Genetic structure of the northwestern Russian wolf populations and gene flow between Russia and Finland

We examined the genetic diversity and structure of wolf populations in northwestern Russia. Populations in Republic of Karelia and Arkhangelsk Oblast were sampled during 1995–2000, and 43 individuals were genotyped with 10 microsatellite markers. Moreover, 118 previously genotyped wolves from the neighbouring Finnish population were used as a reference population. A relatively large amount of genetic variation was found in the Russian populations, and the Karelian wolf population tended to be slightly more polymorphic than the Arkhangelsk population. We found significant inbreeding (F = 0.094) in the Karelian, but not in the Arkhangelsk population. The effective size estimates of the Karelian wolf population based on the approximate Bayesian computation and linkage disequilibrium methods were 39.9 and 46.7 individuals, respectively. AMOVA-analysis and exact test of population differentiation suggested clear differentiation between the Karelian, Arkhangelsk and Finnish wolf populations. Indirect estimates of gene flow based on the level of population differentiation (ϕ _ST  = 0.152) and frequency of private alleles (0.029) both suggested a low level of gene flow between the populations (Nm = 1.4 and Nm = 3.7, respectively). Assignment analysis of Karelian and Finnish populations suggested an even lower number of recent migrants (less than 0.03) between populations, with a larger amount of migration from Finland to Karelia than vice versa. Our findings emphasise the role of physical obstacles and territorial behaviour in creating barriers to gene flow between populations in relatively limited geographical areas, even in large-bodied mammalian species with long-distance dispersal capabilities and an apparently continuous population structure.     

Genetic diversity and population differentiation in the endangered Siberian flying squirrel (<Emphasis Type="Italic">Pteromys volans</Emphasis>) in a fragmented landscape

Siberian flying squirrel (Pteromys volans) has declined in Finland and it is considered an endangered species. We studied microsatellite variation in four flying squirrel populations in a fragmented landscape in Finland to determine the amount of gene flow and genetic diversity in the populations. Demographic data from these areas suggest that the populations are declining. All the populations are significantly differentiated (F _ST = 0.23). The most notable result is the high degree of differentiation between two adjacent populations (F _ST = 0.11) and low genetic variability (number of alleles 3.0) in one of the populations. These findings suggest problems in dispersal and possible fragmentation effects in the landscape where only 10–20% of habitat favorable for the flying squirrel is left. Conservation ensuring dispersal should be urgently considered. Future studies should concentrate on the modeling of the population viability and on the effects of inbreeding in these small populations. Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

Phylogeography of Chinese cherry (Prunus pseudocerasus Lindl.) inferred from chloroplast and nuclear DNA: insights into evolutionary patterns and demographic history

Chinese cherry (Prunus pseudocerasus Lindl.) is a commercially valuable fruit crop in China. In order to obtain new insights into its evolutionary history and provide valuable recommendations for resource conservation, phylogeographic patterns of 26 natural populations (305 total individuals) from six geographic regions were analyzed using chloroplast and nuclear DNA fragments. Low levels of haplotype and nucleotide diversity were found in these populations, especially in landrace populations. It is likely that a combined effect of botanical characteristics impact the effective population size, such as inbreeding mating system, long life span, as well as vegetative reproduction. In addition, strong bottleneck effect caused by domestication, together with founder effect after dispersal and subsequent demographic expansion, might also accelerate the reduction of the genetic variation in landrace populations. Interestingly, populations from Longmen Mountain (LMM) and Daliangshan Mountain (DLSM) exhibited relatively higher levels of genetic diversity, inferring the two historical genetic diversity centers of the species. Moreover, moderate population subdivision was also detected by both chloroplast DNA (G_ST = 0.215; N_ST = 0.256) and nuclear DNA (G_ST = 0.146; N_ST = 0.342), respectively. We inferred that the episodes of efficient gene flow through seed dispersal, together with features of long generation cycle and inbreeding mating system, were likely the main contributors causing the observed phylogeographic patterns. Finally, factors that led to the present demographic patterns of populations from these regions and taxonomic varieties were also discussed.     

Drift happens: Molecular genetic diversity and differentiation among populations of jewelweed (Impatiens capensis Meerb.) reflect fragmentation of floodplain forests

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 F_ST = 0.32, F_ST’ = 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 (F_IS = 0.2–0.9) and F_IS 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.     

