Diversity In Island Populations Research Articles

The great tit HapMap project: A continental-scale analysis of genomic variation in a songbird.

A major aim of evolutionary biology is to understand why patterns of genomic diversity vary within taxa and space. Large-scale genomic studies of widespread species are useful for studying how environment and demography shape patterns of genomic divergence. Here, we describe one of the most geographically comprehensive surveys of genomic variation in a wild vertebrate to date; the great tit (Parus major) HapMap project. We screened ca 500,000 SNP markers across 647 individuals from 29 populations, spanning ~30 degrees of latitude and 40 degrees of longitude - almost the entire geographical range of the European subspecies. Genome-wide variation was consistent with a recent colonisation across Europe from a South-East European refugium, with bottlenecks and reduced genetic diversity in island populations. Differentiation across the genome was highly heterogeneous, with clear 'islands of differentiation', even among populations with very low levels of genome-wide differentiation. Low local recombination rates were a strong predictor of high local genomic differentiation (FST), especially in island and peripheral mainland populations, suggesting that the interplay between genetic drift and recombination causes highly heterogeneous differentiation landscapes. We also detected genomic outlier regions that were confined to one or more peripheral great tit populations, probably as a result of recent directional selection at the species' range edges. Haplotype-based measures of selection were related to recombination rate, albeit less strongly, and highlighted population-specific sweeps that likely resulted from positive selection. Our study highlights how comprehensive screens of genomic variation in wild organisms can provide unique insights into spatio-temporal evolutionary dynamics.

The use of geometric morphometry and traditional methods to analyze intraspecific variability of the first lower molar (m1) of Alexandromys fortis (Arvicolinae) in island and continental populations of Primorye, Russia

The complexity of the structure of the dental surface of the first lower molar (m1) of mainland and island populations of the reed vole Alexandromys fortis (Büchner, 1889) was assessed using two different methods. Using the traditional approach and methods of geometric morphometry (GM), the morphological variability of the anteroconid m1 of this species of the mainland (the south of Primorsky Krai) and the islands of the Peter the Great Gulf was analyzed. The traditional approach was based on describing the folding of the occlusal surface using three features: 1) folding of the lingual side of the anterior unpaired anteroconid loop (AC); 2) the shape of the labial side of the AC; 3) the shape of the fourth lingual reentrant angle. On the mainland part of the species' range, the highest occurrence was shown by morphotype III-C-a, which also predominated in the Late Pleistocene samples of the species in Primorye. The research revealed increased morphotypic diversity in island populations of the reed vole, which is probably due to the phenotypic and genotypic characteristics of the founders of island populations, as well as inbreeding, which can cause the release of hidden diversity and an increase in the number of rare morphotypes. The most numerous morphotype on the De Livrona – Durnovo Islands was II-C-a, rare for the mainland. In general, the most complex forms are present on the islands. Using a geometric morphometry approach, the anteroconid was divided into two separately studied structures: the anterior unpaired loop of the anteroconid (AC) and the base of the anteroconid (AB). The distribution of AC configurations in the space of the two principal components took on an arcuate shape, revealing a “forbidden zone.” The main changes occur on the lingual side of the AC. Regression analysis showed a direct relationship between the length of the contour (mm) and the complication of the shape of the anterior unpaired loop. The base of the anteroconid (AC) also undergoes transformation: it either stretches or contracts, while if the anterior unpaired loop of the anteroconid (AB) is more complex, then simplification and compression of its base is observed (negative regression). Analysis of the results of using two approaches, traditional and GM methods, in the analysis of the variability of the anteroconid section m1 of A. fortis showed extreme subjectivity in the use of the first one and the wide possibilities of the second one for identifying different aspects of molare transformation using mathematical methods.

