Table Of ContentBotanical Journal of the Linnean Society, 2017, 184, 224–237. With 5 figures.
East Asian Arabis species (Brassicaceae) exemplify past
hybridization and subsequent emergence of three main
evolutionary lineages in East Asia, America and the
amphi-Beringian region
D
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MARCUS A. KOCH* and JAN GROSSER w
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Department of Biodiversity and Plant Systematics, Centre for Organismal Studies (COS) Heidelberg, e
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Heidelberg University, Im Neuenheimer Feld 345, 69120 Heidelberg, Germany fro
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Received 4 May 2016; revised 14 October 2016; accepted for publication 26 March 2017 ttp
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Phylogenetic relationships and the evolutionary history of East Asian Arabis spp. (Brassicaceae) were investigated m
using plastid trnL-F and nuclear internal transcribed spacer 1 and 2 sequences (ITS). This study tested the wide- ic.o
spread assumption of the occurrence of Arabis hirsuta in East Asia and, in particular, in China. We were able to up
show that this is not the case. East Asian and North American Arabis are represented by three evolutionary lineages .co
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that arose via reticulate evolution among taxa, which are more closely related to A. planisiliqua subsp. nemorensis /b
and A. ciliata. Early divergence of these three lineages is placed in the Pliocene, mostly probably in East Asia. In otlin
Arabideae, the A. planisiliqua subsp. nemorensis lineage probably served as one parental source; however, this spe- n
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cies shows, at present, a wide Eurasian distribution, but it does not reach East Asia and the amphi-Beringian region. a
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The second parental source was difficult to define, because respective sister species are no longer present in East /a
Asia and all close relatives are distributed in Europe and Asia Minor only. In all three evolutionary lineages amphi- rtic
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Beringian distribution and differentiation patterns date back to the Pleistocene. However, all three lineages have /1
8
had secondary contact and additional reticulate evolutionary patterns among them are demonstrated. 4
/2
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ADDITIONAL KEYWORDS: Arabideae – evolutionary history – internal transcribed spacer 1 and 2 – phylogeny 24
– trnL-F. /38
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INTRODUCTION other genera (e.g. according to Rollins, 1941) such as ue
s
BThraes gseicnaucse aAer acobnisc eLr.n iisn go nme oorfp thhoel omgiocsatl ddiefffiicnuitlito inn. lfilantetaern esdil ipqaureasl,l ealc tcou tmhbee snetp tcuomty lcehdaonngse adn ddu rsiinligq uthees t on 15
Until the late 1980s the genus had been assumed to evolution of tribe Arabideae. Consequently, a series Ja
of phylogenetic studies were needed to unravel the n
be well defined (Al-Shehbaz, 1988) with > 180 spe- u
cies distributed in temperate regions of the Northern pciheysl oggroeunpetsi ca sp opsoistisoinbl oef i ans t mhea nphy yAloragebnise tsipcp c. oanntde xstp oef- ary 2
Hemisphere. It needed another 10 years until the first Brassicaceae (Karl & Koch, 2013). The number of spe- 023
preliminary phylogenetic analyses indicated that tra-
cies in the family characterized by DNA sequences
ditionally circumscribed Arabis is not monophyletic
(e.g. the widely used internal transcribed spacers 1
and probably includes taxa from many different tribes
and 2; Edger et al., 2014) is > 1689 (Koch et al., 2012a;
of Brassicaceae (Koch et al., 1999). It was shown with
Kiefer et al., 2014) out of 3740 species (latest species
these analyses that convergent morphological evo-
count; Hohmann et al., 2015) and almost all genera
lution is the rule rather than the exception and any
and potentially formerly misplaced evolutionary lin-
‘essential character(s)’ differentiating Arabis from
eages have been captured phylogenetically (Kiefer
et al., 2014). Therefore, we feel confident that there are
*Corresponding author. E-mail: [email protected] no or only a few systematically misplaced Arabis rep-
berg.de resentatives left. Meanwhile all accepted Arabis spp.
