High levels of genetic diversity in island populations of the island endemic Suzukia luchuensis (Labiatae)

Genetic diversity and genetic differentiation within and among island populations was examined by allozyme electrophoresis in Suzukia luchuensis (Labiatae), which is endemic to four of the Ryukyu Islands, southern Japan, and one island near Taiwan. Intrapopulation allozyme diversity was very low in all the four Ryukyu Islands, probably due to the effects of random drift in small populations. In contrast, genetic diversity at the species level was high, possibly because of an ancient origin of populations and/or multiple colonization of the species on different islands. Genetic differentiation among the overall populations was high (G(ST)=0.863), while gene flow (Nm) as estimated from allozyme frequency data was 0.041, suggesting that its occurrence among populations is highly restricted. Hierarchical analysis of genetic differentiation indicated that a high proportion of the total allelic variance is attributed to variation among islands, corresponding to the fact that several alleles were fixed on only one island. However, intraisland genetic differentiation was small on all islands except Yonaguni Island, where S. luchuensis is relatively widely distributed. Most diversity was thus due to differences among islands.     

Genetic diversity in the threatened insular endemic plantAster asa-grayi (Asteraceae)

Genetic diversity in an insular endemic plantAster asa-grayi was examined using enzyme electrophoresis. Distribution ofA. asa-grayi is restricted to only four subtropical islands of Japan, and this species is listed as vulnerable to extinction in the Red Data Book of Japanese wild plants. A total of 161 individuals were sampled from five populations on four islands. Genetic diversity values at the population level were very low, compared to other plant species with a similar life history. Genetic variability at the species level is comparable to the mean value of endemic species. Genetic differentiation among populations is extremely high (G_ST= 0.71), indicating that the gene flow among populations is highly impeded, and pollen and seed dispersal is limited due to the pollinators and the seed morphology. This is because the four islands are geographically isolated. Fixation indices suggested that most populations do not randomly cross. To conserve the genetic diversity of the species, artificial crossings among different island populations are necessary.     

Differentiation with drift: a spatio-temporal genetic analysis of Galápagos mockingbird populations (Mimus spp.)

Small and isolated island populations provide ideal systems to study the effects of limited population size, genetic drift and gene flow on genetic diversity. We assessed genetic diversity within and differentiation among 19 mockingbird populations on 15 Galápagos islands, covering all four endemic species, using 16 microsatellite loci. We tested for signs of drift and gene flow, and used historic specimens to assess genetic change over the last century and to estimate effective population sizes. Within-population genetic diversity and effective population sizes varied substantially among island populations and correlated strongly with island size, suggesting that island size serves as a good predictor for effective population size. Genetic differentiation among populations was pronounced and increased with geographical distance. A century of genetic drift did not change genetic diversity on an archipelago-wide scale, but genetic drift led to loss of genetic diversity in small populations, especially in one of the two remaining populations of the endangered Floreana mockingbird. Unlike in other Galápagos bird species such as the Darwin''s finches, gene flow among mockingbird populations was low. The clear pattern of genetically distinct populations reflects the effects of genetic drift and suggests that Galápagos mockingbirds are evolving in relative isolation.     

Genetic structure of continental and island populations of the Mediterranean endemic Cyclamen balearicum (Primulaceae)

Cyclamen balearicum is a self-compatible perennial herb endemic to the western Mediterranean Basin. This species occurs in five geographically isolated terrestrial islands in southern France and on four Balearic islands. In this study, we compare genetic variability and differentiation within and among 11 terrestrial island populations and 17 true island populations. Of nine readable enzyme loci, five were polymorphic in both terrestrial and true islands. F statistics showed a significant heterozygote deficiency in all populations, probably due to high levels of autonomous selfing, restricted gene flow, and subsequent genetic drift. Genetic diversity was higher in terrestrial islands than on the Balearic islands, suggesting that the Balearic islands were colonized when they were in contact with the continent. Population differentiation was greater among terrestrial islands (Fst = 0.417 and Gst = 0.344) than among true islands (Fst = 0.112 and Gst = 0.093). Furthermore, differentiation among populations on the Basses Cévennes terrestrial island was greater (Fst = 0.254) than among populations on the true island of Mallorca (Fst = 0.163). The greater genetic differentiation among terrestrial islands could have been caused by genetic bottlenecks associated with changes in climate and human land use that may have reduced population sizes more severely in terrestrial islands in southern France than on the Balearic islands.     

