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Landscape features often shape patterns of gene flow and genetic differentiation in plant species. Populations that are small and isolated enough also become subject to genetic drift. We examined patterns of gene flow and differentiation among 12 floodplain populations of the selfing annual jewelweed (Impatiens capensis Meerb.) nested within four river systems and two major watersheds in Wisconsin, USA. Floodplain forests and marshes provide a model system for assessing the effects of habitat fragmentation within agricultural/urban landscapes and for testing whether rivers act to genetically connect dispersed populations. We generated a panel of 12,856 single nucleotide polymorphisms and assessed genetic diversity, differentiation, gene flow, and drift. Clustering methods revealed strong population genetic structure with limited admixture and highly differentiated populations (mean multilocus FST = 0.32, FST' = 0.33). No signals of isolation by geographic distance or environment emerged, but alleles may flow along rivers given that genetic differentiation increased with river distance. Differentiation also increased in populations with fewer private alleles (R2 = 0.51) and higher local inbreeding (R2 = 0.22). Populations varied greatly in levels of local inbreeding (FIS = 0.2–0.9) and FIS increased in more isolated populations. These results suggest that genetic drift dominates other forces in structuring these Impatiens populations. In rapidly changing environments, species must migrate or genetically adapt. Habitat fragmentation limits both processes, potentially compromising the ability of species to persist in fragmented landscapes. [ABSTRACT FROM AUTHOR]

Species with narrow environmental tolerances are often distributed within fragmented patches of suitable habitat, and dispersal among these subpopulations can be difficult to directly observe. Genetic data can help quantify gene flow between localities, which is especially important for vulnerable species with a disjunct range. The Shenandoah salamander (Plethodon shenandoah) is a federally endangered species known only from three mountaintops in Virginia, USA. To reconstruct the evolutionary history and population connectivity of this species, we generated both mitochondrial and nuclear data using sequence capture from individuals collected across all three mountaintops. Applying population and landscape genetic methods, we found strong population structure that was independent of geographic distance. Both the nuclear markers and mitochondrial genomes indicated a deep split between the most southern population and the genetically similar central and northern populations. Although there was some mitochondrial haplotype‐splitting between the central and northern populations, there was admixture in nuclear markers. This is indicative of either a recent split or current male‐biased dispersal among mountain isolates. Models of landscape resistance found that dispersal across north‐facing slopes at mid‐elevation levels best explain the observed genetic structure among populations. These unexpected results highlight the importance of incorporating landscape features in understanding and predicting the movement and fragmentation of this range‐restricted salamander species across space. [ABSTRACT FROM AUTHOR]

Changing landscape heterogeneity can influence connectivity and alter genetic variation in local populations, but there can be a lag between ecological change and evolutionary responses. Temporal lag effects might be acute in agroecosystems, where land cover has changed substantially in the last two centuries. Here, we evaluate how patterns of an insect pest's genetic differentiation are related to past and present agricultural land cover change over a 150‐year period. We quantified change in the amount of potato, Solanum tuberosum L., land cover since 1850 using county‐level agricultural census reports, obtained allele frequency data from 7,408 single‐nucleotide polymorphism loci, and compared effects of historic and contemporary landscape connectivity on genetic differentiation of Colorado potato beetle, Leptinotarsa decemlineata Say, in two agricultural landscapes in the United States. We found that potato land cover peaked in Wisconsin in the early 1900s, followed by rapid decline and spatial concentration, whereas it increased in amount and extent in the Columbia Basin of Oregon and Washington beginning in the 1960s. In both landscapes, we found small effect sizes of landscape resistance on genetic differentiation, but a 20× to 1,000× larger effect of contemporary relative to historic landscape resistances. Demographic analyses suggest population size trajectories were largely consistent among regions and therefore are not likely to have differentially impacted the observed patterns of population structure in each region. Weak landscape genetic associations might instead be related to the coarse resolution of our historical land cover data. Despite rapid changes in agricultural landscapes over the last two centuries, genetic differentiation among L. decemlineata populations appears to reflect ongoing landscape change. The historical landscape genetic framework employed in this study is broadly applicable to other agricultural pests and might reveal general responses of pests to agricultural land‐use change. [ABSTRACT FROM AUTHOR]

