A GENETIC PERSPECTIVE OF MAMMALIAN VARIATION AND EVOLUTION IN THE INDONESIAN ARCHIPELAGO: BIOGEOGRAPHIC CORRELATES IN THE FRUIT BAT GENUS CYNOPTERUS

This study investigated allozyme and morphometric variability within the genus Cynopterus, with particular emphasis on C. nusatenggara, which is endemic to Wallacea, the area encompassing the Oriental-Australian biogeographic interface. The genetic distances between Cynopterus species are small by mammalian standards and suggest that this genus has undergone a recent series of speciation events. The genetic distance between populations of C. nusatenggara is strongly correlated with both the contemporary sea-crossing distance between islands and the estimated sea crossing at the time of the last Pleistocene glacial maximum, 18,000 b .p . This observation, together with low levels of population substructure within islands as shown by F-statistics, indicates that the sea is a primary and formidable barrier to gene exchange. The genetic distance and the great-circle geographical distance between the populations of C. nusatenggara are not correlated, although a principal-coordinates analysis of genetic distance reveals relationships between the populations that are similar to their geographical arrangement. A strong negative correlation exists between the level of heterozygosity within island populations of C. nusatenggara and the minimum sea-crossing distance to the nearest large source population. This is interpreted as reflecting an isolation effect of the sea, leading to reduced heterozygosity in populations that have larger sea barriers between them and the large source islands. Independently of this, heterozygosity is negatively associated with longitude, which in turn is associated with systematic changes in the environment such as a gradual decline in rainfall from west to east. The association between heterozygosity and longitude is interpreted as reflecting an association between genetic and environmental variance and supports the niche-width theory of genetic variance. Morphometric variability did not show any of the main effects demonstrated in the genetic data. Furthermore, there was no evidence that, at the level of individuals, genetic and morphometric variability were associated.     

Implications of contrasting patterns of genetic variability in two vespertilionid bats from the Indonesian archipelago

Wallacean island populations of two Vespertilioninae bats, Myotis muricola and Scotophilus kuhlii , which have similar geographical ranges, showed marked contrast in the amount and pattern of genetic variation. Within islands, genetic variation was on average much higher in M. muricola but declined from west to east, whereas all populations of S. kuhlii had uniformly low levels of genetic variation by mammalian standards. S. kuhlii showed little genetic differentiation between islands and estimates of gene flow were substantial whereas island populations of M. muricola differed markedly and there was a strong isolation-by-distance effect associated with the extent of the sea crossing between islands. Furthermore, the lower mean heterozygosity and small genetic distances between eastern island populations of M. muricola is evidence that there has been a bottleneck associated with the colonization of this area. The attenuation of genetic diversity to the east is also seen in some other mammalian species and may indicate limits to dispersal and have implications for species management. The patterns of variability in S. kuhlii may be a consequence of its strong dispersal capacity and close association with human activity, which, together with other factors, suggest a panmictic population.  © 2004 The Linnean Society of London, Biological Journal of the Linnean Society , 2004, 83 , 421–431.     

Genetic variation and island biogreography: Microsatellite and mitochondrial DNA variation in island populations of the Australian bush rat, Rattus fuscipes greyii

To understand the impact of various factors on the maintenance of genetic variation in natural populations, we need to focus on situations where at least some of these factors are removed or controlled. In this study, we used highly variable, presumably neutral, microsatellite and mtDNA markers to assess the nature of genetic variation in 14 island and two mainland populations of the Australian bush rat, where there is no migration between islands. Thus we are controlling for selection and gene flow. Both marker sets revealed low levels of diversity within the small island populations and extreme differentiation between populations. For six microsatellite loci, all of the small island populations had less genetic variation than the mainland populations; reduction in allelic diversity was more pronounced than loss of heterozygosity. Kangaroo Island, the large island population, had similar levels of diversity to the mainland populations. A 442 base pair (bp) section of the mtDNA control region was screened for variation by outgroup heteroduplex analysis/temperature gradient gel electrophoresis (OHA/TGGE). Only three of the 13 small island populations showed haplotypic diversity: Gambier (2), Waldegrave (2), and Eyere (3). The level of haplotypic diversity in the small island populations was similar to that on the mainland, most likely reflecting a recent population bottleneck on the mainland. In contrast, Kangaroo Island had 9 mtDNA haplotypes. The dominant factor influencing genetic diversity on the islands was island size. No correlation was detected between genetic diversity and the time since isolation or distance form the mainland. The combination of genetic drift within and complete isolation among the small island populations has resulted in rapid and extreme population divergence. Population pair-wise comparisons of allele frequency distributions showed significant differences for all populations for all loci (F _st = 0.11–0.84, R _st = 0.07–0.99). For the mtDNA control region, 92.6% of variation was apportioned between populations; only the Pearson islands shared a haplotype. Mantel tests of pair-wise genetic distance with pair-wise geographic distance showed no significant geographical clustering of haplotypes. However, population substructuring was detected within populations where sampling was conducted over a broader geographical range, as indicated by departures from Hardy-Weinberg equilibrium. Thus substructuring in the ancestral population cannot be ruled out. The dominant evolutionary forces on the islands, after the initial founder event, are stochastic population processes such as genetic drift and mutation. This revised version was published online in July 2006 with corrections to the Cover Date.     

