Population structure affected by excess gene flow in self-pollinating Elymus nutans and E. burchan-buddae (Triticeae: Poaceae)

Seed-mediated gene flow can considerably affect population genetic structure of strictly self-pollinating species, but little is known on the extent and nature of such gene flow among pastoral plant populations. Molecular fingerprints provide a powerful tool to address the relevant issues. Genetic structure of 22 populations of two self-pollinating pasture species, Elymus nutans and E. burchan-buddae, collected from various altitudes of the Qinghai–Tibetan Plateau was studied using fluorescence-based amplified fragment length polymorphism technique. Analysis of molecular variance revealed 42.97% and 37.63% among-population variation for the two Elymus species, respectively, indicating that the majority of the total variation presented within populations. This result contradicts the common genetic variation pattern for a selfing plant species: lower genetic variation within populations. Further analysis suggested higher level of gene flow among populations within the same region than among different regions across the sampled area for the two Elymus species. STRUCTURE analyses of the Elymus populations indicated an evident admixture genetic structure, particularly among neighboring populations from the same region, supporting the hypothesis of considerable seed dispersal among populations. The excess within-region gene flow of E. nutans and E. burchan-buddae might be caused by grazing animals that promote seed dispersal when moved around the pastoral lands during foraging. The among-population gene flow promulgated by grazing animals may promote the maintenance of genetic diversity in the pasture species, particularly in small and fragmented populations within a given region.     

The effect of different glaciation patterns over the current genetic structure of the southern beech <Emphasis Type="Italic">Nothofagus antarctica</Emphasis>

Different regional patterns of glaciation are expected to have brought about a differential effect on the present genetic structure of natural tree populations in the temperate regions. The aim of the present study is to test this hypothesis in Nothofagus antarctica, a key tree species of the temperate forests of southern South America. An almost continuous ice layer characterized the region of the Andes south of 41°S, while towards northern latitudes the pattern was more fragmented. Therefore, a higher chance for the location of larger or more numerous glacial refuges in the north of the Argentinean range, leads us to predict a higher genetic diversity in this region. Twelve natural populations of N. antarctica were sampled along the northern half of its Argentinean range, including six above 41°S and six below that latitude. Sampled populations were genetically characterized through cpDNA and isozyme gene markers. Both groups of populations were compared by means of several diversity and differentiation parameters. A genetic structure analysis was conducted with isozyme data through clustering and Bayesian approaches. Based on three polymorphic chloroplast regions, only two haplotypes were distinguished, one corresponding to the nine northernmost sampled populations and the other to the two southernmost ones. Only the population located between those two groups resulted polymorphic. AMOVA analyses also revealed a latitudinal genetic structure for the populations surveyed, and higher levels of genetic variation were recognized in the northern populations.     

Genetic variability and the effect of habitat fragmentation in spotted suslik Spermophilus suslicus populations from two different regions

Endangered species worldwide exist in remnant populations, often within fragmented landscapes. Although assessment of genetic diversity in fragmented habitats is very important for conservation purposes, it is usually impossible to evaluate the amount of diversity that has actually been lost. Here, we compared population structure and levels of genetic diversity within populations of spotted suslik Spermophilus suslicus, inhabiting two different parts of the species range characterized by different levels of habitat connectivity. We used microsatellites to analyze 10 critically endangered populations located at the western part of the range, where suslik habitat have been severely devastated due to agriculture industrialization. Their genetic composition was compared with four populations from the eastern part of the range where the species still occupies habitat with reasonable levels of connectivity. In the western region, we detected extreme population structure (F _ST = 0.20) and levels of genetic diversity (Allelic richness ranged from 1.45 to 3.07) characteristic for highly endangered populations. Alternatively, in the eastern region we found significantly higher allelic richness (from 5.09 to 5.81) and insignificant population structure (F _ST = 0.03). As we identified a strong correlation between genetic and geographic distance and a lack of private alleles in the western region, we conclude that extreme population structure and lower genetic diversity is due to recent habitat loss. Results from this study provide guidelines for conservation and management of this highly endangered species.     

