Phylogeography of a Pantropical Plant with Sea-Drifted Seeds; Canavalia Rosea (Sw.) DC., (Fabaceae) 汎熱帯海流散布植
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(千葉大学学位申請論文) Phylogeography of a pantropical plant with sea‐drifted seeds; Canavalia rosea (Sw.) DC., (Fabaceae) 汎熱帯海流散布植物ナガミハマナタマメ (マメ科)の系統地理 2010 年7月 千葉大学大学院理学研究科 地球生命圏科学専攻 生物学コース Mohammad Vatanparast Phylogeography of a pantropical plant with sea‐drifted seeds; Canavalia rosea (Sw.) DC., (Fabaceae) July 2010 MOHAMMAD VATANPARAST Graduate School of Science CHIBA UNIVERSITY TABLE OF CONTENTS PAGES ABSTRACT 1 GENERAL INTRODUCTION 3 Pantropical plants with sea-drifted seeds species (PPSS) 5 A project on the phylogeography of the PPSS 6 A case study of PPSS: Hibiscus tiliaceus L. 7 Canavalia rosea: a genuine pantropical plant with sea-drifted seeds 8 Overview of this study 10 CHAPTER 1 12 PHYLOGENETIC RELATIONSHIPS AMONG CANAVALIA ROSEA AND ITS ALLIED SPECIES 12 1-1 Introduction 12 1-2 Materials and Methods 15 Taxon sampling 15 DNA extraction, PCR, and sequencing 16 Phylogenetic analyses based on cpDNA sequence data 18 Phylogenetic analyses based on ITS sequence data 19 1-3 Results 21 Phylogenetic analyses based on cpDNA sequence data 21 Phylogenetic analyses based on ITS sequence data 22 1-4 Discussion 24 Phylogenetic relationships among C. rosea and its related species 24 The phylogeographic break in the Atlantic Ocean 25 Origin of the Hawaiian endemic species 26 Future prospects for the evolutionary studies among C. rosea and its allied species 27 Tables and figures 29 i TABLE OF CONTENTS (CONTINUED) PAGES CHAPTER 2 40 GLOBAL GENETIC STRUCTURE OF CANAVALIA ROSEA; EVIDENCE FROM CHLOROPLAST DNA SEQUENCES 40 2-1 Introduction 40 2-2 Materials and Methods 44 Sampling 44 DNA extraction, PCR, and sequencing 44 Haplotype Composition and Network of C. rosea and its allied species 44 Population differentiation 45 Historical migration rates between oceanic regions 46 Estimates of recent migration rates 48 2-3 Results 49 Haplotype Composition and Network of C. rosea and its allied species 49 Population differentiation 50 Historical migration rates between oceanic regions 51 Estimates of recent migration rates 52 2-4 Discussion 54 Gene flow in Indo-Pacific Ocean through Long Distance Seed Dispersal 54 A strong genetic difference between the Indo-Pacific and Atlantic populations of C. rosea 56 2-5 Conclusion 59 Tables and figures 60 GENERAL DISCUSSION 74 REFERENCES 76 ACKNOWLEDGEMENTS 82 BIOGRAPHY 83 ii ABBREVIATIONS AEP Atlantic East Pacific AMOVA Analysis of molecular variance bp base pair cpDNA chloroplast DNA CTAB cetyltrimethyl ammonium bromide ESS Effective sample size FST Fixation index (F-statistices) IGS Intergenic Spacer ITS Internal Transcribed Spacers IWP Indo West Pacific MLE Maximum likelihood estimates nrDNA nuclear ribosomal DNA PCR Polymerase Chain Reaction PCR-SSCP PCR amplification with single-strand conformation polymorphism PCR-SSP PCR amplification with sequence specific primers PPSS Pantropical Plants with Sea-drifted Seeds RCA Rolling Circle Amplification SAMOVA Spatial Analysis of Molecular Variance iii ABSTRACT This study intends to examine the importance of long distance seed dispersal in the recurrent speciation and integration of pantropical plants with sea-drifted seeds (PPSS). I focused on one of genuine member of PPSS; Canavalia rosea (Sw.) DC. and its allied species. Chapter 1 is concerned with the phylogenetic relationships among C. rosea and its allied species as well as Hawaiian endemic species using chloroplast DNA (cpDNA) and internal transcribed spacers (ITS) of nuclear ribosomal DNA (nrDNA) sequences. Phylogenetic analyses using nucleotide sequences of 6 cpDNA regions (ca. 6000 bp) as well as nrDNA ITS for C. rosea and its related species suggested that rapid speciation might occurred among C. rosea and its related species. The phylogenetic results also suggested that Hawaiian endemic subgenus Maunaloa, was monophyletic and closely related to subgenus Canavalia than to other subgenera (Wenderothia and Catodonia). The results suggests that the Hawaiian subgenus originated by single colonization to Hawaiian archipelagos by sea-dispersal. In chapter 2, spatial genetic structure of cpDNA sequences were studied for C. rosea and its related species. In total 515 individuals from 48 populations were surveyed based on partial sequences of 6 cpDNA regions (ca. 2000 bp). Statistical analyses (FST-based and coalescent-based methods) did not show significant genetic differentiation among the C. rosea populations over whole Pacific and Indian Oceanic regions and also within Atlantic region. This suggests that significant gene flow by long distance dispersal of sea-drifted 1 seeds occurs among these oceanic regions. On the other hand, the results of phylogenetic and population genetic analyses confirm the genetic differentiation