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Anagenetic speciation in Ullung Island, Korea: Genetic diversity and structure in the island endemic species, Acer takesimense (Sapindaceae)

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Anagenetic speciation is an important mode of speciation in oceanic islands; one-fourth of the endemic plants are estimated to have been derived via this process. Few studies, however, have critically examined the genetic consequences of anagenesis in comparison with cladogenesis (involved with adaptive radiation). We hypothesize that endemic species originating via anagenetic speciation in a relatively uniform environment should accumulate genetic variation with limited populational differentiation. We undertook a population genetic analysis using nine nuclear microsatellite loci of Acer takesimense, an anagenetically derived species endemic to Ullung Island, Korea, and its continental progenitor A. pseudosieboldianum on the Korean Peninsula. Microsatellite data reveal a clear genetic distinction between the two species. A high F value in the cluster of A. takesimense was found by Bayesian clustering analysis, suggesting a strong episode of genetic drift during colonization and speciation. In comparison with A. pseudosieboldianum, A. takesimense has slightly lower genetic diversity and possesses less than half the number of private and rare alleles. Consistent with predictions, weak geographical genetic structure within the island was found in A. takesimense. These results imply that anagenetic speciation leads to a different pattern of specific and genetic diversity than often seen with cladogenesis.
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REGULAR PAPER
Anagenetic speciation in Ullung Island, Korea: genetic diversity
and structure in the island endemic species, Acer takesimense
(Sapindaceae)
Koji Takayama Byung-Yun Sun Tod F. Stuessy
Received: 6 July 2012 / Accepted: 1 October 2012 / Published online: 23 October 2012
ÓThe Author(s) 2012. This article is published with open access at Springerlink.com
Abstract Anagenetic speciation is an important mode of
speciation in oceanic islands; one-fourth of the endemic
plants are estimated to have been derived via this process.
Few studies, however, have critically examined the genetic
consequences of anagenesis in comparison with cladogenesis
(involved with adaptive radiation). We hypothesize that
endemic species originating via anagenetic speciation in a
relatively uniform environment should accumulate genetic
variation with limited populational differentiation. We
undertook a population genetic analysis using nine nuclear
microsatellite loci of Acer takesimense, an anagenetically
derived species endemic to Ullung Island, Korea, and its
continental progenitor A. pseudosieboldianum on the Korean
Peninsula. Microsatellite data reveal a clear genetic distinc-
tion between the two species. A high Fvalue in the cluster of
A. takesimense was found by Bayesian clustering analysis,
suggesting a strong episode of genetic drift during coloniza-
tion and speciation. In comparison with A. pseudosieboldia-
num,A. takesimense has slightly lower genetic diversity and
possesses less than half the number of private and rare alleles.
Consistent with predictions, weak geographical genetic
structure within the island was found in A. takesimense. These
results imply that anagenetic speciation leads to a different
pattern of specific and genetic diversity than often seen with
cladogenesis.
Keywords Anagenetic speciation Cladogenesis
Endemic plants Korean Peninsula Oceanic island
Phyletic speciation
Introduction
Oceanic islands have long been recognized as fascinating
natural laboratories for the study of evolution (Bramwell
and Caujape
´-Castells 2011; Carlquist 1974; Darwin 1842;
Grant 1996; MacArthur and Wilson 1967; Wallace 1881;
Whittaker 1998). Due to being relatively small land mas-
ses, geographically isolated, with known geological ages,
and relatively simple biota with high levels of endemism,
oceanic islands provide great opportunities for investigat-
ing evolutionary processes of organisms, especially in
contrast to more complex continental situations.
The most commonly described evolutionary process in
oceanic islands has emphasized ‘‘cladogenesis’’ involved
with adaptive radiation. During cladogenesis, an initial
founder population divides into several lineages through
isolation and subsequent adaptation to markedly different
ecological zones, bringing about different morphological or
physiological traits (Carlquist 1974; Futuyma 1997; Rundell
and Price 2009; Schluter 2001), sometimes of a dramatic
nature as seen, for instance, in the silverswords (Asteraceae)
of the Hawaiian Islands (Baldwin 1997; Baldwin and Wessa
2000)orEchium (Boraginaceae) of the Canary Islands (Bo
¨hle
et al. 1996; Marrero-Go
´mez et al. 2000). Morphologically or
physiologically diverging populations accumulate some
genetic differences, but the more conspicuous pattern is
partitioning of the gene pool into restricted genetic lines
(Schluter 1996).
Another speciation process common in oceanic islands is
anagenetic speciation (also known as simple geographical or
K. Takayama (&)T. F. Stuessy
Department of Systematic and Evolutionary Botany,
Biodiversity Center, University of Vienna,
Rennweg 14, 1030 Vienna, Austria
e-mail: gen33takayama@gmail.com
B.-Y. Sun
Faculty of Biological Sciences, College of Natural Sciences,
Chonbuk National University, Chonju, South Korea
123
J Plant Res (2013) 126:323–333
DOI 10.1007/s10265-012-0529-z
phyletic speciation). During anagenetic speciation, an ini-
tial founder lineage simply transforms genetically and
morphologically through time without further specific dif-
ferentiation (Stuessy et al. 1990; Stuessy et al. 2006; Stu-
essy 2007; Whittaker et al. 2008). This speciation process
is important in plant evolution on oceanic islands, with
levels of endemic specific diversity explainable by this
process ranging from 7 to 88 %, with a mean for all islands
of 25 % world-wide (as estimated by floristic surveys;
Stuessy et al. 2006).
It has been hypothesized that the two major modes of
speciation in oceanic islands result not only in distinct
levels of species diversity but also in different levels of
genetic diversity within endemic species (Stuessy 2007).
With both cladogenetic and anagenetic speciation, the
founder populations to the island bring only a small portion
of the genetic variation originally contained in the usually
larger and more broadly distributed continental progenitors
(Frankham 1997). During cladogenesis, the depauperate
gene pool of the founding populations becomes partitioned
and channeled under intense selection into different habi-
tats, leading to noticeable morphological and genetic dif-
ferences among populations. These distinct populations are
worthy of being called different species, but each contains
a low level of genetic variation. During anagenesis, on the
other hand, the initial founder populations accumulate
genetic variation through time within a relatively uniform
environment without any splitting event. Over many gen-
erations, sufficient genetic and morphological divergence
accrues so that recognition of a new species is warranted.
Molecular studies so far completed have revealed higher or
only slightly lower levels of genetic variation in two
anagenetically derived species, Dystaenia takesimana
(Pfosser et al. 2005) and Acer okamotoanum (Takayama
et al. 2012) in Ullung Island, off the coast of Korea, in
comparison to their continental progenitors. The endemic
species also show no geographical partitioning of the
genetic variation within the island. More studies are nee-
ded, however, to synthesize more data and examine more
critically the genetic consequences of anagenetic speciation
in comparison with those from the classical cladogenetic
model.
