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2 Department of Biological Sciences, Florida International University, University Park, Miami, Florida 33199 USA, and The Research Center, The Fairchild Tropical Garden, 11935 Old Cutler Road, Miami, Florida 33156 USA; and 3 Section of Integrative Biology and Institute of Cellular and Molecular Biology, University of Texas, Austin, Texas 78712 USA; and 4 Jardín de Aclimatación de La Orotava, Calle Retama Número 2, Puerto de la Cruz, Tenerife, Canary Islands, E-38400, Spain; and 5 Jardín Botánico Viera y Clavijo, Apartado de Correos Número 14, Tafira Alta, Gran Canaria, Canary Islands, E-35017, Spain
Received for publication July 27, 1999. Accepted for publication December 9, 1999.
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ABSTRACT |
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 TOP ABSTRACT INTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONLITERATURE CITED |
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Key Words: African flora • Asteraceae • biogeography • floristic disjunctions • long-distance dispersal • Macaronesia • Natal • oceanic islands • plant evolution
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INTRODUCTION |
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TOPABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONLITERATURE CITED |
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). Good examples of extremely divergent insular-continental sister taxa include the three genera (i.e., Argyroxiphium DC., Dubautia Gaud., and Wilkesia A. Gray) of the silversword alliance in Hawaii (Baldwin et al., 1991
) and Argyranthemum Sch. Bip. (Asteraceae) in the Canary Islands and Madeira (Francisco-Ortega et al., 1997a, b
). These insular genera are woody and show extraordinary levels of morphological and ecophysiological variation as a result of isolation and adaptation to most of the insular ecosystems of Hawaii and Macaronesia (Baldwin, 1997
; Francisco-Ortega et al., 1997a
). However, molecular data have facilitated the identification of continental relatives of morphologically divergent genera endemic to many oceanic islands. Several excellent examples of the utility of molecular phylogenies include Scalesia Arn. (Asteraceae) in the Galapagos Islands (Schilling, Panero, and Eliasson, 1994
), Ixanthus Griseb. (Gentianaceae) in the Canary Islands (Struwe et al., 1998
; Thiv, Struwe, and Kadereit, 2000
), and Hesperomannia A. Gray (Asteraceae) in the Hawaiian Islands (Kim et al., 1998
).
Seven major volcanic islands, which are situated in close proximity to the western Sahara coast comprise the Canary Islands. It has been suggested that many of the endemic species on these islands have a recent origin from the Mediterranean (Francisco-Ortega et al., 1997a, 1999
; Struwe et al., 1998
; Carvalho and Culham, 1998
; Mort et al., 2000
; Thiv, Struwe, and Kadereit, in press
). In contrast, other endemic species have been linked to the boreotropical flora that existed in most of the northern Hemisphere during the Tertiary (Quézel, 1978
; Mai, 1989
). However, some Canarian endemics have been associated with a xerophytic flora that existed in most of the Saharan-Sahel belt during the late Miocene and Pliocene (Quezel, 1978, 1983
). It has been suggested that this flora, known as the Rand Flora, originated in southeastern parts of South Africa in the Paleocene (Quézel, 1978
; reviewed by Marrero, Almedia, and González-Martín, 1998
). The Rand Flora replaced the tropical and temperate rain forests that existed in the Sahara-Sahel belt during the Paleocene and Oligo-Miocene, respectively (Quézel, 1978
). The existence of this flora is supported by the large number of disjunct taxa distributed along a band stretching from the Namibia desert to the Western Sahara via east Africa (Hamilton, 1974
; Jürgens, 1997
).
