Remote Oceanic Archipelago Research Articles

Inter-archipelago dispersal, anagenetic evolution, and the origin of a rare, enigmatic plant genus on a remote oceanic archipelago.

Island plants have long interested biologists because of their distinctive morphological features and their isolation on small land areas in vast oceans. Studies of insular endemics may include identifying their ancestors, tracing their dispersal to islands, and describing their evolution on islands, including characters adaptive to island life. Thamnoseris is a monospecific genus endemic to the Desventuradas Islands, Chile. Its origins and relationships are unresolved, given the challenges of getting to the islands and accessing plants there. Sequences from ITS of nrDNA and the complete chloroplast genome were employed to resolve phylogenetic relationships of Thamnoseris. Phylogenetic analyses of nuclear and chloroplast sequences showed Thamnoseris nested within or sister to Dendroseris, the largest endemic genus in the Juan Fernández Islands. Thamnoseris evolved from a common ancestor of all or most species of Dendroseris prior to the diversification of Dendroseris in the Juan Fernández archipelago. The ancestor of Thamnoseris dispersed to the Desventuradas archipelago, which consists of the islands San Ambrosio and San Félix, within the past 3 Ma (the age of San Ambrosio). This is the only known example of possible plant dispersa\l between the Juan Fernández and Desventuradas Islands. We also mention two less likely biogeographic scenarios for the origin of Thamnoseris, which has features not seen in Dendroseris: small capitula with yellow florets; style branches barely divergent; and basally swollen subtending involucral bracts, all features associated with selfing and reduced dispersal. Goats and rabbits (now removed) reduced T. lacerata, once very abundant on the Desventuradas Islands, to several plants, making it of extreme conservation concern and worthy of further study.

An updated checklist of Azorean arthropods (Arthropoda).

The Azores is a remote oceanic archipelago of nine islands which belongs to the Macaronesia biogeographical region hosting a unique biodiversity. The present Azorean landscape is strongly modified by the presence of man and only in small areas, where the soil or climate was too rough, have primitive conditions remained unchanged. Despite the fact that most of the Azorean native habitats are now lost, a large number of endemic species are still present and need urgent conservation. The present checklist of terrestrial and freshwater arthropods of the Azores Archipelago is based on all known published literature. The main goal of this work is to list, as rigorously as possible, all the known terrestrial and freshwater arthropods of the Azores. In this way, we are contributing to solve the 'Linnaean' shortfall, i.e. an incomplete taxonomic description of species-level diversity and the Wallacean Biodiversity Shortfall, the incomplete species distribution knowledge. The checklist includes new records of arthropods at island and archipelago levels that were published in the last twelve years. Compared to the last checklist of Azorean arthropods (Borges et al. 2010b), a total of 217 taxa (species and subspecies) are added.Currently, the total number of terrestrial and freshwater arthropod species and subspecies in the Azores is estimated to be 2420 taxa belonging to 14 classes, 53 orders, 440 families, 1556 genera, 2400 species and 149 individual subspecies.The most diverse orders of Azorean arthropods are: Coleoptera (585 taxa), Diptera (423 taxa), Hemiptera (338 taxa), Hymenoptera (163 taxa), Lepidoptera (159 taxa) and Araneae (133 taxa).A total of 276 endemic taxa are currently known (232 species and 44 subspecies), belonging to eight classes and 22 orders. São Miguel, Terceira and Pico are the islands with higher number of endemic species and subspecies. In the Azores, the number of native non-endemic taxa is 793 taxa, totalling 1069 indigenous taxa. Compared to the other nearest Macaronesian archipelagos (Madeira and Canaries), the Azorean arthropod fauna is characterised by a lower percentage of endemism (endemics/indigenous: 26% in Azores, 47% in Madeira Archipelago and 42% in Canary Islands) and a high proportion of exotic introduced taxa (39% in Azores, 19% in Madeira Archipelago and 8% in Canary Islands).Based on recent IUCN Red-listing of Azorean arthropods, a large fraction of the endemic taxa is under high threat.

