Comparison of genetic variation and differentiation using microsatellite markers among three rare threatened and one widespread toad lily species of Tricyrtis section Flavae (Convallariaceae) in Japan

Genetic diversities were examined using six microsatellite markers amplifiable in three rare and one widespread species of Tricyrtis section Flavae, which are endemic to Japan. Contrary to a general expectation, the three rare species, Tricyrtis flava, Tricyrtis ohsumiensis and Tricyrtis perfoliata, have comparable genetic variation at the species level to that of the widespread Tricyrtis nana. This is probably because T. nana has not sufficiently recovered genetic diversity from the bottleneck at speciation or because recent range contractions have occurred in the three rare species. Genetic diversity at the population level was smaller in the putative selfing species T. nana than in the other three outcrossing species. Compared with a preceding study using allozyme markers, the genetic diversity in microsatellite loci was considerably larger, probably resulting from higher mutation rates at the microsatellite loci. Owing to the high genetic diversity of the microsatellite markers, genetic differentiation among populations could be estimated even in T. nana with little allozyme polymorphism.     

Genetic variation and population structure in Korean populations of eurya japonica (Theaceae)

We investigated levels of genetic diversity, population genetic structure, and gene flow in Eurya japonica, a widespread and broad-leaved evergreen dioecious tree native to Japan, China, Taiwan, and the southern and southwestern coast of the Korean Peninsula. Starch-gel electrophoresis was conducted on leaves collected from 1,000 plants in 20 Korean populations. All 12 loci examined were polymorphic in at least one population, and the mean number of alleles per locus was 3.79. In addition, mean observed population heterozygosity (Ho_p = 0.425), expected heterozygosity (He_p = 0.462), and total genetic diversity (H_T = 0.496) were substantially higher than average values for species with similar life history traits. Although significant differences in allele frequency were detected between populations at all loci (P < 0.001), <7% of the genetic variation was found among populations (F_ST = 0.069). There was a significant negative correlation between genetic identity and distance between populations (r = -0.341; P < 0.05), but this explained only a small amount of the diversity among populations. Indirect estimates of the number of migrants per generation (Nm) (3.37, calculated from F_ST; 3.74, calculated from the mean frequency of eight private alleles) indicate that gene flow is extensive among Korean populations of E. japonica. Factors contributing to the high levels of genetic diversity found within populations of E. japonica include large and contiguous populations, obligating outcrossing (dioecious plant), high fecundity, and long generation time. Occasional seed dispersal by humans and pollen movement by domesticated honey bees may further enhance gene flow within the species.     

Allozyme variation and population genetic structure of common wild rice Oryza rufipogon Griff. in China

In order to determine the genetic diversity and genetic structure of populations in common wild rice Oryza rufipogon, an endangered species, allozyme diversity was analyzed using 22 loci in 607 individuals of 21 natural populations from the Guangxi, Guangdong, Hainan, Yunnan, Hunan, Jiangxi and Fujian provinces in China. The populations studied showed a moderate allozyme variability (A=1.33, P=22.7%, Ho=0.033 and He=0.068), which was relatively high for the genus Oryza. The levels of genetic diversity for Guangxi and Guangdong were significantly higher than those for the other regions, and thus South China appeared to be the center of genetic diversity of O. rufipogon in China. A moderate genetic differentiation (F_ST=0.310, I=0.964) was found among the populations studied. Interestingly, the pattern of population differentiation does not correspond to geographic distance. An estimate of the outcrossing rate (t=0.324) suggests that the species has a typical mixed-mating system. The deficit of heterozygotes (F=0.511) indicates that some inbreeding may have taken place in outcrossing asexual populations because of intra-clone outcrossing events and ”isolation by distance” as a result of human disturbance. In order to predict the long-term genetic survival of fragmented populations, further studies on gene flow among the remaining populations and the genetic effects of fragmentation are proposed. Finally, some implications for the conservation of endangered species are suggested. Received: 22 June 1999 / Accepted: 20 December 1999     

Long live the alien: is high genetic diversity a pivotal aspect of crested porcupine (Hystrix cristata) long‐lasting and successful invasion?

