts the genetic assessment of kept trees for their conservation
in future. The phylogenetic analysis using chloroplast ndhF and rpl16 intron indicated
that M. tetramerum is sister to M. pentapetalum, endemic to Haha-jima. Within M.
tetramerum,twosequencetypeswerefoundinchloroplastpsbA-trnHregion.Thisresult
ofgeneticassessmentsuggestedthatwewouldcomeintonextstageforpropagationand
risk aversion on conservation activity.
Key words: Bonin Islands, conservation, endangered species, endemism, genetic assess-
ment, Melastoma tetramerum.
The Bonin (Ogasawara) Islands has a re- and endangered species in the Bonin Islands
cent volcanic origin in the Pacific Ocean and during two decades (Shimozono and Iwa-
consists of four island-groups from north to tsuki 1986, Hirai 2007), and is keeping over
south: the Muko-jima Islands, the Chichi- hundred endemic species of pteridophytes,
jima Islands, the Haha-jima Islands, and the gymnosperms and angiosperms at present. In
Iwo-jima (Volcanic) Islands (cf. Ohi-Toma addition, BGUT has conducted 1) field
etal.2007).InthefloraoftheBoninIslands, observations of growing environment and
there are many endemic plant species demographyinnaturalpopulations,2)propa-
(Toyoda 2003). However, the human activi- gation of endangered species in the green-
ties, invasion of nonnative plant and animal house, and 3) transplantations to native
species as well as aridification and typhoons habitats. Recently, assessment of genetic
have affected the local ecosystem in the variation has also begun for several species
Islands and put most of the native plant spe- (cf. Malaxis boninensis (Koidz.) K. Nakaj.
cies in danger of extinction. and M. hahajimensis S. Kobay. in Ohi-Toma
Koishikawa Botanical Garden of the Uni- et al. 2007), because we should consider the
versity of Tokyo (BGUT) is a key center of evolutionary background and genetic diver-
activities for conservation of the endemic sity of each species to inform conservation
—323—
324 植物研究雑誌 第83巻 第6号 平成20年12月
strategy. Of the activities in BGUT, one of candidum var. candidum in Minami-Iwo-
the most valuable contributions is a conser- jima and throughout East Asia. Of these
vation project of a seriously endangered taxa, M. pentapetalum is often placed under
species, Melastoma tetramerum Hayata M. tetramerum as a variety (Toyoda 1983,
(Japanese name is “Munin-Nobotan”, Fig. Kobayashi and Ono 1984). The recent revi-
1), for which only one wild tree was known sion of Melastoma by Meyer (2001) treated
in the 1980s. it as M. tetramerum. However, M. tetrame-
The genus Melastoma L. contains 22 spe- rum and M. pentapetalum can be distin-
cies of shrubs and small trees in tropical– guished from each other based on floral and
subtropicalAsiaandAustralia(Meyer2001). leaf morphology, chromosome number and
Most species are pioneers and have bird- habitat (Kobayashi and Ono 1984, Iwatsuki
dispersed fruits, which may results in the 1999). Therefore, we follow the system in
frequent formation of small and isolated Flora of Japan (Iwatsuki 1999). The two
populations (Meyer 2001). The recent flora endemic species, M. tetramerum and M.
of Japan recognized three endemic taxa and pentapetalum, are ranked as category IA and
another widespread species of Melastoma in VU in Japanese red data plants, respectively
the Bonin Islands (Iwatsuki 1999): M. (Yahara 2003). Melastoma tetramerum is
tetramerum in Chichi-jima, M. pentapetalum also protected by the law for conservation of
(Toyoda) T. Yamaz. &Toyoda in Haha-jima endangered species of wild fauna and flora
(“Haha-jima-Nobotan”), M. candidum D. (Godo 2007).
Don var. alessandrense S. Kobay. in Kita- Originally, the population size of M.
Iwo-jima (“Iwo-jima-Nobotan”) and M. tetramerum seems to have been quite small,
Fig.1. Melastomatetramerum.A.FlowerofatreeinHigashi-dairapopualtion.B.SeedlingobservedinHigashi-
kaigan(HK)population.C.TreewithfruitsinHKpopulation.D.DeadtreeinHKpopulation.
