Polyploid origin,genetic diversity and population structure in the tetraploid sea lavender <Emphasis Type="Italic">Limonium narbonense</Emphasis> Miller (Plumbaginaceae) from eastern Spain

Limonium narbonense Miller is a fertile tetraploid species with a sporophytic self-incompatibility system. This sea lavender is found in coastal salt marshes which have been under intense human pressure during the past decades resulting in significant habitat fragmentation. Eleven microsatellite loci specifically designed for this species were amplified in 135 individuals from five populations. These markers were used to investigate the polyploid nature, the levels of genetic diversity and population structure in this species. L. narbonense showed high levels of genetic diversity (A = 7.82, P = 100% H _T = 0.446), consistent with its likely autotetraploid origin revealed in this study and obligate outcrossing breeding system. Inbreeding (F _IS) values were low in the three southern populations (mean F _IS = 0.062), and higher in the northern populations (mean F _IS = 0.184). Bayesian analysis of population structure revealed that populations could be grouped into two genetic clusters, one including three southern populations and the other the two northernmost ones. Individuals from the two northernmost populations showed higher admixture of the two genetic clusters than individuals from the three southern ones. A thorough analysis of microsatellite electrophoretic patterns suggests an autotetraploid origin for L. narbonense. The genetic structure revealed in this study is attributed to a recent migration from the southern area. This result suggests a net gene flow from the south to the north, likely facilitated by migratory movements of birds visiting the temporary flooded ponds occupied by L. narbonense.     

Genetic divergence in nuclear genomes between populations of <Emphasis Type="Italic">Fagus crenata</Emphasis> along the Japan Sea and Pacific sides of Japan

Genetic diversity and structure in Fagus crenata were studied by analyzing 14 nuclear microsatellite loci in 23 populations distributed throughout the species’ range. Although population differentiation was very low (F _ST = 0.027; R _ST = 0.041), both neighbor-joining tree and Bayesian clustering analyses provided clear evidence of genetic divergence between populations along the Japan Sea (Japan Sea lineage) and Pacific (Pacific lineage) sides of Japan, indicating that physical barriers to migration and gene flow, notably the mountain ranges separating the populations along the Japan Sea and Pacific sides, have promoted genetic divergence between these populations. The two lineages of the nuclear genome are generally consistent with those of the chloroplast genome detected in a previous study, with several discrepancies between the two genomes. Within-population genetic diversity was generally very high (average H _E = 0.839), but decreased in a clinal fashion from southwest to northeast, largely among populations of the Japan Sea lineage. This geographical gradient may have resulted from the late-glacial and postglacial recolonization to the northeast, which led to a loss of within-population genetic diversity due to cumulative founder effects.     

Host-associated genetic differentiation in rice grasshopper, Oxya japonica, on wild vs. cultivated rice

Rice grasshopper, Oxya japonica, is one of the most important pests in south China, mainly inhabiting fields of wild rice (Oryza rufipogon) and cultivated rice (Oryza sativa). In this study, we used AFLP marker to investigate the genetic diversity and population structure of rice grasshoppers collected from south China, with emphasis on testing the hypothesis that there was significant genetic differentiation among grasshopper populations associated with different hosts (i.e. wild vs. cultivated rice). Seven populations consisting of 104 individuals were sampled from Hainan Island and the mainland of south China. Eight primer combinations produced 564 reliable bands, of which 563 were polymorphic. O. japonica showed considerable genetic variation at population level, with gene diversity (H_E) ranging from 0.1103 to 0.2035. Genetic diversity were studied on seven populations, and generally three populations from wild rice had higher levels of genetic diversity (H_E = 0.1635) than the other four populations feeding on cultivated rice (H_E = 0.1327). We observed high population differentiation, with F_st ranging from 0.4172 to 0.7652 among the seven populations. However, Mantel test detected no significant correlation between genetic distance and geographical distance (r = 0.3541; p = 0.0689). By contrast, we found significant genetic differentiation between groups collected from different hosts. These data suggested that the anthropogenic activity in cultivated rice fields (i.e. pesticides, fertilization and cultivation) could have played an important role in shaping the genetic structure of O. japonica.     

