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1.
Hana Malinska Jennifer A Tate Roman Matyasek Andrew R Leitch Douglas E Soltis Pamela S Soltis Ales Kovarik 《BMC evolutionary biology》2010,10(1):291
Background
Tragopogon mirus and T. miscellus are allotetraploids (2n = 24) that formed repeatedly during the past 80 years in eastern Washington and adjacent Idaho (USA) following the introduction of the diploids T. dubius, T. porrifolius, and T. pratensis (2n = 12) from Europe. In most natural populations of T. mirus and T. miscellus, there are far fewer 35S rRNA genes (rDNA) of T. dubius than there are of the other diploid parent (T. porrifolius or T. pratensis). We studied the inheritance of parental rDNA loci in allotetraploids resynthesized from diploid accessions. We investigate the dynamics and directionality of these rDNA losses, as well as the contribution of gene copy number variation in the parental diploids to rDNA variation in the derived tetraploids. 相似文献2.
Pamela S. Soltis Gregory M. Plunkett Stephen J. Novak Douglas E. Soltis 《American journal of botany》1995,82(10):1329-1341
Genetic diversity in the introduced diploids Tragopogon dubius, T. porrifolius, and T. pratensis and their neoallotetraploid derivatives T. mirus and T. miscellus was estimated to assess the numbers of recurrent, independent origins of the two tetraploid species in the Palouse region of eastern Washington and adjacent Idaho. These tetraploid species arose in this region, probably within the past 50–60 yr, and provide one of the best models for the study of polyploidy in plants. The parental species of both T. mirus and T. miscellus have been well documented, and each tetraploid species has apparently formed multiple times. However, a recent survey of the distributions of these allotetraploids revealed that both tetraploid species have expanded their ranges considerably during the past 50 yr, and several new populations of each species were discovered. Therefore, to evaluate the possibility that these recently discovered populations are of recent independent origin, a broad analysis of genetic diversity in T. mirus, T. miscellus, and their diploid progenitors was conducted. Analyses of allozymic and DNA restriction site variation in all known populations of T. mirus and T. miscellus in the Palouse and several populations of each parental diploid species revealed several distinct genotypes in each tetraploid species. Four isozymic multilocus genotypes were observed in T. mirus, and seven were detected in T. miscellus. Tragopogon mirus possesses a single chloroplast genome, that of T. porrifolius, and two distinct repeat types of the 18S-26S ribosomal RNA genes. Populations of T. miscellus from Pullman, Washington, have the chloroplast genome of T. dubius; all other populations of T. miscellus have the chloroplast DNA of T. pratensis. All populations of T. miscellus combine the ribosomal RNA repeat types of T. dubius and T. pratensis, as demonstrated previously. When all current and previously published data are considered, both T. mirus and T. miscellus appear to have formed numerous times even within the small geographic confines of the Palouse, with estimates of five to nine and two to 21 independent origins, respectively. Such recurrent polyploidization appears to characterize most polyploid plant species investigated to date (although this number is small) and may contribute to the genetic diversity and ultimate success of polyploid species. 相似文献
3.
DOUGLAS E. SOLTIS EVGENY V. MAVRODIEV STEPHEN C. MEYERS PAUL M. SEVERNS LINJING ZHANG MATTHEW A. GITZENDANNER TINA AYERS MICHAEL CHESTER PAMELA S. SOLTIS 《Botanical journal of the Linnean Society. Linnean Society of London》2012,169(2):297-311
The allotetraploids (2n = 24) Tragopogon mirus and T. miscellus have become textbook examples of recently and recurrently formed allopolyploids. Both species formed following the introduction of three diploids, T. dubius, T. porrifolius and T. pratensis (each with 2n = 12), from Europe into the Palouse region of eastern Washington and adjacent Idaho, USA, in the early 1900s. The parentage of both allotetraploids is well documented (T. mirus = T. dubius × T. porrifolius; T. miscellus = T. dubius × T. pratensis), and both allotetraploids have formed repeatedly in the past approximately 80 years in the Palouse. On a larger geographical scale, T. mirus has also been reported from Flagstaff, Arizona (AZ), and more recently from Oregon (OR). However, the populations from OR and AZ have not been previously analysed with molecular markers to test the hypothesis of separate origin (vs. long‐distance dispersal). Here, we show that both the AZ and OR collections of T. mirus combine distinctive parental genotypes and are genetically differentiated from the T. mirus genotypes found in the Palouse. The OR sample of T. mirus has a genetically distinct T. dubius contribution that forms a clade in our analyses with a sample of what has been referred to as T. major (now considered a subspecies of T. dubius). Consistent with other naturally occurring T. mirus populations, plastid sequences indicate that T. porrifolius was the maternal parent for both the AZ and OR collections. Microsatellite data are also consistent with local formation of T. mirus from co‐occurring populations of T. dubius and T. porrifolius in OR and AZ. As with sequence data, T. dubius from OR is distinct from other samples of T. dubius at microsatellite loci, contributing a unique signature to T. mirus from this location. It will be useful to include these additional geographical origins of T. mirus, particularly the more genetically distant sample from OR, in ongoing investigations of the genetic and genomic consequences of recent allopolyploidy. © 2012 The Linnean Society of London, Botanical Journal of the Linnean Society, 2012, 169 , 297–311. 相似文献
4.