The Gonosperminae are one of the 12 currently recognized subtribes of the Anthemideae (Asteraceae) (Bremer and Humphries, 1993
), and provide one of the putative examples of disjunct distributions between the Canary Islands and South Africa (Heywood and Humphries, 1977
; Källersjö, 1985
; Bremer and Humphries, 1993
). The geographical distribution of members of this subtribe appears to support the hypothesis of a Tertiary link between the Canarian and the Rand Floras. The Gonosperminae (Table 1) are composed of two genera endemic to the Canary Islands [i.e., Gonospermum (four species) and Lugoa (one species)] and Inulanthera. The latter genus has ten species restricted to southern Africa (Table 1), although most of the species occur mainly in the Natal-Transvaal zone in northeastern South Africa. Inulanthera was formerly included in the South African genus Athanasia. However, it was elevated to generic level on the basis of chemical and morphological evidence (Källersjö, 1985
).
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A cladistic analysis of the Anthemideae using morphological, cytological and chemical traits provided phylogenetic support for the monophyly of the Gonosperminae (Bremer and Humphries, 1993
). A link between the Canarian and southern Africa genera was previously suggested by Heywood and Humphries (1977)
and Källersjö (1985)
on the basis of inflorescence, leaf, and cypsela characters. However, chemical studies of acetylenes supported a close relationship between the endemic Canarian genera and Tanacetum rather than with any southern African genera (Bohlmann, Burkhardt, and Zdero, 1973
). Such a relationship was also suggested by Bremer and Humphries (1993)
, who indicated that it was likely that the Gonosperminae were related to part of the Tanacetinae.
Tanacetum, with 
150 species, is one of the most poorly understood genera of Anthemideae (Heywood and Humphies, 1977
; Bremer and Humphries, 1993
). Three species of Tanacetum are endemic to the island of Gran Canaria. Tanacetum oshanahanii is extremely rare, with only 15 plants known from a single population on the northern slopes of the lowland scrub of Gran Canaria (Marrero, Febles, and Suárez, 1989
). Tanacetum ptarmiciflorum is also extremely rare and is known only from two populations of the high-altitude pine forest of central Gran Canaria (Febles and Naranjo-Suárez, 1996a
). Tanacetum ferulaceum occurs on southern slopes of the lowland scrub of Gran Canaria where scattered populations with few plants have been reported (Febles and Naranjo-Suárez, 1996b
); however T. ferulaceum var. latipinnum (Svent.) G. Kunkel is restricted to northern slopes of this major ecological zone. Karyological, seed protein, and morphological studies also suggested that the Canarian Tanacetum species are so closely related to Lugoa and Gonospermum that they could be merged into a single endemic genus (Febles, Fernández-Peralta, and González-Aguilera, 1989a, b
; Febles, 1990, 1996
).
In a previous study (Francisco-Ortega et al., 1997b
), we presented a molecular phylogeny of 32 genera of the Anthemideae using the internal transcribed spacers (ITS) of the nuclear ribosomal repeat (nrDNA). The ITS tree indicated that most taxa restricted to Europe, the Mediterranean, Macaronesia, and East Asia formed a strongly supported monophyletic group. Basal to this "Eurasian Clade" were several taxa from South Africa and the Far East. We also showed that none of the taxa of the "Eurasian Clade" has a 17–19 bp insertion in the ITS2 region. However, low bootstrap values did not enable the establishment of well-supported groups among most of the genera of the "Eurasian Clade."
In this paper, we present an ITS phylogeny of Athanasia, Gonospermum, Inulanthera, Lugoa, and a selection of Canarian, Eurasian, North American, and Mediterranean species of Tanacetum as well as several additional genera of the Anthemideae. The first objective of this study was to construct a phylogeny of the Gonosperminae to determine whether the Canarian taxa are more closely related to Eurasian species of Tanacetum and other Eurasian species, or whether they represent a biogeographic link to southern African through Inulanthera. The second objective was to reconstruct the evolutionary history of the insular endemics.