Fremont cottonwood (Populus fremonti) is a foundation riparian tree species that drives community structure and ecosystem processes in southwestern U.S. ecosystems. Despite its ecological importance, little is known about the ecological and environmental processes that shape its genetic diversity, structure, and landscape connectivity. Here, we combined molecular analyses of 82 populations including 1312 individual trees dispersed over the species' geographical distribution. We reduced the data set to 40 populations and 743 individuals to eliminate admixture with a sibling species, and used multivariate restricted optimization and reciprocal causal modeling to evaluate the effects of river network connectivity and climatic gradients on gene flow. Our results confirmed the following: First, gene flow of Fremont cottonwood is jointly controlled by the connectivity of the river network and gradients of seasonal precipitation. Second, gene flow is facilitated by mid-sized to large rivers, and is resisted by small streams and terrestrial uplands, with resistance to gene flow decreasing with river size. Third, genetic differentiation increases with cumulative differences in winter and spring precipitation. Our results suggest that ongoing fragmentation of riparian habitats will lead to a loss of landscape-level genetic connectivity, leading to increased inbreeding and the concomitant loss of genetic diversity in a foundation species. These genetic effects will cascade to a much larger community of organisms, some of which are threatened and endangered. [ABSTRACT FROM AUTHOR]

Sweet chestnut ( Castanea sativa Mill.) is a multipurpose species of great ecological and economic importance in southwest Bulgaria. Bulgarian chestnut forests are severely degraded, however, due to the intensive exploitation and bad management that have occurred over the last 2000 years. Given the urgent need to define conservation strategies to preserve the biodiversity of Bulgarian chestnut, we estimated its genetic variability. A set of eight microsatellite primers were used to analyze the genetic diversity and structure of six C. sativa populations distributed throughout the range of species in Bulgaria. Results showed a generally high level of genetic diversity but little divergence among populations. A significant, positive, within-population inbreeding coefficient (Fis) was observed in four populations. A STRUCTURE analysis revealed three genetic clusters. Using a landscape approach, significant genetic barriers among populations were found by integrating genetics with geographical distance. We hypothesize that one population is a relict from a glacial refugium; the structure of the remaining populations is probably the result of a combination of natural events and human impacts. For the purposes of conservation planning, we have identified populations that are particularly rich in diversity and private alleles that are good candidates for preservation. [ABSTRACT FROM AUTHOR]

The physical and environmental attributes of landscapes often shape patterns of population connectivity by influencing dispersal and gene flow. Landscape effects on movement are typically evaluated for single species. However, inferences from multiple species are required for multi-species management strategies increasingly being applied in conservation. In this study, I compared the spatial genetic patterns of two amphibian species across the northeastern United States and estimated the influence of specific landscape features on the observed genetic structure. The spotted salamander ( Ambystoma maculatum) and wood frog ( Rana sylvatica) share many ecological attributes related to habitat use, phenology and site fidelity. However, I hypothesized that important differences in their movement patterns and life history would create distinct genetic patterns for each species. Using 14 microsatellite loci, I tested for differences in the level of genetic differentiation between the two species across 22 breeding ponds. The effects of eight landscape features were also estimated by evaluating 32 landscape resistance models. Spotted salamanders exhibited significantly higher genetic differentiation than wood frogs. Different landscape features were also identified as potential drivers of the genetic patterns in each species, with little overlap in model support between species. Collectively, these results provide strong evidence that these two amphibian species interact with the landscape in measurably different ways. The distinct genetic patterns observed are consistent with key differences in movement ability and life history between A. maculatum and R. sylvatica. These results highlight the importance of considering more than one species when assessing the impacts of the landscape matrix on population connectivity, even for ecologically similar species within the same habitats. [ABSTRACT FROM AUTHOR]