Limited genetic structure and evidence for dispersal among populations of the endangered Florida grasshopper sparrow, Ammodramus savannarum floridanus

The Florida grasshopper sparrow, Ammodramus savannarum floridanus, is a non-migratory, endangered subspecies endemic to the prairie region of south-central Florida. It has experienced significant population declines and is currently restricted to five locations. We found substantial levels of variation in microsatellites and mtDNA control region sequences, estimates of inbreeding genetic effective population sizes that were much larger than the estimated census size, and no evidence of inbreeding within five sampled populations (n = 105). We also found a lack of genetic structure among populations (F _ST = 0.0123 for microsatellites and θ = 0.008 for mtDNA), and evidence for dispersal between populations, with 7.6% of all individuals identified as immigrants to their population of capture. We suggest that the subspecies be managed as a single management unit on a regional scale rather than as multiple management units on a local subpopulation scale. There is still a limited opportunity to preserve much of the present genetic variation in this subspecies, if immediate measures are taken to reverse the current population decline before this variation is reduced by genetic drift.     

POPULATION STRUCTURE AND LEVELS OF GENE FLOW IN THE MEDITERRANEAN LAND SNAIL ALBINARIA CORRUGATA (PULMONATA: CLAUSILIIDAE)

The amount of gene flow among local populations partly determines the relative importance of genetic drift and natural selection in the differentiation of such populations. Land snails, because of their limited powers for dispersal, may be particularly likely to show such differentiation. In this study, we directly estimate gene flow in Albinaria corrugata, a sedentary, rock-dwelling gastropod from Crete, by mark-recapture studies. In the same area, 23 samples were taken and studied electrophoretically for six polymorphic enzyme loci. The field studies indicate that the population structure corresponds closely to the stepping-stone model: demes are present on limestone boulders that are a few meters apart, and dispersal takes place mainly between adjacent demes. Average deme size (N) is estimated at 29 breeding individuals and the proportion of migrants per generation at 0.195 (Nm = 5.7). We find no reason to assume long-distance dispersal, apart from dispersal along occasional stretches of suitable habitat. Genetic subdivision of the population, as derived from F_ST values, corresponds to the direct estimate only at the lowest spatial level (distance between sample sites < 10 m), where values for Nm of 5.4 and 17.6 were obtained. In contrast, at the larger spatial scales, F_ST values give gene-flow estimates that are incompatible with the expected amount of gene flow at these scales. We explain these discrepancies by arguing that gene flow is in fact extremely limited, making correct estimates of Nm from F_ST impossible at the larger spatial scales. In view of these low levels of gene flow, it is concluded that both genetic drift and natural selection may play important roles in the genetic differentiation of this species, even at the lowest spatial scales.     

Genetic Diversity and Population Structure of Sitodiplosis mosellana in Northern China

The wheat midge, Sitodiplosis mosellana, is an important pest in Northern China. We tested the hypothesis that the population structure of this species arises during a range expansion over the past 30 years. This study used microsatellite and mitochondrial loci to conduct population genetic analysis of S. mosellana across its distribution range in China. We found strong genetic structure among the 16 studied populations, including two genetically distinct groups (the eastern and western groups), broadly consistent with the geography and habitat fragmentation. These results underline the importance of natural barriers in impeding dispersal and gene flow of S. mosellana populations. Low to moderate genetic diversity among the populations and moderate genetic differentiation (F _ST = 0.117) between the two groups were also found. The populations in the western group had lower genetic diversity, higher genetic differentiation and lower gene flow (F _ST = 0.116, Nm = 1.89) than those in the eastern group (F _ST = 0.049, Nm = 4.91). Genetic distance between populations was positively and significantly correlated with geographic distance (r = 0.56, P<0.001). The population history of this species provided no evidence for population expansion or bottlenecks in any of these populations. Our data suggest that the distribution of genetic diversity, genetic differentiation and population structure of S. mosellana have resulted from a historical event, reflecting its adaptation to diverse habitats and forming two different gene pools. These results may be the outcome of a combination of restricted gene flow due to geographical and environmental factors, population history, random processes of genetic drift and individual dispersal patterns. Given the current risk status of this species in China, this study can offer useful information for forecasting outbreaks and designing effective pest management programs.     