Ullung Island is an ideal setting for investigating the
genetic consequences of anagenetic speciation because it
consists of only a single island, and it contains the highest
levels of anagenetic speciation so far recorded among
oceanic islands (Stuessy et al. 2006). Ullung Island is
located 137 km east of the Korean Peninsula, extending
from 37°270to 37°330N and 130°470to 130°560E; the total
area is 73 km
2
and the highest peak is 984 m. It is of
volcanic origin, with no known connections to the penin-
sula, and with a geological age of approximately 1.8 mil-
lion years (Kim 1985). The flora contains approximately
700 vascular plant species including 500 natives of which
37 angiosperms are endemic (Lee and Yang 1981). One of
the important characteristics of the endemics is that most of
them are single representatives of different genera that
appear to have diverged via simple anagenetic change from
continental progenitors (Sun and Stuessy 1998). The rela-
tionships between progenitors in continental areas and
endemic species in Ullung Island have been confirmed in
several genera by phylogenetic studies (Oh et al. 2010;
Pfosser et al. 2002,2005,2011; Yang and Pak 2006; Yang
et al. 2012), indicating that most of the progenitor species
are distributed in the Korean peninsula and/or Japanese
Archipelago.
Two endemic Acer (Sapindaceae) species, A. okamo-
toanum Nakai and A. takesimense Nakai, occur on Ullung
Island. Morphological and phylogenetic studies have
shown that these two endemics are not closely related to
each other but rather have had independent anagenetic
origins from different continental progenitors, A. mono
Maxim. and A. pseudosieboldianum Kom., respectively
(Ackerly and Donoghue 1998; Pfosser et al. 2002; Sun and
Stuessy 1998). Crawford (2010) listed these two species
pairs as good examples of progenitor-derivative speciation,
which would provide appropriate systems for studying
plant speciation. This present paper focuses on the genetic
consequences of anagenetic speciation in one of these
endemic Acer species, A. takesimense.
Acer takesimense is an endemic tree widely distributed
in Ullung Island (Yim et al. 1981). Its putative progenitor,
A. pseudosieboldianum, is found in the cool-temperate
deciduous forests of northeastern Asia, Manchuria, Ussuri
River, China, and Korea (van Gelderen et al. 1994). Nakai
(1918) stated that the former species is closely related to
the latter species, and van Gelderen et al. (1994) treated
A. takesimense as a subspecies of A. pseudosieboldianum.
The species relationships in section Palmata that contain
both species are still unclear. Although it is possible to
consider that A. takesimense might have derived from other
Acer species in section Palmata, recent molecular work
combined with chloroplast DNA, ITS and AFLP data
support that the most probable ancestor of A. takesimense
was A. pseudosieboldianum from the Korean Peninsula
(Pfosser et al. 2002). The AFLP studies also have indicated
that the two species are genetically distinguishable.
In this study we investigate genetic consequences of
anagenetic speciation of A. takesimense from A. pseudo-
sieboldianum by examining patterns of genetic diversity
and structure in populations using nuclear microsatellite
markers. We address three main questions: (1) Is there
clear genetic differentiation between the two species? (2)
How much genetic diversity exists within island popula-
tions of A. takesimense in comparison to continental pop-
ulations of A. pseudosieboldianum? (3) Is there any
324 J Plant Res (2013) 126:323–333
123
geographic structuring of genetic variation among popu-
lations of A. takesimense within the island?
Materials and methods
Plant material
We collected leaf samples from 130 individuals of Acer
takesimense from seven populations in Ullung Island, and
133 individuals of A. pseudosieboldianum from seven
populations in the Korean Peninsula (Table 1; Fig. 1). The
leaf samples were desiccated with silica gel in zip-lock
plastic bags until use in the laboratory. Voucher specimens
of these samples were deposited in JNU and WU.
DNA extraction and microsatellite genotyping
Total genomic DNA was extracted from dried leaves using
the DNeasy 96 Plant Kit (Qiagen, Hilden, Germany). We
selected ten microsatellite markers, which were isolated
from A. pseudosieboldianum according to the repeatability
and scoring convenience of the markers (Takayama et al.
2011). For PCR amplification, we applied the 50-tailed
primer method (Boutin-Ganache et al. 2001) to label
amplified fragments for detection in the capillary sequen-
cer, which was done in the same way as in the previous
study (Takayama et al. 2011). Four combinations of mul-
tiplex PCR amplification were performed using a slightly
modified protocol of the Qiagen Multiplex PCR Kit (Qia-
gen, Hilden, Germany). The multiplex combinations were
as follows: A7DU1, A82LK, A88LE with 6-FAM,
BDG7D, A08Z1, AY8V2 with VIC, APT6F, ASQGF with
NED, AVM1G, AW0F6 with PET. A multiplex PCR
amplification was performed in a final volume of 3 lL with
0.2 lM of each reverse primer, 0.04 lM of each forward
Table 1 Populations of Acer takesimense from Ullung Island and A. pseudosieboldianum from the Korean Peninsula analyzed for genetic
diversity with nuclear microsatellites
Taxon Population Locality Altitude (m) Voucher N
POP
N
Acer takesimense 1 Ullung Island, Taeha-ri-Jung-ri 120 TS17551 ca. 50 20
2 Ullung Island, Namseo-ri 280 TS17589 [100 18
3 Ullung Island, Namyang-ri 120 TS17603 [100 20
4 Ullung Island, Chusan to Nari 220 SUN4117 [100 18
5 Ullung Island, Seongin Mt. 900 SUN4145 ca. 30 16
6 Ullung Island, Sadong-ri 300 TS17617 [100 20
7 Ullung Island, Do-dong National Forest 140 SUN4006 ca. 50 18
Total 130
A. pseudosieboldianum 8 Prov. Chonbuk, Moak Mt. 405 TS16007 ca. 100 17
9 Prov. Chonbuk, Chiri Mt. 1,100 TS16020 [100 20
10 Prov. Chonbuk, Juksang Mt. 850 TS16024 ca. 100 20
11 Prov. Chonbuk, Juksang Mt. 980 TS16030 [100 20
12 Prov. Kyungnam, Palgong Mt. 740 TS17637 [1,000 17
13 Prov. Kyungbuk, Irwol Mt. 820 TS17632 ca. 100 20
14 Prov. Kangwon, Odae Mt. 930 TS16072 [1,000 19
Total 133
TS Tod F. Stuessy, SUN Byung-Yun Sun, N
POP
the estimated number of individuals in population by field observation, Nthe total number of
analyzed samples
CHINA
KOREA
13
11
14
9JAPAN
100 km
Ullung Island 1 km
984 m
2
3
1
67
4
5
812
10
Fig. 1 Location of Ullung Island and populations of Acer takesi-
mense (17) and A. pseudosieboldianum (814) analyzed in this study
J Plant Res (2013) 126:323–333 325
123
primer, and 0.4–0.6 lM of fluorescent dye-labeled primer
(0.6 lM for 6-FAM and VIC, 0.4 lM for NED and PET).