Genomic Insights into the Historical Population Dynamics and Spatial Differentiation of an Endangered Island Endemic Palm,Brahea edulis

Premise of research. Brahea edulis is an endangered palm endemic to the oceanic island of Guadalupe, Mexico, with a small population of just about 4000 individuals; it was chronically grazed by goats for about two centuries. The evolutionary specificities of insular biotas provide unique scenarios for studying the roles of geography, demography, and climate in driving population divergence. A comprehensive comparison between insular and mainland sister species contributes to a much better understanding of the species-specific responses to the ecological drivers of diversity, divergence, and speciation.Methodology. Here we used a comparative approach coupled with genomic (genotyping by sequencing; single-nucleotide polymorphisms) data to analyze samples from island and mainland Brahea palm species and elucidate their diversity, population divergence, and demographic history.Pivotal results. Genetic diversity analyses revealed higher diversity in insular palms compared with their mainland sister species. Genetic relationships among palm individuals on Guadalupe Island resulted in two strongly diverged clusters that reflected their geographic distributions. Divergence among B. edulis populations was mostly driven by the joint effect of low migration and the climatic heterogeneity of the island’s conditions. Using approximate Bayesian analysis, we further evaluated the demographic history of B. edulis. We found the genetic signatures of demographic fluctuations, inferring an effective population size (Ne) reduction that occurred in the late Quaternary and relatively low current Ne.Conclusions. These findings contribute to the ever-growing body of evidence that low genetic diversity in island populations cannot always be generalized. Besides, genetic diversity and differentiation on islands are more likely to be species specific and are strongly influenced by population size and historical factors such as the time since the population was established, ecological characteristics of the island, and anthropogenic impact. Our results also represent groundwork for future conservation and restoration programs for this endangered insular palm species.

Population genomics of invasive rodents on islands: Genetic consequences of colonization and prospects for localized synthetic gene drive.

Introduced rodent populations pose significant threats worldwide, with particularly severe impacts on islands. Advancements in genome editing have motivated interest in synthetic gene drives that could potentially provide efficient and localized suppression of invasive rodent populations. Application of such technologies will require rigorous population genomic surveys to evaluate population connectivity, taxonomic identification, and to inform design of gene drive localization mechanisms. One proposed approach leverages the predicted shifts in genetic variation that accompany island colonization, wherein founder effects, genetic drift, and island‐specific selection are expected to result in locally fixed alleles (LFA) that are variable in neighboring nontarget populations. Engineering of guide RNAs that target LFA may thus yield gene drives that spread within invasive island populations, but would have limited impacts on nontarget populations in the event of an escape. Here we used pooled whole‐genome sequencing of invasive mouse (Mus musculus) populations on four islands along with paired putative source populations to test genetic predictions of island colonization and characterize locally fixed Cas9 genomic targets. Patterns of variation across the genome reflected marked reductions in allelic diversity in island populations and moderate to high degrees of differentiation from nearby source populations despite relatively recent colonization. Locally fixed Cas9 sites in female fertility genes were observed in all island populations, including a small number with multiplexing potential. In practice, rigorous sampling of presumptive LFA will be essential to fully assess risk of resistance alleles. These results should serve to guide development of improved, spatially limited gene drive design in future applications.

In situ glacial survival maintains high genetic diversity of Mussaenda kwangtungensis on continental islands in subtropical China.

Generally, island populations are predicted to have less genetic variation than their mainland relatives. However, a growing number of studies have nevertheless reported exceptions, indicating that the relationships were impacted by several factors, for example, historical processes. In the present study, we chose a group of subtropical islands located in South China as the study system, which are quite younger and much closer to the mainland than most of the previous studied island systems, to test the hypothesis that in situ glacial survival contributes to high levels of genetic diversity in island populations. We conducted a comparison of genetic variation between 12 island and 11 nearby mainland populations of Mussaenda kwangtungensis using eleven nuclear microsatellite and three chloroplast markers, evaluated effects of the island area and distance to mainland on genetic diversity of island populations, and simulated the potential distribution over the past by ecological niche modeling, together with the genetic data to detect the role of islands during the glacial periods. The island populations displayed comparable levels of genetic diversity and differentiation with mainland populations, overall high levels of unique polymorphisms, and the greatest values of specific within‐population genetic diversity. No significant correlation was detected between genetic diversity of island populations and distance to mainland, as well as area of islands, except that allelic richness was significantly positively correlated with the area of islands. Nuclear microsatellites revealed two main clusters, largely corresponding to islands and inland populations, which divergence dated to a time of island formation by ABC analysis. Ecological niche modeling predicted a highly climatic suitability on islands during the last glacial maximum (LGM). Our results suggest that the islands have acted as refugia during the LGM and highlight the role of in situ glacial survival in maintaining high levels of genetic diversity of M. kwangtungensis in continental islands of subtropical China.