© 2017 The Linnean Society of London, Botanical Journal of the Linnean Society, 2017, 184, 224–237 224
EVOLUTIONARY HISTORY OF EAST ASIAN ARABIS 225
are defined phylogenetically as members of Arabideae, A. pycnocarpa M.Hopkins. As a consequence, this has
and any other formerly Arabis taxon has been assigned led not only to difficulties in circumscribing A. hirsuta
to different genera often placed in different tribes (e.g. and its closest relatives on the basis of morpho-
Boechera Á.Löve & D.Löve, Turritis L., Pseudoturritis logical characters, but also to the recognition of
Al-Shehbaz). A. hirsuta in floras and taxonomic treatments from
Arabideae are currently circumscribed with 17 gen- China, Japan, Korea and North America (e.g. Rollins,
era and 508 species (Karl & Koch, 2014; Hohmann 1941, 1993; Jones, 1964; Titz, 1968; Akeroyd, 1993;
et al., 2015). These 17 genera can be assigned to eight Mulligan, 1996). A detailed survey of the European
major evolutionary clades supported significantly by material spanning the Mediterranean, Central Europe
phylogenetic analyses (Karl & Koch, 2013) and a key and the Balkans towards the Caucasus region has been
to the genera was provided by Koch et al. (2012b). presented recently (Karl & Koch, 2014). For that region
D
Many of these clades contain Arabis spp., but a limited it was shown that A. hirsuta is a phylogenetically well- o
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number do not, resulting in Arabis still being para- defined species, and it was also shown that earlier taxo- nlo
phyletic in Arabideae. The first major clade is Arabis nomic concepts circumscribing an A. hirsuta aggregate ad
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alpina L. and its relatives. Arabis alpina is the generic were mostly misleading. It was also demonstrated that d
type and the clade consists exclusively of 12 Arabis European and West Asian species, phylogenetically fro
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spp. (Koch et al., 2006; Ansell et al., 2011; Karl et al., close to A. hirsuta, show consistent phylogenetic place- h
2012). A related clade with only three Arabis taxa is ment comparing plastid and nuclear genome-derived ttp
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the A. auriculata Lam. clade (Karl & Koch, 2013). Two phylogenetic hypotheses. However, first evidence was ://a
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other small lineages with only five and two Arabis provided that various non-European species from East a
d
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spp., respectively, are the A. nordmanniana (Rupr.) Asia and northern America, which are genetically close m
Rupr. and the A. aucheri Boiss. clades (Karl & Koch, to A. hirsuta (based on plastid or nuclear DNA-based ic.o
2013). The fifth ‘main Arabis’ clade consists of > 65 spe- phylogenetic results), underwent a reticulate and com- up
cies, among which are two monotypic genera, namely plex evolutionary history. Therefore, here we focus on .co
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Dendroarabis (C.A.Mey.) D.German & Al-Shehbaz the East Asian, amphi-Beringian and North American /b
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and Pachyneurum Bunge. The largest clade (Draba Arabis taxa to unravel this reticulate evolutionary his- tlin
L. clade with > 400 species) consists of non-Arabis taxa tory in more detail. A particular emphasis is on East n
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only (Jordan-Thaden et al., 2010; Al-Shehbaz et al., Asian populations often recognized as A. hirsuta to n
/a
2014). This is also true for the Aubrieta Adans. clade unravel relationships and the evolutionary history rtic
with c. 20 species (Koch et al., 2017). The final and compared to European A. hirsuta. We evaluate phylo- le
/1
earliest diverging clade in Arabideae, the Scapiarabis genetic analyses of DNA sequence variation from the 8
4
M.A.Koch, R.Karl, D.German & Al-Shehbaz clade, plastid genome (trnL-F) and the nuclear genome (ITS, /2
/2
consists of eight genera exclusively distributed in internal transcribed spacers 1 and 2) to provide a phy- 2
4
the Asian high mountains (Koch et al., 2012b). This logenetic-systematic framework for the various taxa /3
8
short overview indicates that, considering A. alpina as and shed some light on their evolutionary dynamics. 65
4
the type species of Arabis but not being a member of 7
6
the main Arabis clade, future substantial taxonomic b
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changes are required to render Arabis monophyletic MATERIAL AND METHODS gu
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(see also Kadereit et al., 2016). s
Here we focus on some unresolved taxonomic prob- Taxon sampling t on
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lems concerning East Asian taxa belonging to the main Taxon sampling and phylogenetic analyses took 5
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Arabis clade. This clade consists of species from differ- advantage of two former studies and datasets focus- a
n
ent habitats such as alpine environments, lowland flood ing on [dataset 1] Arabideae as a whole (Karl & ua
plains, cold steppe or temperate woodlands all over the Koch, 2013) and [dataset 2] North American Arabis ry 2
0
Holarctic region. Among the c. 60 species we know, 30 (Koch et al., 2010). Additional accessions have been 2
3
are from Europe and among these the A. hirsuta (L.) incorporated from a study focusing on the European
Scop. aggregate is the most complex group. Systematic A. hirsuta complex (Karl & Koch, 2014). In particular,
circumscription and taxonomy and, as a consequence, the identity of material from China, Japan, Korea and
distribution ranges in the latter have been widely East Siberia is still unclear and unsettled. Therefore,
debated among authors (Titz, 1968; for an overview we combined data from the various studies and added
see Karl & Koch, 2014). Key morphological features 23 new accessions not included in those to increase
of relatives of A. hirsuta, such as the appearance of the sample size for China and Russia, thereby balanc-
hemicryptophytes with a rosette, one- or few-leaved ing the number of accessions when comparing Asia
and erect inflorescences with small white flowers and and North America. All Chinese samples newly ana-
more or less erect siliques are also present in distant lysed here were originally collected and documented
species such as A. ciliata Clairv. or amphi-Beringian under the name A. hirsuta. This species delimitation
© 2017 The Linnean Society of London, Botanical Journal of the Linnean Society, 2017, 184, 224–237
226 KOCH and GROSSER
is doubtful, however, and as a result taxon sampling in a 1% agarose gel in TAE-buffer (40 mM Tris base,
and phylogenetic analyses followed a two-step strat- 20 mM acetic acid, 1 mM EDTA; pH 8.0) and stain-
egy. First, all new accessions and their respective DNA ing with ethidium bromide. PCR product clean-up was
sequences were incorporated into the tribe-wide DNA executed using the Wizard SV Gel and PCR Clean-Up
sequence alignments (Karl & Koch, 2013, ‘dataset 1’) System (Promega, Madison, WI, USA). Custom
to test broader phylogenetic relationships in the dif- Sanger-sequencing was performed by GATC Biotech
ficult and complex Arabis and Arabideae. Second, all (Konstanz, Germany) The electropherograms were
available new DNA sequence information from East checked and trimmed to the borders of the analysed
Asian accessions belonging to the ‘main Arabis clade’ markers using the SeqMan DNA-Star Lasergene soft-
(Karl & Koch, 2013) were integrated into the align- ware package (DNASTAR, Madison, WI, USA).
