RECURRENT FORMATION AND POLYPHYLY OF NORDIC POLYPLOIDS IN DRABA (BRASSICACEAE)

Draba (Brassicaceae) is well known for its taxonomic complexity in arctic and alpine floras, and the polyploids in particular present vexing taxonomic problems. It has been suggested that polyploids in Draba may have formed recurrently from different populations of the parental species (polytopy), and it is also possible that a given taxonomic species may actually comprise several polyploid races, each originating from different progenitor species (polyphyly). To unravel the taxonomic complexity of polyploid Draba in the Nordic area, we investigated three of the most morphologically variable species and their possible progenitors using enzyme electrophoresis and restriction site analysis of chloroplast DNA (cpDNA) and nuclear ribosomal RNA genes (rDNA): D. norvegica (6x), D. lactea (6x), and D. corymbosa (16x). Electrophoretic analyses of progeny showed high levels of fixed heterozygosity in all three polyploids, demonstrating that all are genetic alloploids. Electrophoretic and rDNA data indicate that polytopic and/or polyphyletic origins have contributed to the complexity of these polyploids. However, a lack of cpDNA variation among the species limited the usefulness of this molecule for analysis of polyploid origins. The considerable electrophoretic variation observed in D. norvegica necessitates a minimum of three and probably 13 independent origins. Electrophoretic and rDNA data suggest that D. lactea and D. corymbosa are polyphyletic polyploids. Crossing data also support that D. corymbosa is polyphyletic. Given the widespread geographic distributions of these species and their possible progenitors, and that the populations analyzed represent only a small fraction of their geographic distributions, it is likely that these species have formed numerous times in different areas. As more molecular analyses of polyploids are completed, the data continue to suggest that multiple origins of polyploids are the rule rather than the exception.     

Crossing relationships and chromosome numbers of Nordic populations of Draba (Brassicaceae), with emphasis on the D. alpina complex

101 populations of Nordic Draba were investigated for chromosome numbers and crossing relationships. The populations were referred to 16 currently recognized species of Sect. Draba, Sect. Chrysodraba (including the D. alpina complex with D. alpina, D. oxycarpa, and D. corymbosa), and Sect. Drabella. The chromosome data suggest that all populations and species are homoploid. Three species are diploid, and 13 species are polyploids ranging from tetraploid to 16-ploid. Draba alpina is decaploid, D. oxycarpa is octoploid, and D. corymbosa is 16-ploid. The chromosome numbers of D. micropetala (n = 16,4x) and D. adamsii (n = 24,2n = 48, 6x) of Sect. Chrysodraba and D. cinerea (n = 24, 6x) of Sect. Draba were determined for the first time based on Nordic material. The relationships inferred from the crossing data largely agree with those inferred from previously published molecular data, but correspond poorly to relationships inferred from morphology. Inter-populational F₁ hybrids in D. fladnizensis were entirely sterile, suggesting that this predominantly inbreeding diploid species comprises at least two sibling species, possibly isolated by genic barriers. Sterile to semifertile F₁ hybrids with intermediate chromosome numbers were obtained in 19 interspecific combinations. F₂ hybrids were obtained in seven of these combinations. Both Sect. Chrysodraba and the D. alpina complex are probably polyphyletic. The crossing data suggest that the morphologically very similar polyploids D. alpina (10x) and D. oxycarpa (8x) do not have any diploid progenitors in common, and that Sect. Draba forms an intricate allopolyploid complex that also includes D. alpina and D. corymbosa of Sect. Chrysodraba. Draba corymbosa (16x) is probably an intersectional, polyphyletic alloploid derived from D. alpina (10x) and various hexaploids of Sect. Draba. Crossing data also suggest that D. norvegica (6x) is one of the progenitors of the Nordic endemic D. cacuminum (8x). The phenotypic expression of genes encoding taxonomically important indument characters did not follow consistent patterns in interspecific hybrids. This result may explain the discrepancy between genetic and taxonomic relationships in Nordic Draba, and supports the use of wide taxonomic concepts in this highly reticulate genus.     