Population differentiation in the redshank (<Emphasis Type="Italic">Tringa totanus</Emphasis>) as revealed by mitochondrial DNA and amplified fragment length polymorphism markers

The redshank (Tringa totanus) is declining throughout Europe and to implement efficient conservation measures, it is important to obtain information about the population genetic structure. The aim of the present study was two-fold. First, we analysed the genetic variation within and between populations in the Baltic region in southern Scandinavia. Evidence of genetic structure would suggest that different populations might require separate management strategies. Second, in an attempt to study large-scale genetic structure we compared the Baltic populations with redshanks from northern Scandinavia and Iceland. This analysis could reveal insights into phylogeography and long-term population history. DNA samples were collected from six breeding sites in Scandinavia presumed to include two subspecies (totanus and britannica) and a further sample from Iceland (subspecies robusta). Two methods were used to study the population genetic structure. Domain II and III of the mitochondrial control region was analysed by DNA sequencing and nuclear DNA was analysed by screening amplified fragment length polymorphism (AFLP) markers. Mitochondrial DNA showed no variation between individuals in domain II. When analysing an 481 bp fragment of domain III seven haplotypes were found among birds. On the basis of mtDNA sequences, redshanks showed some evidence of a recent expansion from a bottlenecked refugial population. Bayesian analyses of AFLP data revealed a significant genetic differentiation between suggested subspecies but not between populations within the Baltic region. Our results indicate that populations of redshanks in Europe constitute at least three separate management units corresponding to the recognised subspecies.     

Gene flow and population structure of a solitary top carnivore in a human‐dominated landscape

While African leopard populations are considered to be continuous as demonstrated by their high genetic variation, the southernmost leopard population exists in the Eastern and Western Cape, South Africa, where anthropogenic activities may be affecting this population's structure. Little is known about the elusive, last free‐roaming top predator in the region and this study is the first to report on leopard population structuring using nuclear DNA. By analyzing 14 microsatellite markers from 40 leopard tissue samples, we aimed to understand the populations' structure, genetic distance, and gene flow (Nm). Our results, based on spatially explicit analysis with Bayesian methods, indicate that leopards in the region exist in a fragmented population structure with lower than expected genetic diversity. Three population groups were identified, between which low to moderate levels of gene flow were observed (Nm 0.5 to 3.6). One subpopulation exhibited low genetic differentiation, suggesting a continuous population structure, while the remaining two appear to be less connected, with low emigration and immigration between these populations. Therefore, genetic barriers are present between the subpopulations, and while leopards in the study region may function as a metapopulation, anthropogenic activities threaten to decrease habitat and movement further. Our results indicate that the leopard population may become isolated within a few generations and suggest that management actions should aim to increase habitat connectivity and reduce human–carnivore conflict. Understanding genetic diversity and connectivity of populations has important conservation implications that can highlight management of priority populations to reverse the effects of human‐caused extinctions.     

Genetic differentiation in red‐bellied piranha populations (Pygocentrus nattereri,Kner, 1858) from the Solimões‐Amazonas River

Red‐bellied piranhas (Pygocentrus nattereri) are widely caught with different intensities throughout the region of Solimões‐Amazonas River by local fishermen. Thus, the management of this resource is performed in the absence of any information on its genetic stock. P. nattereri is a voracious predator and widely distributed in the Neotropical region, and it is found in other regions of American continent. However, information about genetic variability and structure of wild populations of red‐bellied piranha is unavailable. Here, we describe the levels of genetic diversity and genetic structure of red‐bellied piranha populations collected at different locations of Solimões‐Amazonas River system. We collected 234 red‐bellied piranhas and analyzed throughout eight microsatellite markers. We identified high genetic diversity within populations, although the populations of lakes ANA, ARA, and MAR have shown some decrease in their genetic variability, indicating overfishing at these communities. Was identified the existence of two biological populations when the analysis was taken altogether at the lakes of Solimões‐Amazonas River system, with significant genetic differentiation between them. The red‐bellied piranha populations presented limited gene flow between two groups of populations, which were explained by geographical distance between these lakes. However, high level of gene flow was observed between the lakes within of the biological populations. We have identified high divergence between the Catalão subpopulation and all other subpopulations. We suggest the creation of sustainable reserve for lakes near the city of Manaus to better manage and protect this species, whose populations suffer from both extractive and sport fishing.     