ments focusing in detail on North American Arabis
D
(Koch et al., 2010, ‘dataset 2’). Finally, the dataset o
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used to study East Asian Arabis comprised 140 acces- eDiTing anD sequence alignmenT nlo
sions (Supporting Information, Table S1). This data- New DNA sequence data (ITS and trnL-F) were first ad
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set covered 38 species, but with a particular emphasis added to the large and tribe-wide alignment (‘dataset d
on native East Asian species and on A. hirsuta and 1’) (Karl & Koch, 2013). The alignments did not need fro
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its segregates, which have long been considered to be any further adjustments and consisted of 316 taxa for h
native to East Asia and North America. ITS and trnL-F with a total alignment length of 656 and ttp
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1234 bp, respectively. The nexus input files are provided ://a
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with Supporting Information Tables S2, S3. The com- a
Dna exTracTion, amplificaTion de
prehensive ‘main Arabis clade’ (‘dataset 2’) alignments m
anD sequencing consisted of 122 accessions for ITS and 138 acces- ic.o
Total DNA was extracted either according to an iso- sions for trnL-F (nexus files provided with Supporting up
propanol variant of the CTAB protocol (Doyle & Information Tables S4, S5) with an alignment length of .co
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Doyle, 1987) or using the Invisorb Spin Plant Mini 633 and 750 bp, respectively. For these datasets, Draba /b
KPCitR ( Satmraptleifci cBatiioomne odfi cthael AmGa,r kBeirrsk eunsfeedl d(n, uGcelremara InTyS)., nAel-mSohreohsbaa Lz., aMn.dA T.Komocohs t&im Jao rpdlaonty-cTahrapdae (nT o(Drrr. a&b Aa .Gclaradye); otlinn
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plastid trnL intron and trnL-trnF intergenic spacer) Jordan-Thaden et al., 2010) and A. alpina (A. alpina an
ewpaoaclsyh m ppeerrrifamosreemr ,(e B2di. o0il nimn aMe ,v LoMluugcmCkele2n owafn a2dl5d 0 eμ., 5LG ,U eur Msminaagnn yg1)o0.- TTμahMqe clade, Karl et al., 2012) served as multiple outgroups. /article/1
8
primers used for ITS amplification were originally phylogeneTic analyses 4/2
designed by White et al. (1990) with the modifica- We performed maximum-likelihood (ML) as well as /2
2
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tions of Mummenhoff et al. (1997) made for primer Bayesian Markov chain Monte Carlo (MCMC) (Yang /3
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18F (18F: 5′-GGAAGGAGAAGTCGTAACAA-3′, & Rannala, 1997) analyses. For ML analyses the pro- 6
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25R: 5′-TCCTCCGCTTATTGATATGC-3′). For some gram RAxML was used (Stamatakis, 2006; Silvestro & 47
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fragments, PCR quality was further increased to Michalak, 2012). The best fitting nucleotide substitu- b
y
amplify ITS1 and ITS2 separately using internal tion model was selected using Modeltest v. 3.7 (Posada g
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primers ITS2a (5′-GCAATTCACACCAAGTATCG-3′) & Crandall, 1998): ‘dataset 1’: GTR+Γ for ITS and es
and ITS3 (5′-GCATCGATGAAGAACGTAGC-3′), GTR+I+ Γ for trnL-F; ‘dataset 2’: GTR+I+Γ for ITS and t o
n
respectively. Amplification of the trnL intron and GTR+I+ Γ for trnL-F. Bootstrapping was performed 1
5
the trnL-trnF intergenic spacer was performed with 1000 replicates. In the Bayesian analyses using Ja
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using the primers c, d and e by Taberlet et al. MrBayes v. 3.2.6 (Ronquist & Hülsenbeck, 2003), for u
a
(1991) (c: 5′-CGAAATCGGTAGACGCTACG-3′, ‘dataset 1’ four simultaneous runs with four chains ry
2
d: 5′-GGGGATAGAGGGACTTGAAC-3′, e: each were run for 1 million generations, and in each 0
2
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5′-GGTTCAAGTCCCTCTATCATC CC-3′ ) run 1001 trees were sampled. The first 25% of these
and a primer designed by Dobeš et al. (2004) trees were discarded as burn-in. The temperature of
(5′-GATTTTCAGTCCTCTGCTCTAC-3′) extended by the heated chain was set to 0.01, as this facilitated the
the M13 sequence for subsequent sequencing using most efficient chain-swapping. For ‘dataset 2’, we also
M13 universal sequencing primers. The amplifica- conducted four simultaneous runs with four chains
tions were run on a PTC 200 Peltier Thermal Cycler each and for 15 million (ITS) and 25 million (trnL-F,
(MJ Research, Waltham, MA, USA) under the follow- combined dataset) generations. For efficient swapping
ing conditions: 3 min initial denaturation at 95 °C; 30 of the chains, the temperature was set also to 0.01. In
cycles of amplification with 30 s at 95 °C, 30 s at 44 °C each run, every 15 000th (ITS) or 25 000th (trnL-F)
and 1 min at 72 °C; and 5 min of final elongation at tree was sampled, resulting in 1000 trees each. When
72 °C. PCR success was checked with electrophoresis computing the consensus tree (50% majority rule), the
© 2017 The Linnean Society of London, Botanical Journal of the Linnean Society, 2017, 184, 224–237
EVOLUTIONARY HISTORY OF EAST ASIAN ARABIS 227