Reproductive strategies of diploid and polyploid populations of arcticDraba (Brassicaceae)

132 cultivated populations (2x–16x) of 15 arctic-alpine species ofDraba were investigated to clarify a possible relationship between reproductive strategies and polyploid evolution in the genus. The populations were exclusively sexual and produced viable seed after spontaneous self-pollination, but showed large variation both in traits promoting cross-pollination and in autogamous fruit and seed set. Traits promoting cross-pollination, e.g., floral display, protogyny, and delayed selfing, were positively correlated, and these traits were negatively correlated with autogamous fruit and seed set. All diploid and many polyploid populations had high autogamous seed set and small, unscented, non-protogynous, and rapidly selfing flowers. In contrast, all populations with low autogamous seed set and large, scented, and strongly protogynous flowers with distinctly delayed selfing were polyploid. These results are consistent with those previously obtained from enzyme electrophoresis, suggesting that the genetically depauperate diploids are extreme inbreeders and that the highly fixed-heterozygous polyploids vary from extreme inbreeders to mixed maters. The reproductive data lend additional support to the hypothesis that allopolyploidy in arcticDraba serves as an escape from genetic depauperation caused by uniparental inbreeding at the diploid level.     

Studies on the asian eupatoria

The examination of 1976 herbarium specimens ofEupatorium chinense subsp.sachalinense var.oppositifolium and 908 of var.sachalinense revealed their distinct geographical and ecologial distribution patterns. Var.oppositifolium includes two distinct groups: the diploid type and the polyploid one. The distribution of the diploid type is restricted to the “Sohayaki-Region”, and its habitat appears to be restricted to fragile gravitational slopes and rocky areas which lack tall competitors. In contrast, the polypoid type is widely distributed throughout the Japan Archipelago. The polyploids grow successfully in recently cleared dry habitats and in repeatedly disturbed tall grass and forb communities. Climatic warming after the last-glaciation combined with explosive agricultural developments and the polyploids rapid and tall growth habits with agamospermous reproduction seem to have facilitated their northward migration and distributional expansion. Karyotype analyses were made on 29 populations of var.oppositifolium which comprised eight cytotypes: 2x, 3x, 4x, 5x based on x=10, 3 chromosomally deficient polyploids and an aneuploid with 2n=39. Most populations exhibited various combinations of polyploid cytotypes. Different polyploid cytotypes show no apparent habitat preferences. None of the polyploid cytotypes appear to compete with each other in colonizing and exploiting newly disturbed habitats. This, together with their agamospermous propagation, rare sexuality and random association when colonizing, can result in an intricate mixture of various cytotypes within local populations.     

Genetic variation in sympatric populations of diploid and polyploid brine shrimp (Artemia parthenogenetica)

We examined genetic variation in sympatric diploid and polyploid brine shrimp Artemia parthenogenetica from each of three populations (China, Italy and Spain). Italian and Spanish tetraploids are closely related (I=0.964). Diploids and tetraploids within each of the two European populations are also closely related (mean I=0.905). Most alleles found in diploids also exist in sympatric polyploids. In contrast, the asexual Artemia (2N, 4N and 5N) in our study share few alleles with their close sexual relative, A. tunisiana (mean I=0.002). These results, as well as the work of other authors, strongly suggest that at least the tetraploid Artemia in our study have an autopolyploid origin.Clonal diversity of polyploid Artemia can be very high at least in some population. Both diploids and polyploids had low clonal diversities in the populations dominated by polyploids and high clonal diversities in the population dominated by diploids.The most common genotypes of sympatric diploid and polyploid Artemia frequently differed. Some alleles occurred only in diploids, while others were restricted to polyploids. These results suggest that polyploidy in Artemia has led to genetic divergence from diploid progenitors, and that ploidy-level variation must also be considered in developing an understanding of spatial and temporal allozyme polymorphism in asexual populations.     