Population size and time since island isolation determine genetic diversity loss in insular frog populations

Understanding the factors that contribute to loss of genetic diversity in fragmented populations is crucial for conservation measurements. Land‐bridge archipelagoes offer ideal model systems for identifying the long‐term effects of these factors on genetic variations in wild populations. In this study, we used nine microsatellite markers to quantify genetic diversity and differentiation of 810 pond frogs (Pelophylax nigromaculatus) from 24 islands of the Zhoushan Archipelago and three sites on nearby mainland China and estimated the effects of the island area, population size, time since island isolation, distance to the mainland and distance to the nearest larger island on reduced genetic diversity of insular populations. The mainland populations displayed higher genetic diversity than insular populations. Genetic differentiations and no obvious gene flow were detected among the frog populations on the islands. Hierarchical partitioning analysis showed that only time since island isolation (square‐root‐transformed) and population size (log‐transformed) significantly contributed to insular genetic diversity. These results suggest that decreased genetic diversity and genetic differentiations among insular populations may have been caused by random genetic drift following isolation by rising sea levels during the Holocene. The results provide strong evidence for a relationship between retained genetic diversity and population size and time since island isolation for pond frogs on the islands, consistent with the prediction of the neutral theory for finite populations. Our study highlights the importance of the size and estimated isolation time of populations in understanding the mechanisms of genetic diversity loss and differentiation in fragmented wild populations.     

Extensive clonality and strong differentiation in the insular pacific tree Santalum insulare: implications for its conservation

BACKGROUND AND AIMS: The impact of evolutionary forces on insular systems is particularly exacerbated by the remoteness of islands, strong founder effects, small population size and the influence of biotic and abiotic factors. Patterns of molecular diversity were analysed in an island system with Santalum insulare, a sandalwood species endemic to eastern Polynesia. The aims were to evaluate clonality and to study the genetic diversity and structure of this species, in order to understand the evolutionary process and to define a conservation strategy. METHODS: Eight nuclear microsatellites were used to investigate clonality, genetic variation and structure of the French Polynesian sandalwood populations found on ten islands distributed over three archipelagos. KEY RESULTS: It was found that 58 % of the 384 trees analysed were clones. The real size of the populations is thus dramatically reduced, with sometimes only one genet producing ramets by root suckering. The diversity parameters were low for islands (n(A) = 1.5-5.0; H(E) = 0.28-0.49). No departure from Hardy-Weinberg proportion was observed except within Tahiti island, where a significant excess of homozygotes was noted in the highland population. Genetic structure was characterized by high levels of differentiation between archipelagos (27 % of the total variation) and islands (F(ST) = 0.50). The neighbour-joining tree did not discriminate the three archipelagos but separated the Society archipelago from the other two. CONCLUSIONS: This study shows that clonality is a frequent phenomenon in S. insulare. The genetic diversity within populations is lower than the values assessed in species distributed on the mainland, as a consequence of insularity. But this can also be explained by the overexploitation of sandalwood. The differentiation between archipelagos and islands within archipelagos is very high because of the limited gene flow due to oceanic barriers. Delineation of evolutionary significant units and principles for population management are proposed based on this molecular analysis.     

Genetic structure among populations in the endemic Hawaiian Plantago lineage: insights from microsatellite variation

Endemic Hawaiian species in the genus Plantago show considerable morphological and ecological diversity. Despite their variation, a recent phylogenetic analysis based on DNA sequence data showed that the group is monophyletic and that sequence variation among species and morphotypes is low. This lack of sequence polymorphisms resulted in an inability to resolve species and population affinities within the most recently derived clade of this lineage. To assess species boundaries, population genetic structure and interpopulation connectivity among the morphologically and ecologically distinct populations within this clade, genetic variation was examined using eight microsatellite loci. Within‐population genetic diversity was found to be lowest in the Maunaiu, Hawai'i population of the endangered P. hawaiensis, and highest in the large P. pachyphylla population from 'Eke, West Maui. Isolation by distance across the range of populations was detected and indicated restricted dispersal. This result is likely to be attributable to few interisland dispersal events in the evolutionary history of this lineage. Genetic differentiation within islands tended to be higher among populations occurring in contrasting bog and woodland habitats, suggesting ecological barriers to gene flow and the potential role of ecological divergence in population diversification. Overall, these results are consistent with findings from phylogenetic analysis of the entire lineage. Our data bring new insights regarding patterns of dispersal and population genetic structure to this endemic and endangered group of island taxa. As island environments become increasingly fragmented, information of this type has important implications for the successful management of these fragile populations and habitats.     

