Partitioning Of Genetic Variation Research Articles

Clonality contributes to the spread of Avrainvillea lacerata (Bryopsidales, Chlorophyta) in Hawai'i.

The relative rates of sexual versus asexual reproduction influence the partitioning of genetic diversity within and among populations. During range expansions, asexual reproduction often facilitates colonization and establishment. The arrival of the green alga Avrainvillea lacerata has caused shifts in habitat structure and community assemblages since its discovery in 1981 offshore of O'ahu, Hawai'i. Field observations suggest this species is spreading via vegetative reproduction. To characterize the reproductive system of A. lacerata in Hawai'i, we developed seven microsatellite loci and genotyped 321 blades collected between 2018 and 2023 from three intertidal sites at Maunalua Bay and 'Ewa Beach. We observed one to four alleles at multiple loci, suggesting A. lacerata is tetraploid. Each site was characterized by high genotypic richness (R > 0.8). However, clonal rates were also high, suggesting the vegetative spread of A. lacerata plays a significant role. The importance of clonal reproduction for the persistence of A. lacerata in Hawai'i is consistent with the ecological data collected for this species and observations of other abundant macroalgal invaders in Hawai'i and other regions of the world. These data demonstrate the necessity for implementing appropriate population genetic methods and provide insights into the biology of this alga that will contribute to future studies on effective management strategies incorporating its reproductive system. This study represents one of the few that investigate green algal population genetic patterns and contributes to our understanding of algal reproductive system evolution.

Estimation of Genetic Diversity between and within Biparental Clones and Full-Sib Families of the Chinese Pine Using SSR Markers

Quantifying the genetic diversity present in plant populations is crucial for the success of selection of elite plants and breeding programs. The population structure and partition of genetic variance within and between plant populations allows inferences about the distribution and extent of variation available in plant breeding populations. The Chinese pine (Pinus tabuliformis Carriere) is a native species that is ecologically and economically important to Northern China. Studying the genetic variation and partition of P. tabuliformis will be invaluable for its efficient utilization. In this study, we selected 21 pairs of SSR primers to estimate the genetic diversity of 35 clones from four populations and 216 progenies from 22 full-sib families of P. tabuliformis. Our results showed that P. tabuliformis was a typical outcrossing plant (FIS = −0.053/−0.165) containing moderately high genetic diversity (He = 0.542/0.605) both for the clone populations and the progenies produced by the clone crosses via controlled pollination. The genetic differentiation between the clones (FST = 0.076) was lower than that between the full-sib progenies (FST = 0.155). Such diverse FST may be promoted by different gene flows (Nm = 3.881/1.546) due to distinct pollination patterns. The clustering methods showed a lack of significant division of the clone populations, with a similar genetic admixture found for each of the clones. However, two groups were found between the full-sib families with genetic admixture between them. The analysis of molecular variance (AMOVA) showed that the most plentiful genetic variability exists between the cloned individuals (98%) as well as within the full-sib progenies (89%). Such distribution of genetic variation suggests rich internal variance and thus it is feasible to select the elite plants within each population or family. These results provide genetic materials and theoretical guidance for the selection and breeding of the Chinese pine.

High-Throughput Microsatellite Markers Development for Genetic Characterization of Emerging Sporothrix Species.

Sporotrichosis is the main subcutaneous mycosis worldwide transmitted by animal or plant vectors and often escalates to outbreaks or epidemics. The current cat-transmitted sporotrichosis driven by Sporothrix brasiliensis has become a significant public health issue in South America. Transmission dynamics remain enigmatic due to the lack of development of polymorphic markers for molecular epidemiological analysis. This study used a high-throughput mining strategy to characterize simple sequence repeat (SSR) markers from Sporothrix genomes. A total of 118,140-143,912 SSR loci were identified (82,841-98,369 unique markers), with a 3651.55-3804.65 SSR/Mb density and a majority of dinucleotides motifs (GC/CG). We developed a panel of 15 highly polymorphic SSR markers suitable for genotyping S. brasiliensis, S. schenckii, and S. globosa. PCR amplification revealed 240 alleles in 180 Sporothrix isolates with excellent polymorphic information content (PIC = 0.9101), expected heterozygosity (H = 0.9159), and discriminating power (D = 0.7127), supporting the effectiveness of SSR markers in uncovering cryptic genetic diversity. A systematic population genetic study estimated three clusters, corresponding to S. brasiliensis (population 1, n = 97), S. schenckii (population 2, n = 49), and S. globosa (population 3, n = 34), with a weak signature of mixed ancestry between populations 1 and 2 or 3 and 2. Partitioning of genetic variation via AMOVA revealed highly structured populations (ΦPT = 0.539; Nm = 0.213; p < 0.0001), with approximately equivalent genetic variability within (46%) and between (54%) populations. Analysis of SSR diversity supports Rio de Janeiro (RJ) as the center of origin for contemporary S. brasiliensis infections. The recent emergence of cat-transmitted sporotrichosis in northeastern Brazil indicates an RJ-Northeast migration resulting in founder effects during the introduction of diseased animals into sporotrichosis-free areas. Our results demonstrated high cross-species transferability, reproducibility, and informativeness of SSR genetic markers, helping dissect deep and fine-scale genetic structures and guiding decision making to mitigate the harmful effects of the expansion of cat-transmitted sporotrichosis.