Touchdown thermal cycling programs were used as fol-
lows: initial denaturation at 95 °C for 15 min, followed by
25 cycles of denaturation at 95 °C for 30 s, annealing at
63 °C for 90 s (decreased 0.5 °C per cycle), and extension
at 72 °C for 60 s; and by 20 cycles of denaturation at 95 °C
for 30 s, annealing at 53 °C for 90 s, and extension at
72 °C for 60 s; a final extension step was performed at
60 °C for 30 min. For genotyping, 1.0 lL of 25–40 times
diluted PCR product mix was mixed with 10 lL of HiDi
formamide (Applied Biosystems, Warrington, UK) and
0.1 lL of GeneScan600 LIZ size standard (Applied Bio-
systems) and run on an automated sequencer (ABI 3130xl).
Scoring of fluorescence peaks was performed using
GeneMarker (SoftGenetics LLC).
Data analysis
The statistical significance of deviation from Hardy–
Weinberg equilibrium (HWE), and linkage disequilibrium
between loci in each population, were conducted with the
Markov chain method (10,000 dememorisation steps, 1,000
batches, 500 iterations per batch) using GENEPOP 4.0
(Raymond and Rousset 1995). Null allele frequency was
calculated following Brookfield (1996) using Micro-
Checker 2.2.3 (van Oosterhout et al. 2004).
Genetic diversity, in terms of allelic richness (A
R
),
observed proportion of heterozygotes (H
O
), expected pro-
portion of heterozygotes (H
E
), and total number of alleles,
was evaluated for each species and population using
FSTAT 2.9.3.2 (Goudet 1995). Allelic richness was stan-
dardized for 16 individuals based on minimum sample size
of populations using the rarefaction method (Hurlbert
1971). The inbreeding coefficient (F
IS
) was calculated in
the program. We also counted the number of private alleles
(unique to one group), and rare alleles (defined as alleles
with a frequency \10 % in the total group) per individuals
in each group. Three categories were constructed for these
estimates: (i) each species is treated as a group; (ii) the
seven populations of A. takesimense as a group and the
seven populations of A. pseudosieboldianum as seven dif-
ferent groups; and (iii) each population in both species as a
group.
Genetic variation between taxa, among and within
populations was evaluated by AMOVA using ARLEQUIN
3.5.1.2 (Excoffier et al. 2005). The AMOVA analyses were
done by three categories: (a) all samples from the two
species, (b) A. takesimense, and (c) A. pseudosieboldianum.
Statistical significance of the variance components was
tested by calculating their probabilities based on 1,023
permutations. Genetic distance among populations was
calculated by D
A
genetic distance (Nei et al. 1983), and a
neighbour-joining tree was reconstructed based on the
distance using Populations 1.2.30 (Langella 1999). Statis-
tical significance of the best topology was estimated with
1,000 bootstrap replicates. The Bayesian clustering method
(Falush et al. 2003; Pritchard et al. 2000) implemented in
STRUCTURE 2.3.3 (Falush et al. 2007; Hubisz et al. 2009;
Pritchard et al. 2000) was used for evaluation of genetic
structure as well. We conducted STRUCTURE analyses in
the three categories, (a) all samples from the two species,
(b) A. takesimense, and (c) A. pseudosieboldianum.We
used an admixture model with correlated allele frequency
(after this F-model; Falush et al. 2003) to assign individ-
uals into Kclusters (populations). 20,000 ‘‘burn-in’’ steps
of Chain Monte Carlo searches, followed by 10,000 itera-
tions, and 20 replicate runs were performed at each Kfrom
1 to 10 under the F-model. We adopted the hierarchical
approach for the STRUCTURE analysis employing DKto
determine the uppermost level of structure (Evanno et al.
2005). In the F-model, Kclusters are assumed to have
diverged from a common ancestral population simulta-
neously, and the clusters may have experienced different
degrees of genetic drift since the divergence event (Falush
et al. 2003). Therefore, using the Fmodel we can also
estimate the amount of genetic drift in each of the different
populations, estimated by Fvalues.
To assess a recent population bottleneck, a graphical test
to see whether the allele frequency distribution is approx-
imately L-shaped or not (Luikart et al. 1998), and a test for
the presence of an excess of observed heterozygosity by
using the Wilcoxon signed rank test to evaluate departure
from 1:1 deficiency/excess (Cornuet and Luikart 1996;
Luikart et al. 1998) were conducted using BOTTLENECK
1.2.02 (Piry et al. 1999). In the latter test, heterozygosity
excess was tested under the three mutation models, the
infinite allele model (IAM; Kimura and Crow 1964), step-
wise mutation model (SMM; Ota and Kimura 1973), and
the two-phase model (TPM; Di Rienzo et al. 1994) with
1,000 simulation iterations. We set 90 % single-step, 10 %
multiple-step mutations with a variance among multiple
steps of 12 in the TPM.
Results
Genetic data analysis
Ten microsatellite loci were used to genotype 263 indi-
viduals from 14 populations in Acer takesimense and
A. pseudosieboldianum (Table 1). All ten loci were
amplified in all samples, but locus BDG7D showed com-
plex patterns for genotyping in some samples. Hence, we
used nine loci (excluding BDG7D) for further population
analyses. The range of number of alleles in the nine loci
326 J Plant Res (2013) 126:323–333
123
was from five (A88LE and AVM1G) to 13 (A08Z1), and
the mean was 8.6 in the two species. An exact test for HWE
across populations and loci showed that 24 of 126 deviated
from the HWE (P\0.05) after Bonferroni correction. All
the deviating cases were related to the positive F
IS
, indi-
cating HWE deviation due to heterozygote deficit. There-
fore, we estimated the frequency of null alleles across
populations and loci using Micro-Checker, resulting in an
average frequency from 0.228 (BDG7D) to 0.036 (A88LE),
and 0.135 in all of the nine loci. For loci that showed
significant heterozygote deficit, we generated corrected
genotypic frequencies for putative null alleles using Micro-
Checker. We performed population genetic analyses
(AMOVA, pairwise genetic distance and bottleneck anal-
yses) using both the corrected and non-corrected data sets.
Significant linkage disequilibrium was not found between
any pairwise loci in all populations (P\0.05) after Bon-
ferroni correction.
