Allozyme diversity and genetic structure of the leafy cactus (Pereskia guamacho [Cactaceae])

We examined levels of genetic variation and genetic structure in the leafy cactus (Pereskia guamacho) in arid and semiarid zones in Venezuela. We surveyed genetic diversity within 17 populations using 19 allozyme loci. Genetic diversity was relatively high at both the species (P(s) = 89%, A(s) = 3.26, AP(s) = 3.53, H(es) = 0.24) and population (P(p) = 63%, A(p) = 1.90, AP(p) = 2.42, H(ep) = 0.20) levels. A significant deficit of heterozygote individuals was detected within populations in the Paraguana Peninsula region (F(IS) = 0.301). Relatively low levels of population differentiation were detected at macrogeographic (G(ST) = 0.112) and regional levels (G(ST) = 0.044 for peninsula region and G(ST) = 0.074 for mainland region), suggesting substantial genetic exchange among populations; however, gene flow in this species seems to be regulated by the distance among populations. Overall, estimates of genetic diversity found in P. guamacho are concordant with the pattern observed for other cacti surveyed, namely high levels of polymorphism and genetic diversity with one common allele and several rare alleles per locus. Differences in gene dispersal systems between this species and other cacti studied were not reflected in the patterns of genetic diversity observed. The concentration of the highest estimates of genetic variation in northwestern Venezuela suggests a potential reservoir of plant genetic diversity within xerophilous ecosystems in northern South America.     

Genetic structure of an endangered plant, Antirrhinum microphyllum (Scrophulariaceae): allozyme and RAPD analysis

Thirteen allozyme loci and 68 random amplified polymorphic DNA (RAPD) markers were analyzed to assess the genetic diversity and population structure of threatened Antirrhinum microphyllum (Scrophulariaceae), a narrow endemic of central Spain known from only four populations. According to allozyme data, species genetic diversity (p = 46.15%, A = 2.61, and H(e) = 0.218), as well as within-population genetic diversity (p = 44.23%, A = 2.10, and H(e) = 0.204), were high when compared to average estimates for other narrowly distributed plant species. Ninety-four percent of species genetic diversity corresponded to within-population genetic diversity. Nevertheless, significant differences were found among populations in allele frequencies of four of the six polymorphic loci, and three private alleles were detected. Inbreeding coefficients (F(IS)) suggest that populations are structured in genetic neighborhoods. The RAPDs also showed high levels of genetic diversity (p = 89.71% and H(e) = 0.188 at the species level, and p = 67.65% and H(e) = 0.171 at the population level). Nei's genetic distances estimated both from allozymes and RAPDs indicated low differentiation among populations. In spite of this, the low frequencies of certain alleles and the presence of private alleles indicate that efforts should be made to conserve all four remaining populations.     

The structure of allozyme and leaf shape variation in isolated, range-margin populations of the shrub Hippocrepis emerus (Leguminosae)

We investigated allozyme variation and phenotypic variation in leaf shape in 15 populations of the shrub Hippocrepis emerus (Leguminosae) from the three isolated, regional populations in Scandinavia and analysed patterns of differentiation and the hierarchical structuring of diversity on different geographic scales There are pronounced geographic differences between the Norwegian and Swedish isolates of the species and most of the polymorphic allozyme loci show reciprocal fixation in the two isolates The Scandinavian populations of H emerus are not only disjunct on a macrogeographic scale but also show considerable disjunction within regions Within the Oland regional population, a central group of populations shows low levels of Inter-population differentiation the Gotland group of populations is related to this core group of Oland populations The geographically marginal populations on Oland are spatially isolated and show a higher degree of divergence between populations than does the central group of Oland populations We interpret genetic divergence between the marginal populations in terms of genetic drift - as a result of historical fluctuations in habitat availability and population size     

Low genetic structure in an epiphytic Orchidaceae (Oncidium hookeri) in the Atlantic rainforest of South-eastern Brazil

