Triploid bumblebees indicate a direct cost of inbreeding in fragmented populations

Hymenopteran species with single-locus complimentary sex-determination (sl-CSD) face an additional cost of inbreeding because of a loss of diversity at the sex-determining locus. Laboratory studies of a range of Hymenoptera have found that a small percentage of diploid males produce viable diploid sperm, and that if these males mate, then the resultant females produce triploid offspring that are sterile. Here, we use microsatellite markers to determine the frequency of triploid individuals of Bombus muscorum and B. jonellus in a model island system. Triploids were found in populations of both species. Observed triploid frequencies of up to 8% were detected, and estimated total frequencies peaked at 20% with respect to normal diploid workers. For both species, triploid frequency was negatively correlated with surrogates of population size, providing direct evidence for inbreeding in small populations. Populations limited to <～15 km(2) of suitable habitat were particularly likely to harbour triploids. Estimated total triploid frequencies were higher in B. muscorum than in B. jonellus, perhaps due to the greater dispersal range of the latter species. Implications for the conservation of rare social hymenopterans are discussed.     

Foraging habitats and foraging distances of bumblebees, Bombus spp. (Hym., Apidae), in an agricultural landscape

Abstract: In selected foraging habitats of an agricultural landscape flower visits of bumblebees and community structure of foraging bumblebees were studied, with special regard to the role of crops as super-abundant resources. Most crops represent temporal foraging habitats with high abundance of bumblebees but mainly with low diversity in the bumblebee forage community, in contrast to permanent foraging habitats such as, for example, a hedgerow. The high numbers of bumblebees in the monoculture of crop plantations consisted mainly of short-tongued bumblebee species. The role of foraging distances for the visitation rate of foraging habitats was studied by performing capture–recapture experiments with natural nests of Bombus terrestris , Bombus lapidarius and Bombus muscorum . Differences were found on the species as well as the individual level. The foraging distances of B. muscorum were more restricted to the neighbourhood of the nesting habitat than the foraging activity of B. terrestris and B. lapidarius . High percentages of B. terrestris workers were recaptured while foraging on super-abundant resources in distances up to 1750 m from the nest. Isolated patches of highly rewarding forage crops, in agricultural landscapes, are probably only accessed by bumblebee species with large mean foraging distances, such as the short-tongued B. terrestris . Species like the rare, long-tongued B. muscorum depend on a close connection between nesting and foraging habitat. A restricted foraging radius might be one important factor of bumblebee species loss and potential pollinator limitation in modern agricultural landscapes. Furthermore, long-distance flights of bumblebee pollinators have to be considered in the present discussion on gene flow from transgenic plant species on a landscape scale.     

Estimation of bumblebee queen dispersal distances using sibship reconstruction method

Dispersal ability is a key determinant of the propensity of an organism to cope with habitat fragmentation and climate change. Here we quantify queen dispersal in two common bumblebee species in an arable landscape. Dispersal was measured by taking DNA samples from workers in the spring and summer, and from queens in the following spring, at 14 sites across a landscape. The queens captured in the spring must be full sisters of workers that were foraging in the previous year. A range of sibship reconstruction methods were compared using simulated data sets including or no genotyping errors. The program Colony gave the most accurate reconstruction and was used for our analysis of queen dispersal. Comparison of queen dispersion with worker foraging distances was used to take into account an expected low level of false identification of sister pairs which might otherwise lead to overestimates of dispersal. Our data show that Bombus pascuorum and B. lapidarius queens can disperse by at least 3 and 5 km, respectively. These estimates are consistent with inferences drawn from studies of population structuring in common and rare bumblebee species, and suggest that regular gene flow over several kilometres due to queen dispersal are likely to be sufficient to maintain genetic cohesion of ubiquitous species over large spatial scales whereas rare bumblebee species appear unable to regularly disperse over distances greater than 10 km. Our results have clear implications for conservation strategies for this important pollinator group, particularly when attempting to conserve fragmented populations.     

