Genetic variation in Scandinavian Anthericum liliago (Anthericaceae): allopolyploidy, hybridization and immigration history

 We investigated patterns of isozyme variation and the hierarchic structure of genetic diversity in 25 Scandinavian populations of the lilioid herb, Anthericum liliago. Isozyme data suggest that tetraploid A. liliago has an allopolyploid origin and that A. ramosum may be one of its diploid progenitors. Two populations contained known or suspected hybrids between A. liliago and A. ramosum. Isozymes show that one population from S Sweden contains both triploid (hybrid) and tetraploid individuals whereas a putatively hybrid Danish population represents diploid A. liliago. There is an overall northward and eastward decline in allelic richness in the tetraploid populations, with the highest numbers of alleles in Denmark and SW Sweden. This pattern is consistent with a progressive loss of allelic variation during the species' postglacial colonization of Scandinavia. The between-population component of genetic diversity is 4% (compared with 12% in diploid A. ramosum), the between-region diversity component is 7% and 89% of the total diversity is stored within populations. Received March 13, 2002; accepted September 24, 2002 Published online: December 11, 2002     

Genetic structure and differentiation of wild and domesticated populations of Capsicum annuum (Solanaceae) from Mexico

 Genetic variation and structure of ten wild, three domesticated and one wild-cultivated populations of pepper (Capsicum annuum) from northwestern Mexico were studied in order to find out if the domestication process has reduced the genetic variation of the modern cultivars of this species. The analysis was based on 12 polymorphic loci from nine isozymes. Wild populations were sampled in different habitats along a latitudinal gradient of ca. 500 km. All populations had high genetic variation (i.e. wild: A = 2.72, P = 90.8%, He = 0.445; wild-cultivated: A = 2.50, P = 92.3%, He = 0.461; domesticated: A = 2.60, P = 84.6%, He = 0.408), indicating little genetic erosion in modern cultivars of pepper. Genetic diversity estimated by Nei's method showed that most genetic variation is found within, rather than among populations. However, genetic differentiation is greater among cultivated (G _ST=0.167) than among wild (G _ST=0.056) populations. Wild populations had an average genetic identity (I) of 0.952, indicating little differentiation and high gene flow (Nm=4.21) among these populations. Average genetic identity between wild and domesticated populations was of I=0.818, revealing that the domestication process has modified the genetic composition of commercial varieties of pepper. Changes in genetic composition among commercial varieties seem to have occurred in different directions, as indicated by the average value of I = 0.817 among these populations. The high level of diversity found in wild populations of C. annuum suggests that the wild relatives of cultivated peppers are a valuable genetic resource which must be conserved. Received May 5, 1999 Accepted October 30, 2000     

Microsatellite polymorphism and genetic differentiation in three Norwegian populations of Elymus alaskanus (Poaceae)

 Variation at seven microsatellite loci was investigated in three local E. alaskanus populations from Norway and microsatellite variation was compared with allozyme variation. The percentage of polymorphic loci was 81%, the mean number of alleles per polymorphic locus was 5.7 and expected heterozygosity was 0.37. An F-statistic analysis revealed an overall 48% deficit of heterozygotes over Hardy-Weinberg expectations. Gene diversity is mainly explained by the within population component. The averaged between population differentiation coefficient, F _st , over 7 loci is only 0.13, which accounts for only 13% of the whole diversity and was contrary to allozyme analysis. The mean genetic distance between populations was 0.12. However, a χ² -test showed that allele frequencies were different (p < 0.05) among the populations at 5 of the 7 loci. In comparison with the genetic variation detected by allozymes, microsatellite loci showed higher levels of genetic variation. Microsatellite analysis revealed that population H10576 possesses the lowest genetic variation among the tested three populations, which concur with allozyme analysis. The dendrogram generated by microsatellites agreed very well with allozymic data. Our results suggest that natural selection may be an important factor in shaping the genetic diversity in these three local E. alaskanus populations. Possible explanations for deficit heterozygosity and incongruence between microsatellites and allozymes are discussed. Received November 6, 2001; accepted April 24, 2002 Published online: November 14, 2002 Addresses of the authors: Genlou Sun (e-mail: Genlou.sun@STMARYS.CA), Biology Department, Saint Mary's University, Halifax. Nova Scotia, B3H 3C3, Canada. B. Salomon, R. von Bothmer, Department of Crop Science, The Swedish University of Agricultural Sciences, P.O. Box 44, SE-230 53, Alnarp, Sweden.     

