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

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

Genetic diversity of the Chestnut blight fungus Cryphonectria parasitica in four French populations assessed by microsatellite markers

Microsatellites are powerful markers to infer population genetic parameters. Here, 13 microsatellite loci isolated from a genomic and a cDNA library of Cryphonectria parasitica were used to characterize the genetic diversity and structure of four French populations. Twelve of these loci were polymorphic within populations, and average gene diversity (H_e) was estimated to be 0.35. There was a lower genetic diversity in a south-eastern population relative to three south-western populations. In these three populations, microsatellite genotypic diversity was higher than vegetative compatibility type diversity. A high genetic differentiation (G_ST = 0.27) suggested a low gene flow and/or founder effects of French populations which are in agreement with low dispersal of spores and different introductions of this species in southern France. This study demonstrates the significance of these microsatellite loci to assess gene flow and reproductive system in this important pathogen.     

Conservation of genetic diversity hotspots of the high‐valued relic yellowhorn (Xanthoceras sorbifolium) considering climate change predictions

Genetic structure and major climate factors may contribute to the distribution of genetic diversity of a highly valued oil tree species Xanthoceras sorbifolium (yellowhorn). Long‐term over utilization along with climate change is affecting the viability of yellowhorn wild populations. To preserve the species known and unknown valuable gene pools, the identification of genetic diversity “hotspots” is a prerequisite for their consideration as in situ conservation high priority. Chloroplast DNA (cpDNA) diversity was high among 38 natural populations (H_d = 0.717, K = 4.616, Tajmas’ D = ?0.22) and characterized by high genetic divergence (F_ST = 0.765) and relatively low gene flow (N_m = 0.03), indicating populations isolation reflecting the species’ habitat fragmentation and inbreeding depression. Six out of the studied 38 populations are defined as genetic diversity “hotspots.” The number and geographic direction of cpDNA mutation steps supported the species southwest to northeast migration history. Climatic factors such as extreme minimum temperature over 30 years indicated that the identified genetic “hotspots” are expected to experience 5°C temperature increase in next following 50 years. The results identified vulnerable genetic diversity “hotspots” and provided fundamental information for the species’ future conservation and breeding activities under the anticipated climate change. More specifically, the role of breeding as a component of a gene resource management strategy aimed at fulfilling both utilization and conservation goals.     

Genetic diversity and population structure of a cyprinid fish (Ancherythroculter nigrocauda) in a highly fragmented river

In this study, samples of Ancherythroculter nigrocauda, an endemic fish in the upper Yangtze River, were collected above and below dams in the Longxi River, a tributary of the upper Yangtze River, China, to investigate the genetic impacts of dams. The mitochondrial cytochrome b gene (cyt b) and 13 microsatellite (SSR) loci were used to analyze whether dams have resulted in loss of genetic diversity of the two fragmented populations or caused genetic differentiation between them. The results showed that the haplotype diversity (0.488; 0.486), nucleotide diversity (0.084%; 0.082%) and average expected heterozygosity (0.652; 0.676) of the two populations were all at a low level, and recent bottlenecks were detected. However, there was no genetic differentiation detected by the low genetic differentiation index (F_st, cyt b: ?0.1677, p = 0.99707; SSR: 0.00259, p = 0.81427). Besides, 11 pairs of half‐sibling relationship were found between the two populations indicating that there were individual movements and gene flow between them. This could be the larvae moving from upstream to downstream when water spilled over dams in flooding season. Therefore, our analysis showed that the dams have caused a loss of genetic diversity of the populations of A. nigrocauda in the Longxi River, blocked the active upstream movement but allowing passive downstream drift of larvae.     

Genetic variation and effective population size in isolated populations of coastal cutthroat trout