ALLOZYME DIFFERENTIATION AND GENETIC STRUCTURE IN ISLAND AND MAINLAND JAPANESE POPULATIONS OF CAMPANULA PUNCTATA (CAMPANULACEAE)

Allozyme variation was investigated in 17 Japanese populations of Campanula punctata, ten from the Izu Islands and seven in the mainland (Honshu). The data indicate that there are two groups, a mainland group and an island one, and that the systematically problematic Oshima Island (northernmost Izu island) populations are closely related to those of the other islands. Nei's genetic identity values among islands and among mainland populations were 0.95 and 0.97, respectively, while the value between island and mainland populations was 0.84, suggesting that the island populations are an independent species. Total genetic variation was nearly the same among island and mainland populations. However, the apportionment of variation within and among populations was considerably different; 14% of gene diversity exists among mainland populations, while 31% of the diversity exists among island populations. Mean outcrossing rates of self-incompatible mainland and Oshima populations are 0.62–0.79, supporting xenogamy; those in self-compatible island populations are 0.37–0.57 in the northern islands, indicating a mixed mating system, and 0.16–0.25 in southern ones, indicating dominant inbreeding. Total genetic diversity in each island population decreased with distance from the mainland. Genetic and geological data suggest that the ancestors of insular populations were founded on northern islands in a relatively ancient period and that they dispersed progressively to the southern ones. Chromosome number (2n = 34) and isozyme numbers indicate gene duplications in this species, which suggests it is an ancient polyploid.     

岛屿植物舟山新木姜子居群遗传多样性的RAPD分析

基于随机扩增多态 DNA(RAPD)方法分析了舟山群岛濒危植物舟山新木姜子 (N eolitsea sericea) 6个居群的遗传多样性及分化程度。 10条随机引物扩增出 84个可分析位点 ,多态位点百分比 (PPL)为 3 8.10 %。经 POPOGENE分析发现 ,舟山新木姜子居群平均水平的多态位点百分比 (PPL )为 2 3 .18% ,Nei' s基因多样度 (HE)为 0 .0 793 ,Shannon信息指数 (H )为 0 .12 0 1,与其它岛屿植物比较具有中等偏低水平的遗传多样性 ;岛屿各居群间遗传分化程度较高 (Gst=0 .3 646) ;地理距离与遗传距离之间具有显著相关性 (r=0 .7697,P=96.62 % ) ,岛屿隔离效应是导致居群间遗传分化的重要因素。结合居群遗传多样性及UPGMA聚类分析 ,推测普陀山岛舟山新木姜子部分个体可能为大猫岛迁入的后裔 ,而朱家尖岛舟山新木姜子则由人为移植自普陀山岛。基于舟山新木姜子的物种保护及资源利用 ,建议加强现有自然居群的就地保护 ,促进居群自然更新 ;建立种质资源库 ,收集不同岛屿的种源进行混合繁殖 ,促进基因交流 ;选育优良品系用于海岛植被恢复及园林观赏     

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.     

Large mainland populations of South Island robins retain greater genetic diversity than offshore island refuges

For conservation purposes islands are considered safe refuges for many species, particularly in regions where introduced predators form a major threat to the native fauna, but island populations are also known to possess low levels of genetic diversity. The New Zealand archipelago provides an ideal system to compare genetic diversity of large mainland populations where introduced predators are common, to that of smaller offshore islands, which serve as predator-free refuges. We assessed microsatellite variation in South Island robins (Petroica australis australis), and compared large mainland, small mainland, natural island and translocated island populations. Large mainland populations exhibited more polymorphic loci and higher number of alleles than small mainland and natural island populations. Genetic variation did not differ between natural and translocated island populations, even though one of the translocated populations was established with five individuals. Hatching failure was recorded in a subset of the populations and found to be significantly higher in translocated populations than in a large mainland population. Significant population differentiation was largely based on heterogeneity in allele frequencies (including fixation of alleles), as few unique alleles were observed. This study shows that large mainland populations retain higher levels of genetic diversity than natural and translocated island populations. It highlights the importance of protecting these mainland populations and using them as a source for new translocations. In the future, these populations may become extremely valuable for species conservation if existing island populations become adversely affected by low levels of genetic variation and do not persist.     

