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We have studied the behavior of phase response curves of different oscillatory states in a Belousov–Zhabotinsky reaction by using the amplified Oregonator model. As perturbants we have used bromide ion and silver ion. In case of oxidation spikes, the effect of bromide ion is a phase delay as reported previously. However, when the oscillations stay a considerable time in the oxidized state, bromide ion can cause significant phase advances, whenever the perturbation exceeds a lower critical bromide ion concentration. We are able to model recent experiments performed by Marek and co-workers, which have been claimed to give poor agreements with Oregonator-type of models. We have also compared the effect of a low (104 M-1 s-1) or high (109 M-1 s-1) silver bromide precipitation rate constant on phase response curves when silver ion perturbs oxidation spikes. We find that best agreements with experiments are obtained when the low silver bromide precipitation rate constant is used. The computations exhibit virtually identical behavior whether the rate constant values due to Field, Körös, and Noyes, or to Field and Försterling are used to parametrize the oxybromine chemistry. [ABSTRACT FROM AUTHOR]

A model based on five independent composition variables has been tested by simulating the complex bursting patterns observed experimentally for a Belousov–Zhabotinsky system in a flow reactor. If the system is in a region of constraint space where all stationary states are locally unstable, and if malonic acid concentration in the feed is decreased at constant flow of bromide ion, simple limit-cycle oscillations persist until the system reaches the Hopf bifurcation which generates a stable stationary state with low concentration of bromide ion. If bromide ion concentration in the feed is increased at constant flow of malonic acid, more and more small-amplitude oscillations are interspersed between trains of fewer and fewer large-amplitude excursions until a Hopf bifurcation leads to a stable stationary state with a high concentration of bromide ion. Patterns may be quite complex but usually repeat regularly. If a firing number is defined as ΣS/(ΣS+ΣL), where the summations represent the numbers of small- and large-amplitude oscillations in a complete pattern, then this firing number increases monotonically with increasing bromide ion in the feed. Narrow regions of chaotic mixing of patterns are also observed. The computations agree spectacularly with the careful experimental observations of Maselko and Swinney. Two separate curves are generated by the Hopf bifurcations which limit local stabilities of stationary states containing low and high concentrations of bromide ion, and the intersection of these curves provides a rationale for the ‘‘cross-shaped phase diagrams’’ which define regions of bistability and of oscillations in constraint spaces for such systems. [ABSTRACT FROM AUTHOR]

A stiffly-coupled Oregonator model based on the two independent variables Y and Z has been examined in detail with the use of the stoichiometric factor as a single disposable parameter. The trajectories and periods of the stable limit cycles can be generated with unanticipated accuracy from simple linear differential equations. Transitions between stable limit cycles and stable steady states takes place by means of subcritical Hopf bifurcations. Unstable limit cycles and thresholds of excitability can be recovered by integrating the equations of motion backward in time; such procedures cannot be applied so easily for models based on more than two independent variables. We have examined claims of experimental evidence for saddle-node infinite period (SNIPER) bifurcations and have concluded that all currently available evidence is equivocal. Until unambiguous criteria can be established for identifying SNIPER bifurcations in real systems, and until chemical mechanisms have been proposed which generate such bifurcations, observations should be interpreted by existing models based on Hopf bifurcations. Experimental behaviors are listed which can and cannot be simulated in terms of two independent composition variables. [ABSTRACT FROM AUTHOR]

When a chemical reaction is carried out in a continuously stirred tank reactor, the behavior may be significantly affected by the efficiency with which the entering chemicals are mixed with the main contents of the reactor. We have developed a model for this effect which assumes that a feed of premixed chemicals remains for a while in totally segregated packets before they are rapidly and perfectly mixed with the rest of the system. The time of this initial segregation is affected by the efficiency of stirring in the reactor. The model has been tested by computations on a mechanism developed by Roelofs et al. for a reaction which would oscillate even in a closed system. It has also been tested by computations on the rapid autocatalytic oxidation of cerous ion by bromate in the presence of a small amount of bromide. The results are qualitatively consistent with effects observed experimentally and in computations with other models including a somewhat similar one by Kumpinsky and Epstein. More quantitative tests should recognize the difference whether two streams of chemicals enter the reactor independently or are premixed before they do so. [ABSTRACT FROM AUTHOR]