Studying the evolutionary dynamics of an alien species surviving and continuing to expand after several generations can provide fundamental information on the relevant features of clearly successful invasions. Here, we tackle this task by investigating the dynamics of the genetic diversity in invasive crested porcupine (Hystrix cristata) populations, introduced to Italy about 1500 years ago, which are still growing in size, distribution range and ecological niche. Using genome‐wide RAD markers, we describe the structure of the genetic diversity and the demographic dynamics of the H. cristata invasive populations and compare their genetic diversity with that of native African populations of both H. cristata and its sister species, H. africaeaustralis. First, we demonstrate that genetic diversity is lower in both the invasive Italian and the North Africa source range relative to other native populations from sub‐Saharan and South Africa. Second, we find evidence of multiple introduction events in the invasive range followed by very limited gene flow. Through coalescence‐based demographic reconstructions, we also show that the bottleneck at introduction was mild and did not affect the introduced genetic diversity. Finally, we reveal that the current spatial expansion at the northern boundary of the range is following a leading‐edge model characterized by a general reduction of genetic diversity towards the edge of the expanding range. We conclude that the level of genome‐wide diversity of H. cristata invasive populations is less important in explaining its successful invasion than species‐specific life‐history traits or the phylogeographic history in the native source range.     

GENETIC RELATIONSHIPS AND PATTERNS OF ALLOZYMIC DIVERGENCE IN THE IPOMOPSIS AGGREGATA COMPLEX AND RELATED SPECIES (POLEMONIACEAE)

The Ipomopsis aggregata complex consists of diploid, outcrossing, perennial herbs. The group is highly variable morphologically and is treated as three species: I. aggregata, I. tenuituba, and I. arizonica. Geographic races of I. aggregata and I. tenuituba are recognized as subspecies. Enzyme electrophoresis was used to examine genetic relationships among populations and taxa in the Ipomopsis aggregata complex and some related species. Genetic data for 23 allozyme loci from 60 populations were also used to determine how genetic variation is distributed geographically. Populations in the southwestern United States were more variable than those in the northwest: the center of genetic diversity corresponded to the center of species diversity. Allozymic data provided no evidence of loss of genetic variability associated with recent and rapid divergence. Genetic relationships based on Nei's genetic identity did not correspond to taxonomic relationships. For example, populations of both I. arizonica and I. tenuituba clustered within I. aggregata. Despite relatively high levels of genetic diversity among populations, diversity among taxa was low. Results indicated that floral divergence and concomitant speciation have occurred recently in the Ipomopsis aggregata complex. Allozymic patterns also reflected convergent evolution for floral morphology and possible introgression. Despite morphological differences among species, insufficient evolutionary time has elapsed for allelic fixation at neutral or near-neutral allozyme loci.     

Low Levels of Genetic Diversity within Populations of Hosta clausa (Liliaceae)

Abstract Genetic diversity of Korean populations in Hosta clausa was investigated using starch gel electrophoresis. Hosta clausa is widespread, grows only along streamsides, and has both sexual and asexual reproduction. Populations of the species are small and isolated. Thirty-two percent of the loci examined were polymorphic, and mean genetic diversity within populations (He_p=0.082) was lower than mean estimates for species with very similar life history characteristics (0.131), particularly for its congener H. yingeri (0.250). The mean number of multilocus genotypes per population was 8.7, and genotypic diversity index (D_G) was 0.84. Significant differences in allele frequencies among populations were found in all seven polymorphic loci (P < 0.001). About one-fifth of the total allozyme variation was among populations (G_ST=0.192). Indirect estimate of the number of migrants per generation (Nm=0.48, calculated from mean G_ST) and nine private alleles found indicate that gene movement among populations was low. The low levels of genetic diversity within populations and the relatively high levels of genetic diversity among populations suggest that strong moist habitat preferences, clonal reproduction, low level of gene flow among populations, genetic drift, and historical events may have played roles in the genetic structuring of the species.     