Genetic variation in Hawaiian Drosophila. VIII. Heterozygosity and genic changes in isolated populations of D. engyochracea

Drosophila engyochracea, an endemic Hawaiian fly found only in two, finite populations in Volcano National Park, has extensive electrophoretic heterozygosity on a par with that found in species with much wider distributions. A study of six polymorphic loci in both populations over an 18-month period revealed that the population in the more xeric environment is more dynamic genetically as well as more variable. In addition, genetic changes at one locus, Pgm, are correlated to changes in an environmental moisture parameter. These findings confirm that migration is not necessary to maintain genetic variation in isolated populations and demonstrate that D. engyochracea gene pools are susceptible to errors in Hardy-Weinberg equilibria during specific seasonal periods.Portions of this article were submitted in partial fulfillment for a Doctor of Philosophy degree in Genetics awarded to W. W. M. Steiner by the Department of Genetics, University of Hawaii, Honolulu. Research was supported by NSF Grants GB-23230, GM-27586, and GB-29288.     

Contributo Alla Morfologia della Foglia

Names of 20 presumed taxa in Draba sect. Aizopsis, all based on material from Italy, are considered. Full synonymies are provided, and types are designated (for 14 names) or indicated. Most of the taxa are currently considered unworthy of recognition, of which 16 belong to D. aspera sensu lato. However, the question of whether the Sicilian populations might be distinct from the peninsular populations is still unsettled.     

Polyploid origins in a circumpolar complex in Draba (Brassicaceae) inferred from cloned nuclear DNA sequences and fingerprints

Polyploid evolution has been of major importance in the arctic flora, but rarely addressed on the full circumpolar scale. Herein we study the allopolyploid Draba lactea and its close allies, which form a taxonomically intricate arctic-alpine complex including diploids, tetraploids, and hexaploids. Based on samples from the entire circumpolar area, we inferred the origins of polyploids in this complex using cloned DNA sequences from two nuclear regions (one intron from a gene encoding a second largest subunit in the RNA polymerase family, RPD2, and the ribosomal internal transcribed spacer region, ITS) and DNA fingerprints (random amplified polymorphic DNAs, RAPDs). Although D. lactea and all other polyploids examined in Draba are genetic alloploids showing fixed heterozygosity, the data obtained in the present study suggest that each of the polyploids analyzed here may have originated from a single diploid lineage: hexaploid D. lactea via tetraploid D. lactea from the D. palanderiana lineage (not from the D. fladnizensis and D. nivalis lineages as previously hypothesized), the tetraploid D. turczaninovii from the D. fladnizensis lineage, the tetraploid D. porsildii from the D. lonchocarpa lineage, and a tetraploid here named Draba spB from the D. nivalis lineage. Draba lactea has probably originated several times in the Beringian area, and it is not necessary to invoke complex origins based on a combination of different species lineages as previously suggested.     

Conservation genetics of bull trout: Geographic distribution of variation at microsatellite loci

We describe the genetic population structure of65 bull trout (Salvelinus confluentus)populations from the northwestern United Statesusing four microsatellite loci. Thedistribution of genetic variation as measuredby microsatellites is consistent with previousallozyme and mitochondrial DNA analysis. Thereis relatively little genetic variation withinpopulations (H ^S = 0.000 – 0.404,average H ^S = 0.186, but substantialdivergence between populations (F ^ST = 0.659). In addition, those populations that had low genetic variation forallozymes also tended to have low geneticvariation at microsatellite loci. Microsatellite analysis supports the existenceof at least three major geneticallydifferentiated groups of bull trout: (1)``Coastal' bull trout populations, (2) ``SnakeRiver' populations, which also include the JohnDay, Umatilla, and Walla Walla Rivers and, (3)populations from the upper Columbia River,primarily from the Clark Fork basin. Withinthe major assemblages, populations are furthersubdivided, primarily at the river basin level. Most of the genetic similarities we havedetected probably reflect patterns of historicisolation and gene flow. However, in somecases, genetic drift and low levels ofvariation appear to have influenced therelationships inferred from these data. Finally, we suggest using a hierarchicalapproach to direct management actions inspecies such as bull trout for which most ofthe genetic variation exists among populationsand local populations in close proximitytypically are genetically distinct.     

