Population structure over a broad spatial scale driven by nonanthropogenic factors in a wide‐ranging migratory mammal,Alaskan caribou

Wide‐ranging mammals face significant conservation threats, and knowledge of the spatial scale of population structure and its drivers is needed to understand processes that maintain diversity in these species. We analysed DNA from 655 Alaskan caribou (Rangifer tarandus granti) from 20 herds that vary in population size, used 19 microsatellite loci to document genetic diversity and differentiation in Alaskan caribou, and examined the extent to which genetic differentiation was associated with hypothesized drivers of population subdivision including landscape features, population size and ecotype. We found that Alaskan caribou are subdivided into two hierarchically structured clusters: one group on the Alaska Peninsula containing discrete herds and one large group on the Mainland lacking differentiation between many herds. Population size, geographic distance, migratory ecotype and the Kvichak River at the nexus of the Alaska Peninsula were associated with genetic differentiation. Contrary to previous hypotheses, small Mainland herds were often differentiated genetically from large interconnected herds nearby, and genetic drift coupled with reduced gene flow may explain this pattern. Our results raise the possibility that behaviour helps to maintain genetic differentiation between some herds of different ecotypes. Alaskan caribou show remarkably high diversity and low differentiation over a broad geographic scale. These results increase information for the conservation of caribou and other migratory mammals threatened by population reductions and landscape barriers and may be broadly applicable to understanding the spatial scale and ecological drivers of population structure in widespread species.     

Effect of the landscape matrix on gene flow in a coastal amphibian metapopulation

Functional connectivity is crucial for the persistence of a metapopulation, because migration among subpopulations enables recolonization and counteracts genetic drift, which is especially important in small subpopulations. We studied the degree and drivers of connectivity among occupied patches of a coastal dune metapopulation of the Natterjack Toad (Epidalea calamita Laurenti), on the basis of microsatellite variation. As spatial landscape heterogeneity is expected to influence dispersal and genetic structure, we analyzed which landscape features affect functional connectivity and to what extent. Sixty different landscape resistance scenarios as well as the isolation-by-distance model were compared using two landscape genetics approaches. We identified three subpopulations with unidirectional levels of gene flow among the two most geographically separated subpopulations, while inferred gene flow into the geographically intermediate subpopulation was limited. Urbanization and vegetation height negatively affected connectivity. Low estimates of genetic diversity and effective population size indicate that conservation measures in the smallest and most isolated subpopulation are required.     

Partitioning drivers of spatial genetic variation for a continuously distributed population of boreal caribou: Implications for management unit delineation

Isolation by distance (IBD) is a natural pattern not readily incorporated into theoretical models nor traditional metrics for differentiating populations, although clinal genetic differentiation can be characteristic of many wildlife species. Landscape features can also drive population structure additive to baseline IBD resulting in differentiation through isolation‐by‐resistance (IBR). We assessed the population genetic structure of boreal caribou across western Canada using nonspatial (STRUCTURE) and spatial (MEMGENE) clustering methods and investigated the relative contribution of IBD and IBR on genetic variation of 1,221 boreal caribou multilocus genotypes across western Canada. We further introduced a novel approach to compare the partitioning of individuals into management units (MU) and assessed levels of genetic connectivity under different MU scenarios. STRUCTURE delineated five genetic clusters while MEMGENE identified finer‐scale differentiation across the study area. IBD was significant and did not differ for males and females both across and among detected genetic clusters. MEMGENE landscape analysis further quantified the proportion of genetic variation contributed by IBD and IBR patterns, allowing for the relative importance of spatial drivers, including roads, water bodies, and wildfires, to be assessed and incorporated into the characterization of population structure for the delineation of MUs. Local population units, as currently delineated in the boreal caribou recovery strategy, do not capture the genetic variation and connectivity of the ecotype across the study area. Here, we provide the tools to assess fine‐scale spatial patterns of genetic variation, partition drivers of genetic variation, and evaluate the best management options for maintaining genetic connectivity. Our approach is highly relevant to vagile wildlife species that are of management and conservation concern and demonstrate varying degrees of IBD and IBR with clinal spatial genetic structure that challenges the delineation of discrete population boundaries.     

