Electrophoretic evidence for disomic inheritance and allopolyploid origin of the octoploid Cerastium alpinum (Caryophyllaceae)

The mode of inheritance of six enzyme markers in the octoploid alpine plant Cerastium alpinum was analyzed. Offspring from crosses between heterozygotes showed fixed heterozygosity at malate dehydrogenase-2, phosphoglucoisomerase-2, triosephosphate isomerase-2, and triosephosphate isomerase-3. Phosphoglucomutase-1 also showed fixed heterozygosity except in offspring from one cross. Fixed heterozygosity in five enzyme systems suggests that C. alpinum has originated through at least some allopolyploidization. Offspring from plants heterozygous for two alleles at the menadione reductase-1 (Mr-1) locus did not deviate significantly from a 1:2:1 ratio. The large proportion of homozygotes suggests disomic inheritance because any kind of polysomic inheritance would result in a substantially increased proportion of heterozygotes relative to disomic inheritance. Assuming a diploid model for Mr-1, this locus was used to analyze the population genetic structure within C. alpinum populations. Inbreeding was found in many alpine populations. This may help explain the large genetic distances found among alpine populations in a previous study. The analysis is only based on one segregating locus, and the results should therefore be treated with caution. However, by establishing the mode of inheritance through crosses, we have been able to use a codominant marker in population genetic analysis of an octoploid plant.     

Local-scale genetic structure in the peatmoss Sphagnum fuscum

Sphagnum (peatmoss) dominates huge areas of the Northern Hemisphere and acts as a significant carbon sink on a global scale, yet little is known about the genetic structure of Sphagnum populations. We investigated genetic structure within a population of the common peatmoss Sphagnum fuscum, to assess local patterns of genetic diversity and the spatial extent of clones. One hundred seventeen shoots were sampled from five transects in Fuglmyra, central Norway, and sequenced for three anonymous DNA regions. Five neighbourhood patches were marked along each transect, and from each patch, five stems were sampled for molecular analyses. Seventeen haplotypes could be distinguished and two major groups of haplotypes differed by 12 mutational steps. The two major haplotype groups differed significantly in microhabitat association along the distance to groundwater table and the pH gradients, indicating microhabitat differentiation. The haplotypes within these groups were all genetically similar, differing by one or two mutations. The most common haplotype occurred in four transects separated by 250-m distance. Most of the molecular variation in the population was found among transects, and within patches. Large dominating clones within each transect resulted in low variation explained by the among-patch-within-transect component of spatial structure. Mutation appears to account for a larger proportion of the population variation than recombination. Within the population, vegetative growth and asexual reproduction from gametophyte fragments dominate as the main reproductive mode.     

Electrophoretic evidence for the origin ofDryopteris yakusilvicola (Dryopteridaceae)

To investigate the origin of the triploid agamosporous speciesD. yakusilvicola, an electrophoretic analysis was made for five enzymes of theD. sparsa complex.Dryopteris yakusilvicola showed a monomorphic banding pattern for the five enzymes and was heterozygous in all six gene loci coding them. Comparison of enzyme banding patterns suggests that the genome ofD. yakusilvicola was derived through hybridization betweenD. sabaei and either a sexual tetraploid or an agamosporous triploid ofD. sparsa. Cytological evidence (Darnaediet al., 1989) supports the idea that of the two types ofD. sparsa the sexual tetraploid is a parent. The monomorphic pattern implies thatD. yakusilvicola originated from a single hybrid between the parental species, and that it is a neo-endemic of Yakushima Island.     

Further evidence supporting Morocco as a centre of origin of barley

 Thirty-five populations of H. spontaneum from nine countries, encompassing almost all the known range of distribution of the species, Afghanistan, Crete (Greece), Cyprus, Iran, Iraq, Israel, Libya, Morocco and Turkey, were studied utilizing RFLP markers (21 probes with three restriction enzymes) distributed across all seven barley chromosomes in an attempt to unveil the genetic dissimilarities existing among them. UPGMA clustering, based on the Nei and Li (1979) similarity coefficient, produced a dendrogram where three clusters could be defined: two with a clear geographical distinction (Morocco and Cyprus) and another one grouping all the Asian/Middle Eastern populations, except for an accession from Iran that clustered separately. These results confirm our previous work and suggest that barley domestication could also have taken place outside the Fertile Crescent, particularly in Morocco. Received: 10 October 1998 / Accepted: 27 October 1998     

Molecular evidence for allopolyploid speciation and a single origin of the narrow endemic Draba ladina (Brassicaceae)

