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2 Centre d'Ecologie Fonctionnelle et Evolutive (UPR 9056), C.N.R.S., 1919 route de Mende, 34293 Montpellier Cedex 5, France, and Institut des Sciences de l'Evolution (UMR CNRS 5554), CC 065, Université Montpellier II, Place Eugène Bataillon, 34095 Montpellier Cedex, France; and 4 Laboratoire de Biologie des Populations d'Altitude, CNRS UMR 5553, Université Joseph Fourier, B.P. 53, 38041 Grenoble Cedex 9, France
Received for publication November 16, 1999. Accepted for publication March 16, 2000.
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ABSTRACT |
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 TOP ABSTRACT INTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONLITERATURE CITED |
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Key Words: Caesalpinioideae • cpDNA • introgression • Leguminosae • Leonardoxa • myrmecophytes • phylogeny
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INTRODUCTION |
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TOPABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONLITERATURE CITED |
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Among the six Leonardoxa, two nonmyrmecophytic species (L. romii (De Wild.) Aubrév. and L. bequaertii (De Wild.) Aubrév.) occur in the Congo basin. Léonard (1993)
put these two species into a new genus, Normandiodendron, but he appears not to have been followed by most herbaria, and the two species are usually still classed under Leonardoxa. The four other described taxa of Leonardoxa are located in lower Guinea forests from extreme eastern Nigeria to Gabon. Long considered together as simply L. africana (Baill.) Aubrev., they are treated in a recent morphological analysis as four distinct mostly allopatric subspecies of the L. africana complex (McKey, 2000
). For morphological characters both related and not related to ant-plant interaction, a complete analysis of the L. africana complex revealed strong differences among subspecies, but little variation between populations within each subspecies (McKey, 2000
). Leonardoxa africana subsp. gracilicaulis McKey is a nonmyrmecophyte, only involved in loose associations with opportunistic ants attracted to foliar nectaries (McKey, 1991
). It occurs in southern Cameroon (Fig. 1), Equatorial Guinea, and Gabon. It is most common on hills (submontane forests and lowland forests transitional to them [Gaume, 1998
; McKey, 2000
]). Leonardoxa africana subsp. rumpiensis McKey is a myrmecophyte with hollow internodes, inhabited by a variety of opportunistic ants (Chenuil and McKey, 1996
). This subspecies appears to be very localized in the Rumpi Hills, in the southwestern part of Cameroon (Fig. 1). Leonardoxa africana subsp. letouzeyi McKey is a myrmecophyte found in lowland forests in western Cameroon and extreme eastern Nigeria (Fig. 1). While its juvenile individuals can be occupied by several species of arboricolous ants, mature trees of L. a. letouzeyi are associated specifically with a single ant species, Aphomomyrmex afer Emery (McKey, 1991, 2000
; Gaume and McKey, 1998
). Leonardoxa a. subsp. africana McKey (studied by McKey, 1984
) is morphologically the most specialized Leonardoxa myrmecophyte. It occurs in lowland coastal forest in southern Cameroon (Fig. 1). Leonardoxa a. africana is associated, as early as the seedling stage, with one specific mutualist ant species, Petalomyrmex phylax Snelling.
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). When data exist, they usually concern phylogeny of the ants, e.g., Azteca ants that colonize Cecropia trees (Ayala et al., 1996
) or pseudomyrmecine ants associated with a variety of host-plant families (Ward, 1991
). In the genus Leonardoxa, although the relationships between the two specialized ants (P. phylax and A. afer) are well known (Chenuil and McKey, 1996
), little information is available to infer phylogenetic relationships of the plants. Based on morphological characters not directly related to ant–plant interactions, a first study of only three of the four L. africana subspecies (McKey, 1991
) suggested that the nonmyrmecophytic L. a. gracilicaulis is more primitive in comparison to the two myrmecophytic subspecies that were considered. The first attempt using molecular characters to determine phylogenetic relationships in the genus Leonardoxa was based on Internal Transcribed Spacer (ITS) markers and examined only the four subspecies of the L. africana complex (Chenuil and McKey, 1996
). However, the ITS sequences presented extremely low variation among these four taxa. Only one informative site on 550 sequenced nucleotides was found (Chenuil and McKey, 1996
). Inferring phylogenetic relationships in the genus Leonardoxa would thus require using DNA markers, which evolve more rapidly than do ITS sequences.