Brachyuran crabs (Crustacea, Decapoda) from the remote oceanic Archipelago Trindade and Martin Vaz, South Atlantic Ocean.

Forty species of shore and shallow water brachyuran crabs are reported from the remote oceanic Archipelago Trindade and Martin Vaz (TMV), 11 of which were previously known from Trindade Island, 28 are recorded from the Archipelago for the first time, and one is a new species, Epialtus parvulus sp. nov. This brings the total known shore and shallow water decapod fauna of TMV to 99 species. The opportunity is taken here to elaborate on the taxonomy of the species reported from TMV. One new genus, Mecataleptodius, is recognized for two species, Cancer parvulus Fabricius, 1793, its type species, and Cataleptodius olsoni Manning Chace, 1990, endemic to Ascension Island. The following seven nominal species are synonymized: Acanthonyx dissimulatus Coelho in Coelho Torres, 1993; A. scutiformis (Dana, 1851a); Dromia gouveai Melo Campos Junior, 1999; Epialtus portoricensis Rathbun, 1923; Ranilia guinotae Melo Campos Junior, 1994; R. saldanhai H. Rodrigues da Costa, 1970; and Omalacantha garthi (Lemos de Castro, 1953). TMV is a subset of the western Atlantic crab fauna (23 species or 57.5%), also including 8 (20%) amphi-Atlantic species, 3 (7.5%) amphi-American, 3 (7.5%) endemic, 2 (5%) cosmopolitan, 1 (2.5%) known from both sides of the Atlantic and the Indo-West Pacific. The crab fauna of TMV, Ascension (AS) and Saint Helena (SH) are compared with one another as well as with that of the oceanic islands Fernando de Noronha (FN) and the Rocas Atoll (RA) by means of nonmetric multidimensional scaling (NMDS) applied to a dissimilarity matrix generated by Jaccards coefficient. TMV-FN-RA and AS-SH clustered into two distinct groups according to the composition of their crab fauna. The NMDS analysis ranked the species that cause segregation of the crab faunal assemblages among TMV, AS, and SH, while revealing a gradient in species composition between the two groups of islands (TMV-FN-RA and AS-SH) formed by the amphi-Atlantic species. Island isolation, age and size alone do not explain the existing differences in species richness among TMV, AS and SH. The taxonomic composition of the shallow water fauna in these islands is likely to have been determined by several variables that were interwoven differently along their evolutionary history.

Distribution of testate amoebae in bryophyte communities in São Miguel Island (Azores Archipelago).

BackgroundTestate amoebae are a polyphyletic group of protists living preferentially in soils, freshwaters and wetlands. These Protozoa have a worldwide distribution, but their presence and diversity in the Azores (a remote oceanic archipelago) is poorly known, with only twelve taxa recorded so far. The published information reflects occasional collections from sporadic field visits from naturalists to São Miguel Island, mainly in the nineteenth century. To overcome this limitation, a standardised survey was carried out on the Island, sampling different types of habitats from several localities to provide the distribution and information on species ecology of testate amoebae.New informationIn this study, 43 species of testate amoebae were recorded (within a total of 499 occurrences), belonging to two orders of Protista (26 Arcellinida and 17 Euglyphida). The most frequently occurring testate amoebae were Euglypha strigosa, Trinema lineare, Euglypha rotunda, Assulina muscorum and Cyclopyxis eurystoma. The most diverse genus was Euglypha (six species). A total of 38 species are new records for the Azores Archipelago. These data help to improve knowledge of the geographical distribution of testate amoebae in the northern hemisphere and their diversity in the Azores Archipelago.

Asteroidea (Echinodermata) from shallow-waters of the remote oceanic archipelago Trindade and Martin Vaz, southeastern Atlantic, with taxonomic and zoogeographical notes.