Genetic Diversity and Population Structure of Alnus hirsuta (Betulaceae) in Korea

Alnus hirsuta in Korea was measured to estimate the amount and pattern of genetic diversity and population structure. The mean genetic diversity within populations was 0.166. Korean alder populations have slightly high levels of genetic diversity compared to those of two Canadian alder species. The genetic differentiation among populations accounted for 9% of the total variation. The rate of gene flow was estimated high (Nm=2.63). Analysis of inbreeding coefficient, calculated for all polymorphic loci in each population, showed a substantial heterozygote deficiency relative to Hardy-Weinberg expectations. The mean G _ST value of A. hirsuta in Korea was 0.087. The low value of G _ST in this species, reflecting little spatial genetic differentiation, may indicate extensive gene flow. A relationship between the mean heterozygosity and annual rainfall showed a positive relationship (r ²=0.54, F=4.67). Received 8 August 1998/ Accepted in revised form 7 July 1999     

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.     

Genetic discontinuity among regional populations of <Emphasis Type="Italic">Lophelia pertusa</Emphasis> in the North Atlantic Ocean

Knowledge of the degree to which populations are connected through larval dispersal is imperative to effective management, yet little is known about larval dispersal ability or population connectivity in Lophelia pertusa, the dominant framework-forming coral on the continental slope in the North Atlantic Ocean. Using nine microsatellite DNA markers, we assessed the spatial scale and pattern of genetic connectivity across a large portion of the range of L. pertusa in the North Atlantic Ocean. A Bayesian modeling approach found four distinct genetic groupings corresponding to ocean regions: Gulf of Mexico, coastal southeastern U.S., New England Seamounts, and eastern North Atlantic Ocean. An isolation-by-distance pattern was supported across the study area. Estimates of pairwise population differentiation were greatest with the deepest populations, the New England Seamounts (average F _ST = 0.156). Differentiation was intermediate with the eastern North Atlantic populations (F _ST = 0.085), and smallest between southeastern U.S. and Gulf of Mexico populations (F _ST = 0.019), with evidence of admixture off the southeastern Florida peninsula. Connectivity across larger geographic distances within regions suggests that some larvae are broadly dispersed. Heterozygote deficiencies were detected within the majority of localities suggesting deviation from random mating. Gene flow between ocean regions appears restricted, thus, the most effective management scheme for L. pertusa involves regional reserve networks.     

Genetic structure of refugial populations of the temperate plant Shortia rotundifolia (Diapensiaceae) on a subtropical island

Continental island systems harbour relict biota and populations that might have migrated during glacial periods due to the formation of landbridges. Here we analysed the genetic structure of relict populations of the temperate plant Shortia rotundifolia on the subtropical island of Iriomotejima, Japan. This plant, which inhabits riparian environments, is designated “near threatened”. Only five extant populations have been found on the island. Our analyses of 10 nuclear microsatellite loci detected genetic diversity of H _E = 0.488 and H _O = 0.358 for all populations of S. rotundifolia on the island. A high inbreeding coefficient for all populations together (F _IS = 0.316) and each population separately (F _IS = 0.258–0.497) might be attributable to crossing among closely related descendants within a population, an idea that is supported by the relatedness coefficient. These results and an examination of the populations’ demographic histories suggest that the extant populations on Iriomotejima have not experienced a recent population bottleneck. The five extant populations were genetically differentiated (F _ST = 0.283; P < 0.001), suggesting low seed dispersal by gravity and/or low pollen flow via pollinators in the riparian environment. In addition, population differentiation was not related to genetic distance, implying that at one time, ancestral populations might have been distributed over a wider area of the island. However, population fragmentation and range contraction might have occurred at random during the postglacial period.     