Microhabitat Types Promote the Genetic Structure of a Micro-Endemic and Critically Endangered Mole Salamander (Ambystoma leorae) of Central Mexico

The reduced immigration and emigration rates resulting from the lack of landscape connectivity of patches and the hospitality of the intervening matrix could favor the loss of alleles through genetic drift and an increased chance of inbreeding. In order for isolated populations to maintain sufficient levels of genetic diversity and adapt to environmental changes, one important conservation goal must be to preserve or reestablish connectivity among patches in a fragmented landscape. We studied the last known population of Ambystoma leorae, an endemic and critically threatened species. The aims of this study were: (1) to assess the demographic parameters of A. leorae and to distinguish and characterize the microhabitats in the river, (2) to determine the number of existing genetic groups or demes of A. leorae and to describe possible relationships between microhabitats types and demes, (3) to determine gene flow between demes, and (4) to search for geographic locations of genetic discontinuities that limit gene flow between demes. We found three types of microhabitats and three genetically differentiated subpopulations with a significant level of genetic structure. In addition, we found slight genetic barriers. Our results suggest that mole salamander’s species are very sensitive to microhabitat features and relatively narrow obstacles in their path. The estimates of bidirectional gene flow are consistent with the pattern of a stepping stone model between demes, where migration occurs between adjacent demes, but there is low gene flow between distant demes. We can also conclude that there is a positive correlation between microhabitats and genetic structure in this population.     

Reconstruction of caribou evolutionary history in Western North America and its implications for conservation

The role of Beringia as a refugium and route for trans-continental exchange of fauna during glacial cycles of the past 2million years are well documented; less apparent is its contribution as a significant reservoir of genetic diversity. Using mitochondrial DNA sequences and 14 microsatellite loci, we investigate the phylogeographic history of caribou (Rangifer tarandus) in western North America. Patterns of genetic diversity reveal two distinct groups of caribou. Caribou classified as a Northern group, of Beringian origin, exhibited greater number and variability in mtDNA haplotypes compared to a Southern group originating from refugia south of glacial ice. Results indicate that subspecies R. t. granti of Alaska and R. t. groenlandicus of northern Canada do not constitute distinguishable units at mtDNA or microsatellites, belying their current status as separate subspecies. Additionally, the Northern Mountain ecotype of woodland caribou (presently R. t. caribou) has closer kinship to caribou classified as granti or groenlandicus. Comparisons of mtDNA and microsatellite data suggest that behavioural and ecological specialization is a more recently derived life history characteristic. Notably, microsatellite differentiation among Southern herds is significantly greater, most likely as a result of human-induced landscape fragmentation and genetic drift due to smaller population sizes. These results not only provide important insight into the evolutionary history of northern species such as caribou, but also are important indicators for managers evaluating conservation measures for this threatened species.     

Population structure of caribou in an ice‐bound archipelago

Aim

Archipelagos provide ideal natural systems for testing the effects of isolation and fragmentation of habitats on the genetic makeup of populations—an important consideration, given that many insular species are of conservation concern. Two theories predominate: Island Biogeography Theory (IBT) posits that proximity to the mainland drives the potential for migrants and gene flow. The Central Marginal Hypothesis (CMH) predicts that island populations at the periphery of a species range may experience low gene flow, small population size and high rates of genetic drift. We investigated population genetic structure, genetic diversity and key drivers of diversity for Arctic island‐dwelling caribou (Rangifer tarandus). Our aim was to inform intraspecific units for conservation and decipher how IBT and CMH could act in an archipelago where isolation is highly variable due to sea ice and open water.

Location

Canadian Arctic Archipelago, Canada (Latitude, 55–82°N; Longitude, 61–123°W).

Methods

We genotyped 447 caribou at 16 microsatellite loci; these caribou represented two subspecies (R. t. groenlandicus, R. t. pearyi) and three designatable units. We used hierarchical Bayesian clustering and ordination to determine genetic groups. We evaluated the influence of ecological and geographic variables on genetic diversity using linear mixed‐effects models and compared diversity among mainland and island herds.

