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

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

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

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

Influence of drift and admixture on population structure of American black bears (Ursus americanus) in the Central Interior Highlands,USA, 50 years after translocation

Bottlenecks, founder events, and genetic drift often result in decreased genetic diversity and increased population differentiation. These events may follow abundance declines due to natural or anthropogenic perturbations, where translocations may be an effective conservation strategy to increase population size. American black bears (Ursus americanus) were nearly extirpated from the Central Interior Highlands, USA by 1920. In an effort to restore bears, 254 individuals were translocated from Minnesota, USA, and Manitoba, Canada, into the Ouachita and Ozark Mountains from 1958 to 1968. Using 15 microsatellites and mitochondrial haplotypes, we observed contemporary genetic diversity and differentiation between the source and supplemented populations. We inferred four genetic clusters: Source, Ouachitas, Ozarks, and a cluster in Missouri where no individuals were translocated. Coalescent models using approximate Bayesian computation identified an admixture model as having the highest posterior probability (0.942) over models where the translocation was unsuccessful or acted as a founder event. Nuclear genetic diversity was highest in the source (A_R = 9.11) and significantly lower in the translocated populations (A_R = 7.07–7.34; P = 0.004). The Missouri cluster had the lowest genetic diversity (A_R = 5.48) and served as a natural experiment showing the utility of translocations to increase genetic diversity following demographic bottlenecks. Differentiation was greater between the two admixed populations than either compared to the source, suggesting that genetic drift acted strongly over the eight generations since the translocation. The Ouachitas and Missouri were previously hypothesized to be remnant lineages. We observed a pretranslocation remnant signature in Missouri but not in the Ouachitas.     

Assessment of genetic diversity and mating system of Acacia cyclops restoration and remnant populations

Acacia cyclops, or Ngaamarur, is a common coastal shrub or small tree of the southwest of Western Australia and South Australia used for restoration in these landscapes and elsewhere. Knowledge of genetic diversity and mating systems of restoration populations is often lacking but can help inform likely restoration success. We compared genetic diversity and mating system parameters at three restoration populations of A. cyclops to nearby remnant reference populations. Mean levels of genetic diversity in restoration populations (Na = 1.806, Ne = 1.560, He = 0.270, Ho = 0.359) were not significantly different from those in the reference populations (Na = 1.833, Ne = 1.574, He = 0.269, Ho = 0.352) suggesting diverse seed collections were made for restoration. Allelic genetic divergence among restoration and reference populations was low (D_ST ≤ 0.04) suggesting that seeds were of local provenance. Mating system parameters were similar among restoration (t_m = 0.989, t_m–t_s = 0.010, r_pm = 0.392) and reference populations (t_m = 0.868, t_m–t_s = 0.039, r_pm = 0.410), suggesting functionality of the mating system and restitution of generalist insect pollinator services in restored populations at 7, 10, and 12 years after planting. Lower levels of heterozygosity in progeny compared to adults suggest post‐germination or late‐acting selection against inbred seedlings. Evidence for selection and seedling attrition further emphasizes the benefits of collections from many individuals in well‐connected outcrossed source populations. Overall, results suggest available local genetic diversity was captured and restoration populations have mating systems equivalent to those of reference populations.     

Population genetic structure of island and mainland populations of the quokka, Setonix brachyurus (Macropodidae): a comparison of AFLP and microsatellite markers

Translocation and reintroduction are important tools for the conservation or recovery of species threatened with extinction in the wild. However, an understanding of the potential genetic consequences of mixing populations requires an understanding of the genetic variation within, and similarities among, donor and recipient populations. Genetic diversity was measured using two independent marker systems (microsatellites and AFLPs) for one island and four small remnant mainland populations of Setonix brachyurus, a threatened medium sized macropod restricted to fragmented habitat remnants and two off-shore islands in southwest Australia. Microsatellite diversity in the island population (R _s = 3.2, H _e = 71%) was similar to, or greater than, all mainland populations (R _s = 2.1–3.9, H _e = 34-71%). In contrast, AFLP diversity was significantly lower in the island population (PPL = 20.5; H _j = 0.118) compared to all mainland populations (mean PPL = 79.5–89.7; mean H _j = 0.23–0.29). Microsatellites differentiated all (mainland and island) populations from each other. However, AFLP only differentiated the island population from the mainland populations—all mainland populations were not significantly differentiated from each other for this marker. Given a known time since isolation of the island population from the mainland (6,000 years ago), and an overall more conservative rate of evolution of AFLP markers, our results are consistent with mainland populations fragmenting thousands of years ago (but <6,000 years), probably as a consequence of reduced rainfall and the constriction of the preferred mesic habitat of quokkas. Our results also support a recent history of severe population bottlenecks in mainland populations, and a long history of bottlenecks of the island population, but reflect a recent explosion in numbers since European occupation of the island. Our results indicate that translocation of island populations to supplement mainland populations would introduce genetically markedly differentiated, and possibly maladapted, individuals.     