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MATERIALS AND METHODS |
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TOPABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONLITERATURE CITED |
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; Watson, Evans, and Boluarte, 2000
). Thirteen species of ten Eurasian genera (i.e., Achillea, Anthemis, Argyranthemum, Matricaria, Otospermum, Phalacrocarpum, Prolongoa, Rhodanthemum, Santolina, Tripleurospermum) were also part of the ingroup (Francisco-Ortega et al., 1997b
; Table 1). Ursinia was selected as the outgroup because both morphological (Bremer and Humphries, 1993
) and molecular data (Kim and Jansen, 1995
; Watson, Evans, and Boluarte, 2000
) place it in a basal position in the Anthemideae.
DNA isolation, PCR amplification, and sequencing
Most of the total genomic DNAs were isolated from plants grown in the greenhouses of TEX or ORT. Isolations of some taxa used plant material collected from wild populations and stored in silica gel (Table 1) or from herbarium specimens (i.e., Tanacetum vulgare). The CTAB (cetyltrimethylammonium bromide) technique of Doyle and Doyle (1987)
was used, followed by purification by ultra-centrifugation in CsCl-ethidium bromide gradients. Strategies for PCR (Polymerase Chain Reaction) amplification followed protocols previously used with members of the tribes Anthemideae (Francisco-Ortega et al., 1997b
) and Inuleae (Francisco-Ortega et al., 1999
). PCR products were purified using the QIA-quick PCR purification kit (Qiagen Inc., Valencia, California, USA) and automated sequencing followed the methods outlined in Francisco-Ortega et al. (1999)
.
Sequence aligment and phylogenetic reconstructions
Boundaries of both ITS1 and ITS2 were determined by comparison to published sequences (Baldwin, 1992
; Francisco-Ortega et al., 1997b
). Multiple alignment of ITS sequences was performed using CLUSTAL X (Thompson et al., 1997
) with minor manual adjustments made. All phylogenetic analyses were performed using version 4.0d64 of PAUP* (Swofford, 1999
) with gaps treated as missing. In an additional analysis, gaps were also treated as separate binary characters (absence/presence), which did not effect the resulting phylogenies (data not shown).
An initial phylogenetic reconstruction was done with weighted parsimony analyses using transition:transversion ratios (ts/tv) estimated from the Maximum Likelihood (ML) analysis (see below, ts/tv = 1.9) and weights of 1.0 (unweighted parsimony), 1.1, 1.5, and 2.0 (Swofford et al., 1996
). All parsimony analyses were undertaken using heuristic searches with ACCTRAN, MULPARS, and the TBR options of PAUP using 100 random entries (Maddison, 1991
). Support for monophyletic groups was evaluated using 1000 bootstrap replicates (Felsenstein, 1985
) with ACCTRAN, MULPARS, and TBR options employed in a heuristic search using one random addition sequence of taxa. Limitations of computer memory necessitated restricting the maximum numbers of trees saved to 2000 in each replicate. Consistency Index (CI) (Kluge and Farris, 1969
) and Retention Index (RI) (Farris, 1989
) were also computed.
An additional phylogenetic reconstruction was obtained by ML method using the HKY85 model (Hasegawa, Kishino, and Yano, 1985
) with empirical base frequencies. Among-site rate variation was assessed by the 
-distribution model with estimation of shape parameter. The model for nucleotide substitution was based on estimation of the transition:tranversion ratios. Due to limitations in computer memory, the ML search was undertaken with a reduced number of taxa, including all species of Gonosperminae and Tanacetum and all taxa from South Africa. A heuristic search with a single random entry and the ACCTRAN, MULPARS, and TBR was calculated. Weighted (weights of 1.1, 1.5, and 2.0) and unweighted parsimony analyses were also undertaken with this reduced data set. Heuristic searches and estimation of bootstrap supports for these maximum parsimony analyses were calculated, as indicated above, for the data matrix which included all the taxa. The goals of this second analysis were to test the monophyly of the Canary Island taxa and to reconstruct their evolutionary history.