Genetic diversity
Genetic diversity parameters estimated by the nine
microsatellite loci are shown in Table 2. Populations of
A. takesimense generally showed lower levels of genetic
diversity than populations of A. pseudosieboldianum in
allelic richness, expected heterozygosity, and total number
of alleles according to the Mann–Whitney Utest
(P\0.05). F
IS
values were significantly positive in 11
populations, four of A. takesimense and all of A. pseudo-
sieboldianum (P\0.05) after Bonferroni correction. At
the specific level, A. takesimense possessed half the num-
ber of private and rare alleles of A. pseudosieboldianum.If
A. takesimense is treated as one population, then this
population shows a large number of private and rare alleles
in comparison with each of the seven populations of
A. pseudosieboldianum.
Genetic structure
Genetic variation among and within populations was
examined by AMOVA at different hierarchical levels with
three categories using the corrected and non-corrected data
sets (Table 3). The two data sets showed similar patterns;
in all three categories, most of the variation was found
among individuals within populations (79.0–96.2 %), and
little genetic variation among populations (8.0 and 3.8 %)
in the data sets of A. takesimense.
A neighbour-joining tree of the two species was con-
structed based on D
A
genetic distance (Fig. 2). The cor-
rected and non-corrected data sets show much the same
results; thus we present syntheses from the non-corrected
data only. The populations of each species make two dis-
tinct clusters with 55 % bootstrap values. Genetic distances
among populations of the same species were lower in
A. takesimense (mean 0.105, SD 0.018) than in A. pseudo-
sieboldianum (mean 0.152, SD 0.038) according to the
Mann–Whitney Utest (P\0.05). The mean genetic dis-
tance between populations of the two species was 0.260
(SD 0.036).
The Bayesian clustering analyses implemented in
STRUCTURE are shown in Figs. 3and 4. The uppermost
level of structure was at K=2 based on DKvalue in two
categories, (a) all samples from the two species, and
(c) A. pseudosieboldianum (Fig. 3a, c). On the other hand,
no obvious signal for the uppermost level of structure was
detected in the category (b) A. takesimense (Fig. 3b). In all
samples at K=2, the two clusters correlated well with the
two different species, because cluster I comprised 96 % of
the genotypes in A. takesimense and cluster II comprised
94 % of the genotypes in A. pseudosieboldianum (Fig. 4a).
The Fvalue of cluster I (mean F=0.194, SD 0.003) was
higher than that of cluster II (mean F=0.066, SD 0.002).
In the separate analysis performed for each category, no
clear populational subdivisions were found in each species
(Fig. 4b, c).
Population bottleneck
We tested bottleneck effects using the corrected and non-
corrected data sets. They showed much the same results,
and therefore again we dealt with results from the non-
corrected data only. The mode-shift test detected the evi-
dence of a bottleneck in Population 9 of A. pseudosiebol-
dianum (Table 4). Excess heterozygosity was detected in
Population 5 of A. takesimense and Populations 9 and 14
under IAM (P\0.05) after Bonferroni correction. In
Population 14 excess heterozygosity was detected under
TPM as well. As a result, Populations 9 and 14 of
A. pseudosieboldianum detected recent reduction of pop-
ulation size in multiple analyses (or mutation models).
Discussion
Genetic differentiation between the two species
The genetic difference between the endemic Ullung Island
species Acer takesimense and its progenitor A. pseudosie-
boldianum was clear in both the STRUCTURE analyses
and neighbour joining tree. In the STRUCTURE analyses,
most individuals were assigned to each of the species
clusters, but there were a few individuals that had inter-
mediate genetic components between the two species
(Fig. 4a). Although this might be explained by interspecific
gene flow, a more plausible explanation might be limited
J Plant Res (2013) 126:323–333 327
123
statistical power or size homoplasy of microsatellites. Due
to the isolated geographical distribution of the two species,
restricted to the oceanic island or continental region, the
opportunity for interspecific gene flow would be rare.
Previous AFLP analyses showed consistent patterns for
clear genetic differences between the two species and trnL
Fsequences of cpDNA also had one nucleotide substitution
between the two species (Pfosser et al. 2002). No
Table 2 Genetic diversity parameters estimated by nine microsatellite loci in Acer takesimense and A. pseudosieboldianum
Taxon Population A
R
H
O
H
E
T
A
F
IS
N
P
N
R
i ii iii i ii iii
Acer takesimense 0.28 0.28 0.36 0.26
1 3.67 0.43 0.50 34 0.13 0.00 0.13
2 4.23 0.33 0.57 39 0.42 0.00 0.06
3 3.59 0.41 0.48 34 0.15 0.00 0.00
4 3.83 0.30 0.55 35 0.47 0.04 0.11
5 3.89 0.34 0.58 35 0.41 0.13 0.00
6 3.85 0.47 0.51 36 0.08 0.00 0.03
7 3.71 0.37 0.51 34 0.27 0.00 0.08
Mean 3.82 0.38 0.53 35.3 0.28
A. pseudosieboldianum 0.69 0.85
8 4.71 0.32 0.56 43 0.43 0.00 0.00 0.09 0.06
9 4.91 0.46 0.67 45 0.32 0.00 0.00 0.05 0.05
10 4.80 0.37 0.62 45 0.41 0.18 0.18 0.20 0.18
11 4.02 0.41 0.56 37 0.28 0.00 0.00 0.05 0.00
12 5.25 0.41 0.60 48 0.32 0.18 0.18 0.29 0.29
13 3.79 0.42 0.53 35 0.21 0.03 0.03 0.03 0.03
14 4.73 0.43 0.68 43 0.37 0.05 0.05 0.11 0.05
Mean 4.60 0.40 0.61 42.3 0.33
A
R
, allelic richness; H
O
, the observed proportion of heterozygotes, H
E
, the expected proportion of heterozygotes; T
A
, total number of alleles in
nine microsatellite loci; F
IS
, the inbreeding coefficient (bold indicates departure significantly from zero); N
P
, the number of private alleles per
individuals in each group; N
R
, the number of rare alleles per individuals in each group (defined as alleles with a frequency \10 % in the total
group); The private and rare alleles were counted by (i) each species are treated as a group, (ii) the seven populations of A. takesimense as a group
and the seven populations of A. pseudosieboldianum as seven different groups, (iii) each population in both species as a group
Table 3 Summary of analyses of molecular variance (AMOVA), showing degrees of freedom (df), sum of squares (SS), variance components,
and the total variance contributed by each component (%) and its associated significance (n=1,023 permutations)
Taxon Source of
variation
df Non-corrected data set Corrected data set
SS Variance
components
Total
variance (%)
SS Variance
components
Total
variance (%)
(a) Acer takesimense and
A. pseudosieboldianum
Between taxa 1 108.1 0.366 11.7 35.5 0.128 16.6
Among
populations
12 142.3 0.249 7.9 22.6 0.034 4.4
Within
populations
512 1,293.2 2.526 80.4 311.3 0.608 79.0
(b) A. takesimense Among
populations
6 59.2 0.203 8.0 8.5 0.023 3.8
Within
populations
253 593.8 2.347 92.0 145.2 0.574 96.2
(c) A. pseudosieboldianum Among
populations
6 83.1 0.294 9.8 14.1 0.045 6.5
Within
populations
259 699.4 2.700 90.2 166.1 0.641 93.5
Results using both non-corrected and corrected data sets are shown
328 J Plant Res (2013) 126:323–333
123
difference has been found in ITS sequences, however,
between the two (Cho et al. 1996).