Genetic variation and plant performance in fragmented populations of globeflowers (Trolliuseuropaeus) within agricultural landscapes

The management of remnant populations in highly fragmented landscapes requires a thorough understanding of the processes shaping population persistence. We investigated relationships between population characteristics (i.e. size, density and pollinator abundance), offspring performance, genetic diversity and differentiation in Trollius europaeus, a plant with a nursery pollination system. In 19 populations of different sizes and located in north-east Switzerland, an area which has undergone widespread land use changes over the last decades, we assessed neutral genetic diversity (N _total = 383) using AFLPs and plant performance in a greenhouse experiment (N _total = 584) using competition and control treatments. Overall genetic differentiation was low (F _ST = 0.033) with a marginal significant isolation by distance effect (P = 0.06) indicating (historical) genetic connectivity among the populations. Mean expected heterozygosity was H _E of 0.309 (0.0257–0.393) while inbreeding coefficients (F _IS) were significant in only three populations. Genetic diversity was not related to population size, plant density or pollinator abundance. Plant performance was reduced under competition (P < 0.001) but the severity of competition was independent of genetic diversity and population size. In summary, remnant populations of T. europaeus retain genetic diversity and seem capable of persisting under the present conditions within an agricultural matrix. T. europaeus is a perennial herb, thus it may require several generations for the negative effects of fragmentation and isolation to manifest. Our findings indicate that small populations are as important as large populations for the conservation and management of genetic resources.     

Human disturbance reduces genetic diversity of an endangered tropical tree, <Emphasis Type="Italic">Prunus africana</Emphasis> (Rosaceae)

Human activities such as fragmentation and selective logging of forests can threaten population viability by modification of ecological and genetic processes. Using six microsatellite markers, we examined the effects of forest fragmentation and local disturbance on the genetic diversity and structure of adult trees (N = 110) and seedlings (N = 110) of Prunus africana in Kakamega Forest, western Kenya. Taking samples of adults and seedlings allowed for study of changes in genetic diversity and structure between generations. Thereby, adults reflect the pattern before and seedlings after intensive human impact. Overall, we found 105 different alleles in the six loci examined, 97 in adults and 88 in seedlings. Allelic richness and heterozygosity were significantly lower in seedlings than in adults. Inbreeding increased from adult tree to seedling populations. Genetic differentiation of adult trees was low (overall F _ST = 0.032), reflecting large population sizes and extensive gene flow in the past. Genetic differentiation of seedlings was slightly higher (overall F _ST = 0.044) with all of the 28 pairwise F _ST-values being significantly different from zero. These results suggest that human disturbance in Kakamega Forest has significantly reduced allelic richness and heterozygosity, increased inbreeding and slightly reduced gene flow in P. africana in the past 80–100 years.     

Spatial genetic structure and restricted gene flow in a functionally dioecious fig, <Emphasis Type="Italic">Ficus pumila</Emphasis> L. var. <Emphasis Type="Italic">pumila</Emphasis> (Moraceae)

The mutualism between fig plants and fig wasps has been recognized as one of the most specialized systems of symbiosis. Figs are pollinated by their highly specific pollinating fig wasps, and the pollinating fig wasps are raised within the syconia of figs. Recent studies indicated a difference between monoecious and dioecious figs in the dispersal range of pollinating wasps, which has potential consequences for gene flow. In this study, we detected the gene-flow pattern of the dioecious climbing fig, Ficus pumila L. var. pumila, at both local and regional scales. At the local scale, spatial autocorrelation analysis indicated strong genetic structure at short distances, a pattern of limited gene flow. This result was also supported by a high inbreeding coefficient (F _IS = 0.287) and significant substructuring (F _ST = 0.060; P < 0.001). Further analysis indicated that the effective gene dispersal range was 1,211 m, and the relative contribution of seed dispersal was smaller than that of pollen dispersal. The inferred effective range of pollen dispersal ranged from 989 to 1,712 m, while the effective seed dispersal range was less than 989 m. Lack of long-distance dispersal agents may explain the limited seed dispersal. The high density of receptive fig trees was the most likely explanation for limited pollen dispersal, and the position of syconia and relatively low wind speed beneath the canopy may contribute to this phenomenon. At the regional scale, significant negative correlations (kinship coefficient F _ij ranging from −0.038 to −0.071) existed in all comparisons between the studied population and other populations, and the assignment test grouped almost all individuals of the studied population into a distinct cluster. Asynchronous flowering on the regional scale, which provides a barrier for the pollinating wasps to fly from the studied population to the other populations, is probably responsible for the limited gene flow on the regional scale.     