of the Atlantic populations. This suggests that African and American land masses played roles as geographical barriers to gene flow by sea-dispersal. However, partial gene flow was detected between Atlantic and Indian oceanic regions which suggest that the unity of the species in global scale is kept by long distance seed dispersal over the African continent. Directional gene flow within Atlantic region might be corresponded to the variation of the strength of tropical Atlantic’s major currents which regarded as transatlantic dispersal in Atlantic region. Moreover, highly differentiated populations of C. rosea were detected in the southern Brazil. The South Equatorial Current bifurcating at the north-eastern horn of Brazil to the northward and southward appears to be potential barrier to gene flow and may promote the genetic differentiation of the C. rosea populations in southern Brazil. 2 GENERAL INTRODUCTION “… mammals have not been able to migrate, whereas some plants, from their varied means of dispersal, have migrated across the wide and broken interspaces.” (Darwin, 1859) The term dispersal has two different but interrelated functions in most species. The first one is, range expansion of species, and the second one, gene flow within and among populations. Range expansion is necessary for almost all species, so they have various strategies to expand their distribution ranges (Linhart & Grant, 1996). However, the wider distribution range arisen from dispersal causes high genetic heterogeneity among populations because of increased levels of selection within local populations and/or because of limited levels of genetic exchange among the local populations (Heywood, 1991; Hamrick & Nason, 1996; Linhart & Grant, 1996). When genetic heterogeneity among populations becomes significantly enough, local populations can evolve and eventually form a distinct species (Wright, 1931; Ennos, 1994; Bohonak, 3 1999). Gene flow is one of the most important processes for species to evolve as cohesive units in their distribution range (Mayr, 1963; Levin, 2000; Morjan & Rieseberg, 2004). In fact, if levels of gene flow within and among populations become high (e.g. greater than four migrants per generation), it homogenize the species and prevents genetic divergence of local populations. In many plant species, populations are spatially isolated from each other, often by hundreds of meters or more and seed dispersal represents the only way by which populations can exchange individuals or to expand the distribution ranges (Cain et al., 2000). As there are geographical, ecological or behavioral barriers to seed dispersal, most plant species are not distributed globally (Howe & Smallwood, 1982; Cain et al., 1998; Willson & Traveset, 2000). The biggest barrier for land plants will be the ocean, so that most of the floristic compositions are generally quite different among continents which are divided by oceans. However, there are a few plant species that characterized by their extremely wide distribution ranges across littoral areas in tropics and subtropics worldwide. They are called “pantropical plants with sea-drifted seeds” (Takayama et al., 2006; 2008), referred to as PPSS. A few PPSS are known from various families which can roughly divide into 2 categories. One is genuine PPSS in which a single species distributes around the globe. Canavalia rosea (Sw.) DC. (Fabaceae) and Ipomoea pes-caprae (L.) R. Br. (Convolvulaceae) are in this category. The other one is Sub-PPSS, in which small numbers of closely related species compose the global distribution in total. Hibiscus tiliaceus L., with H. pernambucensis Arruda (Malvaceae), Vigna marina (Burm.f.) Merr. with V. luteola (Jacq.) Benth. (Fabaceae), and species of Rhizophora L. and Entada Adans. are in this category. 4 Pantropical plants with sea-drifted seeds species (PPSS) The main dispersal mode of PPSS is sea-dispersal. Almost all PPSS have seeds or fruits that can float in sea water for long time. The seed coats of these species are hard with lightweight cotyledons and there are air spaces between the folds of the cotyledons which help the seeds to stay impermeable on sea water (Nakanishi, 1988; Loewer, 2005; Thiel & Haye, 2006). Nakanishi (1988) investigated germination and buoyancy of seeds and fruits of seventeen maritime species (including most of PPSS), after immersion in artificial seawater. He revealed that all seeds and fruits tested in the study continued to float in sea water for at least three months (Nakanishi, 1988). These characteristics help PPSS to distribute in wide areas in equatorial belt around the globe. Their distribution ranges are consistent with the areas where the average temperature of Ocean water is around 20 ͦC. In the West Atlantic, they are distributed from Florida to the Uruguay in Southern West Atlantic. In East Atlantic