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.     

Genetic and clonal diversity in Korean populations ofVitex rotundifolia (Verbenaceae)

Vitex rotundifolia L.f. is a woody perennial and has sexual and asexual modes of reproduction. Allozyme study was conducted on 550 plants in 13 Korean populations. The levels of genetic variability and divergence within and among populations, respectively, are considerably lower and higher than the mean values for woody plants with similar life history tralts. Mean percentage of polymorphic loci (P _P), mean number of alleles per locus (A _P), and mean genetic diversity (He _P) within populations ofV. rotundifolia were: 16.7%, 1.21, and 0.047. On average, about 79% of the total variation inV. rotundifolia was common to all populations (meanG _ST=0.208). In addition, significant differences in allele frequencies among populations were found in all polymorphic loci examined (P<0.001). On the other hand, levels of genotypic diversity within and among populations were moderate. About 44% (18/41) of multilocus genotypes were “local genotypes” (genotypes occurring in only one population), whereas only one “widespread genotype” (genotypes occurring in more than 75% of the populations) were detected. The mean number of multilocus genotypes per population (G) and mean genotypic diversity index (D _G) were 8.4 and 0.74, respectively. Most common multilocus genotypes found in populations were homozygous for five polymorphic loci. The abundance of ramets of these genets is responsible for the low levels of expected heterozygosity within populations. The results indicate that clonal reproduction may act as an enhancer of genetic drift by reducing effective size of local populations ofV. rotundifolia.     

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.     

LOCAL GENETIC AND CLONAL STRUCTURE IN THE TROPICAL TERRESTRIAL BROMELIAD,AECHMEA MAGDALENAE

The genetic structure of populations of the clone-forming tropical terrestrial bromeliad, Aechmea magdalenae, was examined by electrophoretic analyses in nine populations occurring on and near Barro Colorado Island, Republic of Panama. For the nine populations as a whole, 33% of the loci were polymorphic and the genetic diversity was 0.121. Within populations, the mean percent of polymorphic loci was 24.1% and the mean genetic diversity was 0.084. About one-third of the total allozyme diversity resided among populations (mean G_ST = 0.356). The distribution of A. magdalenae was patchy in the study area. This, coupled with the relatively small effective population sizes and the possible founding of populations by few individuals may have contributed to the large among-population component of genetic diversity. The extent of clonal growth was inferred by examining the relationship between the proportion of rosette-pairs sharing identical multilocus genotypes and distance between pairs. This method indicates that clonal spread is local; individuals sharing multilocus genotypes most often occur within 10 m of each other.     

Genetic diversity and multilocus genetic structure in the relictual endemic herb<Emphasis Type="Italic"> Japonolirion osense</Emphasis> (Petrosaviaceae)

Plant clonality may greatly reduce effective population size and influence management strategies of rare and endangered species. We examined genetic diversity and the extent of clonality in four populations of the monotypic herbaceous perennial Japonolirion osense, which is one of the most rare flowering plants in Japan. Allozyme analysis revealed moderate levels of genetic variation, and the proportion of polymorphic loci (P=66.7%) was higher than the value for species with similar life-history traits. With four polymorphic loci, 19 multilocus genotypes were observed among 433 aerial shoot samples and 10 (52%) were found only in single populations. The proportion of distinguishable genotypes (PD=0.10) and Simpson's index of diversity (D=0.52) also exhibited moderate levels of genotypic diversity compared to other clonal plants, with genotype frequencies at Hardy-Weinberg equilibrium. The distributions of genotypes were often localized and they were mostly found within a radius of 5 m. Spatial autocorrelation analysis showed that shoot samples located 4 m apart were expected to be genetically independent. The results suggest that the spatial extent of genets was relatively narrow and thus the clonality was not extensive.     