Draba ladina (Brassicaceae) is a small alpine flower endemic to the Swiss Alps. It occurs exclusively at elevations between 2600 and 3000 m and is restricted to less than a dozen mountains in the Lower Engadin. Morphological characters and polyploidy suggest a hybrid origin. Potential diploid progenitor species are distributed widely and often occur sympatrically. To study the evolutionary history of D. ladina we assessed intra- and interspecific sequence variation at noncoding chloroplast DNA loci and nuclear rDNA ITS sequences in D. ladina and its presumed progenitor species D. aizoides, D. dubia, and D. tomentosa. A single ITS (Internal Transcribed Spacer) genotype was found in each of D. aizoides and D. dubia and two in D. tomentosa. Additivity of ITS sequences of D. aizoides and D. tomentosa was found in D. ladina, supporting the hypothesis of an allotetraploid origin. Intraspecific cpDNA variation was found in all diploid species, but not in D. ladina. The single chloroplast DNA haplotype found in the latter was closest to one cpDNA haplotype found in D. tomentosa, suggesting that D. tomentosa was the maternal parent. These results suggest that D. ladina is a relatively young, presumably postglacial, taxon with a single allopolyploid origin.     

Monocotylar seedlings: a review of evidence supporting an origin by fusion

The structure and growth of the seedling, as described in the literature, is discussed for both monocotylar Dicotyledones and for Monocotyledones (several Apiaceae, Ranunculaceae and Gesneriaceae; species of Combretum, Peperomia, Cyclamen, Corydalis and Pinguicula , and also anomalous syncotylar examples of Impatiens, Butomus, Agave, Cordyline, Dioscorea, Pitcairnia and Costus ). In all examples the single cotyledon appears to be derived, phylogenetically, from an ancestral pair which has fused, often with no remaining trace of their double origin, to give an apparatus which buries the unexpanded plumule and radicle deeply in the ground early in germination. No evidence for suppression of one of the ancestral pair of cotyledons was found in any species.
The syncotylar theory of the origin of monocotyledons of Sargant (1903) is supported and extended to apply to all known monocotylar species. The anomalous appearance of paired cotyledons in Agapanthus and Cyrtanthus apparently results from twinning, as known in Sinapis and Centranthus , not to atavistic reformation.     

Molecular evidence for allopolyploid speciation and a single origin of the western Mediterranean orchid Dactylorhiza insularis (Orchidaceae)

The hybrid origin of the western Mediterranean orchid Dactylorhiza insularis was demonstrated by genetic markers. Allozyme data showed that throughout its range D. insularis has an allotriploid constitution and reproduces apomictically. The parental species of D. insularis were identified as D. romana andD. sambucina; they contributed 2 alleles and 1 allele, respectively, at the allozyme loci studied. The maternal species of D. insularis was D. romana , as inferred from cpDNA ( trn L(UAA) intron). High genetic similarities were found when comparing present populations of D. romana and D. sambucina with their respective genomes 'frozen' in D. insularis. Dactylorhiza insularis showed fixed (or nearly fixed) heterozygosity at 11 out of the 19 loci studied, and poor genetic variation: eight multilocus genotypes were detected at allozyme level. No multilocus genotype differs from the most similar one by more than one allele substitution. All D. insularis individuals showed the same cpDNA haplotype (I) , regardless of their geographic origin and multilocus genotype. The I haplotype is similar, but not identical to that found in D. romana (R). No recurrent formation of D. insularis was observed in hybrid zones between D. romana and D. sambucina , where diploid sexual hybrids (F_1; F_n, backcrosses) were detected. Available data agree with a single origin for D. insularis , which possibly occurred in the present postglacial, when D. romana and D. sambucina , expanding from their glacial refugia, came into contact. The genetic homogeneity found between D. romana and D. markusii , both from their locus classicus , indicates that the latter is a junior synonym of D. romana; on the other hand, D. romana and D. sambucina are well differentiated species ( D_Nei = 0.59).     