Influence of translocation strategy and mating system on the genetic structure of a newly established population of island ptarmigan

Island populations and populations established by reintroductions are prone to extinction, in part because they are vulnerable to deterministic and stochastic phenomena associated with geographic isolation and small population size. As population size declines, reduced genetic diversity can result in decreased fitness and reduced adaptive potential, which may hinder short- or long-term population viability. We used 32 microsatellite markers to investigate the conservation genetics of a newly established population of Evermann’s Rock Ptarmigan (Lagopus muta evermanni) at Agattu Island, in the western Aleutian Archipelago, Alaska. We found low genetic diversity (observed heterozygosity = 0.41, allelic richness = 2.2) and a small effective population size (N _e  = 28.6), but a relatively large N _e /N ratio = 0.55, which was attributed to multiple paternity in 80% of the broods and low reproductive skew among males (λ = 0.29). Moreover, successful breeding pairs were less related to each other than random male–female pairs. For conservation efforts based on reintroductions, a mating system with high rates of multiple paternity may facilitate retention of genetic diversity, thereby reducing the potential for inbreeding in small or isolated populations. Our results underscore the importance of quantifying genetic diversity and understanding the breeding behavior of translocated populations.     

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

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

Non‐timber Forest Product Harvest does not Affect the Genetic Diversity of a Tropical Tree Despite Negative Effects on Population Fitness

The level of genetic diversity in a population can affect ecological processes and plant responses to disturbance. In turn, disturbance can alter population genetic diversity and structure. Populations in fragmented and logged habitats often show reduced genetic diversity and increased inbreeding and differentiation. Long‐term harvesting of wild plants (for foliage, bark, and roots), can affect population genetic diversity by altering individual fitness and genetic contribution. Our understanding of these changes in genetic diversity due to the harvesting of plant organs is still limited. We used nine microsatellite markers to study the effect of long‐term bark and foliage harvest by Fulani people on the genetic diversity and structure of 12 populations of African mahogany (Khaya senegalensis) in Benin. We sampled 20 individuals in each population to test the effect of harvesting. For each population, we divided the samples equally between seedling and adults to test if the effects are stronger in seedlings. We found moderate genetic diversity (H_e = 0.53 ± 0.04) and weak but significant differentiation among local populations (F_ST = 0.043, P < 0.001). There was no significant effect of harvest on genetic diversity or structure, although previous work found significant negative effects of harvest on the reproduction of adults, offspring density, and population fitness. Our results suggest that demographic responses to disturbance precede a detectable genetic response. Future studies should focus on using parentage analysis to test if genotypes of harvested parents are directly represented in the offspring populations.     

Genetic impacts of habitat loss on the rare ironstone endemic Tetratheca paynterae subsp. paynterae

Expansion of mining in the banded ironstone ranges of southern Western Australia has focussed attention on the genetic impacts of habitat loss on rare endemic taxa. One example is Tetratheca paynterae subsp. paynterae (Elaeocarpaceae), an insect-pollinated, perennial shrub confined to 4 ha of banded ironstone outcrops in the Windarling Range. Mining removed 1,900 of the 7,700 recorded plants in 2004. Further reductions could occur if it can be demonstrated that the viability of the remaining population is not threatened. To investigate the potential impact of reductions in population size due to mining we first used Bayesian clustering and principal coordinate analysis to define population boundaries based on differentiated gene pools. The level of genetic diversity and spatial genetic structuring was then compared among populations that ranged in size from 46 to 4400 individuals. Analysis with 11 microsatellite loci revealed lower genetic diversity in small populations (A _R = 4.5–4.8) than a large population (A _R = 6.3) together with significant pair-wise differences among populations separated by distances of 80 m or more. Spatial autocorrelation analysis showed the extent of spatial genetic structure differed among populations of different size, consistent with near-neighbour mating and limited dispersal. Fine scale spatial structure was consistent with historically low gene flow. Analysis of the impact of possible expansions in mining revealed small, isolated populations of T. paynterae subsp. paynterae were of high conservation value. While their removal would reduce plant numbers and genetic diversity by less than 5%, unique genotypes will be lost resulting in a 30% decline in genetic differentiation.     