Population genetic analysis of Elliottiaracemosa (Ericaceae), a rare Georgia shrub

Genetic and genotypic diversity found within populations of threatened plant species can have important implications for their conservation and management. In this study we describe genetic and genotypic diversity found within 10 populations of the endemic shrub Elliottiaracemosa (Ericaceae), the Georgia plume. E. racemosa is a threatened species known from fewer than 50 locations, all within the state of Georgia, USA. Seedset is limited to nonexistent in some E. racemosa populations and sexual recruitment has not been documented. However, the species is known to spread vegetatively via root-sprouts. Twenty-one allozyme loci were resolved for E. racemosa, nine of which were polymorphic. Compared with other woody taxa, E. racemosa has low genetic (i.e. allelic) diversity within populations (H_ep = 0.063) and at the species level (H_es = 0.091). Most of the genetic variation (82%) was found within populations, and genetic identities between populations were high (mean I = 0.96). However, genotypic diversity (i.e. the number of multilocus genotypes) differed markedly among populations. Two of the 10 populations consisted almost entirely of single multilocus genotypes, whereas more than 20 multilocus genotypes (in samples of 48 stems) were detected at three sites. Sites in which few multilocus genotypes were detected have low seedset, suggesting that the lack of clonal diversity limits reproduction in some populations of this reportedly self-incompatible species.     

Clonal reproduction and patterns of genotypic diversity in Decodon verticillatus (Lythraceae)

Most perennial plants combine sexual reproduction with some form of clonal propagation. These mixed strategies may produce considerable variation among populations in levels of clonal diversity in response to ecological factors limiting one or other reproductive mode. Surveys of style morph frequencies in 163 populations of the eastern North American, clonal, tristylous aquatic, Decodon verticillatus (L.) Ell. (Lythraceae) suggested a wide range of clonal diversity among populations. Populations consisting of a single style morph were most common at the northern margin of the species' range and could have arisen through severe founder events followed by exclusive clonal propagation. Here, we test this hypothesis by comparing allozyme variation in populations monomorphic and polymorphic for style length located in Ontario and Michigan. Each of the four populations monomorphic for style length were fixed for a single three-locus allozyme genotype while the seven trimorphic and five dimorphic populations contained an average of 26 multilocus genotypes each. Measures of genotypic diversity were high in polymorphic populations (average D = 0.93 ± 0.02 standard error; D = 0.00 for all populations monomorphic for style length). Three of the populations monomorphic for style length were fixed for a heterozygous genotype at one of the loci surveyed, suggesting that each consists of a single clone. In contrast, genotype frequencies in polymorphic populations conformed to Hardy-Weinberg proportions indicative of sexual reproduction. The range of clonal diversity found in D. verticillatus is the largest reported for a clonal plant species, although the literature is too limited to determine whether this is truly unusual. Clonal diversity in D. verticillatus is likely to be regulated largely by ecological factors affecting seed production and establishment. However, genetically based sexual sterility also occurs in some populations.     

Genetic diversity and population structure of Yucca filamentosa (Agavaceae)

Using 19 allozyme loci we studied genetic diversity in 18 populations of Yucca filamentosa (Agavaceae) from the southeastern United States. Of the 19 loci surveyed, 17 (89.5%) were polymorphic in at least one of the populations sampled. There was considerable variation among populations in the percentage of polymorphic loci (range = 31.6-84.2%, mean = 67.6%). Similar heterogeneity among populations was observed for mean number of alleles per polymorphic locus (range = 2.0-3.0; mean = 2.48) and mean expected heterozygosity (range = 0.113-0.288; mean = 0.213). On average, 83% of the total genetic diversity was found within populations. Duplications of three allozyme loci were detected in several populations. The life-history characteristics of Y. filamentosa (a long-lived, semiwoody, predominantly outcrossing monocot with a large geographical range) may contribute to the maintenance of such high levels of genetic diversity. These results contradict expectations of the genetic structure of Y. filamentosa based on observations of the dispersal and pollination behavior of its sole pollinator, Tegeticula yuccasella, the yucca moth.     

Isolation of six microsatellite markers from the pea aphid,Acyrthosiphon pisum (Homoptera,Aphididae)

Using the magnetic particles method, we isolated six polymorphic microsatellite loci from the pea aphid, Acyrthosiphon pisum (Harris), which feeds on a wide range of legume species. The isolated loci were polymorphic, with three to six alleles in 40 aphids. Expected heterozygosities ranged from 0.12 to 0.65. These loci can be used to quantify clonal diversity and compare genetic population structure between sexual and asexual populations.     