Allozyme variation in Mexican species and classification of Datura (Solanaceae)

 Fifty natural Datura populations, belonging to eleven species (D. ceratocaula, D. discolor, D. inoxia, D. kymatocarpa, D. lanosa, D. metel, D. pruinosa, D. quercifolia, D. reburra, D. stramonium, D. wrightii) from Mexico and adjacent USA, were investigated using starch gel electrophoresis. A total of 64 alleles were scored at 17 loci (DIA1, DIA2, GOT1, GOT2, G6PDH, IDH, MDH1, MDH2, MDH3, ME, PGD1, PGD2, PGM1, PGM2, PHI, SAD, SOD). The heterozygosity among the species ranged from 0.166 (D. ceratocaula) to 0.276 (D. wrightii). Most genetic diversity was found within populations (average H_s=0.242), while values between populations are relatively low (average Dst=0.066, Gst=0.171). The analysis of the genetic distance suggested new taxonomic relationships among the species. Rather than supporting the conventional infrageneric classification with three sections, the results revealed that the herbaceous members of the genus Datura form four groups. One group included four of the eight species of the section Dutra and was more similar to the section Ceratocaulis than it was to the other group that contained the remaining taxa of Dutra. Received February 13, 2001 Accepted December 25, 2001     

Genetic variation in Fitzroya cupressoides (alerce), a threatened South American conifer

Fitzroya cupressoides (alerce, Cupressaceae) is a large and exceptionally long-lived conifer, endemic to a restricted area of southern Chile and neighbouring areas of Argentina. As a result of its high economic value, the species has been severely exploited for timber, and remnant populations are fragmented and often highly disturbed. The species is thought to have undergone a major range contraction during the last glaciation. In order to assess the extent of genetic variation using DNA markers within and between populations of this species, samples were obtained from throughout the natural range and analysed for random amplified polymorphic DNA (RAPD) variation. Eight 10-mer and three 15-mer primers were used to produce a total of 54 polymorphic bands. Shannon's diversity estimates were calculated to provide an estimate of the degree of variation within each population. Values varied from 0.343 to 0.636 with only the lowest value differing significantly from the others (Spop = 0.547). This indicated that there is a significant degree of variation within each population, and did not provide evidence for genetic 'bottle-neck' effects within the species. A pairwise distance measure calculated from the RAPD data was used as an input for principal coordinate (PCO) and AMOVA analyses. The first three principal coordinates of RAPD distances described 8.3, 5.9 and 5.4% of the total variance, respectively, and a degree of clustering of samples according to their geographical origin was detectable. AMOVA analysis indicated that although most of the variation (85.6%) was found within populations, a significant proportion (P < 0.002) was attributable to differences between populations. An UPGMA dendrogram constructed using phi ST values derived from AMOVA produced a pattern broadly similar to that produced by the PCO, highlighting differences between three main groups of populations within Chile: those from the northern Coastal Range, the southern Coastal Range and Central Depression, and the Andes. Populations from Argentina also emerged as significantly different from those in Chile. These results are interpreted in the context of the postglacial history of the species, and their implications for the development of conservation strategies for Fitzroya are discussed.     