Following glacial recession in southeast Alaska, waterfalls created by isostatic rebound have isolated numerous replicate populations of coastal cutthroat trout (Oncorhynchus clarkii clarkii) in short coastal streams. These replicate isolated populations offer an unusual opportunity to examine factors associated with the maintenance of genetic diversity. We used eight microsatellites to examine genetic variation within and differentiation among 12 population pairs sampled from above and below these natural migration barriers. Geological evidence indicated that the above-barrier populations have been isolated for 8,000–12,500 years. Genetic differentiation among below-barrier populations (F _ST = 0.10, 95% C.I. 0.08–0.12) was similar to a previous study of more southern populations of this species. Above-barrier populations were highly differentiated from adjacent below-barrier populations (mean pairwise F _ST = 0.28; SD 0.18) and multiple lines of evidence were consistent with asymmetric downstream gene flow that varied among streams. Each above-barrier population had reduced within-population genetic variation when compared to the adjacent below-barrier population. Within-population genetic diversity was significantly correlated with the amount of available habitat in above-barrier sites. Increased genetic differentiation of above-barrier populations with lower genetic diversity suggests that genetic drift has been the primary cause of genetic divergence. Long-term estimates of N _e based on loss of heterozygosity over the time since isolation were large (3,170; range 1,077–7,606) and established an upper limit for N _e if drift were the only evolutionary process responsible for loss of genetic diversity. However, it is likely that a combination of mutation, selection, and gene flow have also contributed to the genetic diversity of above-barrier populations. Contemporary above-barrier N _e estimates were much smaller than long-term N _e estimates, not correlated with within-population genetic diversity, and not consistent with the amount of genetic variation retained, given the approximate 10,000-year period of isolation. The populations isolated by waterfalls in this study that occur in larger stream networks have retained substantial genetic variation, which suggests that the amount of habitat in headwater streams is an important consideration for maintaining the evolutionary potential of isolated populations.     

Crayfish populations genetically fragmented in streams impounded for 36–104 years

1. Dams and their associated impoundments may restrict dispersal and gene flow among populations of numerous freshwater species within stream networks, leading to genetic isolation. This can reduce effective population sizes and genetic diversity, increasing the risk of local extinction.
2. We studied crayfishes from multiple up- and downstream sites in three impounded and two unimpounded streams in the Bear Creek and Cahaba River drainages, Alabama, U.S.A. Using mitochondrial DNA (cytochrome oxidase subunit I gene) sequence data generated from population-level sampling of two abundant native crayfishes, Faxonius validus and Faxonius erichsonianus (Decapoda: Cambaridae), we assessed species’ spatial genetic structure and genetic diversity, estimated the magnitude and directionality of gene flow, and compared results between the species.
3. For both species, levels of genetic diversity (number of haplotypes, and haplotypic and nucleotide diversity) were the same or higher in impounded compared to unimpounded streams. Conversely, crayfish populations in up- and downstream sections of unimpounded streams displayed high genetic similarity and bidirectional gene flow, whereas in impounded streams, crayfish populations typically had greater up- and downstream genetic differentiation and predominantly unidirectional, downstream gene flow.
4. Although impoundments were associated with lower connectivity between up- and downstream sections for F. validus and F. erichsonianus, the magnitude of genetic effects was species-specific, with greater differentiation between F. validus populations up- and downstream of impoundments.
5. In an ecologically short timeframe, impoundments appear to have fragmented stream crayfish populations, and even species with relatively high abundances and large ranges had lower gene flow among populations in impounded streams compared to unimpounded streams. In addition, feedbacks between genetic and demographic effects on fragmented populations may decrease the probability of long-term persistence.

     

Genetic Diversity and Spatial Genetic Structure of the Grassland Perennial Saxifraga granulata along Two River Systems

Due to changes in land use, the natural habitats of an increasing number of plant species have become more and more fragmented. In landscapes that consist of patches of suitable habitat, the frequency and extent of long-distance seed dispersal can be expected to be an important factor determining local genetic diversity and regional population structure of the remaining populations. In plant species that are restricted to riparian habitats, rivers can be expected to have a strong impact on the dynamics and spatial genetic structure of populations as they may enable long-distance seed dispersal and thus maintain gene flow between fragmented populations. In this study, we used polymorphic microsatellite markers to investigate the genetic diversity and the spatial genetic structure of 28 populations of Saxifraga granulata along two rivers in central Belgium. We hypothesized that rivers might be essential for gene flow among increasingly isolated populations of this species. Genetic diversity was high (H_S = 0.68), which to a certain extent can be explained by the octoploid nature of S. granulata in the study area. Populations along the Dijle and Demer rivers were also highly differentiated (G” _ST = 0.269 and 0.164 and D _EST = 0.190 and 0.124, respectively) and showed significant isolation-by-distance, indicating moderate levels of gene flow primarily between populations that are geographically close to each other. Along the river Demer population genetic diversity was higher upstream than downstream, suggesting that seed dispersal via the water was not the primary mode of dispersal. Overall, these results indicate that despite increasing fragmentation populations along both rivers were highly genetically diverse. The high ploidy level and longevity of S. granulata have most likely buffered negative effects of fragmentation on genetic diversity and the spatial genetic structure of populations in riparian grasslands.     