GENETIC STRUCTURE OF NATURAL POPULATIONS IN THE RED ALGAE GELIDIUM CANARIENSE (GELIDIALES,RHODOPHYTA) INVESTIGATED BY RANDOM AMPLIFIED POLYMORPHIC DNA (RAPD) MARKERS1

Random amplified polymorphic DNA (RAPD) marker variation was analyzed in female gametophytes in natural populations of Gelidium canariense (Grunow) Seoane‐Camba ex Haroun, Gil‐Rodríguez, Diaz de Castro et Prud'Homme van Reine from the Canary Islands to estimate the degree and distribution of genetic variability and differentiation. A total of 190 haploid individuals were analyzed with 60 polymorphic RAPDs bands which produced 190 distinct multilocus genotypes. A high level of polymorphism was detected in all populations analyzed. Within‐population gene diversity ranged from 0.156 to 0.264. The populations on the island of Gran Canaria showed higher genetic variation than the other populations analyzed. The partitioning of molecular variance by analysis of molecular variance showed that most genetic variation resides within populations (68.85%). These results suggest that sexual reproduction is the predominant mode of reproduction for G. canariense gametophytic populations, and the main determinant in reaching high levels of genetic diversity. The Neighbor‐Joining tree and FCA analysis displayed two subclusters that correspond to the populations from the western islands (Tenerife, La Palma, Gomera) and the eastern island (Gran Canaria). In addition, we have detected a significant relationship between F_ST/(1?F_ST) and geographical distance consistent with data on water circulation and age of islands. The results obtained agree with an isolation by distance model, with gene flow from eastern to the western islands, and a high level of genetic differentiation between populations (F_ST=0.311, P<0.001).     

Parasites and the island syndrome: the colonization of the western Mediterranean islands by Heligmosomoides polygyrus (Dujardin, 1845)

Aim Populations of free‐living vertebrates on islands frequently differ from their mainland counterparts by a series of changes in morphometric, life‐history, behavioural, physiological and genetic traits, collectively referred to as the ‘island syndrome’. It is not known, however, whether the ‘island syndrome’ also affects parasitic organisms. The present study establishes the colonization pattern of the Mediterranean islands by the nematode Heligmosomoides polygyrus, a direct and specific parasite of rodent hosts of the Apodemus genus, and evaluates the effects of island colonization by this species on two components of the island syndrome: the loss of genetic diversity and the enlargement of the ecological niche. Location Heligmosomoides polygyrus was sampled on seven western Mediterranean islands ? Corsica, Crete, Elba, Majorca, Minorca, Sardinia and Sicily ? as well as in 20 continental locations covering the Mediterranean basin. Methods The mitochondrial cytochrome b gene (690 base pairs) was sequenced in 166 adult H. polygyrus individuals sampled in the 27 continental and island locations. Phylogenetic reconstructions in distance, parsimony, maximum likelihood and Bayesian posterior probabilities were carried out on the whole cytochrome b gene data set. The levels of nucleotide, haplotype and genetic divergence (Kimura two‐parameter distance estimator) diversities were estimated in each island population and in the various continental lineages. Results Phylogenetic reconstructions show that the mainland origins of H. polygyrus were continental Spain for the Balearic Islands (Majorca, Minorca), northern Italy for the Tyrrhenian Islands (Corsica, Sardinia, Elba), southern Italy for Sicily, and the Balkan region for Crete. A comparison of island H. polygyrus populations with their mainland source populations revealed two characteristic components of the island syndrome in this parasite. First, island H. polygyrus populations display a significant loss of genetic diversity, which is related (r² = 0.73) to the distance separating the island from the mainland source region. Second, H. polygyrus exhibits a niche enlargement following insularization. Indeed, H. polygyrus in Corsica is present in both A. sylvaticus and Mus musculus domesticus, while mainland H. polygyrus populations are present exclusively in Apodemus hosts. Main conclusions Our results show that H. polygyrus has undergone a loss of genetic diversity and a niche (host) enlargement following colonization of the western Mediterranean islands. To our knowledge, this study provides the first evidence for components of the ‘island syndrome’ in a parasitic nematode species.     