Genetic structure and AFLP variation of remnant populations in the rare plant Pedicularis palustris (Scrophulariaceae) and its relation to population size and reproductive components

We investigated plant reproduction in relation to genetic structure, population size, and habitat quality in 13 populations of the rare biennial plant Pedicularis palustris with 3-28500 flowering individuals. We used AFLP (amplified fragment length polymorphism) profiles to analyze genetic similarities among 129 individuals (3-15 per population). In a cluster analysis of genetic similarities most individuals (67%) were arranged in population-specific clusters. Analysis of molecular variance indicated significant genetic differentiation among populations and among and within subpopulations (P < 0.001). Gene flow (N(e) m) was low (0.298). On average, plants produced 55 capsules, 17 seeds per fruit, and 42 seedlings in the following growing season. The number of seeds per capsule was independent of population size and of genetic variability. In contrast, the number of capsules per plant (P < 0.05) and the number of seedlings per plant (P < 0.05) were positively correlated with population size. The relation between population size and the number of seeds per plant was not significant (P = 0.075). The number of capsules and of seeds and seedlings per plant (P < 0.01) were positively correlated with genetic variability. Genetic variability was independent of actual population size, suggesting that historical population processes have to be taken into account, too. Stepwise multiple regressions revealed additional significant relationships of habitat parameters (soil pH, C:N ratio), vegetation composition, and standing crop on reproductive components. We conclude that populations of P. palustris are genetically isolated and that reproductive success most likely is influenced by population size, genetic variability, and habitat quality. Management strategies such as moderate grazing, mowing, and artificial gene flow should endeavor to increase population size as well as genetic variation.     

Local genetic differentiation in Proteopsis argentea (Asteraceae), a perennial herb endemic in Brazil

 Proteopsis argentea (Asteraceae, Vernonieae) is a perennial herb endemic to the “campos rupestres” of the Espinha?o Range in Minas Gerais, Brazil, with fragmented populational distribution. Eleven populations were sampled, throughout the entire distribution of the species, and assayed for isozyme variation. Low intra-population genetic diversity was found (P = 19.2; A = 1.30; He = 0.058) whereas species level diversity was higher (P = 55.5, A = 2.0, He = 0.093). The most geographically isolated population showed exclusive alleles at two loci, whereas two populations less than 2 km apart from each other showed inverted frequencies for two alleles. Mean genetic identity was high (I = 0.974), but the large Fst (0.30) indicates that the species could lose an important part of its genetic variation with the extinction of a single population. Our findings indicate that geographic isolation alone cannot explain population differentiation: localized pollinator behaviour and selection, for example, may be contributing to the patterns observed. Received February 18, 2000 Accepted November 1, 2000     

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

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

Allozyme variation in Carex sect. Digitatae – Evidence of introgression, genetic distinctiveness and evolution of taxa

 A subset of populations of the European taxa of Carex sect. Digitatae, including Carex digitata, C. pallens, C. ornithopoda, C. pediformis ssp. rhizodes and C. humilis have been investigated for allozyme variation. The (presumably) distantly related C. pendula was used as a reference taxon. Carex digitata, C. pallens and C. ornithopoda on the one hand, and C. humilis and C. pediformis on the other, shared the majority of the alleles. Cluster analyses based on genetic distances grouped populations of C. digitata and C. ornithopoda in a mixed subcluster whereas all populations of C. pallens formed a subcluster distinct from the digitata/ornithopoda cluster. This in spite of the fact that C. ornithopoda is morphologically clearly distinct from C. digitata whereas C. pallens is barely distinguishable from the latter. Carex pediformis and C. humilis appeared not more genetically similar to C. digitata than to the reference taxon. It is concluded that 1) C. digitata, C. pallens and C. ornithopoda are closely related and most probably forms a monophyletic group, 2) C. pallens is a genetically distinct species, 3) C. pediformis and C. humilis are not closely related to the rest of C. sect. Digitatae, 4) C. pediformis and C. humilis are relatively closely related, 5) introgression do occur between the investigated species but not to such an extent that it can explain major geographic patterns of variation in C. digitata. Received December 21, 2001; accepted November 14, 2002 Published online: March 24, 2003     

Genetic differentiation in silicicolous Echinospartum (Leguminosae) indicated by allozyme variability