The two species differ in morphological features, with
A. takesimense having deeply divided smaller leaves with
usually 13 or more lobes (Sun and Stuessy 1998), and
A. pseudosieboldianum having larger leaves that are much
less divided (Park et al. 1993,1994; Sun and Stuessy
1998). Acer takesimense is also typically more strongly
branched than A. pseudosieboldianum (van Gelderen et al.
1994). Despite these differences, their taxonomic status has
been re-evaluated by Chang (1994), concluding that the
two species should be merged into one. Acknowledging
that the two taxa are closely related, it is our view that the
results support specific recognition based on the following
arguments: (1) each represents a single cluster, with the
average of population differentiation between the two
(D
A
=0.260) being much higher than that among popu-
lations of A. pseudosieboldianum (D
A
=0.152); (2) the
populations of A. takesimense accumulate some private and
rare alleles, suggesting genetic uniqueness; and (3) the two
populational systems are completely geographically
isolated.
Genetic diversity within species and populations
Genetic diversity in terms of allelic richness, expected
heterozygosity, and total number of alleles is generally
lower in the populations of Acer takesimense in compari-
son with those of A. pseudosieboldianum. A smaller
number of alleles in populations of A. takesimense was also
revealed by AFLP analysis (Pfosser et al. 2002). A
reduction of genetic diversity in island populations has
been documented in many instances (Frankham 1997). For
endemic island plants, low levels of genetic diversity have
been commonly observed in Hawaiian, Galapagos, Juan
Fernandez and Bonin Islands (Crawford et al. 2001,2006;
DeJoode and Wendel 1992; Ito et al. 1998). A number of
0.02
9
12
14
11
8
10
13
6
2
3
1
4
5
7
Acer pseudosieboldianum
(Korean peninsula)
Acer takesimense
(Ullung Island)
55
53
Fig. 2 Neighbour-joining tree of the 14 populations of Acer takesi-
mense and A. pseudosieboldianum based on D
A
distance (Nei et al.
1983). Population numbers correspond to Table 1and Fig. 1.
Bootstrap probabilities [50 % are shown above the branches
-5000
-5500
-6000
-6500
-7000
1 2 3 4 5 6 7 8 9 10
ln Pr(X|K)
K
a) Acer takesimense and A. pseudosieboldianum
K
250
200
150
100
50
0
-2000
-2500
-3000
-3500
-4000
1 2 3 4 5 6 7 8 9 10
ln Pr(X|K)
K
b) Acer takesimense
K
50
40
30
20
10
0
-2500
-3000
-3500
-4000
-4500
1 2 3 4 5 6 7 8 9 10
ln Pr(X|K)
K
c) Acer pseudosieboldianum
K
50
40
30
20
10
0
Fig. 3 Results of Bayesian clustering (STRUCTURE, Pritchard et al.
2000)ofAcer takesimense and A. pseudosieboldianum.aAll the
samples of Acer takesimense and A. pseudosieboldianum,bA.
takesimense, and cA. pseudosieboldianum. The solid square plots
give the mean ln Pr(X|K) and ±SD over 20 runs for each value of
K. The open circle plots give DKof Evanno et al. (2005) showing a
peak at the uppermost level of structure at the true value of K
J Plant Res (2013) 126:323–333 329
123
factors may be responsible for explaining the low levels of
genetic diversity seen in endemic island populations, such
as a bottleneck effect during immigration if it were of
relatively recent origin, small population sizes, loss of
populations and genes through island subsidence and ero-
sion, high levels of inbreeding, and cladogenetic specia-
tion. Another possibility is ascertainment bias of the
microsatellite markers. The microsatellite markers used in
this study were isolated from A. pseudosieboldianum
(Takayama et al. 2011). The source species used in isola-
tion of microsatellite markers is sometimes observed to be
more polymorphic than the other species (Ellegren et al.
1997; Forbes et al. 1995).
In Ullung Island, another endemic Acer species, Acer
okamotoanum, also showed slightly lower levels of genetic
diversity in comparison with its progenitor species in the
Korean Peninsula and Japan (Takayama et al. 2012). In
both endemic species of Acer, recent population size
reductions were not clearly detected by statistical tests for
bottlenecks based on the allelic distribution, but strong
episodes of genetic drift during colonization and speciation
on the island were detected, because the Fvalue in
STRUCTURE inferred for these island species was quite
high. Estimated population sizes of these island endemics
were generally smaller than those of the continental pro-
genitors. Reasons for the slightly lower levels of genetic
diversity in the two endemic Acer species in Ullung Island,
therefore, might be due to a combination of bottleneck
effects resulting from immigration, young island age
(1.8 million years, Kim 1985), and small population sizes.
A rather different genetic pattern has been documented
in Dystaenia takesimana (Apiaceae), another endemic
Acer takesimense A. pseudosieboldianum
K = 2
1 2 3 4 5 6 7 8 9 10 11 12 13 14
K = 2
K = 3
K = 4
K = 5
K = 2
K = 3
K = 4
K = 5
1 2 3 4 5 6 7 8 9 10 11 12 13 14
a) Acer takesimense and A. pseudosieboldianum
b) Acer takesimense c) Acer pseudosieboldianum
Fig. 4 Results of Bayesian clustering (STRUCTURE, Pritchard et al.
