Population genetics of threatened wild plants in Japan

Approximately one-fourth of Japan's native plant species are threatened with extinction. To conserve these species, it is critical to evaluate genetic diversity at species-level and population-level. Some factors, including population size and geographic distribution, are known to influence the population genetic diversity of wild plant species. This article briefly reviews the population genetic studies that have been conducted on wild threatened plants in Japan. A large population size or wide geographic distribution does not always lead to large genetic diversity, suggesting that historical factors such as speciation processes and population expansion often play more important roles in determining genetic diversity than the number of remnant individuals. The mating system of a species also affects genetic diversity; predominantly selfing species tend to have smaller genetic diversity than outcrossing congeners. Another issue of concern in the conservation genetics of wild plants in Japan is the genetic diversity of insular endemics, because Japan consists of many islands, and the insular flora contains many endemic and threatened species. Previous studies on endemic plants on the Bonin and the Ryukyu Islands are reviewed. Compared to the cases of the Bonin Islands or other oceanic islands, there is much larger genetic diversity in plants endemic to the Ryukyu Islands. This difference is probably the result of the differences in the geological history of these islands. Electronic Publication     

Deciphering the global phylogeography of a coastal shrub (Scaevola taccada) reveals the influence of multiple forces on contemporary population structure

The phylogeography of coastal plant species is heavily influenced by past sealevel fluctuations, dispersal barriers, and life-history traits, such as long-distance dispersal ability of the propagules. Unlike the widely studied mangroves, phylogeographic patterns have remained mostly obscure for other coastal plant species. In this study, we sampled 42 populations of Scaevola taccada (Gaertn.) Roxb., a coastal shrub of the family Goodeniaceae, from 17 countries across its distribution range. We used five chloroplast DNA (cpDNA) and 14 nuclear microsatellite (simple sequence repeat [SSR]) markers to assess the influence of abiotic factors and population genetic processes on the phylogeographic pattern of the species. Geographical distribution of cpDNA haplotypes suggests that the species originated in Australia, followed by historical dispersal and expansion of its geographic range. Multiple abiotic factors, including the sealevel changes during the Pleistocene, the presence of landmasses like the Malay Peninsula, and contemporary oceanic circulation patterns, restricted gene flow between geographically distinct populations, thereby creating low haplotype diversity and a strong population structure. Population genetic processes acted on these isolated populations, leading to high nuclear genetic diversity and population differentiation, as revealed from analyzing the polymorphic SSR loci. Although genetic divergence was mostly concordant between cpDNA and SSR data, asymmetrical gene flow and ancestral polymorphism could explain the discordance in the detailed genetic structure. Overall, our findings indicate that abiotic factors and population genetic processes interactively influenced the evolutionary history and current phylogeographic pattern of S. taccada across its distribution range.     

Impact of geographical isolation on genetic differentiation in insular and mainland populations of Weigela coraeensis (Caprifoliaceae) on Honshu and the Izu Islands

Aim To provide insights into genetic differentiation between insular endemic Weigela coraeensis var. fragrans and its progenitor variety W. coraeensis var. coraeensis, the population genetic structure of both varieties was examined, and factors promoting genetic differentiation between the two taxa were explored. Location The natural range of W. coraeensis (sensu lato) throughout mainland Japan (Honshu) and the Izu Islands. Methods The analysis included 349 and 504 individuals across the mainland (Honshu) and the Izu Islands, respectively, using 10 allozyme and 10 microsatellite loci. The population genetic structure of W. coraeensis was assessed by analysing genetic diversity indices for each population, genetic differentiation among populations, model‐based Bayesian clustering or distance‐based clustering, and bottleneck tests. Results The level of genetic diversity in each of the populations on the Izu Islands was negatively correlated with geographical distance between each island and the mainland. The populations on the mainland and on the Izu Islands were genetically differentiated to a certain extent; however, the microsatellite analyses suggested that gene flow also occurred between the mainland and the islands, and among individual islands. These microsatellite analyses also suggested recent bottlenecks in several populations in both areas. Main conclusions The decrease in genetic diversity throughout the Izu Islands, which correlated with distance to the mainland, Honshu, may be the result of a repeated founder effect occurring at a series of inter‐island colonizations from north to south. The stepping stone‐like configuration of the islands may have played a role in the dispersal of the species. Geographical isolation by sea would effectively result in genetic differentiation of W. coraeensis between mainland Honshu and the Izu Islands, although some gene flow may still occur between Honshu and the northern Izu Islands. The differentiation process of the endemic plants on the Izu Islands is anagenetic but not completed, and the study of these plants will provide insightful knowledge concerning the evolution of insular endemics.     

