Landscape genetics of the blotched tiger salamander (Ambystoma tigrinum melanostictum)

The field of landscape genetics has great potential to identify habitat features that influence population genetic structure. To identify landscape correlates of genetic differentiation in a quantitative fashion, we developed a novel approach using geographical information systems analysis. We present data on blotched tiger salamanders (Ambystoma tigrinum melanostictum) from 10 sites across the northern range of Yellowstone National Park in Montana and Wyoming, USA. We used eight microsatellite loci to analyse population genetic structure. We tested whether landscape variables, including topographical distance, elevation, wetland likelihood, cover type and number of river and stream crossings, were correlated with genetic subdivision (F(ST)). We then compared five hypothetical dispersal routes with a straight-line distance model using two approaches: (i) partial Mantel tests using Akaike's information criterion scores to evaluate model robustness and (ii) the BIOENV procedure, which uses a Spearman rank correlation to determine the combination of environmental variables that best fits the genetic data. Overall, gene flow appears highly restricted among sites, with a global F(ST) of 0.24. While there is a significant isolation-by-distance pattern, incorporating landscape variables substantially improved the fit of the model (from an r2 of 0.3 to 0.8) explaining genetic differentiation. It appears that gene flow follows a straight-line topographic route, with river crossings and open shrub habitat correlated with lower F(ST) and thus, decreased differentiation, while distance and elevation difference appear to increase differentiation. This study demonstrates a general approach that can be used to determine the influence of landscape variables on population genetic structure.     

Effect of anthropogenic landscape features on population genetic differentiation of Przewalski's gazelle: main role of human settlement

Anthropogenic landscapes influence evolutionary processes such as population genetic differentiation, however, not every type of landscape features exert the same effect on a species, hence it is necessary to estimate their relative effect for species management and conservation. Przewalski's gazelle (Procapra przewalskii), which inhabits a human-altered area on Qinghai-Tibet Plateau, is one of the most endangered antelope species in the world. Here, we report a landscape genetic study on Przewalski's gazelle. We used skin and fecal samples of 169 wild gazelles collected from nine populations and thirteen microsatellite markers to assess the genetic effect of anthropogenic landscape features on this species. For comparison, the genetic effect of geographical distance and topography were also evaluated. We found significant genetic differentiation, six genetic groups and restricted dispersal pattern in Przewalski's gazelle. Topography, human settlement and road appear to be responsible for observed genetic differentiation as they were significantly correlated with both genetic distance measures [F(ST)/(1-F(ST)) and F'(ST)/(1-F'(ST))] in Mantel tests. IBD (isolation by distance) was also inferred as a significant factor in Mantel tests when genetic distance was measured as F(ST)/(1-F(ST)). However, using partial Mantel tests, AIC(c) calculations, causal modeling and AMOVA analysis, we found that human settlement was the main factor shaping current genetic differentiation among those tested. Altogether, our results reveal the relative influence of geographical distance, topography and three anthropogenic landscape-type on population genetic differentiation of Przewalski's gazelle and provide useful information for conservation measures on this endangered species.     

Population subdivision in marine environments: the contributions of biogeography, geographical distance and discontinuous habitat to genetic differentiation in a blennioid fish, Axoclinus nigricaudus

The relative importance of factors that may promote genetic differentiation in marine organisms is largely unknown. Here, contributions to population structure from a biogeographic boundary, geographical distance and the distribution of suitable habitat were investigated in Axoclinus nigricaudus, a small subtidal rock-reef fish, throughout its range in the Gulf of California. A 408-bp fragment of the mitochondrial control region was sequenced from 105 individuals. Variation was significantly partitioned between 28 of 36 possible combinations of population pairs. Phylogenetic analyses, hierarchical analyses of variance and a modified Mantel test substantiated a major break between two putative biogeographic regions. This genetic discontinuity coincides with an abrupt change in ecological characteristics, including temperature and salinity, but does not coincide with known oceanographic circulation patterns or any known historic barriers. There was an overall relationship of increasing genetic distance with increasing geographical distance between population pairs, in a manner consistent with isolation-by-distance. A significant habitat-by-geographical-distance interaction term indicated that, for a given geographical distance, populations separated by discontinuous habitat (sand) are more distinct genetically than are populations separated by continuous habitat (rock). In addition, populations separated by deep open waters were more genetically distinct than populations separated by continuous habitat (rock). These results indicate that levels of genetic differentiation among populations of A. nigricaudus cannot be explained by a single factor, but are due to the combined influences of biogeography, geographical distance and availability of suitable habitat.     

