Population structure of pioneer specialist solitary bee Andrena vaga (Hymenoptera: Andrenidae) in central Europe: the effect of habitat fragmentation or evolutionary history?

Because patchiness of food sources or nesting opportunities frequently limits gene flow, specialists often exhibit distinct population structures in fragmented habitats. We studied the influence of habitat fragmentation on population structure in the solitary bee Andrena vaga, an early spring species that nests exclusively in sandy soil and feeds strictly on willows (Salix spp.). Because the homogenous habitat of the German floodplains, where the species was studied previously, resulted in the species’ weak population structure, we expected more structured populations in central Europe, where the sandy soils essential for nesting are highly fragmented. We analysed 387 females from 21 localities in the Czech Republic and Slovakia using nine microsatellite loci, and we inferred population structure using landscape genetics and Bayesian clustering methods. Contrary to our expectations, habitat fragmentation did not result in increased genetic isolation at the localities; however, two differentiated groups of localities, separated by a wide clinal zone of admixture, were detected within the study area. The observed pattern suggests that dispersive ability of A. vaga compensates the species dependence on unstable fragmented habitats. We propose that the population structure may mirror a secondary contact formed by the expansion of two populations that had been separated in the past. We emphasise the necessity of knowing the studied species’ population history before making conclusions concerning correlations between habitat and population structure, especially in areas of known suture zones created by the secondary contact of populations expanding from separate refugia.     

Devasting effects of river flooding to the ground-nesting bee, <Emphasis Type="Italic">Andrena vaga</Emphasis> (Hymenoptera: Andrenidae), and its associated fauna

Large populations of non-social bees are rarely seen in today's cultural landscapes. One of the few exceptions is the fossorial bee Andrena vaga Panzer, (Andrenidae), a typical insect species of river flood plains, which forms sizeable nesting aggregations along the high water dams of the Upper Rhine, each containing up to several tens of thousands of bees. In May 1999, a record flood of the River Rhine led to extreme water levels at the high water dams of the Upper Rhine. Though natural flooding is often viewed as a management practice with considerable conservation perspectives for river flood plain management, we demonstrate a catastrophic effect of the 1999 inundation on the immature offspring of two affected populations of A. vaga. All immatures in brood cells located low on the landward side of a dam died, very likely because saturation of the soil restricted oxygen availability.The two affected aggregations sited on the high water dam declined in the following year to 23 and 56% of pre-flood size, but not at a neighbouring, non-flooded aggregation. Rare parasites associated with A. vaga also decreased in number following flooding. These results highlight a dilemma on the use of natural flooding of river plains for conservation purposes.     

Genetic consequences of habitat fragmentation and loss: the case of the Florida black bear (<Emphasis Type="Italic">Ursus americanus floridanus</Emphasis>)

Habitat loss and fragmentation can influence the genetic structure of biological populations. We studied the genetic consequences of habitat fragmentation in Florida black bear (Ursus americanus floridanus) populations. Genetic samples were collected from 339 bears, representing nine populations. Bears were genotyped for 12 microsatellite loci to estimate genetic variation and to characterize genetic structure. None of the nine study populations deviated from Hardy–Weinberg equilibrium. Genetic variation, quantified by mean expected heterozygosity (H _E), ranged from 0.27 to 0.71 and was substantially lower in smaller and less connected populations. High levels of genetic differentiation among populations (global F _ST = 0.224; global R _ST = 0.245) suggest that fragmentation of once contiguous habitat has resulted in genetically distinct populations. There was no isolation-by-distance relationship among Florida black bear populations, likely because of barriers to gene flow created by habitat fragmentation and other anthropogenic disturbances. These factors resulted in genetic differentiation among populations, even those that were geographically close. Population assignment tests indicated that most individuals were genetically assigned to the population where they were sampled. Habitat fragmentation and anthropogenic barriers to movement appear to have limited the dispersal capabilities of the Florida black bear, thereby reducing gene flow among populations. Regional corridors or translocation of bears may be needed to restore historical levels of genetic variation. Our results suggest that management actions to mitigate genetic consequences of habitat fragmentation are needed to ensure long-term persistence of the Florida black bear.     