Electrophoretic study and genetic affinity in theCampanula elatines andC. fragilis (Campanulaceae) rock-plants group from Italy and W. Jugoslavia

Variability and genetic divergence of 11 field populations of seven species of theCampanula elatines andC. fragilis rock-plants group from the Mediterranean and pre-Alpine areas have been studied by starch-gel electrophoretic techniques.Campanula isophylla, C. elatines, C. elatinoides, C. fragilis subsp.fragilis and subs.cavolinii, C. garganica were collected in Italy, whilstC. fenestrellata subsp.istriaca andC. portenschlagiana came from W. Jugoslavia. Twelve enzymatic loci for each population were genetically analysed: PGI-1 and 2, PGM-2, IDH-1 and -2, SKDH, ME, ADH, GOT-2, MPI-1 and -2, SOD-1. The genetic distances among the above mentioned entities have been calculated by Nei's index and depicted in a dendrogram.     

Historical effective size and the level of genetic diversity in Drosophila melanogaster and Drosophila pseudoobscura

We report the results of a sequential gel electrophoretic study of protein variation in Drosophila melanogaster and its comparison with D. pseudoobscura. The number of alleles and mean heterozygosity were lower in D. melanogaster than in D. pseudoobscura. On the other hand, geographical populations of Drosophila melanogaster have been shown to be much more differentiated than those of D. pseudoobscura. The results suggest that in D. melanogaster low-frequency alleles have been lost during the colonization process and that major alleles have become differentiated among populations. Population bottlenecks, due to various causes, appear to have played a significant role in the shaping of genetic variation in natural populations of many species. It is proposed that a comparison of genetic variation at homologous gene loci between related species can bring out effects of historical bottlenecks and provide an alternative approach for analyzing causes of genetic variation in natural populations.We thank the Natural Science and Engineering Research Council of Canada for financial support (Grant A0235 to R.S.S.).     

A study of genetic diversity among host-specific populations of the witchweedStriga hermonthica (Scrophulariaceae) in Africa

Striga hermonthica is a root hemiparasite that attacks onlyGramineae, includingSorghum and millet for which it is a principal cause of lowered yield. Enzyme electrophoresis was used to investigate genetic diversity inStriga hermonthica and to determine the level of differentiation between host-specialized populations. Nine genetic loci coding eight enzymes were interpreted and data obtained from three populations: oneSorghum-adapted population from Sudan and two populations from Burkina Faso, oneSorghum-adapted and the other millet-adapted. Levels of polymorphism were similarly high in all three populations (P=0.625, A=2.6–2.8, H=0.293–0.401). Genotypic frequencies at most loci conformed to Hardy-Weinberg expectations in each population, consistent with outcrossing as predicted from previous studies of floral biology. Occasional heterozygote deficiencies were probably the result of Wahlund effect. The mean value of F_ST over the three populations was 0.068, indicating a slight to moderate level of genetic differentiation among the populations. The two Burkina Faso populations were more closely related (S=0.940, D=0.006) than either was to the Sudan population, suggesting that geographic separation is more important than host specialization in contributing to population differentiation. TheSorghum-adapted population was slightly closer to the Burkina FasoSorghum-adapted population (S=0.873, D=0.047) than to Burkina Faso millet-adapted population (S=0.851, D=0.074). The absence of substantial genetic divergence between host-specific populations ofStriga could result either from recent evolution of host-specialized strains or from strong selection for physiological specialization in the face of substantial gene flow between the populations.     