Stephen J. Novak Douglas E. Soltis Pamela S. Soltis 《American journal of botany》1991,78(11):1586-1600
Two of the classic examples of recent allopolyploid speciation are Tragopogon mirus and T. miscellus. Previous studies have documented that both allotetraploids originated within the past 50–60 years; the diploid parents of T. minis are T. dubius and T. porrifolius; those of T. miscellus are T. dubius and T. pratensis. It has now been 40 years since these allotetraploids were first described by Ownbey in 1950. To assess whether population size (the absolute number of plants) and population number of these species have changed during the past 40 years, we determined their distribution and numbers in the Palouse region of eastern Washington and northern Idaho in the spring of 1990. We visited 90 localities, 60 in Washington and 30 in Idaho. Tragopogon minis is found in nine locations, with eight of these sites located in eastern Whitman County, Washington. Tragopogon miscellus is much more widespread, occurring in 38 of 90 locations. The latter species is now one of the most common weeds in the vicinity of Spokane, Washington. Comparison of the current distributions of these species with historical records indicates that both allotetraploids, especially T. miscellus, have increased substantially in both geographic range and numbers. These Tragopogon species offer an excellent model system for testing questions concerning the ecology and population biology of recently derived allotetraploid species and their diploid progenitors. 相似文献
5.
Tragopogon mirus and T. miscellus are classic examples of recent allopolyploid speciation. Previous studies documented that the diploid parents of T. mirus are T. dubius and T. porrifolius and those of T. miscellus are T. dubius and T. pratensis. Restriction fragment analysis of chloroplast DNA (cpDNA) provided additional evolutionary information regarding the origin of the allotetraploids. We analyzed 39 populations of the three diploid and two allotetraploid species with 18 restriction endonucleases. Six restriction site mutations and three length mutations were identified; these unambiguously differentiated the parental diploids. Previous morphological, cytological, and electrophoretic analyses indicated that T. mirus arose independently at least three times. Chloroplast DNA data suggest that T. porrifolius has consistently been the maternal parent of T. mirus. Chloroplast DNA data also document a minimum of two independent origins of T. miscellus: 1) populations from Pullman, Washington, have T. dubius as the maternal parent; 2) all other populations have T. pratensis as the maternal parent. Two restriction site mutations implicate certain populations of T. dubius in the formation of the Pullman populations of T. miscellus. The two rare diploid species, T. porrifolius and T. pratensis, typically appear as maternal parents of the allotetraploids; the widespread and common T. dubius is the maternal parent only for two populations of T. miscellus. These data suggest that pollen load may be an important factor in determining the male and female parents of allopolyploid angiosperms. 相似文献
6.
Multiple independent formations of Tragopogon tetraploids (Asteraceae): evidence from RAPD markers 总被引:3,自引:0,他引:3
Polyploidy is widely recognized as a significant force leading to the formation of new plant species. Estimates of the number of angiosperm species with polyploid origins are as high as ≈ 50%; however, in spite of this prevalence, many aspects of polyploid evolution remain poorly understood. Recent studies have suggested that recurrent origins of polyploid species are the rule rather than the exception. The present study is one of only a few designed to quantify the number of independent origins of a polyploid species. The two tetraploid species Tragopogon mirus and T. miscellus (Asteraceae) arose within the past 50 years in the Palouse region of eastern Washington and adjacent northern Idaho. Previous work using morphology, cpDNA and rDNA restriction site analyses, allozymes, cytology, and flavonoid chemistry established that T. mirus had arisen at least five times, and T. miscellus at least twice, on the Palouse. To assess the frequency of multiple origins of these species more rigorously, seven populations of T. mirus and three populations of T. miscellus that were indistinguishable based on previous markers were surveyed using random amplified polymorphic DNA (RAPD) markers; populations of the diploid progenitor species from the same sites were also analysed. Each tetraploid population had a unique RAPD marker profile, suggesting that each population surveyed originated independently of the other populations in the region. Only two of the tetraploid populations combined the RAPD marker profiles of the diploid progenitors occurring at the same site. Both polyploid species, whose ranges and numbers have greatly increased since their formation in the early part of the twentieth century, have formed repeatedly on a local geographical scale and during a short time frame. Furthermore, each tetraploid species is spreading not primarily by dispersal of propagules from a single population of origin, but through repeated, independent polyploidization events that recreate the polyploid taxa. 相似文献
7.