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

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

Genetic diversity,population structure,and traditional culture of Camellia reticulata

Camellia reticulata is an arbor tree that has been cultivated in southwestern China by various sociolinguistic groups for esthetic purposes as well as to derive an edible seed oil. This study examined the influence of management, socio‐economic factors, and religion on the genetic diversity patterns of Camellia reticulata utilizing a combination of ethnobotanical and molecular genetic approaches. Semi‐structured interviews and key informant interviews were carried out with local communities in China's Yunnan Province. We collected plant material (n = 190 individuals) from five populations at study sites using single‐dose AFLP markers in order to access the genetic diversity within and between populations. A total of 387 DNA fragments were produced by four AFLP primer sets. All DNA fragments were found to be polymorphic (100%). A relatively high level of genetic diversity was revealed in C. reticulata samples at both the species (H_sp = 0.3397, I_sp = 0.5236) and population (percentage of polymorphic loci = 85.63%, H_pop = 0.2937, I_pop = 0.4421) levels. Findings further revealed a relatively high degree of genetic diversity within C. reticulata populations (Analysis of Molecular Variance = 96.31%). The higher genetic diversity within populations than among populations of C. reticulata from different geographies is likely due to the cultural and social influences associated with its long cultivation history for esthetic and culinary purposes by diverse sociolinguistic groups. This study highlights the influence of human management, socio‐economic factors, and other cultural variables on the genetic and morphological diversity of C. reticulata at a regional level. Findings emphasize the important role of traditional culture on the conservation and utilization of plant genetic diversity.     

Diversity and genetic connectivity among populations of a threatened tree (<Emphasis Type="Italic">Dalbergia nigra</Emphasis>) in a recently fragmented landscape of the Brazilian Atlantic Forest

In this study we evaluated the influence of recent landscape fragmentation on the dynamics of remnant fragments from the Brazilian Atlantic Forest. This biome is one of the richest in the world and has been extensively deforested and fragmented. We sampled five populations of the threatened Dalbergia nigra, a tree endemic to the Brazilian Atlantic Forest, two located in a large reserve of continuous forest and three in fragments of different sizes and levels of disturbance. In order to assess historical changes, considering the longevity of the analyzed species, 119 adults and 116 saplings were genotyped for six microsatellite loci. Lower levels of genetic diversity were found in the most impacted fragments when compared to the most preserved population located inside the reserve, and there was significant genetic structure among the populations studied (pairwise F _ST = 0.031–0.152; pairwise D _EST = 0.039–0.301). However, genetic structure among saplings (F _ST = 0.056; D _EST = 0.231) was significantly lower than among adults (F _ST = 0.088; D _EST = 0.275). Estimates of contemporary gene flow based on assignment tests corroborated this result, suggesting that fragmentation led to an increase in gene flow. This connectivity among remnant fragments could mitigate the loss of genetic diversity through a metapopulation dynamic, but the high rate of habitat loss and the unknown long-term genetic effects add uncertainty. These results, taken together with the presence of private alleles in disturbed populations, highlight the importance of preserving the extant fragments.     

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.     

Population genetic diversity of the clonal self‐incompatible herbaceous plant Linaria vulgaris along an urbanization gradient

How increasing urbanization affects biodiversity is one of the most understudied aspects of global change biology. It is, however, known that it may negatively affect plant population genetic diversity in numerous ways, for example through its negative effects on plant population size, between‐population connectivity, and reproductive success. Therefore, it is important to investigate to what extent different levels of urbanization result in these negative phenomena. Here we used microsatellite markers to investigate urbanization effects on the population genetic structure of 23 populations of the self‐incompatible, partially clonal herb Linaria vulgaris which were sampled across a gradient of urbanization. Clonal diversity as measured by the Pareto‐parameter varied between 1.11 and 2.97 and was negatively correlated to both the degree of urbanization and to population size. Urbanization and population size were not interrelated. The least clonally rich populations also experienced significantly reduced seed set. Irrespective of the degree of urbanization, L. vulgaris populations exhibited strong genetic differentiation (F_ST = 0.33) and there was no significant correlation between genetic and geographic distances, suggesting low gene flow among populations. In conclusion, we showed that urbanization negatively affected fitness of L. vulgaris populations through decreasing their clonal diversity and reproductive success, an effect that may be exacerbated by the low gene flow between populations. Although the effect was modest, the results could probably be extrapolated to bigger cities where it would be considerably more pronounced.     