RECENT EVOLUTION AND DIVERGENCE AMONG POPULATIONS OF A RARE MEXICAN ENDEMIC,CHIHUAHUA SPRUCE,FOLLOWING HOLOCENE CLIMATIC WARMING

Fragmentation and reduction in population size are expected to reduce genetic diversity. However, examples from natural populations of forest trees are scarce. The range of Chihuahua spruce retreated northward and fragmented coincident with the warming climate that marked the early Holocene. The isolated populations vary from 15 to 2441 trees, which provided an opportunity to test whether census number is a good predictor of genetic diversity. Mean expected heterozygosity, H_e, based on 24 loci in 16 enzyme systems, was 0.093 for 10 sampled populations, which is within the range reported for conifers. However, estimates varied more than twofold among populations and H_e was closely related to the logarithm of the number of mature trees in the population (r_He,N = 0.93). Diversity among populations, F_ST, was 24.8% of the total diversity, which is higher than that observed in almost all conifer species studied. Nei's genetic distance, D, was not related to geographic distance between populations, and D? was 0.033, which is higher than estimates for most wide-ranging species. Most populations had excess homozygosity and the fixation index, F_IS, was higher than that reported for all but one species of conifer. Nm, the number of migrants per generation, was 0.43 to 0.76, depending on estimation procedure, and is the smallest observed in conifers. The data suggest that populations of Chihuahua spruce have differentiated by drift and that they are effectively isolated. The results illustrate how a combination of paleontological observation and molecular markers can be used to illuminate recent evolutionary events. Multilocus estimates of outcrossing for two small populations were zero (complete selfing) and 0.153, respectively, which are in striking contrast to the near complete outcrossing observed in most conifers. The high fixation index and a high proportion of empty seeds (45%) suggest that inbreeding may be a serious problem for conservation of Chihuahua spruce.     

Genetic variation and population structure in Korean endemic species: III.Hosta minor (Liliaceae)

Hosta minor, an insect-pollinated and rhizomatous herbaceous perennial, occurs in eastern and southern Korean Peninsula. AlthoughH. minor is a Korean endemic species and most populations of the species are scattered, the species maintains considerably high levels of genetic variation within the species, with a moderate level of variation (14%) found among populations. Nineteen of the 29 putative loci resolved (66%) were polymorphic within the species, the mean number of alleles per locus was 2.10 across all populations and averaged 1.68 within populations. In addition, genetic diversity was a considerably higher (for species and population level, mean estimates of genetic diversity were 0.275 and 0.230, respectively) than the average for other long-lived herbaceous perennials. Indirect estimate of the number of migrants per generation (Nm=1.03, calculated from mean G_ST) was moderate. Factors contributing to the high levels of genetic diversity found within populations ofH. minor include population maintenance via sexual and asexual modes of reproduction, primarily outcrossing breeding system, long generation time, probable ancient polyploid origin of the species, and moderate levels of seed dispersal by wind. Human disturbance in South Korea such as road and apartment constructions appears to be the major threat to this genetically diverse species.     

Genetic analyses of the federally endangered Echinacea laevigata using amplified fragment length polymorphisms (AFLP)—Inferences in population genetic structure and mating system

Echinacea laevigata (Boynton and Beadle) Blake is a federally endangered flowering plant species restricted to four states in the southeastern United States. To determine the population structure and outcrossing rate across the range of the species, we conducted AFLP analysis using four primer combinations for 22 populations. The genetic diversity of this species was high based on the level of polymorphic loci (200 of 210 loci; 95.24%) and Nei’s gene diversity (ranging from 0.1398 to 0.2606; overall 0.2611). There was significant population genetic differentiation (G_ST = 0.294; Ө^II = 0.218 from the Bayesian f = 0 model). Results from the AMOVA analysis suggest that a majority of the genetic variance is attributed to variation within populations (70.26%), which is also evident from the PCoA. However, 82% of individuals were assigned back to the original population based on the results of the assignment test. An isolation by distance analysis indicated that genetic differentiation among populations was a function of geographic distance, although long-distance gene dispersal between some populations was suggested from an analysis of relatedness between populations using the neighbor-joining method. An estimate of the outcrossing rate based on genotypes of progenies from six of the 22 populations using the multilocus method from the program MLTR ranged from 0.780 to 0.912, suggesting that the species is predominantly outcrossing. These results are encouraging for conservation, signifying that populations may persist due to continued genetic exchange sustained by the outcrossing mating system of the species.     

