Allozyme diversity and the evolution ofCrepidiastrum (Compositae) on the Bonin (Ogasawara) Islands

The genusCrepidiastrum is distributed in East Asia and includes 7 species. In the Bonin Islands, three species ofCrepidiastrum occur, and all of them are endemic to the islands. For detecting the origin and speciation of these endemic species, electrophoretic studies have been done in three endemic species of the Bonin Islands as well as in the remaining four species ofCrepidiastrum, andYoungia denticulata which is considered to be closely related toCrepidiastrum. A total of 386 individuals were sampled from 14 populations. As a result, 17 loci of 10 enzyme systems were resolved and gene frequencies for each population were calculated. The genetic variability was low in island species, as reported in some oceanic island plants. Four groups were recognized in the dendrogram generated by the UPGMA method. The Bonin endemics were clustered together, suggesting a monophyletic origin.C. ameristophyllum andC. linguaefolium were found to be genetically very similar, and this may suggest recent and rapid speciation within the islands.     

Allozyme diversity and the evolution ofSymplocos (Symplocaceae) on the Bonin (Ogasawara) Islands

To study the origin and speciation of plants in oceanic islands, electrophoretic analyses have been done on three endemic species ofSymplocos in the Bonin Islands as well as on three other species;S. kuroki, S. nakaharae andS. tanakae which are considered to be closely related to the Bonin endemics. There occur three species:S. kawakamii, S. pergracilis andS. boninensis in Bonin. The genusSymplocos is one which is considered to be diversified in the Bonin Islands. Seven enzyme systems presumed to be encoded by 18 loci were examined. The genetic diversity was low in the island species, as reported in some oceanic island plants of Hawaii and the Bonin Islands. The three endemics share high genetic identities and they clustered together in the tree drawn by the UPGMA method, suggesting that they are a monophyletic group, that is, they result from a single introduction.     

Phylogenetic relationships ofCrepidiastrum (Asteraceae) of the Bonin (Ogasawara) Islands based on chloroplast DNA restriction site variation

RFLPs of cpDNA were investigated for seven species ofCrepidiastrum, of which three are endemic to the Bonin Islands. As an outgroup for rooting the tree,Paraixeris denticulata was also examined. Approximately 350 restriction sites were surveyed using 16 restriction enzymes. A total of 26 restriction site mutations were detected, and seven of them were phylogenetically informative. Wagner parsimony analysis resulted in four most parsimonious trees. In the tree obtained, the Bonin endemics are monophyletic with four mutations and a bootstrap value of 0.98 for the branch. This result agrees with that obtained from a previous electrophoretic analysis (Ito and Ono 1990), and supports the hypothesis that the three Bonin endemics have been evolved from a common ancestor. The Bonin endemics cluster together withC. lanceolatum, suggesting that the endemics andC. lanceolatum share a common ancestor, although the bootstrap probability is not very high (0.78) and thus other possibilities cannot be rejected.     

Origin and evolution of endemic plants of the Bonin (Ogasawara) Islands

The Bonin Islands are typical oceanic islands, located at the western part of the North Pacific Ocean and approximately 1,000 km south of mainland Japan. This archipelago consists of about 20 small islands. Although floristic diversity is low due to the small area and limited environmental diversity, the Bonin Islands harbor unique endemic flora as in other well-known oceanic islands. This paper presents a brief summary of the results obtained from recent studies on the endemic flora of the Bonin Islands. The results are reviewed in relation to the four stages of the evolution of endemic flora in the oceanic islands; migration, establishment, enlargement and diversification. The ancestors of the flora originated mostly from tropical and subtropical Southeast Asia or mainland Japan by rare events of long distance dispersal. The proportion of bird-dispersed species is relatively high as for other oceanic islands. Genetic data sets obtained from allozyme variation in some endemic species suggest that migration occurred several million years ago and genetic diversity is correlated with current population size. At the time of establishment, self-compatible plants are expected to have an advantage. However, the percentage of dioecious plants is relatively high. This is partly due to evolutionary changes from hermaphroditic ancestors to dioecy which occurred in two genera in the Bonin Islands. In addition, there are some examples of evolutionary changes from herbaceous ancestors to woody endemics. Adaptive radiation is found in some genera, although the number of congeneric endemic species is less than five. Studies of allozyme variation inPittosporum, Symplocos andCrepidiastrum showed that genetic identity is generally very high between congeneric species in spite of their distinct morphologies. This result suggests that divergence of these species occurred rather recently and distinct morphological differences are based on a limited number of genetic changes.     