We utilize empirically derived estimates of landscape resistance to assess current landscape connectivity of American marten ( Martes americana) in the northern Rocky Mountains, USA, and project how a warming climate may affect landscape resistance and population connectivity in the future. We evaluate the influences of five potential future temperature scenarios involving different degrees of warming. We use resistant kernel dispersal models to assess population connectivity based on full occupancy of suitable habitat in each of these hypothetical future resistance layers. We use the CDPOP model to simulate gene exchange among individual martens in each of these hypothetical future climates. We evaluate: (1) changes in the extent, connectivity and pattern of marten habitat, (2) changes in allelic richness and expected heterozygosity, and (3) changes in the range of significant positive genetic correlation within the northern Idaho marten population under each future scenario. We found that even moderate warming scenarios resulted in very large reductions in population connectivity. Calculation of genetic correlograms for each scenario indicates that climate driven changes in landscape connectivity results in decreasing range of genetic correlation, indicating more isolated and smaller genetic neighborhoods. These, in turn, resulted in substantial loss of allelic richness and reductions in expected heterozygosity. In the U.S. northern Rocky Mountains, climate change may extensively fragment marten populations to a degree that strongly reduces genetic diversity. Our results demonstrate that for species, such as the American marten, whose population connectivity is highly tied to climatic gradients, expected climate change can result in profound changes in the extent, pattern, connectivity and gene flow of populations. [ABSTRACT FROM AUTHOR]

We investigated how landscape features influence gene flow of black bears by testing the relative support for 36 alternative landscape resistance hypotheses, including isolation by distance (IBD) in each of 12 study areas in the north central U.S. Rocky Mountains. The study areas all contained the same basic elements, but differed in extent of forest fragmentation, altitude, variation in elevation and road coverage. In all but one of the study areas, isolation by landscape resistance was more supported than IBD suggesting gene flow is likely influenced by elevation, forest cover, and roads. However, the landscape features influencing gene flow varied among study areas. Using subsets of loci usually gave models with the very similar landscape features influencing gene flow as with all loci, suggesting the landscape features influencing gene flow were correctly identified. To test if the cause of the variability of supported landscape features in study areas resulted from landscape differences among study areas, we conducted a limiting factor analysis. We found that features were supported in landscape models only when the features were highly variable. This is perhaps not surprising but suggests an important cautionary note - that if landscape features are not found to influence gene flow, researchers should not automatically conclude that the features are unimportant to the species' movement and gene flow. Failure to investigate multiple study areas that have a range of variability in landscape features could cause misleading inferences about which landscape features generally limit gene flow. This could lead to potentially erroneous identification of corridors and barriers if models are transferred between areas with different landscape characteristics. [ABSTRACT FROM AUTHOR]

• Premise of the study: Despite rapid growth in the field of landscape genetics, our understanding of how landscape features interact with life history traits to influence population genetic structure in plant species remains limited. Here, we identify population genetic divergence in three species of Penstemon (Plantaginaceae) similarly distributed throughout the Great Basin region of the western United States but with different pollination syndromes (bee and hummingbird). The Great Basin's mountainous landscape provides an ideal setting to compare the interaction of landscape and dispersal ability in isolating populations of different species. • Methods: We used eight highly polymorphic microsatellite loci to identify neutral population genetic structure between populations within and among mountain ranges for eight populations of P. deustus, 10 populations of P. pachyphyllus, and 10 populations of P. rostriflorus. We applied traditional population genetics approaches as well as spatial and landscape genetics approaches to infer genetic structure and discontinuities among populations. • Key results: All three species had significant genetic structure and exhibited isolation by distance, ranging from high structure and low inferred gene flow in the bee-pollinated species P. deustus (FST = 0.1330, RST = 0.4076, seven genetic clusters identified) and P. pachyphyllus (FST = 0.1896, RST = 0.2531, four genetic clusters identified) to much lower structure and higher inferred gene flow in the hummingbird-pollinated P. rostriflorus (FST = 0.0638, RST = 0.1116, three genetic clusters identified). • Conclusions: These three Penstemon species have significant yet strikingly different patterns of population genetic structure, findings consistent with different interactions between landscape features and the dispersal capabilities of their pollinators. [ABSTRACT FROM AUTHOR]