Results

Bayesian clustering revealed nine genetic clusters with differentiation among and within caribou subspecies. Genetic differentiation was explained predominantly by isolation‐by‐distance across all caribou, even at the scale of subspecies. Island caribou were less genetically diverse than mainland herds; individual heterozygosity was negatively correlated with distance‐to‐mainland and the extent of autumn ice‐free coastline and positively correlated with unglaciated island size.

Main conclusions

Our findings underscore the importance of hierarchical analysis when investigating genetic population structure. Genetic diversity and its key drivers lend support to both IBT and CMH and highlight the pending threat of climate change for Arctic island caribou.

     

Linking genetic and ecological differentiation in an ungulate with a circumpolar distribution

Genetic differentiation among populations may arise from the disruption of gene flow due to local adaptation to distinct environments and/or neutral accumulation of mutations and genetic drift resulted from geographical isolation. Quantifying the role of these processes in determining the genetic structure of natural populations remains challenging. Here, we analyze the relative contribution of isolation‐by‐resistance (IBR), isolation‐by‐environment (IBE), genetic drift and historical isolation in allopatry during Pleistocene glacial cycles on shaping patterns of genetic differentiation in caribou/reindeer populations Rangifer tarandus across the entire distribution range of the species. Our study integrates analyses at range‐wide and regional scales to partial out the effects of historical and contemporary isolation mechanisms. At the circumpolar scale, our results indicate that genetic differentiation is predominantly explained by IBR and historical isolation. At a regional scale, we found that IBR, IBE and population size significantly explained the spatial distribution of genetic variation among populations belonging to the Euro‐Beringian lineage within North America. In contrast, genetic differentiation among populations within the North American lineage was predominantly explained by IBR and population size, but not IBE. We also found discrepancies between genetic and ecotype designation across the Holarctic species distribution range. Overall, these results indicate that multiple isolating mechanisms have played roles in shaping the spatial distribution of genetic variation across the distribution range of a large mammal with high potential for gene flow. Considering multiple spatial scales and simultaneously testing a comprehensive suite of potential isolating mechanisms, our study contributes to understand the ecological and evolutionary processes underlying organism–landscape interactions.     

Conservation genetics of the yellow-bellied toad (Bombina variegata): population structure,genetic diversity and landscape effects in an endangered amphibian

Revealing patterns of genetic diversity and barriers for gene flow are key points for successful conservation in endangered species. Methods based on molecular markers are also often used to delineate conservation units such as evolutionary significant units and management units. Here we combine phylo-geographic analyses (based on mtDNA) with population and landscape genetic analyses (based on microsatellites) for the endangered yellow-bellied toad Bombina variegata over a wide distribution range in Germany. Our analyses show that two genetic clusters are present in the study area, a northern and a southern/central one, but that these clusters are not deeply divergent. The genetic data suggest high fragmentation among toad occurrences and consequently low genetic diversity. Genetic diversity and genetic connectivity showed a negative relationship with road densities and urban areas surrounding toad occurrences, indicating that these landscape features act as barriers to gene flow. To preserve a maximum of genetic diversity, we recommend considering both genetic clusters as management units, and to increase gene flow among toad occurrences with the aim of restoring and protecting functional meta-populations within each of the clusters. Several isolated populations with especially low genetic diversity and signs of inbreeding need particular short-term conservation attention to avoid extinction. We also recommend to allow natural gene flow between both clusters but not to use individuals from one cluster for translocation or reintroduction into the other. Our results underscore the utility of molecular tools for species conservation, highlight outcomes of habitat fragmentation onto the genetic structure of an endangered amphibian and reveal particularly threatened populations in need for urgent conservation efforts.