Conservation genomics of urban populations of Streamside Salamander (Ambystoma barbouri).

In Tennessee, populations of the state endangered Streamside Salamander (Ambystoma barbouri) are in decline as their distribution lies mostly within rapidly developing areas in the Nashville Basin. Information regarding the partitioning of genetic variation among populations of A. barbouri and the taxonomic status of these populations relative to northern populations and their congener, the Small-mouthed Salamander (A. texanum), have important implications for management and conservation of this species. Here we combined mitochondrial sequencing and genome-wide single nucleotide polymorphism (SNP) data generated using Genotyping-by-Sequencing (GBS) to investigate patterns of genetic variation within Tennessee populations of A. barbouri, to assess their relationship to populations in Kentucky, and to examine their phylogenetic relationship to the closely related A. texanum. Results from phylogenetic reconstructions reveal a complex history of Tennessee A. barbouri populations with regards to northern populations, unisexual A. barbouri, and A. texanum. Patterns of mitochondrial sequence variation suggest that A. barbouri may have originated within Tennessee and expanded north multiple times into Kentucky, Ohio, Indiana, and West Virginia. Phylogenetic reconstructions based on genome-wide SNP data contradict results based on mitochondrial DNA and correspond to geographic and taxonomic boundaries. Variation in allele frequencies at SNP genotypes, as identified by multivariate analyses and Bayesian assignment tests, identified three evolutionary significant units (ESUs) for A. barbouri within Tennessee. Collectively, these results emphasize the need for prioritizing conservation needs for Tennessee populations of A. barbouri to ensure the long-term persistence of this species.

Population structure and adaptive variation of Helichrysum italicum (Roth) G. Don along eastern Adriatic temperature and precipitation gradient

Immortelle (Helichrysum italicum (Roth) G. Don; Asteraceae) is a perennial plant species native to the Mediterranean region, known for many properties with wide application mainly in perfume and cosmetic industry. A total of 18 wild H. italicum populations systematically sampled along the eastern Adriatic environmental gradient were studied using AFLP markers to determine genetic diversity and structure and to identify loci potentially responsible for adaptive divergence. Results showed higher levels of intrapopulation diversity than interpopulation diversity. Genetic differentiation among populations was significant but low, indicating extensive gene flow between populations. Bayesian analysis of population structure revealed the existence of two genetic clusters. Combining the results of FST - outlier analysis (Mcheza and BayeScan) and genome-environment association analysis (Samβada, LFMM) four AFLP loci strongly associated with the bioclimatic variables Bio03 Isothermality, Bio08 Mean temperature of the wettest quarter, Bio15 Precipitation seasonality, and Bio17 Precipitation of driest quarter were found to be the main variables driving potential adaptive genetic variation in H. italicum along the eastern Adriatic environmental gradient. Redundancy analysis revealed that the partitioning of genetic variation was mainly associated with the adaptation to temperature oscillations. The results of the research may contribute to a clearer understanding of the importance of local adaptations for the genetic differentiation of Mediterranean plants and allow the planning of appropriate conservation strategies. However, considering that the identified outlier loci may be linked to genes under selection rather than being the target of natural selection, future studies must aim at their additional analysis.