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RESULTS |
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TOPABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONLITERATURE CITED |
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), which is also present in the new taxa sequenced for this study. All species from southern Africa have this insertion, which is absent from the remaining taxa of the tribe. An aligned data matrix has been deposited in FTG and is available upon request from the senior author.
Phylogenetic analyses
The strict consensus trees based on the four weighted parsimony analyses have identical topologies (Fig. 1). There is a strong correlation between the geographical distribution of the taxa and this topology. Southern African species are in a basal position, while all Eurasian species and the Canarian members of the Gonosperminae are in a derived position sister to the South African genus Cymbopappus (bootstrap support of 92%). The ITS phylogeny suggests that the Gonosperminae are not monophyletic, and that the subtribe does not represent a biogeographic link between southern Africa and the Canary Islands. The Canarian Gonosperminae appear more closely related to Canarian Tanacetum species than to Inulanthera. The Canary Island taxa of Tanacetum and the Gonosperminae form a monophyletic lineage although this group is not strongly supported by the bootstrap value (40%). Three major lineages are evident in the Canary Islands, including the basalmost lineage of the three Tanacetum species endemic to Gran Canaria. The second lineage includes two Gonospermum species endemic to La Palma and El Hierro while G. fruticosum, G. gomerae, and monotypic Lugoa form the third lineage.
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The ML analysis of the data set that includes all species of Gonosperminae, Tanacetum, and representative South African Anthemideae yields one tree with a -Ln likelihood of 2182.447 (not shown). The transition:transversion ratio is 1.9, and the distribution has a shape parameter of 0.71. This tree has a similar topology to the strict consensus trees based on weighted parsimony (Fig. 2). The Canarian taxa form a monophyletic group with three major clades which is weakly supported (54% bootstrap).
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DISCUSSION |
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TOPABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONLITERATURE CITED |
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; Watson, Evans, and Boluarte, 2000
), suggests that the current subtribal classification of Bremer and Humphries (1993)
must be reevaluated. These molecular phylogenies of the Anthemideae indicate that Chrysantheminae is the only monophyletic subtribe. The lack of support for the current subtribal classification of the Anthemideae is also apparent in molecular phylogenies using the chloroplast gene ndhF and a wider taxonomic sampling of taxa (Watson, Evans, and Boluarte, in press
).
One major taxonomic implication of the ITS phylogeny is that the morphological synapomorphies (i.e., leaves large with many rounded lobes and pappus of teeth projected from the ribs) of the Gonosperminae are either plesiomorphic to the Canary Island taxa or they have originated twice in taxa from distant geographic regions. However, detailed morphological studies of the Canarian taxa of the Gonosperminae reveal that there is considerable variation for these traits (R. Febles, Jardín Botánico Viera y Clavijo, unpublished data). Gonospermum gomerae does not have leaves with rounded lobes. Cypselas without a pappus are found in individuals of G. fruticosum from El Hierro and in G. canariense and in G. elegans. Both Inulanthera and Gonospermum have their capitula in corymbs, a feature that has also been used to suggest a morphological connection between the Canarian and South African members of the Gonosperminae (Källersjö, 1985
). This trait, however, is extremely variable in the tribe and seems to be of little taxonomic value for assessing intergeneric or intertribal relationships.
The ITS phylogeny does not support the Canary Island endemic Lugoa as a distinct genus, because it is nested within Gonospermum. This placement agrees with morphological data; both genera have scales at the base of each floret. The major morphological difference between these genera is that Lugoa has radiate capitula, whereas those of Gonospermum are discoid. The endemic species of Tanacetum also have radiate capitula. However, this character has been demonstrated to be highly plastic in many Asteraceae genera, and is controlled by a single gene (Ford and Gottlieb, 1990
).
