An analysis of genetic diversity and inbreeding in Wuchereria bancrofti: implications for the spread and detection of drug resistance

Estimates of genetic diversity in helminth infections of humans often have to rely on genotyping (immature) parasite transmission stages instead of adult worms. Here we analyse the results of one such study investigating a single polymorphic locus (a change at position 200 of the beta-tubulin gene) in microfilariae of the lymphatic filarial parasite Wuchereria bancrofti. The presence of this genetic change has been implicated in benzimidazole resistance in parasitic nematodes of farmed ruminants. Microfilariae were obtained from patients of three West African villages, two of which were sampled prior to the introduction of mass drug administration. An individual-based stochastic model was developed showing that a wide range of allele frequencies in the adult worm populations could have generated the observed microfilarial genetic diversity. This suggests that appropriate theoretical null models are required in order to interpret studies that genotype transmission stages. Wright's hierarchical F-statistic was used to investigate the population structure in W. bancrofti microfilariae and showed significant deficiency of heterozygotes compared to the Hardy-Weinberg equilibrium; this may be partially caused by a high degree of parasite genetic differentiation between hosts. Studies seeking to quantify accurately the genetic diversity of helminth populations by analysing transmission stages should increase their sample size to account for the variability in allele frequency between different parasite life-stages. Helminth genetic differentiation between hosts and non-random mating will also increase the number of hosts (and the number of samples per host) that need to be genotyped, and could enhance the rate of spread of anthelmintic resistance.     

Population structure of a parasitic plant and its perennial host

Characterization of host and parasite population genetic structure and estimation of gene flow among populations are essential for the understanding of parasite local adaptation and coevolutionary interactions between hosts and parasites. We examined two aspects of population structure in a parasitic plant, the greater dodder (Cuscuta europaea) and its host plant, the stinging nettle (Urtica dioica), using allozyme data from 12 host and eight parasite populations. First, we examined whether hosts exposed to parasitism in the past contain higher levels of genetic variation. Second, we examined whether host and parasite populations differ in terms of population structure and if their population structures are correlated. There was no evidence that host populations differed in terms of gene diversity or heterozygosity according to their history of parasitism. Host populations were genetically more differentiated (F(ST) = 0.032) than parasite populations (F(ST) = 0.009). Based on these F(ST) values, gene flow was high for both host and parasite. Such high levels of gene flow could counteract selection for local adaptation of the parasite. We found no significant correlation between geographic and genetic distance (estimated as pairwise F(ST)), either for the host or for the parasite. Furthermore, host and parasite genetic distance matrices were uncorrelated, suggesting that sites with genetically similar host populations are unlikely to have genetically similar parasite populations.     

Identification of a molecular marker for genotyping human lymphatic filarial nematode parasite Wuchereria bancrofti

In India, Mass Drug Administration is on going towards elimination of lymphatic filariasis in many areas, which might lead to intense selection pressure on the parasite populations and their genetic restructuring. This calls for molecular finger printing of Wuchereria bancrofti parasite populations at national level and monitoring genetic changes in the future. For this purpose a reliable, less expensive, rapid, and reproducible molecular tool is necessary, which is not available for W. bancrofti at this time. We identified robust molecular markers based on the comparison of random amplified polymorphic DNA (RAPD) and amplified fragment length polymorphism (AFLP) profiles and the genetic data generated from parasite populations collected from areas in Northern (Varanasi, Uttar Pradesh state), Southern (Kozhikode, Kerala State) and Central regions (Jagdalpur, Chattisgarh state) of India, where lymphatic filariasis is endemic for many decades. RAPD profiles for these parasite populations were generated using three different primers and the dendrograms constructed using the profiles were all different. In order to identify appropriate RAPD primer(s), we compared the results of RAPD with the fingerprint profile and genetic data obtained by the more reliable AFLP technique, using the parasite populations from the same areas. RAPD marker (OP8) primer produced phylogenetic data almost similar to that of AFLP analysis. The marker was able to reveal variations between the parasite populations collected from Varanasi, Kozhikode, and Jagdalpur. Most importantly, RAPD primer OP8 produced reproducible results, when tested in three different trials. In view of the limited availability of W. bancrofti parasite DNA, along with a lower cost and ease of performance, RAPD appears to be more suitable compared to AFLP at the present juncture, since complete genome information of this parasite is still not available. Thus, RAPD primer OP8 can be a very useful molecular maker for DNA finger printing of W. bancrofti populations at present.     

