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.     

Shell shape and habitat use in the North‐west Pacific land snail Mandarina polita from Hahajima,Ogasawara: current adaptation or ghost of species past?

The endemic land snail genus Mandarina of the Ogasawara Islands provides an excellent model system to investigate adaptive radiation. Previously, it has been shown that coexisting species of the islands segregate by microhabitat, so that they are either predominantly found on the ground in relatively wet and sheltered sites, dry and exposed sites, or else are arboreal. Moreover, shell morphology correlates with microhabitat, so that species in wet and sheltered sites tend to have high-spired shells with a high aperture, and those in dry and exposed sites tend to have relatively low-spired shells with a wide aperture. We have now found that on Hahajima, Mandarina polita have variable shell morphology, and there is a correlation between morphology and the depth of leaf litter, as well as the presence/absence of other terrestrial species. Specifically, when high-spired terrestrial Mandarina ponderosa is present, M. polita tend to be low-spired and have a large aperture, indicative of character displacement. When M. ponderosa is absent, the shell shape of M. polita is much more variable, the overall spire is higher, individuals are found in deeper litter, and there is a strong correlation between litter depth and spire height. We argue that these patterns are due to local adaptation, but it remains possible that they are an artefact due to the 'ghost of species past'.  © 2007 The Linnean Society of London, Biological Journal of the Linnean Society , 2007, 91 , 149–159.     

Plant invasion and speciation along elevational gradients on the oceanic island La Palma,Canary Islands

Ecosystems that provide environmental opportunities but are poor in species and functional richness generally support speciation as well as invasion processes. These processes are expected not to be equally effective along elevational gradients due to specific ecological, spatial, and anthropogenic filters, thus controlling the dispersal and establishment of species. Here, we investigate speciation and invasion processes along elevational gradients. We assess the vascular plant species richness as well as the number and percentage of endemic species and non‐native species systematically along three elevational gradients covering large parts of the climatic range of La Palma, Canary Islands. Species richness was negatively correlated with elevation, while the percentage of Canary endemic species showed a positive relationship. However, the percentage of Canary–Madeira endemics did not show a relationship with elevation. Non‐native species richness (indicating invasion) peaked at 500 m elevation and showed a consistent decline until about 1,200 m elevation. Above that limit, no non‐native species were present in the studied elevational gradients. Ecological, anthropogenic, and spatial filters control richness, diversification, and invasion with elevation. With increase in elevation, richness decreases due to species–area relationships. Ecological limitations of native ruderal species related to anthropogenic pressure are in line with the absence of non‐native species from high elevations indicating directional ecological filtering. Increase in ecological isolation with elevation drives diversification and thus increased percentages of Canary endemics. The best preserved eastern transect, including mature laurel forests, is an exception. The high percentage of Canary–Madeira endemics indicates the cloud forest's environmental uniqueness—and thus ecological isolation—beyond the Macaronesian islands.     

The land fauna of Ascension Island: new data from caves and lava flows,and a reconstruction of the prehistoric ecosystem

Abstract. Terrestrial arthropods were investigated in 1990 and 1995 on Ascension, a young and extremely isolated volcanic island in the equatorial Atlantic. Three new genera (of Araneae, Oribatida and Psocoptera) were discovered and the number of apparently endemic species was increased from fourteen to about twenty-nine. Some 311 species of land animals (a few now extinct) are known to have established themselves on the island; in a few groups there may be significant numbers of unrecorded species. About ninety-five endemic and non-endemic species are considered to be native (including two marine turtles, twelve seabirds and two extinct landbirds); seventy-eight are of doubtful status; and at least 138 were probably introduced by humans. Natural colonists arrived mainly by air (drifting with the wind during migratory movements) but some evidently travelled on floating objects or attached to birds or other animals. Natural colonization was almost entirely from Africa. Before the arrival of humans, Ascension had an early successional ecosystem. The fauna in the lava and cinder deserts of the lowlands—both on the surface and in subterranean cracks and caves—was dominated by taxonomically varied scavengers and mainly arachnid predators. The scattered angiosperms here and in the foothills supported some host-specific herbivores with associated predators; they were also exploited (especially after exceptional rains) by a number of Orthoptera, Hemiptera and Lepidoptera derived from migratory African populations and perhaps reinforced at intervals by additional groups of colonists. The more extensive and largely cryptogamic vegetation on the central peak had a poor fauna probably composed mainly of micro-arthropods. Along coasts, on islets and in the extensive seabird colonies there were additional arthropod species and also a flightless rail and a night heron (both now extinct). Invertebrate stocks that colonized Ascension underwent a variety of evolutionary changes including phyletic evolution leading to endemic status, adaptation to subterranean life (Araneae, Pseudoscorpiones, Collembola and Psocoptera), character release (phorid Diptera), and probably splitting of lineages (speciation) within the island (Isopoda, Collembola and gryllid Orthoptera). The relatively high diversity of Pseudoscorpiones (five species in five genera) and their 100% apparent endemicity is notable. The indigenous fauna of Ascension provides a view of an early stage in the processes of colonization, adaptive evolution and radiation which—over much longer periods—give rise to the richer and more distinctive faunas of older oceanic islands such as Ascension's nearest neighbour, St Helena, where a few invertebrate clades have undergone repetitive speciation and some adaptive radiation.     