Assessing connectivity despite high diversity in island populations of a malaria mosquito.

Documenting isolation is notoriously difficult for species with vast polymorphic populations. High proportions of shared variation impede estimation of connectivity, even despite leveraging information from many genetic markers. We overcome these impediments by combining classical analysis of neutral variation with assays of the structure of selected variation, demonstrated using populations of the principal African malaria vector Anopheles gambiae. Accurate estimation of mosquito migration is crucial for efforts to combat malaria. Modeling and cage experiments suggest that mosquito gene drive systems will enable malaria eradication, but establishing safety and efficacy requires identification of isolated populations in which to conduct field testing. We assess Lake Victoria islands as candidate sites, finding one island 30 km offshore is as differentiated from mainland samples as populations from across the continent. Collectively, our results suggest sufficient contemporary isolation of these islands to warrant consideration as field‐testing locations and illustrate shared adaptive variation as a useful proxy for connectivity in highly polymorphic species.

Bottlenecks, remoteness and admixture shape genetic variation in island populations of Atlantic and Mediterranean common kestrels Falco tinnunculus

We studied genetic diversity and differentiation in island and nearby continental populations of a bird of prey, the common kestrel Falco tinnunculus. We sampled 11 islands in the eastern North Atlantic (Madeira and Canary Islands) and western Mediterranean archipelagos (Balearic Islands) and two continental sites (Iberian Peninsula and north‐west Africa). We used microsatellite (9 loci, n = 470) and mitochondrial data (cytochrome b sequences, n = 244) and applied Bayesian clustering, multivariate frequentist statistics and coalescence analyses. We revealed two main genetic clusters; the first including populations from the Atlantic islands and the second comprising populations from the Balearic Islands, the Iberian Peninsula and north‐west Africa, with additional finer scale structuring. The highest levels of genetic variation were found in Iberian Peninsula, north‐west Africa and Lanzarote island. The lowest diversity was detected in La Palma, the most north‐westerly island of the Canary Islands. The lowest levels of haplotype and nucleotide diversity were observed in Madeira and Gran Canaria and the highest in Menorca. We found evidence of decreasing genetic diversity with increasing severity of a past population bottleneck and, to some extent, with increasing geographic distance from the continent. The two Canary Island subspecies, F. t. dacotiae and F. t. canariensis, have diverged from each other to some degree and from the continental and Balearic conspecifics of F. t. tinnunculus. Samples from Madeira, representing F. t. canariensis, indicated affinities to both Canary Islands and Mediterranean clusters, depending on the marker and methods applied. Our results suggest stronger gene flow between close islands than between distant islands. The genetic structure of an endemic subspecies F. t. dacotiae in the easternmost Canary Islands is suggested to have an origin in a past hybridization between continental F. t. tinnunculus and insular F. t. canariensis.