The original Oregonator model of five irreversible steps and one stoichiometric parameter has been amplified to seven irreversible steps. The amplified model simulates excitability of a reduced steady state induced by silver ions and of an oxidized steady state induced by bromide ions. It also simulates how oscillations during a single run might change from reduction pulses to oxidation pulses. Finally, it simulates a temporary bistability persisting for over two hours in a closed system. If independent measurements determine the rate of enolization of the organic substrate and the rate of reaction of that substrate with the oxidized form of the catalyst, this model may be able to simulate semiquantitatively a large fraction of reported behaviors of catalyzed homogeneous Belousov–Zhabotinsky systems. It will not model systems in which Br2 accumulates or in which there are high-frequency small-amplitude oscillations around an oxidized steady state. Procedures are suggested for simulating such behaviors. [ABSTRACT FROM AUTHOR]

Erigeron geiseri Shinners is a tap-rooted herbaceous daisy occurring from south-eastern Texas to southern Oklahoma. Our study of pollen quality from 67 herbarium specimens supports the hypothesis that the species comprises sexual diploid populations, restricted to southern locations, and polyploid, putatively apomictic, populations that are widespread. We successfully amplified and sequenced ITS and ETS spacer regions of nrDNA for five specimens (two putative sexual diploids, three putative apomictic polyploids). Phylogenetic analysis conducted using maximum likelihood and Bayesian methods support a topology showing that 1) sexual and apomictic populations of E. geiseri form a well-supported monophyletic group, and, 2) E. geiseri is sister to E. strigosus of eastern North America. The results support the classification of E. geiseri with E. strigosus in E. sect. Phalacroloma. [ABSTRACT FROM AUTHOR]

* Premise of the study: Dihaploids result when tetraploids produce reduced eggs that develop without fertilization into diploid progeny. This process is useful for reducing genome complexity and studying trait expression at different ploidal levels. In this study we evaluated genetic inheritance and expression of diplospory (D) and parthenogenesis (P) in a population of dihaploids produced by tetraploid apomictic Erigeron. * Methods: From 400 mostly maternal (tetraploid) progeny, we identified 64 (16%) dihaploids with 2n = 18 (53 plants) or 2n = 19 (11 plants). Differential interference contrast (DIC) imaging of ovules was used to evaluate megasporogenesis (meiosis vs. diplospory) and capacity for parthenogenetic embryo development. Seed production was estimated as the proportion of filled seeds. * Key results: For 60 analyzed dihaploids, diplospory vs. meiosis segregated approximately 1: 1 (P = 0.44) while all exhibited parthenogenetic embryo development. Parthenogenesis for meiotic progeny (n = 27) was observed in approximately 50% of ovules. Apomictic dihaploids (combining D and P;n = 33) produced seeds with mean 24.8% (range 1.3-74.4%) of total flowers. * Conclusions: The dihaploid population consisted of half apomicts (D + P) and half parthenogens (P only). We infer that formation of dihaploid seeds requires the parthenogenesis locus. The highest seed values obtained for diploid apomicts are comparable to those recorded for wild type polyploid apomicts. This is one of the first reports of diploid apomixis in the Asteraceae and it demonstrates that both diplospory and parthenogenesis can be transmitted and expressed at a high level in the diploid condition. [ABSTRACT FROM AUTHOR]

