Genetic diversity of Typha latifolia (Typhaceae) and the impact of pollutants examined with tandem-repetitive DNA probes

Genetic diversity at variable-number-tandem-repeat (VNTR) loci was examined in the common cattail, Typha latifolia (Typhaceae), using three synthetic DNA probes composed of tandemly repeated “core” sequences (GACA, GATA, and GCAC). The principal objectives of this investigation were to determine whether: (1) the previously reported almost complete lack of polymorphism at allozyme loci in this species was indicative of a reduced amount of genetic diversity at VNTR loci as well; (2) VNTR markers were informative about possible clonal propagation; and (3) significant differences in genetic structure of sampling sites were associated with differences in environmental levels of pollutants at those sites. Previously, widespread sampling across the eastern United States, surveying across ten allozyme loci, has detected only two genotypes, involving a difference at a single locus, among 104 populations. In this study, the amount of genetic diversity detected at VNTR loci: (1) among ramets (N = 40; 40 genotypes detected) collected at ∼8-km intervals along a 320-km transect; (2) among ramets (N = 220; 117 genotypes detected) from five study sites separated by 50–3000 m; and (3) even among ramets within each study site [N = 44 per site; from 13 to 34 genotypes detected per site (270 m²)] exceeds that previously found in those more geographically widespread allozyme surveys. Among the 260 ramets analyzed here, the mean number of bands scored per individual was 48.61 (SD = 2.80). Mean genetic similarity among ramets collected along the 320-km transect was 0.91, which was within the range of mean genetic similarity within the five study sites (range: 0.89–0.95). Among the five study sites, 61% of the samples analyzed appeared to be clonal ramets, with up to 12 clones detected for 44 ramets sampled within a site. Clones grew intermingled and ranged up to 39 m in extent. Permutation tests of genetic similarity revealed significant genetic differentiation between each of the five study sites. Consistent with the previous allozyme studies, T. latifolia was characterized by extremely low genetic variation relative to levels of polymorphism detected at VNTR loci in other plant species. Estimated heterozygosity among ramets along the 320-km transect ranged from 0.11 to 0.13, while that within the five study sites ranged from 0.05 to 0.12. Estimates of F_st (0.32–0.41) also indicated considerable genetic subdivision among these stands. Significantly higher genetic diversity was detected at the two study sites that chemistry and toxicity data indicate to be the most severely impacted by pollutants. Although this correlation does not establish cause and effect, the results of this study indicate that the analysis of genetic diversity at VNTR loci may be a useful tool for monitoring anthropogenic-induced changes in the genetic structure of natural populations of plants.     

Genetic variation of <Emphasis Type="Italic">Oplopanax elatus</Emphasis> (Nakai) Nakai (Araliaceae)

Using allozyme analysis, genetic and genotypic variation of rare relict species, a member of one of ancient angiosperm families, Araliaceae, the clonal plant Oplopanax elatus (Nakai) Nakai, was evaluated. Electrophoretic separation of the enzymes is described, and genetic interpretation of the enzymes variation patterns is presented. The values of genetic variation indices obtained were low (P = 25%; A = 1.45: H _o = 0.131; H _e = 0.113) and comparable with the data reported for the rare plant species and the representatives of the family Araliaceae. The main factors responsible for the polymorphism level observed might be the evolutionary history of the species and gene drift. The level of genotypic diversity (G/N = 0.76; D = 0.97) was substantially higher, compared to the values reported for species with vegetative reproduction (D = 0.62). These results suggest certain contribution of the propagation by seeds in the formation of the species of interest.     

Genetic variation and population structure ofCarex breviculmis (Cyperaceae) in Korea

We determined the genetic diversity and population structures ofCarex breviculmis (Cyperaceae) populations in Korea, using genetic variations at 23 allozyme loci.C. breviculmis is a long-lived herbaceous species that is widely distributed in eastern Asia. A high level of genetic variation was found in 15 populations. Twelve enzymes revealed 23 loci, of which 11 were polymorphic (47.8%). Genetic diversity at the speciesand population levels were 0.174 and 0.146, respectively. Total genetic diversity (H_T = 0.363) and within-population genetic diversity (H_s = 0.346) were high, whereas the extent of the population divergence was relatively low (G_ST = 0.063). Deviation from random mating (Fis) within the 15 populations was 0.206. An indirect estimate of the number of migrants per generation(Nm = 3.69) indicated that gene flow was extensive among Korean populations of this species. Analysis of fixation indices revealed a substantial heterozygote deficiency in some populations and at some loci. Genetic identity between popu-lations was high, exceeding 0.956.     