 The genetic identities among several Echinospartum species and the genetic effects of isolation, small population size and decline in the restricted Echinospartum algibicum were studied both at adult and soil seed bank stages. The allozyme data support, to a large extent, population genetic predictions for genetic divergence. The genetic diversity parameters studied demonstrated that the aboveground population of E. algibicum is genetically less diverse than E. ibericum and E. barnadesii. Genetic identity between E. ibericum and E. barnadesii was very high, decreasing to levels considered typical for co-generic taxa between E. ibericum and E. algibicum. With regard to the soil seed bank of E. algibicum, this showed higher genetic variability than the adult population, greater extent of homozygosity, and significantly different allele frequencies at some loci. Despite the small population size, E. algibicum population maintains relatively high levels of genetic diversity both at adult and seed bank stages. Received July 2, 2001 Accepted October 11, 2001     

Genetic diversity among populations and size classes of buckeyes (Aesculus: Hippocastanaceae) examined with multilocus VNTR probes

 Little is known about genetic variation in members of the genus Aesculus (Hippocastanaceae), in particular A. flava (yellow buckeye) and A. glabra (Ohio buckeye). Here, three synthetic DNA probes (composed of tandemly repeated, core sequences) that reveal alleles at multiple variable-number tandem-repeat (VNTR) loci in these two species were used to investigate: 1) levels of genetic variation in one stand of A. flava and three isolated stands of A. glabra; 2) whether the stands of A. glabra are genetically differentiated from one another; 3) whether there has been selection for more heterozygous individuals through time in one stand each of A. flava and A. glabra; and 4) whether a possible genetic bottleneck had occurred during the formation of either species of Aesculus. First, variation of VNTR genetic markers within and among three populations of A. glabra separated by 60–180 km was examined. In each one hectare (ha) population, 22 individuals were randomly sampled. Among the three populations, the mean number of bands scored per individual was 80.35 and the average number of estimated loci surveyed was 54.17. Mean similarity and estimated heterozygosity within populations ranged from 0.634 to 0.743 and from 0.342 to 0.486, respectively. The mean similarity across populations was 0.657, while the mean estimated heterozygosity across populations was 0.484 for A. glabra. The most isolated site was the most genetically differentiated as indicated by differences in levels of similarity, heterozygosity, and Fst value comparisons. In a separate experiment, genetic variation in 22 large (reproductively mature; dbh > 8 cm) individuals was compared with that in 22 small (not yet reproductive; dbh < 1 cm) individuals collected within one ha stands for both A. flava and A. glabra. Mean similarity values among large versus small individuals of A. flava were 0.665 versus 0.662, while for A. glabra the corresponding values were 0.686 versus 0.691, respectively. Permutation tests of these similarity data detected no evidence for size class genetic differentiation in either species (both p-values > 0.050). Further, permutation tests for the number of bands per individual (average band number should be higher in more heterozygous individuals) detected no significant differences between size classes for either species. Thus, evidence of pronounced inbreeding and/or selection altering population genetics within small relative to large individuals was not detected. In addition, comparable similarity and heterozygosity values between these two closely related species (which still maintain an active zone of hybridization) suggests that either: 1) no extreme genetic bottleneck has accompanied the formation of these species from a common ancestor; or 2) signs of such a bottleneck have largely been eliminated. These studies demonstrate the utility of multilocus VNTR DNA probes for investigating genetic variation within and among plant populations, between size classes within a population, and between closely related species. Received May 15, 1998 Accepted September 11, 2001     

Genetic variability in a population of arbuscular mycorrhizal fungi causes variation in plant growth

Different species of arbuscular mycorrhizal fungi (AMF) alter plant growth and affect plant coexistence and diversity. Effects of within-AMF species or within-population variation on plant growth have received less attention. High genetic variation exists within AMF populations. However, it is unknown whether genetic variation contributes to differences in plant growth. In our study, a population of AMF was cultivated under identical conditions for several generations prior to the experiments thus avoiding environmental maternal effects. We show that genetically different Glomus intraradices isolates from one AMF population significantly alter plant growth in an axenic system and in greenhouse experiments. Isolates increased or reduced plant growth meaning that plants potentially receive benefits or are subject to costs by forming associations with different individuals in the AMF population. This shows that genetic variability in AMF populations could affect host-plant fitness and should be considered in future research to understand these important soil organisms.     