Because of its low evolutionary rate, chloroplast DNA (cpDNA) has long been used for phylogenetic studies at high taxonomic levels. Phylogenetic relationships using rbcL sequences, for example, have been inferred at family levels or higher (Zurawski, Clegg, and Brown, 1984
; Chase et al., 1993
). More recently, the design of several universal primers for the amplification of noncoding cpDNA sequences (Taberlet et al., 1991
; Demesure, Sodzi, and Petit, 1995
) has extended the utility of cpDNA to lower taxonomic levels (Olmstead and Palmer, 1994
). Noncoding cpDNA sequences have therefore been successfully used to infer phylogenetic relationships both at intrageneric (Gielly and Taberlet, 1994
; Gielly et al., 1996
; Bruneau, 1996
; Maguire et al., 1997
; Asmussen and Liston, 1998
; Cros et al., 1998
) and intraspecific (Demesure, Comps, and Petit, 1996
; El Mousadik and Petit, 1996
; Dumolin-Lapègue et al., 1997
; Petit et al., 1997
) levels. CpDNA noncoding sequences could thus help to clarify phylogenetic relationships in the genus Leonardoxa and to better understand the evolution of ant–plant mutualism.
The purpose of this paper was to examine phylogenetic relationships in the genus Leonardoxa based on the analysis of the cpDNA trnL (UAA) intron and cpDNA trnL (UAA)–trnF (GAA) intergenic spacer sequences.
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MATERIALS AND METHODS |
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TOPABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONLITERATURE CITED |
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). Preliminary results on phylogenetic relationships in Caesalpinioideae based on trnL intron sequences (Anne Bruneau, Department of Biological Sciences, Montréal University, personal communication) confirm that Brachystegia zenkeri is a valid outgroup species with regard to Leonardoxa, Loesenera, and Hymenostegia.
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20 mg of leaf tissue dried in silica gel (then snap-frozen in liquid nitrogen) with the DNeasy Plant Mini Kit from Qiagen (Courtaboeuf, France), following the manufacturer's protocol. Double-stranded DNA amplifications were performed in a 25-µL volume containing 2.5 mmol/L MgCl, 200 µmol/L of each dNTP, 1 µmol/L of each primer, and 1 U of AmpliTaq GoldTM polymerase (Perkin-Elmer, St Quentin en Yvelines, France). The trnL (UAA) intron was amplified with primers "c" (5'-CGAAATCGGTAGACGCTACG-3') and "d" (5'-GGGGATAGAGGGACTTGAAC-3') (Taberlet et al., 1991
), the trnL (UAA)–trnF (GAA) intergenic spacer was amplified with primers "e" (5'-GGTTCAAGTCCCTCTATCCC-3') and "f" (5'-ATTTGAACTGGTGACACGAG-3') (Taberlet et al., 1991
). Following an activation step of 10 min at 95°C for the enzyme (Perkin-Elmer specification), the Polymerase Chain Reaction (PCR) mixture underwent 35 cycles of 30 s at 95°C, 30 sec at 50°C, and 2 min at 72°C. To remove excess primers and deoxynucleotide triphosphates after amplification, PCR products were purified on QiaQuick PCR columns, according to manufacturer's instructions. Sequencing was performed, on both strands, using the ABI PRISMTM Dye Terminator Cycle Sequencing Ready Reaction Kit (Perkin-Elmer) in a 20-µL volume containing 20 ng of purified DNA and 3.2 pmol of amplification primer, according to the manufacturer's specifications. Sequencing reactions underwent 25 cycles of 30 sec at 96°C, 30 sec at 50 °C, and 4 min at 60°C. Following this step, excess dye terminators were removed by a spin-column purification. Sequencing reactions were electrophoresed for 6 h on a ABI PRISMTM 377 DNA sequencer (Perkin Elmer) in a 5% Long RangerTM gel (FMC).