Madagascar is surrounded by archipelagos varying widely in origin, age and structure. Although small and geologically young, these archipelagos have accumulated disproportionate numbers of unique lineages in comparison to Madagascar, highlighting the role of waif-dispersal and rapid in situ diversification processes in generating endemic biodiversity. We reconstruct the evolutionary and biogeographical history of the genus Psiadia (Asteraceae), a plant genus with near equal numbers of species in Madagascar and surrounding islands. Analyzing patterns and processes of diversification, we explain species accumulation on peripheral islands and aim to offer new insights on the origin and potential causes for diversification in the Madagascar and Indian Ocean Islands biodiversity hotspot. Our results provide support for an African origin of the group, with strong support for non-monophyly. Colonization of the Mascarenes took place by two evolutionary distinct lineages from Madagascar, via two independent dispersal events, each unique for their spatial and temporal properties. Significant shifts in diversification rate followed regional expansion, resulting in co-occurring and phenotypically convergent species on high-elevation volcanic slopes. Like other endemic island lineages, Psiadia have been highly successful in dispersing to and radiating on isolated oceanic islands, typified by high habitat diversity and dynamic ecosystems fuelled by continued geological activity. Results stress the important biogeographical role for Rodrigues in serving as an outlying stepping stone from which regional colonization took place. We discuss how isolated volcanic islands contribute to regional diversity by generating substantial numbers of endemic species on short temporal scales. Factors pertaining to the mode and tempo of archipelago formation and its geographical isolation strongly govern evolutionary pathways available for species diversification, and the potential for successful diversification of dispersed lineages, therefore, appears highly dependent on the timing of arrival, as habitat and resource properties change dramatically over the course of oceanic island evolution. [ABSTRACT FROM AUTHOR]

The article focuses on the sexual degeneration occurring in plants in Great Britain. Asexual reproduction by seed in plants, or apomixis takes place in a diversity of taxa and developed from sexual ancestors. A multi-step development process known as diplospory is initiated when meiosis is altered to produce an unreduced rather than unreduced egg cell. The subsequent occurrence of parthenogenetic development of the unreduced egg gives away genetically maternal progeny.

Apomixis in daisy fleabanes ( Erigeron annuus and E. strigosus) is controlled by two genetically unlinked loci that regulate, independently, the formation of unreduced female gametophytes (apomeiosis, diplospory) and autonomous seed formation (parthenogenesis). In this work, fully apomictic F2s were regenerated by crossing F1s bearing, separately, these two functional regions. Two triploid (3 x = 2n = 27) highly diplosporous F1s served as seed parents to an aneuploid (2 x + 1 = 2n = 19) meiotic pollen donor bearing four AFLP markers linked to parthenogenetic seed formation but producing only abortive embryos and endosperm. Of 408 hybrids, 21 (5.1%) produced seed. Nine of these putative apomicts were tetraploids (4 x), likely combining an unreduced egg from the diplosporous seed parent and a haploid gamete from the pollen parent (3 x + x). The other 12 hybrid apomicts were pentaploid, interpreted as arising from the fusion of an unreduced diplosporous egg with an unreduced sperm cell (3 x + 2 x). Analysis indicated that all but three of the 21 synthetic apomicts recombined markers linked to diplospory and parthenogenesis. In addition, three additional hybrids combined markers linked to the two functional regions but produced only aborted embryos. The apomicts varied in percentage of diplosporous ovules (4.7–95.3% of all ovules produced) and in percentage of ovules that developed into seed (3.8–58.0%). These results support the hypothesis that apomeiosis and autonomous seed formation are genetically distinct, and that the traits can be separated and recombined to create hybrids exhibiting apomixis at near wildtype levels. [ABSTRACT FROM AUTHOR]