first 250 of the sampled trees were discarded (burn- this clade consists of taxa referred to here as clade
in phase). Finally, posterior probabilities of all splits 1 such as A. borealis (Siberia), amphi-Beringian
between the respective runs were compared and cumu- A. pycnocarpa and North American taxa of hybrid ori-
lative split frequency plots were analysed using the gin (see Koch et al., 2010), namely A. eschscholtziana
web-based program AWTY (Nylander et al., 2008) to Andrz. and A. olympica Piper. In this clade 1, Chinese
confirm accomplished convergence between the indi- and Russian accessions form a separate, not signifi-
vidual Bayesian MCMC runs. cantly supported, subclade (A04, light blue). The third
clade recognized with ITS sequence data is clade z
(Fig. 1). This clade consists of Japanese ‘A. hirsuta’.
These accessions have been considered either as ‘true’
RESULTS
A. hirsuta or as a hybrid morphologically similar to
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Taxon iDenTiTy European A. hirsuta. Clade z is nested in a group of o
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Phylogenetic analyses (ML and MrBayes) of ‘data- taxa including European A. hirsuta. However, geo- nlo
set 1’ indicated that all additional Chinese Arabis graphically and evolutionarily more significant is the ad
e
aAcmceesrsiciaonn/sa mbeplhoni-gB etroi ntghiea nE aAsrta bAissi calna daens.d T thhee rNesourltths (faHc.tW thoalft eAx. pHloafnfimsi.l)i qSuoajá (kP e[=rs A.) .R ncehmb.o sruebnsspis. n(Hem.Woroelnf seixs d from
from the Bayesian analysis of ITS and trnL-F are pro- Hoffm.) Rchb.] is found in this group. The latter includes h
vided with Supporting Information (Figs S1 and S2, European A. sagittata (Bertol.) DC. and A. sadina ttps
respectively; results from ML analyses are identical (Samp.) Cout., but A. planisiliqua subsp. nemorensis ://a
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and not shown). Tree topologies are fully congruent is the only European taxon extending its distribution ad
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with results obtained earlier (Karl & Koch, 2013) and range far into Asia. The distribution of accessions with m
none of the newly sequenced accessions resembles available ITS sequence data is shown in Figure 2 and ic.o
true A. hirsuta (Supporting Information, Fig. S1). One signatures refer to Figure 1. With this map there is up
.c
Chinese accession (A04) belongs to the A. pycnocarpa– also an accession of hybridogenous origin indicated om
A. borealis Andrz. ex C.A.Mey. group (trnL-F clade (A70MO). This accession, based on its ITS type and /b
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A, Supporting Information, Fig. S2). The remaining morphology, is close to A. pycnocarpa. Nevertheless, as tlin
accessions (A02, A03, A05–A11) belong to the exclu- discussed later, the accession carries a different plastid ne
a
sively East Asian Arabis clade and are most closely DNA haplotype belonging to the A. paniculata group. n/a
related to Chinese A. paniculata Franch. (trnL-F clade The Bayesian trnL-F phylogenetic tree is shown in rtic
A, Supporting Information, Fig. S2). Figure 3. Consistent with ITS sequence data various le
/1
major clades are recognized. The North American 8
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Arabis clade does not include any amphi-Beringian /2
phylogeneTic analyses of easT asian ArAbis or East Asian taxa. In this clade, the two North /22
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The results from the detailed analyses (‘dataset 2’) American hybrids A. eschscholtziana and A. olympica /3
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provide a number of new and important findings, are found, congruent with the fact that plastid 65
4
which are presented in the following section for ITS genomes are inherited maternally and reflect maternal 76
and trnL-F, separately. For both molecular mark- migration. Sister to the North American taxa is clade by
ers, results from ML and Bayesian analyses are fully G, which comprises the East Asian taxa (e.g. Chinese gu
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congruent with each other and hence only data from A. paniculata), but it also includes the accessions from s
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Bayesian analyses are shown. Japan (‘A. hirsuta’) together with all remaining taxa from n
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The Bayesian ITS phylogenetic tree is shown in Japan, South Korea and Ulong Island. The third clade 5
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Figure 1 and various groups of taxa are supported with A is made up by the amphi-Beringian A. pycnocarpa and a
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high to moderate posterior values. Exclusively, North North Asian A. borealis. This clade also consists of the ua
American Arabis are grouped into one large clade (clade third North American hybridogenous taxon, A. georgiana, ry 2
0
x). This clade includes the ‘purple-flowered’ North which has amphi-Beringian A. pycnocarpa as one 2
3
American Arabis (Koch et al., 2010) and A. georgiana maternal contributor. Arabis planisiliqua subsp.