Population Genetics of the Filarial Worm Wuchereria bancrofti in a Post-treatment Region of Papua New Guinea: Insights into Diversity and Life History

Background

Wuchereria bancrofti (Wb) is the primary causative agent of lymphatic filariasis (LF). Our studies of LF in Papua New Guinea (PNG) have shown that it is possible to reduce the prevalence of Wb in humans and mosquitoes through mass drug administration (MDA; diethylcarbamazine with/without ivermectin). While MDAs in the Dreikikir region through 1998 significantly reduced prevalence of Wb infection, parasites continue to be transmitted in the area.

Methods

We sequenced the Wb mitochondrial Cytochrome Oxidase 1 (CO1) gene from 16 people infected with Wb. Patients were selected from 7 villages encompassing both high and moderate annual transmission potentials (ATP). We collected genetic data with the objectives to (i) document contemporary levels of genetic diversity and (ii) distinguish between populations of parasites and hosts across the study area.

Principle Findings

We discovered 109 unique haplotypes currently segregating in the Wb parasite population, with one common haplotype present in 15 out of 16 infections. We found that parasite diversity was similar among people residing within the same village and clustered within transmission zones. For example, in the high transmission area, diversity tended to be more similar between neighboring villages, while in the moderate transmission area, diversity tended to be less similar.

Conclusions

In the Dreikikir region of PNG there are currently high levels of genetic diversity in populations of Wb. High levels of genetic diversity may complicate future MDAs in this region and the presence of dominant haplotypes will require adjustments to current elimination strategies.     

Clonal diversity of the marine trematode Maritrema novaezealandensis within intermediate hosts: the molecular ecology of parasite life cycles

We quantified the clonal diversity of the New Zealand marine trematode Maritrema novaezealandensis (n = 1250) within Zeacumantus subcarinatus snail (n = 25) and Macrophthalmus hirtipes crab (n = 25) intermediate hosts using four to six microsatellite loci, and investigated the potential biological and physical factors responsible for the observed genetic patterns. Individual snails harboured one to five trematode genotypes and 48% of snails were infected by multiple parasite genotypes. Overall, the number of parasite genotypes did not increase with snail size, but was highest in intermediate-sized snails. Significantly larger numbers of parasite genotypes were detected in crabs (relative to snails; P < 0.001), with 16-25 genotypes recovered from individual crabs. Although crabs are typically infected by small numbers of cercariae sourced from many snails, they are occasionally infected by large numbers of cercariae sourced from single snails. The latter cases explain the significant genetic differentiation of trematode populations detected among their crab hosts (F(ST) = 0.009, P < 0.001). Our results suggest that the timing of infection and/or intraspecific competition among parasite clones within snails determine(s) the diversity of parasite clones that snails harbour. The presence of a large number of infected snails and tidal mixing of cercariae prior to infection results in crabs potentially harbouring hundreds of parasite genotypes despite the crabs' territorial behaviour.     

Impact of single dose of diethylcarbamazine and other antifilarial drug combinations on bancroftian filarial infection variables: assessment after 2 years

The impact of single dose mass drug administration of diethylcarbamazine (DEC), DEC with albendazole (ALB), and ivermectin (IVR) with albendazole, was examined on the human bancroftian filarial infections in village scale trials in south India, from a follow-up study after 2 years. The treatment arms administered with DEC alone and DEC+ALB demonstrated long-term benefits in reducing microfilaraemia significantly (P<0.05), while antigenaemia reduction was negligible. The arm with ALB+IVR did not show such reductions. Among the antigenaemic and microfilaraemic individuals, 87% became amicrofilaraemic in DEC+ALB arm, which were higher than that observed in the other 2 treatment arms. Among amicrofilaraemics (but Ag+), nearly 35% cleared of infection in DEC+ALB, while 26% and 6% in DEC alone and IVR+ALB arms, respectively. The drug combination DEC+ALB was observed to demonstrate a significant impact in reducing filarial infection even after 2 years post treatment.     