2000)ofAcer takesimense and A. pseudosieboldianum.K=2is
shown in aall the samples of Acer takesimense and A. pseudosie-
boldianum, and K=2, 3, 4 and 5 are shown in bA. takesimense, and
cA. pseudosieboldianum. Each individual is represented by a single
vertical line broken into Kcolored segment, with lengths proportional
to each of the Kinferred clusters. Population numbers below graph
correspond to Table 1and Fig. 1
Table 4 Summary of the parameters and results for BOTTLENECK
analyses using non-corrected data sets
Taxon Population BOTTLENECK
Mode
shift
IAM TPM SMM
Acer takesimense 1 NS 0.150 0.500 0.787
2 NS 0.102 0.715 0.820
3 NS 0.326 0.850 0.875
4 NS 0.020 0.527 0.629
5NS0.001 0.455 0.545
6 NS 0.082 0.410 0.674
7 NS 0.500 0.590 0.715
A. pseudosieboldianum 8 NS 0.367 0.936 0.993
9 Shifted
mode
0.001 0.082 0.285
10 NS 0.064 0.545 0.787
11 NS 0.082 0.367 0.455
12 NS 0.213 0.787 0.936
13 NS 0.019 0.285 0.590
14 NS 0.001 0.002 0.007
NS no significance (P\0.05), bold significant (P\0.05) after Bon-
ferroni correction
330 J Plant Res (2013) 126:323–333
123
species in Ullung Island, which showed a slightly higher
level of genetic diversity of AFLPs than its continental
progenitor D. ibukiensis in the Japanese archipelago
(Pfosser et al. 2005). Pfosser et al. (2005) concluded that
D. takesimana may have regained genetic diversity during
or after speciation along with increasing sizes of popula-
tions, because the estimated sizes of populations analysed
were similar or larger than those of D. ibukiensis in the
Japanese archipelago. The equally large sizes of the island
populations of D. takesimana could be an important factor
for explaining their high level of genetic diversity. The
differences of genetic patterns between endemic species of
Acer and Dystaenia may also relate to their distinct
reproductive features. Acer takesimense and A. okamotoa-
num are trees that take several years for flowering (most
Acer species first flower at 5–20 years, van Gelderen et al.
1994), but Dystaenia takesimana is a perennial herb that
flowers annually. In addition, Acer species often are self-
compatible (Gleiser and Verdu
´2005; Gleiser et al. 2008;
Kikuchi et al. 2009), but D. takesimana shows character-
istics of xenogamous plants based on pollen-ovule ratios
and AFLP analysis (Pfosser et al. 2005). The positive F
IS
found in some populations of A. takesimense and
A. pseudosieboldianum also support possible inbreeding in
these species.
Geographical genetic structure within Ullung Island
and the Korean Peninsula
During anagenetic speciation, an initial founder lineage
simply changes through time without further specific dif-
ferentiation (Stuessy 2007; Stuessy et al. 2006). It is rea-
sonable to assume, therefore, that anagenetically derived
species could accumulate genetic variation through time
without any eco-geographical partitioning of this variation.
Acer takesimense possesses half the number of private and
rare alleles of A. pseudosieboldianum, but considering the
difference of total distribution of the two species (small
oceanic island vs. Eastern Asia), the number of alleles in
A. takesimense is relatively high. Over generations, genetic
variation in A. takesimense may indeed have accumulated
through mutation and recombination followed by changes
in allelic frequencies through drift and/or selection. The
seven populations of A. takesimense analysed were col-
lected broadly at different elevations (120–900 m) on
Ullung Island, but only weak geographical genetic struc-
ture was detected in STRUCTURE analysis. The level of
genetic variation among populations was also quite low as
documented with AMOVA. Such a weak geographical
genetic structure within Ullung Island has also been
reported in the anagenetically derived species, A. okamo-
toanum and Dystaenia takesimana (Pfosser et al. 2002;
Takayama et al. 2012). These results are consistent,
therefore, with our initial hypothesis on the genetic con-
sequences of anagenetically derived species. It is also clear
that not all species originating by this mode will have
responded genetically in exactly the same way, depending
upon their history and biology. One might also wish to
argue that the results have been caused by low resolution of
molecular markers. We consider that the markers used in
this study are high enough to detect polymorphisms among
individuals, because the average expected heterozygote of
nine nuclear microsatellite markers was 0.53 and the
probability of identity of multilocus genotypes using the
nine markers was extremely low (0.0013 %). The weak
geographical genetic structure, therefore, suggests that
genetic exchange among populations of A. takesimense
may be occurring frequently throughout Ullung Island.
Acer pseudosieboldianum from continental regions, on
the other hand, shows a noticeable genetic differentiation
in STRUCTURE analysis, because a clear signal was found
at K=2 based on DKvalue. The stronger genetic differ-
entiation found in A. pseudosieboldianum might be
explained by the larger number of individuals and its
broader total distribution. We used seven populations of
A. pseudosieboldianum widely distributed from the south-
ern part of the Korean Peninsula. Since the biological
features such as generation time, habitat preference, and
mode of seed and pollen dispersal would be similar in the
two species, wider distribution of A. pseudosieboldianum
easily allows the differentiation of populations through
fixation of alternative alleles, local adaptation, and genetic
drift involved with demographic changes.
In the structure analysis, the compositions of clusters
between Populations 9 and 13 were quite different from
each other, but there were also multiple clusters mixed
together within the other populations. It is difficult, there-
fore, to see any trend in geographic structure due to genetic
variation. This complex geographic structure could be the
result of their ability for long distance dispersal of seeds
(via the well-known winged samara fruits) and subsequent
genetic exchange, and also changes in population sizes and
distribution throughout the Quaternary glacial period.
Macrofossils and pollen data from the Korean Peninsula
indicate that temperate deciduous broad-leaved forests
broadly declined between ca. 20,700 and 11,500 years BP,
and increased after ca. 11,500 years BP in response to
dramatic climate change during the late Pleistocene and
early Holocene (Chung et al. 2010; Kong 2000). The genus
Acer is a one of the principal components of the deciduous
broad-leaved forests in this region, and they would have
undergone dynamic historical changes in population size
and distribution in the Korean Peninsula. Although our
molecular samples at the populational level were not col-
lected for the purpose of completing a detailed phylogeo-
graphic analysis of the Korean Peninsula, severe recent
J Plant Res (2013) 126:323–333 331
123
(i.e., maximum 4Ne generations ago) bottleneck signals
were detected in the two populations (9 and 14) of
A. pseudosieboldianum, which could support the concept of
recent dramatic distributional changes within this species.
Further study will be required to provide a foundation for
phylogeographic evolutionary insight into progenitor spe-
cies in the Peninsula.
This study adds important new data on the genetic
consequences of anagenetic speciation in oceanic islands.
In cladogenesis, several lines of speciation occur from
founder populations by selection within markedly different
ecological zones that results in different morphological and
physiological traits, and also in genetic portioning of the
founder populations. In anagenetic speciation, as shown in
this study, after a founder event the initial population
expands its distribution range across the entire island, and
in the process accumulates genetic variation through
mutation and recombination. No eco-geographic parti-
tioning of genetic variation results. Over many generations,
island populations simply diverge in genetic and morpho-
logical composition from progenitor populations, and a
new species arises.
Acknowledgments This work was supported by: a Japan Society
for the Promotion of Science (JSPS) Postdoctoral Fellowship for
Research Abroad to KT; the Austrian National Science Foundation
(FWF), grant number P21723-B16 to TS for laboratory work; and the
Korea Environmental Industry & Technology Institute (KEITI), Eco-
star project, grant number 052-08-071 to B-Y S for field collections.
Open Access This article is distributed under the terms of the
Creative Commons Attribution License which permits any use, dis-
tribution, and reproduction in any medium, provided the original
author(s) and the source are credited.