A land snail's view of a fragmented landscape

Habitat fragmentation may influence the genetic structure of populations, especially of species with low mobility. So far, these effects have been mainly studied by surveying neutral markers, and much less by looking at ecologically relevant characters. Therefore, we aimed to explore eventual patterns of covariation between population structuring in neutral markers and variation in shell morphometrics in the forest‐associated snail Discus rotundatus in relation to habitat fragment characteristics. To this end, we screened shell morphometric variability and sequence variation in a fragment of the mitochondrial 16S rDNA gene in D. rotundatus from the fragmented landscape of the Lower Rhine Embayment, Germany. The 16S rDNA of D. rotundatus was highly variable, with a total of 118 haplotypes (384 individuals) forming four clades and one unresolved group. There was a geographic pattern in the distribution of the clades with the river Rhine apparently separating two groups. Yet, at the geographic scale considered, there was no obvious effect of fragmentation on shell morphometrics and 16S rDNA variation because G_ST often was as high within, as between forests. Instead, the age of the habitat and (re‐)afforestation events appeared to affect shell shape and 16S rDNA in terms of the number of clades per site. The ecologically relevant characters thus supported the presumably neutral mitochondrial DNA markers by indicating that populations of not strictly stenecious species may be (relatively) stable in fragments. However, afforestation after large clearcuts and habitat gain after the amendment of deforestation are accompanied by several, seemingly persistent peculiarities, such as altered genetic composition and shell characters (e.g. aperture size). © 2009 The Linnean Society of London, Biological Journal of the Linnean Society, 2009, 98 , 839–850.     

Population genetics and fitness in fragmented populations of the dioecious and endangered <Emphasis Type="Italic">Silene otites</Emphasis> (Caryophyllaceae)

Population fragmentation is often correlated with loss of genetic diversity and reduced fitness. Obligate out-crossing (dioecy) is expected to enhance genetic diversity, reduce genetic differentiation, and avoid inbreeding depression through frequent gene flow. However, in highly fragmented populations dioecy has only diminishing effects upon genetic structure as pollination limitations (e.g. flight distance of pollinators) most often restrict inter-population gene flow in insect pollinated species. In fragmented dry grasslands in northeastern Germany, we analysed genetic structure, fitness, and habitat quality of the endangered dioecious Silene otites (Caryophyllaceae). Using AFLP markers, a high level of differentiation among ten populations was found (F _st = 0.36), while the intra-population genetic diversities (H _E = 0.165–0.240) were similar as compared to hermaphroditic species. There was neither a correlation between geographic and genetic distance nor between genetic diversity and population size, which indicates reduced gene flow among populations and random genetic drift. Plant size was positively correlated with genetic diversity. Seed set and number of juveniles were positively related to population size. Higher total coverage resulted in reduced plant fitness, and the number of juveniles was negatively correlated to cryptogam cover. Additionally, we found a sex ratio bias towards more male plants in larger populations. Overall, our results indicate that on a regional geographic scale dioecy does not necessarily prevent genetic erosion in the case of habitat fragmentation, especially in the absence of long distance seed and pollen dispersal capacity.     

GENE FLOW IN GROUND BEETLES (COLEOPTERA: CARABIDAE) OF DIFFERING HABITAT PREFERENCE AND FLIGHT-WING DEVELOPMENT

Estimates of gene flow vary 100-fold among five carabid species, ranging from the winged lowland subtropical Agonum elongatulum to the flightless montane temperate Platynus angustatus. Results based on Wright's (1943) F_ST method, and Slatkin's (1981) graphical and (1985a) private-allele methods are concordant. Genetic heterogeneity, measured by Wright's F_ST, is not correlated with degree of flight-wing development; one fully winged species exhibits heterogeneity of the same order as a vestigially winged species. Genetic heterogeneity is positively correlated with the average elevation of collection sites for these species. Lower levels of gene flow associated with greater genetic subdivision may occur in upland areas because of habitat fragmentation (due to topographic diversity) and habitat persistence (leading to a lower extinction rate for populations). In at least one species, the distribution of stable infraspecific polymorphisms indicates that the high estimate of present-day gene flow is likely to be due to historical gene flow and not to present-day conditions.     