Intercontinental genetic structure in the amphi‐Pacific peatmoss Sphagnum miyabeanum (Bryophyta: Sphagnaceae)

Unlike seed plants where global biogeographical patterns typically involve interspecific phylogenetic history, spore‐producing bryophyte species often have intercontinental distributions that are best understood from a population genetic perspective. We sought to understand how reproductive processes, especially dispersal, have contributed to the intercontinental ‘Pacific Rim’ distribution of Sphagnum miyabeanum. In total, 295 gametophyte plants from western North America (California, Oregon, British Columbia, Alaska), Russia, Japan, and China were genotyped at 12 microsatellite loci. Nucleotide sequences were obtained for seven anonymous nuclear loci plus two plastid regions from 21 plants of S. miyabeanum and two outgroup species. We detected weak but significant genetic differentiation among plants from China, Japan, Alaska, British Columbia, and the western USA. Alaskan plants are genetically most similar to Asian plants, and British Columbian plants are most similar to those in the western USA. There is detectable migration between regions, with especially high levels between Alaska and Asia (China and Japan). Migration appears to be recent and/or ongoing, and more or less equivalent in both directions. There is weak (but significant) isolation‐by‐distance within geographical regions, and the slope of the regression of genetic on geographical distance differs for Asian versus North American plants. A distinctive Vancouver Island morphotype is very weakly differentiated, and does not appear to be reproductively isolated from plants of the normal morphotype. The intercontinental geographical range of S. miyabeanum reflects recent and probably ongoing migration, facilitated by the production of tiny spores capable of effective long distance dispersal. The results of the present study are consistent with Pleistocene survival of S. miyabeanum in unglaciated Beringia, although we cannot eliminate the possibility that the species recolonized Alaska from Asia more recently. © 2013 The Linnean Society of London, Biological Journal of the Linnean Society, 2014, 111 , 17–37.     

Variation in "biodiversity value" of peatmoss species in Sphagnum section Acutifolia (Sphagnaceae)

Species are the most common currency by which biodiversity is measured, but species are not equivalent in "biodiversity value" because of differences in phylogenetic history and current population processes. Morphologically defined species in Sphagnum section Acutifolia (Bryophyta) were compared with regard to how phylogenetically distinct each is from its sister species and how much nucleotide variation each encompasses. Comparisons were based on sequence variation at seven nuclear and chloroplast loci. Assignment of collections to morphospecies accounted for about 57-75% of the overall nucleotide variation at the seven loci, but morphospecies differed greatly in how much nucleotide diversity they encompass. In addition, morphospecies varied widely in their genetic distinctiveness, estimated as the length of the stem branch from the most recent common ancestor and numbers of differentially fixed and shared polymorphic nucleotides among taxa. Levels of molecular diversity within morphospecies were not correlated with their degree of isolation. Factors that affected the biodiversity value of species include age, mode of origin, demographic history, and reproductive biology.     

Electrophoretic and cytological evidence for genetic heterogeneity and the hybrid origin ofAthyrium oblitescens

Athyrium oblitescens, a putative hybrid species, was examined electrophoretically and cytologically to clarify its origin. Allozyme data showed thatA. oblitescens consisted of at least three allozyme types, designated Type C, Type O and Type W. Genotypic compositions of Type C and Type W suggested that they were derived from independent hybridizations betweenA. otophorum andA. clivicola and betweenA. otophorum andA. wardii, respectively. Contrary to previous reports of tetraploidy inA. oblitescens and its hypothesized parent species, cytological observation revealed that Type C and Type W were both hexaploids. Possible pathways for the origin of these hexaploids are proposed. Type O was not genetically distinct fromA. otophorum by either electrophoretic or cytological analyses, and thus there was no evidence of hybrid origin.     

Electrophoretic evidence for all otetraploid origin of Dactylorhiza purpurella (Orchidaceae)

Evidence from all ozyme markers suggests that the NW European Dactylorhiza purpurella (Orchidaceae) is an allotetraploid which originated from taxa closely related to the present-day D. incarnata s. I. and D. fuchsii/D. maculata . However, Dactylorhiza purpurella deviates more strongly from the allotetraploid condition than other taxa previously investigated in Dactylorhiza (i.e., D. majalis, D. traunsteineri, D. sphagnicola , and D. lapponica ), in that the characteristic incarnata alleles occur at lower frequencies than expected at two loci. It is suggested that D. purpurella arose from parents slightly different from those giving rise to the other allotetraploids, or that the tetraploid genome in D. purpurella has been modified by rare recombination events between homoeologous chromosomes, replacing segments of the incarnata chromosomes with the fuchsii/maculata genome.     