BACKGROUND AND AIMS: Oncidium hookeri is a neotropical species of epiphytic Orchidaceae found in the Brazilian Atlantic rainforest at the top of the Mantiqueira Range of mountains. The genetic variation of O. hookeri was studied to assess the distribution of genetic variability within and among six populations localized in Atlantic rainforest remnants. Gene flow among populations and the occurrence of recent bottlenecks were investigated in order to infer the degree of isolation of these populations. METHODS: Thirteen polymorphic loci were used for allozyme electrophoresis. The data were analysed by means of standard statistical approaches, to estimate gene diversity and the genetic structure of the populations. KEY RESULTS: The mean gene diversity and allelic richness were H(e) = 0.099 and A = 1.75, respectively. F-statistics revealed high heterozygote deficiencies in all populations (F(IS) = 0.43-0.82). Several rare alleles were found in all the populations, and three populations presented private alleles. Low genetic differentiation among O. hookeri populations was detected (F(ST) = 0.029); natural selection may be involved in PGM locus differentiation among populations. The genetic differentiation between paired populations was low, bearing no correlation with geographic distance (Mantel test: r = -0.34, P = 0.72). Only two populations showed signs of recent bottlenecks. CONCLUSIONS: The heterozygote deficiency found seems to be caused by pollinator behaviour; the low frequencies of several alleles of different loci can be maintained due to clonal propagation. Despite the stochastic nature of the wind-dispersal of seeds to long distances, this process may promote an effective gene flow among populations, thus avoiding genetic differentiation.     

Genetic Diversity and Differentiation in Hedychium spicatum, a Valuable Medicinal Plant of Indian Himalaya

Hedychium spicatum, a perennial rhizomatous medicinal plant distributed in subtropical and temperate parts, is considered nearly endemic to the Himalayan region.In this study allozyme markers were utilized to assess genetic variations and relationships among 12 distinct populations of this species from the West Himalaya of India. A high level of genetic diversity was found among the populations. Of the 13 loci generated using eight enzymes, 12 (92%) were polymorphic. F-statistics suggested a prevalence of a high heterozygote excess among populations (F(IS) = -0.51). Gene flow estimates and geographic distances between populations did not correlate significantly (r = -0.0258, P < 0.3550). The excess heterozygosity may be attributed to high pollinator mobility and inbreeding coefficient within the subpopulation, relative to the total F(IS) value. High frequencies of several alleles at different loci probably reflect the breeding pattern, as the species propagates clonally as well as through seeds. We also discuss conservation implications for the target species.     

Conservation Genetics of an Endangered Herb, Hanabusaya asiatica (Campanulaceae)

Abstract: Hanabusaya asiatica (Nakai) Nakai (Campanulaceae), a bee- pollinated, perennial herb, is restricted to the mountainous regions of the eastern-central Korean peninsula. Allozyme analyses for 348 individuals assessed the levels of genetic diversity for five populations. Spatial autocorrelation statistics were also used to examine the spatial distribution of allozyme polymorphisms. The species maintains high levels of allozyme diversity ( H _eS = 0.217) and it exhibits low allozyme differentiation among populations ( G _ST = 0.132) compared with other endemics (mean H _e = 0.096, G _ST = 0.248). There is an apparent pattern of isolation by distance among populations. These results suggest that H. asiatica is at a genetic equilibrium. A considerable deficit in numbers of heterozygotes suggests mating among relatives in populations. At least three populations of H. asiatica should be sampled or conserved to capture or maintain > 99 % of the genetic diversity in the species as a whole. Within local populations, individuals are distributed in a structured, isolation by distance, manner. Approximate genetic patch width in the populations of H. asiatica examined is 5 - 8 m. For conservation purposes, it is suggested that, in general, the sampling of H. asiatica should be conducted at intervals in order to efficiently sample the genetic diversity across an entire population.     