Genetic diversity within and between remnant populations of the endangered calcareous grassland plant <Emphasis Type="Italic">Globularia bisnagarica</Emphasis> L.

Changes in agricultural production methods over the last century have caused a massive reduction and fragmentation of the area of European semi-natural grasslands. It remains unclear whether small and isolated grassland fragments can support viable plant populations in a sustainable way. In our study area in southern Belgium, the extent of calcareous grasslands was reduced from c. 650 ha in 1775 to less than 30 ha in 2004. We used AFLP markers to quantify the effects of present and historical grassland fragmentation on the genetic structure of 27 populations of the rare perennial plant species Globularia bisnagarica. Given the mixed breeding system of the species and the relatively small area of the studied system, the populations were characterized by high genetic differentiation (F _st range: 0.42–0.48; Φ_st=0.53). A Mantel test revealed significant isolation by distance of the populations. Average within population genetic diversity, measured as expected heterozygosity or gene diversity, was low (H _j =0.081) and was negatively related to population isolation. This suggests more gene flow into less isolated populations. Population size and local habitat characteristics did not significantly influence population genetic diversity. Both, high selfing rates in G. bisnagarica and a population genetic response to habitat fragmentation may explain our findings. Finally, a clear geographical clustering was observed, with cluster membership partially explainable by historical grassland connectivity. If populations indeed started to differentiate after fragmentation, this process was not (yet) strong enough to erase the genetic similarity between fragments that historically belonged to the same large grassland fragment.     

Testing hypotheses driving genetic structure in the cooperatively breeding Brown‐headed Nuthatch Sitta pusilla

Habitat fragmentation has often been implicated in the decline of many species. For habitat specialists and/or sedentary species, loss of habitat can result in population isolation and lead to negative genetic effects. However, factors other than fragmentation can often be important and also need to be considered when assessing the genetic structure of a species. We genotyped individuals from 13 populations of the cooperatively breeding Brown‐headed Nuthatch Sitta pusilla in Florida to test three alternative hypotheses regarding the effects that habitat fragmentation might have on genetic structure. A map of potential habitat developed from recent satellite imagery suggested that Brown‐headed Nuthatch populations in southern Florida occupied smaller and more isolated habitat patches (i.e. were more fragmented) than populations in northern Florida. We also genotyped individuals from a small, isolated Brown‐headed Nuthatch population on Grand Bahama Island. We found that populations associated with more fragmented habitat in southern Florida had lower allelic richness than populations in northern Florida (P = 0.02), although there were no differences in heterozygosity. Although pairwise estimates of F_ST were low overall, values among southern populations were generally higher than northern populations. Population assignment tests identified K = 3 clusters corresponding to a northern cluster, a southern cluster and a unique population in southeast Florida; using sampling localities as prior information revealed K = 7 clusters, with greater structure only among southern Florida populations. The Bahamas population showed moderate to high differentiation compared with Florida populations. Overall, our results suggest that fragmentation could affect gene flow in Brown‐headed Nuthatch populations and is likely to become more pronounced over time.     

Demographic bottlenecks and low gene flow in remnant populations of the critically endangered <Emphasis Type="Italic">Berchemiella wilsonii</Emphasis> var<Emphasis Type="Italic">. pubipetiolata</Emphasis> (Rhamnaceae) inferred from microsatellite markers