Phylogeography of Cycas revoluta Thunb. (Cycadaceae) on the Ryukyu Islands: very low genetic diversity and geographical structure

Variations in the chloroplast and mitochondrial DNA of Cycas revoluta Thunb. (Cycadaceae) were examined in 22 populations distributed across the Ryukyu Islands and southern Kyushu. Among the 14,130 bp of sequence examined, only one site mutation and one indel were polymorphic. The identified polymorphisms were located in the spacers between trnS (UGA) and trnfM (CAU) of the chloroplast DNA and between nad1 exon B and exon C of the mitochondrial DNA, respectively. Three haplotypes were identified from the Ryukyu Islands and southern Kyushu. The areas of distribution of the three haplotypes were highly geographically structured. The boundaries of two of the three haplotypes were demarcated by Okinoerabujima Island in the middle Ryukyus. The northern type and southern types lay north and south of the island, respectively. The third haplotype was almost sympatrically distributed with the southern type. The genetic variation within C. revoluta was estimated to be very low (h = 0.641, π = 0.00071) in comparison to its relative in Taiwan, C. taitungensis, which possesses 97 cpDNA haplotypes and 55 mtDNA haplotypes from two relic populations. A reasonable explanation for the low genetic diversity of the cycad on the Ryukyu Islands could be severe bottleneck effects, resulting from the submersion of low islands and the diminished landmass of islands in the interglacial age in the Quaternary period. The geographically restricted nature of the haplotypes could be attributed to vicariance resulting from the land configuration of the Ryukyu Islands, including changes in geography during the interglacial age in the Quaternary.     

Genetic structure of the critically endangered Red‐headed Wood Pigeon Columba janthina nitens and its implications for the management of threatened island populations

The Red‐headed Wood Pigeon Columba janthina nitens is endemic to the Ogasawara Islands, an oceanic island chain located 1000 km south of the main islands of Japan. The subspecies is at high risk of extinction because of its small population size and restricted habitat range. We undertook genetic analyses of this pigeon using sequences of a portion of the mitochondrial control region and five microsatellite markers to estimate the genetic characteristics of two wild populations from the Bonin and Volcano Islands, as well as one captive breeding population. The genetic diversity of the wild individuals was exceptionally low in both the mitochondria (nucleotide diversity = 0.00105) and at the microsatellite (3.2 alleles per locus and H_E = 0.12) loci. Higher numbers of microsatellite genotypes were observed in the Volcano Islands population than in the Bonin Islands population, which may be because of the relatively low impact of human disturbance. The most common mitochondrial haplotypes and microsatellite alleles observed in the two wild populations were completely fixed in the captive population. Our results suggest that the genetic diversity of the captive population needs to be increased. However, introduction of a wild individual into a captive population can lead to a decreased genetic diversity in the wild population and therefore should be done with caution. The genetic differentiation between the Bonin and the Volcano island groups was low, and the populations of the two island groups should be regarded as a single evolutionarily significant unit. However, special consideration is required for habitat conservation in the Volcano Islands, which may be functioning as a sanctuary for the Red‐headed Wood Pigeon. For the long‐term conservation of threatened bird species that live on remote oceanic islands, determination of management units considering gene flow caused by their flying capacity and maintenance of genetically suitable wild and captive populations are essential.     

Phylogeography of the endangered tideland snail Batillaria zonalis in the Japanese and Ryukyu Islands

The phylogeography of the endangered tideland snail Batillaria zonalis in the Japanese and Ryukyu Islands was analyzed on the basis of nucleotide sequences of a mitochondrial gene for cytochrome oxidase c subunit I (COI). Extremely low genetic diversity was found in populations at both the northern and southern boundaries of the geographic distribution of this species in Japan, i.e., Sendai Bay and Iriomotejima Island, respectively, which might be attributed to the population bottleneck due to historical environmental variations and/or the recent foundation of populations in the marginal part of the inhabitable range. Most populations contained unique rare haplotypes, and significant genetic differentiation on the whole was shown, while no clear geographic genetic structure was detected between the Japanese and Ryukyu Islands or over the distribution area of B. zonalis in Japan, with the exception of significant genetic divergences in Ago Bay in the central part of Honshu and the southern part of Okinawajima Island.     