Genetic structure and diversity of natural and domesticated populations of Citrus medica L. in the Eastern Himalayan region of Northeast India

Citron (Citrus medica L.) is a medicinally important species of citrus native to India and occurs in natural forests and home gardens in the foothills of the eastern Himalayan region of northeast India. The wild populations of citron in the region have undergone rapid decline due to natural and anthropogenic disturbances and most of the remaining individuals of citron are found in fragmented natural forests and home gardens in the region. In order to assess the genetic structure and diversity of citron in wild and domesticated populations, we analyzed 219 individuals of C. medica collected from four wild and eight domesticated populations using microsatellite markers. The genetic analysis based on five polymorphic microsatellite loci revealed an average of 13.40 allele per locus. The mean observed and expected heterozygosity values ranged between 0.220–0.540 and 0.438–0.733 respectively among the wild and domesticated populations. Domesticated populations showed close genetic relationships as compared to wild populations and pairwise Nei's genetic distance ranged from 0.062 to 2.091 among wild and domesticated populations. Analysis of molecular variance (AMOVA) showed higher genetic diversity among‐ than within populations. The analysis of population structure revealed five groups. Mixed ancestry of few individuals of different populations revealed exchange of genetic materials among farmers in the region. Citron populations in the region show high genetic variation. The knowledge gained through this study is invaluable for devising genetically sound strategies for conservation of citron genetic resources in the region.     

Sunshine versus gold: The effect of population age on genetic structure of an invasive mosquito

The genetic diversity and structure of invasive species are affected by the time since invasion, but it is not well understood how. We compare likely the oldest populations of Aedes aegypti in continental North America with some of the newest to illuminate the range of genetic diversity and structure that can be found within the invasive range of this important disease vector. Aedes aegypti populations in Florida have probably persisted since the 1600‐1700s, while populations in southern California derive from new invasions that occurred in the last 10 years. For this comparison, we genotyped 1,193 individuals from 28 sites at 12 highly variable microsatellites and a subset of these individuals at 23,961 single nucleotide polymorphisms (SNPs). This is the largest sample analyzed for genetic structure for either region, and it doubles the number of southern California populations previously analyzed. As predicted, the older populations (Florida) showed fewer indicators of recent founder effect and bottlenecks; in particular, these populations have dramatically higher genetic diversity and lower genetic structure. Geographic distance and driving distance were not good predictors of genetic distance in either region, especially southern California. Additionally, southern California had higher levels of genetic differentiation than any comparably sized documented region throughout the worldwide distribution of the species. Although population age and demographic history are likely driving these differences, differences in climate and transportation practices could also play a role.     

Global diversity and genetic contributions of chicken populations from African,Asian and European regions

Genetic diversity and population structure of 113 chicken populations from Africa, Asia and Europe were studied using 29 microsatellite markers. Among these, three populations of wild chickens and nine commercial purebreds were used as reference populations for comparison. Compared to commercial lines and chickens sampled from the European region, high mean numbers of alleles and a high degree of heterozygosity were found in Asian and African chickens as well as in Red Junglefowl. Population differentiation (F_ST) was higher among European breeds and commercial lines than among African, Asian and Red Junglefowl populations. Neighbour‐Net genetic clustering and structure analysis revealed two main groups of Asian and north‐west European breeds, whereas African populations overlap with other breeds from Eastern Europe and the Mediterranean region. Broilers and brown egg layers were situated between the Asian and north‐west European clusters. structure analysis confirmed a lower degree of population stratification in African and Asian chickens than in European breeds. High genetic differentiation and low genetic contributions to global diversity have been observed for single European breeds. Populations with low genetic variability have also shown a low genetic contribution to a core set of diversity in attaining maximum genetic variation present from the total populations. This may indicate that conservation measures in Europe should pay special attention to preserving as many single chicken breeds as possible to maintain maximum genetic diversity given that higher genetic variations come from differentiation between breeds.     