Allozyme variation in the diploid (A genome) populations ofScilla scilloides (Hyacinthaceae)

Allozyme variation at eleven loci encoding seven enzyme systems were examined in 20 populations of diploid (genome AA, 2n = 16)Scilla scilloides in China. In comparison with the average species of seed plants studied, populations of this species display a high amount of genetic variation (A = 2.0, P = 58.6%, H_o = 0.172, and H_e = 0.185). Allozyme variation pattern revealed predominant outcrossing within populations and considerable differentiation (F_ST = 0.314) among populations as well as between the subtropic and temperate regions. The wide distribution, long existence and outcrossing are presumably the main factors responsible for the high genetic diversity within populations. But the gravity dispersal of seeds and pollination by small insects set limits to the increase of genetic variation within populations and promote differentiation between populations and regions. In addition, allozyme variation does not distinguishS. scilloides var.albo-viridis and suggests that subtropic populations may be considered as a genetic entity.     

Disentangling the effects of geographic peripherality and habitat suitability on neutral and adaptive genetic variation in Swiss stone pine

It is generally accepted that the spatial distribution of neutral genetic diversity within a species’ native range mostly depends on effective population size, demographic history, and geographic position. However, it is unclear how genetic diversity at adaptive loci correlates with geographic peripherality or with habitat suitability within the ecological niche. Using exome‐wide genomic data and distribution maps of the Alpine range, we first tested whether geographic peripherality correlates with four measures of population genetic diversity at > 17,000 SNP loci in 24 Alpine populations (480 individuals) of Swiss stone pine (Pinus cembra) from Switzerland. To distinguish between neutral and adaptive SNP sets, we used four approaches (two gene diversity estimates, F_ST outlier test, and environmental association analysis) that search for signatures of selection. Second, we established ecological niche models for P. cembra in the study range and investigated how habitat suitability correlates with genetic diversity at neutral and adaptive loci. All estimates of neutral genetic diversity decreased with geographic peripherality, but were uncorrelated with habitat suitability. However, heterozygosity (H_e) at adaptive loci based on Tajima's D declined significantly with increasingly suitable conditions. No other diversity estimates at adaptive loci were correlated with habitat suitability. Our findings suggest that populations at the edge of a species' geographic distribution harbour limited neutral genetic diversity due to demographic properties. Moreover, we argue that populations from suitable habitats went through strong selection processes, are thus well adapted to local conditions, and therefore exhibit reduced genetic diversity at adaptive loci compared to populations at niche margins.     

Determining population structure and hybridization for two iris species

Identifying processes that promote or limit gene flow can help define the ecological and evolutionary history of a species. Furthermore, defining those factors that make up “species boundaries” can provide a definition of the independent evolutionary trajectories of related taxa. For many species, the historic processes that account for their distribution of genetic variation remain unresolved. In this study, we examine the geographic distribution of genetic diversity for two species of Louisiana Irises, Iris brevicaulis and Iris fulva. Specifically, we asked how populations are structured and if population structure coincides with potential barriers to gene flow. We also asked whether there is evidence of hybridization between these two species outside Louisiana hybrid zones. We used a genotyping‐by‐sequencing approach and sampled a large number of single nucleotide polymorphisms across these species' genomes. Two different population assignment methods were used to resolve population structure in I. brevicaulis; however, there was considerably less population structure in I. fulva. We used a species tree approach to infer phylogenies both within and between populations and species. For I. brevicaulis, the geography of the collection locality was reflected in the phylogeny. The I. fulva phylogeny reflected much less structure than detected for I. brevicaulis. Lastly, combining both species into a phylogenetic analysis resolved two of six populations of I. brevicaulis that shared alleles with I. fulva. Taken together, our results suggest major differences in the level and pattern of connectivity among populations of these two Louisiana Iris species.     