Berchemiella wilsonii var. pubipetiolata (Rhamnaceae) is an endangered plant with only four remnant populations in eastern China. Population genetic information is essential for understanding population history and formulating conservation strategies for this species. Thirteen microsatellite loci were used to investigate genetic variation and population structure of the four remnant populations. Moderate levels of expected heterozygosity (H _E = 0.466–0.543) and low allelic diversity (A = 3.1–3.6 and A _R = 2.2–2.4, respectively) were observed within populations. Bottleneck tests found three out of four populations to deviate from mutation-drift equilibrium under the two-phase model (TPM), suggesting a recent population decline, which is congruent with known demographic history. The evolutionary history of the species seems dominated by genetic drift rather than gene flow. Low historical gene flow was inferred from several different approaches and N _m ranged from 0.582 by the private allele method to 0.783 by the coalescent method. Contemporary gene flow was also found to be even lower for only one first generation migrant was detected with individual-based assignment analysis. Restricted pollen and seed dispersal as well as a recent decline in population size associated with habitat fragmentation may have contributed to low levels of historical and contemporary gene flow, and resulted in a high genetic differentiation. Under this scenario, Berchemiella wilsonii var. pubipetiolata populations are expected to display more pronounced population genetic structure in the future as a result of increased inbreeding and genetic drift.     

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.     

Landscape genetics of a recent population extirpation in a burnet moth species

The intensification of agricultural land use over wide parts of Europe has led to the decline of semi-natural habitats, such as extensively used meadows, with those that remain often being small and isolated. These rapid changes in land use during recent decades have strongly affected populations inhabiting these ecosystems. Increasing habitat deterioration and declining permeability of the surrounding landscape matrix disrupt the gene flow within metapopulations. The burnet moth species Zygaena loti has suffered strongly from recent habitat fragmentation, as reflected by its declining abundance. We have studied its population genetic structure and found a high level of genetic diversity in some of the populations analysed, while others display low genetic diversity and a lack of heterozygosity. Zygaena loti was formerly highly abundant in meadows and along the skirts of forests. However, the species is currently restricted to isolated habitat remnants, which is reflected by the high genetic divergence among populations (F _ST: 0.136). Species distribution modelling as well as the spatial examination of panmictic clusters within the study area strongly support a scattered population structure for this species. We suggest that populations with a high level of genetic diversity still represent the former genetic structure of interconnected populations, while populations with low numbers of alleles, high F _IS values, and a lack of heterozygosity display the negative effects of reduced interconnectivity. A continuous exchange of individuals is necessary to maintain high genetic variability. Based on these results, we draw the general conclusion that more common taxa with originally large population networks and high genetic diversity suffer stronger from sudden habitat fragmentation than highly specialised species with lower genetic diversity which have persisted in isolated patches for long periods of time.     

Population structure of an endangered frog (<Emphasis Type="Italic">Babina subaspera</Emphasis>) endemic to the Amami Islands: possible impacts of invasive predators on gene flow

The otton frog (Babina subaspera) is an endangered species endemic to the Amami Islands, Japan. High predation pressure from an introduced carnivore, the mongoose, has caused declines in the frog populations and created a large habitat gap around an urban area. To promote effective conservation, we investigated the genetic status of the species and examined the effect of the habitat gap on gene flow among populations. Using five polymorphic microsatellite loci and mitochondrial DNA sequences, we investigated genetic diversity, genetic structure and gene flow in B. subaspera populations on the islands of Amami-Oshima and Kakeroma-jima. The expected heterozygosity (H _E) within each locality was generally high (range: 0.67–0.85), indicating that B. subaspera maintains high genetic diversity. However, genetic differentiation was observed, and the two populations, TAG and KAR, showed little gene flow with other populations. The clustering and F _ST analyses also predicted that these two populations were clearly distinct. According to the mitochondrial DNA analysis, the observed genetic differentiation occurred relatively recently. Possible barriers such as mountain ridges, rivers or roads did not result in genetic separation of the populations. These data support the hypothesis that the habitat gap created by an introduced predator prevented the gene flow among B. subaspera populations. When developing conservation strategies for B. subaspera, focus should be directed to these two isolated populations; careful monitoring of population size and genetic diversity should be conducted along with the mongoose elimination project ensues.     