云南48种木兰科野生植物资源遗传多样性研究

为了解云南省木兰科（Magnoliaceae）野生植物资源的遗传多样性,利用ISSR分子标记技术对48种木兰科野生植物资源进行研究。结果表明,10对引物共扩增出151条带,均为多态性条带,多态性条带百分率为100%。总的观测等位基因数（N_a）为2.000 0,有效等位基因数（N_e）为1.564 5,Nei’s基因多样性指数（H）0.337 9,Shannon’s信息指数（I）为0.510 1。总的基因多样性指数（H_t）为0.368 0,属间基因多样性指数（D_st）为0.251 9,占68.4%,基因分化系数（G_st）为0.684 0,基因流（N_m）为0.231 0。UPGMA聚类分析将48种木兰科植物划分为7个类群,各类群并非按照属聚在一起,而是不同属植物相间分布,长喙厚朴（Magnolia rostrata）、素黄含笑（Michelia flaviflora）和球花含笑（M.sphaerantha）可能为云南省木兰科植物中的原始种。48种木兰科野生植物总体具有较高的遗传多样性,但属间遗传变异较高,基因流较小,存在遗传漂变的风险,聚类结果与刘玉壶的分类系统存在分歧,这从分子水平为木兰科植物间的起源、进化与分类提供了重要依据。     

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

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

Conservation Genetics of the Endemic Mexican Heliconia uxpanapensis in the Los Tuxtlas Tropical Rain Forest

Heliconia uxpanapensis (Heliconiaceae) is an outcrossing endemic herb that grows within continuous and fragmented areas of the tropical rain forest of southeast Veracrúz (México). The genetic diversity, population differentiation, and genetic structure of seven populations of the studied species were assessed using inter‐simple sequence repeat) markers. Population differentiation was moderately high (F_ST range: 0.18–0.22) and indirect estimates of gene flow were rather low (Nm=0.65–0.83). Analysis of molecular variance indicated that the populations explained 22.2 percent of the variation, while individuals within the populations accounted for 77.8 percent. The similar and high level of genetic diversity found within populations of the continuous and fragmented forest suggests that H. uxpanapensis has not suffered yet the expected negative effect of fragmentation. Genetic structure analyses indicated the presence of fewer genetic clusters (K=4) than populations (N=7). Three of the four fragmented forest populations were assigned each to one of the clusters found within the continuous forest, suggesting the absence of a negative fragmentation effect on the amount and distribution of genetic variation. Given the significant genetic structure combined with high genetic diversity and low levels of gene flow, theoretical simulations indicated that H. uxpanapensis might be highly susceptible to changes in the mating system, which promotes inbreeding within fragmented populations. Thus, future conservation efforts in this species should be directed to ensure that levels of gene flow among populations are sufficient to prevent an increment in the magnitude of inbreeding within fragments.     

Microsatellite diversity and genetic structure of the commercially important tropical tree species <Emphasis Type="Italic">Eucalyptus urophylla</Emphasis>, endemic to seven islands in eastern Indonesia

Eucalyptus urophylla (Timor mountain gum) is an economically important plantation species that occurs naturally in a series of disjunct populations on the volcanic slopes of seven islands in eastern Indonesia. Twelve microsatellite markers were used to investigate the distribution of nuclear genetic diversity among 19 geographically defined E. urophylla populations. High levels of gene diversity were observed throughout the geographic range (H _E = 0.703 to 0.776). The level of genetic differentiation among populations was low (F _ST = 0.031), but the amount of differentiation increased with geographic distance. A phenogram produced by a neighbor-joining analysis illustrated that populations clustered according to islands. However, a Bayesian clustering approach revealed a more cryptic population structure comprising two genetically homogeneous groups. Gene flow among the populations is likely responsible for the apparent weak influence of geographic insularity on the genetic diversity and structure of the island species. These findings provide direction for conservation and breeding strategies in E. urophylla. Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

Effect of Yangtze River on population genetic structure of the relict plant Parrotia subaequalis in eastern China