Are small populations larger than they seem? Genetic insights into patchily distributed populations ofDrakaea glyptodon(Orchidaceae)

AbstractMany orchids are characterized by small, patchily distributed populations. Resolving how they persist is important for understanding the ecology of this hyper-diverse family, many members of which are of conservation concern. Ten populations of the common terrestrial orchid Drakaea glyptodon from south-western Australia were genotyped with ten nuclear and five plastid simple sequence repeat (SSR) markers. Levels and partitioning of genetic variation and effective population sizes (Ne) were estimated. Spatial genetic structure of nuclear diversity, together with plastid data, were used to infer the effective number of seed parents per population. We found high genetic diversity, Ne values that generally exceed predictions based on the number of flowering individuals and moderate levels of gene flow. Two populations were founded by less than five colonists suggesting some populations are colonized by few seeds, with growth largely resulting from in situ recruitment. A value of 3.65 for mp /ms indicates that pollinators play a greater role than seed in introducing genetic diversity to populations via gene flow. Our results highlight that D. glyptodon is highly effective at persisting in patchily distributed populations. However, it is important to examine how insights from this common, widespread species transfer to species that are rare and/or occur in fragmented landscapes.

Triple full‐sibs: A method for estimating components of genetic variance and progeny selection in plants

AbstractQuantifying the genetic variability present in plant populations is crucial for the success of selection plans. The partitioning of genetic variance into its components allows inferences about the inheritance of quantitative traits and prediction of the gain from selection. The present study aimed to present an alternative method to estimate components of genetic variance with applications in recurrent selection. The mating scheme is based on biparental cyclic crossing involving three parents in each chain, here called the triple full‐sibs (TFS) family, each of which is composed of three biparental progenies in which individuals are full‐sibs within each progeny and half‐sibs among progenies. The progenies are evaluated in experimental trials, and the total effect of progenies is hierarchically partitioned into the effects of TFS families and progenies within families. From the components of variance, additive and dominance variance, as well as the associated errors, can be estimated. Simulated data are used to illustrate the method of analysis and parameter estimation. The method combines the advantages of North Carolina Design I regarding estimation of variance components with the practicality of conventional full‐sib selection. The TFS method allows different selection strategies according to the selection unit and provides expected genetic gain equal to or greater than unrelated full‐sib selection. There is no further advantage to using more than three parents in each chain‐cross.

Genomic Variation Shaped by Environmental and Geographical Factors in Prairie Cordgrass Natural Populations Collected across Its Native Range in the USA.

Prairie cordgrass (Spartina pectinata Link) is a native perennial warm-season (C4) grass common in North American prairies. With its high biomass yield and abiotic stress tolerance, there is a high potential of developing prairie cordgrass for conservation practices and as a dedicated bioenergy crop for sustainable cellulosic biofuel production. However, as with many other undomesticated grass species, little information is known about the genetic diversity or population structure of prairie cordgrass natural populations as compared to their ecotypic and geographic adaptation in North America. In this study, we sampled and characterized a total of 96 prairie cordgrass natural populations with 9315 high quality SNPs from a genotyping-by-sequencing (GBS) approach. The natural populations were collected from putative remnant prairie sites throughout the Midwest and Eastern USA, which are the major habitats for prairie cordgrass. Partitioning of genetic variance using SNP marker data revealed significant variance among and within populations. Two potential gene pools were identified as being associated with ploidy levels, geographical separation, and climatic separation. Geographical factors such as longitude and altitude, and environmental factors such as annual temperature, annual precipitation, temperature of the warmest month, precipitation of the wettest month, precipitation of Spring, and precipitation of the wettest month are important in affecting the intraspecific distribution of prairie cordgrass. The divergence of prairie cordgrass natural populations also provides opportunities to increase breeding value of prairie cordgrass as a bioenergy and conservation crop.

Genetic connectivity between Atlantic bluefin tuna larvae spawned in the Gulf of Mexico and in the Mediterranean Sea.