Genetic diversity in adult and seedling populations of <Emphasis Type="Italic">Primula vulgaris</Emphasis> in a fragmented agricultural landscape

Habitat fragmentation is known to generally reduce the size of plant populations and increase their isolation, leading to genetic erosion and increased between-population genetic differentiation. In Flanders (northern Belgium) Primula vulgaris is very rare and declining. Populations have incurred strong fragmentation for the last decades and are now restricted to a few highly fragmented areas in an intensively used agricultural landscape. Previous studies showed that small populations of this long-lived perennial herb still maintained high levels of genetic variation and low genetic differentiation. This pattern can either indicate recent gene flow or represent historical variation. Therefore, we used polymorphic microsatellite loci to investigate genetic variation and structure in adult (which may still reflect historical variation) and seedling (recent generation, thus affected by current processes) life stages. The recent generation (seedlings) showed a significant loss of observed heterozygosity (H _o) together with lower expected heterozygosity (H _e), a trend for higher inbreeding levels (F _IS) and higher differentiation (F _ST) between populations compared to the adult generation. This might result from (1) a reduction in effective population size, (2) higher inbreeding levels in the seedlings, (3) a higher survival of heterozygotes over time due to a higher fitness of heterozygotes (heterosis) and/or a lower fitness of homozygotes (inbreeding depression), (4) overlapping generations in the adult life stage, or (5) a lack of establishment of new (inbred) adults from seedlings due to degraded habitat conditions. Combining restoration of both habitat quality and gene flow between populations may be indispensable to ensure a sustainable conservation of fragmented populations.     

Patterns of genetic variation in isolated Danish populations of the endangered butterfly Euphydryas aurinia

In the present study, we report an investigation on molecular variation in the endangered univoltine butterfly Euphydryas aurinia (Rottemburg, 1775), a species heavily affected by habitat degradation and fragmentation in Denmark. Levels of genetic variation in extant populations were estimated using six variable number tandem repeat loci and were found to be low compared to other butterfly species with low migration rates. An analysis of genetic structure, based on both allele frequencies and genotype distributions, divided the entire sample into four distinct clusters. This was partially concordant with the a priori subdivision based on collection areas. An overall F_ST value of 0.16 (pairwise values ranging from 0.087–0.276) indicated restrictions of gene flow. Especially two populations had higher F_ST values than the others, suggesting their isolation, and showed signs of bottlenecks/founder events. One population deviated significantly from Hardy–Weinberg equilibrium, suggesting a possible Wahlund effect or the presence of null alleles. The results suggest habitat fragmentation, resulting in genetic drift and possibly inbreeding. Future management is therefore recommended to increase gene flow between the remaining populations while habitats are restored in order to increase carrying capacity. © 2008 The Linnean Society of London, Biological Journal of the Linnean Society, 2008, 95 , 677–687.     

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.     

River fragmentation increases localized population genetic structure and enhances asymmetry of dispersal in bullhead (Cottus gobio)

Man-made habitat fragmentation is a major concern in river ecology and is expected to have particularly detrimental effects on aquatic species with limited dispersal abilities, like the bullhead (Cottus gobio). We used ten microsatellite markers to investigate small-scale patterns of gene flow, current dispersal and neutral genetic diversity in a morphologically diverse river where fragmented and unfragmented sections could be compared. We found high genetic differentiation between sampling sites with a maximum F _ST of 0.32 between sites separated by only 35 km. A significant increase of genetic differentiation with geographical distance was observed in the continuous river section as well as in the full dataset which included headwater populations isolated by anthropogenic barriers. Several lines of evidence are consistent with the hypothesis that such barriers completely block upstream movement while downstream dispersal may be little affected. In the unfragmented habitat, dispersal rates were also higher in the direction of water flow than against it. The resulting asymmetry in gene flow likely contributes to the decrease of genetic variation observed from the lower reaches towards the headwaters, which is particularly pronounced in physically isolated populations. Our findings suggest that headwater populations, due to their isolation and low genetic variation, may be particularly vulnerable to extinction.     

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.     