Phylogeography of Eastern Polynesian sandalwood (Santalum insulare), an endangered tree species from the Pacific: a study based on chloroplast microsatellites

Aim Patterns of genetic variation within forest species are poorly documented in island ecosystems. The distribution of molecular variation for Santalum insulare, an endangered tree species endemic to the islands of eastern Polynesia, was analysed using chloroplast microsatellite markers. The aims were to quantify the genetic diversity; to assess the genetic structure; and to analyse the geographical distribution of the diversity within and between archipelagoes. The ultimate goal was to pre‐define evolutionary significant units (ESUs) for conservation and restoration programmes of this species, which constitutes a natural resource on small, isolated islands. Location Eleven populations, each representative of one island, covering most of the natural occurrence of S. insulare were sampled: five populations from the Marquesas Archipelago; three from the Society Archipelago; and three from the Cook–Austral Archipelago. These South Pacific islands are known for their high degree of plant endemism, and for their human occupation by Polynesian migrations. The extensive exploitation of sandalwood by Europeans nearly 200 years ago for its fragrant heartwood, used overseas in incense, carving and essential oil production for perfume, has dramatically reduced the population size of this species. Methods We used chloroplast microsatellites, which provide useful information in phylogeographical forest tree analyses. They are maternally inherited in most angiosperms and present high polymorphism. Among the 499 individuals sampled, 345 were genotyped successfully. Classical models of population genetics were used to assess diversity parameters and phylogenetic relationships between populations. Results Four microsatellite primers showed 16 alleles and their combinations provided 17 chlorotypes, of which four exhibited a frequency > 10% in the total population. The gene diversity index was high for the total population (H_e = 0.82) and varied among archipelagoes from H_e = 0.40 to 0.67. Genetic structure is characterized by high levels of differentiation between archipelagoes (36% of total variation) and between islands, but differentiation between islands varied according to archipelago. The relationship between genetic and geographical distance confirms the low gene flow between archipelagoes. The minimum spanning tree of chlorotypes exhibits three clusters corresponding to the geographical distribution in the three main archipelagoes. Main conclusions The high level of diversity within the species was explained by an ancient presence on and around the hotspot traces currently occupied by young islands. Diversity in the species has enabled survival in a range of habitats. Relationships between islands show that the Cook–Austral chlorotype cluster constitutes a link between the Marquesas and the Society Islands. This can be explained by the evolution of the island systems over millions of years, and extinction of intermediary populations on the Tuamotu Islands following subsidence there. Based on the unrooted neighbour‐joining tree and on the genetic structure, we propose four ESUs to guide the conservation and population restoration of Polynesian Sandalwood: the Society Archipelago; the Marquesas Archipelago; Raivavae Island; and Rapa Island.     

Allozyme diversity and history of distribution expansion in the maritime perennial plant Hedyotis strigulosa (Rubiaceae), distributed over the wide latitudes in the Japanese Archipelago

Allozyme diversity was examined in 30 populations of the maritime perennial plant Hedyotis strigulosa var. parviflora , which is distributed from subtropical islands to the central mainland of Japan. Genetic diversity within populations tended to be larger in southern island populations than in northern mainland populations. In the southern part of the distribution, the population size is generally large and populations are distributed more continuously than in the northern area, resulting in the larger effective size of southern populations as a whole. These factors play a major role in maintaining greater genetic diversity in the southern populations. By contrast, genetic diversity in the northern populations is very low, probably resulting from bottlenecks of population establishments during recolonization from refugial area to the northern areas. Geographically close populations were located near each other in the multidimensional scaling and the phenogram based on genetic distances, suggesting that gene flow among remote populations is rather limited. The pattern of genetic diversity in H. strigulosa var. parviflora is likely caused by the distribution expansion of the species; in the last glacier era, the species was restricted to the southern area; its advance to the northern area is relatively recent. Another variety endemic only to the Daito Islands, H. strigulos a var. luxurians , has lower genetic diversity than H. strigulosa var. parviflora and has genetically diverged from H. strigulosa var. parviflor a.  © 2008 The Linnean Society of London, Biological Journal of the Linnean Society , 2008, 93 , 679–688.     