Environmental factors affecting population level genetic divergence of the striped field mouse (<Emphasis Type="Italic">Apodemus agrarius</Emphasis>) in South Korea

The cognizing of connectivity among small mammal populations across heterogeneous landscapes is complicated due to complex influences of landscape and anthropogenic factors on gene flow. A landscape genetics approach offers inferences on how landscape features drive population structure. Through a landscape genetics approach, we investigated influences of geographical, environmental, and anthropogenic features on populations of Apodemus agrarius, the striped field mouse, the prime vector of hemorrhagic fever by a landscape genetic approach. We identified landscape features that might affect the population structure of striped field mice by analyzing microsatellite markers of 197 striped field mice from 21 populations throughout South Korea. We developed Maximum-likelihood population effects models based on landscape distances and resistance matrices and pairwise F_ST values for meta-populations of striped field mouse. We also conducted Mantel and partial Mantel tests to investigate geographic patterns of genetic similarities. In Mantel and partial Mantel tests, the F_ST was significantly correlated with all three models of movement; movement cost, Euclidian distance and least-cost distance, although the magnitudes of correlations varied. The 4 top-ranked models included three variables; temperature, precipitation and one human disturbance factor (population). We did not attain a significant effect for anthropogenic factors on genetic similarities among populations in the Korean striped field mouse, but we confirmed a significant association for genetic similarity with climatic features (temperature and precipitation).     

Genetic variation at allozyme and RAPD loci in sessile oak Quercus petraea (Matt.) Liebl.: the role of history and geography

The nuclear genetic variation within and among 21 populations of sessile oak was estimated at 31 RAPD loci in conjunction with previous estimates of variation at eight allozyme loci. The aim of the study was to assess the relative role of isolation-by-distance and postglacial history on patterns of nuclear variation. Because of its small effective population size and maternal transmission, the chloroplast genome is a good marker of population history. Both kinds of nuclear variation (RAPD and allozyme) were therefore compared, first, to the geographical distances among populations and, secondly, to chloroplast DNA restriction polymorphism in the same populations. Multiple Mantel tests were used for this purpose. Although RAPDs revealed less genetic diversity than allozymes, levels of genetic differentiation ( G _ST) were identical. The standard genetic distance calculated at all RAPD loci was correlated with geographical distances but not with the genetic distance calculated from chloroplast DNA data. Conversely, allozyme variation was correlated with chloroplast DNA variation, but not with geography. Possibly, divergent selection at two allozyme loci during the glacial period could explain this pattern. Because of its greater number of loci assayed, RAPDs probably provided a less biased picture of the relative role of geography and history.     

Long-term effects of translocation and release numbers on fine-scale population structure among coho salmon (Oncorhynchus kisutch)

Management actions, such as translocations, reintroductions and supportive breeding, can have both negative and positive effects on population recovery. Several studies have examined the incidence of introgression following such actions, but few studies have explored the effect of release numbers on gene flow between closely related recipient populations. We examined population structure of coho salmon in Puget Sound (Washington State, USA) to evaluate the relationship between the number of individuals transferred between rivers, and the number released within rivers, on inter- and intrariver population divergence. Eleven microsatellite loci were surveyed in 23 hatchery and wild samples collected from 11 rivers within and one hatchery outside Puget Sound. Pairwise genetic divergences between most populations were significant, but the population structure could not be explained by an isolation-by-distance model (Mantel test, P > 0.05). In contrast, we detected significant hatchery influence on population structure. The numbers of fish transferred among rivers between 1952 and 2004 was negatively correlated with differentiation between rivers (partial Mantel test, P = 0.005) but not within rivers (t-test, P = 0.41). Number of fish released from hatcheries that collect broodstock locally was negatively correlated with population structure within rivers (t-test P = 0.002), and between nearby rivers (partial Mantel P = 0.04). Our results indicate that the population structure can, to some degree, be altered by the number of individuals transferred and by local release number of individuals in ongoing artificial propagation programs. The findings presented here emphasize the need to control the number of individuals that are either inadvertently introduced, or are deliberately released under conservation scenarios.     