Data analysis and phylogeny assessment
Multiple alignment of the sequences was obtained using the CLUSTAL program (Higgins, Fuchs, and Blesby, 1992
) implemented in the Sequence Navigator 1.0.1 software (Perkin-Elmer). The different mutational events (substitutions as well as insertions/deletions) were coded in a single matrix of unordered multistate characters, the nucleotide stretch corresponding to one insertion/deletion (or two overlapping insertions/deletions) being conservatively treated as a single site (Gielly and Taberlet, 1994
). A maximum parsimony analysis was conducted using the beta version 4.0.0b2 of PAUP (written by David L. Swofford) after random addition of sequences. The phylogenies were assessed for each region using the branch and bound method of PAUP (character optimisation ACCTRAN, MULPARS and TBR branch swapping options). The robustness of nodes was inferred by a bootstrap analysis of 2000 replicates of the previous branch and bound search (Felsenstein, 1985
).
Preliminary studies on Caesalpinioideae based on trnL intron sequences (Anne Bruneau, personal communication) have shown that taxa of the tribe Detarieae are characterized by a large AT-rich insertion, which can be highly homoplasious. In our sequences, this insertion corresponds to the region between bp 360 and bp 470 (Anne Bruneau, personal communication). This region includes eight mutations, of which four are informative. We conducted analyses both including and excluding this region and found that the topology of the single most parsimonious tree was the same in both cases. We thus decided to retain this region in the analyses presented here, trnL intron sequences alignments being unambiguous for the taxa considered.
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RESULTS |
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TOPABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONLITERATURE CITED |
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Within the L. africana complex, three major cpDNA clades (Fig. 2) can be identified. Clade (1) concerns L. a. letouzeyi from Korup. Clade (2) groups three populations of the specialized myrmecophyte L. a. africana (all populations of this taxon studied except for Southern Bakundu) and three populations of L. a. gracilicaulis (all studied except for Nta Ali). Less supported than the two others (defined by only one character), clade (3) groups several populations belonging to different subspecies.
The examination of these clades shows that the different populations of L. africana cluster together partly independently of their taxonomic status: variations in cpDNA sequences do not entirely match with the distinct morphological entities. For example, sequences for three populations of L. a. africana, a specialized myrmecophyte, and three populations of L. a. gracilicaulis, the nonmyrmecophyte, are nearly identical, with one single mutational event in one population of L. a. gracilicaulis. Despite a high degree of morphological and ecological divergence, most of the populations of L. a. africana and L. a. gracilicaulis are thus grouped in the same clade.
However, populations sharing the same cpDNA sequences are not haphazardly located, and tree analysis clearly reveals a geographical structuring in cpDNA polymorphism (Fig. 3): (1) Leonardoxa a. letouzeyi from Korup, corresponding to our first clade, is the westernmost population of Leonardoxa we examined. (2) The geographical location of the six populations corresponding to the second clade suggests that this clade represents the southern part of the range of the L. africana complex. (3) The populations of the third clade are all located geographically between Korup and the six populations grouped in the second clade. Leonardoxa a. rumpiensis seems closely related to the northernmost population of L. a. africana from Southern Bakundu. Further to the north, L. a. letouzeyi from Islaib Road and the nonmyrmecophyte L. a. gracilicaulis from Nta Ali, the northernmost population of L. a. gracilicaulis, have unresolved positions as part of the third clade.