Genetic differentiation among populations of an oceanic island: The case of Metrosideros boninensis, an endangered endemic tree species in the Bonin Islands

Conservation of endemic species on oceanic islands is an essential issue for biodiversity conservation. Metrosideros boninensis (Myrtaceae) is an endangered tree species endemic to the Bonin Islands of the western North Pacific Ocean. This species is considered to be extremely rare with less than 400 adult individuals, a number that has fluctuated between the 1880s and 1980s through human influence. We analyzed the genetic diversity and genetic structure of this species using amplified fragment length polymorphism markers and microsatellite markers. Genetic diversity of M. boninensis was extremely low compared to related taxa and similar endemic species from small islands. This low genetic diversity might be attributed to a stepwise colonization process with repeated founder bottlenecks in the dispersal pathway to the Bonin Islands. Populations of M. boninensis showed significant genetic differentiation and isolation by distance over a small geographical scale, despite the fact that this species should have extensive gene dispersal ability. This genetic differentiation might be caused by limited gene flow via pollen and seed among populations and genetic drift amid a small number of remnant individuals. Taken together, these findings suggest that the genetic diversity and connectivity of tree populations on islands are more vulnerable to habitat fragmentation than previously thought. We offer some recommendations for management to ameliorate habitat fragmentation and biological invasion.     

Allozyme variation in the endangered insular endemic Castilleja grisea

BACKGROUND AND AIMS: Genetic diversity in Castilleja grisea, an endangered, perennial herb endemic to San Clemente Island, California was investigated. Subsequent to the elimination of goats from the island in 1992, many populations of C. grisea have reappeared and have been increasing in size. METHODS: Nineteen populations were surveyed for their genotype at 19 allozyme loci. KEY RESULTS: At the taxon level, 57.9 % of loci are polymorphic with A(P) = 3.09 and H(E) = 0.137. Populations averaged 33.0 % polymorphic loci with A(P) = 2.43 and H(E) = 0.099. Most variation is found within rather than among populations (G(ST) = 0.128), although differentiation among populations is significant. Genetic identities range from I = 0.960 to I = 1.000 with mean I = 0.990. There is no significant relationship between genetic and geographic distance. Gene flow among populations is Nm = 2.50 based on private alleles and Nm = 1.70 based on F(ST). Outcrossing rates based on fixation indices average t = 1.01, indicating a primarily out-crossed mating system. CONCLUSIONS: The observed genetic variation is moderately high, unusually so for an insular endemic species, suggesting that C. grisea may not have lost substantial genetic variation during 150 years of overgrazing, and indicating that it is unlikely to be endangered by genetic factors.     

Distribution of genetic diversity within and between Western Mediterranean island populations of the black rat Rattus rattus (L. 1758)

Genetic diversity was estimated by allozyme analysis at 26 loci in black rat populations (Rattus rattus) from 15 western Mediterranean islands (Hyéres, Corsica, Sardinia and related islets). Although overall variability levels were low (H = 0.025), the mean heterozygosity values for the islands were similar to those for three reference mainland populations. Within the islands, however, genetic diversity varied in relation to island size and geographic isolation. In particular, most small insular populations were significantly more variable than those on both large and isolated islands. The generic relationships between island populations were established by F_ST analyses indicating possible geographic origins and patterns of colonization. The maintenance of unexpectedly high levels of variability in the small island populations is discussed in relation to changes in the demographic and social structure observed in these populations. These island populations of black rat illustrate how genetic diversity may be efficiently maintained in a series of interconnected spatially fragmented populations.     

Allozyme diversity and genetic divergence of the dolly varden Salvelinus malma Walbaum from the Kuril islands

Genetic variation was studied in the southern subspecies of the Asian Dolly Varden Salvelinus malma krascheninnikovi from the Kuril Islands. Thirty-six genetic loci controlling 19 enzyme systems were analyzed in 13 Dolly Varden populations from the Shumshu, Paramushir, Onekotan, Rasshua, Simushir, Urup, Iturup, and Kunashir islands. In the studied populations, the proportion of polymorphic loci was 35 to 85% and the mean heterozygosity was 0.104 to 0.173; populations from the Kunashir Island were characterized by maximum heterozygosity. In the island populations examined, significant inter-population heterogeneity of allele frequencies was found for all studied population pairs. For the total population of all islands, the inter-population diversity (GST = 0.188) was comparable to this parameter for the total population from the Kunashir Island (GST = 0.170). Genetic distances between populations did not correlate with the corresponding geographical distances, which indicates the lack of a pronounced gene exchange between the island populations. Cluster analysis and multidimensional scaling based on genetic distances did not reveal clear groups among the studied populations but indicated greater similarity within the Iturup-Simushir-Urup-Paramushir group and a greater genetic divergence of the Kunashir, Onekotan, Rasshua, and especially Shumshu populations. In the Shumshu population, allele frequencies indicate the admixture of genes of the northern Dolly Varden. The observed pattern of genetic differentiation was probably caused largely by genetic drift under the conditions of a limited gene flow because of homing (which is typical of the Dolly Varden) and the presence of isolated nonanadromous populations. The population-genetic analysis of the Dolly Varden from the Kuril Islands does not give grounds to distinguish any other isolated Dolly Varden species in this region than S. malma, which is represented by the southern form S. m. krascheninnikovi with an admixture of the northern form S. m. malma in the Shumshu Island.     