Genetic structure and historical diversification of catfish Brachyplatystoma platynemum (Siluriformes: Pimelodidae) in the Amazon basin with implications for its conservation

Brachyplatystoma platynemum is a catfish species widely distributed in the Amazon basin. Despite being considered of little commercial interest, the decline in other fish populations has contributed to the increase in the catches of this species. The structure, population genetic variability, and evolutionary process that have driven the diversification of this species are presently unknown. Considering that, in order to better understand the genetic structure of this species, we analyzed individuals from seven locations of the Amazon basin using eight molecular markers: control region and cytochrome b mtDNA sequences, and a set of six nuclear microsatellite loci. The results show high levels of haplotype diversity and point to the occurrence of two structured populations (Amazon River and the Madeira River) with high values for F_ST. Divergence time estimates based on mtDNA indicated that these populations diverged about 1.0 Mya (0.2–2.5 Mya 95% HPD) using cytochrome b and 1.4 Mya (0.2–2.7 Mya 95% HPD) using control region. During that time, the influence of climate changes and hydrological events such as sea level oscillations and drainage isolation as a result of geological processes in the Pleistocene may have contributed to the current structure of B. platynemum populations, as well as of differences in water chemistry in Madeira River. The strong genetic structure and the time of genetic divergence estimated for the groups may indicate the existence of strong structure populations of B. platynemum in the Amazon basin.     

Genetic structure of chukar partridge ( Alectoris chukar) populations in the Longdong Loess Plateau, China

This study used polymerase chain reaction (PCR) and dideoxy direct sequencing methods to analyze the genetic structure of the chukar partridge (Alectoris chukar) in the Longdong Loess Plateau, northwestern China. A total of 491 nucleotides of mitochondrial DNA from the control region gene were sequenced for 78 chukar partridges from eight different populations. The 24 variable positions defined 25 haplotypes. The high gene flow (Nm=3.75) implied little genetic differentiation between the eight populations. All the populations shared the haplotype C_1, which suggested that they all came from a common ancestor. The 25 haplotypes were spread through the populations, but could be clustered into two groups. The haplotype similar index between the two groups was only 0.15, with a genetic distance of 0.43%. The genetic variation was significantly different between the two groups, which had been isolated for all of recorded history. The genetic structure of chukar partridge populations in the Plateau appears to be the result of the synergistic effect of a glacier, along with debris flow and human activities since the middle of the Pleistocene.Communicated by F. Bairlein     

Population structure and colonization of Bactrocera dorsalis (Diptera: Tephritidae) in China,inferred from mtDNA COI sequences

The oriental fruit fly, Bactrocera dorsalis, is a serious pest of fruits and vegetables in South‐east Asia, and, because of quarantine restrictions, impedes international trade and economic development in the region. Revealing genetic variation in oriental fruit fly populations will provide a better understanding of the colonization process and facilitate the quarantine and management of this species. The genetic structure in 15 populations of oriental fruit fly from southern China, Laos and Myanmar in South‐east Asia was examined with a 640‐bp sequence of the mitochondrial cytochrome oxidase subunit I (COI) gene. The highest levels of genetic diversity were found in Laos and Myanmar. Low to medium levels of genetic differentiation (F_ST ≤ 0.134) were observed among populations. Pooled populations from mainland China differed from those in Laos and Myanmar (F_ST = 0.024). Genetic structure across the region did not follow the isolation‐by‐distance model. The high genetic diversity observed in Laos and Myanmar supports the South‐east Asian origin of B. dorsalis. High genetic diversity and significant differentiation between some populations within mainland China indicate B. dorsalis populations have been established in the region for an extended period of time. High levels of genetic diversity observed among the five populations from Hainan Island and similarity between the Island and Chinese mainland populations indicate that B. dorsalis was introduced to Hainan from the mainland and has been on the island for many years. High genetic diversity in the recently established population in Shanghai (Pudong) suggests multiple introductions or a larger number of founders.     