December2008 JournalofJapaneseBotanyVol.83No.6 325
and only three trees were reported in the first ing large typhoons. Several trees in HK have
field expedition after retrocession of the five-veined leaves against the tree with
BoninIslandstotheJapaneseGovernmentin three-veined leaves in HD. It shows that the
1968 (Iwatsuki and Shimozono 1989, Ono new HK population may keep different ge-
1993, Shimizu 1998). In the 1970s, two trees netic variation from the tree in HD, but the
out of the three died and the only a single genetic assessment of the species has been
tree remained in humid and lightly shaded not conducted.
area of Higashi-daira (abbreviated as HD) in In this study, we report recent fluctuation
Chichi-jima. Consequently, BGUT started of this newly discovered HK population
the conservation project of the species in based on field observation over the last dec-
1983.Ithasmainlyadoptedrepetitiveactsof ade and genetic assessment using chloroplast
propagation from cutting and selfed seeds in DNA for M. tetramerum for its future con-
thegreenhouseandtransplantationsofyoung servation.
trees to native habitats (Iwatsuki and
Shimozono 1989, Hirai 2007). Fortunately, Recent population fluctuations of HK
in May 1993, over 200 trees of M. tetra- population and transplanted trees
merum were discovered in Higashi-kaigan Following the discovery of the HK popu-
(abbreviated as HK) area 2 km away from lation, in a preliminary expedition in 1993,
HD area (Ono 1993), although the last origi- 125 adult trees were recorded. Observation
nal tree in HD finally died in 1995. The for growing condition of trees has been con-
emergence of these trees might be attributed ductedfrom1996tothepresent.Thepopula-
to the species’s characteristic of pioneer tion fluctuation is summarized in Table 1.
plant, which appeared in forest gaps follow- Adult trees in HK population gradually died
Table1. RecentfluctuationofadulttreesandseedlingsinHigashi-kaigan(HK)populationandsummertimeand
annualprecipitationsinChichi-jima
Precipitation(mm)
Numberof Numberof Reductionrate Numberof
Year
adulttrees flowerings ofadulttrees wildseedlings
July Aug annual
1993 125 – – – 46.5 105.0 887.5
1994 – – – – 245.0 50.5 1045.0
1995 – – – – 11.5 50.5 1091.0
1996 64 – – – 87.5 138.5 1112.0
1997 44 – 0.313 – 14.5 33.0 1799.5
1998 31 – 0.295 – 161.5 408.5 1466.5
1999 31 – 0.000 – 83.0 67.5 1600.0
2000 31 – 0.000 – 299.5 172.0 1592.0
2001 30 – 0.032 – 82.0 37.0 1351.0
2002 29 21 0.033 – 108.5 63.5 1129.0
2003 27 12 0.069 – 82.0 49.0 1128.5
2004 18 14 0.333 111 63.0 132.0 934.0
2005 15 6 0.167 42 63.5 30.5 1751.0
2006 9 5 0.400 35 13.5 157.5 1247.0
2007 1* 0 0.889 534(74)** 77.5 42.5 1132.0
*thislastreminingtreeisonthevergeofthedeath.
**numberinparenthesesisanumberofover10cmhigh.
326 植物研究雑誌 第83巻 第6号 平成20年12月
(Fig. 1D) and the number of adult trees re- 2007. Ironically, this emergence of seedlings
duced to only 9 after 14 years. In 2006, may be resulted from the appearance of
given the situation above mentioned, plants forest gap after typhoon, which damaged the
propagated by branch cutting from the last adult trees in HK population.
nine trees were kept in a greenhouse of the Heretofore, BGUT has conducted repeti-
BGUT. tive transplantations of young trees to native
One of factors for this reduction is that the habitats. Some of transplanted trees are
trees may have come to the end of their life. growing, flowering and bearing fruits at sev-
ThelifeexpectancyofM.tetramerumisesti- eral points in Chichi-jima. However, most of
mated as twenty to thirty years. On the other transplanted trees were progressively blight-
hand, the growth of this species is suscepti- ing, and its survival rate is merely approxi-
ble to soil water condition, air humidity con- mately 30 (cid:1). In addition, because most
dition and light condition, and the species is transplanted trees are clones derived from a
easily damaged by briny air (Iwastuki and single tree in HD and selfed seeds of a few
Shimozono 1989). When the precipitation in trees in HK, there remain problems that need
summer (July and August) is not low, the re- to be overcome for its conservation.
duction rate of adult trees tends to be rela-
tively low (Table 1). The climate conditions Genetic assessment for phylogeny, intra-
in the Bonin Islands periodically fluctuate, and inter-specific variations
and it is influenced by the El Niño-Southern We should consider how we preserve the
oscillation (Tagami 1991). The rapid reduc- last remaining wild population of M.