Using multiple landscape genetic approaches to test the validity of genetic clusters in a species characterized by an isolation‐by‐distance pattern

Bayesian clustering methods are typically used to identify barriers to gene flow, but they are prone to deduce artificial subdivisions in a study population characterized by an isolation‐by‐distance pattern (IbD). Here we analysed the landscape genetic structure of a population of wild boars (Sus scrofa) from south‐western Germany. Two clustering methods inferred the presence of the same genetic discontinuity. However, the population in question was characterized by a strong IbD pattern. While landscape‐resistance modelling failed to identify landscape features that influenced wild boar movement, partial Mantel tests and multiple regression of distance matrices (MRDMs) suggested that the empirically inferred clusters were separated by a genuine barrier. When simulating random lines bisecting the study area, 60% of the unique barriers represented, according to partial Mantel tests and MRDMs, significant obstacles to gene flow. By contrast, the random‐lines simulation showed that the boundaries of the inferred empirical clusters corresponded to the most important genetic discontinuity in the study area. Given the degree of habitat fragmentation separating the two empirical partitions, it is likely that the clustering programs correctly identified a barrier to gene flow. The differing results between the work published here and other studies suggest that it will be very difficult to draw general conclusions about habitat permeability in wild boar from individual studies.     

Genetic variation in Echinacea angustifolia along a climatic gradient

BACKGROUNDS AND AIMS: Echinacea angustifolia is a widespread species distributed throughout the Great Plains region of North America. Genetic differentiation among populations was investigated along a 1500 km north-south climatic gradient in North America, a region with no major geographical barriers. The objective of the study was to determine if genetic differentiation of populations could be explained by an isolation-by-distance model or by associations with climatic parameters known to affect plant growth and survival. METHODS: Historical climatic data were used to define the nature of the climatic gradient and AFLP markers were used to establish patterns of population genetic differentiation among ten Echinacea populations collected from North Dakota to Oklahoma. A total of 1290 fragments were scored using six EcoRI/MseI and three PstI/MseI primer combinations. Assessment of the correlation between climatic, genetic and geographic distances was assessed by Mantel and partial Mantel tests. KEY RESULTS: PstI/MseI combinations produced significantly fewer fragments, but a larger percentage was unique compared with EcoRI/MseI markers. Using estimates of F(ST), populations in Oklahoma and southern Kansas were identified as the most divergent from the other populations. Both the neighbour-joining tree and principal co-ordinate analysis clustered the populations in a north-south spatial orientation. About 60% of the genetic variation was found within populations, 20% among populations and the remaining 20% was partitioned among groups that were defined by the topology of the neighbour-joining tree. Significant support was found for the isolation-by-distance model independent of the effects of annual mean precipitation, but not from annual mean temperature and freeze-free days. CONCLUSIONS: Echinacea angustifolia populations exhibit genetic divergence along a north-south climatic gradient. The data support an isolation-by-distance restriction in gene flow that is independent of annual mean precipitation.     

The effect of landscape features on population genetic structure in Yunnan snub-nosed monkeys (Rhinopithecus bieti) implies an anthropogenic genetic discontinuity