Mitochondrial DNA variation in natural populations of endangered Indian Feather-Back Fish, Chitala chitala

Genetic variation at mitochondrial cytochrome b (cyt b) and D-loop region reveals the evidence of population sub-structuring in Indian populations of highly endangered primitive feather-back fish Chitala chitala. Samples collected through commercial catches from eight riverine populations from different geographical locations of India were analyzed for cyt b region (307 bp) and D-loop region (636–716 bp). The sequences of the both the mitochondrial regions revealed high haplotype diversity and low nucleotide diversity. The patterns of genetic diversity, haplotypes networks clearly indicated two distinct mitochondrial lineages and mismatch distribution strongly suggest a historical influence on the genetic structure of C. chitala populations. The baseline information on genetic variation and the evidence of population sub-structuring generated from this study would be useful for planning effective strategies for conservation and rehabilitation of this highly endangered species.     

Effects of topography on dispersal of black-billed magpie Pica pica sericea revealed by population genetic analysis

This study was conducted using random amplified polymorphic DNA analysis to examine whether the effects of topographical structure on the dispersal of black-billed magpie Pica pica sericea are reflected in its population genetic structure. The black-billed magpie is typically seen in the lowlands and is remarkably sedentary in Korea and Japan. The unweighted pair-group method of clustering analysis showed two main clusters: five populations in the western region of the Bekdudegan mountains (WRBM) in one cluster and five populations in the eastern region of the Bekdudegan mountains (ERBM), including the Japanese population in the other cluster. The populations in WRBM appeared to be diverged from the populations in ERBM. Analysis of molecular variance revealed that the populations in ERBM were more genetically divergent from each other than were those in WRBM. The high-rising mountains, very rugged topographical features and the sea in ERBM may have resulted in a lower dispersal rate and larger genetic variation among populations in ERBM compared to those in WRBM. These results suggest that the topographical structure may have an influence on the dispersal and population genetic structure of the black-billed magpie. Electronic Publication     

Landscape conservation genetics of <Emphasis Type="Italic">Dipteryx alata</Emphasis> (“baru” tree: Fabaceae) from Cerrado region of central Brazil

In this paper random amplified polymorphic DNA (RAPD) was used to evaluate the degree of among-population differentiation and associated spatial patterns of genetic divergence for Dipteryx alata Vogel populations from Cerrado region of central Brazil, furnishing support for future programs of conservation of this species. We analyzed patterns of genetic and spatial population structure using 45 RAPD loci scored for 309 trees, sampled from five different regions with two populations each. Genetic structure analysis suggested that panmixia null hypothesis can be rejected, with significant among-population components of 15%. Hierarchical partition by Analysis of Molecular Variance (AMOVA) shows that 5% of genetic variation is within regions, whereas 10% of variation is among regions, and these results were confirmed by a Bayesian analyses on HICKORY. The Mantel correlogram revealed that this divergence is spatially structured, so that local populations situated at short geographic distances could not be considered independent units for conservation and management. However, genetic discontinuities among populations were found in the northwest and southeast parts of the study area, corresponding to regions of recent socio-economic expansion and high population density, respectively. Taking both geographic distances and genetic discontinuities into account it is possible to establish a group of population to be conserved, covering most of D. alata geographic distribution and congruent with previously established priority areas for conservation in the Cerrado region.     

Phylogeography in a galling insect, grape phylloxera, Daktulosphaira vitifoliae (Phylloxeridae) in the fragmented habitat of the Southwest USA

