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PubMed1999

An Essay on Juvenility, Phase Change, and Heteroblasty in Seed Plants.

Phase change (the change from nonreproductive to reproductive status) and heteroblasty (ontogenetic changes in vegetative metamers) are two determinants of longitudinal asymmetry in plants. These concepts are critically important to understanding the regulation of plant development as well as morphological evolution and life-history variation. Since Goebel, the two have been conflated. This article questions how phase change and heteroblasty are delimited and explores some of the problems that arise in the explicit or implicit link between them, given that several lines of evidence indicate that they are distinct and independent facets of plant development. It is suggested that problems are perpetuated through use of the terms "juvenile" and "adult" to describe both phenomena.

Journal Article↗
PubMed1991

Genetic analysis of the morphological differences between maize and teosinte.

Molecular marker loci were used to investigate the inheritance of morphological traits that distinguish maize (Zea mays ssp. mays) from a closely related wild relative, teosinte (Z. mays ssp. mexicana). Regression and interval mapping analyses gave largely congruent results concerning the numbers of loci controlling the morphological traits and the magnitudes of their effects; however, interval mapping tended to give larger estimates for the magnitudes of the effects of the morphological trait loci. This tendency was exaggerated for traits that were non-normally distributed. Variation for most inflorescence traits is controlled by one or two regions of the genome with large effects plus several other regions with relatively small effects. As such, the data are congruent with a mode of inheritance for most traits involving one or two major loci plus several minor loci. Regions of the genome with large effects on one trait consistently had smaller effects on several other traits, possibly as a result of pleiotropy. Most of the variation for the dramatic differences in inflorescence morphology between maize and teosinte is explained by five restricted regions of the genome. One of these regions encompasses a previously described gene, tb1 (teosinte branched), and the effects of this region on inflorescence architecture are similar to the known effects of tb1. Implications of this work for the genetic basis of morphological evolution in plants are discussed.

Biological Evolution↗
PubMed2003

Quantitative trait loci responsible for variation in sexually dimorphic traits in Drosophila melanogaster.

To understand the mechanisms of morphological evolution and species divergence, it is essential to elucidate the genetic basis of variation in natural populations. Sexually dimorphic characters, which evolve rapidly both within and among species, present attractive models for addressing these questions. In this report, we map quantitative trait loci (QTL) responsible for variation in sexually dimorphic traits (abdominal pigmentation and the number of ventral abdominal bristles and sex comb teeth) in a natural population of Drosophila melanogaster. To capture the pattern of genetic variation present in the wild, a panel of recombinant inbred lines was created from two heterozygous flies taken directly from nature. High-resolution mapping was made possible by cytological markers at the average density of one per 2 cM. We have used a new Bayesian algorithm that allows QTL mapping based on all markers simultaneously. With this approach, we were able to detect small-effect QTL that were not evident in single-marker analyses. Our results show that at least for some sexually dimorphic traits, a small number of QTL account for the majority of genetic variation. The three strongest QTL account for >60% of variation in the number of ventral abdominal bristles. Strikingly, a single QTL accounts for almost 60% of variation in female abdominal pigmentation. This QTL maps to the chromosomal region that Robertson et al. have found to affect female abdominal pigmentation in other populations of D. melanogaster. Using quantitative complementation tests, we demonstrate that this QTL is allelic to the bric a brac gene, whose expression has previously been shown to correlate with interspecific differences in pigmentation. Multiple bab alleles that confer distinct phenotypes appear to segregate in natural populations at appreciable frequencies, suggesting that intraspecific and interspecific variation in abdominal pigmentation may share a similar genetic basis.

Animals↗
PubMedDate not supplied

Hypothesis testing in evolutionary developmental biology: a case study from insect wings.

Developmental data have the potential to give novel insights into morphological evolution. Because developmental data are time-consuming to obtain, support for hypotheses often rests on data from only a few distantly related species. Similarities between these distantly related species are parsimoniously inferred to represent ancestral aspects of development. However, with limited taxon sampling, ancestral similarities in developmental patterning can be difficult to distinguish from similarities that result from convergent co-option of developmental networks, which appears to be common in developmental evolution. Using a case study from insect wings, we discuss how these competing explanations for similarity can be evaluated. Two kinds of developmental data have recently been used to support the hypothesis that insect wings evolved by modification of limb branches that were present in ancestral arthropods. This support rests on the assumption that aspects of wing development in Drosophila, including similarities to crustacean epipod patterning, are ancestral for winged insects. Testing this assumption requires comparisons of wing development in Drosophila and other winged insects. Here we review data that bear on this assumption, including new data on the functions of wingless and decapentaplegic during appendage allocation in the red flour beetle Tribolium castaneum.