The Tibetan Plateau is one of the top 10 biodiversity hotspots in the world and acts as a modern harbour for many rare species because of its relatively pristine state. In this article, we report a landscape genetic study on the Yunnan snub-nosed monkey ( Rhinopithecus bieti ), a primate endemic to the Tibetan Plateau. DNA was extracted from blood, tissue and fecal samples of 135 wild individuals representing 11 out of 15 extant monkey groups. Ten microsatellite loci were used to characterize patterns of genetic diversity. The most striking feature of the population structure is the presence of five subpopulations with distinct genetic backgrounds and unique spatial regions. The population structure of R. bieti appears to be shaped by anthropogenic landscape features as gene flow between subpopulations is strongly impeded by arable land, highways and human habitation. A partial Mantel test showed that 36.23% ( r  =   0.51, P  =   0.01) of the genetic distance was explained by habitat gaps after controlling for the effect of geographical distance. Only 4.92% of the genetic distance was explained by geographical distance in the partial Mantel test, and no significant correlation was found. Estimation of population structure history indicates that environmental change during the last glacial maximum and human impacts since the Holocene, or a combination of both, have shaped the observed population structure of R. bieti . Increasing human activity on the Plateau, especially that resulting in habitat fragmentation, is becoming an important factor in shaping the genetic structure and evolutionary potential of species inhabiting this key ecosystem.     

Genome-wide association to fine-scale ecological heterogeneity within a continuous population of Biscutella laevigata (Brassicaceae)

Gene flow, drift and selection can be detected through different signatures across the genome and the landscape. Genetic discontinuities along with their correlation to environmental features can be used to tease out isolation-by-distance and isolation-by-time from processes related to selection. Using spatial statistics (spatial autocorrelation methods, canonical correspondence analysis and partial Mantel tests) dealing with genome-wide amplified fragment length polymorphism (AFLP) under unlikely Hardy-Weinberg assumptions, this study investigates 124 individuals within a continuous population of the autopolyploid Biscutella laevigata (Brassicaceae). Fine-scale spatial genetic structure was strong and the mosaic-like distribution of AFLP genotypes was consistently associated with habitat factors, even when controlled for geographical distances. The use of multivariate analyses enabled separation of the factors responsible for the repartition of the genetic variance and revealed a composite effect of isolation by distance, phenological divergence and local adaptation to habitats characterised by different solar radiation regimes. These results suggest that the immigrant inviability barrier facilitated the maintenance of adapted subpopulations to distinct environmental conditions at the local scale.     

Genetic structure in fragmented populations of Hippophae rhamnoides ssp. sinensis in China investigated by ISSR and cpSSR markers

Hippophae rhamnoides ssp. sinensis is an ecologically and economically important species that has been widely used as a pioneer plant in China. In this study, we employed both nuclear ISSR and maternal cpSSR markers to survey the genetic diversity and structure of populations of ssp. sinensis representing three different landscapes, the northwestern desert and grassland region, the alpine vegetation region of the Qinghai-Tibetan Plateau, and the northeastern humid forest region. In all, 12 natural populations with a scattered distribution in the area were studied. The genetic diversities of populations were found to be uneven, and the total genetic diversity was low on the basis of both types of marker. Mantel tests based on both individual Euclidean distance matrices and population genetic distance (measured by ??pt) matrices showed that the two marker systems detected similar trends with respect to genetic distances between populations. The analysis of molecular variance (AMOVA) revealed significant differentiation among populations and among regions for both types of marker. Although the detected pattern of isolation-by-distance among all sampled populations confirmed the earlier colonization pathway, the low level of gene flow and the lack of isolation by distance within each region suggested the presence of an additional dispersal barrier. UPGMA dendrograms and PCA plots also revealed clear clustering and significant regional differentiation. Our results indicate that the genetic structure of ssp. sinensis has been affected by habitat fragmentation and restricted population sizes. We propose that the biology of reproduction and ecology have played determinant roles in the development of the regional structure of populations. The genetic information obtained will help to establish conservation strategies and programs for sustainable management of H. rhamnoides ssp. sinensis.     