Parrotia subaequalis (Hamamelidaceae) is a Tertiary relic species endemic in eastern China. We used inter‐simple sequence repeat (ISSR) markers to access genetic diversity and population genetic structure in natural five populations of P. subaequalis. The levels of genetic diversity were higher at species level (H = 0.2031) but lower at population level (H = 0.1096). The higher genetic diversity at species levels might be attributed to the accumulation of distinctive genotypes which adapted to the different habitats after Quaternary glaciations. Meanwhile, founder effects on the early stage, and subsequent bottleneck of population regeneration due to its biological characteristics, environmental features, and human activities, seemed to explain the low population levels of genetic diversity. The hierarchical AMOVA revealed high levels (42.60%) of among‐population genetic differentiation, which was in congruence with the high levels of Nei's genetic differentiation index (G_ST = 0.4629) and limited gene flow (N_m = 0.5801) among the studied populations. Mantel test showed a significant isolation‐by‐distance, indicating that geographic isolation has a significant effect on genetic structure in this species. Unweighted pair‐group method with arithmetic average clustering, PCoA, and Bayesian analyses uniformly recovered groups that matched the geographical distribution of this species. In particular, our results suggest that Yangtze River has served as a natural barrier to gene flow between populations occurred on both riversides. Concerning the management of P. subaequalis, the high genetic differentiation among populations indicates that preserving all five natural populations in situ and collecting enough individuals from these populations for ex situ conservation are necessary.     

Microsatellite analysis of the natterjack toad (Bufo calamita) in Denmark: populations are islands in a fragmented landscape

The European natterjack toad (Bufo calamita) has declined rapidly in recent years, primarily due to loss of habitat, and in Denmark it is estimated that 50% of the isolated populations are lost each decade. To efficiently manage and conserve this species and its genetic diversity, knowledge of the genetic structure is crucial. Based on nine polymorphic microsatellite loci, the genetic diversity, genetic structure and gene flow were investigated at 12 sites representing 5–10% of the natterjack toad localities presently known in Denmark. The expected heterozygosity (H _E) within each locality was generally low (range: 0.18–0.43). Further analyses failed to significantly correlate genetic diversity with population size, degree of isolation and increasing northern latitude, indicating a more complex combination of factors in determining the present genetic profile. Genetic differentiation was high (overall θ = 0.29) and analyses based on a Bayesian clustering method revealed that the dataset constituted 11 genetic clusters, defining nearly all sampling sites as distinct populations. Contemporary gene flow among populations was undetectable in nearly all cases, and the failure to detect a pattern of isolation by distance within major regions supported this apparent lack of a gene flow continuum. Indications of a genetic bottleneck were found in three populations. The analyses suggest that the remaining Bufo calamita populations in Denmark are genetically isolated, and represent independent units in a highly fragmented gene pool. Future conservation management of this species is discussed in light of these results. Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

Gene flow in an endangered willow <Emphasis Type="Italic">Salix hukaoana</Emphasis> (Salicaceae) in natural and fragmented riparian landscapes

Salix hukaoana is an endangered riparian pioneer tree that is distributed within a restricted area of Japan. Microsatellite genetic variations and genetic structures were investigated in 80 subpopulations patchily distributed within five river basins with varying degrees of habitat fragmentation. The correlation between geographic distance and genetic distance based on the Bayesian assignment test was significant across relatively intact riparian habitats, with steeper slopes of regression for more densely grouped subpopulations, suggesting restricted gene flow. However, the correlation became less apparent with increasing spacing of the habitat patches. These contradictory results are attributed to the increased chance of long-distance dispersal of sexual propagules among more isolated habitat patches. The observed accumulation of genetic diversity with increasing distance downstream along a few, but not all, of the rivers and the results of assignment tests suggested a downstream directionality of gene flow. The results of this study illustrate the patterns of genetic diversity and contemporary dispersal of S. hukaoana, and provide important insights into understanding the gene dispersal of riparian trees and into the conservation of genetic resources for this species.     

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

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

Genetic diversity of insular natural populations of <Emphasis Type="Italic">Festuca pratensis</Emphasis> Huds.: RAPD analysis

In natural populations of Festuca pratensis Huds. from the islands of Onega Lake, the level of genetic diversity was evaluated. In three populations variability of 64 RAPD loci was tested. The level of genetic diversity (P _95% = 30.2; H _exp = 0.093) was low for a cross-pollinating plant species. Furthermore, genetic similarity between the plants from insular populations was found to be high (I _N = 0.887). It was demonstrated that genetic variation among the population accounted for at most 5.3% of total genetic diversity, which, however, was higher than the F _ST values for continental populations (F _ST = 0.022). It was suggested that specific features of the genetic structure of insular population, i.e., low gene diversity within the populations along with high differentiation among the populations, were caused by the gene flow attenuation, as a result of isolation, and intensification of inbreeding. These features had negative effect on total population adaptation.     