Low level of allozyme polymorphism in relict aquatic plants of the Far East Nelumbo komarovii Grossh. and Euryale ferox Salisb.

Using allozyme analysis, genetic variation of two relict aquatic plants from Primorsky krai, Komarov lotus (Nelumbo komarovii Grossh.) and Gorgon plant (Euryale ferox Salisb.), was examined. The absence of allozyme variation in the Primorye populations of Nelumbo komarovii along with low polymorphism level in the population of Euryale ferox (P ₉₅ = 7.69; A = 1.07; H _o = 0.072; H _e = 0.038) was demonstrated. Since the data for the species examined are reported for the first time ever, the phenotypes and genetic interpretation of the enzyme systems tested are presented. The isoenzyme profiles of N. komarovii were compared with the data reported for N. nucifera from China. The absence of allozyme variation in N. komarovii, along with extremely low level of variation revealed for E. ferox, is discussed in association with the evolutionary histories of these species, their dispersal after the Pleistocene-Holocene cooling, and survival on this territory in range boundaries.     

Genetic diversity and structure in a natural Elymus caninus population from Denmark based on microsatellite and isozyme analyses

 Genetic diversity in a natural Elymus caninus population from Denmark was assessed using isozyme and microsatellite markers. A total of 119 individuals from 46 maternal plants were assayed. Microsatellite loci are shown to display higher levels of variation than isozyme loci. The mean number of alleles per locus was 1.04 for isozymes and 1.38 for microsatellites. The percentage of polymorphic loci for isozymes and microsatellites was 4.7% and 23.6% across the maternal plant, respectively. The genetic diversity at population level was 0.1 for isozymes, and 0.63 for microsatellites. The mean genetic diversity at maternal plant level was 0.027 for isozyme loci and 0.117 for microsatellite loci. The average of total allozyme diversity (H_T) was 0.22. The average of total microsatellite diversity was 0.56. Isozyme and microsatellite variation showed the same pattern of differentiation between maternal plants. More than 75% total genetic diversity was found among maternal plants. About 25% total genetic diversity was detected within maternal plants. Ten (22.7%) maternal plants produced heterozygous offspring at allozyme loci, and 30 (68.2%) maternal plants gave heterozygous offspring at microsatellite loci. Both types of markers revealed a relatively high genetic diversity in this population. Received November 7, 2000 Accepted February 15, 2001     

Abundant genetic diversity of the wild rice Zizania latifolia in central China revealed by microsatellites

Wild rice Zizania latifolia is a perennial emergent aquatic plant widely distributed across China. Wild populations of Z. latifolia are important to aquatic ecosystems and are valuable genetic resources for breeding. However, they have been faced with significant habitat losses in recent decades. For 10 nuclear microsatellites, high levels of genetic diversity (H_E = 0.572–0.636) were found across seven surveyed populations from central China. The main factors responsible for that were its long life history and predominant outcrossing reproductive system. Low genetic differentiation among populations was found based on Wright's F_ST = 0.098. Similarly, AMOVA analysis showed only 7.73% of the total molecular variation was attributed to inter‐population differentiation. The weak population structure of Z. latifolia could be due to high gene flow mediated by water or birds (Nm = 2.30, M = 2.18). Importantly, most populations exhibited mutation‐drift disequilibrium, suggesting a recent population decline. Based on the results, wild populations of Z. latifolia are expected to lose genetic diversity and increase genetic structure in future generations. Therefore, conservation management is urgently needed to maintain the genetic resources of Z. latifolia.     

Nitrogen fertilizer and gender effects on the secondary metabolism of yaupon,a caffeine-containing North American holly

Females and males of sexually dimorphic species have distinct resource demands due to differential allocation to reproduction. Sexual allocation theory predicts that functional traits will diverge between sexes to support these demands. However, such dimorphism may be masked by the impact of current reproduction on source-sink interactions between vegetative and reproductive organs. We ask whether natural selection has led to genetic dimorphism in homologous physiological traits between sexes of the dioecious willow shrub, Salix glauca. In a common garden experiment we compared physiological responses to drought stress by male and female ramets in the absence of confounding demands from reproductive structures. Ramets experienced similar pre-dawn leaf water status (Ψ_l) as parental genets in flower within the natural population, indicating that experimental dry-down mirrored environmental conditions in nature. Male and female ramets achieved similar instantaneous water use efficiency, based on the ratio of carbon gain to water loss, under wet and dry conditions. However, female ramets experienced greater water stress (i.e., more negative Ψ_l) than males under dry conditions. Lower Ψ_l for female ramets may partly reflect the maintenance of conductance under drought; males, in contrast, maintain Ψ_l under drought by reducing conductance. Differences between sexes in terms of conductance and leaf water status of the vegetative ramets were absent in a concomitant comparison of parental flowering plants. Our results show (1) genetic divergence in physiology between sexes of S. glauca occurs in the absence of gender-specific reproductive sinks, (2) males are the more physiologically plastic sex with respect to water use, and (3) paradoxically, divergence in water relations between sexes is not detectable at sexual maturity under natural conditions.     