We studied the population genetics of Podocnemis unifilis turtles within and among basins in the Orinoco and Amazon drainages using microsatellites. We detected high levels of genetic diversity in all sampled localities. However, 'M-ratio' tests revealed a substantial recent population decline in ten localities, in accord with current widespread exploitation. Our results reveal a consistent pattern across multiple analyses, showing a clear subdivision between the populations inhabiting the Amazon and Orinoco drainages despite a direct connection via the Casiquiare corridor, and suggesting the existence of two biogeographically independent and widely divergent lineages. Genetic differentiation followed an isolationby- distance model concordant with hypotheses about migration. It appears that migration occurs via the flooded forest in some drainages, and via river channels in those where geographic barriers preclude dispersal between basins or even among nearby tributaries of the same basin. These observations caution against making generalizations based on geographically restricted data, and indicate that geographically proximate populations may be demographically separate units requiring independent management. [ABSTRACT FROM AUTHOR]

In west-central Texas, USA, abatement efforts for the gray fox (Urocyon cinereoargenteus) rabies epizootic illustrate the difficulties inherent in large-scale management of wildlife disease. The rabies epizootic has been managed through a cooperative oral rabies vaccination program (ORV) since 1996. Millions of edible baits containing a rabies vaccine have been distributed annually in a 16-km to 24-km zone around the perimeter of the epizootic, which encompasses a geographic area .4 3 105 km2. The ORV program successfully halted expansion of the epizootic into metropolitan areas but has not achieved the ultimate goal of eradication. Rabies activity in gray fox continues to occur periodically outside the ORV zone, preventing ORV zone contraction and dissipation of the epizootic. We employed a landscape-genetic approach to assess gray fox population structure and dispersal in the affected area, with the aim of assisting rabies management efforts. No unique genetic clusters or population boundaries were detected. Instead, foxes were weakly structured over the entire region in an isolation by distance pattern. Local subpopulations appeared to be genetically non-independent over distances .30 km, implying that long-distance movements or dispersal may have been common in the region. We concluded that gray foxes in west-central Texas have a high potential for long-distance rabies virus trafficking. Thus, a 16-km to 24-km ORV zone may be too narrow to contain the fox rabies epizootic. Continued expansion of the ORV zone, although costly, may be critical to the long-term goal of eliminating the Texas fox rabies virus variant from the United States. [ABSTRACT FROM AUTHOR]

Habitat loss and fragmentation are the leading causes of species’ declines and extinctions. A key component of studying population response to habitat alteration is to understand how fragmentation affects population connectivity in disturbed landscapes. We used landscape genetic analyses to determine how habitat fragmentation due to timber harvest affects genetic population connectivity of the coastal tailed frog ( Ascaphus truei), a forest-dwelling, stream-breeding amphibian. We compared rates of gene flow across old-growth (Olympic National Park) and logged landscapes (Olympic National Forest) and used spatial autoregression to estimate the effect of landscape variables on genetic structure. We detected higher overall genetic connectivity across the managed forest, although this was likely a historical signature of continuous forest before timber harvest began. Gene flow also occurred terrestrially, as connectivity was high across unconnected river basins. Autoregressive models demonstrated that closed forest and low solar radiation were correlated with increased gene flow. In addition, there was evidence for a temporal lag in the correlation of decreased gene flow with harvest, suggesting that the full genetic impact may not appear for several generations. Furthermore, we detected genetic evidence of population bottlenecks across the Olympic National Forest, including at sites that were within old-growth forest but surrounded by harvested patches. Collectively, this research suggests that absence of forest (whether due to natural or anthropogenic changes) is a key restrictor of genetic connectivity and that intact forested patches in the surrounding environment are necessary for continued gene flow and population connectivity. [ABSTRACT FROM AUTHOR]