Genetic structure of kestrel populations and colonization of the Cape Verde archipelago

Genetic diversity and population structure were studied in eight populations of the kestrel Falco tinnunculus to identify the genetic consequences of spatial distribution and to infer the colonization patterns of the Cape Verde archipelago. We studied genetic differentiation and gene flow among seven island populations and one mainland population using nine microsatellite loci. Within the archipelago, differentiation was strong and genetic diversity and heterozygosity were low but variable among populations. Two subspecies F. tinnunculus neglectus on the northwestern islands and F. tinnunculus alexandri on all the other islands were identified as genetically distinct units. F. t. alexandri could be further separated into two groups on eastern and southern islands. Populations are probably founded by birds originating from the mainland. Immigration is more likely to the eastern and southern populations, whereas the northwestern islands with the lowest genetic diversity and highest differentiation are likely to exhibit fewer founding events by immigrants. The number of founding events on each island may depend not only on geographical distance to neighbouring populations, but also on directional immigration due to the northeastern trade winds. This may explain differences in genetic differentiation and diversity between populations and subspecies and may enable allopatric speciation.     

Genetics,Evolution, and Conservation of Island Plants

Islands are ideal model systems for testing ecological and evolutionary theory. This article reviews and synthesizes the findings of 24 studies of population genetics of island plants to gain insight into ecological and evolutionary processes on these unique, insular habitats. The studies reviewed found evidence for limited gene flow among islands and high genetic structure, but few tested for isolation by distance or among models of gene flow. Few studies compared diversity on islands with mainland populations or tested for bottlenecks, and the small number that did produced split results. Studies of rare species generally found that multiple islands would need to be protected to preserve genetic diversity. This review shows that surprisingly little work has been done to test theory using studies of population genetics on islands, and further work on testing among models of gene flow and examining population bottlenecks would be especially useful.     

Integrated species delimitation and conservation implications of an endangered weevil Pachyrhynchus sonani (Coleoptera: Curculionidae) in Green and Orchid Islands of Taiwan

Oceanic islands are productive habitats for generating new species and high endemism, which is primarily due to their geographical isolation, smaller population sizes and local adaptation. However, the short divergence times and subtle morphological or ecological divergence of insular organisms may obscure species identity, so the cryptic endemism on islands may be underestimated. The endangered weevil Pachyrhynchus sonani Kôno (Coleoptera: Curculionidae: Entiminae: Pachyrhynchini) is endemic to Green Island and Orchid Island of the Taiwan‐Luzon Archipelago and displays widespread variation in coloration and host range, thus raising questions regarding its species boundaries and degree of cryptic diversity. We tested the species boundaries of P. sonani using an integrated approach that combined morphological (body size and shape, genital shape, coloration and cuticular scale), genetic (four genes and restriction site‐associated DNA sequencing, RAD‐seq) and ecological (host range and distribution) diversity. The results indicated that all the morphological datasets for male P. sonani, except for the colour spectrum, reveal overlapping but statistically significant differences between islands. In contrast, the morphology of the female P. sonani showed minimum divergence between island populations. The populations of P. sonani on the two islands were significantly different in their host ranges, and the genetic clustering and phylogenies of P. sonani established two valid evolutionary species. Integrated species delimitation combining morphological, molecular and ecological characters supported two distinct species of P. sonani from Green Island and Orchid Island. The Green Island population was described as P. jitanasaius sp.n. Chen & Lin, and it is recommended that its threatened conservation status be recognized. Our findings suggest that the inter‐island speciation of endemic organisms inhabiting both islands may be more common than previously thought, and they highlight the possibility that the cryptic diversity of small oceanic islands may still be largely underestimated.