R.M.Harper. Arabis georgiana is of hybrid origin nemorensis is sister to clade A. This is a finding that
between a taxon from clade x and a member from the indicates again (similar to ITS data and the genetic
second large clade y (A. pycnocarpa; see also Koch et al., similarity of Japanese accessions with A. planisiliqua
2010). Clade y consists of the early diverging East Asian subsp. nemorensis) that progenitors of A. planisiliqua
taxa (group 2, Fig. 1) [e.g. A. paniculata from China, subsp. nemorensis must have had a wider distribution
others such as A. bijuga Watt. and A. amplexicaulis towards the Far East. This idea is also supported by the
Edgew., East Asian A. stelleri DC., A. flagellosa Miq., fact that A. planisiliqua subsp. nemorensis is the only
A. serrata Franch. & Sav., A. nipponica (Franch European Arabis sp. with a documented distribution
& Sav.) H.Boissieu and endemic A. takesimana range reaching the Urals (Jalas & Suominen, 1994) and
Nakai from Ulong island, Palau] (Fig. 2). In addition, may even span further into western and eastern Siberia,
© 2017 The Linnean Society of London, Botanical Journal of the Linnean Society, 2017, 184, 224–237
228 KOCH and GROSSER
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Figure 1. Phylogenetic tree from Bayesian analysis based on nuclear encoded ITS DNA sequence data. The three major
clades combining taxa from East Asia, the amphi-Beringean region and North America analysed here are indicated (clades
x, y; clade z exclusively combines taxa from Japan and Korea). In clade y, several clades and groups are indicated (clade 1
and A04 subclade; group 2 and Arabis paniculata), which show a significant geographical distribution pattern also
confirmed by plastid DNA sequence data (Figs 2, 3). Several accessions from clade z are indicated with provisional name
‘A. ×hirsuta’ without further taxonomic value. Bayesian posterior probabilities are indicated with branches if > 50%.
© 2017 The Linnean Society of London, Botanical Journal of the Linnean Society, 2017, 184, 224–237
EVOLUTIONARY HISTORY OF EAST ASIAN ARABIS 229
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Figure 2. Distribution map of accessions from clades y and z analysed for ITS sequence variation (see Fig. 1). .o
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but then documented probably erroneously as A. hirsuta, might have an even deeper evolutionary history and we m
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A. sagittata or A. gerardii Besser (Bush, 1939; Doronkin, do not know its closest relatives. This lineage must have o
1994; Knjasev, 2010.). Some more detailed information migrated to East Asia even earlier than the other line- tlinn
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about the spatio-temporal patterns is obtained when age, because the two subgroups in this lineage diverged a
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divergence-time estimates are included, which have from each other 4 Mya, with one subgroup diversifying /a
been taken and re-drawn from Karl & Koch (2013) in East Asia and the other subgroup migrating to North rtic
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(Fig. 3). These estimates indicate that the two major America and diversifying in parallel on that continent. /1
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splits occurred during the Pliocene: North American The various lineages must have had temporarily sec- 4/2
Arabis vs. East Asian Arabis diverging c. 4 Mya, and ondary contact (Fig. 5). Arabis pycnocarpa and A. borea- /2
2
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amphi-Beringian Arabis (clade A) plus A. planisiliqua lis most probably originated via hybridization between /3
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subsp. nemorensis vs. European Arabis hirsuta and the first A. planisiliqua subsp. nemorensis-derived 6
5
its relatives diverging c. 3 Mya. The amphi-Beringian lineage and East Asian Arabis and subsequently 47
6
taxa evolved later during the Pleistocene with the expanded its range towards an amphi-Beringian dis- b
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split between A. planisiliqua subsp. nemorensis and tribution range. Arabis planisiliqua subsp. nemorensis g
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A. pycnocarpa dated to c. 1.5 Mya. The distribution map relatives also hybridized with East Asian Arabis giv- e
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of plastid DNA types sorted for the various lineages ing rise to the ‘A. hirsuta’ in Japan (Koch et al., 2010). t o
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is shown with Figure 4. The hybridogenous accession ‘Tertiary’ contact between A. pynocarpa (hybrid ori- 1
5
A70MO consistently carries a clade G haplotype. gin) and East Asian Arabis is exemplified by acces- J
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sion A70MO, which might indicate even more u
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complex reticulate speciation processes. Such ‘tertiary’ ry
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hybridization also occurred in North America. Arabis 0
DISCUSSION 2
pycnocarpa relatives continued hybridizing with North 3
phylogeographical implicaTions American purple-flowered Arabis and at least four taxa
From the ITS- and trnL-F-derived phylogenetic trees arose independently: A. eschscholtziana, A. olympica,
(Figs 1, 3), we can develop a spatio-temporal hypothesis A. georgiana and A. oregana Rollins (see also Koch
for the evolution of (a) East Asian, (b) amphi-Beringian et al., 2010). All these secondary and tertiary reticu-
and (c) North American Arabis spp. (Fig. 5). Two old late speciation processes must have occurred during
evolutionary lineages were present in Siberia and East the Pleistocene and are also supported by polyploidy
Asia 1.5–4.0 Mya. One lineage is closely related to the documented in all (when known) of the taxa of puta-
European A. hirsuta group and this lineage expanded its tive hybrid origins (Koch et al., 2010; BrassiBase, http://
distribution far towards the East with A. planisiliqua brassibase.cos.uni-heidelberg.de/: Koch et al., 2012a;
subsp. nemorensis and its progenitors. The other lineage Kiefer et al., 2014) (compiled in Table 1).