Isolation and characterization of microsatellite loci in <Emphasis Type="Italic">Melicope quadrilocularis</Emphasis> (Rutaceae), an endemic plant species of the Bonin Islands,Japan, and cross-species amplification in closely related taxa

Twelve microsatellite loci were isolated and characterized for Melicope quadrilocularis, an insular endemic tree species of the Bonin Islands. The observed number of alleles at each locus ranged from 1 to 18. The range of expected heterozygosity was 0.0000–0.9445. The inter-specific applicability of these loci was evaluated by analyzing two other endemic species and one endemic variety of Melicope that are also distributed on the Bonin Islands. All primer pairs for the 12 loci tested successfully amplified the loci in all taxa, except for primers for four loci in M. nishimurae.     

Ecological and genetic differentiation in Persea boninensis (Lauraceae) endemic to the Bonin (Ogasawara) Islands

Persea boninensis (Lauraceae) is an endemic tree species distributed throughout the Bonin Islands. It grows in a wide range of environments from dry to mesic forests, and has multiple flowering peaks that may correspond to different habitats on Chichijima Island of the Bonin Islands. We predicted that P. boninensis is differentiated into two groups with different habitats on these islands. We examined and compared the flowering phenology, morphology, and genetics of populations of species growing in dry and mesic forests. We also performed preliminary artificial crossing experiments. Based on our results, P. boninensis on the Chichijima Islands can be clearly divided into two genetic groups with different habitats and flowering times. Although the flowering time difference could act as an effective pre‐zygotic isolation mechanism between the two groups, there was still a 1‐month overlap in flowering time. Furthermore, our artificial crossing experiments between the two groups resulted in plants that set seeds. Therefore, there was no evidence of reproductive isolation after fertilization. Differences in flowering time as well as in growth habitat will have to occur to maintain genetic differentiation between the two groups of P. boninensis.     

Identification and characterization of eight microsatellite loci in Machilus pseudokobu (Lauraceae), an endemic species of the Bonin Islands

Eight microsatellite loci were identified and characterized for the endangered Machilus pseudokobu (Lauraceae), an endemic tree species of the Bonin Islands. The observed number of alleles at each locus ranged from 1 to 20 with an average of 6.2, and the expected heterozygosity ranged from 0.00 to 0.83 with an average of 0.47. All eight loci were screened in cross-amplification tests for two other endemic Machilus species that also inhabit the Bonin Islands. All loci were successfully amplified in these species.     

Dioecism of the genusCallicarpa (Verbenaceae) in the Bonin (Ogasawara) Islands

The morphology and function of the flowers of three species of the genusCallicarpa, C. glabra, C. nisnimurae andC. subpubescens, endemic to the Bonin Islands, revealed that all three species were dioecious. Male plants had short-styled flowers with sterile ovaries, while female plants had long-styled flowers with non-germinating inaperturate pollen grains. Such dioecism has never been reported from the family Verbenaceae. This curious sexual system with non-germinating pollen grains may have been maintained as a reward to insect pollinators.     

Pollination and reproduction of Psychotria homalosperma,an endangered distylous tree endemic to the oceanic Bonin (Ogasawara) Islands,Japan