Trindade and Martin Vaz (TMV) is a highly isolated, oceanic volcanic archipelago located approximately 1200 km off the Brazilian coast and about 4200 km away from the nearest African coast. It has been almost 70 years since the first sea star, "Astropecten sp.", was recorded from Trindade in 1951. In the following years (1955-1971; 2006) six sea star species were added to the archipelago's fauna. After that period, however, research on shallow water echinoderms has not been conducted in TMV and no further sea star species have been recorded from there since. From 2012 to 2019, 263 daytime SCUBA diving and intertidal samplings conducted at TMV yielded 91 lots of sea stars in 7 species: Linckia guildingi Gray, 1840; Oreaster reticulatus (Linnaeus, 1758); Astropecten aff. antillensis Lütken, 1859; Copidaster lymani A. H. Clark, 1948; Luidia alternata alternata (Say, 1825); Mithrodia clavigera (Lamarck, 1816); and Ophidiaster guildingi Gray, 1840. The last five species in this list represent new records to the archipelago, with C. lymani also being the first record of the species in the southwestern Atlantic. Five shallow water species previously known from TMV have not been observed in the present survey: Asterinides folium (Lütken, 1860), Astropecten brasiliensis Müller Troschel, 1842, Astropecten cingulatus Sladen, 1883, Linckia nodosa Perrier, 1875, and Ophidiaster alexandri Verrill, 1915. Twelve sea star species are currently known from shallow waters of TMV. A list of all sea star species known from shallow waters (intertidal down to 100 meters) of the tropical southern-central Atlantic oceanic archipelagoes and islands (Ascension, Cape Verde, Fernando de Noronha, Gulf of Guinea, Rocas Atoll, Saint Helena, Trindade and Martin Vaz) with their gross distribution in the Atlantic Ocean was compiled in order to explore the existence of patterns of geographic distribution for the shallow water sea star species in the tropical southern-central Atlantic oceanic islands. It has been found that 44% of the species from TMV are of western Atlantic affinity, 33% amphi-Atlantic, and 22% circumtropical in distribution. No endemic sea star species are known from TMV to date. The even more remote Ascension (ASC) and Saint Helena (STH) are more of a mosaic than TMV. The ASC and STH fauna consist of 8 and 11 sea star species, respectively. Their endemic component totals to 25% and 27%, respectively. STH has more amphi-Atlantic and eastern Atlantic sea star species (27% each) than ASC (25% and 12.5%, respectively). Twenty-five percent of the sea star species in ASC are circumtropical in distribution, whereas no circumtropical species have been found in STH. The western Atlantic (WA) component comparatively to the eastern Atlantic (EA) one is of minor significance in STH (18% versus 27%, respectively), whereas the WA and EA components contribute equally to the taxonomic composition in ASC (12.5% each). However, patterns of faunal affinities in both islands are actually taxon-dependent.

Paguroids (Decapoda: Anomura: Diogenidae and Paguridae) of the remoteoceanic Archipelago Trindade and Martin Vaz, off southeast Brazil,with new records, description of three new species and zoogeographical notes.