Microsatellite DNA evidence for genetic drift and philopatry in Svalbard reindeer

Mainland populations of Arctic reindeer and caribou Rangifer tarandus often undergo extensive movements, whereas populations on islands tend to be isolated and sedentary. To characterize the genetic consequences of this difference, levels of genetic diversity and subdivision of Svalbard reindeer (R. t. platyrhynchus) from two adjacent areas on Nordenskjiöldland, Spitsbergen were estimated using data from up to 14 microsatellites. The mean number of alleles per locus in Svalbard reindeer was 2.4 and mean expected heterozygosity per locus was 0.36. The latter value was significantly lower than in Canadian caribou and Norwegian reindeer but higher than in some other cervid species. Large samples of females (n = 743) and small samples of males (n = 38) from two sites ≈ 45 km apart showed genetic subdivision, which could be due to local population fluctuations or limited gene flow. To our knowledge, this is the first study to report significant differentiation at microsatellite loci in Rangifer at such short geographical distances. Neither population showed genetic evidence for recent population bottlenecks when loci unbiased with respect to heterozygosity were analysed. In contrast, false signals of a recent bottleneck were detected when loci upwardly biased with respect to heterozygosity were analysed. Thus, Svalbard reindeer appeared to conform to the paradigm of island populations made genetically depauperate by genetic drift.     

Effects of ecogeographic variables on genetic variation in montane mammals: implications for conservation in a global warming scenario

Aim Evolutionary theory predicts that levels of genetic variation in island populations will be positively correlated with island area and negatively correlated with island isolation. These patterns have been empirically established for oceanic islands, but little is known about the determinants of variation on habitat islands. The goals of this study were twofold. Our first aim was to test whether published patterns of genetic variation in mammals occurring on montane habitat islands in the American Southwest conformed to expectations based on evolutionary theory. The second aim of this research was to develop simple heuristic models to predict changes in genetic variation that may occur in these populations as a result of reductions in available mountaintop habitat in response to global warming. Location Habitat islands of conifer forest on mountaintops in the American Southwest. Methods Relationships between island area and isolation with measures of allozyme variation in four species of small mammal, namely the least chipmunk (Tamias minimus), Colorado chipmunk (Tamias quadrivittatus), red squirrel (Tamiasciurus hudsonicus), and Mexican woodrat (Neotoma mexicana), were determined using correlation and regression techniques. Significant relationships between island area and genetic variation were used to develop three distinct statistical models with which to predict changes in genetic variation following reduction in insular habitat area arising from global warming. Results Patterns of genetic variation in each species conformed to evolutionary predictions. In general, island area was the most important determinant of heterozygosity, while island isolation was the most important determinant of polymorphism and allelic diversity. The heuristic models predicted widespread reductions in genetic variation, the extent of which depended on the population and model considered. Main conclusions The results support a generalized pattern of genetic variation for any species with an insular distribution, with reduced variation in smaller, more isolated populations. We predict widespread reductions in genetic variation in isolated populations of montane small mammals in the American Southwest as a result of global warming. We conclude that climate‐induced reductions in the various dimensions of genetic variation may increase the probability of population extinction in both the short and long term.     

Genetic variation and structure of house sparrow populations: is there an island effect?