To evaluate the sufficiency of US federal critical habitat designations and a proposed conservation plan in promoting the long-term persistence of the endangered plant Astragalus albens, patterns of genetic diversity and landscape connectivity were examined. A. albens harbors substantial genetic variation and shows no evidence of historic bottlenecks, suggesting little risk of extinction due to genetic homogeneity (A =2.40; P =0.50) or inbreeding (f =−0.08) within occurrences. Low genetic differentiation among occurrences (θ p =0.01) indicates relatively high gene flow or little genetic drift. The 91 patches of A. albens were connected into a single network at a distance of 2100m; 94% of patches were <1000m from at least one other patch. Managing ecological conditions that maintain large population sizes and connectivity among populations throughout the species’ ecological and geographic ranges will most likely conserve existing diversity. Both reserve networks partially accomplish these goals by including most extant occurrences and >89% of the aerial extent of the species, including the largest populations, and capturing all detected alleles. However, both conservation networks fail to conserve occurrences from one portion of the species’ range, possibly speeding loss of unique local adaptations. In addition, connectivity of the whole network is reduced with the 65 patches designated as critical habitat being connected at a distance of 6200m and the proposed reserve sites being connected at a distance of 9500m. Although total network connectivity would be reduced, connectivity at scales most relevant to gene flow (e.g., <1000m) remains sufficiently in tact to provide a relatively promising outlook for species persistence. [Copyright &y& Elsevier]

Spatial and temporal landscape patterns have long been recognized to influence biological processes, but these processes often operate at scales that are difficult to study by conventional means. Inferences from genetic markers can overcome some of these limitations. We used a landscape genetics approach to test hypotheses concerning landscape processes influencing the demography of Lahontan cutthroat trout in a complex stream network in the Great Basin desert of the western US. Predictions were tested with population-and individual-based analyses of microsatellite DNA variation, reflecting patterns of dispersal, population stability, and local effective population sizes. Complementary genetic inferences suggested samples from migratory corridors housed a mixture of fish from tributaries, as predicted based on assumed migratory life histories in those habitats. Also as predicted, populations presumed to have greater proportions of migratory fish or from physically connected, large, or high quality habitats had higher genetic variability and reduced genetic differentiation from other populations. Populations thought to contain largely non-migratory individuals generally showed the opposite pattern, suggesting behavioral isolation. Estimated effective sizes were small, and we identified significant and severe genetic bottlenecks in several populations that were isolated, recently founded, or that inhabit streams that desiccate frequently. Overall, this work suggested that Lahontan cutthroat trout populations in stream networks are affected by a combination of landscape and metapopulation processes. Results also demonstrated that genetic patterns can reveal unexpected processes, even within a system that is well studied from a conventional ecological perspective. [ABSTRACT FROM AUTHOR]