tion of the adult trees from 1993 to the pre- tetramerum. One of valuable tools for con-
sent might be related to the climate servation in future is genetic assessment for
oscillation, but we have not been able to the species (Yukawa and Kikuchi 2007). In
clarify the factors yet. In addition, the Bonin the past, we have propagated clone plants
Islands were largely damaged by a big ty- from cuttings and selfed seeds. However, if
phoon in 2007, and it resulted in the death of we can interbreed individuals with different
most original adult trees in HK population. genetic variation, we may be able to increase
At present, a remaining tree is on the verge and keep genetic diversity of the species.
of the death. Moreover, we should understand the
InHKpopulation,severaltreeshaveflow- evolutional history of M. tetramerum.
ered and set fruits after their emergence Therefore, this study attempted first to check
(Table 1, Fig. 1C), and natural seedlings the phylogenetic position of the endemic
were first observed in 1995. Since, many species of Melastoma in the Bonin Islands
seedlings have been observed (Fig. 1B). based on phylogenetic analysis using ndhF
Although we do not have detail records of and rpl16 intron sequences, which were used
seedling numbers until 2001, we have con- to infer the phylogeny of Melastomeae in
firmed that only five of them, which derived Melastomataceae (Renner and Meyer 2001).
from a part of natural seedlings recorded in We used two samples of M. tetramerum
1998, are growing to adult trees. Since 2004, from HD and HK populations, one of M.
the fluctuation of seedlings derived from pentapetalum from Haha-jima and some
original adult trees in HK population was Melastoma species, which are kept in
recorded (Table 1). In 2005 and 2006 the BGUT, and added data of Renner and Meyer
seedling numbers were reducing, but over (2001) from GenBank (Table 2). The proce-
five hundred seedlings, of which over 10 cm duresofDNAextraction,PCRamplification,
height were seventy four, were observed in and direct sequencing were used the same
December2008 JournalofJapaneseBotanyVol.83No.6 327
methods in Ohi-Toma et al. (2007). The ob- Next, to grasp the intra- and inter-specific
tained sequences have registered in the DNA variation for M. tetramerum and M.
Data Bank of Japan (DDBJ). Multiple se- pentapetalum, we surveyed nucleotide se-
quence alignment was manually conducted, quence variation on six regions of chloro-
and recognized indels were coded by binary plast DNA using 10 trees of M. tetramerum
scoring. Phylogenetic analysis was con- including the last tree from HD kept in
ducted by maximum parsimony method BGUT and five trees of M. pentapetalum
using PAUP (Swofford 2002). The detail of from Mt. Chibusa in Haha-jima. Nucleotide
analysis is explained in the legend of Figure sequences between M. tetramerum and M.
2. One substitution was found between rpl16 pentapetalum were distinctly differentiated
intron sequences of M. tetramerum and M. in two substitutions and length variation on
pentapetalum. The resultant phylogenetic fourpartsofmononucleotiderepeats(poly-A
tree (Fig. 2) indicated that the two Bonin andpoly-T)(Table3).Thisresultsupportsto
specieswerecloselyrelatedanddistinctlyfar recognition as different species. In addition,
from other species, but their sister species we found two sequence types (Mt-T9 and
were not detected. Although we need to col- Mt-T10), differed by repeat number of poly-
lect samples from a wide geographical range T on psbA-trnH region (T9 or T10), among
to understand the origin of Bonin Mela- 10 trees of M. tetramerum. The last tree in
stoma, this result may suggest that the Bonin HD, which has been used for propagation
species was differentiated from ancestors and transplantation, and four trees from HK
through an extended period of isolation. have Mt-T9 type and the other five trees
Table2. Listofsamplesusedinthephylogeneticanalysis
DDBJaccessionnumber
Taxon source
ndhF rpl16 intron
Melastomatetramerum Hayata Higashi-daira,BGUT92-318 AB436362 AB436371
Higashi-kaigan,BGUTHK035 AB436363 AB436372
M.pentapetalum(Toyoda) Mt.ChibusainHaha-jima,BGUT00-12 AB436365 AB436374
T.Yamaz.&Toyoda
M.candidumD.Donvar. candidum unknown,BGUT90-332 AB436369 AB436378
M.candidumD.Don Kita-Iwo-jima,BGUT94.7.7 AF270754 AF270751
var.alessandrenseS.Kobay.