Conservation genetics of the annual hemiparasitic plant <Emphasis Type="Italic">Melampyrum sylvaticum</Emphasis> (Orobanchaceae) in the UK and Scandinavia

Melampyrum sylvaticum is an endangered annual hemiparasitic plant that is found in only 19 small and isolated populations in the United Kingdom (UK). To evaluate the genetic consequences of this patchy distribution we compared levels of diversity, inbreeding and differentiation from ten populations from the UK with eight relatively large populations from Sweden and Norway where the species is more continuously distributed. We demonstrate that in both the UK and Scandinavia, the species is highly inbreeding (global F _IS = 0.899). Levels of population differentiation were high (F’_ST = 0.892) and significantly higher amongst UK populations (F’_ST = 0.949) than Scandinavian populations (F’_ST = 0.762; P < 0.01). The isolated populations in the UK have, on average, lower genetic diversity (allelic richness, proportion of loci that are polymorphic, gene diversity) than Scandinavian populations, and this diversity difference is associated with the smaller census size and population area of UK populations. From a conservation perspective, the naturally inbreeding nature of the species may buffer the species against immediate effects of inbreeding depression, but the markedly lower levels of genetic diversity in UK populations may represent a genetic constraint to evolutionary change. In addition, the high levels of population differentiation suggest that gene flow among populations will not be effective at replenishing lost variation. We thus recommend supporting in situ conservation management with ex situ populations and human-mediated seed dispersal among selected populations in the UK.     

Genetic structure of Brandt’s vole (<Emphasis Type="Italic">Lasiopodomys brandtii</Emphasis>) populations in Inner Mongolia,China, based on microsatellite analysis

Brandt’s vole (Lasiopodomys brandtii) distribution is discontinuous in Inner Mongolia with some populations isolated from others. Recently, some isolated populations have suffered extinction, and the factors responsible remain elusive. Genetic drift is one of the processes affecting population genetic differentiation, and can play a substantial role in the divergence of small, isolated populations. Using seven microsatellite markers, we genotyped four geographically isolated populations of Brandt’s vole, all of which exhibit episodic fluctuations in population density. The results showed a strong genetic differentiation among the geographically distinct populations (total F _ST = 0.124) and in particular, one population (Zhengxiangbaiqi) was isolated from all others (F _ST values were greatest between Zhengxiangbaiqi and other populations). Furthermore, high levels of inbreeding (F _IS values ranged from 0.205 to 0.290) within each distinct population suggest that inbreeding has and is likely occurring in Brandt’s vole populations. These processes can decrease average individual fitness and consequently increase the risk of extinction of the species.     

Using genetic evaluation to guide conservation of remnant Juniperus communis (Cupressaceae) populations

• Many critically endangered plant species exist in small, genetically depauperate or inbred populations, making assisted gene flow interventions necessary for long‐term population viability. However, before such interventions are implemented, conservation practitioners must consider the genetic and demographic status of extant populations, which are strongly affected by species’ life‐history traits. In northwestern Europe, Juniperus communis, a dioecious, wind‐pollinated and bird‐dispersed gymnosperm, has been declining for the past century and largely exists in small, isolated and senescent populations.
• To provide useful recommendations for a recovery plan involving translocation of plants, we investigated genetic diversity and structure of populations in Belgium using four microsatellite and five plastid single‐nucleotide polymorphism (SNP) markers.
• We detected no clonality in the populations, suggesting predominantly sexual reproduction. Populations exhibited high genetic diversity (H_e = 0.367–0.563) and low to moderate genetic differentiation (F_ST ≤ 0.133), with no clear geographic structure. Highly positive inbreeding coefficients (F_IS = 0.221–0.507) were explained by null alleles, population substructuring and biparental inbreeding. No isolation by distance was observed among distant populations, but isolation at close geographic proximity was found. Patterns were consistent with high historical gene flow through pollen and seed dispersal at both short and long distances. We also tested four pre‐germination treatments among populations to improve germination rates; however, germination rates remained low and only cold‐stratification treatments induced germination in some populations.
• To bolster population regeneration, introductions of cuttings from several source populations are recommended, in combination with in situ management practices that improve seedling survival and with ex situ propagation.