Amplified fragment length polymorphism analysis of Mythimna separata (Lepidoptera: Noctuidae) geographic and melanic laboratory populations in China

Genetic diversity within and among three wild-type natural populations and one melanic laboratory population of Mythimna separata (Walker) (Lepidoptera: Noctuidae) were evaluated using amplified fragment length polymorphism (AFLP) analysis. Although extensive genetic diversity occurs among individuals from different geographic populations (P = 54.5%, h = 0.209, I = 0.305), the majority of the genetic diversity is within populations and not between populations (G(ST) = 0.172), indicating high gene flow (N(M) = 2.403) and suggesting that M. separata in northern China are a part of a single large metapopulation. Genetic diversity in the natural populations was significantly higher than that in the melanic laboratory population (with P = 43.4% versus P = 25.9%, h = 0.173 versus h = 0.086, and I = 0.251 versus I = 0.127), suggesting that the melanic laboratory population is narrowly genetic-based and genetically uniform. Genetic similarities based on AFLP data were calculated, and cluster analysis was preformed to graphically display groupings between individuals and populations. Individuals from the same region were not grouped together in cluster analysis of three natural populations, whereas melanic individuals from laboratory population were grouped together very well. Four subpopulations were clustered into two broad groups. Melanic laboratory population became a single group, which had apparent differentiation from the other group in which three natural subpopulations were included. These results indicated that although high genetic variability existed among the individuals of natural populations, there was little genetic differentiation among three geographic populations that could be explained by the effects of the long distance migration of the oriental armyworm in China enhanced the level of gene flow. Influences of migration on the genetic polymorphism and differentiations that make a significant contribution to evolution in this insect are reviewed.     

Genetic evidence for male-biased dispersal in the Siberian jay (Perisoreus infaustus) based on autosomal and Z-chromosomal markers

Sex-bias in natal dispersal patterns can have important genetic and evolutionary consequences; however, reliable information about sex-biased dispersal can be difficult to obtain with observational methods. We analysed the sex-specific patterns of genetic differentiation among three Siberian jay (Perisoreus infaustus) populations, using 11 autosomal and six Z-chromosomal microsatellite markers. Irrespective of marker-type and indices used (viz. F(ST), average pairwise relatedness and effective number of immigrants), all analyses provided strong evidence for male-biased dispersal. Population structuring at autosomal loci (F(ST) =0.046, P<0.05) exceeded that at Z-chromosomal loci (F(ST) =0.033, P<0.05), and levels of introgression were inferred to be significantly higher for Z-chromosomal when compared to autosomal loci. Of the three populations studied, levels of genetic variability were the lowest in the southernmost fringe population, despite the fact that it harboured a group of divergent Z-chromosomal haplotypes that were not found in the other two populations. In general, the results provide strong genetic evidence for male-biased dispersal in Siberian jays, where observational data have previously suggested male philopatry. The results also highlight the utility of Z-chromosomal markers for gaining insights into the genetic diversity and structuring of populations.     