Digestibility of columnar cacti pollen grains in the glosophagine bats Glossophaga longirostris and Leptonycteris curasoae (Chiroptera: Phyllostomidae)

We examined the protoplasmic assimilation of columnar cacti pollen grains in two species of Venezuelan desert glosophagine bats, Glossophaga longirostris and Leptonycteris curasoae, by determining the amount of empty (digested) pollen grains found in their fecal samples. To determine the amount of empty pollen grains, the fecal samples were stained to differ between empty and full (non-digested) pollen grains. The number of empty and full pollen grains observed in the fecal samples were corrected using the amount of aborted pollens present (before anthesis) in flowers of the columnar cacti species (Subpilocereus repandus, Stenocereus griseus and Pilosocereus tillianus) used by bats as food in the study site; G. longirostris and L. curasoae digested 64.2% and 71.3% of all the pollens fed, respectively. These high values confirm the importance of pollen in the diet of these bats, given its high nitrogen level.     

Genetic diversity and phylogenetic relatedness among six endemic Pterostylis species (Orchidaceae; series Grandiflorae) of Western Australia, as revealed by allozyme polymorphisms

Starch gel electrophoresis was employed to survey the allozyme polymorphism and phylogenetic relationships among 35 populations covering six closely related Western Australian endemic Pterostylis species (series Grandiflorae); viz P. rogersii, P. aspera, P. angusta, P. hamiltonii, P. scabra and P. aff. alata. The aim of this study was to determine intraspecific and interspecific genetic diversity and species relationships based on allozyme analysis. The frequencies of 56 alleles at 12 enzyme systems coded by 15 loci were determined along with a mean intraspecific genetic identity value. Allozyme markers clearly discriminated populations belonging to different species. Nei's genetic distance/identity co-efficient was used to measure the level of genetic differentiation among populations and species. Based on these values, a dendrogram was constructed which revealed that all the populations clustered into groups corresponding to the respective species. Gene diversity analysis among all the species revealed total genetic diversity H(t) of 0.23 with co-efficient of gene differentiation 10% (G(st)=0.10). Mean genetic variability (H(e)=0.136, P=40%) was also higher than for other outbreeding plant species. Mean genetic identity coefficient of populations of all species was 0.859 which increased to 0.877 upon exclusion of P. aff. alata, indicating a high degree of similarity among all species except P. aff. alata which segregated distinctively from the rest. Overall, the investigation provided independent support for the morphological segregation of these taxa.     

Spatial genetic structure and clonal diversity of island populations of lady's slipper (Cypripedium calceolus) from the Biebrza National Park (northeast Poland)

Three populations of the rare and endangered plant species Cypripedium calceolus were included in a study of genetic diversity and spatial genetic structure in the Biebrza National Park, northeast Poland. Analysis of 11 allozyme loci indicate that the populations of this species contained high genetic variability (P = 45.5%, A= 1.73). On the other hand, the genetic differentiation (FST = 0.014, P < 0.05) among C. calceolus populations was very low when compared to other species with similar life history characteristics. The observed high rate of gene flow (Nm = 18) may suggest that the populations studied derived from each other in the recent past. Five polymorphic allozyme markers identified 109 multilocus genotypes in three populations and the majority of them (67%) were population-specific. One of the populations studied, characterized by particularly extensive vegetative reproduction, showed the lowest clonal diversity (G/N = 0.15) and heterozygosity (HO = 0.111) values and the highest FIS(0.380), when compared to other two populations (G/N = 0.26-0.27, HO= 0.166-178, FIS = 0.024-0.055). This may indicate that clonal reproduction has an important influence on the genetic structure of C. calceolus populations. The longevity of genets, the out-crossing breeding system and the presence of recruitment from seeds are factors maintaining genetic diversity in C. calceolus.     

Allozyme diversity in Pinus virginiana (Pinaceae): intraspecific and interspecific comparisons