Animals↗
PubMed1995

Molecular phylogeny and divergence times of drosophilid species.

The phylogenetic relationships and divergence times of 39 drosophilid species were studied by using the coding region of the Adh gene. Four genera--Scaptodrosophila, Zaprionus, Drosophila, and Scaptomyza (from Hawaii)--and three Drosophila subgenera--Drosophila, Engiscaptomyza, and Sophophora--were included. After conducting statistical analyses of the nucleotide sequences of the Adh, Adhr (Adh-related gene), and nuclear rRNA genes and a 905-bp segment of mitochondrial DNA, we used Scaptodrosophila as the outgroup. The phylogenetic tree obtained showed that the first major division of drosophilid species occurs between subgenus Sophophora (genus Drosophila) and the group including subgenera Drosophila and Engiscaptomyza plus the genera Zaprionus and Scaptomyza. Subgenus Sophophora is then divided into D. willistoni and the clade of D. obscura and D. melanogaster species groups. In the other major drosophilid group, Zaprionus first separates from the other species, and then D. immigrans leaves the remaining group of species. This remaining group then splits into the D. repleta group and the Hawaiian drosophilid cluster (Hawaiian Drosophila, Engiscaptomyza, and Scaptomyza). Engiscaptomyza and Scaptomyza are tightly clustered. Each of the D. repleta, D. obscura, and D. melanogaster groups is monophyletic. The splitting of subgenera Drosophila and Sophophora apparently occurred about 40 Mya, whereas the D. repleta group and the Hawaiian drosophilid cluster separated about 32 Mya. By contrast, the splitting of Engiscaptomyza and Scaptomyza occurred only about 11 Mya, suggesting that Scaptomyza experienced a rapid morphological evolution. The D. obscura and D. melanogaster groups apparently diverged about 25 Mya. Many of the D. repleta group species studied here have two functional Adh genes (Adh-1 and Adh-2), and these duplicated genes can be explained by two duplication events.

Animals↗
PubMed1992

Character analysis and the integration of molecular and morphological data in an understanding of sand dollar phylogeny.

Reconciling discordant morphological and molecular phylogenies remains a problem in modern systematics. By examining conflicting DNA-hybridization and morphological phylogenies of sand dollars, I show that morphological criteria may be used to help evaluate the reliability of molecular phylogenies where they differ from morphological trees. All available criteria for assessing the reliability of DNA-hybridization phylogenies suggest that the sand dollar DNA-hybridization phylogeny is robust. Standard homology-recognition criteria are used to assess the a priori reliabilities of the morphological attributes associated with the node drawn into question by the DNA data, and it is shown that these attributes are among the least phylogenetically informative of all the morphological characters. Moreover, the questioned node has the smallest number of supporting characters, and most of these characters are associated with the food grooves, which suggests that they may be functionally correlated. Thus, on the basis of the analysis of the morphological data and given the robustness of the DNA tree, the DNA phylogeny is preferred. Further, paleobiogeographic data support the DNA tree rather than the morphological tree, and a plausible heterochronic mechanism has been proposed that may account for the homoplasious morphological evolution that must have occurred if the DNA tree is correct.

Animals↗
PubMed2001

Nonequilibrium dynamics of the complex Ginzburg-Landau equation: analytical results.

We present a detailed analytical and numerical study of nonequilibrium dynamics for the complex Ginzburg-Landau equation. In particular, we characterize evolution morphologies using spiral defects. This paper is the first in a two-stage exposition. Here, we present analytical results for the correlation function arising from a single-spiral morphology. We also critically examine the utility of the Gaussian auxiliary field ansatz in characterizing a multispiral morphology. In the next paper of this exposition we will present detailed numerical results.

Journal Article↗
PubMed2001

Nonequilibrium dynamics in the complex Ginzburg-Landau equation.

Results from a comprehensive analytical and numerical study of nonequilibrium dynamics in the two-dimensional complex Ginzburg-Landau equation have been presented. In particular, spiral defects have been used to characterize the domain growth law and the evolution morphology. An asymptotic analysis of the single-spiral correlation function shows a sequence of singularities-analogous to those seen for time-dependent Ginzburg-Landau models with O(n) symmetry, where n is even.

Journal Article↗
PubMed2004

Anomalous self-assembly of gelatin in ethanol-water marginal solvent.