Population genetic structure of Venezuelan chiropterophilous columnar cacti (Cactaceae)

We conducted allozyme surveys of three Venezuelan self-incompatible chiropterophilous columnar cacti: two diploid species, Stenocereus griseus and Cereus repandus, and one tetraploid, Pilosocereus lanuginosus. The three cacti are pollinated by bats, and both bats and birds disperse seeds. Population sampling comprised two spatial scales: all Venezuelan arid zones (macrogeographic) and two arid regions in northwestern Venezuela (regional). Ten to 15 populations and 17-23 loci were analyzed per species. Estimates of genetic diversity were compared with those of other allozyme surveys in the Cactaceae to examine how bat-mediated gene dispersal affects the population genetic attributes of the three cacti. Genetic diversity was high for both diploid (P(s) = 94.1-100, P(p) = 56.7-72.3, H(s) = 0.182-0.242, H(p) = 0.161-0.205) and tetraploid (P(s) = 93.1, P(p) = 76.1, H(s) = 0.274, H(p) = 0.253) species. Within-population heterozygote deficit was detected in the three cacti at macrogeographic (F(IS) = 0.145-0.182) and regional (F(IS) = 0.057-0.174) levels. Low genetic differentiation was detected at both macrogeographic (G(ST) = 0.043-0.126) and regional (G(ST) = 0.009-0.061) levels for the three species, suggesting substantial gene flow among populations. Gene exchange among populations seems to be regulated by distance among populations. Our results support the hypothesis that bat-mediated gene dispersal confers high levels of genetic exchange among populations of the three columnar cacti, a process that enhances levels of genetic diversity within their populations.     

Patterns of genetic diversity in outcrossing and selfing populations of Arabidopsis lyrata

Arabidopsis lyrata is normally considered an obligately outcrossing species with a strong self-incompatibility system, but a shift in mating system towards inbreeding has been found in some North American populations (subspecies A. lyrata ssp. lyrata). This study provides a survey of the Great Lakes region of Canada to determine the extent of this mating system variation and how outcrossing rates are related to current population density, geographical distribution, and genetic diversity. Based on variation at microsatellite markers (progeny arrays to estimate multilocus outcrossing rates and population samples to estimate diversity measures) and controlled greenhouse pollinations, populations can be divided into two groups: (i) group A, consisting of individuals capable of setting selfed seed (including autogamous fruit set in the absence of pollinators), showing depressed outcrossing rates (T(m) = 0.2-0.6), heterozygosity (H(O) = 0.02-0.06) and genetic diversity (H(E) = 0.08-0.10); and (ii) group B, consisting of individuals that are predominantly self-incompatible (T(m) > 0.8), require pollinators for seeds set, and showing higher levels of heterozygosity (H(O) = 0.13-0.31) and diversity (H(E) = 0.19-0.410). Current population density is not related to the shift in mating system but does vary with latitude. Restricted gene flow among populations was evident among all but two populations (F(ST) = 0.11-0.8). Group A populations were more differentiated from one another (F(ST) = 0.78) than they were from group B populations (F(ST) = 0.59), with 41% of the variation partitioned within populations, 47% between populations, and 12% between groups. No significant relationship was found between genetic and geographical distance. Results are discussed in the context of possible postglacial expansion scenarios in relation to loss of self-incompatibility.     

Allozyme diversity and genetic structure of the leafy cactus (Pereskia guamacho [Cactaceae])

We examined levels of genetic variation and genetic structure in the leafy cactus (Pereskia guamacho) in arid and semiarid zones in Venezuela. We surveyed genetic diversity within 17 populations using 19 allozyme loci. Genetic diversity was relatively high at both the species (P(s) = 89%, A(s) = 3.26, AP(s) = 3.53, H(es) = 0.24) and population (P(p) = 63%, A(p) = 1.90, AP(p) = 2.42, H(ep) = 0.20) levels. A significant deficit of heterozygote individuals was detected within populations in the Paraguana Peninsula region (F(IS) = 0.301). Relatively low levels of population differentiation were detected at macrogeographic (G(ST) = 0.112) and regional levels (G(ST) = 0.044 for peninsula region and G(ST) = 0.074 for mainland region), suggesting substantial genetic exchange among populations; however, gene flow in this species seems to be regulated by the distance among populations. Overall, estimates of genetic diversity found in P. guamacho are concordant with the pattern observed for other cacti surveyed, namely high levels of polymorphism and genetic diversity with one common allele and several rare alleles per locus. Differences in gene dispersal systems between this species and other cacti studied were not reflected in the patterns of genetic diversity observed. The concentration of the highest estimates of genetic variation in northwestern Venezuela suggests a potential reservoir of plant genetic diversity within xerophilous ecosystems in northern South America.     