Comparative genetic analyses of historical and contemporary collections highlight contrasting demographic histories for the bumble bees Bombus pensylvanicus and B. impatiens in Illinois

Direct comparison of genetic patterns between museum specimens and contemporary collections can be a powerful approach for detecting recent demographic changes. Using microsatellite markers, we examined historical and contemporary genetic variation from an apparently declining bumble bee species, Bombus pensylvanicus , and from a stable species, Bombus impatiens , in central Illinois. For each species, we genotyped specimens from the Illinois Natural History Survey collected from three populations between 1969–1972 and from a resurvey of the same areas conducted in 2008. Population structure in B . pensylvanicus increased markedly over the last four decades (from θ_ST = 0.001 to 0.027) while no structure was detected in B . impatiens for either time period (θ_ST = –0.006 to –0.003). Changes in genetic diversity were not significant for either species, although small reductions were observed for B . pensylvanicus in all three populations. Coalescent simulations incorporating both contemporary and historical samples suggest that this small change is not surprising for recent population declines, as large reductions in genetic diversity were only apparent under the most severe bottleneck scenarios. These results demonstrate how comparisons of genetic patterns between temporal periods and species can help elucidate potential threats to population health and suggest several strategies that might be useful in the conservation of B . pensylvanicus in the Midwestern USA.     

Extremely low effective population sizes, genetic structuring and reduced genetic diversity in a threatened bumblebee species, Bombus sylvarum (Hymenoptera: Apidae)

Habitat fragmentation may severely affect survival of social insect populations as the number of nests per population, not the number of individuals, represents population size, hence they may be particularly prone to loss of genetic diversity. Erosion of genetic diversity may be particularly significant among social Hymenoptera such as bumblebees (Bombus spp.), as this group may be susceptible to diploid male production, a suggested direct cost of inbreeding. Here, for the first time, we assess genetic diversity and population structuring of a threatened bumblebee species (Bombus sylvarum) which exists in highly fragmented habitat (rather than oceanic) islands. Effective population sizes, estimated from identified sisterhoods, were very low (range 21-72) suggesting that isolated populations will be vulnerable to loss of genetic variation through drift. Evidence of significant genetic structuring between populations (theta = 0.084) was found, but evidence of a bottleneck was detected in only one population. Comparison across highly fragmented UK populations and a continental population (where this species is more widespread) revealed significant differences in allelic richness attributable to a high degree of genetic diversity in the continental population. While not directly related to population size, this is perhaps explained by the high degree of isolation between UK populations relative to continental populations. We suggest that populations now existing on isolated habitat islands were probably linked by stepping-stone populations prior to recent habitat loss.     

Habitat quality limits gene flow between populations of <Emphasis Type="Italic">Bombus ruderatus</Emphasis> in the South Island,New Zealand

One of the primary reasons for the decline of some bumblebee species has been habitat loss and fragmentation through land use change. Habitat fragmentation can limit connectivity between populations and gene flow between bumblebee populations can be limited by open water and human altered landscapes, however the influence of landscape features on gene flow has only been examined in non-declining species. The ruderal bumblebee, Bombus ruderatus, was successfully introduced to and is now relatively common in New Zealand, providing an opportunity to examine the biology of a species that is now rare in its native range in the UK. In this study, we examine the genetic structuring of B. ruderatus populations in the South Island of New Zealand and we demonstrate that a relatively simple classification of the landscape, into either good or poor foraging habitat at coarse resolution (800 m²), can predict levels of gene flow. We found populations of B. ruderatus as far apart as 160 km showing no significant genetic differentiation. However, this level of gene flow appears to be reliant upon continuous suitable habitat, as other populations <100 km apart were found to be significantly differentiated. These results suggest that corridors of continuous habitat are required to facilitate gene flow over large distances for this species.     

Genetic diversity and parasite prevalence in two species of bumblebee

Many bumblebee species have been suffering from significant declines across their ranges in the Northern Hemisphere over the last few decades. The remaining populations of the rare species are now often isolated due to habitat fragmentation and have reduced levels of genetic diversity. The persistence of these populations may be threatened by inbreeding depression, which may result in a higher susceptibility to parasites. Here we investigate the relationship between genetic diversity and prevalence of the parasitic mite Locustacarus buchneri in bumblebees, using the previously-studied system of Bombus muscorum and Bombus jonellus in the Western Isles of Scotland. We recorded L. buchneri prevalence in 17 populations of B. muscorum and 13 populations of B. jonellus and related the results to levels of heterozygosity. For B. muscorum, we found that prevalence of the mite was higher in populations with lower genetic diversity but there was no such relationship in the more genetically diverse B. jonellus. In contrast to population-level measures of genetic diversity, the heterozygosity of individual bees was not correlated with infection status. We suggest population-level genetic homogeneity may facilitate parasite transmission and elevate prevalence, with potential consequences for population persistence.     