Experimental evidence for a persistent spore bank in Sphagnum

Spore capsules of four Sphagnum species were buried at different depths in peat on a bog. Spore viability was determined after 0, 1, 2 and 3 yr. Viability generally declined with time, but viable spores were still found at all depths after 3 yr. The light-coloured spores of S. balticum and S. tenellum retained their viability better than the darker spores of S. fuscum and S. lindbergii . Survival was highest under wet but aerobic conditions, but was also high under humid or periodically desiccated conditions. By contrast, most spores stored under wet, anaerobic conditions died within 2–3 yr. These results, and predictions from them, are not consistent with earlier results for spores of long-lived and dominant bryophytes, or for seeds of phanerogams of undisturbed wetlands and forests. There was no correlation between spore size and longevity across species, but the small spores from small capsules of S. balticum and S. tenellum generally showed higher viability than those from the medium-sized and large capsules of the same species. This suggests a positive intraspecific relationship between longevity and dispersal distance. There was an indication of conditional dormancy, controlled by weather, in Sphagnum spores. The experiments indicate that Sphagnum spores can form a long-term persistent spore bank under suitable conditions, with a half-life of between 1 and 20 yr (mean across species of 2.6 and 5.0 yr at two depths studied), and with potential values in individual spore capsules of several decades, or even of centuries. Sphagnum spores kept refrigerated showed 15–35% viable spores after 13 yr. The capacity to form a persistent spore bank that can be activated whenever favourable conditions occur might help explain the wide geographical distribution of many Sphagnum species in the boreal and temperate zones, where they have managed to colonize almost every suitable patch of acidic, nutrient-poor wetland.     

The allopolyploid origin of Spiranthes hongkongensis (Orchidaceae)

Morphological and ecological similarities between Spiranthes hongkongensis Hu et Barretto and S. sinensis (Pers.) Ames suggest a close evolutionary relationship. The hypothesis that S. hongkongensis evolved through natural hybridization between S. sinensis and S. spiralis was tested using isozyme electrophoresis. A total of 28 isozyme loci were interpreted in the diploid species S. sinensis and S. spiralis, and “fixed heterozygosity” owing to gene duplication was observed at ten of these loci in S. hongkongensis. Isozyme phenotypes provided strong evidence for an allotetraploid origin of S. hongkongensis, with S. sinensis and most likely S. spiralis as its diploid progenitors. Chromosomal counts of S. hongkongensis gave a tetraploid number of ≈60. The allotetraploid species is self-fertile, and completely isolated by sterility barriers from S. sinensis. Premating isolation also exists between S. hongkongensis and S. sinensis due to earlier flowering and autogamy in S. hongkongensis, which may account for the rarity of natural hybrids in the sites of sympatry. The role of the autogamous breeding system in the establishment and spread of S. hongkongensis is discussed.     

Parental origin and genome evolution in the allopolyploid Iris versicolor

BACKGROUND AIMS: One of the classic examples of an allopolyploid is Iris versicolor, 'Blue Flag' (2n = 108), first studied by Edgar Anderson and later popularized by George Ledyard Stebbins in cytogenetics and evolutionary text-books. It is revisited here using modern molecular and cytogenetic tools to investigate its putative allopolyploid origin involving progenitors of I. virginica (2n = 70) and I. setosa (2n = 38). METHODS: Genomic in situ hybridization (GISH), fluorescent in situ hybridization (FISH) and Southern hybridization with 5S and 18-26S ribosomal DNA (rDNA) probes were used to identify the parental origin of chromosomes, and to study the unit structure, relative abundance and chromosomal location of rDNA sequences. KEY RESULTS: GISH shows that I. versicolor has inherited the sum of the chromosome complement from the two progenitor species. In I. versicolor all the 18-26S rDNA units and loci are inherited from the progenitor of I. virginica, those loci from the I. setosa progenitor are absent. In contrast 5S rDNA loci and units from both progenitors are found, although one of the two 5S loci expected from the I. setosa progenitor is absent. CONCLUSIONS: These data confirm Anderson's hypothesis that I. versicolor is an allopolyploid involving progenitors of I. virginica and I. setosa. The number of 18-26S rDNA loci in I. versicolor is similar to that of progenitor I. virginica, suggestive of a first stage in genome diploidization. The locus loss is targeted at the I. setosa-origin subgenome, and this is discussed in relation to other polyploidy systems.     

Experimental evidence supporting a mathematical theory of the physiological mechanism regulating follicle development and ovulation number