Pamela S. Soltis Xiaoxian Liu D. Blaine Marchant Clayton J. Visger Douglas E. Soltis 《Philosophical transactions of the Royal Society of London. Series B, Biological sciences》2014,369(1648)
Nearly four decades ago, Roose & Gottlieb (Roose & Gottlieb 1976 Evolution
30, 818–830. (doi:10.2307/2407821)) showed that the recently derived allotetraploids Tragopogon mirus and T. miscellus combined the allozyme profiles of their diploid parents (T. dubius and T. porrifolius, and T. dubius and T. pratensis, respectively). This classic paper addressed the link between genotype and biochemical phenotype and documented enzyme additivity in allopolyploids. Perhaps more important than their model of additivity, however, was their demonstration of novelty at the biochemical level. Enzyme multiplicity—the production of novel enzyme forms in the allopolyploids—can provide an extensive array of polymorphism for a polyploid individual and may explain, for example, the expanded ranges of polyploids relative to their diploid progenitors. In this paper, we extend the concept of evolutionary novelty in allopolyploids to a range of genetic and ecological features. We observe that the dynamic nature of polyploid genomes—with alterations in gene content, gene number, gene arrangement, gene expression and transposon activity—may generate sufficient novelty that every individual in a polyploid population or species may be unique. Whereas certain combinations of these features will undoubtedly be maladaptive, some unique combinations of newly generated variation may provide tremendous evolutionary potential and adaptive capabilities. 相似文献
8.
Cytological studies have shown many newly formed allopolyploids (neoallopolyploids) exhibit chromosomal variation as a result of meiotic irregularities, but few naturally occurring neoallopolyploids have been examined. Little is known about how long chromosomal variation may persist and how it might influence the establishment and evolution of allopolyploids in nature. In this study we assess chromosomal composition in a natural neoallotetraploid, Tragopogon mirus, and compare it with T. miscellus, which is an allotetraploid of similar age (~40 generations old). We also assess whether parental gene losses in T. mirus correlate with entire or partial chromosome losses. Of 37 T. mirus individuals that were karyotyped, 23 (62%) were chromosomally additive of the parents, whereas the remaining 14 individuals (38%) had aneuploid compositions. The proportion of additive versus aneuploid individuals differed from that found previously in T. miscellus, in which aneuploidy was more common (69% Fisher''s exact test, P=0.0033). Deviations from parental chromosome additivity within T. mirus individuals also did not reach the levels observed in T. miscellus, but similar compensated changes were observed. The loss of T. dubius-derived genes in two T. mirus individuals did not correlate with any chromosomal changes, indicating a role for smaller-scale genetic alterations. Overall, these data for T. mirus provide a second example of prolonged chromosomal instability in natural neoallopolyploid populations. 相似文献
9.
V. Vaughan Symonds Pamela S. Soltis Douglas E. Soltis 《Evolution; international journal of organic evolution》2010,64(7):1984-2003
Polyploidy is a major feature of angiosperm evolution and diversification. Most polyploid species have formed multiple times, yet we know little about the genetic consequences of recurrent formations. Among the clearest examples of recurrent polyploidy are Tragopogon mirus and T. miscellus (Asteraceae), each of which has formed repeatedly in the last ~80 years from known diploid progenitors in western North America. Here, we apply progenitor‐specific microsatellite markers to examine the genetic contributions to each tetraploid species and to assess gene flow among populations of independent formation. These data provide fine‐scale resolution of independent origins for both polyploid species. Importantly, multiple origins have resulted in considerable genetic variation within both polyploid species; however, the patterns of variation detected in the polyploids contrast with those observed in extant populations of the diploid progenitors. The genotypes detected in the two polyploid species appear to represent a snapshot of historical population structure in the diploid progenitors, rather than modern diploid genotypes. Our data also indicate a lack of gene flow among polyploid plants of independent origin, even when they co‐occur, suggesting potential reproductive barriers among separate lineages in both polyploid species. 相似文献
10.