Population structure and genetic diversity distribution in wild and cultivated populations of the traditional Chinese medicinal plant Magnolia officinalis subsp. biloba (Magnoliaceae)

Magnolia officinalis subsp. biloba, a traditional Chinese medicinal plant, experienced severe declines in the number of populations and the number of individuals in the late 20th century due to the widespread harvest of the subspecies. A large-scale cultivation program was initiated and cultivated populations rapidly recovered the loss in individual plant numbers, but wild populations remained small as a consequence of cutting. In this study, the levels of genetic variation and genetic structure of seven wild populations and five domestic populations of M. officinalis subsp. biloba were estimated employing an AFLP methodology. The plant exhibited a relatively high level of intra-population genetic diversity (h = 0.208 and H _j = 0.268). The cultivated populations maintained approximately 95% of the variation exhibited in wild populations, indicating a slight genetic bottleneck in the cultivated populations. The analysis of genetic differentiation revealed that most of the AFLP diversity resided within populations both for the wild group (78.22%) and the cultivated group (85.92%). Genetic differentiation among populations in the wild group was significant (F _ST = 0.1092, P < 0.005), suggesting wild population level genetic structure. Principal coordinates analysis (PCO) did not discern among wild and cultivated populations, indicating that alleles from the wild population were maintained in the cultivated gene pool. Results from the present study provide important baseline data for effectively conserving the genetic resources of this medicinal subspecies.     

High genetic diversity with low connectivity among Mauritia flexuosa (Arecaceae) stands from Ecuadorean Amazonia

Mauritia flexuosa dominated palm swamps are an important forest resource covering over 30,000 km² across the Amazon basin. In Ecuadorean Amazonia, Mauritia flexuosa, a dioecious and arborescent palm species, forms small and isolated populations or large and dense stands on poorly drained soils. How these populations are genetically interconnected and how genetic diversity varies between cohorts of different ages remains little studied although they are important for conservation of these ecosystems. The genetic structure of Mauritia flexuosa was studied in five natural stands using eight microsatellite loci and two cohorts (seedling and adults). In addition, age structure and sex ratio within the stands were assessed using transects. The age structure of the studied Mauritia flexuosa stands is represented by a high number of seedlings (mean = 1,153.6/ha) and adults (mean = 563.2/ha), with a sex ratio favoring female individuals (1.42:1). These stands are also characterized by a fine‐scale genetic structure, high observed heterozygosity (mean: H_{O seedlings}=0.52; H_{O adults}=0.52), high inbreeding (mean: F_{IS seedlings} = 0.26; F_{IS adults} = 0.26), low number of migrants (N_m=0.29), strong genetic differentiation (mean: pairwise R_ST/ D‐values _seedlings = 0.08/ 0.74; mean R_ST/D‐values _adults = 0.17/ 0.76), and an average effective population size (N_e) of 191.42 individuals. No intergenerational genetic variation was detected between seedlings and adults. We suggest that the high genetic diversity and inbreeding as well as the strong differentiation among stands of these populations could be explained, at least partially, by a low genetic connectivity among populations. Destructive harvesting of its fruits and defaunation will be major threats to Mauritia flexuosa populations in the future. Abstract in Spanish is available with online material     

Genetic diversity in fragmented populations of the critically endangered spider orchid Caladenia huegelii: implications for conservation

The Orchidaceae is characterised by a diverse range of life histories, reproductive strategies and geographic distribution, reflected in a variety of patterns in the population genetic structure of different species. In this study, the genetic diversity and structure was assessed within and among remnant populations of the critically endangered sexually deceptive orchid, Caladenia huegelii. This species has experienced severe recent habitat loss in a landscape marked by ancient patterns of population fragmentation within the Southwest Australian Floristic Region, a global biodiversity hotspot. Using seven polymorphic microsatellite loci, high levels of within-population diversity (mean alleles/locus = 6.73; mean H _E = 0.690), weak genetic structuring among 13 remnant populations (F _ST = 0.047) and a consistent deficit of heterozygotes from Hardy–Weinberg expectation were found across all populations (mean F _IS = 0.22). Positive inbreeding coefficients are most likely due to Wahlund effects and/or inbreeding effects from highly correlated paternity and typically low fruit set. Indirect estimates of gene flow (Nm = 5.09 using F _ST; Nm = 3.12 using the private alleles method) among populations reflects a historical capacity for gene flow through long distance pollen dispersal by sexually deceived wasp pollinators and/or long range dispersal of dust-like orchid seed. However, current levels of gene flow may be impacted by habitat destruction, fragmentation and reduced population size. A genetically divergent population was identified, which should be a high priority for conservation managers. Very weak genetic differentiation indicates that the movement and mixing of seeds from different populations for reintroduction programs should result in minimal negative genetic effects.     

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.     