Aim The Southwest USA is characterized by fragmented habitat for a range of species in a manner analogous to island systems. This can restrict gene flow among populations and may promote genetic differentiation and the evolution of endemic populations or species among the forested terrestrial islands. The region has experienced cycles of cooling and warming throughout the Pleistocene and the current isolation among populations may date back only c. 11,000 years. Thus, some studies have found genetic structure that predates the current distribution of organisms. The effect of habitat fragmentation on genetic structure was tested using DNA sequences in a highly specialized herbivorous insect, grape phylloxera, Daktulosphaira vitifoliae, that exhibits poor dispersal capacity and natal‐host associated mating that would seem to predispose it to genetic differentiation. Location Southwestern USA. Methods Phylogenetic trees and statistical parsimony networks were estimated from 458 bp of the mitochondrial cytochrome oxidase I gene sampled from 12 populations in Arizona and New Mexico. Results There was no evidence that populations were differentiated at the level of canyon or mountain range but significant structure was found at the larger level of geographic region. The pattern was confounded by the polyphyly of Southwest (SW) grape phylloxera relative to eastern populations and the coexistence of two highly divergent lineages within populations. Main conclusions An early split of grape phylloxera into the SW has resulted in some differentiation between populations in the Transition and Sonoran + Chihuahuan geographic regions. It is hypothesized that this differentiation has been overlaid by a more recent introduction of haplotypes from midwestern USA populations that occur primarily in the Transition region. The importance of sampling broadly is stressed.     

Low diversity but high differentiation: the population genetics of Aglaope infausta (Zygaenidae: Lepidoptera)

Aim Aglaope infausta is a thermophilous Zygaenid of Atlanto-Mediterranean origin, distributed in Portugal, Spain, France and north-western Italy reaching its north-eastern distribution limit in western Germany. The local, regional and inter-regional genetic structure of this species is studied in this analysis. Location and methods The allozymes of 456 individuals from 12 populations (11 from western Germany and one from southern Portugal) were studied by electrophoresis. Results Six of the 19 loci analysed were monomorphic. Genetic differentiation between populations was high (F_ST: 0.404), while the mean genetic diversity was low (H_e: 3.4%). Most (96.5%) of the genetic variance between populations was between the Portuguese and the German samples, but also the differentiation within Germany was considerable (F_SR: 0.101). In Germany, A. infausta occurs in two major regions (middle Rhine and Nahe) that are geographically separated, and 55.5% of the genetic variance was found between these two regions. The populations of both areas do not differ in their genetic diversity, but those of the middle Rhine have significantly higher genetic distances among them than the Nahe populations (0.020 and 0.015, respectively). F_ST was also higher in the middle Rhine region than in the Nahe region (0.089 and 0.045, respectively). Main conclusions Aglaope infausta shows a very low level of genetic heterogeneity for a lepidopteran species. However, this genetic poverty is not affecting the species’ viability. During the ice ages, differentiation into two genetic lineages occurred, most probably in a south-western and a south-eastern differentiation centre in Iberia. The gap in the distribution range in Germany is clearly reflected in the genetic structure. This differentiation must have developed relatively quickly because western Germany most probably was colonized during the climatic optimum 6000 years ago.     

High intra-population genetic variability and inter-population differentiation in a plateau specialized fish, <Emphasis Type="BoldItalic">Triplophysa orientalis</Emphasis>

Triplophysa orientalis (Herzenstein) is one of the Nemacheilinae (Cypriniformes: Balitoridae) fish species distributed in the Tibetan Plateau area. In order to understand the impact of plateau uplift on population history and the isolation effect of plateau lakes on T. orientalis, we examined its genetic structure and phylogenetic relationships. A total of 98 individuals from five wild populations, three from plateau lakes and two from branch rivers in upper reaches of the Yangtze River, in the eastern peripheral of the Tibetan Plateau were sampled. An 848 base pair fragment from the mitochondrial DNA (mtDNA) control region was sequenced for analyses. Overall, very high intra-population genetic variability was found in all populations except for one lake population (Rannicuo); nucleotide diversity ranged from 0.0025 to 0.0159 and haplotype diversity ranged from 0.641 to 0.879. Furthermore, the genetic distance between river populations (0.0326) was much higher than that among lake populations (Rannicuo and Barencuo 0.0035, Bannicuo and Yibicuo 0.0038, Rannicuo and Yibicuo 0.0049). Additionally, the analysis of molecular variance demonstrated that most of the observed genetic variability occurred among populations, accompanied with significant Fst values except for that between the Yibicuo and Barencuo populations. This evidence suggested a strong population structure of the species and a lack of inter-population connection. Lastly, the rate of migration indicated there were large historic gene flows among lake populations. Demographic analysis also indicated there were bottlenecks or expansions in three lake populations, suggesting a potential isolation effect of plateau lakes on population differentiation. Molecular dating of intra-specific divergence showed the plateau uplift has shaped the genetic structure of T. orientalis.     