Two of the four members of subsection Contortae of the genus Pinus occur in the southeastern United States: Pinus virginiana, which ranges throughout the southern and central Appalachian Mountains, and P. clausa, which is restricted to Florida and southern Alabama. We examined allozyme variation within P. virginiana and genetic relationships between this species and the two varieties of P. clausa (var. clausa and var. immuginata). P. virginiana maintains more genetic diversity at both the species (Hes = 0.139) and population (Hep = 0.128) levels than the other three species in the subsection, which may reflect the combination of its widespread distribution and the absence of cone serotiny. Genetic differentiation among populations in P. virginiana was relatively low (GST = 0.053), but significant contrasts in allozyme frequencies and genetic diversity were apparent between populations to the northwest vs. outheast of the Appalachian Mountains. These regional differences likely resulted initially from historical processes that occurred during the Pleistocene and early Holocene, and have been reinforced by modern selective pressures and barriers to gene flow. The mean genetic distance between populations of P. virginiana and P. clausa (D = 0.071) was greater than that between populations of the two varieties of P. clausa (D = 0.012), which suggests that the two varieties diverged at some point after the separation of the two species.     

Genetic variation and evolution of Polaskia chichipe (Cactaceae) under domestication in the Tehuacán Valley, central Mexico

Polaskia chichipe is a columnar cactus under artificial selection in central Mexico because of its edible fruits. Our study explored the effect of human manipulation on levels and distribution of genetic variation in wild, silviculturally managed and cultivated sympatric populations. Total genetic variation, estimated in nine populations with five microsatellite loci, was H(T) = 0.658 +/- 0.026 SE, which was mainly distributed within populations (H(S) = 0.646) with low differentiation among them (F(ST) = 0.015). Fixation index (F(IS)) in all populations was positive, indicating a deficit of heterozygous individuals with respect to Hardy-Weinberg expectations. When populations were pooled by management type, the highest expected heterozygosity (H(E) = 0.631 +/- 0.031 SE) and the lowest fixation index (F(IS) = 0.07) were observed in wild populations, followed by cultivated populations (H(E) = 0.56 +/- 0.03 SE, F(IS) = 0.14), whereas the lowest variation was found in silviculturally managed populations (H(E) = 0.51 +/- 0.05 SE, F(IS) = 0.17). Low differentiation among populations under different management types (F(ST) 0.005, P < 0.04) was observed. A pattern of migration among neighbouring populations, suggested from isolation by distance (r2 = 0.314, P < 0.01), may have contributed to homogenizing populations and counteracting the effects of artificial selection. P. chichipe, used and managed for at least 700 generations, shows morphological differentiation, changes in breeding system and seed germination patterns associated with human management, with only slight genetic differences detected by neutral markers.     

Conservation genetics of the endangered Iberian steppe plant Ferula loscosii (Apiaceae)

Ferula loscosii (Lange) Willk (Apiaceae) is a threatened endemic species native to the Iberian Peninsula. The plant has a narrow and disjunct distribution in three regions, NE, C and SE Spain. Genetic variability within and among 11 populations from its natural distribution was assessed using allozymes. Intermediate levels of genetic diversity were detected in F. loscosii (P(99%) = 36.83; H(E) = 0.125; H(T) = 0.152). However, the highest genetic diversity (58%) corresponded to the threatened populations from SE and C Spain (H(T) = 0.169) rather than the more abundant and larger populations from NE Spain (Ebro valley) (H(T) = 0.122). Low to moderate levels of genetic structure were found among regional ranges (G(ST) = 0.134), and several statistical spatial correlation analyses corroborated substantial genetic differentiation among the three main regional ranges. However, no significant genetic differentiation was found among the NE Spain populations, except for a northernmost population that is geographically isolated. Outcrossing mating and other biological traits of the species could account for the maintenance of the present values of genetic diversity within populations. The existence of an ancestral late Tertiary wider distribution of the species in SE and C Spain, followed by the maintenance of different Quaternary refugia in these warmer areas, together with a more recent and rapid post-glacial expansion towards NE Spain, are arguments that could explain the low genetic variability and structure found in the Ebro valley and the higher levels of diversity in the southern Iberian populations.     