Conservation genetics of two island endemic Ribes spp. (Grossulariaceae) of Sardinia: survival or extinction?

Measuring levels of population genetic diversity is an important step for assessing the conservation status of rare or endangered plant species and implementing appropriate conservation strategies. Populations of Ribes multiflorum subsp. sandalioticum and R. sardoum, two endangered endemic species from Sardinia, representing the whole genus on the island, were investigated using ISSR and SSR markers to determine levels and structure of genetic variability in their natural populations. Results indicated medium to low genetic diversity at the population level: Nei's gene diversity for ISSR markers ranged from 0.0840 to 0.1316; the expected heterozygosity (H_E) for SSR ranged from 0.4281 to 0.7012. In addition, only one remnant population of R. sardoum showed a high level of inbreeding, in accordance with its very small size. Regarding the structure of the six R. sandalioticum populations, both principal coordinates analysis (PCoA) and STRUCTURE analysis of ISSR and SSR data highlighted low population structure, although two populations appeared to be clearly distinct from the others. The genetic pattern of the two taxa associated with their different ecological positions indicated resilience of R. sandalioticum populations in fresh and humid habitats and uncertain future resistance for the residual R. sardoum population in xeric calcareous stands. Hence, this study highlights the importance of an integrated conservation approach (genetic plus in situ and ex situ conservation studies/measures) for activating management programmes in these endemic and threatened taxa that can be considered as crop wild relatives of cultivated Ribes species.     

Can a seed bank provide demographic and genetic rescue in a declining population of the endangered shrub <Emphasis Type="Italic">Acacia pinguifolia</Emphasis>?

Many threatened species suffer reduced genetic diversity as a result of small population size and isolation. However, species with a persistent seed bank may be buffered against genetic loss as seed banks are expected to accumulate the reproductive output of many seasons. For fire-dependent species in decline, prescribed ecological burning may be a means to stimulate germination and recover genetic diversity stored in the seed bank, providing a demographic and genetic rescue effect. Here we investigated the effectiveness of this strategy in a small, isolated and inbred population of the endangered shrub, Acacia pinguifolia. We surveyed genetic diversity and structure of remnant populations of A. pinguifolia and monitored regeneration before and after burning. Germination was stimulated by fire, but seedling numbers 18 months post-fire were low and barely above the number of adults killed by the fire. Genetic diversity was marginally higher in the post-fire seedling cohort than the pre-fire adults (H_E = 0.1 vs. 0.09, respectively). Outcrossing rates of open-pollinated seed from surrounding plants suggested moderately high levels of self-fertilisation (t _m  = 0.65) and analysis of fine-scale genetic structure implied pollen and seed dispersal over distances of several metres, suggesting that restricted gene flow and inbreeding may act to limit genetic diversity in the seed bank. We conclude that prescribed burning has not been immediately successful as a recovery strategy for this relictual population of A. pinguifolia, though future monitoring may detect additional recruits. Alternative conservation strategies, including performing inter-population crosses, may be required to restore genetic diversity and ameliorate extinction risks.     

Genetic diversity within a threatened,endemic North American species, <Emphasis Type="Italic">Euphorbia telephioides</Emphasis> (Euphorbiaceae)

The southeastern United States and Florida support an unusually large number of endemic plant species, many of which are threatened by anthropogenic habitat disturbance. As conservation measures are undertaken and recovery plans designed, a factor that must be taken into consideration is the genetic composition of the species of concern. Here we describe the levels, and partitioning, of genetic diversity in 17 populations of the rare and threatened Florida endemic, Euphorbia telephioides (telephus spurge). Species-wide genetic diversity was high (P_s = 91%, AP_s = 3.81, A_s = 3.57 and H_es = 0.352) as was mean population genetic diversity (P_p = 81%, AP_p = 2.98, A_p = 2.59 and H_ep = 0.320) which ranks it among the highest 10% of plant species surveyed. Partitioning of genetic variation (G_st = 0.106) was low compared to other herbaceous outcrossing perennials indicating high historical gene flow across its limited geographic range. Among population G_st values within the three Florida counties in which it occurs, Gulf (0.084), Franklin (0.059) and Bay Counties (0.033), were also quite low. Peripheral populations did not generally have reduced genetic variation although there was significant isolation by distance. Rarefaction analysis showed a non-significant relationship between allelic richness and actual population sizes. Our data suggest that E. telephioides populations were probably more continuously distributed in Bay, Gulf and Franklin Counties and that their relative contemporary isolation is a recent phenomenon. These results are important for developing a recovery plan for this species.     