Jennifer A Tate Prashant Joshi Kerry A Soltis Pamela S Soltis Douglas E Soltis 《BMC plant biology》2009,9(1):80
Background
Polyploidy (whole-genome duplication) is an important speciation mechanism, particularly in plants. Gene loss, silencing, and the formation of novel gene complexes are some of the consequences that the new polyploid genome may experience. Despite the recurrent nature of polyploidy, little is known about the genomic outcome of independent polyploidization events. Here, we analyze the fate of genes duplicated by polyploidy (homoeologs) in multiple individuals from ten natural populations of Tragopogon miscellus (Asteraceae), all of which formed independently from T. dubius and T. pratensis less than 80 years ago. 相似文献11.
This study demonstrates that homoeologous genes in two diploid plant species that specify different amounts of an enzyme maintain the same relative level of expression in an allotetraploid derivative. The three predominant alcohol dehydrogenase (ADH) isozymes (DD, DP, PP) in seeds of the recently evolved allotetraploid plant Tragopogon miscellus (Compositae) are dimers specified by Adh3-D and Adh3-P genes derived from its diploid progenitors T. dubius and T. pratensis. Seeds of T. pratensis contain twice as much ADH activity as those of T. dubius, while T. miscellus is intermediate. The three isozymes were similar in a number of catalytic properties; the densitometric ratio of the isozymes purified from T. miscellus was 1 DD:4DP:4PP for both ADH activity and protein; and dissociation-reassociation of the DP enzyme gave a 1:2:1 ratio of the three isozymes. Therefore, the enzymes were similar in specific activity, but twice as many P as D subunits were present in active enzymes in T. miscellus, precisely the difference in activity between the parents. In T. miscellus, the specific activity of ADH and its activity per mg tissue are intermediate to those of the diploids, because relative expression of the Adh gene in each genome is not influenced by the presence of the other genome. 相似文献
12.
EVGENY V. MAVRODIEV IRSHAD NAWCHOO PAMELA S. SOLTIS DOUGLAS E. SOLTIS 《Botanical journal of the Linnean Society. Linnean Society of London》2008,158(3):391-398
Tragopogon kashmirianus (Asteraceae: Lactuceae) (2n = 24) was described based on collections from Kashmir. The tetraploid is morphologically similar to allotetraploid T. mirus from North America that has formed in western North America from the introduced T. dubius (2n = 12) and T. porrifolius (salsify; 2n = 12). Singh and Kachroo (1976 ) suggested that T. kashmirianus might have formed from the same diploid parental combination as T. mirus. To determine this, we investigated internal and external transcribed spacers (ITS, ETS) and five plastid regions of T. kashmirianus and species reported from Kashmir, northern India and neighbouring countries (T. badachschanicus, T. longirostris, T. porrifolius, T. pratensis, T. orientalis, T. subalpinus, T. trachycarpus, T. gracilis and T. dubius). Molecular data indicate that the parents of T. kashmirianus are not the European T. porrifolius and T. dubius. The exact parentage of T. kashmirianus is still unclear, but if it is an allotetraploid, at least one parent is a species native to Kashmir/India. Alternatively, it may represent an autopolyploid, again with the diploid parent native to Kashmir/India. We also found that ‘T. dubius’ from Kashmir is phylogenetically and morphologically distinct from collections of T. dubius from Europe and probably represents a previously unrecognized species. © 2008 The Linnean Society of London, Botanical Journal of the Linnean Society, 2008, 158 , 391–398. 相似文献
13.