Genetic Diversity and Geographic Differentiation in the Threatened Species Dysosma pleiantha in China as Revealed by ISSR Analysis

Dysosma pleiantha, an important threatened medicinal plant species, is restricted in distribution to southeastern China. The species is capable of reproducing both sexually and asexually. In this study, inter-simple sequence repeat marker data were obtained and analyzed with respect to genetic variation and genetic structure. The extent of clonality, together with the clonal and sexual reproductive strategies, varied among sites, and the populations under harsh ecological conditions tended to have large clones with relatively low clonal diversity caused by vegetative reproduction. The ramets sharing the same genotype show a clumped distribution. Across all populations surveyed, average within-population diversity was remarkably low (e.g., 0.111 for Nei’s gene diversity), with populations from the nature reserves maintaining relatively high amounts of genetic diversity. Among all populations, high genetic differentiation (AMOVA: Φ_ST = 0.500; Nei’s genetic diversity: G _ST = 0.465, Bayesian analysis: Φ_B = 0.436) was detected, together with an isolation-by-distance pattern. Low seedling recruitment due to inbreeding, restricted gene flow, and genetic drift are proposed as determinant factors responsible for the low genetic diversity and high genetic differentiation observed.     

Population Genetic structure ofPotentilla fragariodes var.major (Rosaceae) in Korea

The genetic diversity and population structure of eighteenPotentilla fragariodes var.major (Rosaceae) populations in Korea were determined using genetic variations at 22 allozyme loci. The percent of polymorphic loci within the enzymes was 66.7%. Genetic diversity at the species level and at the population level was high (Hes = 0.203; Hep = 0.185, respectively), whereas the extent of the population divergence was relatively low (G_ST = 0.069). F_IS, a measure of the deviation from random mating within the 18 populations, was 0.075. An indirect estimate of the number of migrants per generation (Nm = 3.36) indicated that gene flow was high among Korean populations of the species. In addition, analysis of fixation indices revealed a slight heterozygote deficiency in some populations and at some loci. Wide geographic ranges, perennial herbaceous nature and the persistence of multiple generations are associated with the high level of genetic variation. AlthoughP. fragariodes var.major usually propagated by asexually-produced ramets, we could not rule out the possibility that sexual reproduction occurred at a low rate because each ramet may produce terminal flowers. Mean genetic identity between populations was 0.983. It is highly probable that directional movement toward genetic uniformity in a relatively homogeneous habitat operates among Korean populations ofP. fragariodes var.major.     

Genetic structure and mating system of Stemonoporus oblongifolius (Dipterocarpaceae) in Sri Lanka

The genetic structure and mating system of an endemic Sri Lankan dipterocarp, Stemonoporus oblongifolius, was examined using allozyme analyses. Considering the small geographic distribution of the species, which is confined to the Peak Wilderness Sanctuary range, the species and population level genetic diversity are exceptionally high (H_e = 0.342 and 0.282, respectively). Although the populations sampled are separated by a maximum distance of only 10 kilometers, a fair amount of genetic structuring was detected (G_ST = 0.163). The mating system could contribute to the maintenance of a high level of genetic diversity, but in itself is insufficient to explain the high values for this study. The multilocus outcrossing rate, quantified for one population, was high (84%), with evidence for apomixis in one tree. Other factors potentially contributing to the high observed allozyme diversity in this species would be large effective population sizes, introgression of genes from sympatric species, and retention of ancient allozyme polymorphism. Gene flow among populations, estimated to be high, would have to be through pollen dispersal, since the large, resinous seeds typically fall and germinate beneath the maternal tree and are not known to be dispersed by any animal.     