Population genetic structure and intrapopulation levels of genetic variation have important implications for population dynamics and evolutionary processes. Habitat fragmentation is one of the major threats to biodiversity. It leads to smaller population sizes and reduced gene flow between populations and will thus also affect genetic structure. We use a natural system of island and mainland populations of house sparrows along the coast of Norway to characterize the different population genetic properties of fragmented populations. We genotyped 636 individuals distributed across 14 populations at 15 microsatellite loci. The level of genetic differentiation was estimated using F‐statistics and specially designed Mantel tests were conducted to study the influence of population type (i.e. mainland or island) and geographic distance on the genetic population structure. Furthermore, the effects of population type, population size and latitude on the level of genetic variation within populations were examined. Our results suggest that genetic processes on islands and mainland differed in two important ways. First, the intrapopulation level of genetic variation tended to be lower and the occurrence of population bottlenecks more frequent on islands than the mainland. Second, although the general level of genetic differentiation was low to moderate, it was higher between island populations than between mainland populations. However, differentiation increased in mainland populations somewhat faster with geographical distance. These results suggest that population bottleneck events and genetic drift have been more important in shaping the genetic composition of island populations compared with populations on the mainland. Such knowledge is relevant for a better understanding of evolutionary processes and conservation of threatened populations.     

Genetic diversity and structure of the invasive tree Miconia calvescens in Pacific islands

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. Location Invasive populations were included from northern and southern Pacific islands including the Hawaiian Islands (Hawaii, Kauai and Maui), Marquesas Islands (Nuku Hiva), Society Islands (Tahiti, Tahaa, Moorea, Raiatea) and New Caledonia. Methods We used 9 codominant microsatellite and 77 highly variable dominant intersimple sequence repeat markers (ISSRs) to characterize and compare genetic diversity among and within invasive miconia populations. For the codominant microsatellite data we calculated standard population genetic estimates (heterozygosity, number of alleles, inbreeding coefficients, etc.) and described population genetic structure using AMOVA, Mantel tests (to test for isolation by distance), unweighted pair‐group method with arithmetic averages (UPGMA) cluster analysis and principal components analysis (PCA). We also tested for the presence of a population bottleneck and used a Bayesian analysis of population structure in combination with individual assignment tests. For the dominant ISSR data we used AMOVA, PCA, upgma and a Bayesian approach to investigate population genetic structure. Results Both markers types showed little to no genetic differentiation among miconia populations from northern and southern Pacific hemispheres (AMOVA: microsatellite, 3%; ISSR, 0%). Bayesian and frequency‐based analysis also failed to support geographical genetic structure, confirming considerable low genetic differentiation throughout the Pacific. Molecular data furthermore showed that highly successful miconia populations throughout the Pacific are currently undergoing severe bottlenecks and high levels of inbreeding (f = 0.91, ISSR; F_IS = 0.27, microsatellite). Main conclusions The lack of population genetic structure is indicative of similar geographical sources for both hemispheres and small founding populations. Differences in invasive spread and distribution among Pacific islands are most likely the result of differences in introduction dates to different islands and their accompanying lag phases. Miconia has been introduced to relatively few tropical islands in the Pacific, and the accidental introduction of a few or even a single seed into favourable habitats could lead to high invasive success.     

Prey‐associated head‐size variation in an invasive lizard in the Hawaiian Islands

Biological invasions are recognized as a primary driver of large‐scale changes in global ecosystems. This study addresses ecomorphological variation in head size within and among populations of an ecologically destructive invasive predator, and evaluates the potential roles of environmental components in phenotypic differentiation. We used four size‐corrected measurements of head morphology in Jackson's chameleons, Trioceros jacksonii xantholophus (N = 319), collected from multiple Hawaiian Islands to assess phenotypic variation among and within islands. Results of analysis of variance (ANOVA) comparing chameleon head size (PC1) among islands revealed significant differences (mean difference > 5%) associated with variation in both rainfall and diet composition using Mann–Whitney U‐tests and chi‐squared analyses. These results suggest that morphological differentiation among populations from different islands has occurred over a relatively short ecological timescale, and is likely the result of ecomorphological adaptation to differences in exploited prey hardness. Intra‐island allopatric population variation, however, was also detected in this study. Although we might expect that genetic change is the more likely explanation for differences between islands than within, and that plasticity may be more likely an explanation for the within‐ than the between‐island differences, it is also possible that both within‐ and between‐island patterns are the results of genetic change, or of plasticity.     