Biogeographic implications
There are several examples of plant groups with a disjunct distribution between the Macaronesian islands and southern or eastern Africa. Morphological comparisons suggested that these taxa are natural groups and that they represent floristic links between the Macaronesian archipelagos and Africa (reviewed in Bramwell, 1972, 1978, 1985
; Sunding, 1979
). The best known examples include: Echium L. (Boraginaceae) from Macaronesia and Lobostemum Lehm. (Boraginaceae) from South Africa (Bramwell, 1973
; Pérez de Paz and Pardo, 1994
); the Canarian endemic Phyllis L. (Rubiaceae) and the predominantly South African genera Anthospermum L. and Galopina Thunb. (Rubiaceae) (Puff, 1982
); Parolinia Webb (Brassicaceae) from the Canaries and the mostly east African Diceratella Boiss. (Brassicaceae) (Bramwell, 1985
); and the three Canarian genera of the Bencomia Webb & Berthel. alliance (Rosaceae) (i.e., Bencomia, Dendriopoterium Svent., and Marcetella Svent.), which have been associated with arborescent east African genera of the tribe Sanguisorbeae (i.e., Hagenia J.F. Gmel. and Cliffortia L.) (Bramwell, 1985
). However, few phylogenetic analyses have been produced that test these putative relationships between the Canary Islands and Africa. Two recent chloroplast DNA (cpDNA) phylogenies within the Rubiaceae (Bremer, 1996
; Andersson and Rova, 1999
) support a relationship between the Canarian endemic genus Phyllis and Anthospermum, Galopina and Nenax Gaertn.
In other cases, molecular phylogenies do not support putative biogeographic connections between the Canary Islands and south or east Africa. A combined ITS and cpDNA phylogeny of Echium strongly supports a close relationship between the Macaronesian and predominantly Mediterranean species of this genus (Böhle, Hilger, and Martin, 1996
) rather than to the South African genus Lobostemum Lehm. (Bramwell, 1973
; Pérez de Paz and Pardo, 1994
). The origin of the Bencomia alliance provides another example in which a relationhip between the floras of Macaronesia and distant regions of Africa is not supported by phylogenetic studies. The three endemic genera in the Canary Islands are part of a clade formed mostly by Mediterranean species of Sanguisorba L. and Sarcopoterium Spach. (Helfgott et al., 2000
).
We are not suggesting that biogeographical links between the floras of the Macaronesian islands and south and east Africa do not exist. However, in many cases these putative relationships are not based on a phylogenetic framework and, therefore. may not reflect true biogeographical connections. An example of the utility of phylogenetic studies for identifying floristic affinities between the Macaronesian islands and east Africa is provided by the two Canarian endemic species of Solanum L. (Solanaceae) (i.e., S. lidii Sunding and S. vespertilio Aiton). Morphological characters place these two taxa with the Mexican species S. tridynamum Dunal [Solanum sect. Nycterium (Vent.) Dunal], suggesting a floristic connection between the New World and Macaronesia (Whalen, 1984
). However, a cpDNA restriction site phylogeny (Olmstead and Palmer, 1997
) showed that the Canarian taxa are sister to east African Solanum, providing one of the clearest cases of a biogeographical link between Macaronesia and East Africa.
Interisland colonization and adaptive radiation
Very few studies of Macaronesian plants have identified monophyletic groups of species restricted to single islands (Francisco-Ortega et al., 1996a, b
; Kim et al., 1996
; Panero et al., 1999
; Mort et al., in press
). In most cases, interisland colonization between similar ecological zones has been the primary pattern of species diversification including the Aeonium Webb & Berthel. alliance (Crassulaceae), Argyranthemum, Crambe L. (Brassicaceae), Pericallis D.Don (Asteraceae), and the woody Sonchus L. alliance (Asteraceae). The only exceptions are in Argyranthemum and the woody Sonchus alliance in Madeira, where monophyletic assemblages of species occur on the same island but in different ecological zones. The Madeiran archipelago is situated 1000 km north of the Canaries, making dispersal between these two archipelagos much more difficult than among the Canary Islands. Therefore, it is not surprising that the Madeiran endemics of Argyranthemum and Sonchus form distinct monophyletic groups.