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.     

Cryptic diversity in Black rats Rattus rattus of the Galápagos Islands,Ecuador

Human activity has facilitated the introduction of a number of alien mammal species to the Galápagos Archipelago. Understanding the phylogeographic history and population genetics of invasive species on the Archipelago is an important step in predicting future spread and designing effective management strategies. In this study, we describe the invasion pathway of Rattus rattus across the Galápagos using microsatellite data, coupled with historical knowledge. Microsatellite genotypes were generated for 581 R. rattus sampled from 15 islands in the archipelago. The genetic data suggest that there are at least three genetic lineages of R. rattus present on the Galápagos Islands. The spatial distributions of these lineages correspond to the main centers of human settlement in the archipelago. There was limited admixture among these three lineages, and these finding coupled with low rates of gene flow among island populations suggests that interisland movement of R. rattus is rare. The low migration among islands recorded for the species will have a positive impact on future eradication efforts.     

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.     

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.     

Impact of introduced honeybees, Apis mellifera, upon native bee communities in the Bonin (Ogasawara) Islands

The Bonin (Ogasawara) Islands are oceanic islands located in the northwest Pacific, and have ten native (nine endemic) bee species, all of which are nonsocial. The European honeybee (Apis mellifera), which was introduced to the islands for apiculture in the 1880s, became naturalized in a few islands shortly after introduction. To detect the impact of the honeybees upon native bee diversity, we analyzed pollen harvest by honeybees and surveyed the relative abundance of honeybees and native bees on flowers on several islands. Both hived and feral honeybee colonies were active throughout the year, harvesting pollen of both native and alien flowers and from both entomophilous and anemophilous flowers. Honeybees strongly depended on the alien plants, especially during winter to spring when native melittophilous flowers were rare. From June to November, honeybees exhaustively utilized native flowers, which had originally been utilized and pollinated by native bees. On Chichi and Haha Islands, where human disturbance of forests has been severe, both native and alien flowers were dominated by honeybees, and native bees were rare or extinct even in well-conserved forests. In contrast, on Ani Island and Haha's satellite islands where primary forests were well conserved and honeybees were still uncommon or absent, native bees remained dominant. These results suggest that competition for nectar and pollen of the native flowers between honeybees and native bees favors honeybees on the disturbed islands, which are thoroughly invaded by alien nectariferous, sometimes aggressive, weedy plants. Received: May 8, 1998 / Accepted: May 6, 1999     

The origin of Rattus rattus on the Îles Éparses,Western Indian Ocean

Tollenaere et al. (Journal of Biogeography, 2010, 37 , 398–410) present a phylogeographic analysis of Rattus rattus for the Western Indian Ocean, with particular emphasis on Madagascar, but do not include samples from three island groups centrally located in the Mozambique Channel. Haplotypes from these islands provide additional information on the colonization pathways of R. rattus in the Western Indian Ocean region. For each of the three Îles Éparses groups in the Mozambique Channel, we test the competing hypotheses that colonization by R. rattus was most likely: (1) from the Arabian Peninsula, (2) from East Africa, (3) from Madagascar, or (4) from independent shipping. These results are combined with historical observations of the presence of R. rattus on these islands to give stronger inference on the colonization pathways. Additionally, more accurate colonization dates provide guidance for contemporary conservation management.     