A brief evolutionary excursion comes to an end: the genetic relationship of British species of Gentianella sect. Gentianella (Gentianaceae)

 There is much taxonomic confusion in the genus Gentianella section Gentianella, five species of which are found in Britain. Gentianella anglica is a British endemic restricted in its distribution to the chalk downland of southern England. It is considered to be threatened because of habitat loss, and due to hybridisation with the closely related, widely distributed G. amarella. The Red Data Book species, G. uliginosa, shares morphological similarities with the other two species but has a very restricted distribution. Individual plants from populations across the range of these three species were analysed using AFLPs and universal cpSSRs to determine the degree of genetic variability within and between them, and to look for evidence of hybridisation. Samples of the two other Gentianella section Gentianella species found in Britain, G. campestris and G. germanica, were also included in the study. The analysis of chloroplast SSRs was not informative for G. anglica, G. amarella and G. uliginosa, while G. campestris and G. germanica differed from each other and the other three species at a single locus. Principal co-ordinate analysis of the AFLP data revealed only three distinct groups: one group contained G. campestris samples, another contained all samples of G. germanica, and a third contained all individuals from the other three species. In mixed populations of G. anglica and G. amarella, individuals of the two species were genetically more similar to each other than they were to individuals of the same species from other populations. It is proposed that G. anglica may be an early flowering form of G. amarella that has been created and maintained as a consequence of former grassland management practices. Received May 20, 2002; accepted October 28, 2002 Published online: March 31, 2003     

Gender plasticity in Sagittaria sagittifolia (Alismataceae), a monoecious aquatic species

 Aquatic plants are well known for their high degree of phenotypic plasticity in vegetative structures, particularly leaves. Less well understood is the extent to which their sexuality can be modified by environmental conditions. Here we investigate gender plasticity in the European clonal monoecious aquatic Sagittaria sagittifolia (Alismataceae) to determine how floral sex ratios may vary with plant size and inflorescence order. We sampled two populations from aquatic habitats in East Anglia, U.K. and measured a range of plant attributes including ramet size and the number of female and male flowers per inflorescence. The two populations exhibited similar patterns of phenotypic gender, despite contrasting patterns of total allocation to female and male flower number. Plants produced male-biased floral sex ratios but female flower number increased from the first to the second inflorescence whereas male flower number decreased. Size-dependent gender modification occurred in both populations, but the patterns of allocation to female flower production differed between the two populations. Our results are consistent with the view that monoecy is a sexual strategy that enables plants to adjust female and male allocation in response to changing environmental conditions. Received September 16, 2002; accepted October 23, 2002 Published online: March 20, 2003     

Allozymic diversity of Allium tricoccum (Ait.) Solander var. burdickii Hanes in isolated populations of Nova Scotia (Canada)

 Allium tricoccumvar. burdickii is a rare species in Nova Scotia, growing in isolated populations. Genetic variation was investigated in three populations using cellulose acetate gel electrophoresis. The results showed that all 13 enzyme loci were polymorphic. An excess of heterozygotes was found in all populations. A total of 29 genotypes were detected in the populations. Very few genotypes were common to two populations and none to the three populations. Genetic diversity among populations was compared with geographic distance and previous work. The comparison of the genetic distance matrix to the geographic distance matrix indicated no relationship. F-statistics suggested that the populations are predominantly maintained through vegetative propagation. Occasional sexual reproduction and gene flow might occur in order to maintain high level of variation among populations. Environmental conditions could also influence population genetic structure as they occur in highly different habitats. Received November 13, 2000 Accepted February 26, 2001