Development of microsatellite markers for Quercus miyagii Koidz. (Fagaceae), an endemic species in the Ryukyu Islands, Japan

Quercus miyagii is an endemic tree species in the Ryukyu Islands, Japan. We isolated and characterized 15 microsatellite loci in this species. The number of alleles ranged from 2 to 16 and expected heterozygosities from 0.07 to 0.92. This set of markers is potentially useful to investigate the genetic structure, gene flow, and the biogeographic history of Q. miyagii in the Ryukyu Islands, Japan.     

Genetic structure of island populations of <Emphasis Type="Italic">Prunus lannesiana</Emphasis> var. <Emphasis Type="Italic">speciosa</Emphasis> revealed by chloroplast DNA,AFLP and nuclear SSR loci analyses

The wild flowering cherry Prunus lannesiana var. speciosa is highly geographically restricted, being confined to the Izu Islands and neighboring peninsulas in Japan. In an attempt to elucidate how populations of this species have established we investigated the genetic diversity and differentiation in seven populations (sampling 408 individuals in total), using three kinds of genetic markers: chloroplast DNA (cpDNA), amplified fragment length polymorphisms (AFLPs), and 11 nuclear SSR polymorphic loci. Eight haplotypes were identified based on the cpDNA sequence variations, 64 polymorphic fragments were scored for the AFLP markers, and a total of 154 alleles were detected at the 11 nuclear SSR loci. Analysis of molecular variance showed that among-population variation accounted for 16.55, 15.04 and 7.45% of the total detected variation at the cpDNA, AFLPs, and SSR loci, respectively. Thus, variation within populations accounted for most of the genetic variance for all types of markers, although the genetic differentiation among populations was also highly significant. For cpDNA variation, no clear structure was found among the populations, except that of the most distant island, although an “isolation by distance” pattern was found for each marker. Both neighbor-joining trees and structure analysis indicate that the genetic relationships between populations reflect geological variations between the peninsula and the islands and among the islands. Furthermore, hybridization with related species may have affected the genetic structure, and some genetic introgression is likely to have occurred.     

Population genetic structure of Sorex unguiculatus and Sorex caecutiens (Soricidae, Mammalia) in Hokkaido, based on microsatellite DNA polymorphism

We investigated the genetic structure of Sorex unguiculatus and Sorex caecutiens populations in Hokkaido, Japan, using hypervariable microsatellite DNA markers. We used five microsatellite loci to type 475 S. unguiculatus individuals from 20 localities on the Hokkaido mainland and four localities from each of four offshore islands (and 11 shrews from one locality in southern Sakhalin for a particular analysis). We used six microsatellite loci to type 240 S. caecutiens individuals from 13 localities on the Hokkaido mainland. Genetic variation was high in mainland populations of both species and low in the island populations of S. unguiculatus. Allelic richness and island size were positively correlated for S. unguiculatus, suggesting that genetic drift occurred on those islands due to small population size. In addition, four insular populations of S. unguiculatus were genetically differentiated from the mainland populations, although clear phylogeographic clustering was not confirmed among populations on the Hokkaido mainland for either S. unguiculatus or S. caecutiens. Heterozygosity excess was observed in more than half of the populations including the mainland populations of the two species, suggesting recent bottleneck events in these populations. Population dynamics of the shrews might be explained by a metapopulation scheme. According to autocorrelation analysis, the extent of non-random spatial genetic structure was approximately 100 km. Isolation by distance was observed in S. unguiculatus, but not in S. caecutiens although there is a positive trend. The lack of correlation for S. caecutiens might have been due to small sample size. Thus, no obvious differences in population genetic structure were found between the two species on the Hokkaido mainland in the present study, while previous investigations using mitochondrial DNA sequences inferred that these two species might have rather different biogeographic histories.     