© 2017 The Linnean Society of London, Botanical Journal of the Linnean Society, 2017, 184, 224–237
230 KOCH and GROSSER
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Figure 3. Phylogenetic tree from Bayesian analysis of plastid trnL-F DNA sequence data. The three major clades (North
American Arabis clade, clade G from East Asia and clade A with an amphi-Beringean distribution) are indicated. The geo-
graphical distribution of accessions from clade A and clade G (including A. paniculata group) is shown in Figure 4. Several
accessions from clade G are indicated with provisional name ‘A. ×hirsuta’ without further taxonomic value. Bayesian pos-
terior probabilities are indicated with branches if > 50%. Divergence time estimates are redrawn from Karl & Koch (2013).
© 2017 The Linnean Society of London, Botanical Journal of the Linnean Society, 2017, 184, 224–237
EVOLUTIONARY HISTORY OF EAST ASIAN ARABIS 231
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Figure 4. Distribution map of accessions from clades A and G analysed for trnL-F (see Fig. 3). .o
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Figure 5. Phylogeographical scenario of the evolution of the different Arabis lineages in East Asia, the amphi-Beringian
region and North America. The distribution map represents the plastid DNA haplotype map (see Fig. 4), and clade names
are taken from the plastid DNA-derived phylogenetic hypothesis shown in Figure 3, reflecting the maternal lineages,
hypothesized divergence time and migration history.
The overall spatio-temporal phylogeographical pat- genus Draba (Karl & Koch, 2013; Jordan-Thaden &
tern found in East Asian Arabis is comparable with Koch, 2008; Jordan-Thaden et al., 2010, 2013). The
patterns found in other groups of Brassicaceae. In Scapiarabis clade consists of seven genera and its
Arabideae, comprising 508 species distributed in 17 early radiation started 6.9–7.9 Mya (Koch et al., 2012b)
genera, this is particularly true for the Scapiarabis in the East Asian high mountains. The early evolu-
clade (Koch et al., 2012b; Karl & Koch, 2013) and the tion might have also involved reticulate processes,
© 2017 The Linnean Society of London, Botanical Journal of the Linnean Society, 2017, 184, 224–237
232 KOCH and GROSSER
Table 1. Chromosome numbers of the various Arabis taxa major split separating Chinese populations from west-
analysed herein. The more unusual or rare ploidy level ern Himalayan species is dated at c. 2.1 Mya. These
description is in parentheses. Data are compiled from the divergence times might indicate ancient differentia-
literature, and a comprehensive survey and documenta- tion processes not affected by Pleistocene glaciation
tion is found with BrassiBase (Koch et al., 2012a; Kiefer and deglaciation cycles and also highlight past retic-
et al., 2014) ulate evolution close to the transition of major geo-
logical epochs (e.g. Miocene to Pliocene, Pliocene to
North American Arabis
Pleistocene: Kagale et al., 2014; Hohmann et al., 2015;
Huang et al., 2016). Notably, many members of the
A. aculeolata 2n = 4x = 32
Scapiarabis clade have long been considered as ‘true’
A. blepharophylla 2n = 2x = 16
Arabis spp. and it is impossible to define the vari-
A. crucisetosa 2n = 4x = 32 D
ous genera using characteristic and unique morpho- o
A. eschscholtziana 2n = 8x = 64 w
A. furcata not known logical characters because any character used in keys nlo
A. georgiana 2n = (4x)/8x = (32)/64 and species descriptions is homoplastic in Arabideae. ade
Draba is another example, which is better defined d
A. macdonaldiana 2n = 2x = 16 morphologically, consisting of c. 390 species and with a fro
A. modesta 2n = (2x)/4x = (16)/32 m