Production of male flowers does not decrease with plant size in insect‐pollinated Sagittaria trifolia,contrary to predictions of size‐dependent sex allocation

Abstract It has been proposed that relative allocation to female function increases with plant size in animal‐pollinated species. Previous investigations in several monoecious Sagittaria species seem to run contrary to the prediction of size‐dependent sex allocation (SDS), throwing doubt on the generalization of SDS. Plant size, phenotypic gender, and flower production were measured in experimental populations of an aquatic, insect‐pollinated herb Sagittaria trifolia (Alismataceae) under highly different densities. The comparison of ramets produced clonally can reduce confounding effects from genetic and environmental factors. In the high‐density population, 48% of ramets were male without female flowers, but in the low‐density population all ramets were monoecious. We observed allometric growth in reproductive allocation with ramet size, as evident in biomass of reproductive structures and number of flowers. However, within both populations female and male flower production were isometric with ramet size, in contrast to an allometric growth in femaleness as predicted by SDS. Phenotypic gender was not related to ramet size in either population. The results indicated that large plants may increase both female and male function even in animal‐pollinated plants, pointing towards further studies to test the hypothesis of size‐dependent sex allocation using different allocation currencies.     

Maintenance of Phenotypic and Genotypic Diversity in Managed Populations of Stenocereus Stellatus (Cactaceae) by Indigenous Peoples in Central Mexico

The columnar cactus Stenocereus stellatus is used in Central Mexico for its edible fruits which are harvested in wild, managed in situ and cultivated populations. Management in situ of wild populations is conducted by selectively sparing and enhancing the abundance of plants with desirable phenotypes when fields are cleared for agricultural use. Cultivation of desirable phenotypes is carried out by vegetative propagation in homegardens. Effects of human management on morphological and genetic variation of S. stellatus were analyzed by comparing morphological diversity indices (MD, based on Simpson’s index) and expected (H_e) heterozygosity indices from allozyme analysis, in wild, managed in situ, and cultivated populations from La Mixteca and the Tehuacán Valley regions. Morphological diversity was similar among regions, but populations from the wetter La Mixteca region averaged higher genetic variation (H_e = 0.279) than populations from Tehuacán (H_e = 0.265). On average, populations manipulated by people had higher levels of variation (MD = 0.479 ± 0.012, H_e = 0.289 in cultivated populations; MD = 0.461 ± 0.014, H_e = 0.270 in managed in situ populations) than wild populations (MD = 0.408 ± 0.017, H_e = 0.253), which is apparently due to a continual introduction and replacement of plant materials in the manipulated populations. The results illustrate that human management may not only maintain but also increase both morphological and genetic diversity of manipulated plant populations in relation to that existing in the wild. Managed in situ and cultivated populations of S. stellatus are important reservoirs of variation, and are crucial for the general maintenance of diversity in wild populations. These populations may play a principal role in designing strategies for the conservation of variation of this cactus.     

Population density and module demography in Trapa natans (Trapaceae), an annual,clonal aquatic macrophyte

The effects of population density on module demography were studied in Trapa natans L., an annual aquatic macrophyte capable of extensive clonal propagation. At low density, the floating plants produced ten times as many ramets (clonal offshoots) as those at high density. Module mortality occurred at three levels: leaf, ramet (shoot), and genet (genetic individual). There was 100-fold variation in the size of nuts containing germinable seeds. In early summer there was a highly significant linear relationship between dry mass of nuts and the total mass of ramets that each had produced. In early summer most (73–83%) of the variation in total plant biomass was attributable to variation in initial nut size. However the significance of initial nut size was diminished later in the season. The great success of the exotic weed T. natans at colonizing and monopolizing an aquatic habitat is a function of its highly productive clonal growth response to low-density conditions, combined with greater proportional allocation of biomass to reproductive structures, resulting in greatly increased nut production at low initial density. The species appears able to develop and maintain a population at extremely high density: plant buoyancy and the production of large, well-protected nuts allow rapid early growth from the sediment each year and early pre-emption of the water surface.     