Conservation genetics of Butte County meadowfoam (Limnanthes floccosa ssp. californica Arroyo), an endangered vernal pool endemic

The endangered annual plant Limnanthes floccosa ssp. californica Arroyo is restricted to vernal pools in Butte County, California. To identify populations with unique genetic resources, guide reintroduction efforts, and design seed collection scenarios for long-term ex situ seed storage we determined extant genetic diversity and structure by surveying 457 individuals from 21 distinct populations using nine polymorphic microsatellite markers. We found low within population genetic diversity: low allelic diversity (1.9 [0.06 SE] alleles/locus); low heterozygosity (H _obs = 0.10 ± 0.018, H _exp = 0.19 ± 0.015), and a high fixation index (0.556 ± 0.044). The number of polymorphic loci ranged between 11 and 89%. Bayesian ordination determined 20 distinct populations and we found high genetic structure among these (F _st = 0.65, P < 0.0001). We identified notable gene flow barriers across populations, confirming regional structuring between three previously defined population density centers and two outlying populations (F _st = 0.21, P < 0.0001). Population size estimates ranged between ~50 and >5,000 extant plants per site. Our study confirms previous isozyme-based results and suggests that the loss of any population would represent a significant loss in the species’ genetic diversity. Recovery requires active restoration of existing populations and permanent habitat protection. We recommend close comparison of microhabitats of declining populations with genetically similar populations, to determine the potential for human assisted gene flow via seed movement to recover declining populations.     

Genotypic and phenotypic consequences of reintroduction history in the black-footed ferret (<Emphasis Type="Italic">Mustela nigripes</Emphasis>)

Population augmentation with translocated individuals has been shown to alleviate the effects of bottlenecks and drift. The first step to determine whether restoration for genetic considerations is warranted is to genetically monitor reintroduced populations and compare results to those from the source. To assess the need for genetic restoration, we evaluated genetic diversity and structure of reintroduced (n = 3) and captive populations of the endangered black-footed ferret (Mustela nigripes). We measured genotypic changes among populations using seven microsatellite markers and compared phenotypic changes with eight morphometric characters. Results indicated that for the population which rapidly grew post-reintroduction, genetic diversity was equivalent to the captive, source population. When growth languished, only the population that was augmented yearly maintained diversity. Without augmentation, allelic diversity declined precipitously and phenotypic changes were apparent. Ferrets from the genetically depaupertate population had smaller limbs and smaller overall body size than ferrets from the two populations with greater diversity. Population divergence (F _ST = 0.10 ± 0.01) was surprisingly high given the common source of populations. Thus, it appears that 5–10 years of isolation resulted in both genotypic divergence and phenotypic changes to populations. We recommend translocation of 30–40 captive individuals per annum to reintroduction sites which have not become established quickly. This approach will maximize the retention of genetic diversity, yet maintain the beneficial effects of local adaptation without being swamped by immigration.     

Population genetic structure of the Korean threadsail filefish (Stephanolepis cirrhifer) based on microsatellite marker analysis

The threadsail filefish Stephanolepis cirrhifer is one of the most important commercial fish resources in Korea. However, its natural populations have declined drastically over the last several decades. To investigate the genetic characteristics of the threadsail filefish for conservation and management purposes, its genetic variation was analyzed in Korean fishing grounds using 11 microsatellite loci. All populations showed moderate genetic diversity (mean number of alleles (N_A) = 8.6, expected heterozygosity (He) = 0.73), representing a slightly lower level of genetic variability than other congeneric species. The presence of a weak genetic population substructure was detected (F_ST = 0.023, R_ST = 0.030, P < 0.001), but this substructure did not feature significant isolation based on the distance between populations. This differentiation may be primarily attributable to genetic differences between populations from Geomundo and other localities, based on relative low level of gene flow, a high level of pairwise F_ST and R_ST or the position of this population in a phylogenetic tree. An analysis of molecular variance (AMOVA) also revealed a greater part of the variation within the population and genetic differentiation among the samples analyzed and identified two genetic clusters. The possibility of a recent genetic bottleneck was observed in some populations of S. cirrhifer. Given the prevailing ocean currents and the intensity of threadsail filefish harvesting activities in Korea, the possibility that human harvest and stock enhancement activities may have partially contributed to our detected genetic pattern cannot be excluded. Management strategies that take these findings into account might lower the risk of harmful genetic change in the species.     