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DISCUSSION |
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TOPABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONLITERATURE CITED |
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had removed L. bequaertii and L. romii from Leonardoxa, establishing for these two Congolean species the genus Normandiodendron. This separation was justified by observations on seedling morphology and several other characters. However, this generic delimitation may not be supported by several other morphological characters (F. Breteler, Department of Plant Taxonomy, Wageningen Agricultural University, personal communication), and in current practice the two species are still attached to Leonardoxa. Our study shows clearly a relatively strong divergence between sequences of the L. africana complex and those of the two Congolean Leonardoxa species. Even in our limited sampling of other Detarieae genera, they are separated by three species belonging to two different genera, Hymenostegia and Loesenera, that were considered as potential outgroups to Leonardoxa. Leonardoxa bequaertii and L. romii should thus not be considered as species of Leonardoxa. While generic limits are presently unclear in tribe Detarieae (F. Breteler, personal communication), our results strongly support the separation of the two Congolean species from Leonardoxa as proposed by Léonard (1993)
.
The Leonardoxa africana complex
In recent studies, cpDNA noncoding regions have consistently exhibited lower levels of informative characters than do nuclear loci such as 18–28S ribosomal ITS (Gielly et al., 1996
; Small et al., 1998
; Kim et al., 1999
). Within the L. africana complex, cpDNA markers seem to provide more phylogenetic information than ITS. In sequencing 1300 bp of two noncoding cpDNA regions, 13 phylogenetically informative characters were found for the four L. africana subspecies considered by Chenuil and McKey (1996)
, whereas only one was found for the 550 sequenced nucleotides of the ITS locus (Chenuil and McKey, 1996
). However, sampling in each of the two studies is not comparable. The ITS regions were sequenced only for one individual of each of the four subspecies of the L. africana complex. We thus have no certitude about the comparison of evolutionary rates in nuclear and chloroplast markers studied for Leonardoxa.
Although divergence seems higher for cpDNA noncoding sequences than for ITS sequences, relationships in the L. africana complex remain largely unresolved. For example, it is impossible to distinguish with these neutral molecular markers between the specialized mymecophyte L. a. africana and the nonmyrmecophyte L. a. gracilicaulis, despite the high degree of morphological and ecological divergence between the two subspecies. Moreover, in the L. africana complex, variation in cpDNA sequences does not reflect morphological variation between putative subspecies (McKey, 2000). Several nonexclusive hypotheses could explain the lack of congruence between clades suggested by chloroplast and morphological characters in L. africana.
1) For plants, predicting the genetic cohesiveness of a group using only morphological characters can be difficult (Schaal et al., 1998
) because morphological divergences between alleged subspecies could be due only to environmental conditions, or to parallel evolution of morphological characters in the different populations. In our case, the division of L. africana into four taxonomic entities could be unjustified, and variations in morphological characters would be explained by a high plasticity of the species in relation to variable environmental pressures, such as herbivory. However, morphological characters both related and unrelated to ant–plant relationships are strongly congruent in all populations of each assumed subspecies and character differences are maintained when plants are grown under similar environmental conditions (McKey, 2000
). Moreover, two extremely divergent forms of L. africana are found side by side in the locality of Boundé, which is inconsistent with the hypothesis of an environmental influence on morphological characters. This sole zone of contemporary sympatry between two L. africana subspecies, represented here by populations in Boundé, is interpreted as a secondary contact between L. a. africana and L. a. gracilicaulis, the latter having colonized this lowland site from nearby hills, by way of the river (McKey, 2000
). Of the four subspecies, these two represent the two morphological extremes, and maintain their distinctness in this zone of sympatry. For all these reasons, we do not retain the hypothesis that morphological divergences found between the different Leonardoxa would be only explained by different environmental conditions.