Genetic uniformity characterizes the invasive spread of water hyacinth (Eichhornia crassipes), a clonal aquatic plant

Aquatic plant invasions are often associated with long‐distance dispersal of vegetative propagules and prolific clonal reproduction. These reproductive features combined with genetic bottlenecks have the potential to severely limit genetic diversity in invasive populations. To investigate this question we conducted a global scale population genetic survey using amplified fragment length polymorphism markers of the world’s most successful aquatic plant invader –Eichhornia crassipes (water hyacinth). We sampled 1140 ramets from 54 populations from the native (South America) and introduced range (Asia, Africa, Europe, North America, Central America and the Caribbean). Although we detected 49 clones, introduced populations exhibited very low genetic diversity and little differentiation compared with those from the native range, and ～80% of introduced populations were composed of a single clone. A widespread clone (‘W’) detected in two Peruvian populations accounted for 70.9% of the individuals sampled and dominated in 74.5% of the introduced populations. However, samples from Bangladesh and Indonesia were composed of different genotypes, implicating multiple introductions to the introduced range. Nine of 47 introduced populations contained clonal diversity suggesting that sexual recruitment occurs in some invasive sites where environmental conditions favour seedling establishment. The global patterns of genetic diversity in E. crassipes likely result from severe genetic bottlenecks during colonization and prolific clonal propagation. The prevalence of the ‘W’ genotype throughout the invasive range may be explained by stochastic sampling, or possibly because of pre‐adaptation of the ‘W’ genotype to tolerate low temperatures.     

Allozyme Diversity and Population Genetic Structure of Pinus densata Master in Northwestern Yunnan, China

We investigated the levels and patterns of genetic diversity of Pinus densata Master in Yunnan. Horizontal starch-gel electrophoresis was performed on macrogametophytes collected from nine populations in northwestern Yunnan, China. Compared with other gymnosperm species, P. densata has higher mean values for all measures of genetic diversity. Allozyme polymorphism (0.99 criterion) was 97.0% and 71.4% at the species and population levels, respectively. The average number of alleles per locus was 3.1 and 2.0 at the species and population levels. Mean expected heterozygosity was substantially higher in P. densata than average values investigated for other gymnosperms both at the population (H _ep = 0.174±0.031) and at the species (H _es = 0.190) levels. Of the total genetic variation, less than 12% was partitioned among populations (G _ST = 0.112). Our allozyme survey supports the suggestion that the observed higher diversity in P. densata may be attributed partly to its hybrid origin between two genetically distinct species, P. yunnanensis and P. tabulaeformis. In addition, we suggest that introgression would give rise to the increase in genetic diversity occurring in P. densata.     

The ‘paradigm of extremes’: extremely low genetic diversity in an extremely narrow endemic species, Coristospermum huteri (Umbelliferae)

Low levels of genetic diversity in endemic species are generally attributable to the small size of their populations. This lack of genetic variability will, predictably, be more evident in those species that occur in only one or a very few localities with a total population consisting of a few dozen individuals, or sometimes fewer (i.e. ‘extremely narrow endemics’, ENEs). We used allozyme electrophoresis to survey the genetic variability of Coristospermum huteri, an endemic species from the island of Majorca (Balearic Islands, W. Mediterranean Basin) with a single natural population of about 100 individuals. As expected, allozyme variability was virtually nil for this species (P = 8.3 %, A = 1.08, H _e = 0.022), which seems to be a general rule for ENEs (mean H _e = 0.057). A founder effect associated with a dispersal event from the continent is probably behind the lack of genetic diversity in this highly threatened species. Preservation of the mountain summit where the plant is found (Puig Major) is essential for the survival of C. huteri, and would also guarantee the conservation of other ENEs and rare and threatened species.     

GENETIC DIVERSITY AND CLONAL STRUCTURE IN A COLUMNAR CACTUS,LOPHOCEREUS SCHOTTII

In southern Arizona the columnar cactus, Lophocereus schottii, inhabits desert riparian environments. Reproduction in this part of its range is predominantly asexual and occurs by either the dispersal of stems in the immediate vicinity of parents or the long-distance transport of detached stem pieces downstream by floodwaters. Genetic diversity and clonal structure of eight populations of L. schottii in Organ Pipe Cactus National Monument, Arizona, were examined. In all populations ramets were mapped and stem tissue from each ramet was examined electrophoretically. At the species level, 44.4% of the loci were polymorphic and the genetic diversity was 0.145. Within populations, the mean proportion of polymorphic loci and genetic diversity were 34.4% and 0.126%, respectively. Although most of the allozyme variation was within populations, appreciable heterogeneity was found among populations (G_ST = 0.130). Genetic and genotypic diversity was greatest in three of the four populations located in the principal area of L. schottii occurrence in the monument. Genotypic diversity was lowest in the smallest population and in the most isolated population. Ramets in all populations were spatially aggregated. Plant pairs with identical multilocus genotypes were usually ≤ 10 m apart, but some widely separated individuals had identical genotypes. Occasional long-distance dispersal of stems and the periodic recruitment of seedlings have caused genets to intermingle, promoting outcrossing and maintaining genetic diversity.     