Apomictic complexes in flowering plants often harbor multiple sexual taxa, which must be studied to interpret accurately the origin and diversity of apomictic derivatives. The daisy fleabane group in North America (Erigeron sect. Phalacroloma) includes the widespread polyploid apomictic taxa E. annuus, E. strigosus, and E. tenuis, as well as recently discovered sexual diploid populations in the southeastern United States (E. soigosus var. calcicola, E. strigosus var. dolomiticola, sexual E. strigosus var. strigosus). Phylogenetic analysis for 35 sexual populations was conducted using sequences from the internal and external transcribed spacers (ITS and ETS) of ribosomal DNA. Results indicate that the three groups of sexual plants form separate monophyletic clades and that edaphic specialization is ancestral in the group. Sequence analysis for sexual E. strigosus var. strigosus was confounded by the fact that 13 of 31 samples (42%) possessed nucleotide polymorphisms at 1.0–1.8% of sites. However, analysis of the genomic sequence for plants with low polymorphism levels in conjunction with analysis of cloned PCR products for plants with high levels of intra-individual polymorphism indicated that three combinations of haplotypes (N I + N II, two plants; N I + N III, five plants; N II + N III, six plants) accounted for the majority of sequence polymorphisms encountered. These data are consistent with historical diversification and subsequent reticulate evolution at the diploid level in sexual E. strigosus var. soigosus. [ABSTRACT FROM AUTHOR]

Erigeron strigosus is widespread in North America and has heretofore been considered to be uniformly apomictic. The recent description of new varieties of E. strigosus in Alabama, Georgia, and Tennessee on dolomitic and calcareous glades (E. strigosus var. dolomiticola and E. strigosus var. calcicola) and the discovery of a third, yet unnamed taxon on the coastal plain of the southeastern United States (E. strigosus var. nov.) prompted this investigation of their cytology and reproductive attributes. Here, we report that all three varieties are diploid (2n=18) and sexual, with tetrasporic female gametophyte development. In addition, B-chromosomes were observed in three instances in E. strigosus var. nov. On average, pollen of sexual E. strigosus is uniformly small (average 14.9 μm diameter) and of high quality (84.2% viability), although low pollen viability was observed in eight of 36 plants, and exceptionally large, putatively unreduced grains were observed in low frequency in two plants. [ABSTRACT FROM AUTHOR]

Examines two independent loci control agamospermy in the triploid flowering plant Erigon annuus. Context of agamospermy via gametophytic apomixis in flowering plants; Association between markers with polysomic inheritance and parthenogenesis; Analysis on the link between diplospory and parthenogenesis.

Studies the segregation for asexual seed production of hybrids resulting from a cross between diploid sexual Erigeron strigosus and triploid agamospermous Erigeron annuus. Distribution of chromosome numbers; Diplosporous versus meiotic megagametohyte development; Inheritance of diplospory in Erigeron.

Presents phylogenetic analysis of nucleotide sequence data of Astereae (Asteraceae or Compositae) from the internal transcribe spaces of nuclear ribosomal DNA. Astereae as the largest tribe of Asteraceae in North America; Taxonomic and geographic sampling; Polyphyletic assemblage; Length variation and base composition; High level Astereae relationships.

Focuses on the Gibbs function and its application to chemical systems and subsystems. Definition of Gibbs function and the constraints on it; Discussions on the possibility of applying G to an Anistropic solid; Ways in which to determine G in the bates-Tykoid system; Summary of conclusions; Implications for the teaching of thermodynamics.

Assesses the variation and population structure in Erigeron compositus. Characterization of individual multilocus genotypes within putative agamospermously producing plant populations; Determination of the cytotype and pollen-producing capacity of specimens of each genotype; Evaluation of genetic variability within and among agamospermos populations.

Presents a discussion of an irreversible process in a system whose initial state is two rigid flasks, isolated by a stopcock. The conflicting solutions; Argument based on the pressure upon the system; Argument based on the extensiveness of the Gibbs free energy; A resolution of the apparent paradox; Conclusions.