2) A possible explanation for the low molecular divergence could be that divergence in the L. africana complex occurred recently (Orr and Smith, 1998
), such that neutral markers, such as ITS, cpDNA introns, and intergenic spacers, would not have had sufficient time to be fixed in the different populations. In contrast, morphological characters, which can be under strong selection pressures, may be highly differentiated between sites. Was divergence in the L. africana complex relatively recent, i.e., during the Pleistocene? The limited degree of phenotypic differentiation between subspecies of L. africana, and their distribution patterns, resemble patterns in some vertebrate species of central and west African forests. In these (Grubb, 1982
; Mayr and O'Hara, 1986
; Amiet, 1987
) and in some plant groups (Sosef, 1994
), such patterns are usually postulated to be due to range shifts (especially reduction to refugia) and genetic differentiation during Pleistocene climatic fluctuations. The region occupied by the L. africana complex is known to have undergone climatic-vegetational cycles, with shifts in elevational distribution of different vegetation types during the Pleistocene (Maley, 1996
). Under this hypothesis, the divergence between subspecies of L. africana would, as postulated by Chenuil and McKey (1996)
, be much more recent than that between their associated specific ants, presumed to be older than 4 mya (millions of years), and associated ants and plants could not have cospeciated. However, tropical tree species sometimes present relatively low degrees of divergence despite surprisingly long periods of separation (e.g., morphological divergence between taxa endemic to East African coastal forests and their relatives in the central African forest block [Lovett, 1993a
, b]). Moreover, this hypothesis alone cannot explain why the geographical distribution of chloroplast alleles seems not to be random.
3) Lack of congruence between chloroplast and morphological characters in a phylogenetic analysis could reflect an ancestral polymorphism in cpDNA, each current population having haphazardly fixed one allelic form or another (Rieseberg and Brunsfeld, 1992
; Mason-Gamer, Holsinger, and Jansen, 1995
). For the L. africana complex, however, the distribution of chloroplast alleles seems not to be random: a comparison of cpDNA phylogenetic relationships with the location of each population in Cameroon underlines the existence of a geographical structuring.
4) An alternative or complementary hypothesis to ancestral polymorphism or to recent evolution would be past introgressive events (Rieseberg and Brunsfeld, 1992
; Mason-Gamer, Holsinger, and Jansen, 1995
; Soltis and Kuzoff, 1995
) between populations of different subspecies, combined with strong directional selection in certain environments that created morphological divergence despite gene flow (Orr and Smith, 1998
). This hypothesis is only applicable to allopatric (or parapatric) taxa and could thus explain the lack of molecular divergence between allopatric subspecies of L. africana. Chloroplast capture is considered to be an important factor that can distort phylogenetic relationships at low taxonomic levels (Soltis and Kuzoff, 1995
). This hypothesis would be in accordance with the observation, for the L. africana complex, of a geographical structuring in cpDNA polymorphism. Moreover, observations of some morphological characters support the hypothesis of hybridization events. For instance, L. a. gracilicaulis from Nta Ali has strong hybrid morphological characters, such as slightly swollen stems and some cauliflorous individuals (whereas L. a. gracilicaulis from other populations have axillary inflorescences on young twigs [Gaume, 1998
; McKey, 2000
]). The presence of L. a. letouzeyi in lowland forests at the base of Nta Ali (L. a. gracilicaulis is restricted to the summit of the hill, above 1000 m) suggests the possibility of pollen exchange between L. a. gracilicaulis and L. a. letouzeyi, despite their supposed different pollinators (McKey, 2000)
. Similarly, the northernmost population of L. a. africana, from the Southern Bakundu Forest Reserve, shows some characters that may be affected by hybridization. Although the population of Southern Bakundu can be unequivocally assigned to L. a. africana (McKey, 2000
), some characters, such as flower color (flowers are violet, like those of L. a. rumpiensis, whereas L. a. africana from more southerly populations have pink flowers [Gaume, 1998
; McKey, 2000
]) suggest that past introgression events could have occurred in this population. Ant associations in this population of L. a. africana also suggest that it may have had a complex history. The mutualist ant Petalomyrmex phylax specifically associated with L. a. africana in all other populations is absent here, but a specific parasite of the L. a. africana x P. phylax mutualism (the myrmicine Cataulacus mckeyi), is present, along with a diversity of other opportunistic ants (McKey, 2000
).