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... In anagenetic speciation, a founder population arriving on an oceanic island proliferates in a favorable uniform environment and spreads over the island, gradually accumulates genetic variation through mutation and recombination in isolated environments, and eventually diverges from continental source populations in genetic composition and morphological characteristics (Stuessy et al., 2006(Stuessy et al., , 2014Stuessy, 2007;Takayama et al., 2015). Unlike adaptive radiation, the investigation of anagenetic speciation has been limited to a few geographical regions, primarily to the Juan Fernández Islands in the Pacific Ocean (López-Sepúlveda et al., 2013Takayama et al., 2015) and Ulleung Island in East Asia (Pfosser et al., 2005;Takayama et al., 2012Takayama et al., , 2013. The expected genetic outcomes of speciation via cladogenesis or anagenesis are different. ...
... Recently, three endemic plants, Rubus takesimensis Nakai (Yang et al., 2019), Campanula takesimana Nakai (Cheong et al., 2020), and Phedimus takesimensis (Nakai) 't Hart (Seo et al., 2020) have been investigated based on maternally inherited plastid DNA sequences, whereas Dystaenia takesimana (Nakai) Kitag. (Pfosser et al., 2005), Acer okamotoanum Nakai (Pfosser et al., 2002;Takayama et al., 2012), and Acer takesimense Nakai (Pfosser et al., 2002;Takayama et al., 2013) have been previously investigated based on nuclear microsatellite and amplified fragment length polymorphism markers. Their respective genetic patterns in geographic source areas and genetic variations appear to be complex. ...
... Their respective genetic patterns in geographic source areas and genetic variations appear to be complex. It has been demonstrated that D. takesimana, A. takesimense, and A. okamotoanum show higher or slightly lower levels of genetic variation than their continental progenitor species (Pfosser et al., 2002(Pfosser et al., , 2005Takayama et al., 2012Takayama et al., , 2013. However, the populations of R. takesimensis on Ulleung Island show significantly lower genetic diversity than its continental progenitor, R. crataegifolius, without geographical population structuring on the island (Yang et al., 2019). ...
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Of the two major speciation modes of endemic plants on oceanic islands, cladogenesis and anagenesis, the latter has been recently emphasized as an effective mechanism for increasing plant diversity in isolated, ecologically homogeneous insular settings. As the only flowering cherry occurring on Ulleung Island in the East Sea (concurrently known as Sea of Japan), Prunus takesimensis Nakai has been presumed to be derived through anagenetic speciation on the island. Based on morphological similarities, P. sargentii Rehder distributed in adjacent continental areas and islands has been suggested as a purported continental progenitor. However, the overall genetic complexity and resultant non-monophyly of closely related flowering cherries have hindered the determination of their phylogenetic relationships as well as the establishment of concrete continental progenitors and insular derivative relationships. Based on extensive sampling of wild flowering cherries, including P. takesimensis and P. sargentii from Ulleung Island and its adjacent areas, the current study revealed the origin and evolution of P. takesimensis using multiple molecular markers. The results of phylogenetic reconstruction and population genetic structure analyses based on single nucleotide polymorphisms detected by multiplexed inter-simple sequence repeat genotyping by sequencing (MIG-seq) and complementary cpDNA haplotypes provided evidence for (1) the monophyly of P. takesimensis ; (2) clear genetic differentiation between P. takesimensis (insular derivative) and P. sargentii (continental progenitor); (3) uncertain geographic origin of P. takesimensis , but highly likely via single colonization from the source population of P. sargentii in the Korean Peninsula; (4) no significant reduction in genetic diversity in anagenetically derived insular species, i.e., P. takesimensis , compared to its continental progenitor P. sargentii ; (5) no strong population genetic structuring or geographical patterns in the insular derivative species; and (6) MIG-seq method as an effective tool to elucidate the complex evolutionary history of plant groups.
... In addition, both nuclear (ITS; 95% BS) and chloroplast (four noncoding [60,61]) and Scrophularia takesimensis (Scrophulariaceae; [62]). However, the single origin of P. takesimensis is in line with other anagenetically derived endemics, such as Dystaenia takesimana (Apiaceae; [63]), Hepatica maxima (Ranunculaceae; [64]), Acer okamotoanum (Sapindaceae; [65]), A. takesimense (Sapindaceae; [66]), Fagus multinervus (Fagaceae; [67]), and Campanula takesimana (Campanulaceae; [68]). Therefore, despite the geographical proximity of Ulleung Island to possible source areas, a single origin for anagenetically originated endemics is the norm, with few exceptions. ...
... These results, however, should be interpreted cautiously given the uneven sampling of progenitor and derivative species pairs. Nevertheless, these results are consistent with previously studied taxa, such as Rubus takesimensis [61], Acer takesimense and A. okamotoanum [65,66], and Dystaenia takesimana [63]. ...
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Phedimus takesimensis (Ulleungdo flat-leaved stonecrop) is endemic to Ulleung and Dokdo Islands off the east coast of the Korean Peninsula. It was suggested that P. takesimensis originated via anagenetic speciation from the continental progenitor species P. kamtchaticus or P. aizoon. However, little is known of the phylogenetic relationships and population genetic structure among species of Phedimus in the Korean Peninsula and Ulleung/Dokdo Islands. We inferred the phylogenetic relationships among congeneric species in Korea based on nuclear ribosomal DNA internal transcribed spacer and chloroplast noncoding regions. We also sampled extensively for P. takesimensis on Ulleung Island and the continental species, P. kamtschaticus and P. aizoon, to assess the genetic consequences of anagenetic speciation. We found (1) the monophyly of P. takesimensis, (2) no apparent reduction in genetic diversity in anagenetically derived P. takesimensis compared to the continental progenitor species, (3) apparent population genetic structuring of P. takesimensis, and (4) two separate colonization events for the origin of the Dokdo Island population. This study contributes to our understanding of the genetic consequences of anagenetic speciation on Ulleung Island.
... In addition, it has been reported that overall 22% of all endemic plants of oceanic islands are derived from anagenetic speciation (Stuessy et al. 2006). However, considering its importance, few studies shed light on the origin of endemic species and genetic patterns resulting from anagenesis (López-Sepúlveda et al. 2013;Pfosser et al. 2006;Takayama et al. 2012Takayama et al. , 2013Takayama et al. , 2015. ...
... Although it was recently confirmed that some of the endemic species originated via hybridization (Gil and Kim 2016;Shin et al. 2014), the predominant mode of generating the diversity of endemic plant lineages on Ulleung Island was considered anagenetic speciation. Several studies have confirmed the origin of endemic vascular plant species via anagenesis and have addressed the genetic consequences of anagenetic speciation (e.g., Pfosser et al. 2002Pfosser et al. , 2006Pfosser et al. , 2011Takayama et al. 2012Takayama et al. , 2013. ...