Trindade and Martin Vaz (TMV) is a highly isolated, oceanic volcanic archipelago located some 1200 km off the Brazilian coast and about 4200 km away from the nearest African coast. For almost 100 years Calcinus tibicen (Herbst, 1791) was the only hermit crab species known from TMV. From 2012 to 2018, 263 daytime SCUBA diving and intertidal samplings conducted at TMV yielded 1075 paguroid specimens in 10 species, three of which are established herein as new species: Iridopagurus martinvaz sp. nov., Nematopagurus micheleae sp. nov., and Pagurus carmineus sp. nov. Iridopagurus margaritensis García-Gómez, 1983, and Phimochirus leurocarpus McLaughlin, 1981, both only known from the northern hemisphere, are recorded for the first time from the southwestern Atlantic. Opportunity was taken herein to include hitherto unreported or little known specimens from along the Vitória-Trindade Seamount Chain, namely, Dardanus venosus H. Milne Edwards, 1848, Nematopaguroides pusillus Forest de Saint Laurent, 1968, Pagurus provenzanoi Forest de Saint Laurent, 1968, and Phimochirus holthuisi (Provenzano, 1961). The lectotype of Pagurus venosus H. Milne Edwards, 1848 is designated as the neotype for the obscure Pagurus arrosor divergens Moreira, 1905, which thus becomes an objective junior synonym of the former. A list of all paguroid species known from the tropical southern-central Atlantic oceanic archipelagoes and islands (Ascension, Cape Verde, Fernando de Noronha, Gulf of Guinea, Rocas Atoll, Saint Helena, Trindade and Martin Vaz) with their gross distribution in the Atlantic Ocean is provided. Investigation on the existence of patterns of geographic distribution for the paguroid fauna of the tropical southern-central Atlantic oceanic islands showed that 70% percent of the paguroids from TMV are western Atlantic in origin and 30% endemic. No amphi-Atlantic paguroid species are known from TMV. Conversely, the affinity of Ascension's (33%) and Saint Helena's (50%) paguroids is with the eastern Atlantic; no western Atlantic paguroids have been reported from these two islands so far. Exploration on the existence of trends of correlation between islands area and species richness through the Spearman's coefficient of correlation showed that the patterns in the number of paguroid species cannot be explained by variation in island area alone (rs = 0.4728; p = 0.28571).

Hypotheses to explain the few early coastal archaeological deposits in Sāmoa: Preliminary evaluations

The Remote Oceanic archipelagos from Vanuatu to Sāmoa were first occupied 3000 years ago by populations with Lapita pottery at over 100 colonization sites. In Sāmoa, however, the first millennium of settlement is comprised of only a few isolated archaeological sites, and only one with Lapita pottery. This unique archaeological record is typically explained as a result of isostatic subsidence that destroyed or displaced more numerous coastal colonization sites. Three additional hypotheses may account for this pattern. First, few coastal flats may have existed for settlement, limiting occupation of the archipelago. Second, terrestrial geological processes may have destroyed what were once more numerous sites. Third, the few early and isolated sites in Sāmoa may reflect a small population of colonists resulting from demographic processes, including wave-front population density, or the Allee effect. We conducted a preliminary examination of the first two alternative hypotheses through a programme of coring and excavation across three coastlines on ‘Upolu island, Sāmoa. Sub-surface sediment data suggest both hypotheses may be valid explanations in different coastal settings. We propose additional research to test this possibility.

Reproductive ethology of the Fijian predator-inquiline wasp Pseudofoenus extraneus (Hymenoptera: Gasteruptiidae: Hyptiogastrinae)

ABSTRACTParasitoid wasps of the subfamily Hyptiogastrinae (Gasteruptiidae) are known to lay eggs in the nests of solitary bees and wasps. Their larvae are considered predator-inquilines, consuming the host’s eggs and larvae and then the nest provisions. Pseudofoenus extraneus is endemic to Fiji, and the only member of the subfamily Hyptiogastrinae known to have colonised the archipelago. The host relationships and oviposition sequence of this species have not been previously reported. We show that the primary host is the halictine bee Homalictus fijiensis and describe P. extraneus behaviour around Homalictus nest aggregations and the entering of host nests. Wasps were observed entering Homalictus nests on nine occasions, as well as perching near nests and antennating nest entrances. The high abundance of H. fijiensis in Fiji may help to explain how a parasitoid was able to successfully invade such a remote oceanic archipelago as Fiji.