Population genetic structure of the endangered and endemic medicinal plant <Emphasis Type="Italic">Commiphora</Emphasis><Emphasis Type="Italic">wightii</Emphasis>

Commiphora wightii is a medicinally important endangered species endemic to the Thar Desert of Rajasthan, India and adjoining areas of Pakistan. The populations of this species are declining sharply because of its extensive use as a natural herb. Random amplified polymorphic DNA analysis was conducted to find the genetic variation among 7 populations of C. wightii. Of the 100 random primers screened, 44 primers yielded 220 loci. Statistical analysis indicated low genetic diversity (H _pop = 0.0958; I = 0.1498; mean polymorphic loci = 14.28%), and high genetic differentiation among the populations (G _ST = 0.3990; AMOVA Φ _ST of 0.3390; Bayesian θ ^(II) = 0.3002). The low genetic diversity may be due to geographic isolation and restricted gene flow (N _m = 0.7533) between the fragmented populations. Unsustainable utilization of the plant has fragmented the population continuum which served the purpose of genetic exchange between populations. Mantel’s test was performed which revealed a highly significant positive correlation between genetic and geographic distance (r ² = 0.614, P = 0.023) among the populations studied. Low variation can also be attributed to poor seed setting and the slow growth pattern of the species, which is also an apomict. In UPGMA dendrogram the Commiphora wightii samples were divided into two major and one minor cluster. These findings can serve as a guide to preserving the genetic resources of this medicinal plant species.     

Highly differentiated populations of the narrow endemic and endangered species Primula cicutariifolia in China,revealed by ISSR and SSR

The perennial herb Primula cicutariifolia Pax is an endangered and endemic species with narrow distribution in eastern Anhui and Zhejiang provinces of China. In this study, the levels of genetic variation and the pattern of genetic structure in five natural populations of P. cicutariifolia were assessed by inter-simple sequence repeats (ISSR) and simple sequence repeat (SSR) markers. Both markers revealed that there was remarkably low genetic variation within populations (e.g., H_e = 0.19 and 0.18, for ISSR and SSR respectively) and high differentiation among populations (G_ST = 0.714 and 0.611; Φ_ST = 0.698 and 0.599, for ISSR and SSR respectively). The level of population genetic diversity was correlated to population size only detected by ISSR markers. The genetic structure of P. cicutariifolia may be explained by limited gene flow that was caused by habitat fragmentation and limited seeds and pollen dispersal ability, self breeding system and biennial life form. To protect and avoid disappearance of P. cicutariifolia, much more attentions should be paid to protect all the remnant populations and their habitats, and three management units, i.e. Tianmushan, Damodao, and Panan units, were proposed.     

Population genetic structure of <Emphasis Type="Italic">Tamarix chinensis</Emphasis> in the Yellow River Delta,China

Tamarix chinensis, with its important ecological significance, is a vital dominant plant in the Yellow River Delta of China. To understand its genetic structure and population dynamics, five populations of T. chinensis, consisting of 140 individuals, were analyzed in this study using inter simple sequence repeat markers. Seventy-eight polymerase chain reaction fragments were scored, of which 62 were polymorphic. The mean percentage of polymorphic loci (P), the mean Nei’s gene diversity (h), and the mean Shannon’s information index (I) were 79.5%, 0.239, and 0.363, respectively. These indexes indicated that a moderate level of genetic diversity existed in T. chinensis populations of the Yellow River Delta. Both analysis of molecular variance (AMOVA) (Φ _st = 0.169) and Popgene (G _st = 0.159) analyses revealed the low level of genetic differences among the five populations of T. chinensis. The results implied that relatively frequent gene flow existed among populations. However, slightly uneven genetic diversity was also found among populations. Unweighted pair group method with arithmetic mean and principal component analysis showed that populations with similar soil salinity had a close relationship, rather than populations with closer geographical distance. A significant negative correlation between genetic diversity and soil salinity of the five populations (r = −0.958, p < 0.01) showed that soil salinity played an important role in shaping the population genetic structure of T. chinensis in the Yellow River Delta, China.