The highly migratory Atlantic bluefin tuna (ABFT) is currently managed as two distinct stocks, in accordance with natal homing behavior and population structuring despite the absence of barriers to gene flow. Larval fish are valuable biological material for tuna molecular ecology. However, they have hardly been used to decipher the ABFT population structure, although providing the genetic signal from successful breeders. For the first time, cooperative field collection of tuna larvae during 2014 in the main spawning area for each stock, the Gulf of Mexico (GOM) and the Mediterranean Sea (MED), enabled us to assess the ABFT genetic structure in a precise temporal and spatial frame exclusively through larvae. Partitioning of genetic diversity at nuclear microsatellite loci and in the mitochondrial control region in larvae spawned contemporarily resulted in low significant fixation indices supporting connectivity between spawners in the main reproduction area for each population. No structuring was detected within the GOM after segregating nuclear diversity in larvae spawned in two hydrographically distinct regions, the eastern GOM (eGOM) and the western GOM (wGOM), with the larvae from eGOM being more similar to those collected in the MED than the larvae from wGOM. We performed clustering of genetically characterized ABFT larvae through Bayesian analysis and by Discriminant Analysis of Principal Components (DAPC) supporting the existence of favorable areas for mixing of ABFT spawners from Western and Eastern stocks, leading to gene flow and apparent connectivity between weakly structured populations. Our findings suggest that the eastern GOM is more prone for the mixing of breeders from the two ABFT populations. Conservation of this valuable resource exploited for centuries calls for intensification of tuna ichthyoplankton research and standardization of genetic tools for monitoring population dynamics.

Decreased coevolutionary potential and increased symbiont fecundity during the biological invasion of a legume-rhizobium mutualism.

Although most invasive species engage in mutualism, we know little about how mutualism evolves as partners colonize novel environments. Selection on cooperation and standing genetic variation for mutualism traits may differ between a mutualism's invaded and native ranges, which could alter cooperation and coevolutionary dynamics. To test for such differences, we compare mutualism traits between invaded- and native-range host-symbiont genotype combinations of the weedy legume, Medicago polymorpha, and its nitrogen-fixing rhizobium symbiont, Ensifer medicae, which have coinvaded North America. We find that mutualism benefits for plants are indistinguishable between invaded- and native-range symbioses. However, rhizobia gain greater fitness from invaded-range mutualisms than from native-range mutualisms, and this enhancement of symbiont fecundity could increase the mutualism's spread by increasing symbiont availability during plant colonization. Furthermore, mutualism traits in invaded-range symbioses show lower genetic variance and a simpler partitioning of genetic variance between host and symbiont sources, compared to native-range symbioses. This suggests that biological invasion has reduced mutualists' potential to respond to coevolutionary selection. Additionally, rhizobia bearing a locus (hrrP) that can enhance symbiotic fitness have more exploitative phenotypes in invaded-range than in native-range symbioses. These findings highlight the impacts of biological invasion on the evolution of mutualistic interactions.

Ecological niche modelling and phylogeography reveal range shifts of pawpaw, a North American understorey tree

AbstractAimPredictions of species' responses to accelerating global climate change require an understanding of historical range shifts. However, large‐scale phylogeographical studies of Eastern North American understorey plant taxa are relatively scarce. Here we employ ecological niche modelling and genetic analyses for inference of optimal pawpaw habitat in the past and future.LocationIn all, 26 states in the eastern United States.TaxonAsimina triloba (L.) Dunal (Annonaceae).MethodsThe present‐day niche of Asimina triloba was modelled in Maxent using seven bioclimatic variables, elevation and location data from field samples and herbarium specimens. To model historically optimal habitats, the present‐day model was projected onto rasters of seven bioclimatic variables and elevation representing the last glacial maximum (~22,000 years before present [YBP]) and the mid‐Holocene (~6,000 YBP). Predicted habitat suitability for 2070 was also modelled. Additionally, 62 populations were genotyped with nine nuclear microsatellite loci and statistically analysed. Levels and partitioning of genetic variation within and among populations were estimated within a geographical context.ResultsModels indicate that optimal habitat 22,000 YBP was severely restricted to mostly now‐submerged Gulf of Mexico and southeastern US coastlines. By 2070, models suggest that optimal habitat will expand substantially northward relative to the present. Species‐level genetic diversity (HE = 0.765) is high and genetic structure among populations is moderate (GST = 0.202). Structure indicates that there are two population clusters straddling the Appalachian Mountains.Main conclusionsModels suggest that 22,000 YBP A. triloba was restricted to two major refugia in narrow bands of mostly now‐submerged habitat and possibly several small inland refugia. Molecular data are consistent suggesting that the eastern refugia expanded to give rise to the eastern cluster which is characterized by higher genetic diversity. The Gulf of Mexico refugium likely gave rise to populations in the western cluster, which is characterized by lower genetic diversity.