A. nutallii 2n = 4x = 32 Ninocrluthdeirnng Hseevmerisapl hmeraej o–r Scolaudtehs A amnedr liicnaena dgiesst.r iIbnu ptiaorn- http
A. olympica not known s
A. oregana 2n = (2x)/4x = (16)/32 ticular, the species-rich group III (circum-north and ://a
c
A. patens not known Asia) (Jordan-Thaden et al., 2013) comprises > 160 ad
e
amphi-Beringean Arabis species and splits off from the other two main lineages m
A. pycnocarpa 2n = 4x/(8x) = 32/(64) at the Miocene–Pliocene boundary. Nevertheless, it ic.o
East Asian Arabis started to diversify later at the Pliocene–Pleistocene up
.c
A. amplexicaulis 2n = 2x/(4x) = 16/(32) boundary (Karl & Koch, 2013). Other examples for o
m
A. bijuga not known Pleistocene amphi-Beringian or East Asian – North /b
o
A. borealis 2n = 4x = 32 American diversification are from Noccaea Moench tlin
A. flagellosa 2n = 4x = 32 (tribe Coluteocarpeae, Koch & Al-Shehbaz, 2004), ne
a
A. japonica 2n = 2x = 16 Boechera A.Löve & D.Löve (tribe Boechereae, Kiefer n
/a
A. nipponica 2n = 4x = 32 & Koch, 2012; Kiefer et al., 2009) with more species rtic
A. paniculata not known found in North America compared to East Asia or le
/1
A. serrata 2n = 4x = 32 Cardamine L. (Cardamineae, Lihová et al., 2006), and 8
4
A. stelleri 2n = 4x = 32 Arabidopsis (DC.) Heynh. (tribe Camelineae, Schmickl /2
/2
A. takesimana not known et al., 2008, 2009) with a higher species number found 2
4
European in East Asia than in North America. In general, these /3
8
A. ciliata 2n = 2x = 16 few examples highlight the evolutionary dynamics of 65
4
A. collina 2n = 2x/4x = 16/32 Brassicaceae in Eurasia and East Asia with one major 7
6
A. cretica 2n = 2x = 16 centre of diversity in the Irano-Turanian region (Koch b
y
A. hirsuta 2n = 4x = 32 & Kiefer, 2006), this probably also being the centre of gu
e
A. juressi 2n = 4x = 32 origin (Hedge, 1976), and its strong and multiple affin- s
A. planisiliqua subsp. nemorensis 2n = 2x = 16 ities to North America (e.g. Cardinal-McTeaque et al., t on
A. procurrens 2n = 2x/4x = 16/32 2016) pre-dating the Pleistocene. 15
A. pubescens 2n = 2x = 16 Ja
n
A. pumila 2n = 4x = 32 u
a
A. sachokiana 2n = 2x = 16 Taxonomic commenTs anD implicaTions ry 2
A. sadina 2n = 4x = 32 0
Based on the presented results, few taxonomic impli- 2
3
A. sagittata 2n = 2x = 16
cations are worthy of discussion in any detail. Arabis
A. scabra 2n = 2x = 16
nemorensis is often treated as a subspecies or even as
A. scopoliana 2n = 4x = 32
a synonym of A. planisiliqua. If accepting one taxon
A. serpyllifolia 2n = 2x = 16
only, the annual to biennial A. nemorensis s.l. repre-
A. stellulata 2n = 2x = 16
sents a diploid species in the A. hirsuta aggregate with
A. stenocarpa 2n = 2x = 16
a distribution from south-eastern and central Europe
A. vochinensis 2n = 2x/(4x) = 16/(32)
towards Russia, Ukraine and perhaps Kazakhstan and
east of the Ural Mountains. Here, the taxon bridges
because of a major incongruence when comparing the gap towards the annual/biennial A. borealis
plastid DNA- and nuclear DNA-derived evolutionary and A. pycnocarpa, which are not members of the
hypotheses. Based on nuclear DNA sequence data, a A. hirsuta aggregate (Koch et al., 2010). Contemporary
© 2017 The Linnean Society of London, Botanical Journal of the Linnean Society, 2017, 184, 224–237
EVOLUTIONARY HISTORY OF EAST ASIAN ARABIS 233
taxonomic checklists (Warwick et al., 2006; The Plant and a clear separation (including potential hybrids
List, 2013) deal with A. nemorensis as a synonym of among them and other taxa) will require dense, pop-
A. planisiliqua, but often differentiated further at the ulation-based sampling in morphological, ecological
subspecific level as A. planisiliqua subsp. nemorensis. and molecular analyses (e.g. Oyama, 1993a, b, 1994;
However, both taxa should be treated as discrete Oyama et al., 1993).