Landscape features such as mountains, rivers, and ecological gradients may strongly affect patterns of dispersal and gene flow among populations and thereby shape population dynamics and evolutionary trajectories. The landscape may have a particularly strong effect on patterns of dispersal and gene flow in amphibians because amphibians are thought to have poor dispersal abilities. We examined genetic variation at six microsatellite loci in Columbia spotted frogs (Rana luteiventris) from 28 breeding ponds in western Montana and Idaho, USA, in order to investigate the effects of landscape structure on patterns of gene flow. We were particularly interested in addressing three questions: (i) do ridges act as barriers to gene flow? (ii) is gene flow restricted between low and high elevation ponds? (iii) does a pond equal a‘randomly mating population’ (a deme)? We found that mountain ridges and elevational differences were associated with increased genetic differentiation among sites, suggesting that gene flow is restricted by ridges and elevation in this species. We also found that populations of Columbia spotted frogs generally include more than a single pond except for very isolated ponds. There was also evidence for surprisingly high levels of gene flow among low elevation sites separated by large distances. Moreover, genetic variation within populations was strongly negatively correlated with elevation, suggesting effective population sizes are much smaller at high elevation than at low elevation. Our results show that landscape features have a profound effect on patterns of genetic variation in Columbia spotted frogs. [ABSTRACT FROM AUTHOR]

Spatial patterns of intraspecific variation are shaped by geographical distance among populations, historical changes in gene flow and interactions with local environments. Although these factors are not mutually exclusive and operate on both genomic and phenotypic variation, it is unclear how they affect these two axes of variation. We address this question by exploring the predictors of genomic and phenotypic divergence in Icterus gularis, a broadly distributed Middle American bird that exhibits marked geographical variation in body size across its range. We combined a comprehensive single nucleotide polymorphism and phenotypic data set to test whether genome-wide genetic and phenotypic differentiation are best explained by (i) isolation by distance, (ii) isolation by history or (iii) isolation by environment. We find that the pronounced genetic and phenotypic variation in I. gularis are only partially correlated and differ regarding spatial predictors. Whereas genomic variation is largely explained by historical barriers to gene flow, phenotypic diversity can be best predicted by contemporary environmental heterogeneity. Our genomic analyses reveal strong phylogeographical structure coinciding with the Chivela Pass at the Isthmus of Tehuantepec that was formed during the Pleistocene, when populations were isolated in north-south refugia. In contrast, we found a strong association between body size and environmental variables, such as temperature and precipitation. The relationship between body size and local climate is consistent with a pattern produced by either natural selection or environmental plasticity. Overall, these results provide empirical evidence for why phenotypic and genomic data are often in conflict in taxonomic and phylogeographical studies., (© 2020 John Wiley & Sons Ltd.)

Population divergence can occur due to mechanisms associated with geographic isolation and/or due to selection associated with different ecological niches. Much of the evidence for selection-driven speciation has come from studies of specialist insect herbivores that use different host plant species; however, the influence of host plant use on population divergence of generalist herbivores remains poorly understood. We tested how diet breadth, host plant species and geographic distance influence population divergence of the fall webworm (Hyphantria cunea; FW). FW is a broadly distributed, extreme generalist herbivore consisting of two morphotypes that have been argued to represent two different species: black-headed and red-headed. We characterized the differentiation of FW populations at two geographic scales. We first analysed the influence of host plant and geographic distance on genetic divergence across a broad continental scale for both colour types. We further analysed the influence of host plant, diet breadth and geographic distance on divergence at a finer geographic scale focusing on red-headed FW in Colorado. We found clear genetic and morphological distinction between red- and black-headed FW, and Colorado FW formed a genetic cluster distinct from other locations. Although both geographic distance and host plant use were correlated with genetic distance, geographic distance accounted for up to 3× more variation in genetic distance than did host plant use. As a rare study investigating the genetic structure of a widespread generalist herbivore over a broad geographic range (up to 3,000 km), our study supports a strong role for geographic isolation in divergence in this system., (© 2019 John Wiley & Sons Ltd.)