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Scrophularia takesimensis is a critically endangered endemic species of Ulleung Island, Korea. A previous molecular phylogenetic study based on nuclear ribosomal DNA (nrDNA) internal transcribed spacer (ITS) sequences with very limited sampling suggested that it is most closely related to the clade comprising S. alata and S. grayanoides. To determine the origin of S. takesimensis, we sampled a total of 171 accessions including S. takesimensis (9 populations and 63 individuals) and two closely related species, S. alata (11 populations and 68 individuals) and S. grayanoides (5 populations and 40 individuals) from eastern Asia and sequenced ITS and two chloroplast DNA (cpDNA) non-coding regions. Previously sequenced representative species of Scrophularia (109 taxa for ITS and 80 taxa for cpDNA) were combined with our data set and analyzed. While the global scale ITS phylogenetic tree suggests monophyly for each of the three eastern Asian species, S. takesimensis appears to be more closely related (albeit weakly) to a clade containing eastern North American/Caribbean species than to either S. alata or S. grayanoides. By contrast, the global scale cpDNA phylogenetic tree demonstrates that the eastern North America/Caribbean clade is sister to a clade comprising the three eastern Asian species. In addition, the monophyletic S. takesimensis is deeply embedded within paraphyletic S. alata, sharing its most recent common ancestor with populations from Japan/Sakhalin. Two divergent, geographically structured cp haplotype groups within S. takesimensis suggest at least two independent introductions from different source areas. A new and accurate chromosome number of S. takesimensis (2n = 94) is reported and some conservation strategies are discussed.
... As Dokdo is composed of oceanic islands that have never been connected to the mainland, its isolation has provided unique conditions for the development of vegetation, making it highly valued for its biogeographic and evolutionary diversity (Sun et al 1996;Hyun and Kwon 2006). The oceanic islands that form Dokdo are also considered a tremendously valuable area for research seeking to demonstrate the flow of genetic or intraspecific variations, as well as evolutionary processes (Paulay 1994;Cowie and Holland 2006;Takayama et al. 2013). ...
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Dokdo, a group of oceanic islands located in the East Sea near Ulleungdo Island, Korea, has great biological and ecological diversity. The ecosystem of Dokdo is considered unique because the oceanic climate differs from that of mainland Korea, and the islands have remained isolated for an extended period due to its geographic features. Biological surveys of insects were conducted five times on Dongdo and twice on Seodo in 2019 and 2020. From these surveys, we could find a total of ten orders, 82 families, and 190 species of insects, including two newly described species: Geocoris (Geocoris) pallidipennis (Costa) (Hemiptera: Lygaeidae) and Tephrochlamys japonica (Okadome) (Diptera: Heleomyzidae). These survey results suggest that Dokdo is very important from both academic and conservation perspectives. Establishing a complete database of Dokdo insects will require continued investigations. Such a database would provide basic information for inferring correlations with mainland species.
... The precise levels of these characteristics are determined by the diversity of ecological habitats and the degree of geographic isolation from the mainland. Many prior studies have focused on patterns of speciation [16][17][18] and diversification [19] as well as comparisons of genetic diversity between mainland and island populations [20,21]. On the other hand, continental islands were often created by sea-level change during the Pleistocene glacial and interglacial periods [22]. ...
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Saussurea polylepis Nakai is an herbaceous perennial endemic to Korea and is highly restricted to several continental islands in the southwestern part of the Korean Peninsula. Given its very narrow geographical distribution, it is more vulnerable to anthropogenic activities and global climate changes than more widely distributed species. Despite the need for comprehensive genetic information for conservation and management, no such population genetic studies of S. polylepis have been conducted. In this study, genetic diversity and population structure were evaluated for 97 individuals from 5 populations (Gwanmaedo, Gageodo, Hongdo, Heusando, and Uido) using 19 polymorphic microsatellites. The populations were separated by a distance of 20–90 km. We found moderate levels of genetic diversity in S. polylepis (Ho = 0.42, He = 0.43). This may be due to long lifespans, outcrossing, and gene flow, despite its narrow range. High levels of gene flow (Nm = 1.76, mean Fst = 0.09), especially from wind-dispersed seeds, would contribute to low levels of genetic differentiation among populations. However, the small population size and reduced number of individuals in the reproductive phase of S. polylepis can be a major threat leading to inbreeding depression and genetic diversity loss. Bayesian cluster analysis revealed three significant structures at K = 3, consistent with DAPC and UPGMA. It is thought that sea level rise after the last glacial maximum may have acted as a geographical barrier, limiting the gene flow that would lead to distinct population structures. We proposed the Heuksando population, which is the largest island inhabited by S. polylepis, as a source population because of its large population size and high genetic diversity. Four management units (Gwanmaedo, Gageodo, Hongdo-Heuksando, and Uido) were suggested for conservation considering population size, genetic diversity, population structure, unique alleles, and geographical location (e.g., proximity).
... The Ulleung Island is of volcanic origin, located 137 km east of the Korean Peninsula with a high amount of plant endemics (Lee and Yang 1981). Most of them diverged via simple anagenetic change from continental progenitors (for example, Oh et al. 2010;Yang et al. 2012;Takayama 2013). Thus, the morphological and genetic features of R. brachycarpum in this island reflect the general microevolutionary processes of the biota here. ...
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Rhododendron brachycarpum is an ecologically important tree species with a narrow, fragmented geographic range in East Asia. R. brachycarpum is distributed primarily in Korea and Japan, with two small isolated populations in the Russian Far East. We obtained 124 samples from seven populations of R. brachycarpum, representing all geographical regions of its entire natural range, and we utilized microsatellite markers to estimate the level of genetic variation within and between populations. A total of 200 alleles based on 14 nuclear microsatellites loci were identified. High diversity (He = 0.556–0.626) was observed in populations from Korea and Japan. In contrast, in peripheral populations from Russia diversity was quite low (He = 0.100–0.369) with a high coefficient of inbreeding (FIS = 0.471–0.526). Strong population differentiation (FST = 0.356) and clear distinction among the geographical groups (FCT = 0.227) were revealed. Bayesian clustering and principal coordinate analyses indicated that two Russian populations, Sikhote-Alin and Iturup Island, represent extremes of two different migration routes, with one derived from the mainland and one from Japan.
... Such data allow for alternative speciation models and estimation of the extent of gene flow that has accompanied speciation (e.g., Nielsen 2004, 2007;Hey 2006Hey , 2010aLi et al. 2010). In addition, estimates of divergence timescales based on analysis of multilocus population genetic data in a coalescent framework provide good temporal hierarchies for understanding the roles of geological events in triggering speciation (Wakeley 2003;Takayama et al. 2013). ...
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