Microsatellite Markers Reveal Genetic Variation within Sclerotinia sclerotiorum Populations in Irrigated Dry Bean Crops in Brazil

Microsatellites are powerful markers to infer population genetic parameters. We used 10 microsatellite loci to characterize the genetic diversity and structure of 79 samples of Sclerotinia sclerotiorum isolated from four Brazilian dry bean populations and observed that eight of them were polymorphic within populations. We identified 102 different haplotypes ranging from 6 to 18 per locus. Analyses based on genetic diversity and fixation indices indicated variability among and within populations of 28.79% (F_ST = 28793) and 71.21%, respectively. To examine genetic relatedness among S. sclerotiorum isolates, we used internal spacer (ITS1‐5.8S‐ITS2) restriction fragment length polymorphism (PCR‐RFLP) and sequencing analysis. PCR‐RFLP analysis of these regions failed to show any genetic differences among isolates. However, we detected variability within the sequence, which does not support the hypothesis of clonal populations within each population. High variability within and among populations may indicate the introduction of new genotypes in the areas analysed, in addition to the occurrence of clonal and sexual reproduction in the populations of S. sclerotiorum in the Brazilian Cerrado.     

Distribution of genetic diversity among disjunct populations of the rare forest understory herb, Trillium reliquum

We assessed genetic diversity and its distribution in the rare southeastern US forest understory species, Trillium reliquum. In all, 21 loci were polymorphic (PS=95.5%) and the mean number of alleles per polymorphic locus was 3.05. However, genetic diversity was relatively low (Hes=0.120) considering the level of polymorphism observed for this outcrossing species. A relatively high portion of the genetic diversity (29.7%) was distributed among populations. There was no relationship between population size and genetic diversity, and we did not detect significant inbreeding. These results are best explained by the apparent self-incompatibility of this species, its longevity and clonal reproduction. To address questions regarding the history of T. reliquum's rarity, we compared results for T. reliquum with that of its more common and partially sympatric congener, T. cuneatum. Despite shared life history traits and history of land use, we observed significant genetic differences between the two species. Although T. cuneatum contains slightly lower polymorphism (Ps=85%), we detected significantly higher genetic diversity (Hes=0.217); most of its genetic diversity is contained within its populations (GST=0.092). Our results suggest that not only is there little gene flow among extant T. reliquum populations, but that rarity and population isolation in this species is of ancient origins, rather than due to more recent anthropogenic fragmentation following European colonization. The Chattahoochee River was identified as a major barrier to gene exchange.     

Genetic diversity and morphological differentiation in Liatris helleri (Asteraceae), a threatened plant species

Liatris helleri (Asteraceae) is an insect-pollinated herbaceous perennial endemic to several high-elevation sites in the Blue Ridge Mountains of North Carolina. Allozymes were used to describe the genetic diversity and population structure in nine populations of this rare, federally listed species. Differences in leaf morphology were also examined for greenhouse-grown plants representing several populations. The proportion of the total genetic diversity found among populations, as indicated by the allozyme data, was 16%. Higher levels of population differentiation were found for differences in leaf shape; population of origin accounted for 37% of the variation in maximum leaf width, while families within populations accounted for 7%. In contrast to many endemic species, L. helleri maintains fairly high levels of genetic diversity. For the species, the percent polymorphic loci was 87.5, the average number of alleles at variable loci was 3.00 and the gene diversity was 0.276. Mean population values were percent polymorphic loci =58.4, mean number of alleles per polymorphic locus =2.59 and gene diversity =0.219. The estimated gene flow was low (Nm=0.85–1.32) and a relatively high correlation (r=0.55; p<0.005) was found between linear geographic and genetic distance. This suggests that the populations are partially isolated by distance, despite the limited range (<60 km) of the species. We recommend that population distinetiveness be maintained in restoration efforts.     