Genetic diversity in harvested and protected populations of wild American ginseng, Panax quinquefolius L. (Araliaceae)

Genetic diversity was examined at 16 allozyme loci in 21 wild populations of the medicinal plant American ginseng, Panax quinquefolius L. (Araliaceae). This species has been harvested from forests in North America for more than 250 years. Average expected heterozygosity was significantly greater within protected populations (H(e) = 0.076) than within populations in which harvesting was permitted (H(e) = 0.070). More notably, genetic structure was greater among unprotected populations (G(ST) = 0.491) than among protected populations (G(ST) = 0.167). These differences in the level and distribution of genetic diversity in American ginseng populations indicate that harvesting may have significant evolutionary implications for this species. Age class structure also shifted toward smaller, nonreproductive plants in unprotected populations. Juvenile plants had lower genetic diversity (H(e) = 0.067) than reproductive plants (H(e) = 0.076) suggesting that conserving a proportion of the largest (oldest) plants in each population is important to protect reproductive fitness and the evolutionary potential of the species. Due to its high genetic structure, conservation recommendations include protecting populations throughout the range of P. quinquefolius.     

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.     

在韩国境内Potentilla fragarioides var .sprengeliana的遗传多样性和种群结构(英文)

根据 2 2个等位酶位点遗传变异 ,探讨了韩国境内委陵菜 (PotentillafragarioidesL .var.sprengeliana)的遗传多样性和种群结构。酶位点的多态位点百分比为 5 9 1%。种和种群水平上的遗传多样性比较高 ,分别为Hes=0 .2 10 ,Hep=0 .199;而种群的分化水平则相对较低 (GST=0 .0 74)。 19个种群中随机交配的偏差为FIS=0 .331。每代迁移数的间接估计 (Nm=3.15 )表明该种在韩国的种群间基因流较高。另外 ,固定指数分析显示在一些种群和位点有轻微的杂合子缺乏。种群间平均遗传一致度为 0 985。这些韩国委陵菜种群存在于较为均一的生境 ,这很有可能是造成其种群遗传一致性较高的原因。     

Genetic diversity in Mediterranean diploid and tetraploid Bromus L. (section Bromus Sm.) populations.

The levels of genetic diversity assessed from allozyme data were investigated in 25 populations of Mediterranean Bromus intermedius, B. squarrosus, B. lanceolatus, and B. hordeaceus from Algeria. The geographically restricted diploids B. intermedius and B. squarrosus displayed less genetic diversity (the mean population gene diversity of Nei (Hu) ranged from 0.03 to 0.12) than the widespread tetraploid colonizers B. lanceolatus and B. hordeaceus (Hu = 0.07-0.27). Deviations from Hardy-Weinberg expectations in diploid populations of B. intermedius and B. squarrosus were observed owing to heterozygote excess at several loci and suggested that these self-fertilizing species may have substantial amounts of allogamy. Tetraploid populations of B. lanceolatus and B. hordeaceus were largely homozygous at homologous loci and frequently exhibited intergenomic fixed heterozygosity in accordance with their alloploid origin. Genetic variation at the infraspecific level was mostly distributed within populations in the four species, B. hordeaceus showing the lowest level of interpopulation differentiation (Gst = 0.06) and the highest level of gene flow (Nm = 3.75). Consistent gene flows are in agreement with the strongest intercontinental invasive behaviour of B. hordeaceus. Less differentiation was reported in the literature among later introduced B. hordeaceus populations from England and Australia, indicating reduced differentiation under the process of colonization. Moderate divergence occured among the four taxa, with interspecific genetic identities ranging from 0.87 to 0.93. In spite of substantial genetic similarity, species were clearly differentiated, with each tetraploid being more closely related to a diploid: B. hordeaceus to B. squarrosus and B. lanceolatus to B. intermedius.     

Mating patterns and genetic diversity in the wild daffodil Narcissus longispathus (Amaryllidaceae)

Despite the importance of Narcissus to ornamental horticulture, there have been no population genetic studies of wild species, many of which have narrow distributions. Here, we measure selfing rates and levels of genetic diversity at allozyme loci in six populations of Narcissus longispathus, a self-compatible daffodil endemic to a few mountain ranges in southeastern Spain. The populations were distributed among four distinct river valleys encompassing two main watersheds in the Sierra de Cazorla mountains. Selfing rates averaged 0.37 (range 0.23-0.46), resulting in significant inbreeding coefficients for the progeny (f = 0.324). In contrast, estimates of inbreeding in parental genotypes were not significantly different from zero (f = 0.001), indicating that few selfed offspring survive to maturity because of inbreeding depression. Species-wide estimates of genetic diversity for the six populations were P(s) = 0.38, H(es) = 0.119 and A(s) = 1.27 with significant genetic differentiation among populations theta = 0.15. The observed patterns of genetic differentiation among populations are likely influenced by the mating system, and a combination of local topography, watershed affinities and gene flow.     