     

Integrating ecological and genetic structure to define management units for caribou in Eastern Canada

Genetic diversity is a key parameter to delineate management units, but many organisms also display ecological characteristics that may reflect potential local adaptations. Here, we used ecological and genetic information to delineate management units for a complex system involving several ecotypes of caribou (Rangifer tarandus) from Québec and Labrador, eastern Canada. We genotyped 560 caribou at 16 microsatellite loci and used three Bayesian clustering methods to spatially delineate and characterize genetic structure across the landscape. The different approaches employed did not converge on the same solution, and differed in the number of inferred genetic clusters that best fit the dataset but also in the spatial distribution of genetic variation. We reconciled variability among the methods using a synthetic approach that considers the sum of the partitions obtained by each of them and retrieved six genetically distinct groups that differ in their spatial extent across the range of caribou in the study area. These genetic groups are not consistent with the presently defined ecological designations for this species. Combining both genetic and ecological criteria, we distinguished eight independent management units. Overall, the management units we propose should be the focus of conservation and management actions aimed to maximize genetic and ecological diversity and ensure the persistence of caribou populations inhabiting increasingly disturbed landscapes.     

Identification of subpopulations from connectivity matrices

Dispersal on the landscape/seascape scale may lead to complex spatial population structure with non‐synchronous demography and genetic divergence. In this study we present a novel approach to identify subpopulations and dispersal barriers based on estimates of dispersal probabilities on the landscape scale. A theoretical framework is presented where the landscape connectivity matrix is analyzed for clusters as a signature of partially isolated subpopulations. Identification of subpopulations is formulated as a minimization problem with a tuneable penalty term that makes it possible to generate population subdivisions with varying degree of dispersal restrictions. We show that this approach produces superior results compared to alternative standard methods. We apply this theory to a dataset of modeled dispersal probabilities for a sessile marine invertebrate with free‐swimming larvae in the Baltic Sea. For a range of critical connectivities we produce a hierarchical partitioning into subpopulations spanning dispersal probabilities that are typical for both genetic divergence and demographic independence. The mapping of subpopulations suggests that the Baltic Sea includes a fine‐scale (100–600 km) mosaic of invisible dispersal barriers. An analysis of the present network of marine protected areas reveal that protection is very unevenly distributed among the suggested subpopulations. Our approach can be used to assess the location and strength of dispersal barriers in the landscape, and identify conservation units when extensive genotyping is prohibitively costly to cover necessary spatial and temporal scales, e.g. in spatial management of marine populations.     

Individual genetic diversity correlates with the size and spatial isolation of natal colonies in a bird metapopulation

The genetic consequences of small population size and isolation are of central concern in both population and conservation biology. Organisms with a metapopulation structure generally show effective population sizes that are much smaller than the number of mature individuals and this can reduce genetic diversity especially in small sized and isolated subpopulations. Here, we examine the association between heterozygosity and the size and spatial isolation of natal colonies in a metapopulation of lesser kestrels (Falco naumanni). For this purpose, we used capture-mark-recapture data to determine the patterns of immigration into the studied colonies, and 11 highly polymorphic microsatellite markers that allowed us to estimate genetic diversity of locally born individuals. We found that individuals born in smaller and more isolated colonies were genetically less diverse. These colonies received a lower number of immigrants, supporting the idea that both reduced gene flow and small population size are responsible for the genetic pattern observed. Our results are particularly intriguing because the lesser kestrel is a vagile and migratory species with great movement capacity and dispersal potential. Overall, this study provides evidence of the association between individual heterozygosity and the size and spatial isolation of natal colonies in a highly mobile vertebrate showing relatively frequent dispersal and low genetic differentiation among local subpopulations.     

A comparison of individual‐based genetic distance metrics for landscape genetics

A major aim of landscape genetics is to understand how landscapes resist gene flow and thereby influence population genetic structure. An empirical understanding of this process provides a wealth of information that can be used to guide conservation and management of species in fragmented landscapes and also to predict how landscape change may affect population viability. Statistical approaches to infer the true model among competing alternatives are based on the strength of the relationship between pairwise genetic distances and landscape distances among sampled individuals in a population. A variety of methods have been devised to quantify individual genetic distances, but no study has yet compared their relative performance when used for model selection in landscape genetics. In this study, we used population genetic simulations to assess the accuracy of 16 individual‐based genetic distance metrics under varying sample sizes and degree of population genetic structure. We found most metrics performed well when sample size and genetic structure was high. However, it was much more challenging to infer the true model when sample size and genetic structure was low. Under these conditions, we found genetic distance metrics based on principal components analysis were the most accurate (although several other metrics performed similarly), but only when they were derived from multiple principal components axes (the optimal number varied depending on the degree of population genetic structure). Our results provide guidance for which genetic distance metrics maximize model selection accuracy and thereby better inform conservation and management decisions based upon landscape genetic analysis.     