Distyly is usually rare or not observed in species thriving on oceanic islands. The rarity of this breeding system is probably because of the difficulty of colonization for distylous plants and the paucity of pollinators on oceanic islands. However, the endemic and endangered tree Psychotria homalosperma has maintained its distylous nature in the oceanic Bonin Islands, Japan. To understand how the distylous breeding system of P. homalosperma has been maintained on these islands and to characterize the reproduction systems, we studied the pollination and reproductive biology of this species. Specifically, we observed current flower visitors and estimated their effects on plant reproduction. We also examined the floral traits and floral volatiles of P. homalosperma to infer its original pollinators, because plant–pollinator relationships in the Bonin Islands have recently been disrupted by anthropological activities. Finally, we examined the fruit set and pollen tube growth in the stigmas under hand and open pollination. Although original pollinators were presumed to be moths with long proboscises, the introduced honeybee, Apis mellifera, was the most common flower visitor. The honeybee carried pollen grains only unidirectionally, from the short‐ to long‐styled morphs, because it could not reach the hidden stigmas of the short‐styled flowers, and long‐styled flowers set fruits 1.7–38 times more than short‐styled ones. This case study indicates that the instability of pollinator fauna can cause distylous species to be rare on oceanic islands.     

Development of microsatellite markers for <Emphasis Type="Italic">Metrosideros boninensis</Emphasis> (Myrtaceae), an endangered endemic plant species from the Bonin Islands,Japan

Metrosideros boninensis is an endangered endemic plant species from the Bonin Islands. We isolated and characterized nine microsatellite loci in this species. The expected heterozygosities of these nine markers ranged from 0.127 to 0.768. These markers described here will be useful for investigating the genetic diversity, genetic structure and gene flow, and planning for conservation of M. boninensis.     

Phylogenetic analysis of Asian<Emphasis Type="Italic"> Symplocos</Emphasis> (Symplocaceae) based on nuclear and chloroplast DNA sequences

Thirty species and one variety of Symplocos (Symplocaceae), including all taxa distributed in Japan, were phylogenetically analyzed with DNA sequence data. The evolution of morphological characters is discussed on the basis of the phylogenetic relationships obtained. All species were Asian, except one, S. austromexicana, from Mexico. The nuclear ribosomal internal transcribed spacer (ITS) region and two intergenic spacer regions, between trnL and trnF, and between trnH and psbA of chloroplast DNA were used. The topologies of trees obtained from ITS and the chloroplast intergenic spacers are largely congruent. S. sonoharae, the representative of the subgenus Symplocos in Asia, was sister to all other species. The position of the American species, S. austromexicana, which also belongs to the subgenus Symplocos, was not well resolved. The phylogenetic tree based on combined sequence data largely supports the monophyletic origin of the infrageneric sections proposed earlier. However, the phylogenetic relationship between them is not well resolved, probably due to rapid diversification. The section Palura, a deciduous group, is well defined in the DNA analysis, suggesting its independent status in the genus Symplocos. In spite of their morphological divergence, the three endemic species of the Bonin Islands are monophyletic. The occurrence of curved seeds seems to be homoplastic, scattered over the phylogenetic tree without showing a particular infrageneric relationship.     

Isolation of polymorphic microsatellite loci in Livistona chinensis (Jacq.) R.Br. ex Mart. var. boninensis Becc., an endemic palm species of the oceanic Bonin Islands, Japan

A set of microsatellites markers were developed for Livistona chinensis var. boninensis, an endemic palm tree of the Bonin Islands. We obtained 123 sequences containing unique microsatellites from an enriched library. Twelve loci were screened for their feasibility using 32 trees. They showed polymorphisms with two to nine alleles per locus. No significant deviation from Hardy–Weinberg equilibrium was observed for 11 loci. No genotypic disequilibrium was detected between any two of the loci. Total exclusionary powers for the first and the second parents were 0.978774 and 0.998987, respectively. These markers will allow us to investigate the gene flow within/among populations of the species.     

Microsatellite loci development in endangered pamphagid grasshoppers endemic to the Canary Islands (Orthoptera)

The five recognized endemic pamphagid species (Orthoptera) of the Canary Islands have restricted and fragmented ranges due to habitat decline. Seven polymorphic microsatellite markers have been developed for Acrostira tamarani, and the performance of primer pairs amplifying these loci in related taxa has been tested. The number of alleles in A. tamarani samples taken from two distant localities in the island of Gran Canaria ranged from two to eight per locus. Observed heterozygosities were from 0.151 to 0.559. Up to four primer pairs amplified in related species with moderate heterozigosities (maximum of 0.687 and 10 alleles for Ata67 locus in Purpuraria erna). These markers could be useful tools to study the population structure and management of endemic threatened pamphagids of the Canary archipelago.     