Phylogeography in continuous space: coupling species distribution models and circuit theory to assess the effect of contiguous migration at different climatic periods on genetic differentiation in Busseola fusca (Lepidoptera: Noctuidae)

Current population genetic models fail to cope with genetic differentiation for species with large, contiguous and heterogeneous distribution. We show that in such a case, genetic differentiation can be predicted at equilibrium by circuit theory, where conductance corresponds to abundance in species distribution models (SDMs). Circuit‐SDM approach was used for the phylogeographic study of the lepidopteran cereal stemborer Busseola fuscaFüller (Noctuidae) across sub‐Saharan Africa. Species abundance was surveyed across its distribution range. SDMs were optimized and selected by cross‐validation. Relationship between observed matrices of genetic differentiation between individuals, and between matrices of resistance distance was assessed through Mantel tests and redundancy discriminant analyses (RDAs). A total of 628 individuals from 130 localities in 17 countries were genotyped at seven microsatellite loci. Six population clusters were found based on a Bayesian analysis. The eastern margin of Dahomey gap between East and West Africa was the main factor of genetic differentiation. The SDM projections at present, last interglacial and last glacial maximum periods were used for the estimation of circuit resistance between locations of genotyped individuals. For all periods of time, when using either all individuals or only East African individuals, partial Mantel r and RDA conditioning on geographic distance were found significant. Under future projections (year 2080), partial r and RDA significance were different. From this study, it is concluded that analytical solutions provided by circuit theory are useful for the evolutionary management of populations and for phylogeographic analysis when coalescence times are not accessible by approximate Bayesian simulations.     

Population genetics of the common long-armed octopus Octopus minor (Sasaki, 1920) (Cephalopoda: Octopoda) in Chinese waters based on microsatellite analysis

Octopus minor (Sasaki, 1920) is a commercially important cephalopod in Chinese waters. To provide a theoretical basis for resource protection and sustainable management, we investigated genetic structure of ten O. minor populations in Chinese waters using microsatellite DNA markers. Eight microsatellite loci revealed high allelic diversity with 11–26 alleles per locus. Observed and expected heterozygosity varied from 0.412 to 0.900 and from 0.337 to 0.845, respectively. The overall F_ST value was 0.198, indicating great genetic differentiation among populations. The F_ST value between Yilan and other populations reached more than 0.3 that may be indicative of subspecies rank. Mantel test showed significant correlations between genetic and geographic distance (R = 0.383, P = 0.004) indicating that genetic differentiation of O. minor conformed to a pattern of isolation-by-distance. Using the Neighbor-joining method, cluster analysis divided nine populations into three groups and divided ten populations into two groups wherein Yilan was distinguished from the other populations. Analysis based on F_ST, D_c values and clustering highlighted the heterogeneity of Yilan and the relative homogeneity between Yilan and Ganyu. The significant population genetic structure of O. minor is related to the combined effects of geographical barriers, current features and life history characteristics.     

Primate communities are structured more by dispersal limitation than by niches

1.?A major goal in community ecology is to identify mechanisms that govern the assembly and maintenance of ecological communities. Current models of metacommunity dynamics differ chiefly in the relative emphasis placed on dispersal limitation and niche differentiation as causal mechanisms structuring ecological communities. Herein we investigate the relative roles of these two mechanisms in structuring primate communities in Africa, South America, Madagascar and Borneo. 2.?We hypothesized that if dispersal limitation is important in structuring communities, then community similarity should depend on geographical proximity even after controlling for ecological similarity. Conversely, if communities are assembled primarily through niche processes, then community similarity should be determined by ecological similarity regardless of geographical proximity. 3.?We performed Mantel and partial Mantel tests to investigate correlations among primate community similarity, ecological distance and geographical distance. Results showed significant and strongly negative relationships between diurnal primate community similarity and both ecological similarity and geographical distance in Madagascar, but significant and stronger negative relationships between community similarity and geographical distance in African, South American and Bornean metacommunities. 4.?We conclude that dispersal limitation is an important determinant of primate community structure and may play a stronger role in shaping the structure of some terrestrial vertebrate communities than niche differentiation. These patterns are consistent with neutral theory. We recommend tests of functional equivalence to determine the extent to which neutral theory may explain primate community composition.     