PATTERNS OF REPRODUCTION,GENETIC DIVERSITY,AND GENETIC DIFFERENTIATION IN CALIFORNIA POPULATIONS OF THE GENICULATE CORALLINE ALGA LITHOTHRIX ASPERGILLUM (RHODOPHYTA)1

The reproductive composition and genetic diversity of populations of the red seaweed Lithothrix aspergillum Gray (O. Corallinales) were studied at three southern California sites (Shaw's Cove and Treasure Island, Laguna Beach; Indian Rock, Santa Catalina Island) and at a fourth site (Bodega Bay) located in northern California. Sexually reproducing populations were confined to southern California. Diploid individuals were numerically dominant over haploid (gametophytic) individuals at all sites. Intertidal and subtidal subpopulations from Shaw's Cove differed in their reproductive profiles. Most intertidal specimens found on emersed surfaces were densely branched, turf-forming, and bore tetrasporangial (68.6%), carposporangial (11.4%), or spermatangial (5.7%) conceptacles, reflecting a sexual life history; none produced asexual bispores. In contrast, 74.3% of the larger, loosely branched subtidal specimens bore bisporangial conceptacles indicative of asexual reproduction. Nearly 70% of the Indian Rock thalli showed no evidence of conceptacle formation. Only asexual, diploid bispore-producing thalli were obtained from the Bodega Bay site. Genetic diversity (mean number of alleles per locus, percent of polymorphic loci, and average expected heterozygosity) of diploid L. aspergillum populations varied with life-history characteristics and geographic location. A total of 30 alleles was inferred from zymograms of 16 loci examined by starch-gel electrophoresis; of these loci, 11 were polymorphic. The genetic diversity of sexual, diploid populations of L. aspergillum (alleles per locus [A/L] = 1.4-1.5; percent polymorphic loci [%P] = 37.5-50.0) was relatively high compared with other red seaweeds. Lowest diversity (A/L = 1.0; %P = 0.0) occurred in the exclusively asexual Bodega Bay population which consisted of genetic clones. All sexual L. aspergillum populations deviated significantly from Hardy-Wein-berg expectations due to lower than expected heterozygosity. Genetic differentiation (Wright's F_statistic [F_ST]; Nei's Genetic Distance [D]) among sexually reproducing southern California populations was low (F_ST= 0.030) on a local scale (ca. 5 km), suggesting high levels of gene flow, but high genetic differention (F_ST= 0.390 and 0.406) occurred among southern California populations separated by ca. 70 km. Very high genetic differentiation (F_ST= 0.583–0.683) was obtained between northern and southern California populations separated by 700–760 km. Our genetic and reproductive data suggest that the L. aspergillum population from Bodega Bay is sustained by perennation, vegetative propagation, or asexual reproduction by bispores and may represent an isolated remnant or a population established by a founder event.     

Allozyme diversity in the federally threatened golden paintbrush, <Emphasis Type="Italic">Castilleja levisecta</Emphasis> (Scrophulariaceae)

Castilleja levisecta (Scrophulariaceae), the golden paintbrush, is an insect-pollinated herbaceaous perennial found in the Pacific Northwest. Currently restricted to two island populations off British Columbia and nine populations (eight on islands) in Washington, C. levisecta is a rare species threatened with extinction. Allozymes were used to describe genetic diversity and structure in these eleven populations. Despite its threatened status and small geographic range, exceptionally high levels of genetic diversity are maintained within C. levisecta. All sixteen of the loci resolved were polymorphic within the species (P_s=100%), while the mean percentage of loci polymorphic within populations (P_p) was 65.7%. The mean number of alleles per polymorphic locus (AP_s) was 2.94 within the species and averaged 2.38 within populations (AP_p). Genetic diversity (H_es) was 0.285 for the species, whereas mean population genetic diversity (H_ep) was 0.213. Smaller populations had, on average, fewer observed alleles and less genetic diversity. A significant negative correlation (r = –0.72) was found between genetic identity and geographic distance, indicating reduced gene flow between distant populations. The most geographically isolated population was one of the larger populations, one of the most genetically diverse and the most genetically divergent. A wide range of pairwise population genetic identities (I = 0.771 – 0.992) was found, indicating considerable genetic divergence between some populations. Overall, 19% of the total genetic diversity was distributed among populations. Results of this survey indicate that genetic augmentation of existing populations is unnecessary. The high allelic diversity found for the species and within its populations holds promise for conservation and restoration efforts to save this rare and threatened plant species.     