Roman Matyášek Eva Dobešová Dalibor Húska Ivana Ježková Pamela S. Soltis Douglas E. Soltis Aleš Kovařík 《The Plant journal : for cell and molecular biology》2016,85(3):362-377
Uniparental silencing of 35S rRNA genes (rDNA), known as nucleolar dominance (ND), is common in interspecific hybrids. Allotetraploid Tragopogon mirus composed of Tragopogon dubius (d) and Tragopogon porrifolius (p) genomes shows highly variable ND. To examine the molecular basis of such variation, we studied the genetic and epigenetic features of rDNA homeologs in several lines derived from recently and independently formed natural populations. Inbred lines derived from T. mirus with a dominant d‐rDNA homeolog transmitted this expression pattern over generations, which may explain why it is prevalent among natural populations. In contrast, lines derived from the p‐rDNA dominant progenitor were meiotically unstable, frequently switching to co‐dominance. Interpopulation crosses between progenitors displaying reciprocal ND resulted in d‐rDNA dominance, indicating immediate suppression of p‐homeologs in F1 hybrids. Original p‐rDNA dominance was not restored in later generations, even in those segregants that inherited the corresponding parental rDNA genotype, thus indicating the generation of additional p‐rDNA and d‐rDNA epigenetic variants. Despite preserved intergenic spacer (IGS) structure, they showed altered cytosine methylation and chromatin condensation patterns, and a correlation between expression, hypomethylation of RNA Pol I promoters and chromatin decondensation was apparent. Reversion of such epigenetic variants occurred rarely, resulting in co‐dominance maintained in individuals with distinct genotypes. Generally, interpopulation crosses may generate epialleles that are not present in natural populations, underlying epigenetic dynamics in young allopolyploids. We hypothesize that highly expressed variants with distinct IGS features may induce heritable epigenetic reprogramming of the partner rDNA arrays, harmonizing the expression of thousands of genes in allopolyploids. 相似文献
14.
María Ferriol Hugo Merle Alfonso Garmendia 《Botanical journal of the Linnean Society. Linnean Society of London》2014,176(1):82-98
Survival of polyploids in nature depends on several factors, including competition from diploid relatives and increased genetic diversity. Unlike other reported Centaurea polyploid complexes, diploid Centaurea aspera and tetraploid Centaurea seridis coexist in hybrid zones with frequent triploid individuals. The polyploid origin of C. seridis, the genetic diversity and population structure of the three cytotypes, and the degree of genetic differentiation among them were analyzed in seven mixed‐ploidy zones, involving different subspecies and ecological conditions. Ploidy was determined by flow cytometry. Microsatellite data suggested an allopolyploid origin of C. seridis. In the contact zones, diploids and tetraploids were genetically differentiated. When compared with the related C. aspera, a low genetic diversity was observed in C. seridis, which is uncommon in tetraploids. Furthermore, although diploid individuals were grouped in a single widespread genetic cluster, tetraploids were grouped in two highly differentiated clusters and showed significant isolation by distance. This genetic pattern in C. seridis may be related to a minimal gene flow with diploid relatives and/or other genetic factors, such as rare polyploidization events, founder effects or an increased selfing rate. Neither taxonomic assignment at subspecies level, nor ecological conditions could explain the genetic differentiation between tetraploid clusters. © 2014 The Linnean Society of London, Botanical Journal of the Linnean Society, 2014, 176 , 82–98. 相似文献
15.
16.
Jaume Pellicer FLS Sònia Garcia Joan Vallès Katsuhiko Kondo FLS Teresa Garnatje 《Botanical journal of the Linnean Society. Linnean Society of London》2013,171(4):655-666
Fluorescence in situ hybridization (FISH) with 35S and 5S rDNA probes was used to characterize cytogenetically representatives of Artemisia subgenus Dracunculus and allied species and to explore their evolution following polyploidization. At the diploid level two rDNA loci were observed in most species belonging to the A. dracunculus complex, a pattern considered to be the ancestral state for diploid Artemisia. In contrast, representative species from the Eurasian grade which belong to the other major lineage of the subgenus had more heterogeneous rDNA profiles, with three to five loci at the diploid level. Divergent patterns of locus evolution were also detected in polyploids, with the number and distribution of rDNA loci broadly fitting the two main diversification lineages in the subgenus. In the polyploid complex of A. dracunculus, the number of rDNA loci was almost proportional to ploidy, although monoploid genome size was shown to decrease with increasing ploidy. However, in polyploids from the Eurasian grade we found a remarkable reduction in the number of rDNA sites, suggesting that these species might have experienced either a complete loss of loci or a significant reduction in the number of repeats following polyploid formation. © 2013 The Linnean Society of London, Biological Journal of the Linnean Society, 2013 , 171 , 655–666. 相似文献
17.
18.