Population genetic structure in Myrtus communis L. in a chronically fragmented landscape in the Mediterranean: can gene flow counteract habitat perturbation?

Ancient managed landscapes provide ideal opportunities to assess the consequences of habitat fragmentation on the patterns of genetic diversity and gene flow in long-lived plant species. Using amplified fragment length polymorphism (AFLP) and allozyme markers, we quantified seed-mediated gene flow and population genetic diversity and structure in 14 populations of Myrtus communis (myrtle), a common endozoochorous shrub species of forest patches in lowland agricultural Mediterranean areas. Overall, allozyme diversity for myrtle was low (P₉₅   =   25%; A   =   1.411; H_e = 0.085) compared to other known populations, and a significant portion of populations (57%) had lower levels of allelic diversity and/or heterozygosity than expected at random, as shown by simulated resampling of the whole diversity of the landscape. We found significant correlations between allozyme variability and population size and patch isolation, but no significant inbreeding in any population. Genetic differentiation among populations for both allozyme and AFLP markers was significant (Φ_ST = 0.144 and Φ_ST = 0.142, respectively) but an isolation-by-distance pattern was not detected. Assignment tests on AFLP data indicated a high immigration rate in the populations ( ca. 20–22%), likely through effective seed dispersal across the landscape by birds and mammals. Our results suggest that genetic isolation is not the automatic outcome of habitat destruction since substantial levels of seed-mediated gene flow are currently detectable. However, even moderate rates of gene flow seem insufficient in this long-lived species to counteract the genetic erosion and differentiation imposed by chronic habitat destruction.     

Population structure,dispersal and colonization history of the garden bumblebee <Emphasis Type="Italic">Bombus hortorum</Emphasis> in the Western Isles of Scotland

New methods of analysing genetic data provide powerful tools for quantifying dispersal patterns and reconstructing population histories. Here we examine the population structure of the bumblebee Bombus hortorum in a model island system, the Western Isles of Scotland, using microsatellite markers. Following declines in other species, B. hortorum is the only remaining long-tongued bumblebee species found in much of Europe, and thus it is of particular ecological importance. Our data suggest that populations of B. hortorum in western Scotland exist as distinct genetic clusters occupying groups of nearby islands. Population structuring was higher than for other bumblebee species which have previously been studied in this same island group (F_st = 0.16). Populations showed significant isolation by distance. This relationship was greatly improved by using circuit theory to allow dispersal rates to differ over different landscape features; as we would predict, sea appears to provide far higher resistance to dispersal than land. Incorporating bathymetry data improved the fit of the model further; populations separated by shallow seas are more genetically similar than those separated by deeper seas. We argue that this probably reflects events following the last ice age when the islands were first colonized by this bee species (8,500–5,000 ybp), when the sea levels were lower and islands separated by shallow channels would have been joined. In the absence of significant gene flow these genetic clusters appear to have since diverged over the following 5,000 years and arguably may now represent locally adapted races, some occurring on single islands.     

Genetic effects of habitat fragmentation and population isolation on Etheostoma raneyi (Percidae)

The use of genetic methods to quantify the effects of anthropogenic habitat fragmentation on population structure has become increasingly common. However, in today’s highly fragmented habitats, researchers have sometimes concluded that populations are currently genetically isolated due to habitat fragmentation without testing the possibility that populations were genetically isolated before European settlement. Etheostoma raneyi is a benthic headwater fish restricted to river drainages in northern Mississippi, USA, that has a suite of adaptive traits that correlate with poor dispersal ability. Aquatic habitat within this area has been extensively modified, primarily by flood-control projects, and populations in headwater streams have possibly become genetically isolated from one another. We used microsatellite markers to quantify genetic structure as well as contemporary and historical gene flow across the range of the species. Results indicated that genetically distinct populations exist in each headwater stream analyzed, current gene flow rates are lower than historical rates, most genetic variation is partitioned among populations, and populations in the Yocona River drainage show lower levels of genetic diversity than populations in the Tallahatchie River drainage and other Etheostoma species. All populations have negative F_IS scores, of which roughly half are significant relative to Hardy–Weinberg expectations, perhaps due to small population sizes. We conclude that anthropogenic habitat alteration and fragmentation has had a profoundly negative impact on the species by isolating E. raneyi within headwater stream reaches. Further research is needed to inform conservation strategies, but populations in the Yocona River drainage are in dire need of management action. Carefully planned human-mediated dispersal and habitat restoration should be explored as management options across the range of the species.     