Local endemism and within‐island diversification of shrews illustrate the importance of speciation in building Sundaland mammal diversity

Island systems are important models for evolutionary biology because they provide convenient, discrete biogeographic units of study. Continental islands with a history of intermittent dry land connections confound the discrete definitions of islands and have led zoologists to predict (i) little differentiation of terrestrial organisms among continental shelf islands and (ii) extinction, rather than speciation, to be the main cause of differences in community composition among islands. However, few continental island systems have been subjected to well‐sampled phylogeographic studies, leaving these biogeographic assumptions of connectivity largely untested. We analysed nine unlinked loci from shrews of the genus Crocidura from seven mountains and two lowland localities on the Sundaic continental shelf islands of Sumatra and Java. Coalescent species delimitation strongly supported all currently recognized Crocidura species from Sumatra (six species) and Java (five species), as well as one undescribed species endemic to each island. We find that nearly all species of Crocidura in the region are endemic to a single island and several of these have their closest relative(s) on the same island. Intra‐island genetic divergence among allopatric, conspecific populations is often substantial, perhaps indicating species‐level diversity remains underestimated. One recent (Pleistocene) speciation event generated two morphologically distinct, syntopic species on Java, further highlighting the prevalence of within‐island diversification. Our results suggest that both between‐ and within‐island speciation processes generated local endemism in Sundaland, supplementing the traditional view that the region's fauna is relictual and primarily governed by extinction.     

Genetic variation of pantropical Terminalia catappa plants with sea‐drifted seeds in the Bonin Islands: suggestions for transplantation guidelines

The Bonin Islands are endowed with endemic species. However, these species are at risk of extinction because of the exuberance of invasive alien plants. Therefore, native plant species should be revegetated after eradicating alien plants. We investigated the genetic variation of Terminalia catappa populations in the Bonin Islands by using nuclear (n) microsatellites (simple sequence repeats [SSRs]) and chloroplast (cp) DNA. No significant differences were observed in the genetic diversity of nSSRs among 22 populations. However, recent bottlenecks were detected in three populations on the Chichijima Island group. nSSR variation and cpDNA haplotypes suggested the presence of two genetically distinct groups in the Mukojima and Chichijima Island groups and the Hahajima Island group. A similar genetic structure was observed in plants and animals in the Bonin Islands. Populations on the three islands, which were separated from other islands in each island group when the water depth was 50‐m lower than the present level, were dominated by unique nSSRs clusters, suggesting that historical changes in island connections during the Pleistocene era affected genetic substructuring. These results suggested that different factors contributed to the genetic structure of T. catappa on different geographic scales. At the whole‐island level, the genetic structure was determined by long‐distance seed dispersal by ocean currents. At the island‐group level, the genetic structure was determined by historical changes in island connections caused by changes in the sea level due to glacial–interglacial transition. These findings would help in establishing transplantation zone borders for revegetating T. catappa on the Bonin Islands.     

Phylogeographical structure in the coastal species Senecio rodriguezii (Asteraceae), a narrowly distributed endemic Mediterranean plant

Aim Our goals were (1) to assess the levels of chloroplast DNA variation in a narrowly distributed plant restricted to continental islands, (2) to ascertain whether a phylogeographical structure is present in plants restricted to coastal linear systems, and (3) to interpret the results in the light of the known palaeogeography of these islands. Location The Eastern Balearic Islands (Majorca and Minorca) in the Western Mediterranean Basin. Methods Sampling included 134 individuals from 28 populations of Senecio rodriguezii covering the entire range of the species. Sequences of the chloroplast genome (trnT–trnL spacer) were obtained and parameters of population genetic diversity and substructure were determined (h_sh_t, G_st). The geographical structure of genetic variation was assessed by an analysis of molecular variance (AMOVA). Additionally, a spatial AMOVA (SAMOVA) was used to identify groups of populations that were geographically homogeneous and maximally differentiated from each other. Finally, a pattern of isolation by distance was assessed by testing the correlation between the matrix of pairwise Φ_ST values and the matrix of geographical distances between pairs of populations using a Mantel test. Results Seven haplotypes were detected in S. rodriguezii. Only two of them were shared between islands; all of the others were restricted to Majorca (two) or Minorca (three). Overall, we found high levels of genetic diversity and significant geographical structuring of cpDNA markers. Most of the variation detected can be attributed to differences among populations (84.6%), but there was also a significant differentiation between the islands. Main conclusions Our results support the view that the Balearic Islands constitute a reservoir of genetic diversity, not only for widespread Mediterranean taxa, but also for endemic ones. The intraspecific genetic structure found in S. rodriguezii suggests that its population history was dominated by both expansion and contraction events. This has resulted in a species that is highly structured genetically, showing very few shared haplotypes between islands, and a high number of haplotypes restricted to small geographical areas within the islands. Changes in habitat availability and dynamic processes of population fragmentation and connectivity due to repeated cycles of sea‐level changes during the Quaternary are the possible underlying factors that have shaped the cpDNA pool of this endemic species on a regional scale.     