Where can introduced populations learn their tricks? Searching for the geographical source of a species introduction to the Galápagos archipelago

We seek to understand the potential genetic impact of introduced species in an ecosystem where conservation efforts and pressure from development co-occur: the Galapagos Archipelago. To date, the introduced weevil Galapaganus h. howdenae is found only in Santa Cruz Island; however it has recently expanded its range beyond the Agricultural Zone into the highlands. We are focusing on comparisons between continental and introduced populations to clarify whether the current genetic patterns in introduced populations can reflect recovery from a past bottleneck and predict its invasive potential. A second objective is to narrow down the geographic source of the introduction and confirm their origin from a single introduction pulse. We found comparable microsatellite genetic diversity featuring many island-specific alleles, but reduced mitochondrial haplotype diversity in the islands. Additionally, both markers showed signals of population expansion and homogeneously distributed variation in the introduced range, in contrast to structured continental populations. The addition of mitochondrial sequences to the microsatellite dataset in the Approximate Bayesian Computation analyses (Diyabc) favors a single introduction pulse from the Northern Manabi area; a scenario that is in agreement with the haplotype network. An origin from higher elevation habitats provides clues about the environmental amplitude of the naturalized populations. However, given that a large percentage of the microsatellite variation in island populations is due to new island alleles, the answer to the question “where can introduced populations learn their tricks?” could be: right at their new location.

Uncovering discordance between taxonomy and evolutionary history in Florida raccoons

Due to perceived isolation of near shore islands, there are currently five subspecies of raccoons (Procyon lotor) recognized in Florida, USA. In this study, we elucidated molecular genetic differences between subspecies using 173 samples from eight localities collected throughout Florida. We sequenced two mitochondrial genes and genotyped eight nuclear microsatellite loci to test two hypotheses: (1) the five morphologically and geographically defined subspecies of raccoons in Florida represent genetically distinct populations and (2) due to differing habitat availability between island and mainland subspecies, island populations would exhibit reduced levels of genetic diversity compared with mainland populations. Our mitochondrial results identified 37 unique haplotypes, many of which are shared between described subspecies. However, our analyses of genetic differentiation suggest a recent restriction of gene flow among three clusters of raccoons, which do not correlate to traditional geographies for subspecies identification. Finally, we provide evidence of reduced genetic diversity in island populations compared with their mainland counterparts using both mitochondrial and microsatellite data, which demonstrate that haplotype diversity, allelic richness, and heterozygosity are significantly reduced in island sites. These data stress the importance of using multiple lines of evidence when naming taxa to ensure concordance between evolutionary history and taxonomy.

Patterns of genetic diversity in Phoenix canariensis, a widespread oceanic palm (species) endemic from the Canarian archipelago

Understanding how genetic diversity is structured on oceanic island taxa requires the integration of physical, biological and anthropomorphic factors. Founder effects coupled with limited dispersal over sea barriers typically result in low levels of genetic variation in island populations. In widespread species, restriction in gene flow across large areas leads to patterns of isolation by distance (IBD), but recent population-based studies indicate that genetic structure on islands can be complex even at local scales. Here, we investigated the patterns of genetic variation in a widespread island palm (Phoenix canariensis) displaying reproductive syndromes associated with extensive dispersal (wind pollination and zoochory). Genetic variation was assessed at eight nuclear microsatellite loci in 330 individuals of 15 Canarian populations. Our results showed that levels of within-population genetic diversity in P. canariensis depend on the island considered, with a strong decreasing pattern from the easternmost and oldest island to the westernmost and youngest islands. A Mantel test supported a stepping-stone model of differentiation across the archipelago that fits the sequence of island emergence, and results from ABC and clustering analyses also corresponded with this progression rule. In addition, our analyses were congruent with the idea that the only large population found on Lanzarote has an anthropogenic origin. Despite the high dispersal potential of P. canariensis, our analyses suggest that the geographical configuration of the Canary Islands and a relatively recent pattern of differentiation across islands appear to have had a primary influence on the genetic structure of this island taxon.