Limiting inbreeding in disjunct and isolated populations of a woody shrub

Pollen movements and mating patterns are key features that influence population genetic structure. When gene flow is low, small populations are prone to increased genetic drift and inbreeding, but naturally disjunct species may have features that reduce inbreeding and contribute to their persistence despite genetic isolation. Using microsatellite loci, we investigated outcrossing levels, family mating parameters, pollen dispersal, and spatial genetic structure in three populations of Hakea oldfieldii, a fire‐sensitive shrub with naturally disjunct, isolated populations prone to reduction in size and extinction following fires. We mapped and genotyped a sample of 102 plants from a large population, and all plants from two smaller populations (28 and 20 individuals), and genotyped 158–210 progeny from each population. We found high outcrossing despite the possibility of geitonogamous pollination, small amounts of biparental inbreeding, a limited number of successful pollen parents within populations, and significant correlated paternity. The number of pollen parents for each seed parent was moderate. There was low but significant spatial genetic structure up to 10 m around plants, but the majority of successful pollen came from outside this area including substantial proportions from distant plants within populations. Seed production varied among seven populations investigated but was not correlated with census population size. We suggest there may be a mechanism to prevent self‐pollination in H. oldfieldii and that high outcrossing and pollen dispersal within populations would promote genetic diversity among the relatively small amount of seed stored in the canopy. These features of the mating system would contribute to the persistence of genetically isolated populations prone to fluctuations in size.     

Genetic diversity assessment of bittersweet (Solanum dulcamara,Solanaceae) germplasm using conserved DNA‐derived polymorphism and intron‐targeting markers

Bittersweet (Solanum dulcamara), a European native weed, is widespread across a variety of habitats and often occurs as a coloniser of open, disturbed, ephemeral environments or wetlands, although it is also found in mountain habitats and on forest edges. As recent studies have shown the potential utility of the species in plant breeding programs, we assembled a collection of bittersweet germplasm from natural populations found in Europe. This collection was analysed with conserved DNA‐derived polymorphism (CDDP) and intron‐targeting (IT) markers to assess genetic diversity found within and among the populations. We found that there is limited genetic variability within the collected S. dulcamara accessions, with a greater proportion of allelic variation distributed among populations and considerably greater population structure at higher regional levels. Although bittersweet is an outcrossing species, its population structure might be affected by its perennial self‐compatible nature, reducing genetic diversity within regional populations and enhancing inbreeding leading to high interpopulation or spatial differentiation. We found that populations have been separated by local selection of alleles, resulting in regional differentiation. This has been accompanied by concurrent loss of genetic diversity within populations, although this process has not affected species‐level genetic diversity. Germplasm collecting strategies should be aimed at preserving overall genetic diversity in bittersweet nightshade by expanding sampling to southern Europe and to smaller regional geographic levels in northern and central Europe.     

Genetic divergence of three freshwater isopod species from southern New Zealand

Aim We examined the biogeography of three freshwater isopod species (Austridotea annectens, A. lacustris, A. benhami), and tested the hypotheses that genetic differences would: (1) exist between geographic locations; and (2) correspond to known geological events (e.g. appearance of islands leading to the availability of habitat). Location Southern New Zealand, including South Island, Stewart Island, Campbell Island and Chatham Islands. Methods We examined specimens throughout the known species range from 12 populations of A. lacustris, five populations of A. annectens, and three populations of A. benhami, using mitochondrial DNA (cytochrome c oxidase I) sequence analyses. Results We resolved three main clades corresponding to the three species, with 16% sequence divergence between A. annectens and A. benhami, and 31% divergence between these species and A. lacustris. Divergence within A. benhami was < 2.0%. However, divergence within A. lacustris reached up to 10% with four main groupings: (1) Chatham Islands; (2) Campbell Island; (3) Fiordland; and (4) east coast South Island and Stewart Island. Divergence within A. annectens reached up to 4.4%, with two main groupings: (1) Chatham Islands and (2) east coast South Island and Stewart Island. Patterns of genetic divergence were most likely the result of geographical isolation among A. lacustris and A. annectens populations. In particular, the divergence of A. lacustris and A. annectens on Chatham Islands may correspond to the availability of this habitat c. 4 Ma, whereas the divergence of A. lacustris on the much older Campbell Island and in Fiordland may indicate either a rare founder event or a change in ocean circulation that resulted in their isolation from a once more widespread gene pool. Main conclusions The three New Zealand species of Austridotea are genetically distinct, with up to 31% divergence between species. Genetic variability was highest between populations of the two most widely distributed species, and divergence was greatest on islands distant from mainland New Zealand and in the discrete Fiordland region. The magnitude of genetic divergence of isopods on the Auckland and Chatham Islands is consistent with these populations having been founded in the Pliocene via oceanic dispersal from mainland New Zealand.     