Colonization and diversification of the white-browed shortwing (Aves: Muscicapidae: Brachypteryx montana) in the Philippines

Molecular phylogenetic approaches have greatly improved our knowledge of the pattern and process of biological diversification across the globe; however, many regions remain poorly documented, even for well-studied vertebrate taxa. The Philippine archipelago, one of the least-studied ‘biodiversity hotspots’, is an ideal natural laboratory for investigating the factors driving diversification in an insular and geologically dynamic setting. We investigated the history and geography of diversification of the Philippine populations of a widespread montane bird, the White-browed Shortwing (Brachypteryx montana). Leveraging dense archipelago-wide sampling, we generated a multi-locus genetic dataset (one nuclear and two mtDNA markers), which we analyzed using phylogenetic, population genetic, and coalescent-based methods. Our results demonstrate that Philippine shortwings (1) likely colonized the Philippines from the Sunda Shelf to Mindanao in the late Miocene or Pliocene, (2) diversified across inter-island barriers into three divergent lineages during the Pliocene and early Pleistocene, (3) have not diversified within the largest island, Luzon, contrary to patterns observed in other montane taxa, and (4) colonized Palawan from the oceanic Philippines rather than from Borneo, challenging the assumption of Palawan functioning exclusively as a biogeographic extension of the Sunda Shelf. Additionally, our finding that divergent (c. 4.0 mya) lineages are coexisting in secondary sympatry on Mindanao without apparent gene flow suggests that the speciation process is likely complete for these shortwing lineages. Overall, these investigations provide insight into how topography and island boundaries influence diversification within remote oceanic archipelagos and echo the results of many other studies in demonstrating that taxonomic diversity continues to be underestimated in the Philippines.

Shallow-water bryozoans from the Azores (central North Atlantic): native vs. non-indigenous species, and a method to evaluate taxonomic uncertainty

Bryozoan records from the shores and upper shelf (≤50 m depth) of the remote Azores Archipelago (central North Atlantic) have been analyzed, along with unpublished data and data from recent surveys. A checklist of 67 shallow-water species is hereby compiled for the region, of which more than one third represent records from campaigns conducted during the last 20 years. A classification on the origin of the species indicates that the majority (62%) are cryptogenic while 27% (n = 18) are considered native. Given the natural limitations for genetic exchange between the archipelago’s bryozoan populations and those from neighboring shores, the taxa presently considered as cryptogenic may yield a considerable amount of endemic species after taxonomic revision. The remaining 11% are confirmed as non-indigenous species, highlighting the importance of human-mediated transport in considerably enhancing the diversity of bryozoans in remote oceanic archipelagos, which would otherwise be off-limits to their natural dispersal capacity. In view of the need to quantitatively evaluate the certainty of species-level identification when assembling such biodiversity inventories, we have developed a method to attribute a degree of certainty to species records. The application of this method to the current checklist highlights the importance of further studies to ascertain the identification of many species recorded for the Azores, and to be able to categorize them confidently as either native, cryptogenic or non-indigenous.

A new species of Pachycheles (Crustacea: Anomura: Porcellanidae), with taxonomic remarks on two other porcelain crabs from the remote oceanic archipelago of Trindade and Martin Vaz, South Atlantic Ocean

Three species in two genera of porcelain crabs are reported from the remote oceanic archipelago of Trindade and Martin Vaz one of which, Pachycheles meloi, new to science. The new species is morphologically similar to Pachycheles riisei (Stimpson, 1858) from the inner continental shelf between Florida (USA) and São Paulo (Brazil), of which Pachycheles meloi sp. nov. differs by a suite of carapace and appendage characters, including the presence of a pair of male gonopods on the second abdominal segment (absent in P. riisei). The new species is additionally compared to other congeners. Opportunity is taken to elaborate on the taxonomy of Petrolisthes amoenus (Guérin-Méneville, 1855) and Petrolisthes marginatus (Stimpson, 1859). The Trindade and Martin Vaz Archipelago contain a strongly depauperate porcellanid fauna of western Atlantic affinities.