M.malabathricumL. Malaysia,BGUT90-133 AB436370 AB436379
subsp.malabathricum
M.malabathricumL. Thailand,BGUT00-30 AF272800 AF294470
subsp.normale(D.Don)R.C.Srivastava
M.sanguineumSims unknown,BGUTB71 AF215564 AF215607
RennerandMeyer(2001) AF272802 AF210377
M.sp. unknown,BGUT91-218 AF215565 AF279745
Dichaetantheraarborea RennerandMeyer(2001) AF215570 AF210378
D.asperrima RennerandMeyer(2001) AB436364 AB436373
Dissotisfruticosa RennerandMeyer(2001) AB436368 AB436377
Heterotisrotundifolia RennerandMeyer(2001) AB436366 AB436375
Osbekiachinensis RennerandMeyer(2001) AB436367 AB436376
328 植物研究雑誌 第83巻 第6号 平成20年12月
Fig.2. PhylogenetictreeofMelastomabasedonnucleotidesequencesofndhFgeneandrpl16intron.Strictcon-
sensustreewasconstructedfromeightmostparsimonioustrees(treelength(cid:1)131,consistencyindex(cid:1)0.8779,
rescaled consistency index (cid:1)0.7183). Sequences of species with asterisk were data of Renner and Meyer
(2001),andtheiraccessionnumbersrefertoTable2.Dichaetantheraspecieswereusedasoutgroupspecies.
Search for most parsimonious tree was conducted by branch and bound search option on parsimony analysis
inPAUP(Swofford2002).CharacterchangeswerereconstructedonthestrictconsensustreewithACCTRAN
characteroptimizationoptioninPAUP.Valuesonbranchesarebootstrapprobabilities.whichwereexamined
by1,000permutationswiththesametreesearchprocedureoption.
have Mt-T10 type. The detected sequence can get much genetic diversity information
differentiation is small, but it is valuable for using genome wide genetic assessments, cf.
conservation of M. tetramerum in future. AFLP, we can progress to the next stage for
This result suggests that trees in the HK conservation activity. Moreover, we should
population are derived from at least two dif- conduct risk aversion of the endangered spe-
ferent mother trees, because the chloroplast cies in several botanical gardens based on
genome is maternally inherited in most an- their genotypes. In that case of M. tetrame-
giosperms. rum, according to the result of this study, we
can select and share at least two individuals
Conservation in future with different DNA types.
As clones of the 10 last adult trees of M.
tetramerum in HD and HK populations are This study is one of the conservation pro-
kept in BGUT, we will be able to cross trees jects based in Botanical Gardens, Graduate
of Mt-T9 and Mt-T10 types for propagation School of Science, the University of Tokyo
when they bloom in the near future. If we in cooperation with Tokyo Metropolitan
December2008 JournalofJapaneseBotanyVol.83No.6 329
MelastomaTable3.Nucleotidesequencevariation(substitutionsandmononucleotiderepeats)onsixregionsofchloroplastDNAintheBonin (i)(ii)(iii)(iv)(v)(vi)rpl16tnLtrnL-trnFrps16petBpsbA-trnHintronintronintronintronlocality(serialnumberof*NTaxonDNAtype**individualsinHK)(1,025bp)(865–868bp)(605–606bp)(596–597bp)(252–253bp) M.tetramerumMt-T9TA10T12A12T10+CT95HD,HK(018,081,084,088)Mt-T10TA10T12A12T10+CT105HK(006,035,044,083,093)M.pentapetalumMpGA12T13A11T11+AT105Mt.Chibusa,Haha-jima Mononucleotiderepeats(poly-Aandpoly-T)areindicatedascombinationofnucleotideanditsnumberofrepeat.PrimersforPCRamplificationandsequencing:(i)“F71”ofJordanetal.