Distribution and forage use of exotic bumblebees in South Island, New Zealand

The rapid decline in bumblebee populations within Europe has been linked to habitat loss through agricultural intensification, and a consequential reduction in the availability of preferred forage plants. The successful introduction of four European Bombus species to the South Island of New Zealand from England (in 1885 and 1906) provides an opportunity to determine how important different forage plants (also introduced from the U.K.) are to two severely threatened European bumblebee species (Bombus ruderatus and B. subterraneus). In January 2003 we conducted a survey of bumblebee populations across 70 sites in the central and southern South Island, recording which plant species were being used as pollen and nectar sources for each Bombus species. All four bumblebee species showed a clear preference for plants of European origin. Only B. terrestris, the most polylectic species, was recorded feeding on native plant species. The longer-tongued bumblebees, B. hortorum, B. ruderatus, and B. subterraneus, foraged predominantly on just two plant species; Trifolium pratense for both nectar and pollen, and Echium vulgare for nectar. These plant species are now declining in abundance in the U.K. Our results provide support for the hypothesis that the loss of flower-rich meadows, particularly those containing populations of Fabaceae species with long corollae, is responsible for the decline of bumblebee species across Europe. Comparison with earlier bumblebee surveys suggests that long-tongued bumblebees may also be in decline in New Zealand, particularly B. subterraneus which is now very localised and scarce.     

Dispersal and population structure of two sympatric species of the mediterranean land snail genus Mastus (Gastropoda, Pulmonata, Enidae)

We studied the population dynamics of Mastus by investigating the effects of population structure, spatial ecology and biology of reproduction on the genetic diversity of two sympatric Mastus species endemic to the island of Crete. Over a period of 27 months, we carried out both mark–recapture and random quadrat sampling techniques in order to assess the dispersal trends, the aggregation patterns, the neighbourhood size and the habitat preferences of these species. There were 154 recorded movements for M. butoti and 114 for M. cretensis . Mean monthly dispersal was estimated at d  = 0.5 m for M. butoti and d  = 1 m for M. cretensis . Both species showed a random dispersal pattern but tended to aggregate in the field. Their populations were found to be highly structured owing to their highly parsimonious dispersal behaviour and the very low population densities, estimated at D  = 2.07 ± 0.16 and D  = 0.73 ± 0.16 individuals m⁻² for M. butoti and M. cretensis , respectively. The neighbourhood size did not exceed 150 individuals for either species. The habitat occupied by each species changed during the active season, but both the immature and the adult individuals of each species seemed to prefer the same habitats throughout the active season. Partial population activation during the active season was observed in both species. We conclude that the population structure, the partial population activation and the species-specific reproductive strategies have a profound effect on maintaining the genetic diversity of the genus' populations.  © 2004 The Linnean Society of London, Biological Journal of the Linnean Society , 2004, 83 , 131–144.     

Absolute configuration of chiral terpenes in marking pheromones of bumblebees and cuckoo bumblebees

The absolute configurations of citronellol, 2,3-dihydrofarnesol, and 2,3-dihydrofarnesal in male marking pheromones of seven species of bumblebees and cuckoo bumblebees were determined by enantioselective gas chromatography on a capillary column coated with 60% heptakis(2,3-di-O-acetyl-6-O-TBDMS)-beta-cyclodextrin in polysiloxane PS 268. Pure (-)-S-enantiomers of all three terpenes were found in the labial glands of all investigated specimens of the following species: Bombus (Bombus) terrestris, B. (Bombus) lucorum, B. (Pyrobombus) pratorum, B. (Pyrobombus) pyrenaeus, B. (Pyrobombus) jonellus, B. (Pyrobombus) impatiens, and the cuckoo bumblebee B. (Ashtonipsithyrus) bohemicus. Within species, specimens were collected at different localities and in different years. Except for 2,3-dihydrofarnesol in B. terrestris, this is the first report on the absolute configuration of terpenes in marking pheromones of bumblebees.     

Forward to the north: two Euro-Mediterranean bumblebee species now cross the Arctic Circle

In recent decades, several animal and plant species have been in regression (population size decrease and geographical distribution shrinking). This loss of biodiversity can be due to various factors such as the destruction and fragmentation of habitat, urban development, pesticides or climate change. However, some species benefit from these changes and expand their distribution. Here we report observations (in 2013 and 2014) of two Euro-Mediterranean bumblebee species: Bombus terrestris for the first time and Bombus lapidarius, north of the Arctic Circle in Fennoscandia.     