Light scattering, rheology, and atomic force microscope (AFM) studies have been performed on solutions of a polyampholyte (gelatin) prepared in water-ethanol marginal solvent. At ethanol concentration approximately 45+/-2% v/v anomalous aggregation led to formation of fractal (on hydrophilic substrates; glass, quartz and silicon) aggregate of polypeptide molecules having fractal dimension d(f) in 2D=1.60+/-0.08. The time evolution morphology of these self-assembled and self-organized structures formed on hydrophilic substrates was driven by selective ethanol evaporation and was observed by an AFM. These fractal aggregates eventually transformed into near-spherical clusters with fractal corona having same fractal dimension (d(f)=1.58+/-0.05) and finally, the corona separated and regular aggregates were formed. The kinetics of aggregation on substrates could be modeled through random sequential adsorption of particles with continuum power-law size distribution. The temporal growth of aggregate hydrodynamic radius R(h)(t) and scattered intensity I(s)(t) measured in the bulk were observed to exhibit; R(h)-t(z) and I(s)-t(z)-with z=1/d(f), giving a fractal dimension d(f) in 3D approximately equal to 2.6+/-0.2, which is discussed within the framework of Smoluchowski aggregation kinetics. This growth in R(h) is accompanied by narrowing down of the particle size distribution. Solution rheology at this ethanol concentration revealed minimum thixotropy and maximum infinite shear viscosity features.

Journal Article↗
PubMed2000

Enhanced instability in thin liquid films by improved compatibility

We investigated experimentally the morphological evolution of thin polydimethylsiloxane films sandwiched between a silicon wafer and different bounding liquids with interfacial tensions varying by 2 orders of magnitude. It is shown that increasing the compatibility between film and bounding liquid by adding a few surfactant molecules results in a faster instability of shorter characteristic wavelength. Inversely, based on the characteristic parameters describing the instability we determined extremely small interfacial tensions with a remarkable accuracy.

Journal Article↗
PubMed2002

Origin of the stability of Ge(105) on si: a new structure model and surface strain relaxation.

The structure of Ge(105)-(1 x 2) grown on Si(105) is examined by scanning tunneling microscopy (STM) and first-principles calculations. The morphology evolution with an increasing amount of Ge deposited documents the existence of a tensile surface strain in Si(105) and its relaxation with increasing coverage of Ge. A detailed analysis of high-resolution STM images and first-principles calculations produce a new stable model for the Ge(105)-(1 x 2) structure formed on the Si(105) surface that includes the existence of surface strain. It corrects the model developed from early observations of the facets of "hut" clusters grown on Si(001).

Journal Article↗
PubMed2002

Competing roughening mechanisms in strained heteroepitaxy: a fast kinetic Monte Carlo study.

We study the morphological evolution of strained heteroepitaxial films using kinetic Monte Carlo simulations in two dimensions. A novel Green's function approach, analogous to boundary integral methods, is used to calculate elastic energies efficiently. We observe island formation at low lattice misfit and high temperature that is consistent with the Asaro-Tiller-Grinfeld instability theory. At high misfit and low temperature, islands or pits form according to the nucleation theory of Tersoff and LeGoues.

Journal Article↗
PubMed2004

Liquid-liquid transition in the molecular liquid triphenyl phosphite.

We found both nucleation-growth-type and spinodal-decomposition-type transformation from one liquid state to another in a "molecular liquid," triphenyl phosphite (TPP). Binodal and spinodal temperatures of this transition at ambient pressure were determined by the characteristics of morphological evolution, domain-growth kinetics, and rheological evolution. Furthermore, a distinct thermal signature of the glass transition of a second liquid was also detected in addition to that of an ordinary liquid. These findings strongly suggest the existence of a liquid-liquid transition; more precisely, a transformation of one supercooled liquid to a glassy state of another liquid, in TPP.

Journal Article↗
PubMed2004

Kinetic roughening of ion-sputtered Pd(001) surface: beyond the Kuramoto-Sivashinsky model.

We investigate the kinetic roughening of Ar+ ion-sputtered Pd(001) surface both experimentally and theoretically. In situ real-time x-ray reflectivity and in situ scanning tunneling microscopy show that nanoscale adatom islands form and grow with increasing sputter time t. Surface roughness W(t) and lateral correlation length xi(t) follow the scaling laws W(t) approximately t(beta) and xi(t) approximately t(1/z) with the exponents beta approximately 0.20 and 1/z approximately 0.20, for an ion beam energy epsilon=0.5 keV, which is inconsistent with the prediction of the Kuramoto-Sivashinsky (KS) model. We thereby extend the KS model by applying the coarse-grained continuum approach of the Sigmund theory to the order of O(inverted Delta(4),h(2)), where h is the surface height, and derive a new term of the form inverted Delta(2)(inverted Delta h)(2) which plays a decisive role in describing the observed morphological evolution of the sputtered surface.