Allozyme and chloroplast DNA variation in island and mainland populations of the rare Spanish endemic, Silene hifacensis (Caryophyllaceae)

Silene hifacensis is a narrowly endemicplant, restricted to a few small populations onlimestone cliffs in the Spanish province ofAlicante and on the Balearic island of Ibiza.The species was collected to extinction in itsoriginal mainland location by the early 20thcentury. Attempts have been made to reintroduceS. hifacensis to this area butconservation efforts are limited by a lack ofinformation on the geographic structure ofgenetic variation in the species. We usednuclear (allozyme) and chloroplast DNA (cpDNA)PCR/RFLP markers to investigate the structureof genetic variation in 2 mainland and 6 Ibizanpopulations. Levels of allozyme variation werelow, with a mean of 2 alleles per polymorphiclocus. Mean (over polymorphic loci) totalallozyme diversity (H_tot) was 0.203 and meanwithin-population diversity (H_pop) was 0.085. Mostdiversity was explained by thebetween-population diversity component (G_pop.reg =57%). Both mainland populations showedallozyme fixation. Three composite cpDNAhaplotypes were identified. The first is uniqueto a mainland population that is alsoallozymically distinct from all the otherpopulations. The second haplotype is found inthe other mainland population and one Ibizanpopulation: these two populations areallozymically identical. The remaining Ibizanpopulations contain the third haplotype. Thegeographic distribution of allozymes and cpDNAhaplotypes is discussed in terms of populationhistory, dispersal and, speculatively, in termsof the possibility that there has beenundocumented translocation of material betweenpopulations.     

Genetic diversities of four little-known species of Malesherbia (Malesherbiaceae) endemic to the arid inter-Andean valleys of Peru

Few studies of genetic variation have been conducted on plants of the Pacific coastal desert and neighboring Andes of Peru, although the region has many endemic taxa. Enzyme electrophoresis was employed to examine allozyme diversities of four species of the family Malesher-biaceae, an endemic to the arid Andes and coastal desert. One population ofMalesherbia splendens and two ofM. tubulosa, both endemics of the department of Lima, one population ofM. weberbaueri var.weberbaueri, an endemic of the Andean department Huancavélica, and the two Lima populations ofM. scarlatiflora were studied. Fifteen loci were examined for all populations and an additional seven loci were resolved forM. weberbaueri andM. splendens. Malesherbia splendens, which is known from three populations, has a low mean number of alleles per locus (A), proportion of polymorphic loci (P), and expected heterozygosity (H_s) (A=1.214, P=0.214, H_s=0.057).Malesherbia weberbaueri (A=1.231, P=0.154, H_s=0.079) andM. scarlatiflora (A=1.364, P=0.273, H_t=0.083) both have average expected heterozygosities and relatively low mean numbers of alleles per locus and proportions of polymorphic loci. InM. tubulosa, all measures of genetic diversity are high in comparison with other endemics (A=1.818, P=0.364, H_t=0.206).Malesherbia tubulosa has high interpopulation differentiation, whereasM. scarlatiflora has low among-population diversity. The relatively low allozyme diversities, restricted habitats, narrow ranges ofM. splendens andM. weberbaueri, and the morphological similarities of all four species suggest that they evolved recently by founder events. Greater allozyme diversities inM. tubulosa could be attributable to its maintenance of larger populations in a greater variety of habitats.     

Mating system and population genetic structure of Bruguiera gymnorrhiza (Rhizophoraceae), a viviparous mangrove species in China

In order to explain the diversity patterns and develop the conservation strategies, the population genetic structures and the mating systems of Bruguiera gymnorrhiza from the coastlines of south China were investigated in this study. The mating system parameters were analyzed using progeny arrays for allozyme markers. The multilocus outcrossing rates (tm) ranged from 0.845 (Fugong) to 0.267 (Dongzhai harbor). High allozyme variations within the five collected populations were determined and compared with the published data of other plant species with the mixed mating systems. At species level, the percentage of polymorphic loci (P) was 80%, the average number of alleles per locus (A) was 2.440, and the heterozygosity (He) was 0.293. The total gene diversity within each population (H_S = 0.2782) and the coefficient of genetic differentiation (G_ST = 0.0579) among the populations were estimated. On the basis of this population genetic structure, it is suggested that the gene flow (Nm = 3.85) is quite high, which is possibly related to its water-dispersed hypocotyls. It is also suggested that the mating system of this species is of mixed mating.