Distance,elevation and environment as drivers of diversity and divergence in bumble bees across latitude and altitude

Identifying drivers of dispersal limitation and genetic differentiation is a key goal in biogeography. We examine patterns of population connectivity and genetic diversity using restriction site‐associated DNA sequencing (RADseq) in two bumble bee species, Bombus vosnesenskii and Bombus bifarius, across latitude and altitude in mountain ranges from California, Oregon and Washington, U.S.A. Bombus vosnesenskii, which occurs across a broader elevational range at most latitudes, exhibits little population structure while B. bifarius, which occupies a relatively narrow higher elevation niche across most latitudes, exhibits much stronger population differentiation, although gene flow in both species is best explained by isolation with environmental niche resistance. A relationship between elevational habitat breadth and genetic diversity is also apparent, with B. vosnesenskii exhibiting relatively consistent levels of genetic diversity across its range, while B. bifarius has reduced genetic diversity at low latitudes, where it is restricted to high‐elevation habitat. The results of this study highlight the importance of the intersect between elevational range and habitat suitability in influencing population connectivity and suggest that future climate warming will have a fragmenting effect even on populations that are presently well connected, as they track their thermal niches upward in montane systems.     

Small-Scale Fragmentation Effects on Local Genetic Diversity in Two Phyllostomid Bats with Different Dispersal Abilities in Panama

Habitat fragmentation is one of the greatest threats to biodiversity. Despite their importance for conservation, the genetic consequences of small-scale habitat fragmentation for bat populations are largely unknown. In this study, we linked genetic with ecological and demographic data to assess the effects of habitat fragmentation on two species of phyllostomid bats ( Uroderma bilobatum and Carollia perspicillata ) that differ in their dispersal abilities and demographic response to fragmentation. We hypothesized that population differentiation and the effect of habitat fragmentation on levels of genetic diversity will be a function of the species' mobility. We sequenced mtDNA from 232 bats caught on 11 islands in Gatún Lake, Panamá, isolated from the mainland for ca 90 yr, and in adjacent, continuous forest on the mainland. Populations of both species showed significant genetic differentiation ( F _ST). Consistent with our prediction, population subdivision was lower in the highly mobile U. bilobatum ( F _ST= 0.01) compared to the less vagile C. perspicillata ( F _ST= 0.06), and only the latter species showed a pattern indicative of isolation by distance and, in addition, an effect of fragmentation. Genetic erosion as a result of fragmentation was also only detectable in the less mobile species, C. perspicillata , where haplotype diversity was lower in island compared to mainland populations. Our results suggest that some Neotropical bat species are prone to loss of genetic variation in response to anthropogenic small-scale habitat fragmentation. In this context, our findings point toward mobility as a good predictor of a species' vulnerability to fragmentation and altered population genetic structure.     

Reconstructing demographic events from population genetic data: the introduction of bumblebees to New Zealand

Four British bumblebee species (Bombus terrestris, Bombus hortorum, Bombus ruderatus and Bombus subterraneus) became established in New Zealand following their introduction at the turn of the last century. Of these, two remain common in the United Kingdom (B. terrestris and B. hortorum), whilst two (B. ruderatus and B. subterraneus) have undergone marked declines, the latter being declared extinct in 2000. The presence of these bumblebees in New Zealand provides an unique system in which four related species have been isolated from their source population for over 100 years, providing a rare opportunity to examine the impacts of an initial bottleneck and introduction to a novel environment on their population genetics. We used microsatellite markers to compare modern populations of B. terrestris, B. hortorum and B. ruderatus in the United Kingdom and New Zealand and to compare museum specimens of British B. subterraneus with the current New Zealand population. We used approximate Bayesian computation to estimate demographic parameters of the introduction history, notably to estimate the number of founders involved in the initial introduction. Species-specific patterns derived from genetic analysis were consistent with the predictions based on the presumed history of these populations; demographic events have left a marked genetic signature on all four species. Approximate Bayesian analyses suggest that the New Zealand population of B. subterraneus may have been founded by as few as two individuals, giving rise to low genetic diversity and marked genetic divergence from the (now extinct) UK population.     