Integrating Genetics and Metapopulation Viability Analysis to Inform Translocation Efforts for the Last Northern Leopard Frog Population in Washington State, USA

Population genetic and population viability analyses are powerful instruments that can be used to evaluate the status o populations of conservation concern. However, these two methods are rarely integrated. To better understand the status of the last know Northern Leopard Frog (Lithobates pipiens) population in Washington state, USA, and investigate the potential for translocation efforts we analyzed 96 genetic samples from 2004 and 294 genetic samples from 2014 by using seven microsatellite loci and integrate population genetic data with population viability models. Partitioning of genetic diversity indicated the presence of thre subpopulations in the area, aligning with Washington Department of Fish and Wildlife subunit designation within the watershed. I both years, heterozygosity and average number of alleles per locus were low for all subpopulations (0.20–0.36 and 1.86–2.50, respectively) Point estimates of gene flow out of two of the three subpopulations decreased from 2004 to 2014 based on G″ST (a measure of geneti differentiation) and migration estimates from BayesAss. Summed effective population size for the entire area by using tempora estimates was estimated to be small, with large amounts of uncertainty (sum of 98.4 individuals, 95% confidence interval: 15.6–infinit individuals). Population viability models using genetic estimates of number of adults and migration rates suggest that adults may be th optimal life history stage for successful direct translocation; however, because only metamorphs can be routinely collected, translocatio with head-starting was modeled and active management strategies may be necessary to establish new populations.

303 ASAS-EAAP Talk: On the estimation of genetic parameters from molecular data

Abstract We deal with several problems that arise when inferring genetic parameters at the level of quantitative trait loci (QTL) from molecular data such as SNP markers. Linkage Disequilibrium (LD) is recognized as a factor creating ambiguity in the partition of genetic variance. Here, using a simple model with three loci (one QTL and two markers), it is shown that the markers generate apparent AxA and DxD epistasis, even if only third order disequilibrium exists and the QTL is dominant. The problem of “phantom epistasis” is not alleviated by larger sample sizes (de los Campos et al., 2019). We also show that markers can give a distorted picture of the genetic correlation between traits: The genomic correlation could be greater, lower or even of opposite sign than the true genetic correlation. Therefore, speculating about genetic correlations and even about their causes (e.g., pleiotropy) using genomic data is often conjectural. Thirdly, we examine the problem of directional selection generating negative linkage disequilibrium (“Bulmer effect”) in the short term from a genomic selection perspective. It seems that the reduction in response due to the Bulmer effect is the same for genomic selection as for selection based on traditional BLUP. However, the reduction in response with genomic selection is greater than when selection is based directly on phenotypes only (Van Grevenhof et al. 2012). It is also expected that directional selection for a polygenic trait should increase recombination rate, provided there is genetic variance for recombination. It is then of relevance to ask whether recombination rates could be manipulated in order to increase selection response (Battagin et al., 2016). Finally, we consider that recombination and epistasis are closely intertwined: Epistasis generate LD and recombination break them up. Then, we should expect genomes to be modular: regions with low recombination containing functionally related genes loosely linked to other regions.

Assessing under-Estimation of Genetic Diversity within Wild Potato (Solanum) Species Populations

Genebanks seek to understand the partitioning of genetic diversity among species, populations, and individuals in their collections since this informs decisions for adopting the most effective sampling strategy. Recent reports have suggested that diploid wild species have much less heterogeneity within populations than cultivated forms. We here review past empirical phenotypic trait variation data and examine previous and new DNA marker datasets. We also examine simulation datasets and calculations designed to mimic the effects of artificial biases against wild species heterozygosity due to ascertainment, ploidy, and allele frequencies. Trait data suggests large practical variation exists within populations. Similarly, DNA markers on multiple individuals within diploid wild potato species populations show that substantial heterogeneity in a species is partitioned within populations. Simulations illustrate that biases due to ascertainment, ploidy, and allele frequencies account for much of the apparent homogeneity of wild diploid potato species.

Evolutionary responses of marine organisms to urbanized seascapes.