Genetic diversity of the traditional Chinese medicinal plant Ypsilandra thibetica (Melanthiaceae): Applications for conservation

Twelve microsatellite markers were developed to determine the genetic diversity and genetic structure of Ypsilandra thibetica, represented by a total of 90 individuals from six natural populations. All twelve microsatellite loci were polymorphic, and the results indicated that a high genetic diversity was present within populations (mean R_S = 4.996; mean H_E = 0.615), with high levels of genetic structure (mean F_ST = 0.165; mean F_IS = 0.692) among populations. This pattern is likely attributable to consanguineous mating, and this hypothesis is supported by a low relatedness coefficient. Our study suggested that environment factors might restrict gene flow among populations. In addition, physical distances between populations were not related to genetic distances, implying that ancestral populations might have been distributed over a wider area. These results suggest that Y. thibetica should be a high priority for conservation managers.     

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.     

Genetic diversity and population structure of the endangered conifer Taxus wallichiana var. mairei (Taxaceae) revealed by Simple Sequence Repeat (SSR) markers

Taxus wallichiana var. mairei is an endangered conifer with important medicinal value in southern China. Nuclear SSR markers were employed to assess genetic diversity and structure of 13 geographically disjunct populations. The present study revealed a moderate genetic diversity (H_E = 0.538) and low genetic differentiation (F_ST = 0.159). And most populations encountered in severe inbreeding and bottleneck effect. No significant genetic structure was detected by IBD and Structure analysis, which was supported by AMOVA analysis. The present results could be ascribed to an earlier period of more pronounced gene flow when the species had a more continuous distribution. However, the 13 studied populations were divided into four clusters based on the UPGMA dendrogram; these clusters were almost congruent with their geographical distributions. Vital areas such as southern mountains of Sichuan basin, Nanling Mts. and the margin of this yew's distribution range had a high priority for conservation.     

Mitochondrial DNA diversity of the vulnerable Chinese Egret (Egretta eulophotes) from China

The genetic diversity and population structure of the vulnerable Chinese Egret (Egretta eulophotes) were surveyed in the present study from three archipelagoes that cover the most southerly to the very northerly parts of the Chinese distribution range of this species, using a 433-bp fragment of the mitochondrial control region (CR). Among 90 individual samples, 31 different haplotypes were defined by 30 polymorphic sites. Overall haplotype diversity, nucleotide diversity and mean sequence divergence (p-distance) of this egret were 0.920, 0.0088 and 1.11%, respectively. NJ tree and parsimony network for the CR haplotypes of the Chinese Egret showed little genetic structure, and analysis of molecular variance indicated low but significant genetic differentiation (haplotype-based Φ_ST = 0.03267, P < 0.05 and distance-based Φ_ST = 0.04194, P < 0.05) among populations. The significant Fu’s F _S tests (Fu’s F _S  = −16.946, P < 0.01) and mismatch distribution analysis (τ = 4.463, SSD = 0.0081, P = 0.12) suggested that the low genetic differentiation and little geographical structure of the genetic differentiation might be explained by the population expansion. The Mantel test (haplotype-based F _ST, r = 0.639, P = 0.34 and distance-based F _ST, r = 0.947, P = 0.15) suggest that the significant genetic differentiation among populations was likely due to isolation by distance.     

Genetic analysis of two Portuguese populations of <Emphasis Type="Italic">Ruditapes decussatus</Emphasis> by RAPD profiling

The clam Ruditapes decussatus is commercially important in the south of Portugal. The random amplified polymorphic DNA (RAPD) technique was applied to assess the genetic diversity and population structure of two Portuguese populations occurring in the Ria Formosa (Faro) and the Ria de Alvor, respectively. Twenty-five individuals of each population were investigated by RAPD profiles. Genetic diversity within populations, measured by the percentage of polymorphic loci (%P), varied between 68.57% (Alvor) and 73.88% (Faro). Shannon’s information index (H) and Nei’s gene diversity (h) were 0.281 and 0.176, respectively, for the Alvor population and 0.356 and 0.234 for the Faro population. Overall, genetic variation within R. decussatus populations was high. The total genetic diversity (H _T) was explained by a low variation between populations (G _ST = 0.145), which is consistent with high gene flow (N _m = 2.9). The analysis of molecular variance (AMOVA) showed that 65% of variability is within populations and 35% between populations (Φ_PT = 0.345; P ≥ 0.001). The value of Nei’s genetic distance was 0.0881, showing a low degree of population genetic distance, despite the different geographic origin. This is the first study on the population genetics of R. decussatus by RAPD technique. The results may be useful for restocking programs and aquaculture.     

