Molecular Phylogenetics of the Macaronesian-Endemic Genus
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Molecular Ecology (2005) 14, 1177–1189 doi: 10.1111/j.1365-294X.2005.02487.x MolecularBlackwell Publishing, Ltd. phylogenetics of the Macaronesian-endemic genus Bystropogon (Lamiaceae): palaeo-islands, ecological shifts and interisland colonizations JENNIFER L. TRUSTY,*¶ RICHARD G. OLMSTEAD,† ARNOLDO SANTOS-GUERRA,‡ SUSANA SÁ-FONTINHA,§ and JAVIER FRANCISCO-ORTEGA* *Department of Biological Sciences, Florida International University, University Park Campus, Miami, FL 33199, USA †Department of Biology, University of Washington, PO Box 355325, Seattle, WA 98195, USA, ‡Jardín de Aclimatación de La Orotava, Calle Retama Num. 2, Puerto de La Cruz, E-38400, Tenerife, Canary Islands, Spain, §Parque Natural da Madeira/CEM, Caminho do Meio, Bom Sucesso, PT-9050-251, Funchal, Madeira, Portugal, ¶Fairchild Tropical Botanic Garden, 11935 Old Cutler Road, Coral Gables, FL 33156, USA Abstract A molecular phylogenetic study of Bystropogon L’Hèr. (Lamiaceae) is presented. We per- formed a cladistic analysis of nucleotide sequences of the internal transcribed spacers (ITS), of the nuclear ribosomal DNA, and of the trnL gene and trnL-trnF intergenic spacer of the chloroplast DNA. Bystropogon odoratissimus is the only species endemic to the Canary Islands that occurs in the three palaeo-islands of Tenerife. This species is not part of an early diverging lineage of Bystropogon and we suggest that it has a recent origin. This phylogenetic pattern is followed by most of the species endemic to the palaeo-islands of Tenerife. The two sections currently recognized in Bystropogon form two monophyletic groups. Taxa belonging to the section Bystropogon clade show interisland colonization limited to the Canary Islands with ecological shifts among three ecological zones. Taxa from the section Canariense clade show interisland colonization both within the Canary Islands and between the Canary Islands and Madeira. Speciation events within this clade are mostly limited to the laurel forest. The genus has followed a colonization route from the Canaries towards Madeira. This route has also been followed by at least five other plant genera with species endemic to Macaronesia. Major incongruences were found between the current infrasectional classification and the molecular phylogeny, because the varieties of Bystropogon origanifolius and Bystropogon canariensis do not form two monophyletic groups. The widespread B. origanifolius appears as progenitor of the other species in section Bystropogon with a more restricted distribution. Keywords: adaptive radiation, biogeography, evolution, molecular phylogenetics, oceanic islands, quantum speciation Received 20 October 2004; revision received 6 January 2005; accepted 6 January 2005 plant speciation processes in archipelagos worldwide Introduction (Baldwin et al. 1998; Juan et al. 2000; Emerson 2002; Silvertown The Macaronesian Islands comprise the Atlantic archipel- 2004; Valido et al. 2004). Research into the interisland rela- agos of the Azores, Madeira, Selvagens, Canaries, and Cape tionships of Macaronesian endemics gives insight into Verde. In the last 10 years, many evolutionary biology the relative roles of dispersal and ecological adaptation studies have focused on this region, and these island systems as evolutionary avenues (Francisco-Ortega et al. 1996, 2002; have played an important role in the understanding of Panero et al. 1999). However, none of these studies have focused on interpreting phylogenetic patterns in the frame- Correspondence: Javier Francisco-Ortega, Fax: 1305 3481986; E-mail: work of the geological history of Macaronesia. The island [email protected] of Tenerife (Canary Islands) has a complex geological history © 2005 Blackwell Publishing Ltd 1178 J. L. TRUSTY ET AL. Fig. 1 Geographical distribution of Bystro- pogon in the Canary and the Madeira Islands. The palaeo-islands of Adeje, Anaga, and Teno are indicated by hatched shading. and is a good model system to investigate these kind of The Macaronesian-endemic genus Bystropogon L’Hèr. questions. Three of the mountain systems of this island, (Lamiaceae) presents an opportunity to address the role Anaga, Adeje, and Teno, are considered ‘palaeo-islands’ played by the geologically old island areas in the diversi- (Ancochea et al. 1990; Marrero & Francisco-Ortega 2001; fication of island endemics. Bystropogon has seven species Marrero 2004; Fig. 1). These regions are estimated to be and four varieties (La Serna-Ramos 1984; Fig. 1). Two of between 4 (Anaga) and 12 (Adeje) million years (Myr) the species are restricted to the island of Madeira (Bystro- old; Teno is approximately 6 Myr old (Thirlwall et al. pogon maderensis and Bystropogon punctatus), while the rest 2000; Guillou