Conclusions
The analysis of cpDNA sequences in the genus Leonardoxa emphasizes the complexity of relationships between morphological and molecular markers. In the L. africana complex, the lack of congruence between clades suggested by morphological and molecular characters, as well as the low level of cpDNA divergence between populations, suggests the possibility of gene flow or introgressive events between parapatric subspecies. The comparison of phylogenetic data from nuclear markers with our chloroplast data should permit us to examine the hypothesis of past introgressive events in Leonardoxa. This represents the next step in our attempt to understand the evolutionary history of ant–plant associations in this genus.
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FOOTNOTES |
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3 Author for reprint requests (e-mail: brouat{at}cefe.cnrs-mop.fr
).
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LITERATURE CITED |
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TOPABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONLITERATURE CITED |
|---|
Asmussen, C. B., And A. Liston. 1998 Chloroplast DNA characters, phylogeny, and classification of Lathyrus (Fabaceae). American Journal of Botany 85: 387–401
Ayala, F. J., J. K. Wetterer, J. T. Longino, And D. L. Hartl. 1996 Molecular phylogeny of Azteca ants (Hymenoptera: Formicidae) and the colonization of Cecropia trees. Molecular Phylogenetics and Evolution 5: 423–428[CrossRef][ISI][Medline]
Breteler, F. 1995 The boundary between Amherstieae and Detarieae (Caesalp.). In M. D. Crisp and J. J. Doyle [eds.], Advances in Legume Systematics, part 7, 53–61. Royal Botanic Gardens, Kew, Richmond Surrey, UK
Bruneau, A. 1996 Phylogenetic and biogeographical patterns in Erythrina (Leguminosae: Phaseoleae) as inferred from morphological and chloroplast DNA characters. Systematic Botany 21: 587–605
Chase, M. W., et al. 1993 Phylogenetics of seed plants: an analysis of nucleotide sequences from the plastid gene rbcL. Annals of the Missouri Botanical Garden 80: 528–580[CrossRef][ISI]
Chenuil, A., and D. McKey. 1996 Molecular phylogenetic study of a myrmecophyte symbiosis: did Leonardoxa/ant associations diversify via cospeciation? Molecular Phylogenetics and Evolution 6: 270–286[CrossRef][ISI][Medline]
Cros, J., M. C. Combes, P. Trouslot, F. Anthony, S. Hamon, A. Charrier, and P. Lashermes. 1998 Phylogenetic analysis of chloroplast DNA variation in Coffea L. Molecular Phylogenetics and Evolution 9: 109–117[CrossRef][ISI][Medline]
Davidson, D. W., and D. McKey. 1993 Ant-plant symbioses: stalking the Chuyachaqui. Trends in Ecology and Evolution 8: 326–332[CrossRef]
Demesure, B., B. Comps, and R. J. Petit. 1996 Chloroplast DNA phylogeography of the common beech (Fagus sylvatica L.) in Europe. Evolution 50: 2515–2520[CrossRef][ISI]
———, N. Sodzi, and R. J. Petit. 1995 A set of universal primers for amplification of polymorphic non-coding regions of mitochondrial and chloroplast DNA in plants. Molecular Ecology 4: 129–131[Medline]
Dumolin-Lapegue, S., B. Demesure, S. Fineschi, V. Le Corre, and R. J. Petit. 1997 Phylogeographic structure of white oaks throughout the European continent. Genetics 146: 1475–1487[Abstract]