Patterns of Genetic and Reproductive Traits Differentiation in Mainland vs. Corsican Populations of Bumblebees

Populations on islands often exhibit lower levels of genetic variation and ecomorphological divergence compared to their mainland relatives. While phenotypic differentiation in characters, such as size or shape among insular organisms, has been well studied, insular differentiation in quantitative reproductive traits involved in chemical communication has received very little attention to date. Here, we investigated the impact of insularity on two syntopic bumblebee species pairs: one including species that are phylogenetically related (Bombus terrestris and B. lucorum), and the other including species that interact ecologically (B. terrestris and its specific nest inquiline B. vestalis). For each bumblebee species, we characterized the patterns of variation and differentiation of insular (Corsican) vs. mainland (European) populations (i) with four genes (nuclear and mitochondrial, 3781 bp) and (ii) in the chemical composition of male marking secretions (MMS), a key trait for mate attraction in bumblebees, by gas chromatography-mass spectrometry (GC-MS). Our results provide evidence for genetic differentiation in Corsican bumblebees and show that, contrary to theoretical expectations, island populations of bumblebees exhibit levels of genetic variation similar to the mainland populations. Likewise, our comparative chemical analyses of MMS indicate that Corsican populations of bumblebees are significantly differentiated from the mainland yet they hold comparative levels of within-population MMS variability compared to the mainland. Therefore, insularity has led Corsican populations to diverge both genetically and chemically from their mainland relatives, presumably through genetic drift, but without a decrease of genetic diversity in island populations. We hypothesize that MMS divergence in Corsican bumblebees was driven by a persistent lack of gene flow with mainland populations and reinforced by the preference of Corsican females for sympatric (Corsican) MMS. The impoverished Corsican bumblebee fauna has not led to relaxation of stabilizing selection on MMS but to consistent differentiation chemical reproductive traits on the island.

Large-Scale Survey of Mitochondrial D-Loop of the Red-Crowned Crane <i>Grus japonensis</i> in Hokkaido, Japan by Convenient Genotyping Method

The Red-crowned Crane, Grus japonensis, is an endangered species of crane that has two separate breeding populations, one in the Amur River basin (continental population) and the other in eastern or northern Hokkaido, Japan (island population). So far, only two haplotypes (Gj1 and Gj2) have been identified in the mitochondrial D-loop in island population, whereas seven haplotypes have been found in continental population (Gj3-Gj9). We developed a rapid and inexpensive method of extensive genotyping of D-loop haplotypes in Red-crowned Cranes, based on amplification refractory mutation system (ARMS) PCR assay. Two hundred and three cranes in eastern Hokkaido were studied with this method and supplemental DNA sequencing. Only two haplotypes, Gj1 and Gj2, were confirmed in eastern Hokkaido with Gj2 as a major haplotype. Additionally, only Gj2 was identified in twelve feathers from both sexes found in northern Hokkaido. These results suggest scarce genetic diversity in island population of Red-crowned Cranes in Hokkaido, Japan.

Small population size and extremely low levels of genetic diversity in island populations of the platypus, Ornithorhynchus anatinus.

Genetic diversity generally underpins population resilience and persistence. Reductions in population size and absence of gene flow can lead to reductions in genetic diversity, reproductive fitness, and a limited ability to adapt to environmental change increasing the risk of extinction. Island populations are typically small and isolated, and as a result, inbreeding and reduced genetic diversity elevate their extinction risk. Two island populations of the platypus, Ornithorhynchus anatinus, exist; a naturally occurring population on King Island in Bass Strait and a recently introduced population on Kangaroo Island off the coast of South Australia. Here we assessed the genetic diversity within these two island populations and contrasted these patterns with genetic diversity estimates in areas from which the populations are likely to have been founded. On Kangaroo Island, we also modeled live capture data to determine estimates of population size. Levels of genetic diversity in King Island platypuses are perilously low, with eight of 13 microsatellite loci fixed, likely reflecting their small population size and prolonged isolation. Estimates of heterozygosity detected by microsatellites (HE= 0.032) are among the lowest level of genetic diversity recorded by this method in a naturally outbreeding vertebrate population. In contrast, estimates of genetic diversity on Kangaroo Island are somewhat higher. However, estimates of small population size and the limited founders combined with genetic isolation are likely to lead to further losses of genetic diversity through time for the Kangaroo Island platypus population. Implications for the future of these and similarly isolated or genetically depauperate populations are discussed.