黑头酸臭蚁微卫星标记的分离与开发(英文)

【目的】本研究旨在分离黑头酸臭蚁Tapinoma melanocephalum基因组微卫星标记,确定这些微卫星位点的多态性。【方法】使用454 GS-FLX焦磷酸测序技术开发来自中国华南陆地和岛屿的11个黑头酸臭蚁地理种群基因组微卫星位点。从随机设计的100对微卫星引物中筛选出10对引物,用于确定黑头酸臭蚁4个地理种群［东澳岛(DAD)、荷包岛(HBD)、梅州(MZ)和山咀(SJ)］10个微卫星位点的多态性,分析种群遗传多样性和种群分化。【结果】从11个黑头酸臭蚁地理种群基因组中成功开发和分离10对微卫星引物。在DAD, HBD, MZ和SJ 4个地理种群中,10个微卫星位点中7个有高多态性,这10个位点均显著偏离Hardy-Weinberg平衡;每个位点的等位基因数量(A)是3.50~9.00个,每个地理种群每个位点等位基因丰富度(A_R)在1.992~12.938之间。岛屿地理种群(DAD和HBD)的AR和预期杂合度(H_E)与大陆地理种群(MZ和SJ)的相比差异不显著。4个地理种群均显示高水平遗传分化(F_ST=0.15969);HBD和MZ种群与其他配对地理种群相比,遗传分化较高(F_ST=0.185),基因流较低,说明这两个种群基因流被限制。此外,遗传变异来自种群内个体之间。【结论】筛选新的微卫星位点能够为研究黑头酸臭蚁种群结构和繁殖结构提供有效工具,以深入了解其传播机制。     

基于叶绿体基因序列rbcL-accD研究莛子藨的分子遗传多样性和谱系地理结构

莛子藨是莛子藨属的一种多年生草本植物,主要分布在青藏高原东北部及邻近高山地区和日本,为东亚特有种。本文基于叶绿体DNA基因间隔区rbcL-accD序列,对莛子藨物种水平的序列特征、分子遗传多样性和谱系地理结构进行研究。分析结果发现该区域莛子藨种群的遗传变异主要来自于居群间（72.28%）,优势单倍型（H2）广泛分布,特有单倍型分散在多个居群。居群间遗传分化系数N_STST,没有检测到显著谱系地理结构,而且居群间基因流较低（N_m=0.096）,青藏高原及其邻近地区特殊地形和生态环境造成的地理隔离或者生境异质化可能是现有单倍型分布格局形成的原因。种群动态历史分析显示莛子藨经历过不显著的种群选择或者扩张事件,综合分析推测莛子藨居群应该是在间冰期或者冰期后从不同避难所扩散形成现在的分布格局,具体避难所还需进一步深入研究才能确认。     

中国穗状狐尾藻遗传多样性的初步分析

利用叶绿体DNA三个片段(trnK-matK、trnL-trnF、rpl32-trnL)对中国大陆广布的水生植物穗状狐尾藻(Myriophyllum spicatum L.)的遗传多样性进行了初步分析,以探讨其自然居群的遗传结构及具有广泛分布格局的可能机制。AMOVA分析显示,穗状狐尾藻8个居群间的遗传变异为84.97%,而居群内的遗传变异为15.03%,居群遗传分化系数(Fst)为0.85,表明穗状狐尾藻具有较高的遗传多样性(Hd=0.83)且主要存在于居群间,奠基者效应可能导致了最初的遗传差异,而隔离障碍(Nm=0.09)又进一步导致了居群间的遗传分化。基于17个单倍型构建的系统发育树和网络关系图均显示,单倍型H5和H6在居群中的分布范围最广且出现频率最高,表明H5和H6可能为最古老的祖先单倍型。Mantel检验表明居群间的遗传距离与地理距离之间不存在显著的相关性,失配分布检测结果显示穗状狐尾藻在历史上曾发生过扩张事件,而Tajima’s、FuLi’s D*和F*检测发现,该物种不存在明显的谱系地理格局,这可能与穗状狐尾藻种子的长距离扩散有关。     

Genetic assessment of captive Chinese water deer populations in Zhoushan Archipelago,China

Chinese water deer is a rare and vulnerable animal in China because of the poaching for medical use and the habitat loss. In this study, the genetic diversity and population genetic structure of 40 Chinese water deer from three populations in Zhoushan Archipelago were investigated with ten highly polymorphic microsatellite loci, including 4 screened from the nuclear DNA in the study, and 6 selected from the literature. According to the results, these captive populations had a higher genetic diversity than other rare cervid species, such as forest musk deer. No signs of inbreeding were detected. Low genetic differentiation among these populations was found. The probable reasons included the isolation by distance, the exchange among islands, or the supplement of the wild Chinese water deer. We proposed the deer raisers to strengthen the exchanges from different islands or mainland, and if possible, some deer would be returned to the wild to expand the wild population.     