Distyly and incompatibility in Psychotria homalosperma (Rubiaceae), an endemic plant of the oceanic Bonin (Ogasawara) Islands

Distyly rarely occurs on oceanic islands. Indeed, this form of polymorphism is absent on the Hawaiian Islands and in New Zealand. However, Psychotria homalosperma (Rubiaceae), which is endemic to the oceanic Bonin Islands of Japan, was presumed to maintain a distylous breeding system and floral morphology. We investigated the floral and reproductive characteristics of this species and examined incompatibility in self- and intramorph pollination. Psychotria homalosperma is morphologically and functionally distylous, based on findings with the examined populations, but its stigma and anther heights are not exactly reciprocal between the two morphs. This is the second example of distyly among the flora from the Bonin Islands, the other being the endemic P. boninensis. Both of these distylous species contrast with the Hawaiian Psychotria species, which have already become dioecious. The flowers of the long (L)-styled (pin) morph of the Bonin Islands plants are completely self- and intramorph incompatible, while the flowers of the short (S)-styled (thrum) morphs are partially intramorph compatible. The S-styled morph was more abundant in the examined populations from three islands of the archipelago, probably due to the existence of partial S–S intramorph compatibility.     

Morphological Variation of Three Endemic Species of Callicarpa (Verbenaceae) in the Bonin (Ogasawara) Islands

Abstract A total of 22 population samples of three endemic species of Callicarpa in the Bonin Islands (the Chichijima Islands and the Hahajima Islands) were examined for nine leaf characters to clarify the present status of morphological variations. Results showed that three species are distinetly recognizable and have their own patterns of variation. Callicarpa glabra and C. nishimurae were relatively less variable and adapted to limited habitats only in the Chichijima Islands. Thus these species were regarded as specialized species. C. subpubescens was more variable than the above two species and distributed widely in both of the two island groups. This species was morphologically differentiated between the two island groups. In the Hahajima Islands where two other species were not distributed, several plants of C. subpubsecens were similar to C. glabra. The populations of C. subpubescens in the Hahajima Islands were inter-populationally more variable than those in the Chichijima Islands. C. subpubescens occupied various habitats within the Bonin Islands and was regarded as a diversified species.     

Development and diversity of microsatellite markers for endangered species Clinostigma savoryanum

A set of microsatellite markers was developed for Clinostigma savoryanum, an endemic palm species distributed in the Bonin Islands. We obtained 233 sequences that were unique, containing microsatellites from an enriched library. Twelve loci were screened for their feasibility to be used as high resolution genetic markers using each 30 individuals from two insular populations, Haha-jima and Mukou-jima. They showed polymorphisms of two to eight alleles per locus and expected heterozygosities of 0.124–0.789. There is no evidence for significant scoring error due to stuttering, large allele dropout and null alleles at 95% confidence interval except for the presence of null alleles in CLS00-77 of Mukou-jima population.     

Dioecy in the endemic genusDendrocacalia (Compositae) on the Bonin (Ogasawara) Islands

Dendrocacalia crepidifolia Nakai (Compositae, Senecioneae), the only species of this arboreal genus endemic to Haha Island in the Bonin Islands, was found to be dioecious. Male flowers differ from female ones in having a stunted style (style in female exserted from corolla and deeply bifurcating) and anthers filled with fertile pollen (anthers in the female lacking pollen). The size of the corolla and number of florets per head were similar between male and female flowers. The crown area of this arboreal species was also similar in male and female plants. The sex ratio was 0.55 male, not significantly different from 0.5. Both sexes produced nectar of similar sugar concentration (ca. 50%). The flowers are pollinated by feral honeybees (Apis mellifera), but they are thought to have been pollinated by small, lesshairy, endemic solitary bees before honeybees were introduced and subsequently became the dominant bee species on the island. The evolution of dioecy ofDendrocacalia on the island is thought to stem from the deleterious effects of inbreeding that are inherent in plants with geitonogamy. The increased geitonogamy on the island has resulted from increased woodiness (i.e., increased number of flowers per plant) and the original dependence on endemic bee pollinators, which are now endangered.     