Genetic evidence of fragmented populations and inbreeding in the Colombian endemic Dahl’s toad-headed turtle (<Emphasis Type="Italic">Mesoclemmys dahli</Emphasis>)

Population fragmentation is one of the most concerning consequences of habitat fragmentation, as small and isolated populations suffer increased genetic drift and inbreeding. However, the extent to which habitat fragmentation leads to population fragmentation depends not only on the landscape structure, but also on the response of organisms to it. This behavioral component makes it difficult to detect population fragmentation even if the habitat is fragmented, unless appropriate tools are used. In this study, we used a molecular approach to evaluate if Dahl’s toad-headed turtle (Mesoclemmys dahli) population was fragmented, given that it occurs in a very restricted area within the most degraded biome of Colombia, the tropical dry forest. We developed a panel of 15 microsatellite loci in order to perform the first genetic assessment of M. dahli across its complete geographic range. We found that M. dahli has significant genetic structure with at least four subpopulations, with surprisingly moderate to high levels of genetic diversity. Despite high levels of genetic diversity, subpopulations are very small (effective population sizes?<?50) and isolated, with little to no contemporary gene flow among them. As a consequence, mating among related individuals has been occurring, and all four populations are showing high degrees of inbreeding. To counteract this threat, we recommend an urgent genetic rescue strategy accompanied by habitat restoration, and advocate for a new conservation status assessment, not based on geographic range, but on adult population size and level of fragmentation.     

Landscape determinants of genetic differentiation,inbreeding and genetic drift in the hazel dormouse (<Emphasis Type="Italic">Muscardinus avellanarius</Emphasis>)

The dispersal process is crucial in determining the fate of populations over time, but habitat fragmentation limits or prevents it. Landscape genetic is an effective tool to assess the degree to which dispersal still occurs in fragmented landscapes. The purpose of this study was to investigate the landscape determinants of genetic differentiation in the hazel dormouse (Muscardinus avellanarius), a forest-dependent species of conservation concern. By comparing subpopulations in a continuous (SLR) and a fragmented (VTH) population, we (i) searched for the presence of Isolation-by-Resistance (IBR); (ii) estimated migration rates; (iii) evaluated the degree of inbreeding and genetic drift, and searched for their landscape determinants. We found an IBR effect in VTH, which heavily hindered the dispersal process. The overall number of migrants among VTH subpopulations was very low (1 per generation, compared to 15 in SLR), although a between-patch displacement of about 4 km along a well-structured hedgerow probably occurred. The inbreeding (F?>?0.2 in most subpopulations) and the genetic drift (four out five subpopulations showed private alleles on several loci, with relatively high frequencies) are of particular concern in VTH. However, they were found to be limited in large patches or in patches connected by hedgerows with a high number of neighbouring patches. As a conservation strategy in the VTH landscape, characterized by small patches, we suggest that the dispersal process among subpopulations is enhanced to sustain a functional metapopulation. For this purpose, an effective ecological network should be created by enhancing the continuity and the internal features of hedgerows.     

High genetic connectivity and introgression from domestic reindeer characterize northern Alaska caribou herds

Defining genetic populations and detecting hybridization with introduced or domestic taxa are two major concerns for the conservation of population-level diversity. We studied the genetic population structure of large, migratory caribou herds (Rangifer tarandus granti) on Alaska’s North Slope and their potential hybridization with introduced domestic reindeer (R. t. tarandus). Using a population genetics approach, we determined: (1) whether the four caribou herds could be differentiated; (2) how distance and population size appear to drive genetic population structure; and (3) how contact with reindeer has affected the genetic identity of herds. Samples from four caribou herds (n = 245) and reindeer (n = 67) were analyzed at 19 microsatellite loci. We found that North Slope caribou are isolated by distance, with no differentiation among herd pairs except for the most geographically distant herds (F _st  = 0.003, Jost’s D = 0.023; P-values < 0.001). We detected reindeer-caribou admixture in all populations except Kodiak Island, including 8 % of individuals in caribou herds and 14 % of individuals in Seward Peninsula reindeer herds. However, considering the stable or increasing trend in North Slope herds, reindeer introgression has had no apparent deleterious effect on herd demographics. Our findings indicate long-term genetic exchange among North Slope caribou herds when their ranges overlap, and suggest that herd size may influence susceptibility to reindeer introgression. As North Slope herd ranges are increasingly altered by industrial development, this study can provide a baseline for detecting potential future impacts to what are currently large, diverse, and naturally evolving herds.     