Extinction threats of a narrowly endemic shrub, Stachyurus macrocarpus (Stachyuraceae) in the Ogasawara Islands

Stachyurus macrocarpus is a narrowly endemic endangered shrub of which only one population remains on Chichi-jima Island (Ogasawara). We surveyed its population dynamics and reproductive states for 4 years and analyzed the population viability. In a survey of its entire distribution range, a total of 87 S. macrocarpus individuals have been found and 68 individuals have been confirmed in 2007. Thus, the actual population size is estimated to be less than 100 individuals. Environmental conditions and the results of a hand-pollination experiment suggest that low fruit setting in both sexes (female: 4.9–11.2%; hermaphrodite: 0.0%) may be caused by resource limitation. In addition, fruit predation by alien Rattus rattus was observed despite the rare fruit setting. The small effective population size (23.1–24.6 individuals) and hermaphrodite-biased sex ratio (46 hermaphrodites:12 females) would increase the risk of extinction. The habitat of S. macrocarpus was limited to dense scrubland and forest understory, and seedling regeneration was very scarce. During the survey period, 19 individuals (21.8%) were found dead, there were only two seedling recruitments, and the annual population growth rate was 0.979. The lack of occurrence on the south and west slopes and the shortness of shrubs in open spaces suggests that S. macrocarpus suffers stress from both dryness and frequent typhoons. However, S. macrocarpus also exhibited high mortality of shoot in forest understories. These findings suggest that the suitable habitat of S. macrocarpus is likely to be narrow in Ogasawara. While the recent increase of goat grazing has not affected individual mortality, 58.6% of shoots that had been grazed by goats were dead within 2 years. As elasticity analysis had shown that larger individuals make a greater contribution to the population growth rate, repeated goat grazing would impact the S. macrocarpus population in the near future by decreasing the vitality of larger individuals. Emergency measures for protecting the shrub from goat grazing and reinforcing the population through nursery cultivation were proposed.     

The bark and ambrosia beetles (Curculionidae, Scolytinae) of Cocos Island, Costa Rica and the role of mating systems in island zoogeography

Cocos Island is a small oceanic island midway between Costa Rica and the Galápagos Archipelago; about 2 Myr in age, it is the only tropical oceanic island in the eastern Pacific with tropical wet forest. We identified several hundred bark beetle specimens collected during recent expeditions by INBio, the National Biodiversity Institute of Costa Rica, and re-examined all specimens from earlier collections. We report 19 species in ten genera, seven or eight of which are endemic, making scolytines the largest group of beetles known from the island. We describe as new Pycnarthrum pseudoinsulare , Xyleborinus cocoensis , and Xyleborus sparsegranulosus , resurrect Xyleborus bispinatus as separate from X. ferrugineus , and report six other species as new to Cocos Island. Three-quarters of the scolytines reproduce by brother–sister mating, and we argue that inbreeders are superior island colonists because they are less affected than are outbreeders by problems of mate location and inbreeding depression. The fauna and flora of Cocos Island arrived by dispersal and human transport. We examine natural colonization patterns for the fauna, using the distributions of the relatives of island endemics: most colonization came from the Americas, but the closest relatives to some endemics are found on Caribbean or Galápagos islands. © 2006 The Linnean Society of London, Biological Journal of the Linnean Society , 2006, 89 , 729–743.     

The structure of the cutaneous pedal glands in the banded snail Cepaea hortensis (Müller, 1774)

Although gastropods have been crawling through the ocean and on the land for 60 million years, we still know very little about the sticky mucus produced in their foot. Most research has been focused on marine species in particular and, to a lesser extent, on the well‐known terrestrial species Arion vulgaris and Cornu aspersum. Within this study, we aim to characterize the foot anatomy of a smaller representative of the family Helicidae, the banded snail Cepaea hortensis. We are particularly interested in the microanatomy of the foot glands, their position, and the histochemical nature of their secretory content. Characterization of the dorsal foot region of Cepaea hortensis reveals four glands, differing in their size and in the granules produced. Histochemically, three of them react positively for sugars (PAS staining and lectin affinity tests for mannose, glucose and N‐acetyl‐d ‐glucosamine) and acidic proteins (positive Alcian blue and Toluidine blue staining), indicating the presence of acidic glycosaminoglycans. The fourth gland type does not react to any of these dyes. The ventral pedal region includes two different gland types, which are positive for the presence of acidic glycoproteins, with a lectin affinity for mannose only. A comparison with Helix pomatia indicates differences regarding the number of glands and their contents. In Helix, only three gland types are described in the dorsal region of the foot, which show a similar granular appearance but nevertheless differ in their chemical composition. Congruently, there are two gland types in the ventral region in both species, whereas in Helix an additional sugar moiety is found. This raises the question whether these differences between the pedal glandular systems of both helicid species are the result of protection or size‐related adaptations, as they occur in the same habitat.