Genetic Diversity in Cymophyllus fraserianus (Cyperaceae), a Rare Monotypic Genus

Cymophyllus fraserianus (Fraser's sedge) is a rare perennial evergreen herb found in late-successional forest communities in the Appalachian Mountains of the U.S. Genetic diversity was assessed at 19 allozyme loci for 12 populations sampled from the southern and central portions of the range of this primitive monotypic genus. Species variation was comparable to that found for other narrowly distributed species, although mean population genetic diversity was somewhat higher. Sixteen of the 19 loci (84%) were polymorphic, with a mean of 46% polymorphic within populations. On average, 2.7 alleles were detected per polymorphic locus. Genetic diversity within populations (Hep) averaged 0.113, whereas species' genetic diversity (Hes) was 0.131. Although a twofold range of within-population genetic diversity (Hep = 0.075-0.158) was found, less than 13% of the genetic variation was distributed among populations (G(ST) = 0.129). An indirect estimate of historical levels of gene flow (Nm = 1.69) was consistent with the high mean genetic identity (mean I = 0.96) found between populations. Despite the relictual nature of C. fraserianus, its rarity and fragmented distribution, genetic diversity within the genus is typical of herbs with similar life-history characteristics. No association was found between geographic and genetic distances between populations (r = -0.01; p > 0.9), suggesting that present day populations are relatively isolated.     

Genetic variation and clonal structure of the rare,riparian shrub <Emphasis Type="Italic">Spiraea virginiana</Emphasis> (Rosaceae)

Genetic diversity is often considered important for species that inhabit highly disturbed environments to allow for adaptation. Many variables affect levels of genetic variation; however, the two most influential variables are population size and type of reproduction. When analyzed separately, both small population size and asexual reproduction can lead to reductions in genetic variation, although the exact nature of which can be contrasting. Genetic variables such as allelic richness, heterozygosity, inbreeding coefficient, and population differentiation have opposite predictions depending upon the trait (rarity or clonality) examined. The goal of this study was to quantify genetic variation and population differentiation in a species that resides in a highly stochastic environment and is both rare and highly clonal, Spiraea virginiana, and to determine if one trait is more influential genetically than the other. From populations sampled throughout the natural range of S. virginiana, we used microsatellite loci to estimate overall genetic variation. We also calculated clonal structure within populations, which included genotypic richness, evenness, and diversity. Gene flow was investigated by quantifying the relationship between genetic and geographic distances, and population differentiation (θ) among populations. Observed heterozygosity, genotypic richness, and inbreeding coefficients were found to be representative of high clonal reproduction (averaging 0.505, 0.1, and –0.356, respectively) and the number of alleles within populations was low (range = 2.0–3.6), being more indicative of rarity. Population differentiation (θ) among populations was high (average = 0.302) and there was no relationship between genetic and geographic distances. By examining a species that exhibits two traits that both can lead to reduced genetic variation, we may find an enhanced urgency for conservation. Accurate demographic counts of clonal species are rarely, if ever, possible and genetic exploration for every species is not feasible. Therefore, the conclusions in this study can be potentially extrapolated to other riparian, clonal shrubs that share similar biology as S. virginiana.     

Population genetics of the fissiparous holothurian Stichopus chloronotus (Aspidochirotida) on the Great Barrier Reef, Australia

 Population genetic structure was studied in one nearshore and two offshore populations of Stichopus chloronotus, a common holothurian species on Indo-Pacific coral reefs. Genetic variation at five polymorphic loci was examined using allozyme electrophoresis. The nearshore population consisted almost exclusively of male individuals, and more males than females were found in all populations studied. Deviations of heterozygosity from that predicted under Hardy-Weinberg equilibrium indicated that asexual reproduction occurred in all populations. Estimates of the level of asexual reproduction using the ratios of the number of sexually produced individuals to sample size, observed genotypic diversity to expected genotypic diversity, and number of genotypes to sample size confirmed that this reproductive mode was more important at the nearshore reef compared to the two offshore reefs. There were large differences in genotypic frequencies between males and females. F-statistics on clonal genotypic frequencies were not statistically significant between populations for neither females or males, suggesting high dispersal of larvae between reefs. A higher mortality of females during larval or early post-settlement stages, or reduced dispersal capability of female larvae are the most likely reasons for biased sex ratios. Accepted: 23 November 1998     