Genetic markers distinguishing between the two subspecies of the rosy bitterling,Rhodeus ocellatus (Cyprinidae)

Eleven populations of the rosy bitterling,Rhodeus ocellatus, from different localities in Japan, were genetically compared at 16 protein-coding loci using starch-gel electrophoresis. Two loci,Ldh-2 andPgdh, were demonstrated as diagnostic markers for the identification of two subspecies;R. ocellatus kurumeus, which is native to Japan, andR. ocellatus ocellatus, which was introduced from China. The two subspecies were distinguished by the complete substitution of different alleles between them. Population ofR. ocellatus kurumeus occurring in Yao City, Osaka, and in Kanzaki, Saga Prefecture were genetically closely related to each other (genetic distance: D=0.056) but distantly so toR. ocellatus ocellatus from Saitama Prefecture (D=0.202 or 0.265). Electrophoretic analyses also elucidated the existence of hybrid populations of the two subspecies. The populations ofR. ocellatus kurumeus in Yao City had lower genetic variability and a lower incidence of white coloration on the ventral fins than populations of the same in Saga Prefecture. The present study strongly implies that the introduction of the foreign freshwater fishes with subspecific differentiation, into the original range of indigenous subspecies, should be averted not to bring the genetic pollution.     

Population genetic diversity in the polyploid complex of wheatgrasses using isoenzyme and RAPD data

Thirty five bands (alleles) from six enzyme systems and fifty seven random amplified polymorphic DNA (RAPD) fragments were selected to analyse the genetic diversity of 33 polyploid wheatgrasses (Triticeae) populations of species Thinopyrum junceiforme and Elytrigia pycnantha, and two hybrids, one pentaploid and one novel 9-ploid. Dice’s similarity coefficient, the UPGMA-derived phenograms from RAPD, and allozymes markers showed that the clustering of wheatgrass populations was based on ploidy level. These markers had similar levels of diversity between populations, with high genetic similarity within the same ploidy-level and within population’s individuals. The tetraploid Th. junceiforme populations are closely related, with a large similarity distances varied from 0.8 to 1. Based on the isozyme and RAPD analyses, diploid taxa are related to polyploids with similarity coefficients 0.4.     

Strong genetic differentiation of the East-Himalayan <Emphasis Type="Italic">Megacodon stylophorus</Emphasis> (Gentianaceae) detected by Inter-Simple Sequence Repeats (ISSR)

Megacodon stylophorus (Clarke) Smith is a perennial alpine herb endemic to the species-rich eastern Himalayan region. Its populations are locally scattered as isolated patches throughout this region. Genetic variation within and among six populations of this species was assessed using ISSR fingerprinting with 13 primers. High levels of genetic diversity exist within species (P = 69.83%, H_T = 0.1949 and H_sp = 0.3047), while the within-population diversity is low (P = 11.21%, H_E = 0.0532 and H_pop = 0.0792). Extraordinarily high levels of genetic differentiation were detected among populations based on various statistics, including Neis genetic diversity analysis (72.7%), Shannons diversity index (74.01%) and AMOVA (80.70%). That is, populations shared low levels of genetic identity (I = 0.8203 ± 0.0430). This genetic structure was probably due to severe genetic drift of the small-sized patchy populations resulting from postglacial habitat fragmentations. The observed genetic structure of the populations implies that as many populations as possible should be considered for any in situ and ex situ conservation practice on this species.     

Genetic variation and phylogeographic history of <Emphasis Type="Italic">Picea likiangensis</Emphasis> revealed by RAPD markers

Repeated cycles of retreat and recolonization during the Quaternary ice ages are thought to have greatly influenced current species distributions and their genetic diversity. It remains unclear how this climatic oscillation has affected the distribution of genetic diversity between populations of wind-pollinated conifers in the Qinghai-Tibetan region. In this study, we investigated the within-species genetic diversity and phylogenetic relationships of Picea likiangensis, a dominant forest species in this region using polymorphic DNA (RAPD) markers. Our results suggest that this species has high overall genetic diversity, with 85.42% of loci being polymorphic and an average expected heterozygosity (H _E) of 0.239. However, there were relatively low levels of polymorphism at population levels and the differences between populations were not significant, with percentages of polymorphic bands (PPB) ranging from 46.88 to 69.76%, Nei’s gene diversity (H _E) from 0.179 to 0.289 and Shannon’s indices (Hpop) from 0.267 to 0.421. In accordance with our proposed hypothesis, a high level of genetic differentiation among populations was detected based on Nei’s genetic diversity (G _ST = 0.256) and AMOVA analysis (Phi _st = 0.236). Gene flow between populations was found to be limited (Nm = 1.4532) and far lower than reported for other conifer species with wide distribution ranges from other regions. No clusters corresponding to three morphological varieties found in the south, north and west, respectively, were detected in either UPGMA or PCO analyses. Our results suggest that this species may have had different refugia during the glacial stages in the southern region and that the northern variety may have multiple origins from these different refugia.     