THE RELEVANCE OF GENE FLOW IN METAPOPULATION DYNAMICS OF AN OCEANIC ISLAND ENDEMIC,OLEA EUROPAEA SUBSP. GUANCHICA

Theoretical and empirical studies suggest that geographical isolation and extinction–recolonization dynamics are two factors causing strong genetic structure in metapopulations, but their consequences in species with high dispersal abilities have not been tested at large scales. Here, we investigated the effect of population age structure and isolation by distance in the patterns of genetic diversity in a wind‐pollinated, zoochorous tree (Olea europaea subsp. guanchica) sporadically affected by volcanic events across the Canarian archipelago. Genetic variation was assessed at six nuclear microsatellites (nDNA) and six chloroplast fragments (cpDNA) in nine subpopulations sampled on four oceanic islands. Subpopulations occurring on more recent substrates were more differentiated than those on older substrates, but within‐subpopulation genetic diversity was not significantly different between age groups for any type of marker. Isolation‐by‐distance differentiation was observed for nDNA but not for cpDNA, in agreement with other metapopulation studies. Contrary to the general trend for island systems, between‐island differentiation was extremely low, and lower than differentiation between subpopulations on the same island. The pollen‐to‐seed ratio was close to one, two orders of magnitude lower than the average estimated for other wind‐pollinated, animal‐dispersed plants. Our results showed that population turnover and geographical isolation increased genetic differentiation relative to an island model at equilibrium, but overall genetic structure was unexpectedly weak for a species distributed among islands. This empirical study shows that extensive gene flow, particularly mediated by seeds, can ameliorate population subdivision resulting from extinction–recolonization dynamics and isolation by distance.     

Genetic structure of the Canarian palm tree (Phoenix canariensis) at the island scale: does the ‘island within islands’ concept apply to species with high colonisation ability?

• Oceanic islands are dynamic settings that often promote within‐island patterns of strong population differentiation. Species with high colonisation abilities, however, are less likely to be affected by genetic barriers, but island size may impact on species genetic structure regardless of dispersal ability.
• The aim of the present study was to identify the patterns and factors responsible for the structure of genetic diversity at the island scale in Phoenix canariensis, a palm species with high dispersal potential. To this end, we conducted extensive population sampling on the three Canary Islands where the species is more abundant and assessed patterns of genetic variation at eight microsatellite loci, considering different within‐island scales.
• Our analyses revealed significant genetic structure on each of the three islands analysed, but the patterns and level of structure differed greatly among islands. Thus, genetic differentiation fitted an isolation‐by‐distance pattern on islands with high population densities (La Gomera and Gran Canaria), but such a pattern was not found on Tenerife due to strong isolation between colonised areas. In addition, we found a positive correlation between population geographic isolation and fine‐scale genetic structure.
• This study highlights that island size is not necessarily a factor causing strong population differentiation on large islands, whereas high colonisation ability does not always promote genetic connectivity among neighbouring populations. The spatial distribution of populations (i.e. landscape occupancy) can thus be a more important driver of plant genetic structure than other island, or species′ life‐history attributes.

     

Contrasting genetic responses to population fragmentation in a coevolving fig and fig wasp across a mainland–island archipelago