et al. 2004). Volcanic activity during the late of the species are endemic to the Canary Islands. Among Tertiary and early Quaternary led to the merger of these the Canary Islands, only Tenerife and La Palma harbour three palaeo-islands, which eventually formed the current single-island endemics of this genus. Bystropogon odoratis- island of Tenerife approximately 1 million years ago (Ma) simus and Bystropogon plumosus are restricted to Tenerife, (Ancochea et al. 1990). These three regions have a high whereas Bystropogon wildpretii is endemic to La Palma. All number of endemics (Bramwell & Bramwell 1974; Santos- the species of Bystropogon are abundant with the exception Guerra & Fernández-Galván 1983; Martín et al. 1999), and of B. odoratissimus and B. wildpretti. some authors have suggested that they have some of the Bystropogon odoratissimus is restricted to the three palaeo- oldest plant lineages of the archipelago (reviewed by islands of Tenerife. This species has a disjunct distribution Marrero & Francisco-Ortega 2001; Marrero 2004). and is found only in Teno, Anaga, and Adeje. This unique © 2005 Blackwell Publishing Ltd, Molecular Ecology, 14, 1177–1189 BYSTROPOGON PHYLOGENY 1179 biogeographical pattern is not known for any other plant an extremely common understory species in the pine forest species of Tenerife and has led some authors to consider belt. Occasionally, this species can be found in the lowland B. odoratissimus to be part of an ancient lineage of the genus scrub and laurel forests areas of Tenerife. (Hernández & García 1996). In this study we present a molecular phylogenetic study Two widespread Bystropogon species, B. canariensis and of the genus Bystropogon based on nucleotide sequences B. origanifolius, are highly polymorphic and form two spe- of the nuclear and chloroplast genomes. The three major cies complexes. Bystropogon origanifolius has three varieties objectives of our study were (i) to determine if B. odora- restricted to Gran Canaria (var. canariae), El Hierro (var. tissimus is part of a early diverging lineage of Bystropogon ferrensis), and La Palma (var. palmensis). Bystropogon origan- and investigate the biogeographical role played by the ifolius var. origanifolius is endemic to the islands of La Gomera three palaeo-islands of Tenerife; (ii) to discuss the main and Tenerife. Bystropogon canariensis has two varieties. The ecological and geographical avenues followed by the genus type variety canariensis occurs on the islands of Gran Canaria, during its evolutionary history in the context of other La Palma, and Tenerife, while B. canariensis var. smithianus Macaronesian-endemic groups; and (iii) to determine if the occurs on four islands, La Gomera, El Hierro, La Palma, molecular phylogeny of the genus is concordant with the and Tenerife. latest taxonomic classification of Bystropogon. The latest taxonomic revision of Bystropogon produced by La Serna-Ramos (1984) recognized two sections: Bystro- Materials and methods pogon section Bystropogon and Bystropogon section Canariense La Serna. Bystropogon canariensis and the two Madeiran Plant materials species, B. maderensis and B. punctatus, were placed in Bystropogon section Canariense. The remaining four species The ingroup consisted of 17 taxa representing all the species comprise Bystropogon section Bystropogon. and varieties of Bystropogon in Macaronesia from the two The three species of Bystropogon section Canariense are sections currently recognized by La Serna-Ramos (1984). primarily restricted to the laurel forest ecological zone When a species was found on multiple islands, a single (Pruno hixae-Lauretea novocanariensis) (La Serna-Ramos 1984; representative from each island was included in the analysis. Capelo et al. 1999; Jardim & Francisco 2000). This vegetation Mentha L., Minthostachys (Benth.) Spach, Pycnanthemum zone is found on the northern slopes of the islands which Michx., and Ziziphora L. were chosen as the outgroups. The are under the direct influence of the humid and cool north- outgroup was selected based on a previous phylogenetic eastern trade winds and receive approximately 1000 mm study of the tribe Mentheae (Trusty et al. 2004). Details of of average rainfall per year (Fernández-Palacios 1999). the plant material, including voucher information, accession Two species of Bystropogon section Bystropogon (i.e. B. provenance, and nucleotide sequence identification, are origanifolius and B. wildpretii) are confined mostly to the pine listed in Table 1. forest ecological zone (Chamaecytiso-Pinetea canariensis) (La Serna-Ramos 1984). This ecological zone only occurs in the DNA extraction, PCR amplification, and sequencing Canary Islands and is situated above the laurel forest (on the northern slopes of the islands) or above the lowland DNA was extracted from either