Asphodelus tenuifolius andA. fistulosus (Liliaceae) are morphologically,genetically, and biologically different species

The biological analysis of six populations ofAsphodelus tenuifolius and 12 populations ofA. fistulosus has confirmed that they are separate species. Both their floral structures (length of the tepals, stamens, anthers and style) and also their pollen size are clearly different.A. tenuifolius has only the 2n = 28 chromosome race, whileA. fistulosus has 2n = 28 and 2n = 56.A. tenuifolius is genetically less variable thanA. fistulosus and they have different electrophoretic mobilities. Gene duplication phenomena exist in the 2n = 28 level of both species.     

Karyology and evolution inSesamoides (Resedaceae)

The meiotic behaviour abnormalities, fertility and size of pollen of 6 taxa ofSesamoides have been analysed. Besides diploids (2x), polyploids (4x, 6x, 8x) have been found. The chromosome base number is x = 10, but an origin from x = 5 is suggested.     

Allozyme variation in the annual weed species complexPolygonum aviculare (Polygonaceae) in relation to ploidy level and colonizing ability

Variation at six polymorphic enzymatic loci was studied in 50 populations of the selfing annualPolygonum aviculare from Belgium. The results show that theP. aviculare complex has an allopolyploid origin and comprises two main genetic entities, viz.P. aviculare subsp.depressum (2n = 4x = 40), restricted to urban sites subject to trampling stress, andP. aviculare subsp.aviculare (2n = 4x = 40, 2n = 6x = 60), with a wider ecological amplitude. The latter had a higher genetic diversity and a higher frequency of fixed heterozygosity than the former. WithinP. aviculare subsp.aviculare, genetic diversity and ecological amplitude correlated positively with ploidy level. Additionally, stronger genetic differentiation among and lower variation within populations was found in urban areas than in cultivated fields.     

Contrasting patterns of geographic variation in the cosmopolitan sibling species Drosophila melanogaster and Drosophila simulans

An electrophoretic study was carried out to compare the geographic pattern of genetic variation in Drosophila simulans with that of its sibling species, Drosophila melanogaster. An identical set of 32 gene-protein loci was studied in four geographically distant populations of D. simulans and two populations of D. melanogaster, all originating from Europe and Africa. The comparison yielded the following results: (1) tropical populations of D. simulans were, in terms of the number of unique alleles, average heterozygosity per locus, and percentage of loci polymorphic, more variable than conspecific-temperate populations; (2) some loci in both species showed interpopulation differences in allele frequencies that suggest latitudinal clines; and (3) temperate-tropical genetic differentiation between populations was much less in D. simulans than in D. melanogaster. Similar differences between these two species have previously been shown for chromosomal, quantitative, physiological, and middle-repetitive DNA variation. Estimates of N _m (number of migrants per generation) from the spatial distribution of rare alleles suggest that both species have similar levels of interpopulation gene flow. These observations lead us to propose two competing hypotheses: the low level of geographic differentiation in D. simulans is due to its evolutionarily recent worldwide colonization and, alternatively, D. simulans has a narrower niche than D. melanogaster. Geographic variation data on different genetic elements (e.g., mitochondrial DNA, two-dimensional proteins, etc.) are required before these hypotheses can be adequately tested.We thank the Natural Science and Engineering Research Council of Canada for financial support (Grant A0235 to R.S.S.).