Levels of gene flow among populations of a wolf spider in a recently fragmented habitat: current versus historical rates

Gene flow among populations is important for countering the deleterious effects of random genetic drift and inbreeding, as well as spreading beneficial mutations. Wind-driven aerial dispersal is known to occur in numerous plants and invertebrates. Its evolution suggests that historically, suitable habitat patches were dense enough to make such undirected dispersal evolutionarily advantageous. Using microsatellite markers we assessed the population genetic structure of seven populations of a wolf spider (Rabidosa rabida) capable of ballooning. Historically, each spider population received a mean of 1.5 migrants per generation from the other six populations. Over the past several generations the number of migrants reaching a population is only 0.2. This statistically significant reduction in gene flow coincides with high levels of habitat fragmentation and suggests that undirected aerial dispersal is ineffective in this fragmented landscape. Further, individuals within populations showed signficantly elevated levels of homozygosity relative to Hardy–Weinberg expectations, suggesting that cursorial dispersal may be very limited and genetic structure within populations exists. Inbreeding coefficients averaged 0.18 over all seven populations with very little variation among populations (s = 0.02). Fitness was lower in smaller populations relative to larger ones. Altered landscapes pose evolutionary dilemmas for many metapopulations and species that depend on undirected movement for dispersal may be particularly vulnerable to habitat fragmentation.     

Anthropogenic fragmentation may not alter pre‐existing patterns of genetic diversity and differentiation in perennial shrubs

Many plant species have pollination and seed dispersal systems and evolutionary histories that have produced strong genetic structuring. These genetic patterns may be consistent with expectations following recent anthropogenic fragmentation, making it difficult to detect fragmentation effects if no prefragmentation genetic data are available. We used microsatellite markers to investigate whether severe habitat fragmentation may have affected the structure and diversity of populations of the endangered Australian bird‐pollinated shrub Grevillea caleyi R.Br., by comparing current patterns of genetic structure and diversity with those of the closely related G. longifolia R.Br. that has a similar life history but has not experienced anthropogenic fragmentation. Grevillea caleyi and G. longifolia showed similar and substantial population subdivision at all spatial levels (global F′_ST = 0.615 and 0.454; S_p = 0.039 and 0.066), marked isolation by distance and large heterozygous deficiencies. These characteristics suggest long‐term effects of inbreeding in self‐compatible species that have poor seed dispersal, limited connectivity via pollen flow and undergo population bottlenecks because of periodic fires. Highly structured allele size distributions, most notably in G. caleyi, imply historical processes of drift and mutation were important in isolated subpopulations. Genetic diversity did not vary with population size but was lower in more isolated populations for both species. Through this comparison, we reject the hypothesis that anthropogenic fragmentation has impacted substantially on the genetic composition or structure of G. caleyi populations. Our results suggest that highly self‐compatible species with limited dispersal may be relatively resilient to the genetic changes predicted to follow habitat fragmentation.     

Habitat fragmentation influences genetic diversity and differentiation: Fine‐scale population structure of Cercis canadensis (eastern redbud)

Forest fragmentation may negatively affect plants through reduced genetic diversity and increased population structure due to habitat isolation, decreased population size, and disturbance of pollen‐seed dispersal mechanisms. However, in the case of tree species, effective pollen‐seed dispersal, mating system, and ecological dynamics may help the species overcome the negative effect of forest fragmentation. A fine‐scale population genetics study can shed light on the postfragmentation genetic diversity and structure of a species. Here, we present the genetic diversity and population structure of Cercis canadensis L. (eastern redbud) wild populations on a fine scale within fragmented areas centered around the borders of Georgia–Tennessee, USA. We hypothesized high genetic diversity among the collections of C. canadensis distributed across smaller geographical ranges. Fifteen microsatellite loci were used to genotype 172 individuals from 18 unmanaged and naturally occurring collection sites. Our results indicated presence of population structure, overall high genetic diversity (H_E = 0.63, H_O = 0.34), and moderate genetic differentiation (F_ST = 0.14) among the collection sites. Two major genetic clusters within the smaller geographical distribution were revealed by STRUCTURE. Our data suggest that native C. canadensis populations in the fragmented area around the Georgia–Tennessee border were able to maintain high levels of genetic diversity, despite the presence of considerable spatial genetic structure. As habitat isolation may negatively affect gene flow of outcrossing species across time, consequences of habitat fragmentation should be regularly monitored for this and other forest species. This study also has important implications for habitat management efforts and future breeding programs.