Towards a review of the decapod crustacea from the remote oceanic archipelago of Trindade and Martin Vaz, south Atlantic Ocean: new records and notes on ecology and zoogeography

The remoteness of the Trindade and Martin Vaz young volcanic archipelago (TMV) raises questions about the source of its marine benthic fauna and levels of endemism. Addressing these questions requires a comprehensive knowledge of the taxonomic composition of the marine fauna of the islands. A five-year survey in the shallow marine waters (up to 30 m) and a literature review on the data published for TMV have been conducted to document the biodiversity of the benthic fauna. Here we report on ten new records of decapod crustaceans from TMV: Gnathophyllum americanum and Thor amboinensis are circumtropical in distribution, whereas Stenopus hispidus, Gnathophylloides mineri and Parribacus antarcticus are disjunct circumtropical species as their distribution in the Atlantic Ocean is limited eastwardly to TMV or Ascension Island (S. hispidus), therefore, do not extending into the eastern Atlantic. Gnathophyllum circellum and Thor manningi are western Atlantic species, with G. circellum previously known only from the Caribbean Sea. Pontonia manningi, Tuleariocaris neglecta and Enoplometopus antillensis are amphi-Atlantic in distribution. Two of the above species are recorded from the southwestern Atlantic for the first time: Gnathophyllum circellum and Tuleariocaris neglecta. These new records corroborate that the marine benthic invertebrate fauna of the TMV archipelago is actually a mosaic of amphi-Atlantic, eastern Atlantic, central Atlantic (insular), endemic and circumtropical species, with a strong western Atlantic component.

Narrow water barriers prevent multiple colonizations and limit gene flow among California Channel Island wild buckwheats (Eriogonum: Polygonaceae)

The relative roles of chance colonization and subsequent gene flow in the development of insular endemic biotas have been extensively studied in remote oceanic archipelagos, but are less well characterized on nearshore island systems. The current study investigated patterns of colonization and divergence between and within two wild buckwheat species (Polygonaceae), Eriogonum arborescens and E. giganteum, endemic to the California Channel Islands to determine whether geographical isolation is driving diversification. Using plastid and nuclear sequence data and microsatellite allele frequencies, we determined that gene flow in these Eriogonum spp. is restricted by isolation. The data suggest that successful colonization of and gene flow among the islands are infrequent. Colonization appears to have followed a stepping-stone model that is consistent with a north-to-south pattern across the islands. This colonization pattern coupled with relatively little post-colonization inter-island gene flow, particularly among southern islands, has generated a pattern of more divergent lineages on the isolated southern islands. These results run counter to the general expectation that all islands close to a continental source should receive a high level of gene flow. Finally, management recommendations focused on protecting the lineages from loss of private alleles and the erosion of the remaining genetic diversity are offered.

Is the sword moss (Bryoxiphium) a preglacial Tertiary relict?

The disjunction of floras between East Asia, Southeast North America, West North America, and Southwest Eurasia has been interpreted in terms of the fragmentation of a once continuous mixed mesophytic forest that occurred throughout the Northern Hemisphere due to the climatic and geological changes during the late Tertiary. The sword moss, Bryoxiphium, exhibits a distribution that strikingly resembles that of the mesophytic forest elements such as Liriodendron and is considered as the only living member of an early Tertiary flora in Iceland. These hypotheses are tested here using molecular dating analyses and ancestral area estimations. The results suggest that the extant range of Bryoxiphium results from the fragmentation of a formerly wider range encompassing North America and Southeast Asia about 10 million years ago. The split of continental ancestral populations is too recent to match with a continental drift scenario but is spatially and temporally remarkably congruent with that observed in Tertiary angiosperm relict species. The timing of the colonization of Iceland from Macaronesian ancestors, about two million years ago, is, however, incompatible with the hypothesis that Bryoxiphium is the only living member of an early Tertiary flora of the island. Alaska was recurrently colonized from East Asia. The ability of Bryoxiphium to overcome large oceanic barriers is further evidenced by its occurrence on remote oceanic archipelagos. In particular, Madeira was colonized twice independently from American and East Asian ancestors, respectively. The striking range disjunction of Bryoxiphium is interpreted in terms of its mating system, as the taxon exhibits a very singular pattern of spatial segregation of the sexes.