Exploring demographic, physical, and historical explanations for the genetic structure of two lineages of Greater Antillean bats

Observed patterns of genetic structure result from the interactions of demographic, physical, and historical influences on gene flow. The particular strength of various factors in governing gene flow, however, may differ between species in biologically relevant ways. We investigated the role of demographic factors (population size and sex-biased dispersal) and physical features (geographic distance, island size and climatological winds) on patterns of genetic structure and gene flow for two lineages of Greater Antillean bats. We used microsatellite genetic data to estimate demographic characteristics, infer population genetic structure, and estimate gene flow among island populations of Erophylla sezekorni/E. bombifrons and Macrotus waterhousii (Chiroptera: Phyllostomidae). Using a landscape genetics approach, we asked if geographic distance, island size, or climatological winds mediate historical gene flow in this system. Samples from 13 islands spanning Erophylla's range clustered into five genetically distinct populations. Samples of M. waterhousii from eight islands represented eight genetically distinct populations. While we found evidence that a majority of historical gene flow between genetic populations was asymmetric for both lineages, we were not able to entirely rule out incomplete lineage sorting in generating this pattern. We found no evidence of contemporary gene flow except between two genetic populations of Erophylla. Both lineages exhibited significant isolation by geographic distance. Patterns of genetic structure and gene flow, however, were not explained by differences in relative effective population sizes, island area, sex-biased dispersal (tested only for Erophylla), or surface-level climatological winds. Gene flow among islands appears to be highly restricted, particularly for M. waterhousii, and we suggest that this species deserves increased taxonomic attention and conservation concern.     

Subpopulation genetic structure of a plant panmictic population of Castanea sequinii as revealed by microsatellite markers

Castanea squinii Dode,an endemic tree widely distributed in China,plays an important role both in chestnut breeding and forest ecosystem function.The spatial genetic structure within and among populations is an important part of the evolutionary and ecological genetic dynamics of natural populations,and can provide insights into effective conservation of genetic resources.In the present study,the spatial genetic structure of a panmictic natural population of C.sequinii in the Dabie Mountain region was investigated using microsatellite markers.Nine prescreened microsatellite loci generated 29-33 alleles each,and were used for spatial autocorrelation analysis.Based on Moran's I coefficient,a panmictic population of C.sequinii in the Dabie Mountain region was found to be lacking a spatial genetic structure.These results suggest that a high pollen-mediated gene flow among subpopulations counteract genetic drift and/or genetic differentiation and plays an important role in maintaining a random and panmictic population structure in C.sequinii populations.Further,a spatial genetic structure was detected in each subpopulation's scale (0.228 km),with all three subpopulations showing significant fine-scale structure.The genetic variation was found to be nonrandomly distributed within 61 m in each subpopulation (Moran's I positive values).Although Moran's I values varied among the different subpopulations,Moran's I in all the three subpopulations reached the expected values with an increase in distances,suggesting a generally patchy distribution in the subpopulations.The fine-scale structure seems to reflect restricted seed dispersal and microenvironment selection in C.sequinii.These results have important implications for understanding the evolutionary history and ecological process of the natural population of C.sequinii and provide baseline data for formulating a conservation strategy of Castanea species.     