Lymphatic filariasis elimination in the Dominican Republic: History,progress, and remaining steps

Lymphatic filariasis (LF) is a mosquito-transmitted parasitic disease that is a leading cause of disability globally. The island of Hispaniola, which the Dominican Republic shares with Haiti, accounts for approximately 90% of LF cases in the Americas region. In 1998, the Dominican Ministry of Public Health created the Program to Eliminate Lymphatic Filariasis (PELF) with the goal of eliminating LF transmission by 2020. Baseline mapping revealed 19 (12% of total) endemic municipalities clustered into three geographic foci (Southwest, La Ciénaga and East), with a total at-risk population of 262,395 people. Beginning in 2002, PELF sequentially implemented mass drug administration (MDA) in these foci using albendazole and diethylcarbamazine (DEC). In total, 1,174,050 treatments were given over three to five annual rounds of house-to-house MDA per focus with a median coverage of 81.7% (range 67.4%–92.2%). By 2018, LF antigen prevalence was less than 2% in all foci, thus meeting criteria to stop MDA and begin post-treatment surveillance (PTS). This success has been achieved against a shifting landscape of limited domestic funding, competing domestic public health priorities, and sporadic external donor support. Remaining steps include the need to scale-up morbidity management and disability prevention services for LF and to continue PTS until LF transmission is interrupted across Hispaniola.     

Genetic Structure Within and Among Populations of Saruma henryi, an Endangered Plant Endemic to China

The endangered perennial plant Saruma henryi Oliv. is endemic to China and has phylogenetic, ecological, and medicinal value. We used 10 microsatellite (SSR) loci to investigate genetic diversity and differentiation in 16 natural populations. Genetic diversity was high at the species level (H(E) = 0.9427, h = 0.9410, I = 3.0213) and low at the population level (H(E) = 0.4441, h = 0.4307, I = 0.6822). Pronounced genetic differentiation was detected among populations (G(ST) = 0.5428, F(ST) = 0.5524), in line with the limited among-population gene flow (Nm = 0.21). The significant isolation-by-distance pattern revealed by a Mantel test (r = 0.311, P = 0.001) suggested a clear geographic tendency in the distribution of genetic variability. Bayesian assignment and principal coordinates analyses supported the clustering of 16 populations into three groups. The present SSR results were also compared with previously published ISSR results. These results have significant implications for conservation of the species.     

Microsatellite and mitochondrial haplotype diversity reveals population differentiation in the tiger shrimp (Penaeus monodon) in the Indo-Pacific region

The black tiger shrimp (Penaeus monodon) is an ecologically and economically important penaeid species and is widely distributed in the Indo-Pacific region. Here we investigated the genetic diversity of P. monodon (n = 355) from eight geographical regions by genotyping at 10 microsatellite loci. The average observed heterozygosity at various loci ranged from 0.638 to 0.743, indicating a high level of genetic variability in this region. Significant departures from Hardy-Weinberg equilibrium caused by heterozygote deficiency were recorded for most loci and populations. Pairwise F(ST) and R(ST) values revealed genetic differentiation among the populations. Evidence from the assignment test showed that the populations in the West Indian Ocean were unique, whereas other populations examined were partially admixed. In addition, the non-metric multidimensional scaling analysis indicated the presence of three geographic groups in the Indo-Pacific region, i.e. the African populations, a population from western Thailand and the remaining populations as a whole. We also sequenced and analysed the mitochondrial control region (mtCR) in these shrimp stocks to determine whether the nuclear and mitochondrial genomes show a similar pattern of genetic differentiation. A total of 262 haplotypes were identified, and nucleotide divergence among haplotypes ranged from 0.2% to 16.3%. Haplotype diversity was high in all populations, with a range from 0.969 to 1. Phylogenetic analysis using the mtCR data revealed that the West Indian Ocean populations were genetically differentiated from the West Pacific populations, consistent with the microsatellite data. These results should have implications for aquaculture management and conservation of aquatic diversity.     