Isozyme variation under different modes of reproduction in two clonal winter annuals, Sedum rosulato-bulbosum and Sedum bulbiferum (Crassulaceae)

We studied isozyme variation in two annual species that produce bulbils, Sedum rosulato-bulbosum , which includes both sexually reproducing plants and obligate clonal plants that result from triploidy (fertile and sterile S. rosulato-bulbosum , respectively), and an obligate clonal plant, Sedum bulbiferum , to examine the relationship between reproductive mode and isozyme variation. The sterile S. rosulato-bulbosum population exhibited no genotypic variation, but showed high genetic variation (gene diversity, H _e  = 0.60) because five of the six loci that we analyzed were heterozygous. Almost all ramets of S. bulbiferum across 20 populations shared an identical isozyme phenotype, although we could not identify the genetic basis of the phenotype. In contrast, fertile S. rosulato-bulbosum exhibited genotypic variation across the species, but comprised genotypically uniform and polymorphic populations whose genotypic variations correlated positively with the genetic variations within the populations ( H _e at the genet level per population ranged from 0.08 to 0.37). Genetic drift and habitat conditions inhibiting seedling recruitment may have caused this among-population variation. The results for sterile and fertile S. rosulato-bulbosum suggest that exclusive clonal reproduction causes low genotypic variation, but maintains genetic variation within individuals. Factors that affect the maintenance of genetic variation in these plants are discussed on the basis of these findings.     

Genetic diversity of the Chestnut blight fungus Cryphonectria parasitica in four French populations assessed by microsatellite markers

Microsatellites are powerful markers to infer population genetic parameters. Here, 13 microsatellite loci isolated from a genomic and a cDNA library of Cryphonectria parasitica were used to characterize the genetic diversity and structure of four French populations. Twelve of these loci were polymorphic within populations, and average gene diversity (H_e) was estimated to be 0.35. There was a lower genetic diversity in a south-eastern population relative to three south-western populations. In these three populations, microsatellite genotypic diversity was higher than vegetative compatibility type diversity. A high genetic differentiation (G_ST = 0.27) suggested a low gene flow and/or founder effects of French populations which are in agreement with low dispersal of spores and different introductions of this species in southern France. This study demonstrates the significance of these microsatellite loci to assess gene flow and reproductive system in this important pathogen.     

High genetic diversity in Sarracenia leucophylla(Sarraceniaceae), a carnivorous wetland herb

Eighteen allozyme loci were used to examine genetic diversity in 10 natural populations of Sarracenia leucophylla Raf., a pitcher plant restricted to the southeastern United States. One ex situ population propagated for restoration in Georgia was also analyzed. S. leucophylla is an insect-pollinated, outcrossing perennial wetland herb that is threatened over much of its geographic range. Fifteen loci (83.3%) were polymorphic, with a mean number of alleles of 3.33. Compared to species having similar life-history traits and to previously analyzed Sarracenia species, S. leucophylla displayed unexpectedly high genetic diversity. For example, genetic diversity within the species (Hes) was 0.224 and mean population genetic diversity (Hep) was 0.183. Although small S. leucophylla populations maintained less genetic diversity than larger ones, these differences were not statistically significant. Nonetheless, this suggests that small populations may have lost rare alleles. Statistically significant genetic differentiation among populations was found (theta = 0.192, P < .01), although it was not atypical considering the species' life-history characteristics. A significant correlation (P < .01) between genetic and geographic distance was found, indicating an isolation-by-distance effect. However, the correlation coefficient for this relationship was low (r = 0.46), suggesting that factors other than gene flow play a prominent role in the geographic distribution of genetic diversity within the species. The ex situ population captured most of the allozyme variation found in its source population.