Differences in spatial genetic structure and diversity in two mosses with different dispersal strategies in a fragmented landscape

The Thousand-Island Lake (Zhejiang Province, China) was artificially isolated 50 years ago and provides an interesting model for investigating the impact of fragmentation on the spatial genetic structure in plant populations. Using variation from inter-simple sequence repeat markers and DNA sequences in two moss species with contrasting reproductive strategies, Hypnum plumaeforme and Pogonatum inflexum, we investigate the effect of sexual and asexual reproduction on molecular diversity and spatial genetic structure in this fragmented landscape. In H. plumaeforme, which mostly reproduces asexually, genetic diversity of island populations was significantly higher than that of lakeside populations. In the frequently fertile P. inflexum, conversely, genetic diversity was not significantly different between island and lakeside populations. Furthermore, a clear island versus lakeshore structure emerged from the spatial analysis of genetic variation in H. plumaeforme, but not in P. inflexum. We conclude that differences in reproductive strategies have a substantial effect on spatial genetic structure. In addition, landscape fragmentation may lead to the exacerbation of genetic differentiation in species with limited dispersal abilities at this scale, causing substantial spatial genetic structure.

Mandible asymmetry and genetic diversity in island populations of the common shrew,Sorex araneus

Mandibles from 13 island and six mainland populations of common shrews from the west coast of Scotland were subjected to geometric morphometric analysis in order to investigate the relationship between genetic diversity and fluctuating asymmetry. Although population mean shape fluctuating asymmetry (FA) and size FA were significantly inversely correlated with population genetic diversity this result was substantially due to one island. Sanda, the smallest island with by far the lowest genetic diversity, also had the highest FA. When Sanda was removed from the analysis, the relationship was not significant. There was no relationship between genetic diversity and FA at the individual level, whether measured as mean locus heterozygosity or d(2). In general, if genetic variation affects FA at all, the effect is weak and may only be of biological interest in very small populations.

Genetic differentiation and natural hybridization between the Sardinian endemicManiola nuragand the EuropeanManiola jurtina

The Mediterranean island of Sardinia is known for its multitude of unique genetic lineages. We view one of them in a larger phylogeographic context. The endemic Sardinian Meadow Brown butterfly, Maniola nurag, is restricted to the mountainous areas of the island, whereas its widespread close relative, Maniola jurtina, also occurs on the coast. At intermediate altitudes the species' distributions overlap. There, a number of individuals exhibit phenotypic characteristics intermediate between the two species. We examined patterns of intra- and interpopulation variation in 10 M. nurag populations from Sardinia and 16 M. jurtina populations from Sardinia and continental Europe, as well as 17 intermediate individuals, sampled in 1999-2002, by means of allozyme markers, combining it with a morphometric analysis based on 18 wing-characters of 52 males. At the 15 loci studied (aldolase, aat-1, aat-2, g6pdh, gpd, idh-1, idh-2, mdh-1, mdh-2, mpi, me, leu-ala, pgi, pgm, and 6pgdh), 76 different alleles were detected, 63 of which were shared by M. nurag and M. jurtina. None of the loci was found to be alternatively fixed between the two species. In that respect, this study testifies to the difficulties that may arise when trying to identify hybrids from genotypic data. Levels of genetic variation in island populations (M. jurtina: H(O) = 0.137-0.189; M. nurag: H(O) = 0.141-0.270) were comparable to those of mainland M. jurtina (H(O) = 0.141-0.236). A Bayesian admixture analysis supported the hypothesis of mixed (hybrid) ancestry of individuals occurring at intermediate altitudes. Similarly, neighbour-joining and unweighted pair-group method with arithmetic averaging (UPGMA) analyses, as well as morphometrics hinted at the existence of a Maniola-hybrid zone in Sardinia at intermediate altitudes. We discuss the results in the light of the phylogeography of other Sardinian taxa with the aim to reach a general understanding of the biogeographic history of this island's endemic species.