As part of ongoing efforts to understand and document the flora of the southeastern United States, a number of taxonomic changes at generic, specific, and infraspecific rank are made. We also discuss and clarify the recommended taxonomy for other taxa (not requiring nomenclatural acts) and present a point of view about the practical and philosophic basis for making taxonomic changes in an allegedly well-understood flora. The genera (and families) affected are Endodeca (Aristolochiaceae), Erigeron, Pityopsis, and Solidago (Asteraceae), Tillandsia (Bromeliaceae), Carex (Cyperaceae), Baptisia and Indigofera (Fabaceae), Salvia and Scutellaria (Lamiaceae), Stenanthium (Melanthiaceae), Epidendrum (Orchidaceae), and Andropogon, Coleataenia, Dichanthelium, Digitaria, and Panicum (Poaceae). [ABSTRACT FROM AUTHOR]

As part of ongoing efforts to understand and document the flora of the southeastern United States, a number of taxonomic changes at generic, specific, and infraspecific rank are made. We also discuss and clarify the recommended taxonomy for other taxa (not requiring nomenclatural acts) and present a point of view about the practical and philosophic basis for making taxonomic changes in an allegedly well-understood flora. The genera (and families) affected are Allium (Alliaceae), Erigeron, Liatris, and Trilisa (Asteraceae), Calycanthus (Calycanthaceae), Gaylussacia (Ericaceae), Dalea and Mimosa (Fabaceae), Hydrophyllum (Hydrophyllaceae), Didymoglossum (Hymenophyllaceae), Monarda (Lamiaceae), Kosteletzkya and Sida (Malvaceae), Narthecium (Nartheciaceae), Agalinis, Melampyrum, and Orobanche/Aphyllon/Myzorrhiza (Orobanchaceae), Dichanthelium and Elymus (Poaceae), Clematis (Ranunculaceae), and Maianthemum (Ruscaceae). [ABSTRACT FROM AUTHOR]

Aim The aims of this study were (1) to investigate whether the two growth forms of Darwiniothamnus Harling (Asteraceae) originated from the colonization of a single ancestor, (2) to identify the closest relative(s) of Darwiniothamnus, and (3) to review molecular phylogenies from other plant groups to infer the origin of Galápagos endemics. Location Darwiniothamnus is endemic to the Galápagos Islands. Methods All putative relatives of Darwiniothamnus plus 38 additional species were included. Nucleotide sequences of the internal transcribed spacers of the nuclear ribosomal DNA were used for Bayesian and parsimony analyses. Results Darwiniothamnus is polyphyletic. Two species ( D. lancifolius (Hook. f.) Harling and D. tenuifolius (Hook. f.) Harling) are woody shrubs that usually grow to 1–2 m in height; they belong to a clade composed of species otherwise restricted to the Caribbean. These two species are sister to Erigeron bellidiastroides Griseb., a herbaceous species endemic to Cuba. The third species ( D. alternifolius Lawesson & Adsersen) is a perennial herbaceous plant, woody at the base and reaching only up to 50 cm in height. It is sister to two Chilean (Coquimbo–Valparaiso region) species that also have a perennial herbaceous habit: E. fasciculatus Colla and E. luxurians (Skottsb.) Solbrig. They are placed in an assemblage restricted to South America. The review of previous molecular phylogenetic studies revealed that two of the endemic genera and endemic species of three non-endemic genera have their closest relatives in South America. Endemic species belonging to three non-endemic genera have sister species in North America or the West Indies. One endemic genus and endemic species in three non-endemic genera have sister taxa with a widespread continental distribution, or their molecular phylogenies yielded equivocal results. Main conclusions The flora of Galápagos has affinities with both North America (including the Antilles) and South America. Darwiniothamnus exhibits both patterns: two species of this genus are sister to a taxon endemic to Cuba, supporting a connection between the Cocos plate and the West Indies; the third species, D. alternifolius, provides a link with the Coquimbo–Valparaiso region, suggesting a biogeographical connection between the Nazca plate and southern South America. [ABSTRACT FROM AUTHOR]