大别山山核桃种群遗传多样性研究

为了更有效地保护和合理开发大别山山核桃(Carya dabieshanensis)资源,该文利用RAPD分子标记技术,对3个天然大别山山核桃种群的90个单株的遗传多样性、种群内和种群间的遗传变异进行了研究,结果表明:20对10 bp随机引物共检测到238条谱带,其中多态带为162条,占68.1%。遗传多样性分析结果显示: Shannon多样性指数为0.476 1,58.18%的变异分布于群体内,而种群间变异占了41.82%;Nei指数群体总基因多样度为0.314 5,群体内平均基因多样度(H_S)为0.186 5,群体间的基因多样度(H_ST)为0.128 0,群体Nei基因分化系数(G_ST)为0.406 7,说明40.67%的变异存在于种群间,群体内的变异占了总变异的59.33%,与Shannon多样性指数相比基本一致,均表明种群内有较丰富的遗传变异,这为优良品种选育提供广阔前景;种群间的基因流(N_m)为0.730 6,证明种群间遗传交换较小,这与环境适应性和高山阻隔有一定的关系。     

Microsatellite markers reveal a spectrum of population structures in the malaria parasite Plasmodium falciparum

Multilocus genotyping of microbial pathogens has revealed a range of population structures, with some bacteria showing extensive recombination and others showing almost complete clonality. The population structure of the protozoan parasite Plasmodium falciparum has been harder to evaluate, since most studies have used a limited number of antigen-encoding loci that are known to be under strong selection. We describe length variation at 12 microsatellite loci in 465 infections collected from 9 locations worldwide. These data reveal dramatic differences in parasite population structure in different locations. Strong linkage disequilibrium (LD) was observed in six of nine populations. Significant LD occurred in all locations with prevalence <1% and in only two of five of the populations from regions with higher transmission intensities. Where present, LD results largely from the presence of identical multilocus genotypes within populations, suggesting high levels of self-fertilization in populations with low levels of transmission. We also observed dramatic variation in diversity and geographical differentiation in different regions. Mean heterozygosities in South American countries (0.3-0.4) were less than half those observed in African locations (0. 76-0.8), with intermediate heterozygosities in the Southeast Asia/Pacific samples (0.51-0.65). Furthermore, variation was distributed among locations in South America (F:(ST) = 0.364) and within locations in Africa (F:(ST) = 0.007). The intraspecific patterns of diversity and genetic differentiation observed in P. falciparum are strikingly similar to those seen in interspecific comparisons of plants and animals with differing levels of outcrossing, suggesting that similar processes may be involved. The differences observed may also reflect the recent colonization of non-African populations from an African source, and the relative influences of epidemiology and population history are difficult to disentangle. These data reveal a range of population structures within a single pathogen species and suggest intimate links between patterns of epidemiology and genetic structure in this organism.     

Genetic diversity and differentiation of core vs. peripheral populations of eastern white cedar, Thuja occidentalis (Cupressaceae)