Journal Article↗
PubMed2001

A new look at microbial leaching patterns on sulfide minerals.

Leaching patterns on sulfide minerals were investigated by high-resolution scanning electron microscopy (SEM). Our goal was to evaluate the relative contributions of inorganic surface reactions and reactions localized by attached cells to surface morphology evolution. Experiments utilized pyrite (FeS(2)), marcasite (FeS(2)) and arsenopyrite (FeAsS), and two iron-oxidizing prokaryotes in order to determine the importance of cell type, crystal structure, and mineral dissolution rate in microbially induced pit formation. Pyrite surfaces were reacted with the iron-oxidizing bacterium Acidithiobacillus ferrooxidans (at 25 degrees C), the iron-oxidizing archaeon 'Ferroplasma acidarmanus' (at 37 degrees C), and abiotically in the presence of Fe(3+) ions. In all three experiments, discrete bacillus-sized (1-2 µm) and -shaped (elliptical) pits developed on pyrite surfaces within 1 week of reaction. Results show that attaching cells are not necessary for pit formation on pyrite. Marcasite and arsenopyrite surfaces were reacted with A. ferrooxidans (at 25 degrees C) and 'F. acidarmanus' (at 37 degrees C). Cell-sized and cell-shaped dissolution pits were not observed on marcasite or arsenopyrite at any point during reaction with A. ferrooxidans, or on marcasite surfaces reacted with 'F. acidarmanus'. However, individual 'F. acidarmanus' cells were found within individual shallow (<0.5 µm deep) pits. The size and shape (round rather than elliptical) of the pits conformed closely to the shape of F. acidarmanus (cells) pits on arsenopyrite. We infer these pits to be cell-induced. We attribute the formation of pits readily detectable (by SEM) to the higher reactivity of arsenopyrite compared to pyrite and marcasite under the conditions the experiment was conducted. These pits contributed little to the overall surface topographical evolution, and most likely did not significantly increase surface area during reaction. Our results suggest that overall sulfide mineral dissolution may be dominated by surface reactions with Fe(3+) rather than by reactions at the cell-mineral interface.

Journal Article↗
PubMed1986

Histopathologic and immunopathologic study of pyoderma gangrenosum.

Sixty-three patients with pyoderma gangrenosum were seen and studied at the Mayo Clinic from 1971 to 1980. Biopsies from the erythematous border or necrotic edge of the pyoderma gangrenosum lesions usually demonstrated a characteristic pathogenic morphologic evolution. The early lesions revealed mild to moderate perivascular lymphocytic infiltrate associated with endothelial swelling. The fully developed lesions demonstrated necrosis in addition to a dense lymphocytic infiltration surrounding as well as involving the blood vessels. Extravasation of erythrocytes and thrombosis sometimes were seen. Ulceration, infarction, and abscess formation were found in the later stages of evolution. Direct immunofluorescence results were positive in the blood vessels of 36 of 65 (55%) specimens. IgM, C3, and fibrin were found in the papillary and reticular dermal vessels. IgG and IgA were only occasionally present. Pyoderma gangrenosum appears to be a reactive process that is manifested as a vasculitis. Biopsy material from the advancing active erythematous border has early characteristic dermatopathologic findings of lymphocytic vasculitis. Cutaneous vascular immune deposits suggest an immune pathogenesis of either an immune complex disease or lymphocytotoxic reaction.

Biopsy↗
PubMed1996

Extra-acral calcifying aponeurotic fibroma: a distinctive case with 23-year follow-up.

Calcifying aponeurotic fibroma (CAF) is an unusual but well-characterized soft tissue neoplasm that typically involves the digits of children and frequently recurs locally. This report describes a case from the subcutis of the lumbosacral region. A 26-year-old man initially presented at age 3 and developed three recurrences over a 23-year period each at approximately 8-year intervals (ages 10, 18, and 26). The microscopic findings in all recurrences showed a lobulated, poorly circumscribed proliferation of dense fibrous tissue containing epithelioid-like fibroblasts, multinucleated cells, and islands of metaplastic chondroid differentiation with focal calcification. Despite origin from an unusual anatomic site, this case reported herein demonstrates the classical morphologic features and clinical history of CAF which showed little in the way of morphologic evolution despite 23 years of persistence. The clinical and histologic features helpful in distinguishing CAF from infantile fibromatosis and soft tissue chondroma are discussed.

Adult↗