species, as suggested by Titz (1976) and confirmed
by molecular analysis (Karl & Koch, 2014). Arabis
nemorensis is a hygrophilous lowland taxon occurring reTiculaTe evoluTion, hybriDizaTion
in riparian sites and wet meadows, forests and rud- anD polyploiDizaTion
eral places across north-eastern Europe (from north- Brassicaceae are characterized by an enormous
eastern France to central European Russia; Jalas & abundance of polyploids. This is true at various
D
Souminen, 1994), whereas A. planisiliqua is a xerophil- evolutionary and temporal scales. An ancient pal- o
w
ous taxon from (sub-) Mediterranean south-western aeopolyploidization event characterizes the early nlo
Europe (Jalas & Souminen, 1994), which preferably evolution of the whole family and is referred to as ad
e
grows on dry, rocky places. In accordance with Titz ‘alpha-WGD’ (whole-genome duplication). This ances- d
(1976) we recommend assignment of A. planisiliqua tral Brassicaceae-specific palaeopolyploidization fro
m
for the south-western taxon and A. nemorensis for the event was first shown by Vision et al. (2000) and h
north-eastern taxon analysed here. Bowers et al. (2003) and later confirmed by other ttp
s
Our results from phylogenetic analyses have dem- workers (e.g. Schranz et al., 2012; Haudry et al., 2013; ://a
c
onstrated that any accession analysed here from East Hofberger et al., 2013). Hence, this early polyploidiza- a
d
e
Asia and originally considered to be A. hirsuta (e.g. tion has affected the radiation of the family, perhaps m
voucher documentation, treatment in floras) is rep- because this genome duplication triggered subse- ic.o
resenting either distinct and different species or is quent structural elaboration of glucosinolates as an up
.c
of hybrid origin (but also not involving A. hirsuta). effective insect-defence mechanism, which then coin- o
m
However, the most recent Flora of China (www.eFlo- cided with family-wide radiation processes (Edger /b
o
ras.org, FOC Vol. 8, p. 116) describes the species distri- et al., 2015; Soltis & Soltis 2016). In addition, a tlin
bution of A. hirsuta covering all of China and Korea. series of subsequent lineage-specific polyploidization n
e
a
Furthermore, the most recent Database of Japanese events have been already characterized such as in n
/a
flora (http://herbaria.plants.ox.ac.uk/bol/florajapan) Brassiceae (Lysák et al., 2005) or Biscutelleae (Geiser rtic
lists A. hirsuta as an accepted taxon for Japan. Other et al., 2016). The data are summarized in Hohmann le
/1
accepted taxa listed from Japan in that database are: et al. (2015), and these variously confirmed mesopol- 8
4
A. serrata, A. stelleri, A. flagellosa, A. pendula L. and yploidization events again affected 424 ‘present-day’ /2
/2
A. tanakena Makino (the last two of which are not ana- species distributed among different lineages. A past 2
4
lysed here). Arabis nipponica [mentioned in this list as polyploidization is considered as mesopolyploidiza- /3
8
A. hirsuta subsp. nipponica (Franch. & Sav.) Kitam.], tion if the parental subgenomes in mesopolyploids are 65
4
A. japonica (mentioned in the list with various subspe- only discernible by comparative genetic and genomic 7
6
cies, not analysed here; often treated also as variety of approaches and, with time passing, these mesopoly- b
y
A. stelleri: e.g. Qyama, 1994) and Arabis takesimana ploids undergo diploidization and often extensive gu
e
are kept in synonymy of A. hirsuta, A. stelleri reshuffling of genes and genomic regions (Mandáková s
t o
and A. serrata, respectively. Our sampling does not et al., 2010; Lysák & Koch, 2011). Unpublished data n
1
allow a comprehensive solution of the taxonomic prob- and work in progress by these authors indicate that 5
J
lems with Japanese and South Korean Arabis taxa, even more tribes are affected by mesopolyploidiza- a
n
but some conclusions can be drawn from our molecu- tion events and in summary perhaps at least 20% ua
lar datasets. (1) There is no A. hirsuta in Japan and of all species have to be considered mesopolyploid. ry 2
0
Korea. However, A. nipponica is indeed closest to the It has been shown that these old polyploidization 2
3
accessions from Japan analysed here (kept under events coincide well, with a lag phase, with subse-
a provisional name ‘A. × hirsuta’, Figs 1, 3) and it quent diversification and often radiation (Hohmann
might be best to treat them all under a morphologi- et al., 2015). However, the extent of reticulate evolu-
cally more broadly defined A. nipponica. (2) Arabis tion giving rise to these new lineages is unclear. If
takesimana should be kept separate from A. serrata. we finally have a closer look at the occurrence of neo-
Our data demonstrate no close relationships between polyploids (characterized by increased chromosome
A. takesimana and A. serrata from Japan. (3) Arabis number and genome size, redundant gene content
flagellosa is characterized by a distinct genetic clus- and often extant diploid ancestors) on a family-wide
ter, which also merits separate recognition. (4) Arabis scale, we observe > 43% polyploids and 63% poly-
serrata and A. stelleri are closely related to each other ploids are found in Arabideae, the most species-rich
© 2017 The Linnean Society of London, Botanical Journal of the Linnean Society, 2017, 184, 224–237
Description:East Asian Arabis species (Brassicaceae) exemplify past hybridization and subsequent emergence of three main evolutionary lineages in East Asia,