The ITS phylogeny of Gonospermum, Lugoa, and the Canarian species of Tanacetum enables an evaluation of the relative importance of interisland colonization and insular radiation in the evolution of Canary Island endemics. The three species of Tanacetum from the central island of Gran Canaria show insular radiation into three major ecological zones (Fig. 2). This is the first known case of a monophyletic plant group which has experienced several ecological shifts on a single island of the Canarian archipelago. In contrast, populations of Gonospermum and Lugoa from the western islands of La Gomera, El Hierro, La Palma, and Tenerife are correlated with major ecological zones (Fig. 2). The two endemics of the pine forest of La Palma and El Hierro form a monophyletic group. This pattern is also evident for the three lowland scrub species from different islands. Thus, the major mode of species diversification in the western Canary Islands is interisland colonization between the same ecological zones.
Within the broad limits of the lowland scrub, there is some degree of ecological specialization. Lugoa primarily occurs at low-elevation stands of this major ecological zone, but is restricted to the northeastern peninsula of Anaga. In contrast, G. gomerae tends to grow at higher elevations, and scattered populations are found in northeastern La Gomera. Likewise G. elegans is associated with the low-elevation dry pine forests of southern El Hierro, whereas G. canariensis has a broader ecological distribution and occurs in both the dry and subhumid pine forests of La Palma.
Conclusions
Molecular phylogenies are providing new perspectives to our understanding of the origin and evolution of the Macaronesian flora. The disjunct distribution between Macaronesia-northwest Africa and east Africa for many plant groups [e.g., Aeonium, Campylanthus Roth (Scrophulariaceae), Canarina L. (Campanulaceae), Erucastrum C. Presl. (Brassicaceae), Euphorbia balsamifera (Euphorbiaceae), Hemicrambe fruticulosa Webb (Brassicaceae), and "draco tree" Dracaena (Dracaenaceae)] clearly indicate that there are floristic links between the Canaries and distant regions of Africa (Sunding, 1979
; Bramwell, 1985
). Molecular phylogenies have confirmed these biogeographical patterns in some groups, but have rejected it for others. These phytogeographic connections cannot be extended to other elements of the flora until phylogenetic studies include all of the putative continental relatives. The same kind of generalization cannot be made regarding the evolutionary history of Macaronesian endemics. We have shown that the Canarian endemics of Gonospermum, Lugoa and Tanacetum have experienced both adaptive radiation (Tanacetum) and interisland colonization (Gonospermum-Lugoa). This pattern has also been reported for the Canarian and Madeiran species of Argyranthemum and Sonchus (Kim et al., 1996
; Francisco-Ortega et al., 1997a
). In Argyranthemum, hybridization has also been an important evolutionary process (Francisco-Ortega et al., 1997a
).
In other groups such as the Aeonium alliance (Crassulaceae) (Uhl, 1961
; Bramwell, 1977
; Liu, 1989
), Dactylis glomerata L. (Poaceae) (Lumaret, 1997
), Lotus L. subgen. Pedrosia Lowe (Fabaceae) (Ortega, 1976
), Sideritis L. (Lamiaceae) (Marrero, 1992
), and Tolpis Adanson (Jarvis, 1980
) changes in chromosome numbers also have been reported; however, this represents a small fraction of the endemic flora of the islands. Although chromosomal changes have played a role in the evolution of some groups, adaptive radiation, interisland colonization, and hybridization appear to be more important in species diversification of the endemic Macaronesian flora. The emerging picture from molecular phylogenies is that each group has unique evolutionary patterns in the islands. These patterns or modes can only be revealed after rigorous phylogenetic, morphological, ecological, and cytological studies.
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FOOTNOTES |
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6 Author for correspondence at Florida International University (e-mail: ortegaj{at}fiu.edu
).
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LITERATURE CITED |
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