A genetic demographic analysis of Lake Malawi rock‐dwelling cichlids using spatio‐temporal sampling

We estimated the effective population sizes (N_e) and tested for short‐term temporal demographic stability of populations of two Lake Malawi cichlids: Maylandia benetos, a micro‐endemic, and Maylandia zebra, a widespread species found across the lake. We sampled a total of 351 individuals, genotyped them at 13 microsatellite loci and sequenced their mitochondrial D‐loop to estimate genetic diversity, population structure, demographic history and effective population sizes. At the microsatellite loci, genetic diversity was high in all populations. Yet, genetic diversity was relatively low for the sequence data. Microsatellites yielded mean N_e estimates of 481 individuals (±99 SD) for M. benetos and between 597 (±106.3 SD) and 1524 (±483.9 SD) individuals for local populations of M. zebra. The microsatellite data indicated no deviations from mutation–drift equilibrium. Maylandia zebra was further found to be in migration–drift equilibrium. Temporal fluctuations in allele frequencies were limited across the sampling period for both species. Bayesian Skyline analyses suggested a recent expansion of M. zebra populations in line with lake‐level fluctuations, whereas the demographic history of M. benetos could only be estimated for the very recent past. Divergence time estimates placed the origin of M. benetos within the last 100 ka after the refilling of the lake and suggested that it split off the sympatric M. zebra population. Overall, our data indicate that micro‐endemics and populations in less favourable habitats have smaller N_e, indicating that drift may play an important role driving their divergence. Yet, despite small population sizes, high genetic variation can be maintained.     

Comparisons of genetic diversity in a narrow endemic, Impatiens hypophylla, and in its widespread congener, I. textori (Balsaminaceae)

Genetic diversity in two species of Impatiens in Korea was investigated using starch gel electrophoresis. Impatiens hypophylla is a rare species endemic to southwestern Japan and southeastern Korea, whereas I. rextori is widespread in East Asia. Impatiens textori has considerably higher genetic diversity than I. hypophylla . For example, mean values of genetic diversity within populations (He) of I. textori and I. hypophylla were 0.206 and 0.102, respectively. The high outcrossing rate (mean 1 = 0.89), abundance and widespread distribution, and large population size may be factors responsible for the maintenance of high levels of genetic variation in I. textori . Analyss of fixation indices indicated that considerable population substructuring within populations of I. hypophylla , partly resulting from inbreeding and/or genetic drift in small populations coupled with limited gene flow (mean F_IS= 0.699). However, the degree of population divergence observed in I. hypophylla (mean G_ST= 0.059) was considerably lower than that in other plants with similar life history traits. It is supposed that similar selection at populations of I. hypophylla examined might maintain similar gene frequencies in isolated populations.     