El Mousadik, A., and R. J. Petit. 1996 Chloroplast DNA phylogeography of the argan tree of Morocco. Molecular Ecology 5: 547–555[CrossRef][Medline]
Felsenstein, J. 1985 Confidence limits on phylogenies: an approach using the bootstrap. Evolution 39: 783–791[CrossRef][ISI]
Gaume, L. 1998 Mutualisme, parasitisme et évolution des symbioses plantes-fourmis: le cas de Leonardoxa (Légumineuse) et de ses fourmis associées. Ph.D. dissertation, Ecole Nationale Supérieure Agronomique de Montpellier, France
———, and D. McKey. 1998 Protection against herbivores of the myrmecophyte Leonardoxa africana (Baill.) Aubrev. T3 by its principal ant inhabitant Aphomomyrmex afer Emery. Comptes Rendus de l'Académie des Sciences de Paris, Sciences de la Vie/Life Sciences 321:593–601
Gielly, L., and P. Taberlet. 1994 The use of chloroplast DNA to resolve plant phylogenies: noncoding versus rbcL sequences. Molecular Biology and Evolution 11: 769–777[Abstract]
———, Y. M. Yuan, P. Küpfer, and P. Taberlet. 1996 Phylogenetic use of noncoding regions in the genus Gentiana L.: chloroplast trnL (UAA) intron versus nuclear ribosomal internal transcribed spacer sequences. Molecular Phylogenetics and Evolution 5: 460–466[CrossRef][ISI][Medline]
Grubb, P. 1982 Refuges and dispersal in the speciation of African mammals. In G. T. Prance [ed.], Biological diversification in the tropics, 537–553. Columbia University Press, New York, New York, USA
Higgins, D. G., R. Fuchs, and A. Blesby. 1992 CLUSTAL: a new multiple sequence alignment program. Comparative Applied Biosciences 8: 189–191
Kim, S.-C., D. J. Crawford, R. K. Jansen, and A. Santos-Guerra. 1999 The use of a non-coding region of chloroplast DNA in phylogenetic studies of the subtribe Sonchinae (Asteraceae: Lactuceae). Plant Systematics and Evolution 215: 85–99[CrossRef][ISI]
Léonard, J. 1993 Notes sur les genres Schotia Jacq. et Leonardoxa Aubrév., et sur le nouveau genre Normandiodendron J. Léonard (Caesalpiniaceae africaines). Bulletin du Jardin Botanique National de Belgique 1–4: 433–451
Lovett, J. C. 1993a Climatic history and forest distribution in eastern Africa. In J. C. Lovett and S. K. Wasser [eds.], Biogeography and ecology of the rain forests of eastern Africa, 23–29. Cambridge University Press, Cambridge, UK
———. 1993b Eastern Africa moist forest flora. In J. C. Lovett and S. K. Wasser [eds.], Biogeography and ecology of the rain forests of eastern Africa, 33–35. Cambridge University Press, Cambridge, UK
Maguire, T. L., J. G. Conran, G. G. Collins, and M. Sedgley. 1997 Molecular analysis of interspecific and intergeneric relationships of Banksia using RAPDs and non-coding chloroplast DNA sequences. Theoretical and Applied Genetics 95: 253–260[CrossRef][ISI]
Maley, J. 1996 The African rain forest—main characteristics of changes in vegetation and climate from the Upper Cretaceous to the Quaternary. Proceedings of the Royal Society of Edinburgh 104B: 31–73
Mason-Gamer, R. J., K. E. Holsinger, and R. K. Jansen. 1995 Chloroplast DNA haplotype variation within and among populations of Coreopsis grandifolia (Asteraceae). Molecular Evolution and Biology 12: 371–381
Mayr, E., and R. J. O'Hara. 1986 The biogeographic evidence supporting the Pleistocene forest refuge hypothesis. Evolution 40: 55–67