Isolation and characterization of Ligustrum micranthum (Oleaceae) microsatellite loci using paired‐end Illumina reads

Twenty‐six microsatellite loci were developed and characterized for Ligustrum micranthum, a species endemic to the Ogasawara Islands, Japan. The genetic structure of this species must be clarified in order to restore the island's ecosystem. A total of 8511 primer pairs were designed from de novo sequencing. Of the 48 primer pairs selected, amplification and polymorphisms were tested using one population each from the Chichijima and Hahajima Islands of the Ogasawara Islands. Twenty‐six microsatellite loci were successfully amplified and the number of alleles for these loci ranged from five to 31 per locus, and the mean expected heterozygosities were 0.858 and 0.849, respectively. No significant deviation from the Hardy–Weinberg equilibrium was observed in either population, and no significant linkage disequilibrium was detected between any locus pair. The microsatellite loci reported in this study can be used in future studies to evaluate the genetic structure and mating system of L. micranthum.     

First record of potential bird pollination in the holoparasitic genus Orobanche L.

Pollinators play an important role in the reproduction of zoophilous plants. A shift in pollinators has often been observed for oceanic island plants, probably because of the differences in fauna. In this study, we obtained data on pollinator shifts from insects to birds in Orobanche boninsimae (Orobanchaceae), a holoparasitic plant species endemic to the Bonin (Ogasawara) Islands, oceanic islands in the Pacific. We observed pollination and measured seed viability in O. boninsimae and its continental sister species O. coerulescens. We found that two passerine birds, the Japanese white-eye (Zosterops japonicus) and bulbul (Hypsipetes amaurotis squameiceps), visited the flowers and sucked the nectar of O. boninsimae, while only insects visited those of O. coerulescens. Viable seeds were produced under pollinator-excluded treatments in the two Orobanche species, indicating that the seeds were produced by automatic self-pollination and/or apomixis. These results suggest that O. boninsimae may be pollinated by birds and can produce seeds by automatic self-pollination/apomixis. This is the first record of visitation of the genus Orobanche by birds. Studies of pollination systems in native plants on the Bonin Islands are few compared to those on other oceanic islands, and O. boninsimae may provide a valuable example of pollinator shifts in the Bonin Islands.     

Beetle responses to artificial gaps in an oceanic island forest: implications for invasive tree management to conserve endemic species diversity

Natural forests are often replaced by invasive alien trees on isolated oceanic islands. Adequate eradication of invasive trees should be conducted with the goal of biodiversity conservation, because islands support many endemic organisms that depend on native forests. An invasive alien tree, Bischofia javanica Blume (Euphorbiaceae), has invaded and replaced natural forests on the oceanic Ogasawara (Bonin) Islands, Japan, in the northwestern Pacific Ocean. To determine how the removal of B. javanica trees affects insect diversity, we examined flying beetles captured using Malaise traps in B. javanica forests on Hahajima. The abundance, species density, and species composition of wood-boring beetles (Coleoptera: Cerambycidae, Elateridae, Mordellidae, and Scolytidae) were compared between closed-canopy sites and gaps created by girdling B. javanica trees in alien forests during two seasons (June–July and October–November 2005). Of the collected beetles, 75.8, 87.5, 90.0, and 0.0% of cerambycid, elaterid, mordellid, and scolytid beetle species, respectively, were endemic to the Ogasawara Islands. More cerambycid, elaterid, and mordellid individuals were captured in June–July than in October–November; the number of scolytid individuals did not differ between seasons. More cerambycid, elaterid, and scolytid individuals were captured in artificial gaps than on the closed-canopy forest floor. Although fewer mordellid individuals were captured in gaps, more endemic mordellids were captured in gaps. More cerambycid and scolytid species were captured in artificial gaps than in closed-canopy areas. The positive responses of beetles to artificial gaps suggest that the removal of B. javanica increases beetle diversity and the abundance of endemic beetles.