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     

Genetic diversity and gene flow estimates among three populations of Botryodiplodia theobromae causing die-back and bark canker of pear in Punjab

Three populations of Botryodiplodia theobromae causing die-back and bark canker of pear in Punjab were analysed to know about the genetic diversity, gene flow, heterogeneity and the probable rate of spread of races capable of overcoming the resistance present in elite cultivars. There was no relationship between the morphologically similar isolates and their pathogenic behaviour. Majority of the isolates of B. theobromae within and among the populations produced lesions of 1.9–7.2 × 0.8–3.1 cm size on detached pear twigs cv. Punjab Beauty. Incubation period and per cent infection also varied within and among the three populations of the pathogen. The genetic diversity was calculated on the basis of allele frequencies of nine simple sequence repeat (SSR) markers using Nei's genetic diversity formulae. Allele frequencies (X_ij ) varied significantly among the three populations ranging from 0.0 to 1.0. The mean genetic diversities within population (H _S) also varied in all the locations ranging from 0.18 to 0.36 indicating a high genetic diversity within the population. The total genetic diversity across all the populations (H _T) ranged between 0.1 and 0.5 with a mean of 0.36, and differed significantly from the mean H _S (0.25). Diversity indices of SSR loci varied from low (H _S < 0.1) to high (H _S > 0.4) across all the populations (G _ST) of B. theobromae in Punjab which were consistent over the presumed SSR loci with a mean G _ST of 0.29. The lower G _ST values of 0.13, 0.10, 0.11 and 0.13 were observed at LAS15-16, LAS27-28, BOT17-18 and BOT35-36 loci, respectively, showing high genetic diversity among all the isolates. However, at BOT19-20 locus, the G _ST value observed was 0.72 thereby indicating low diversity in the population at this locus. Out of 25 loci, 8 loci showed the gene flow (Nm) < 1 indicating a high genetic differentiation within the population and the remaining 6 loci showed the Nm > 1 indicating the frequent existence of gene flow across the populations of B. theobromae. Pairwise comparison (G _ST) values among all the loci were ranging from 0.18 to 0.19, which indicate a low genetic differentiation among the populations of B. theobromae. The high genetic diversity (H _S) within the population was observed in the present study suggesting that B. theobromae possess high variability in Punjab. Keeping this in view, new races would be expected soon outside the state of origin, as naturally occurring gene flow is likely to be increased by the human activity for comprehensive cultivation of pear in the near future. Therefore, it is difficult to predict the durability of resistant sources in Punjab, which in turn emphasises the identification and introgression of R genes into commercial cultivars.     

Genetic diversity of the endangered Chinese endemic herb Primulina tabacum (Gesneriaceae) revealed by amplified fragment length polymorphism (AFLP)

Primulina tabacum Hance, is a critically endangered perennial endemic to limestone area in South China. Genetic variability within and among four extant populations of this species was assessed using AFLP markers. We expected a low genetic diversity level of this narrowly distributed species, but our results revealed that a high level of genetic diversity remains, both at population level (55.5% of markers polymorphic, H _E = 0.220, I _S = 0.321), and at species level (P = 85.6% of markers polymorphic, H _E = 0.339, I _S = 0.495), probably resulting from its refugial history and/or breeding system. High levels of genetic differentiation among populations was apparent based on Nei’s genetic diversity analysis (G _st=0.350). The restricted gene flow between populations is a potential reason for the high genetic differentiation. The population genetic diversity of P. tabacum revealed here has clear implications for conservation and management. To maintain present levels of genetic diversity, in situ conservation of all populations is necessary.     

青藏高原濒危植物唐古特大黄的遗传多样性

唐古特大黄(Rheum tanguticum)是中国传统的中藏药材,近几年由于生境的严重破坏,已濒临灭绝,并被列入濒危植物名单。为了探索唐古特大黄物种濒危的原因并保护其野生资源,本研究采集了9个居群87个个体的唐古特大黄样本,基于该物种的叶绿体基因trn S-G序列对其进行了遗传多样性研究。结果表明,唐古特大黄物种具有较高的遗传多样性水平(Ht=0.694),其中95.97%的遗传分化来自于居群间(G_(ST)=0.960),4.03%的遗传分化来自于居群内(Hs=0.028)。AMOVA分析也显示唐古特大黄居群间基因流较小(N_m=0.01),存在较高的遗传分化(F_(ST)=0.9631)。唐古特大黄较高的遗传多样性水平可能与该物种较长的进化史和生活史有关,居群间较高的遗传分化可能与高山地区特殊的地理环境和人类活动有关。根据研究结果,建议对唐古特大黄所有野生居群进行就地保护,同时收集种质资源开展异地繁殖工作,以保护物种的遗传多样性,维持其进化潜力。