Island biogeography theory is one of the most influential paradigms in ecology. That island characteristics, including remoteness, can profoundly modulate biological diversity has been borne out by studies of animals and plants. By contrast, the processes influencing microbial diversity in island systems remain largely undetermined. We sequenced arbuscular mycorrhizal (AM) fungal DNA from plant roots collected on 13 islands worldwide and compared AM fungal diversity on islands with existing data from mainland sites. AM fungal communities on islands (even those >6000 km from the closest mainland) comprised few endemic taxa and were as diverse as mainland communities. Thus, in contrast to patterns recorded among macro-organisms, efficient dispersal appears to outweigh the effects of taxogenesis and extinction in regulating AM fungal diversity on islands. Nonetheless, AM fungal communities on more distant islands comprised a higher proportion of previously cultured and large-spored taxa, indicating that dispersal may be human-mediated or require tolerance of significant environmental stress, such as exposure to sunlight or high salinity. The processes driving large-scale patterns of microbial diversity are a key consideration for attempts to conserve and restore functioning ecosystems in this era of rapid global change.

Aim This study investigates the amount and distribution of genetic variation within and among populations of the highly invasive tree, Miconia calvescens (Melastomataceae; hereafter miconia), in tropical island habitats that are differently impacted (distribution and spread) by this weed.

The genus Adansonia has a disjunct geographical distribution: six species are endemic in Madagascar, one in Africa, and one in Australia. The well‐known African baobab (Adansonia digitata) is an iconic tree with considerable ethnobotanical significance. In contrast to the other seven species, which are diploid, A. digitata is tetraploid. A common ancestor of A. digitata and the other diploid baobab species would be diploid; however, there are no diploid species recorded on the African mainland. Examining variation in floral and pollen characters and chromosome number in specimens from Africa identified a new diploid baobab species, Adansonia kilima sp. nov., which co‐exists with A. digitata in Africa. Adansonia kilima is restricted to moderate elevations (650–1500 m), in contrast to A. digitata, which is widespread throughout Africa but prefers elevations below 800 m. Adansonia kilima is superficially similar to A. digitata, but can be differentiated on the basis of floral morphology, pollen, and chromosome number. We used two chloroplast DNA markers and the nuclear ITS to examine phylogenetic relationships within Adansonia. Three lineages were observed: one containing the Malagasy species, one containing the Australian species, and one containing the African species. The relationships between these clades were difficult to resolve, but a link between the African and Australian clades emerged when the analysis used fewer replicate samples of individual Malagasy taxa, included indel characters and included fewer outgroup taxa. The ITS phylogeny demonstrated that A. digitata and A. kilima are genetically similar, suggesting that tetraploidy evolved relatively recently.

BackgroundThe mass extirpation of the island of Moorea's endemic partulid tree snail fauna, following the deliberate introduction of the alien predator Euglandina rosea, represents one of the highest profile conservation crises of the past thirty years. All of the island's partulids were thought to be extirpated by 1987, with five species persisting in zoos, but intensive field surveys have recently detected a number of surviving wild populations. We report here a mitochondrial (mt) phylogenetic estimate of Moorean partulid wild and captive lineage survival calibrated with a reference museum collection that pre-dates the predator's introduction and that also includes a parallel dataset from the neighboring island of Tahiti.ResultsAlthough severe winnowing of Moorea's mt lineage diversity has occurred, seven of eight (six Partula; two Samoana) partulid tip clades remain extant. The extinct mt clade occurred predominantly in the P. suturalis species complex and it represented a major component of Moorea's endemic partulid treespace. Extant Moorean mt clades exhibited a complex spectrum of persistence on Moorea, in captivity, and (in the form of five phylogenetically distinct sister lineages) on Tahiti. Most notably, three Partula taxa, bearing two multi-island mt lineages, have survived decades of E. rosea predation on Moorea (P. taeniata) and in the valleys of Tahiti (P. hyalina and P. clara). Their differential persistence was correlated with intrinsic attributes, such as taxonomy and mt lineages, rather than with their respective within-island distribution patterns.ConclusionConservation efforts directed toward Moorean and Tahitian partulids have typically operated within a single island frame of reference, but our discovery of robust genealogical ties among survivors on both islands implies that a multi-island perspective is required. Understanding what genetic and/or ecological factors have enabled Partula taeniata, P. hyalina and P. clara to differentially survive long-term direct exposure to the predator may provide important clues toward developing a viable long term conservation plan for Society Island partulid tree snails.

Aim  To explore the potential of genetic processes and mating systems to influence successful plant invasions, we compared genetic diversity of the highly invasive tropical treelet, Miconia calvescens, in nine invasive populations and three native range populations. Specifically, we tested how genetic diversity is partitioned in native and invaded regions, which have different invasion histories (multiple vs. single introductions). Lastly, we infer how levels of inbreeding in different regions impact invasion success. Location  Invaded ranges in the Pacific (Hawaii, Tahiti, New Caledonia) and Australia and native range in Costa Rica. Methods  Genetic diversity was inferred by analysing variation at nine microsatellite loci in 273 individuals from 13 populations of M. calvescens. Genetic structure was assessed using amova, isolation by distance (IBD) within regions, a Bayesian clustering approach, and principal coordinates analysis. Results  Microsatellite analysis revealed that invaded regions exhibit low levels of allelic richness and genetic diversity with few private alleles. To the contrary, in the native range, we observed high levels of allelic richness, high heterozygosity and 78% of all private alleles. Surprisingly, despite evident genetic bottlenecks in all invasive regions, similarly high levels of inbreeding were detected in both invasive and native ranges (FIS: 0.345 and 0.399, respectively). Bayesian clustering analysis showed a lack of geographical structure in the Pacific and evidence of differing invasion histories between the Pacific and Australia. While Pacific populations are derived from a single introduction to the region, multiple introductions have taken place in Australia from different source regions. Main conclusions  Multiple introductions have not resulted in increased genetic diversity for M. calvescens invasions. Moreover, similar inbreeding levels between native and invaded ranges suggests that there is no correlation between levels of inbreeding and levels of standing genetic diversity for M. calvescens. Overall, our results show that neither inbreeding nor low genetic diversity is an impediment to invasion success.

The spectacular partulid tree snail fauna of the Society Islands has been almost completely extirpated in recent decades following the deliberate introduction of the alien carnivorous snail Euglandina rosea. The greatest loss has occurred on the island of Raiatea, French Polynesia, home to an estimated 34 species (including 33 single-island endemics), all of which have been deemed extirpated in the wild. However, we report here the February 2006 discovery of two surviving Raiatean partulid lineages on the upper slopes of Mount Tefatua, the highest peak on the island. They have been identified using morphological and molecular phylogenetic analyses, the latter approach employing available museum and captive reference samples. One population, at 750 m elevation, consisted of Samoana attenuata. It has a multi-island distribution within the archipelago and surviving populations persist also on Tahiti and Moorea. A second population, present just below the summit at 950 m, consisted of a previously unstudied morphospecies and it has been formally described as Partula meyeri. It is unclear if a stable altitudinal refuge from E. rosea predation exists on Mount Tefatua but the unexpected discovery of these two surviving montane populations raises the possibility of preserving some fraction of Raiatea's endemic tree snail diversity in the wild.

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Article impact statement: Combining native and non‐native species to evaluate biodiversity is overly simplistic and may undermine the conservation of ecosystems.