Timing and Number of Colonizations but Not Diversification Rates Affect Diversity Patterns in Hemosporidian Lineages on a Remote Oceanic Archipelago

Parasite diversity on remote oceanic archipelagos is determined by the number and timing of colonizations and by in situ diversification rate. In this study, we compare intra-archipelago diversity of two hemosporidian parasite genera, Plasmodium and Leucocytozoon, infecting birds of the Mascarene archipelago. Despite the generally higher vagility of Plasmodium parasites, we report a diversity of Plasmodium cytochrome b haplotypes in the archipelago much lower than that of Leucocytozoon. Using phylogenetic data, we find that this difference in diversity is consistent with differences in the timing and number of colonizations, while rates of diversification do not vary significantly between the two genera. The prominence of immigration history in explaining current diversity patterns highlights the importance of historical contingencies in driving disparate biogeographic patterns in potentially harmful blood parasites infecting island birds.

Biogeography and morphological evolution in a Pacific island ant radiation

While insular radiations are documented for many terrestrial arthropods, few examples are known for eusocial insects. This study seeks to ascertain whether the spinescence observed among Fijian Pheidole ants was inherited from an oversea ancestor or is evidence of ecological release from interspecific competitors. We broaden our understanding of morphological convergence, insular radiation and Pacific biogeography by testing three hypotheses proposed previously for the Fijian Pheidole roosevelti group: (i) the group is monophyletic; (ii) spinescence is a plesiomorphic trait inherited from an overseas ancestor; and (iii) the group is closely related to spinescent New Guinean relatives. The analysis included the fragments of two mitochondrial genes (COI, cytb) and two nuclear genes (H3, EF1α-F2) from 66 taxa, including all members of the roosevelti group, representatives from the spinescent subgenus Pheidolacanthinus, Fijian congeners and widespread Pacific congeners. Our results yield new insights into the biogeographic history of Fiji, reveal a fascinating example of convergent evolution and serve as a novel example of ecological release occurring within an insular eusocial insect lineage. These findings recover the history of a presumably unremarkable ant species that colonized a remote oceanic archipelago in the Miocene (17-10 Ma) and radiated across the emerging islands into niche-space occupied elsewhere in the Pacific by distantly related spinescent congeners. We propose the radiation of Fijian Pheidole into spinescent morphotypes was the consequence of ecological opportunities afforded by the absence of competing ant lineages with conspicuous epigaeic foraging strategies.

Multiple colonizations of a remote oceanic archipelago by one species: how common is long‐distance dispersal?

AbstractAim It is well established that many groups of plants and animals have undergone long‐distance dispersal, but the extent to which this continues beyond initial colonization is largely unknown. To provide further insight into the frequency of gene flow mediated by long‐distance dispersal, we investigated the origins of the fern Asplenium hookerianum on the Chatham Islands, and present a review of the contribution of molecular data to elucidating the origins of this archipelago’s biota.Location Chatham Islands and New Zealand. A. hookerianum is scarce on the Chatham Islands but common in New Zealand, some 800 km to the west.Methods We compared chloroplast trnL–trnF DNA sequence data from Chatham Islands’A. hookerianum with extensive phylogeographic data for this genetically variable species in mainland New Zealand.Results Our sequencing revealed the presence of two haplotypes in Chatham Islands’A. hookerianum. These haplotypes differed by four mutational events and were each more closely related to haplotypes found in New Zealand than to each other.Main conclusions Despite the rarity of A. hookerianum on the Chatham Islands, its populations there appear to derive from at least two long‐distance dispersal events from New Zealand, these possibly originating from different areas. We suggest that long‐distance transoceanic dispersal, and the gene flow it can mediate, may be more common than is generally appreciated.