Multiple spatial scale patterns of genetic diversity in riparian populations of Ainsliaea faurieana (Asteraceae) on Yakushima Island, Japan

Habitat and geographical features of river systems strongly influence gene flow and spatial genetic patterning in riparian plant populations. We investigated the patterns of genetic diversity within and among populations of Ainsliaea faurieana relative to different spatial conditions (along a river, among rivers, and among regions on an island), based on nuclear and chloroplast microsatellite DNA variations. Within an individual river system, we found higher haplotype diversities in downstream populations, and in a Bayesian analysis of recent migration, we detected unidirectional gene movements from upstream to downstream, indicating water-mediated dispersal along the river. Mantel tests detected no isolation-by-distance in genetic variation, suggesting the maintenance of a metapopulation with wide-range seed dispersal by water. Moreover, the observed high level of genetic differentiation, especially in the cpDNA (F(ST) = 0.539), indicated a metapopulation structure with frequent extinction and colonization. On a larger scale, we found high population differentiation and clear genetic structuring among regions, suggesting that gene flow was restricted by geographical features (mountains separating river systems) for relatively long periods. Our findings of genetic structures based on different spatial conditions elucidated patterns and ranges of historical and contemporary gene movement in a plant species that is persistent in extremely disturbed riparian environments.     

Comparative population structure and genetic diversity of Arceuthobium americanum (Viscaceae) and its Pinus host species: insight into host-parasite evolution in parasitic angiosperms

In a recent study we revealed that the parasitic angiosperm Arceuthobium americanum is comprised of three distinct genetic races, each associated with a different host in regions of allopatry. In order to assess the role of host identity and geographical isolation on race formation in A. americanum, we compared the genetic population structure of this parasite with that of its three principal hosts, Pinus banksiana, Pinus contorta var. latifolia and Pinus contorta var. murrayana. Despite the fact that A. americanum was divided into three genetic races, hosts were divided into only two genetic groups: (i) Pinus banksiana and hybrids, and (ii) P. contorta var. latifolia and var. murrayana. These findings suggest that factors such as geographical isolation and adaptation to different environmental conditions are important for race formation in the absence of host-driven selection pressures. To assess factors impacting population structure at the fine-scale, genetic and geographical distance matrices of host and parasite were compared within A. americanum races. The lack of a relationship between genetic and geographical distance matrices suggests that isolation-by-distance plays a negligible role at this level. The effect of geographical isolation may have been diminished because of the influence of factors such as random seed dispersal by animal vectors or adaptation to nongeographically patterned environmental conditions. Host-parasite interactions might also have impacted the fine-scale structure of A. americanum because the parasite and host were found to have similar patterns of gene flow.     

Genetic population structure and contemporary dispersal patterns of a recent European invader, the Chinese mitten crab, Eriocheir sinensis

Genetic studies of recently established populations are challenging because the assumption of equilibrium underlying many analyses is likely to be violated. Using microsatellites, we investigated determinants of genetic structure and migration among invasive European-Chinese mitten crab populations, applying a combination of traditional population genetic analyses and nonequilibrium Bayesian methods. Consistent with their recent history, invasive populations showed much lower levels of genetic diversity than a native Chinese population, indicative of recent bottlenecks. Population differentiation was generally low but significant and especially pronounced among recently established populations. Significant differentiation among cohorts from the same geographical location (River Thames) suggests the low effective population size and associated strong genetic drift that would be anticipated from a very recent colonization. An isolation-by-distance pattern appears to be driven by an underlying correlation between geographical distance and population age, suggesting that cumulative homogenizing gene flow reduces founder bottleneck-associated genetic differentiation between longer-established populations. This hypothesis was supported by a coalescent analysis, which supported a drift + gene flow model as more likely than a model excluding gene flow. Furthermore, admixture analysis identified several recent migrants between the UK and Continental European population clusters. Admixture proportions were significantly predicted by the volume of shipping between sites, indicating that human-mediated transport remains a significant factor for dispersal of mitten crabs after the initial establishment of populations. Our study highlights the value of nonequilibrium methods for the study of invasive species, and also the importance of evaluating nonequilibrium explanations for isolation by distance patterns.     