In higher vertebrates, follicular development is regulated so that the number of follicles that periodically mature and ovulate is controlled within a narrow range. Lacker has proposed a simple mathematical model of follicle development that can account for the regulation of ovulation number. To support the assumption of the theory that follicle interactions are mediated by estradiol acting as a chemical messenger to communicate follicular maturity to the pituitary and other follicles, we have presented data to demonstrate that in the rabbit physiological concentrations of circulating estradiol inhibit follicle maturation. Implants containing estradiol were placed subcutaneously after surgical rupture of the existing follicles that were 1 mm in diameter or larger. Serum estradiol concentrations were maintained near physiological concentrations by the implants. Concentrations of circulating estradiol were 74 +/- 5.7 pg/ml in the untreated groups, whereas the concentrations with the implants were increased by approximately 50 pg/ml/implant over this basal concentration with a range of 100-300 pg/ml. In the control groups, the average number of follicles before surgical rupture was 27 +/- 2.9 and there was no significant difference (p greater than 0.05) in the number of follicles, 26 +/- 1.9, three days after follicle rupture. The follicles ranged in size from 1 mm to 4 mm, and only those over 3 mm were considered mature. In the first group of animals with implants, the total number of follicles before surgery was 19 +/- 3; three days after follicle rupture, the number of follicles was only 9 +/- 1.1.(ABSTRACT TRUNCATED AT 250 WORDS)     

Local adaptations in bryophytes revisited: the genetic structure of the calcium‐tolerant peatmoss Sphagnum warnstorfii along geographic and pH gradients

Bryophytes dominate some ecosystems despite their extraordinary sensitivity to habitat quality. Nevertheless, some species behave differently across various regions. The existence of local adaptations is questioned by a high dispersal ability, which is thought to redistribute genetic variability among populations. Although Sphagnum warnstorfii is an important ecosystem engineer in fen peatlands, the causes of its rather wide niche along the pH/calcium gradient are poorly understood. Here, we studied the genetic variability of its global populations, with a detailed focus on the wide pH/calcium gradient in Central Europe. Principal coordinates analysis of 12 polymorphic microsatellite loci revealed a significant gradient coinciding with water pH, but independent of geography; even samples from the same fens were clearly separated along this gradient. However, most of the genetic variations remained unexplained, possibly because of the introgression from phylogenetically allied species. This explanation is supported by the small heterogeneous cluster of samples that appeared when populations morphologically transitional to S. subnites, S. rubellum, or S. russowii were included into the analysis. Alternatively, this unexplained variation might be attributed to a legacy of glacial refugia with recently dissolved ecological and biogeographic consequences. Isolation by distance appeared at the smallest scale only (up to 43 km). Negative spatial correlations occurred more frequently, mainly at long distances (up to 950 km), implying a genetic similarity among samples which are very distant geographically. Our results confirm the high dispersal ability of peatmosses, but simultaneously suggested that their ability to cope with a high pH/calcium level is at least partially determined genetically, perhaps via specific physiological mechanisms or a hummock‐forming ability.     

Genetic analysis of the peatmoss Sphagnum cribrosum (Sphagnaceae) indicates independent origins of an extreme infra‐specific morphology shift

Within Sphagnum cribrosum, a dioicous aquatic peatmoss, a unique morphological variant (the ‘waveform’), found at only two lakes in North Carolina, has a branching architecture that is extremely differentiated from anything otherwise known in Sphagnum, although the plants are microscopically indistinguishable from S. cribrosum. At one site where the two morphologies co‐occur, 60 years of field observations demonstrate the persistence of each morphology, even where the two forms grow intermixed. We conducted a reciprocal transplant experiment in which waveform and normal plants maintained their divergent morphologies for 8 months. We sampled populations throughout the range and conducted genetic and phylogenetic analyses with microsatellite markers and DNA sequences to investigate the genetic context of the waveform morphology within S. cribrosum. Haplotype networks from DNA sequences showed the two waveform populations are separated by 11 substitutions across three loci. Microsatellite analyses using nonparametric clustering and admixture models also indicated genetic dissimilarity between genotypes with waveform morphology at the two lakes. Both molecular datasets suggest that the waveform morphology had at least two independent origins, despite the proximity of the two lakes where it occurs uniquely. Given the clonal nature of the waveform, it is unlikely to form a cohesive evolutionary lineage deserving of taxonomic status. The analysis also revealed a genetically diverse population in Georgia as the potential source of variation found in all other populations of S. cribrosum. © 2012 The Linnean Society of London, Biological Journal of the Linnean Society, 2012, 106 , 137–153.     

Electrophoretic identification of polyploidCamellia japonica (Theaceae) cultivars and evidence for their sexual origin

Electrophoretic examination of allozymes from 189Camellia japonica cultivars revealed some banding patterns not explainable by codominant diploid genetics. At several loci encoding dimeric enzymes, 5 and 6 banded patterns were observed in 7 cultivars. These patterns are interpreted as resulting from triploidy or aneuploidy, where three variant alleles code for products which are electrophoretically distinguishable and associate to form three homodimers and three heterodimers. The presence of allozyme multiplicity in these clones suggests a sexual rather than a somatic mode of triploid origin.