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

AbstractAim 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 in island populations of tuatara (Sphenodon spp) inferred from microsatellite markers

Tuatara (Sphenodon spp) populations are restricted to 35 offshore islands in the Hauraki Gulf, Bay of Plenty and Cook Strait of New Zealand. Low levels of genetic variation have previously been revealed by allozyme and mtDNA analyses. In this new study, we show that six polymorphic microsatellite loci display high levels of genetic variation in 14 populations across the geographic range of tuatara. These populations are characterised by disjunct allele frequency spectra with high numbers of private alleles. High F ST (0.26) values indicate marked population structure and assignment tests allocate 96% of all individuals to their source populations. These genetic data confirm that islands support genetically distinct populations. Principal component analysis and allelic sequence data supplied information about genetic relationships between populations. Low numbers of rare alleles and low allelic richness identified populations with reduced genetic diversity. Little Barrier Island has very low numbers of old tuatara which have retained some relictual diversity. North Brother Island’s tuatara population is inbred with fixed alleles at 5 of the 6 loci.

Nest Depredation, Brood Parasitism, and Reproductive Variation in Island Populations of Song Sparrows (Melospiza Melodia)

Abstract Theory suggests that the persistence of metapopulations will be influenced by the degree of synchrony in the dynamics of their component populations. Various studies have shown that climate can promote synchrony in the size of adjacent populations linked by dispersal, but fewer studies have examined the effects of climate on underlying demographic rates. We studied annual variation in the timing of breeding and reproductive rates in Song Sparrow (Melospiza melodia) on islands linked by dispersal to determine whether biotic factors acting at local scales or climatic factors acting at a regional scale were more influential of variation in demography. The onset of egg laying varied markedly among years but was roughly synchronous across islands within years. Despite this synchrony, island populations varied markedly in reproductive rate, mainly from spatial variation in nest depredation and brood parasitism. In general, populations farther from Vancouver Island and with fewer resident predators experienced less nest depredation and brood parasitism, and higher reproductive rates, than populations closer to Vancouver Island. Our results show that even when climate acts regionally to synchronize reproductive timing in adjacent populations, its effects on reproductive rate may be overridden by biotic factors that vary among populations. Depredación de Nidos, Parasitismo de Cría y Variación Reproductiva en Poblaciones Isleñas de Melospiza melodia

Phylogeography of plants in Taiwan and the Ryukyu Archipelago

AbstractTaiwan and Ryukyus constitute an archipelago lying on the western rim of the Pacific Ocean. In contrast to volcanic islands that often arise sequentially, these continental islands emerged almost simultaneously as the Luzon arc collided with the Eurasian margin some 9 million years ago (Mya). Taiwan and Ryukyus attained their modern features and their current flora and fauna from the adjacent mainland and from tropical Asia only 5–6 Mya. Quaternary glaciation led to a drop in sea level of the South China Sea and a land bridge that connected the Taiwan‐Ryukyu Archipelago to the mainland, which allowed plants and animals to migrate across what was previously ocean. These islands provided refugia for northern species that migrated south during glacial periods, as indicated by unanticipated high levels of genetic diversity in island populations of plants like Cunninghamia and Pinus. For most insect‐pollinated species, allozymes and nuclear DNA markers indicate significant genetic differentiation between populations and between geographical regions of the archipelago. In contrast, organelle based DNA markers suggest a migrant‐pool model, where colonists are recruited from a random sample of source populations. Consistent with this model, low elevation species have high genetic heterogeneity within populations and low levels of genetic differentiation between populations. In contrast, colonization of alpine species appeared to follow a phalanx model due to the limited availability of high elevation habitats. Genetic differentiation was detected between fragmented populations of the alpine species. A scenario of stepwise colonization from the mainland to near and then distant islands remains to be tested, although several studies indicate no such pattern. These conflicting results challenge the ability to define clear conservation criteria for the rare plant species of the archipelago.