Quantitative trait, genetic, environmental, and geographical distances among populations of the C4 grass Trachypogon plumosus in Neotropical savannas

Venezuelan savannas are exposed to land‐use changes and biological invasions which compromise their persistence and function. The native C₄ grass Trachypogon plumosus is the most important component of the savannas under diverse combinations of climate and soils, suggesting substantial interpopulation variation. We examined quantitative traits and isozyme variation of nine populations of this grass and related these estimates to geographical and environmental features of sampled locations. Isozyme diversity estimates were based on 10 polymorphic enzyme systems whereas 21 quantitative traits, from field and controlled growth conditions, were evaluated. Distance matrices for quantitative traits, isozyme, geographical and environmental data were subjected to clustering analysis. Correspondence between quantitative trait distance and genetic distance, and their association to geographical and environmental distances were analysed with Mantel tests. All quantitative traits differed significantly among populations. The average Q_ST calculated for eight quantitative traits measured in the greenhouse was 0.157. Isozyme diversity differed significantly among populations. About 28% of total isozyme variation occurred among populations. Significant positive associations were detected between environmental, quantitative field traits, and geographical distance as well as between the later and genetic distances. Genetic distances did not correspond significantly with quantitative traits nor did environmental distances. Ecologically meaningful associations were detected between field quantitative traits, environmental, and geographical data using cluster analysis. Our results support the hypothesis that processes of the neutral type are mainly responsible for the variation patterns observed in T. plumosus populations in Venezuelan savannas. Variation observed for quantitative traits among populations seems to be due to the effect of environmental conditions on phenotypically plastic traits, and not the result of directional selection favouring different phenotypes in different populations.     

Landscape features affect gene flow of Scottish Highland red deer (Cervus elaphus)

Landscape features have been shown to strongly influence dispersal and, consequently, the genetic population structure of organisms. Studies quantifying the effect of landscape features on gene flow of large mammals with high dispersal capabilities are rare and have mainly been focused at large geographical scales. In this study, we assessed the influence of several natural and human-made landscape features on red deer gene flow in the Scottish Highlands by analysing 695 individuals for 21 microsatellite markers. Despite the relatively small scale of the study area (115 × 87 km), significant population structure was found using F -statistics ( F _ST = 0.019) and the program structure , with major differentiation found between populations sampled on either side of the main geographical barrier (the Great Glen). To assess the effect of landscape features on red deer population structure, the ArcMap GIS was used to create cost-distance matrices for moving between populations, using a range of cost values for each of the landscape features under consideration. Landscape features were shown to significantly affect red deer gene flow as they explained a greater proportion of the genetic variation than the geographical distance between populations. Sea lochs were found to be the most important red deer gene flow barriers in our study area, followed by mountain slopes, roads and forests. Inland lochs and rivers were identified as landscape features that might facilitate gene flow of red deer. Additionally, we explored the effect of choosing arbitrary cell cost values to construct least cost-distance matrices and described a method for improving the selection of cell cost values for a particular landscape feature.     

Habitat differentiation vs. isolation-by-distance: the genetic population structure of Elymus athericus in European salt marshes

We investigated genetic differentiation among populations of the clonal grass Elymus athericus, a common salt-marsh species occurring along the Wadden Sea coast of Europe. While E. athericus traditionally occurs in the high salt marsh, it recently also invaded lower parts of the marsh. In one of the first analyses of the genetic population structure in salt-marsh species, we were interested in population differentiation through isolation-by-distance, and among strongly divergent habitats (low and high marsh) in this wind- and water-dispersed species. High and low marsh habitats were sampled at six sites throughout the Wadden Sea. Based on reciprocal transplantation experiments conducted earlier revealing lower survival of foreign genotypes we predicted reduced gene flow among habitats. Accordingly, an analysis with polymorphic cross-species microsatellite primers revealed significant genetic differentiation between high and low marsh habitats already on a very small scale (< 100 m), while isolation-by-distance was present only on larger scales (60-443 km). In an analysis of molecular variance we found that 14% of the genetic variance could be explained by the differentiation between habitats, as compared to only 8.9% to geographical (isolation-by-distance) effects among six sites 2.5-443 km distant from each other. This suggests that markedly different selection regimes between these habitats, in particular intraspecific competition and herbivory, result in habitat adaptation and restricted gene flow over distances as small as 80 m. Hence, the genetic population structure of plant species can only be understood when considering geographical and selection-mediated restrictions to gene flow simultaneously.