McKey, D. 1984 Interaction of the ant plant Leonardoxa africana (Caesalpiniaceae) with its obligate inhabitants in a rain forest in Cameroon. Biotropica 16: 81–99[CrossRef][ISI]
———. 1991 Phylogenetic analysis of the evolution of a mutualism: Leonardoxa (Cesalpiniaceae) and its associated ants. In C. Huxley and D. F. Cutler [eds.], Ant plant interactions, 310–334. Oxford University Press, Oxford, UK
———. 2000 Leonardoxa africana (Leguminosae: Caesalpinioideae): a complex of mostly allopatric subspecies. Adansonia, sér 3, 22: 71–109
Olmstead, R. G., and J. D. Palmer. 1994 Chloroplast DNA systematics: a review of methods and data analysis. American Journal of Botany 81: 1205–1224[CrossRef][ISI]
Orr, M. R., and T. B. Smith. 1998 Ecology and speciation. Trends in Ecology and Evolution 13: 502–505[CrossRef]
Petit, R. J., E. Pineau, B. Demesure, R. Bacilieri, A. Ducousso, and A. Kremer. 1997 Chloroplast DNA footprints of postglacial recolonization by oaks. Proceedings of the National Academy of Sciences, USA 94: 9996–10001
Rieseberg, L. H., and S. J. Brunsfeld. 1992 Molecular evidence and plant introgression. In P. S. Soltis, D. E. Soltis, and J. J. Doyle [eds.], Molecular systematics of plants, 151–176. Chapman and Hall, New York, New York, USA
Schaal, B. A., D. A. Hayworth, K. M. Olsen, J. T. Rauscher, and W. A. Smith. 1998 Phylogeographic studies in plants: problems and prospects. Molecular Ecology 7: 465–474[CrossRef]
Small, R. L., J. A. Ryburn, R. C. Cronn, T. Seelanan, and J. F. Wendel. 1998 The tortoise and the hare: choosing between noncoding plastome and nuclear ADH sequences for phylogeny reconstruction in a recently diverged plant group. American Journal of Botany 85: 1301–1315
Soltis, D. E., and R. K. Kuzoff. 1995 Discordance between nuclear and chloroplast phylogenies in the Heuchera group (Saxifragaceae). Evolution 49: 727–742[CrossRef][ISI]
Sosef, M. S. M. 1994 Refuge Begonias: taxonomy, phylogeny, and historical biogeography of Begonia sect. Loasibegonia and sect. Scutobegonia in relation to glacial rain forest refuges in Africa. Wageningen Agricultural University Papers, 94–1: Studies in Begoniaceae V. Wageningen Agricultural University, Wageningen, Netherlands
Taberlet, P., L. Gielly, G. Pautou, and J. Bouvet. 1991 Universal primers for amplification of three non-coding regions of chloroplast DNA. Plant Molecular Biology 17: 1105–1109[CrossRef][ISI][Medline]
Ward, P. S. 1991 Phylogenetic analysis of pseudomyrmecine ants associated with domatia—bearing plants. In C. Huxley and D. F. Cutler [eds.], Ant plant interactions, 335–352. Oxford University Press, Oxford, UK
Zurawski, G., M. T. Clegg, and A. D. H. Brown. 1984 The nature of nucleotide sequence divergence between barley and maize chloroplast DNA. Genetics 106: 735–749
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  S. Hartmann, J. D. Nason, and D. Bhattacharya Phylogenetic origins of Lophocereus (Cactaceae) and the senita cactus-senita moth pollination mutualism Am. J. Botany, July 1, 2002; 89(7): 1085 - 1092. [Abstract] [Full Text] [PDF]
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: L. a. africana; 
: L. a. gracilicaulis; 
: L. a. letouzeyi; 
: L. a. rumpiensis. B: Boundé; D: Dikomé Balué; E: Ebogo; Eb: Ebodjé; I: Islaib Road; K: Korup: M: Mamelles; MtK: Mont Kala; N: Nta Ali; S: Southern Bakundu