Many of the world's major cities are located in coastal zones, resulting in urban and industrial impacts on adjacent marine ecosystems. These pressures, which include pollutants, sewage, runoff and debris, temperature increases, hardened shorelines/structures, and light and acoustic pollution, have resulted in new evolutionary landscapes for coastal marine organisms. Marine environmental changes influenced by urbanization may create new selective regimes or may influence neutral evolution via impacts on gene flow or partitioning of genetic diversity across seascapes. While some urban selective pressures, such as hardened surfaces, are similar to those experienced by terrestrial species, others, such as oxidative stress, are specific to aquatic environments. Moreover, spatial and temporal scales of evolutionary responses may differ in the ocean due to the spatial extent of selective pressures and greater capacity for dispersal/gene flow. Here, we present a conceptual framework and synthesis of current research on evolutionary responses of marine organisms to urban pressures. We review urban impacts on genetic diversity and gene flow and examine evidence that marine species are adapting, or are predicted to adapt, to urbanization over rapid evolutionary time frames. Our findings indicate that in the majority of studies, urban stressors are correlated with reduced genetic diversity. Genetic structure is often increased in urbanized settings, but artificial structures can also act as stepping stones for some hard‐surface specialists, promoting range expansion. Most evidence for rapid adaptation to urban stressors comes from studies of heritable tolerance to pollutants in a relatively small number of species; however, the majority of marine ecotoxicology studies do not test directly for heritability. Finally, we highlight current gaps in our understanding of evolutionary processes in marine urban environments and present a framework for future research to address these gaps.

The influence of fire and silvicultural practices on the landscape-scale genetic structure of an Australian foundation tree species

Natural disturbance regimes in forest ecosystems are being rapidly modified by anthropogenic pressures, including silvicultural practices and climate change. Australian forests dominated by mountain ash (Eucalyptus regnans) are critically endangered, with wildfires and clearfell logging predicted to cause ecosystem collapse within the next 50 years. To investigate the influence of disturbance on patterns and extent of genetic diversity in mountain ash, we compare replicated sites with three different disturbance histories (undisturbed, burnt, and logged). We employ genetic analysis at five chloroplast microsatellite loci and 2866 nuclear single-nucleotide polymorphisms (SNPs) to estimate within- and among- population genetic diversity, and assess the extent of fine-scale spatial genetic structure among individuals, for the three disturbance treatments. Consistent with the expectation of extensive pollen dispersal but limited seed dispersal, we detected low levels of genetic differentiation at nuclear SNPs (FST = 0.067), and very high levels of differentiation at cpDNA microsatellites (FST = 0.751). While differences among treatments at nuclear SNPs were small, we found stronger spatial genetic structure in the undisturbed treatment, higher levels of genetic differentiation in the logged treatment and greater partitioning of genetic diversity among logged sites. Analysis of cpDNA revealed significantly higher levels of total and within-site genetic diversity in the logged treatment than the burnt or undisturbed treatments, with haplotypes entering the system via the use of non-local seed in the regeneration process. We suggest that artificial regeneration activities should utilise a greater number of maternal parents, which could be achieved via variable retention harvesting or utilising a regional admixture provenancing approach.

Strong genetic differentiation among populations of Fosterella rusbyi (Bromeliaceae) in Bolivia

AbstractThe terrestrial bromeliad Fosterella rusbyi is endemic to the Bolivian Andes, where it mainly grows on steep, exposed slopes along roadsides and riverbeds in the seasonally dry tropical forest (SDTF) and the mesic montane forest (Yungas) biomes. We hypothesize that allopatric speciation may have been a main driver of diversification in Fosterella since the Miocene and that the scattered distribution of suitable habitats fostered the evolution of the high degree of endemism observed today. To provide further information relating to this hypothesis, we analysed the partition of genetic diversity and the extent of gene flow among natural populations of F. rusbyi using plastid and nuclear microsatellite markers. Nineteen plastid haplotypes were found, but the mean haplotype diversity per population was low. Nuclear microsatellite markers revealed 177 different multilocus genotypes (MLGs), of which 31 occurred in more than one plant. Recurrent MLGs were found in 76 plants that were therefore identified as clones. A considerable deficit of heterozygotes was detected at all nuclear loci. Geographical and genetic distances between populations were only weakly correlated with each other. Genetic divergence between populations was extremely high for both marker classes, suggesting that seed and pollen flow are low, even over short distances. The observed patterns are consistent with our hypothesis that newly available sites are sporadically colonized by one or a few founders, followed by in situ population expansion via vegetative propagation, self-pollination and/or biparental inbreeding, genetic differentiation among persistent populations and, ultimately, allopatric speciation.