用分子标记揭示植物随机大居群中亚居群的遗传结构——茅栗自然居群空间遗传结构的SSR分析

采用微卫星标记对茅栗(Castanea sequinii)随机大居群以及其中各亚居群的遗传结构进行了空间自相关分析,以探讨植物自然居群内遗传变异的分布特征及其形成机制。通过9对微卫星引物所产生的119个多态位点,测定了大别山区域内茅栗居群以及各亚居群的空间自相关系数Moran's I值。结果表明:大别山分布的野生茅栗为一个缺乏空间结构的随机大居群,茅栗亚居群之间频繁的花粉流削弱了地理隔离导致的遗传漂变或分化作用在维系居群随机遗传结构中具有的重要作用。但是,在接近亚居群大小的地域范围内(0.228 km)具有一定的空间结构,即小地域尺度中的亚居群存在着空间遗传结构。取样的3个亚居群在小格局范围内都存在一定的空间结构,遗传变异基本上呈非随机分布,在短距离内(61 m)3个亚居群一致表现出不同程度的显著正相关,而随着距离的增加,Moran's I值虽然在不同亚居群间存在一定差异变化,但是总体而言趋向预期值,即不存在空间结构,说明其遗传变异在亚居群内只是在短距离内形成一定的空间结构。研究认为有限的种子散播以及微生境选择等因素可能是产生这种小格局的遗传结构的主要原因。上述研究结果有助于进一步了解植物随机大居群的进化历史和生态过程,同时也为栗属植物中国特有种的保育策略提供了科学依据。     

Significance of caribou (Rangifer tarandus) ecotypes from a molecular genetics viewpoint

Three caribou ecotypes are present in easternNorth America: the mountain caribou which isfound south of the St. Lawrence River, thebarren-ground caribou which calves in thetundra, and in between, the forest-dwellingecotype which lives all year long in the borealforest. Blood and muscle samples were collectedfrom seven populations and characterized ateight microsatellite loci to test thehypotheses that forest-dwelling andbarren-ground ecotypes constitute a singlemetapopulation and that geographical isolationresults in reduced genetic diversity. The meannumber of alleles per locus, allelic richness,and observed and expected heterozygositydeclined from north to south and were thesmallest in isolated forest-dwellingpopulations. Correspondence analysis showedthree groups of samples corresponding to thethree ecotypes. Gene flow estimates weremoderate or high among all forest-dwellingpopulations and particularly between those <200 km apart. Our results suggest that thethree caribou ecotypes represent three distinctgenetic entities and that the forest-dwellingpopulations in the continuous range form ametapopulation. Genetic diversity was lower inisolated populations but does not seem to be ofimmediate concern for conservation. We proposethat management strategies should favorincrease in caribou numbers in order to avoidextinction due to stochastic events and tomaintain local biodiversity. In the continuousrange, conservation strategies of cariboupopulations must be planned on a large scale tomaintain occasional exchanges betweenpopulations, thus preserving genetic diversity.     

Fine-scale analysis reveals cryptic landscape genetic structure in desert tortoises

Characterizing the effects of landscape features on genetic variation is essential for understanding how landscapes shape patterns of gene flow and spatial genetic structure of populations. Most landscape genetics studies have focused on patterns of gene flow at a regional scale. However, the genetic structure of populations at a local scale may be influenced by a unique suite of landscape variables that have little bearing on connectivity patterns observed at broader spatial scales. We investigated fine-scale spatial patterns of genetic variation and gene flow in relation to features of the landscape in desert tortoise (Gopherus agassizii), using 859 tortoises genotyped at 16 microsatellite loci with associated data on geographic location, sex, elevation, slope, and soil type, and spatial relationship to putative barriers (power lines, roads). We used spatially explicit and non-explicit Bayesian clustering algorithms to partition the sample into discrete clusters, and characterize the relationships between genetic distance and ecological variables to identify factors with the greatest influence on gene flow at a local scale. Desert tortoises exhibit weak genetic structure at a local scale, and we identified two subpopulations across the study area. Although genetic differentiation between the subpopulations was low, our landscape genetic analysis identified both natural (slope) and anthropogenic (roads) landscape variables that have significantly influenced gene flow within this local population. We show that desert tortoise movements at a local scale are influenced by features of the landscape, and that these features are different than those that influence gene flow at larger scales. Our findings are important for desert tortoise conservation and management, particularly in light of recent translocation efforts in the region. More generally, our results indicate that recent landscape changes can affect gene flow at a local scale and that their effects can be detected almost immediately.