Genetic diversity in natural populations of Piper cernuum

Piper cernuum is a native plant of the Brazilian Atlantic rain forest. This work studies the distribution of allozyme diversity in P. cernuum natural populations in order to establish a strategy for sustainable management and conservation. Leaf samples were collected in two Brazilian states. High divergences among populations (F(SR) = 0.380) and low divergences among regions (F(RT) = -0.069) and among gaps of the same population (F(GT) = 0.062) were found. No association between the geographical variation and the genetic distance was detected. An excess of heterozygotes was detected in the populations (F(IS) = -0.170), suggesting selection in favor of heterozygotes. The results, and the fact that the species depends on constant gap formation for maintenance of its dynamism, suggest that the founder effect is largely responsible for the structuring of populations. For sustainable management, the maintenance of plants/reproductive branches in the gaps is of major importance. The genotypes produced in these gaps are responsible for the establishment of new gaps and are the foundation for new populations, maintaining the dynamics of allele movement.     

Reproductive biology and genetic diversity of a cryptoviviparous mangrove aegiceras corniculatum (Myrsinaceae) using allozyme and intersimple sequence repeat (ISSR) analysis

Mangroves consist of a group of taxonomically diverse species representing about 20 families of angiosperms. However, little is known about their reproductive biology, genetic structure, and the ecological and genetic factors affecting this structure. Comparative studies of various mangrove species are needed to fill such gaps in our knowledge. The pollination biology, outcrossing rate, and genetic diversity of Aegiceras corniculatum were investigated in this study. Pollination experiments suggested that the species is predominantly pollinator-dependent in fruit setting. A quantitative analysis of the mating system was performed using progeny arrays assayed for intersimple sequence repeat (ISSR) markers. The multilocus outcrossing rate (tm) was estimated to be 0.653 in a wild population. Both allozyme and ISSR were used to investigate genetic variation within and among populations. The combined effects of founder events and enhanced local gene flow through seedling dispersal by ocean currents apparently played an important role in shaping the population genetic structure in this mangrove species. Both allozyme variation (P = 4.76%, A = 1.05, HE = 0.024) and ISSR diversity (P = 16.18%, A = 1.061, HE = 0.039) were very low at the species level, in comparison with other woody plants with mixed-mating or outcrossing systems. Gene differentiation among populations was also low: allozyme GST = 0.106 and ISSR GST = 0.178. The unusually high genetic identities (0.997 for allozyme and 0.992 for ISSR loci), however, suggest that these populations are probably all descended from a common ancestral population with low polymorphism.     

Regional patterns of genetic diversity in Pinus flexilis (Pinaceae) reveal complex species history

Pinus flexilis (limber pine) is patchily distributed within its large geographic range; it is mainly restricted to high elevations in the Rocky Mountains and the Basin and Range region of western North America. We examined patterns of allozyme diversity in 30 populations from throughout the species' range. Overall genetic diversity (H(e) = 0.186) was high compared with that of most other pine species but was similar to that of other pines widespread in western North America. The proportion of genetic diversity occurring among populations (G(ST) = 0.101) was also high relative to that for other pines. Observed heterozygosity was less than expected in 28 of the 30 populations. When populations were grouped by region, there were notable differences. Those in the Basin and Range region had more genetic diversity within populations, a higher proportion of genetic diversity among populations, and higher levels of inbreeding within populations than populations from either the Northern or Utah Rocky Mountain regions. Patterns of genetic diversity in P. flexilis have likely resulted from a complex distribution of Pleistocene populations and subsequent gene flow via pollen and seed dispersal.