Genetic Differentiation and Spatial Structure of Phellinus noxius,the Causal Agent of Brown Root Rot of Woody Plants in Japan

Phellinus noxius is a pathogenic fungus that causes brown root rot disease in a variety of tree species. This fungus is distributed in tropical and sub-tropical regions of Southeast and East Asia, Oceania, Australia, Central America and Africa. In Japan, it was first discovered on Ishigaki Island in Okinawa Prefecture in 1988; since then, it has been found on several of the Ryukyu Islands. Recently, this fungus was identified from the Ogasawara (Bonin) Islands, where it has killed trees, including rare endemic tree species. For effective control or quarantine methods, it is important to clarify whether the Japanese populations of P. noxius are indigenous to the area or if they have been introduced from other areas. We developed 20 microsatellite markers from genome assembly of P. noxius and genotyped 128 isolates from 12 of the Ryukyu Islands and 3 of the Ogasawara Islands. All isolates had unique genotypes, indicating that basidiospore infection is a primary dissemination method for the formation of new disease foci. Genetic structure analyses strongly supported genetic differentiation between the Ryukyu populations and the Ogasawara populations of P. noxius. High polymorphism of microsatellite loci suggests that Japanese populations are indigenous or were introduced a very long time ago. We discuss differences in invasion patterns between the Ryukyu Islands and the Ogasawara Islands.     

Mitochondrial DNA variation in Nicobarese Islanders.

The aboriginal populations living in the Nicobar Islands are hypothesized to be descendants of people who were part of early human dispersals into Southeast Asia. However, analyses of ethnographic histories, languages, morphometric data, and protein polymorphisms have not yet resolved which worldwide populations are most closely related to the Nicobarese. Thus, to explore the origins and affinities of the Nicobar Islanders, we analyzed mitochondrial DNA (mtDNA) hypervariable region 1 sequence data from 33 Nicobarese Islanders and compared their mtDNA haplotypes to those of neighboring East Asians, mainland and island Southeast Asians, Indians, Australian aborigines, Pacific Islanders, and Africans. Unique Nicobarese mtDNA haplotypes, including five Nicobarese mtDNA haplotypes linked to the COII/tRNA(Lys) 9-bp deletion, are most closely related to mtDNA haplotypes from mainland Southeast Asian Mon-Kmer-speaking populations (e.g., Cambodians). Thus, the dispersal of southern Chinese into mainland Southeast Asia may have included a westward expansion and colonization of the islands of the Andaman Sea.     

Phylogeography of Arcterica nana (Ericaceae) suggests another range expansion history of Japanese alpine plants

We conducted a phylogeographic study on the alpine plant Arcterica nana based on haplotypes of chloroplast DNA. Using a sequence of approximately 1,071 bp of intergenic spacers of chloroplast DNA (trnT-L, psbB–psbF), we detected 13 haplotypes among 193 individuals sampled from 22 populations. Two dominant haplotypes were distributed over the entire range of this species in Japan, and we found several local private haplotypes. An analysis of molecular variance (AMOVA) indicated no geographic structure within the haplotype distribution. In addition, the genetic distance was not related to its corresponding geographic distance (Mantel test: r=−0.049, P=0.66), indicating a homogeneous geographic structure throughout the entire distribution range in the Japanese archipelago. The most parsimonious explanation for this geographic structure is that A. nana spread across its extant distribution range in the Japanese archipelago through a recent range expansion event. However, this pattern is inconsistent with the previous phylogeography of Japanese alpine plants, which reveals that haplotypes in central Honshu are differentiated from those in more northern regions. Arcterica nana may have experienced a different history from other alpine plants, suggesting that the history of Japanese alpine flora may include at least two different geographic radiation patterns.     

Interisland gene flow among populations of the buff‐banded rail (Aves: Rallidae) and its implications for insular endemism in Oceania