? Premise of the study: Geographically peripheral (marginal) populations are expected to have lower genetic diversity and higher genetic differentiation than geographically core (central) populations as a result of supposedly lower effective population size (N(e)) and higher genetic drift, founder effect, fragmentation, and isolation in peripheral than in core populations. Here we address this issue for a long-lived plant species, eastern white cedar (Thuja occidentalis). ? Methods: Genetic diversity and population structure of 13 natural populations of eastern white cedar from its Canadian eastern peripheral and core natural ranges in New Brunswick, Nova Scotia, and Prince Edward Island were studied using six nuclear microsatellite DNA markers. ? Key results: The core populations of eastern white cedar had significantly higher allelic diversity (mean A = 8.83, A(r) = 8.13, A(e) = 4.03) and N(e) (428) than the peripheral populations (A = 6.64, A(r) = 6.15, A(e) = 3.12, N(e) = 198). However, expected heterozygosity was similar in the core (H(e) = 0.64) and peripheral (H(e) = 0.60) populations. Genetic differentiation was significantly higher among the peripheral (F(ST) = 0.089) than among the core (F(ST) = 0.032) populations. No genetic differentiation (F(ST)/Φ(RT) = 0.000) was detected between core and peripheral regions. ? Conclusions: Peripheral populations have significantly lower N(e) and genetic diversity in terms of allelic diversity (richness) and significantly higher genetic differentiation than the core populations of eastern white cedar in its Canadian eastern range. However, core and peripheral populations have similar levels of expected heterozygosity. Implications for conservation of eastern white cedar genetic resources are discussed.     

Genetic structure of populations of the human hookworm, Necator americanus, in China

Twenty-one to 58 individual Necator americanus were sampled from each of four villages in south-western China. Each nematode was sequenced for 588 bp of the mitochondrial cytochrome oxidase I gene. Allelic and nucleotide diversity varied two-fold among villages. Overall FST among populations was approximately 0.28, but this large value resulted from one low-diversity population that had a large genetic distance to the other three populations (F(ST) = 0.10 without that population). There was no correlation between geographical and genetic distance among sites. Thus, the genetic structure of this species in China may be characterized by variable effective sizes and uneven movement among sites. We discuss the implications of this genetic structure for vaccine development and the spread of drug resistance in human hookworms, and compare the genetic structure of hookworms with that of other nematodes.     

山东实生板栗居群遗传多样性ISSR分析

采用ISSR分子标记技术对山东省内的10个板栗居群共279个个体的遗传多样性水平及居群遗传结构进行了研究。10个引物共检测到116个位点,其中101个位点为多态位点,占87.07%。POPGENE分析结果表明:板栗具有丰富的遗传变异(在物种水平上,He=0.2697,H0=0.3999;在居群水平上,PPL=64.58,He=0.2004,H0=0.3010)。Neis遗传多样性分析和AMOVA分析表明,各居群间产生了一定程度的遗传分化(GST=0.2414,FST=0.2224)。居群间一定程度的遗传分化可能是由于生境破坏和基因流的障碍(Nm=0.8743)引起。UPGMA聚类分析可知,临沭、莒南、郯城和费县4个居群优先聚成一支,而莱阳居群单独聚为一支。     

Consequences of multiple mating‐system shifts for population and range‐wide genetic structure in a coastal dune plant

Evolutionary transitions from outcrossing to selfing can strongly affect the genetic diversity and structure of species at multiple spatial scales. We investigated the genetic consequences of mating‐system shifts in the North American, Pacific coast dune endemic plant Camissoniopsis cheiranthifolia (Onagraceae) by assaying variation at 13 nuclear (n) and six chloroplast (cp) microsatellite (SSR) loci for 38 populations across the species range. As predicted from the expected reduction in effective population size (N_e) caused by selfing, small‐flowered, predominantly selfing (SF) populations had much lower nSSR diversity (but not cpSSR) than large‐flowered, predominantly outcrossing (LF) populations. The reduction in nSSR diversity was greater than expected from the effects of selfing on N_e alone, but could not be accounted for by indirect effects of selfing on population density. Although selfing should reduce gene flow, SF populations were not more genetically differentiated than LF populations. We detected five clusters of nSSR genotypes and three groups of cpSSR haplotypes across the species range consisting of parapatric groups of populations that usually (but not always) differed in mating system, suggesting that selfing may often initiate ecogeographic isolation. However, lineage‐wide genetic variation was not lower for selfing clusters, failing to support the hypothesis that selection for reproductive assurance spurred the evolution of selfing in this species. Within three populations where LF and SF plants coexist, we detected genetic differentiation among diverged floral phenotypes suggesting that reproductive isolation (probably postzygotic) may help maintain the striking mating‐system differentiation observed across the range of this species.