     

Genetic diversity of the black mangrove (Avicennia germinans L.) in Colombia

This study analyzed the genetic diversity and patterns of genetic structure in Colombian populations of Avicennia germinans L. using microsatellite loci. A lower genetic diversity was found on both the Caribbean (Ho = 0.439) and the Pacific coasts (Ho = 0.277) than reported for the same species in other locations of Central American Pacific, suggesting the deterioration of genetic diversity. All the populations showed high inbreeding coefficients (0.131–0.462) indicating heterozygotes deficience. The genetic structure between the Colombian coasts separated by Central American Isthmus was high (F_RT = 0.39) and the analyses of the genetic patterns of A. germinans revealed a clear differentiation of populations and no-recent gene flow evidence between coasts. Genetic structure was found within each coast (F_ST = 0.10 for the Caribbean coast and F_ST = 0.22 for the Pacific coast). The genetic patterns along the two coasts appear to reflect a forcing by local geomorphology and marine currents. Both coasts constitute a different Evolutionary Significant Unit, so we suggest for future transplantations plans that propagules or saplings of the populations of the Caribbean coast should not be mixed with those of the Pacific Colombian coast. Besides, we suggest that reforestation efforts should carefully distinguish propagules sources within each coast.     

Detecting a hierarchical genetic population structure: the case study of the Fire Salamander (Salamandra salamandra) in Northern Italy

The multistep method here applied in studying the genetic structure of a low dispersal and philopatric species, such as the Fire Salamander Salamandra salamandra, was proved to be effective in identifying the hierarchical structure of populations living in broad‐leaved forest ecosystems in Northern Italy. In this study, 477 salamander larvae, collected in 28 sampling populations (SPs) in the Prealpine and in the foothill areas of Northern Italy, were genotyped at 16 specie‐specific microsatellites. SPs showed a significant overall genetic variation (Global F_ST = 0.032, P < 0.001). The genetic population structure was assessed by using STRUCTURE 2.3.4. We found two main genetic groups, one represented by SPs inhabiting the Prealpine belt, which maintain connections with those of the Eastern foothill lowland (PEF), and a second group with the SPs of the Western foothill lowland (WF). The two groups were significantly distinct with a Global F_ST of 0.010 (P < 0.001). While the first group showed a moderate structure, with only one divergent SP (Global F_ST = 0.006, P < 0.001), the second group proved more structured being divided in four clusters (Global F_ST = 0.017, P = 0.058). This genetic population structure should be due to the large conurbations and main roads that separate the WF group from the Prealpine belt and the Eastern foothill lowland. The adopted methods allowed the analysis of the genetic population structure of Fire Salamander from wide to local scale, identifying different degrees of genetic divergence of their populations derived from forest fragmentation induced by urban and infrastructure sprawl.     

Inferring demographic processes from the genetic structure of a metapopulation of <Emphasis Type="Italic">Boltonia decurrens</Emphasis>(Asteraceae)

Boltonia decurrens(Asteraceae), a federally listed, threatened floodplain species, requires regular flooding for suitable habitat and seed dispersal. Flood suppression and habitat destruction have resulted in fewer than 25 populations remaining throughout its 400 km range. Because individual populations are widely interspaced (>10 km) and subject to frequent extinction and colonization, seed dispersal along the river, not pollen flow, is likely the primary determinant of population genetic structure. We used neutral genetic markers (isozymes) assayed for fourteen populations to determine which demographic processes contribute to the genetic structure of B. decurrens. Significant genetic differentiation was detected among populations (F _ST=0.098, P< 0.05) but not among regions (F _RT=0.013, P> 0.05), suggesting that long-distance dispersal events occur and involve seed from a small number of populations. Correspondingly, we found no evidence of isolation by distance, and admixture analyses indicate that colonization events involve seed from 3 to 5 source populations. Individual populations exhibited high levels of fixation (mean F _IS=0.192, P< 0.05), yet mean population outcrossing rates were high (t _m=0.87–0.95) and spatial autocorrelation analyses revealed no fine-scale within population structure, indicating that inbreeding alone cannot explain the observed fixation. Rather, genetic bottlenecks, detected for 12 of 14 populations, and admixture at population founding may be important sources of fixation. These observations are consistent with a metapopulation model and confirm the importance of regular flooding events, capable of producing suitable habitat and dispersing seed long distances, to the long-term persistence of B. decurrens.