Studies of fragmented habitat, such as island archipelagos, provide insights into the microevolutionary processes that drive early stages of diversification. Here, we examined genetic variation and gene flow among populations of the widespread buff‐banded rail Gallirallus philippensis in Oceania to understand the factors that promote speciation associated within this bird lineage. We analysed mtDNA Control Region sequences and six microsatellite loci from a total of 152 individuals of buff‐banded rail on islands and continental areas. We used a phylogeographic model‐testing approach and a structured spatial design ranging from within to among archipelagoes in the south Pacific. Buff‐banded rail populations in the Philippines archipelago and nearby Palau and Wallacea had high genetic diversity while those in geographically distant Australia showed lower variation. Other archipelagos sampled were found to have less genetic diversity and included haplotypes closely related to Wallacea (Bismarck, Vanuatu, New Caledonia) or Australia (New Zealand, Samoa, Fiji, Cocos Islands). Nucleotide diversity and allele frequency declined with degree of geographic isolation but haplotype diversity remained more even. However, both nucleotide and haplotype diversities were positively correlated with land area. Microsatellite data for a subset of locations showed moderate to high genetic differentiation and significant pairwise F_ST despite a relatively high migration rate. Our results are mostly consistent with a model of abrupt genetic changes due to founder events with multiple dispersals into Australia from Wallacea and Bismarck. Australia has probably been the source of birds for islands in the Pacific. This is shown by decreasing genetic diversity and growing genetic differentiation when distances separating populations increased from Australia. A history of range expansion and divergent natural selection may help explain the existence of numerous sympatric Gallirallus island endemics.     

Genetic diversity,structure, and demography of Pandanus boninensis (Pandanaceae) with sea drifted seeds,endemic to the Ogasawara Islands of Japan: Comparison between young and old islands

Pandanus boninensis, endemic to the Ogasawara Islands, Japan, is distributed on both the older Bonin and younger Volcano Islands. In this study, we conducted population genetic analyses of P. boninensis on these islands to examine the population diversity and structure across old and young islands, to assess potential differences in population demography with island age, and to collect any evidence of migration between old and young islands. We found that the genetic diversity of expressed sequence tag (EST)–based microsatellite (SSR) markers, the nucleotide diversity of nuclear DNA sequences, and the haplotype diversity of chloroplast DNA on young islands were lower than those on old islands. Clustering analyses of EST‐SSR indicated that populations on old islands were strongly diverged from those on young islands. Approximate Bayesian computation analysis of EST‐SSR suggested that population expansion occurred on old islands while population reduction occurred on young islands. We also found evidence of migration among old islands (mostly from south to north), while it appears that there have been very few migration events between old and young islands. These differences could be due to the fact that young islands tend to be geographically isolated and support smaller populations that began a shorter time ago from limited founders. The P. boninensis populations on the Volcano Islands are interesting from an evolutionary perspective as they constitute a classic example of the early stages of progressive colonization on oceanic islands with small effective population sizes and low genetic diversity.     

Characterization of six microsatellite loci in the mangrove cricket Apteronemobius asahinai

The mangrove cricket Apteronemobius asahinai is endemic to mangrove forest floors in China, Southeast Asia and the Ryukyu archipelago (Amamiohsima, Okinawa, Miyako, Ishigaki and Iriomote Islands) of Japan. We developed six polymorphic microsatellite markers for the mangrove cricket from genomic DNA libraries enriched for CA, GA, AAG and ATG motifs. The M13‐tailed primer method was used in the process of screening of amplification and polymorphism of primers. A total of 64 specimens from two populations (one from Okinawa and the other from Iriomote) were genotyped for allelic diversity. The average number of alleles per locus was 4.67 and 6.67 for Okinawa and Iriomote populations, respectively. A significant genetic differentiation was detected between the two populations (pairwise F_ST 0.2404). These polymorphic microsatellite loci will be useful in ongoing studies of the population genetic structure of the mangrove cricket including several populations in the Ryukyu archipelago.     

Phylogeographic patterns and demographic history of Schiedea globosa (Caryophyllaceae) on the Hawaiian Islands

Geomorphological changes have been demonstrated to have had profound impacts on biodiversity, often leading to demographic expansions and contractions and allopatric divergence of taxa. We examined DNA sequence variation at two nuclear and one maternally inherited plastid locus among 10 populations of Schiedea globosa on the Hawaiian Islands to assess the primary factors shaping genetic structure, phylogeographic patterns, and the importance of geographic isolation to population divergence. Schiedea globosa has characteristics that may promote gene flow, including wind pollination and rafting of plants in ocean currents. However, we detected significant differentiation among populations on all islands except Hawaii, with the maternally inherited plastid locus having the greatest genetic structure (F(ST) = 0.81). Migration rates across all loci are less than one migrant per generation. We found evidence of growth in several populations and on the islands of Molokai and Maui, which supports population expansion associated with the formation of Maui Nui during the last glacial maximum. Similar to data for many other Hawaiian taxa, these data suggest S. globosa originated on Oahu and subsequently colonized Molokai, Maui, and Hawaii in progression. Given the high level of genetic structure, allopatric divergence will likely contribute to further divergence of populations.