Distribution, habitat profile and genetic variability of Namibian succulent Lithops ruschiorum

Background: The species-rich flora of southern Africa comprises a high number of endemics, including succulents such as the flowering stones in the genus Lithops, but conservation status for these species is not well underpinned because detailed field data and assessments of genetic diversity are lacking.Objectives: We wanted to assess plant abundance and identify factors that may affect survival in Lithops ruschiorum through carefully conducted field surveys, and to determine amount and partitioning of genetic variation by amplified fragment length polymorphism (AFLP) analysis.Method: Field surveys were carried out in nine populations in Namibia. The most meticulously studied population was divided into 51 sites, while another 43 sites were recognised in the remaining eight populations. At each site, occupied area and number of plants were recorded as well as altitude, aspect, slope, soil texture and substrate. Amplified fragment length polymorphism markers were employed to study 52 individuals from seven populations.Results: In total, 8465 individuals were recorded. Plant density and/or plant number was associated with aspect, slope, soil texture, substrate and geographic distance from the coast. Analysis of molecular variation showed that 95% of the variability occurs within populations. Genetic and geographic distances among populations were correlated suggesting an isolation-by-distance pattern.Conclusion: Results are concordant with a strong impact of fog-based precipitation on plant density in the coastal populations, whereas rain probably is more important at one population which is situated further inland. Within-population genetic variation was medium high as usually reported for perennial, outcrossing species, but the low population differentiation implies considerable gene flow and/or population fragmentation.

Analysis of genetic diversity and spatial structure in Tunisian populations ofHordeum marinumssp.marinumbased on molecular markers

AbstractHordeum marinumcommonly known as sea barley is a salinity-tolerant species of grass. In the current study, 150 lines from ten populations ofH. marinumssp.marinumcollected from five Tunisian bioclimatic sites were screened for polymorphism with 13 selected random amplified polymorphic DNA primers. Results exhibited a high level of polymorphism (160 polymorphic bands with an average of 12.46 per primer) and a high level of genetic diversity in all the studied populations (on averageUHe= 0.247 andI= 0.358). High discrimination capacity was found for the 13 primers and a combination of three allowed assignation of a unique profile for each of the 150 lines. The partition of genetic diversity with Analysis of Molecular Variance suggested that the majority of genetic variation (67%) was within populations. The components between-populations within ecoregions and between-ecoregions explained 21 and 12%, respectively, of the total genetic variance. There was no significant association of population differentiation (ФPT) with geographical distance or altitudinal difference. Results also showed that the 150 lines grouped into three clusters with no respect to geographic origin. A sub-set of 13 lines was identified, which captured the maximum genetic diversity of the entire collection. The genetic variation found in this collection ofH. marinumis deemed to be useful in formulating conservation strategies for this species.

An approach to genetic resources conservation of peripheral isolated plant populations: the case of an island narrow endemic species

This study reinforces the argument that forest genetic resources for peripheral isolated plant populations (PIPP) need to come under rationalistic assessment, for developing and proposing conservation strategies of forest genetic resources. Cedrus brevifolia is a narrow endemic island tree occurring in a sole population. Using biparentally and paternally inherited microsatellites, the genetic contribution and genetic variation patterns within sites (subpopulations) and within plantations of this species were assessed. The C. brevifolia population recorded uneven partition of genetic diversity at the site and at local scales; mirroring the demography and genetic evolutionary factors that occurred in long-term at the intra-species level. Results from the plantations imply that screening and rejection of unsuitable seedlings before plantation establishment did not influence the genetic divergence of planted trees from the general genetic pool of natural population. Based on these outcomes, numerous conservation measures are proposed, towards maintaining the species’ genetic resources. These measures need to ensure the dynamic processes within stands. Thus, this study argues that for PIPP which recorded high genetic diversity and non-uniform distribution of genetic viability (complex genetic patterns), the several small conservation units seem to be the most rationalistic conservation units. In such case, forest genetic micro-reserves (GMR) can be enacted, where on-the-point dynamic in situ conservation activities can be adopted, while the GMR could be used for ex situ conservation purposes. In conclusion, in PIPP the maintenance of genetic diversity should be regarded as one of the main prerequisites for sustainable management and long-term survival of the species.