(1996)and“R1516”ofKelchnerandClark(1997),(ii)&(iii)thesetworegionswereamplifiedtogetherbyusingprimers“c”and“f”,andprimers“d”and“e”wereusedinsequencing(Taberletetal.1991),(iv)“1F”and“2R”ofNishizawaandWatano(2000),(v)“1F”and“2R”ofNishizawaandWatano(2000),(iv)Hamilton(1999).DDBJaccessionNos.ofsequences:(i)refertoTable2;(ii)&(iii)Mt:AB443868,Mp:AB443869;(iv)Mt:AB443941,Mp:AB443942;(v)Mt:AB443943,Mp:AB443944;(iv)Mt-T9:AB443945,Mt-T10:AB443946,Mp:AB443947.*N:numberofexaminedsamples.**AbbreviationsofHDandHKare“Higashi-daira”and“Higashi-kaigan”inChichi-jima,respectively. JKRIOHIKMOGEGHNwwoeeniohoainorersaanlmdobidayvhcvttCLrA8piJcMgjipCBBIMi6M-Ka(Pflt(Jfi3aanaaosisninneinaeTOuAihaIairnibni3her59Mmhveoecunuyoooozm.clpurctrKpeeelpnorodlgH:y-t8rrpayirOwlatrkkau.ntuo:eimlesloa7aatCelaha,Kmci.aWtel..ndaapwts4iieilsfe.doSnnio.ngcnr0s2onhneefraifT1hlbsseoe2nc3m.2Kapsioieeagli.ayo.1tsdKirim.ttnr9rucl.ne0Mntpo0aSdcB0assooeO2ssreivr7cS.advCT9scx0tT.eenek–ePapndac.0nmm0eMla–eoPeqnG.ga.lie3)r.7weigy4.endc.h.v7e0otx1oaro2n,.BfmnCn,uaalasDB.:i.caeo3-Gtauyo.isn1tc9ffaao1dtisdeiiKcCtinaoHRr9Dan.r.llC.3kcLds.Bnr9aen9ue,a(d(tpovadetota.loSa1)ewJdM-svi9EoaaR.iacculaietlgia)u.dnfOJSs.tatuob9aahbnna.wkhb,(nsn.KMnoraeaectaaerWSnrBMgo9rPoCiigiwilonadiseJrndknvoMattamlticloJpnoteCt9fafi.haHnteaaonamiooendivs.aeennar.ottdoc-.psaytVtyReosodG:entPnyordneel1.tKigerih.ag25Mdtgayaea,FntalzrfeoiordspiPo9oert.aoanlnern08csraecEyneoOsomeohnY.nusolfAam9lrlsg.MpssoEtnnae0:naornfceaued.vmKtropIhht7ieoveulsnsae17ok(taarnotoovo1srecoMmht.bta.eohLtcfaklYt.sn9e.lmytthfpeorn0lyBii)paaiageFteWetaan.iaco8uMmcen2lflLs.7Mio.Postnnrgarcaramutwi.oi4.ch-8eH0ii–vlin.ctDdhte2asp.mINctsmnreo1ed.tweoat:0nai1aitstasryeOT0hv.hetcpasone9inc,lobld1etagA1)3ecevlt0eseal.naoia(rrTDen8–gonrfuTpie.ocer1oo8)ooegoecr0nxdfaEsat9Ha..ngpeBnsoirN.cnn5doruunfMeojp,5.deoatomso.aecsseoephPs–snNktilooBr.a5steanAKPio.picohsaSnette.uilye3iyt.ltindnw:i)r.tootlefrl)Icrlyeaeerlccrlor,ou9.uoaie.1d.anJisianr1e4rntiuanlsmmgrsc7am..ioFnp7eas:oote8n3p8Atrvycmftitret.ennpvp:alJncI:oaeoiai1e:oaee,IpolAsnmDoprcgl.iuo.trwkrcrn5ragm5apn6lorpuMenonJee(sil7iisaiia–ies1tKp.a3unauPle.rlvre.oiohn4ft41ro1aa3Yteaetas–Jtti3aaeEoonef.ied–sBiln66ttMfD3lnadi–o6nC8roieiinufaa.sars7.:6Jpen2oos,o5san6ds2nNns.kcisap.Nhg6niJ31aae4nncmt2n.eHt–3tdeilAla.ieswndvA–9ooy.Bs5aoitmaaca35taapunpsri5heai69mKmatcnh.r(hxiroeonn81nhaiulsonoti9iitic76atititi)ethnna.dndp5–hngneaaeasss----f--:i.,...
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東馬哲雄, 小牧義輝, 平井一則, 邑田 仁：絶滅
危惧種ムニンノボタン (ノボタン科) の最近の個
体群動態と今後の保全に向けての遺伝的評価 の計10個体の系統保存を行うと共に, 今後の保全
ムニンノボタンは小笠原固有種の中でも最も絶 活動のために遺伝的多様性解析を進めている. 葉
滅の危機に瀕している種の1つである. 1980年代 緑体DNAの解析からは, ムニンノボタンは母島
には現存個体が父島・東平に1個体だけであると 固有種ハハジマノボタンに近縁であること, ムニ
思われていたが, 1993年に父島・東海岸で200個 ンノボタン種内ではpsbA-trnH領域に2種類のハ
体以上の成木個体が発見された. その後, 東海岸 プロタイプが存在することが明らかになった. 今
集団について継続的観察を行ってきたが, 個体数 後は, ハプロタイプを考慮した増殖・危険分散を
が年々減少し, 2007年には成木個体のほとんど全 行う必要がある.
てが枯死した. この状況を受けて, 東平と東海岸 (東京大学大学院理学系研究科附属植物園)