CONTRIBUTIONS OF SEXUAL AND ASEXUAL REPRODUCTION TO POPULATION STRUCTURE IN THE CLONAL SOFT CORAL,ALCYONIUM RUDYI

Numerous studies of population structure in sessile clonal marine invertebrates have demonstrated low genotypic diversity and nonequilibrium genotype frequencies within local populations that are monopolized by relatively few, highly replicated genets. All of the species studied to date produce planktonic sexual propagules capable of dispersing long distances; despite local genotypic disequilibria, populations are often panmictic over large geographic areas. The population structure paradigm these species represent may not be typical of the majority of clonal invertebrate groups, however, which are believed to produce highly philopatric sexual propagules. I used allozyme variation to examine the population structure of the temperate soft coral, Alcyonium rudyi, a typical clonal species whose sexually produced larvae and asexually produced ramets both have very low dispersal capabilities. Like other clonal plants and invertebrates, the local population dynamics of A. rudyi are dominated by asexual reproduction, and recruitment of new sexually produced genets occurs infrequently. As expected from its philopatric larval stage, estimates of genetic differentiation among populations of A. rudyi were highly significant at all spatial scales examined (mean θ = 0.300 among 20 populations spanning a 1100-km range), suggesting that genetic exchange seldom occurs among populations separated by as little as a few hundred meters. Mapping of multilocus allozyme genotypes within a dense aggregation of A. rudyi ramets confirmed that dispersal of asexual propagules is also very limited: members of the same genet usually remain within < 50 cm of one another on the same rock surface. Unlike most previously studied clonal invertebrates, populations of A. rudyi do not appear to be dominated by a few widespread genets: estimates of genotypic diversity (G_o) within 20 geographically distinct populations did not differ from expectations for outcrossing, sexual populations. Despite theoretical suggestions that philopatric dispersal combined with typically small effective population sizes should promote inbreeding in clonal species, inbreeding does not appear to contribute significantly to the population structure of A. rudyi. Genet genotype frequencies conformed to Hardy-Weinberg expectations in all populations, and inbreeding coefficients (f) were close to zero. In general, the population structure of A. rudyi did not differ significantly from that observed among outcrossing sexual species with philopatric larval dispersal. Age estimates suggest, however, that genets of A. rudyi live for many decades. Genet longevity may promote high genotypic diversity within A. rudyi populations and may be the most important evolutionary consequence of clonal reproduction in this species and the many others that share its dispersal characteristics.     

Genetic Variation in Hippophae rhamnoides ssp. sinensis (Elaeagnaceae) Revealed by RAPD Markers

Hippophae rhamnoides ssp. sinensis is endemic to China, and it is a dioecious, outcrossing plant. Although many studies have been undertaken mainly on its agricultural, nutritional, medical, and ornamental value, little is known about its population genetics. This study uses random amplified polymorphic DNA to investigate the genetic diversity and population genetic structure of 13 natural populations of the subspecies sinensis. Fifteen primers amplified 107 reproducible bands, with 95 (88.79%) being polymorphic. The gene diversity within population was 0.168, considerably lower than that of tree species and most perennial, outcrossing species, but higher than that of annual or short-lived, selfing species. The Gst value showed that 18.3% of the total genetic variation resided among populations, a little lower than that of outcrossing species. The present results are quite similar to those previously reported in another subspecies, H ssp. . rhamnoides rhamnoides. The low genetic differentiation among populations in ssp. sinensis may be attributed to the long-distance dispersal of seeds facilitated by birds, in addition to its characteristics of outcrossing, wind pollination, and widespread distribution. No association between genetic distance and geographical distribution was found. The population relationships revealed by the UPGMA dendrogram parallel this result, in that genetic distance did not increase with geographic separation. This pattern of population differentiation may imply the adaptation of ssp. s populations to the local environment, given that its habitats vary greatly across its distribution.     

Genetic variation and population structure in Korean populations of sand dune speciesSalsola komarovi (Chenopodiaceae)

Salsola komarovi lljin is a herbaceous annual native to the sand dunes and beaches of Japan, northern China, Sakhalln and Korea. Starch-gel electrophoresis was conducted on leaves and stems collected from 300 plants in eight Korean populations. The mean number of alleles per locus (A _p=1.51), mean expected heterozygosity (He _p=0.116), and total genetic diversity (H _T=0.279) were comparable with those for species with similar life history and ecological traits. A general conformance of genotype frequencies to Hardy-Weinberg expectations (meanF _IS=−0.030) indicates thatS. komarovi is an outcrossing species. Slightly more than 20% of the genetic variation was found among populations (F _ST=0.204). In addition, significant differences in allele frequency were detected between populations at all 11 polymorphic loci (P<0.001). Nei's genetic identities range from 0.885 to 0.985 with a mean of 0.942. However, indirect estimates of the number of migrant per generation (0.97, calculated fromF _ST and 0.31, calculated from seven private alleles) indicate that the levels of gene flow is low among Korean populations. Although the species maintains a moderate level of genetic variation within populations, the small, isolated natural populations of the species have been severely destructed by human activities, particularly in summer season. If this is true, conservation efforts should be focused on those populations that currently maintain the most genetic diversity (e.g., populations of Cheju Island and coast of the southwestern Korean Peninsula).