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 variability and structure of natural and domesticated populations of Caribbean pine (Pinus caribaea Morelet)

 Isozyme analysis of seed samples derived from natural and managed populations of the tropical pine Pinus caribaea vars ‘bahamensis’ and ‘caribaea’ was used to assess population genetic structure in its native range and to detect changes occurring during early domestication of the species. Baseline data from natural populations of the two varieties showed that populations sampled as seed are characterized by high gene diversity (mean H_e=0.26) and a low level of inbreeding ( mean F_is=0.15). A UPGMA tree of genetic relatedness among populations indicates that the two varieties represent distinct evolutionary units. Within each variety there is significant differentiation among populations, and this is greater for the more fragmented populations of var ‘bahamensis’ (F_st=0.08) than for var ‘caribaea’ (F_st=0.02). Seed from a seed orchard population of var ‘caribaea’ established within its natural range showed no change in genetic diversity but did show a reduced inbreeding coefficient (F_is=0.09) compared with its progenitor populations, suggesting a decrease in selfing and/or biparental inbreeding. A bulked seed sample from an exotic plantation of var ‘bahamensis’ in Australia displayed a large increase in the inbreeding coefficient (F_is=0.324) compared with that found in natural populations, possibly due to elevated self-fertilization. Finally, a bulked seed sample from an exotic plantation population of var ‘caribaea’ from China showed enhanced genetic diversity, an increase in the inbreeding coefficient and more linkage disequilibrium than its presumed progenitor populations. It was also genetically divergent from them. RFLP analysis of chloroplast DNA variation in the Chinese sample suggested that seeds of the related taxa P. elliottii and P. taeda, or seeds derived from hybridization with these taxa growing in the seed production area, had been included in the seed crop during harvesting. We conclude that monitoring of appropriate genetic markers may be an effective means of identifying potentially deleterious genetic changes occurring during forest tree domestication. Received: 10 August 1998 / Accepted: 8 September 1998     

Genetic diversity and structure of Pinus dabeshanensis revealed by expressed sequence tag-simple sequence repeat (EST-SSR) markers

Assessing patterns of genetic variation in rare endangered species is critical for developing both in situ and ex situ conservation strategies. Pinus dabeshanensis Cheng et Law is an endangered species endemic to the Dabieshan Mountains of eastern China. To obtain fundamental information of genetic diversity, population history, effective population size, and gene flow in this species, we explored patterns of genetic variation of natural populations, in addition to an ex situ conserved population, using expressed sequence tag-simple sequence repeats (EST-SSR) markers. Our results revealed moderate levels of genetic diversity (e.g., H_E = 0.458 vs. H_E = 0.423) and a low level of genetic differentiation (F_ST = 0.028) among natural and conserved populations relative to other conifers. Both contemporary and historical migration rates among populations were high. Bayesian coalescent-based analyses suggested that 3 populations underwent reductions in population size ca. 10,000 yr ago, and that two populations may have experienced recent genetic bottlenecks under the TPM. Bayesian clustering revealed that individuals from the ex situ population were largely assigned to the ‘red’ cluster. Additionally, our results identified private alleles in the natural populations but not in the ex situ population, suggesting that the ex situ conserved population insufficiently represents the genetic diversity present in the species. Past decline in population size is likely to be due to Holocene climate change. Based on the genetic information obtained for P. dabeshanensis, we propose some suggestions for the conservation and efficient management of this endangered species.     

Genetic differences between continuous and disjunct populations: some insights from sal (<Emphasis Type="Italic">Shorea robusta</Emphasis> Roxb.) in Nepal

Sal (Shorea robusta Gaertn., Dipterocarpaceae) is a wind-pollinated tropical tree species found in southern Asia. We investigated the genetic diversity and structure at four microsatellites of 15 populations comprising continuous-peripheral and disjunct-peripheral populations in Nepal. Estimates of genetic diversity (N _A = 8.98, H _O = 0.62, H _E = 0.69) were similar when compared with those of other tropical tree species. A higher level of genetic diversity was observed in continuous-peripheral populations (N _A = 9.61, H _O = 0.67, H _E = 0.72) as compared to disjunct-peripheral (N _A = 8.04, H _O = 0.55, H _E = 0.64). Population differentiation was higher among disjunct-peripheral populations (F _ST = 0.043) than among continuous peripherals (F _ST = 0.012). There was a significant association between gene flow distances and genetic differentiation (r ² = 0.128, P ≤ 0.007). No spatial arrangement of populations according to their geographical locations was found. Based on observed genetic diversity protection of some populations in continuous-peripheral range are suggested for the sustainable conservation of genetic resources of the species while protection of some disjunct-peripheral populations are also recommended for conserving rare alleles.     

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.