Interacting species of pollinator–host systems, especially the obligate ones, are sensitive to habitat fragmentation, due to the nature of mutual dependence. Comparative studies of genetic structure can provide insights into how habitat fragmentation contributes to patterns of genetic divergence among populations of the interacting species. In this study, we used microsatellites to analyse genetic variation in Chinese populations of a typical mutualistic system – Ficus pumila and its obligate pollinator Wiebesia sp. 1 – in a naturally fragmented landscape. The plants and wasps showed discordant patterns of genetic variation and geographical divergence. There was no significant positive relationship in genetic diversity between the two species. Significant isolation‐by‐distance (IBD) patterns occurred across the populations of F. pumila and Wiebesia sp. 1 as whole, and IBD also occurred among island populations of the wasps, but not the plants. However, there was no significant positive relationship in genetic differentiation between them. The pollinator populations had significantly lower genetic variation in small habitat patches than in larger patches, and three island pollinator populations showed evidence of a recent bottleneck event. No effects of patch size or genetic bottlenecks were evident in the plant populations. Collectively, the results indicate that, in more fragmented habitats, the pollinators, but not the plants, have experienced reduced genetic variation. The contrasting patterns have multiple potential causes, including differences in longevity and hence number of generations experiencing fragmentation; different dispersal patterns, with the host's genes dispersed as seeds as well as a result of pollen dispersal via the pollinator; asymmetrical responses to fluctuations in partner populations; and co‐existence of a rare second pollinating wasp on some islands. These results indicate that strongly interdependent species may respond in markedly different ways to habitat fragmentation.     

Historical fragmentation of islands and genetic drift in populations of Galápagos lava lizards (Microlophus albemarlensis complex)

The formation of islands following a rise in sea level at the end of Pleistocene is expected to disrupt the equilibrium between genetic drift and gene flow in species with limited ability to disperse. Here, we test the hypothesis that genetic drift in isolation has caused the differentiation of Galápagos lava lizards ( Microlophus albemarlensis complex) found on 12 islets that are likely to have been connected to a larger island, Isla Santa Cruz, during the late Pleistocene. Using 11 microsatellite loci, screened on 524 individuals from 17 localities distributed among and within 15 islands, we found marked differences in allelic richness and heterozygosity. Genetic differentiation was strong (global F _ST = 0.44), with pairwise differences found among populations on islets being larger than differences among three localities sampled within Isla Santa Cruz. As expected under a scenario of drift in isolation, there was a positive correlation of genetic diversity with island size, no relationship between genetic and geographical distance and a strong negative correlation between heterozygosity and measures of genetic differentiation. We conclude that seawater is a significant barrier to gene flow in lava lizards on this timescale. Our results suggest that the shallow diversification of the M. albemarlensis complex is not due to recent gene flow and that genetic drift may have played a substantial role in observed patterns of phenotypic variation among islands.     

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.     

Insight into an island radiation: the Tarentola geckos of the Cape Verde archipelago

Aim To reassess the relationships between Tarentola geckos from the Cape Verde Islands by including specimens from all islands in the range. To determine the variation within forms by sequencing over 400 specimens, thereby allowing the discovery of cryptic forms and resolving some of the issues raised previously. This extensive sampling was also used to shed light on distributions and to explain genetic diversity by comparing the ages and ecological and geological features of the islands (size, elevation and habitat diversity). Location The Cape Verde Islands: an oceanic archipelago belonging to the Macaronesian biogeographic region, located around 500 km off Senegal. Methods A total of 405 new specimens of Tarentola geckos were collected from nine islands with very different geological histories, topography, climate and habitats. Mitochondrial cytochrome b (cyt b) gene and 12S rRNA partial sequences were obtained and analysed using phylogenetic methods and networks to determine molecular diversity, demographic features and phylogeographic patterns. Results The phylogenetic relationships between all known forms of Cape Verdean Tarentola specimens were estimated for the first time, the relationships between new forms were assessed and previously hypothesized relationships were re‐examined. Despite the large sample size, low intraspecific diversity was found using a 303‐bp cyt b fragment. Star‐like haplotype networks and statistical tests suggest the past occurrence of a rapid demographic and geographical expansion over most of the islands. Genetic variability is positively correlated with size, elevation and habitat diversity of the islands, but is not linearly related to the age of the islands. Biogeographical patterns have, in general, high concordance with phylogenetic breaks and with the three eco‐geographical island groups. Volcanism and habitat diversity, both tightly linked with island ontogeny, as postulated by the general dynamic model of oceanic island biogeography, as well as present and historical size of the islands appear to be the main factors explaining the genetic diversity of this group. Main conclusions The Tarentola radiation was clarified and is clearly associated with the geological and ecological features of the islands. Two factors may account for the low intraspecific variation: (1) recent volcanic activity and high ecological stress, and (2) poor habitat diversity within some islands. More studies are needed to align taxonomy with phylogenetic relationships, whereas GIS modelling may help to predict precise species distributions.     

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.