Phylogeography and genetic effects of habitat fragmentation on endangered Taxus yunnanensis in southwest China as revealed by microsatellite data

It is not known how the profoundly complex topography and habitat heterogeneity generated by the uplift of the Qinghai‐Tibetan Plateau (QTP) during the late Tertiary affected population genetic structure of endangered Taxus yunnanensis. In addition, the effects of habitat fragmentation due to anthropogenic disturbance on genetic diversity and population differentiation of this species have not been studied. T. yunnanensis is an ancient tree/shrub mainly distributed in southwest China. Recently, the species has suffered a sharp decline due to excessive logging for its famous anticancer metabolite taxol, resulting in smaller and more isolated populations. To understand the phylogeography and genetic consequences of habitat fragmentation of this endangered species, using 11 polymorphic microsatellites, we genotyped 288 individuals from 14 populations from a range‐wide sampling in China. Our results suggest that two different population groups that were once isolated have persisted in situ during glacial periods in both areas, and have not merged since. Habitat fragmentation has led to significant genetic bottlenecks, high inbreeding and population divergence in this species. The two different population groups of T. yunnanensis could be attributed to restricted gene flow caused through isolation by geographical barriers and by habitat heterogeneity during uplift of the QTP, or the existence of two separate glacial refugia during the Pleistocene. In situ and ex situ conservation of the two Evolutionarily Significant Units (ESUs), artificial gene flow between populations and a comprehensive understanding of the pollination system in this endangered species are suggested from this study.     

Diversity and genetic connectivity among populations of a threatened tree (<Emphasis Type="Italic">Dalbergia nigra</Emphasis>) in a recently fragmented landscape of the Brazilian Atlantic Forest

In this study we evaluated the influence of recent landscape fragmentation on the dynamics of remnant fragments from the Brazilian Atlantic Forest. This biome is one of the richest in the world and has been extensively deforested and fragmented. We sampled five populations of the threatened Dalbergia nigra, a tree endemic to the Brazilian Atlantic Forest, two located in a large reserve of continuous forest and three in fragments of different sizes and levels of disturbance. In order to assess historical changes, considering the longevity of the analyzed species, 119 adults and 116 saplings were genotyped for six microsatellite loci. Lower levels of genetic diversity were found in the most impacted fragments when compared to the most preserved population located inside the reserve, and there was significant genetic structure among the populations studied (pairwise F _ST = 0.031–0.152; pairwise D _EST = 0.039–0.301). However, genetic structure among saplings (F _ST = 0.056; D _EST = 0.231) was significantly lower than among adults (F _ST = 0.088; D _EST = 0.275). Estimates of contemporary gene flow based on assignment tests corroborated this result, suggesting that fragmentation led to an increase in gene flow. This connectivity among remnant fragments could mitigate the loss of genetic diversity through a metapopulation dynamic, but the high rate of habitat loss and the unknown long-term genetic effects add uncertainty. These results, taken together with the presence of private alleles in disturbed populations, highlight the importance of preserving the extant fragments.     

Spatial genetic structure of an endangered orchid <Emphasis Type="Italic">Cypripedium calceolus</Emphasis> (Orchidaceae) at a regional scale: limited gene flow in a fragmented landscape

Plant species that are capable of propagating clonally are expected to be less vulnerable to habitat fragmentation due to their long life span. Cypripedium calceolus L. is a rare, clonal, long-lived orchid species. It has suffered marked decline because of habitat loss and fragmentation and over-collection, yet an IUCN report on this species does not regard fragmentation as a major threat to the species. We applied 13 nuclear microsatellites and cpDNA sequences to identify the patterns of population structure, genetic diversity and connectivity of six remnant local populations of C. calceolus in highly fragmented Gdańsk Pomerania region (N Poland). Despite severe (80%) loss of localities in the studied area we found that the local populations retain high levels of clonal (R 0.86–1) and genetic diversity (H_e = 0.572). However, their differentiation is relatively high (F_ST = 0.132 for nuclear SSR and F_ST = 0.363 for cpDNA) despite close geographic proximity (0.6–57 km). Bayesian clustering classified populations according to their geographic origin with little admixture. Low genetic connectivity between the remnant populations shows that the current gene flow is too low to serve as a cohesive force in a fragmented habitat, which may impede a quick response to environmental change. The species’ ability to retain ancestral variation may help withstand fragmentation, but in the light of observed extirpation rate it should be rather considered as a factor that only delays local populations’ extinction. This leads to the conclusion that habitat loss and fragmentation should be regarded as a real threat to stability of C. calcelolus populations.