E Dobe?ová H Malinská R Matyá?ek A R Leitch D E Soltis P S Soltis A Kova?ík 《Heredity》2015,114(3):356-365
To study the relationship between uniparental rDNA (encoding 18S, 5.8S and 26S ribosomal RNA) silencing (nucleolar dominance) and rRNA gene dosage, we studied a recently emerged (within the last 80 years) allotetraploid Tragopogon mirus (2n=24), formed from the diploid progenitors T. dubius (2n=12, D-genome donor) and T. porrifolius (2n=12, P-genome donor). Here, we used molecular, cytogenetic and genomic approaches to analyse rRNA gene activity in two sibling T. mirus plants (33A and 33B) with widely different rRNA gene dosages. Plant 33B had ~400 rRNA genes at the D-genome locus, which is typical for T. mirus, accounting for ~25% of total rDNA. We observed characteristic expression dominance of T. dubius-origin genes in all organs. Its sister plant 33A harboured a homozygous macrodeletion that reduced the number of T. dubius-origin genes to about 70 copies (~4% of total rDNA). It showed biparental rDNA expression in root, flower and callus, but not in leaf where D-genome rDNA dominance was maintained. There was upregulation of minor rDNA variants in some tissues. The RNA polymerase I promoters of reactivated T. porrifolius-origin rRNA genes showed reduced DNA methylation, mainly at symmetrical CG and CHG nucleotide motifs. We hypothesise that active, decondensed rDNA units are most likely to be deleted via recombination. The silenced homeologs could be used as a ‘first reserve'' to ameliorate mutational damage and contribute to evolutionary success of polyploids. Deletion and reactivation cycles may lead to bidirectional homogenisation of rRNA arrays in the long term. 相似文献
19.
Origins of polyploids: an example from peonies (Paeonia) and a model for angiosperms 总被引:5,自引:0,他引:5
TAO SANG JIN PAN DAMING ZHANG DIANE FERGUSON CHAO WANG KAI-YU PAN DE-YUAN HONG 《Biological journal of the Linnean Society. Linnean Society of London》2004,82(4):561-571
The majority of tetraploid peonies are allopolyploids derived from crosses between phylogenetically distinct diploid lineages. Tetraploid Paeonia obovata was previously considered to be an autopolyploid because it is morphologically indistinguishable from the diploid of the same species. The presence of the Adh2 gene in tetraploid P. obovata but the inability to amplify the Adh2 gene from Chinese diploids of P. obovata, however, suggests that the tetraploid was not an autotetraploid derivative of the geographically adjacent diploid populations in China. The Adh gene phylogenies rather suggest that the tetraploid originated from crosses between two geographical races of diploid P. obovata distributed in China and Japan. The intermediate status of tetraploid P. obovata between auto‐ and allopolyploidy highlights the need for population genetic analyses of polyploid origins along the continuous range of genomic divergence. Here we present a model that describes the probabilities of polyploid formation and establishment as a function of genomic divergence between diploid progenitors. The probability of polyploid formation (Pf) is obtained from the multiplication of the probability of production of unreduced gametes (Pg) and the probability of ‘hybridization’ (Ph). Pf stays relatively stable when the genomic divergence is low, and then decreases progressively rapidly with the increase of genomic divergence between diploid progenitors. The probability of polyploid establishment (Pe), which depends on the rate of appearance of stable beneficial gene combinations and the rate of fertility restoration, is positively correlated with the genomic divergence of diploid parents. Multiplication of Pf and Pe gives an overall probability of polyploid origins (Po) that varies continuously along the genomic divergence between diploid progenitors. © 2004 The Linnean Society of London, Biological Journal of the Linnean Society, 2004, 82 , 561–571. 相似文献
20.
The systematics of Botrychium subgenus Botrychium has been controversial, primarily because reduction in frond size and complexity has limited the number of characters available for discrimination of species. The recognition of many polyploid species has magnified the difficulty of classification because allopolyploids are often morphologically intermediate between their progenitor diploids. In order to evaluate species limits and sectional boundaries, we surveyed and compared 16 of the 24 currently recognized species for isozymic variation. Little or no intrapopulational variation was detected, but the variation present was consistent with the hypothesis that Botrychium species are primarily inbreeding. Interspecific comparisons distinguished six diploid species and provided evidence of molecular differentiation between the cryptic sister species B. lunaria and B. crenulatum. Evidence of possible progenitor/descendant relationships was found for certain diploid/polyploid relationships. Using enzyme bands shared between species, realignment of the sectional assignment of several species is proposed. Anomalous banding patterns in certain individuals suggested that gene silencing or homoeologous chromosome pairing might be operating in B. minganense, B. hesperium, and B. matricariifolium. Isozyme data also showed that some populations of species presumed to be uniformly diploid possessed isozyme patterns typical of polyploids. All available molecular data indicate that members of Botrychium subgenus Botrychium are actively evolving at diploid and polyploid levels. 相似文献