THE INFLUENCE OF INTRASPECIFIC VARIATION IN DISPERSAL STRATEGIES ON THE GENETIC STRUCTURE OF PLANTHOPPER POPULATIONS

The hypothesis that levels of gene flow among populations are correlated with dispersal ability has typically been tested by comparing gene flow among species that differ in dispersal abilities, an approach that potentially confounds dispersal ability with other species-specific differences. In this study, we take advantage of geographic variation in the dispersal strategies of two wing-dimorphic planthopper species, Prokelisia marginata and P. dolus, to examine for the first time whether levels of gene flow among populations are correlated with intraspecific variation in dispersal ability. We found that in both of these coastal salt marsh–inhabiting species, population-genetic subdivision, as assessed using allozyme electrophoresis, parallels geographic variation in the proportion of flight-capable adults (macropters) in a population; in regions where levels of macroptery are high, population genetic subdivision is less than in regions where levels of macroptery are low. We found no evidence that geographic variation in dispersal capability influences the degree to which gene flow declines with distance in either species. Thus, both species provided evidence that intraspecific variation in dispersal strategies influences the genetic structure of populations, and that this effect is manifested in population-genetic structure at the scale of large, coastal regions, rather than in genetic isolation by distance within a region. This conclusion was supported by interspecific comparisons revealing that: (1) population-genetic structure (G_ST) of the two Prokelisia species correlated negatively with the mean proportion of flight-capable adults within a region; and (2) there was no evidence that the degree of isolation by distance increased with decreasing dispersal capability. Populations of the relatively sedentary P. dolus clustered by geographic region (using Nei's distances), but this was not the case for the more mobile P. marginata. Furthermore, gene flow among the two major regions we surveyed (Atlantic and Gulf Coasts) has been substantial in P. marginata, but relatively less in P. dolus. The results for P. marginata suggest that differences in the dispersal strategies of Atlantic and Gulf Coast populations occur despite extensive gene flow. We argue that gene flow is biased from Atlantic to Gulf Coast populations, indicating that selection favoring a reduction in flight capability must be intense along the Gulf. Together, the results of this study provide the first rigorous evidence of a negative relationship within a species between dispersal ability and the genetic structure of populations. Furthermore, regional variation in dispersal ability is apparently maintained by selective differences that outweigh high levels of gene flow among regions.     

Living in isolation – population structure,reproduction, and genetic variation of the endangered plant species Dianthus gratianopolitanus (Cheddar pink)

The endangered plant species Dianthus gratianopolitanus exhibits a highly fragmented distribution range comprising many isolated populations. Based upon this pattern of distribution, we selected a study region in Switzerland with a lower magnitude of isolation (Swiss Jura) and another study region in Germany with a higher degree of isolation (Franconian Jura). In each region, we chose ten populations to analyze population structure, reproduction, and genetic variation in a comparative approach. Therefore, we determined population density, cushion size, and cushion density to analyze population structure, investigated reproductive traits, including number of flowers, capsules, and germination rate, and analyzed amplified fragment length polymorphisms to study genetic variation. Population and cushion density were credibly higher in German than in Swiss populations, whereas reproductive traits and genetic variation within populations were similar in both study regions. However, genetic variation among populations and isolation by distance were stronger in Germany than in Switzerland. Generally, cushion size and density as well as flower and capsule production increased with population size and density, whereas genetic variation decreased with population density. In contrast to our assumptions, we observed denser populations and cushions in the region with the higher magnitude of isolation, whereas reproductive traits and genetic variation within populations were comparable in both regions. This corroborates the assumption that stronger isolation must not necessarily result in the loss of fitness and genetic variation. Furthermore, it supports our conclusion that the protection of strongly isolated populations contributes essentially to the conservation of a species' full evolutionary potential.