Organisms typically show evidence of adaptation to features within their local environment. However, many species undergo long-distance dispersal or migration across larger geographic regions that consist of highly heterogeneous habitats. Therefore, selection may influence adaptive genetic variation associated with landscape features at residing sites and along migration routes in migratory species. We tested for genomic adaptation to landscape features at natal spawning sites and along migration paths to the ocean of anadromous steelhead trout (Oncorhynchus mykiss) in the Columbia River Basin. Results from multivariate ordination, gene-environment association and outlier analyses using 24,526 single nucleotide polymorphisms (SNPs) provided evidence that adaptive allele frequencies were more commonly associated with landscape features along migration paths than features at natal sites (91.8% vs. 8.2% of adaptive loci, respectively). Among the 45 landscape variables tested, migration distance to the ocean and mean annual precipitation along migration paths were significantly associated with adaptive genetic variation in three distinct genetic groups. Additionally, variables such as minimum migration water temperature and mean migration slope were significant only in inland stocks of steelhead that migrate up to 1,200 km farther than those near the coast, indicating regional differences in migratory selective pressures. This study provides novel approaches for investigating migratory corridors and some of the first evidence that environment along migration paths can lead to substantial divergent selection. Consequently, our approach to understand genetic adaptation to migration conditions can be applied to other migratory species when migration or dispersal paths are generally known., (© 2017 John Wiley & Sons Ltd.)

Local adaptation is pervasive in forest trees, which are characterized by large effective population sizes spanning broad climatic gradients. In addition to having relatively contiguous populations, many species also form isolated populations along the rear edge of their range. These rear-edge populations may contain unique adaptive diversity reflecting a history of selection in marginal environments. Thus, discovering genomic regions conferring local adaptation in rear edge populations is a key priority for landscape genomics to ensure conservation of genetic resources under climate change. Here, we report on adaptive gene-environment associations in single nucleotide polymorphisms (SNPs) from 27 genes in the Populus flowering time gene network, analyzed on a range-wide collection of >1000 balsam poplar trees, including dense sampling of the southern range edge. We use a combined approach of local adaptation scans to identify candidate SNPs, followed by modeling the compositional turnover of adaptive SNPs along multivariate climate gradients using gradient forests (GF). Flowering time candidate genes contained extensive evidence of climate adaptation, namely outlier population structure and gene-environment associations, along with allele frequency divergence between the core and edge of the range. GF showed strong allele frequency turnover along gradients of elevation and diurnal and temperature variability, as well as threshold responses to summer temperature and precipitation, with turnover especially strong in edge populations that occur at high elevation but southerly latitudes. We discuss these results in light of how climate may disrupt locally adaptive gene-environment relationships, and suggest that rear edge populations hold climate-adaptive variants that should be targeted for conservation., (© The American Genetic Association 2017. All rights reserved. For permissions, please e-mail: journals.permissions@oup.com.)

Unlabelled: • Premises of the study: Understanding the influence of recent glacial and postglacial periods on species' distributions is key for predicting the effects of future environmental changes. We investigated the influence of two physiographic landscapes on population structure and postglacial colonization of two white pine species of contrasting habitats: P. monticola, which occurs in the highly mountainous region of western North America, and P. strobus, which occurs in a much less mountainous area in eastern North America.•, Methods: To characterize the patterns of genetic diversity and population structure across the ranges of both species, 158 and 153 single nucleotide polymorphism (SNP) markers derived from expressed genes were genotyped on range-wide samples of 61 P. monticola and 133 P. strobus populations, respectively.•, Key Results: In P. monticola, a steep latitudinal decrease in genetic diversity likely resulted from postglacial colonization involving rare long-distance dispersal (LDD) events. In contrast, no geographic patterns of diversity were detected in P. strobus, suggesting recolonization via a gradually advancing front or frequent LDD events. For each species, structure analyses identified two distinct southern and northern genetic groups that likely originated from two different glacial lineages. At a finer scale, and for the two species, smaller subgroups were detected that could be remnants of cryptic refugia.•, Conclusion: During postglacial colonization, the western and eastern North American landscapes had different impacts on genetic signatures in P. monticola compared with P. strobus. We discuss the importance of our findings for conservation programs and predictions of species' response to climate change., (© 2015 Her Majesty the Queen in Right of Canada. Published by the Botanical Society of America.)