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D A Levin

Publications and source records attributed to D A Levin.

17 recordsLinked to original sources
PubMed2003

Rapid response to artificial selection on flower size in Phlox.

Quantitative characters are often said to evolve rather slowly, taking many generations to exhibit appreciable differences among populations. We tested this notion experimentally by performing bi-directional selection on corolla diameter of plants from a wild population of Phlox drummondii for three generations. By monitoring flower size, tube length and stigma-anther proximity of flowers, we obtained the direct and indirect responses to selection, and calculated genetic correlations, realized and narrow sense heritabilities using offspring-mother regression. Realized heritability of flower size was high (0.83), whereas genetic correlations among traits were weak or not significant. The per-generation average of the response in corolla diameter was about 5%. We found that P. drummondii has a great capacity to respond rapidly to selection, and this capacity may be in part responsible for the observed high degree of differentiation within the species. We also concluded that rapid evolution of morphological floral traits is possible.

Analysis of Variance↗
PubMed2000

Directional selection on initial flowering date in Phlox drummondii (Polemoniaceae).

The fitness effects due to initial flowering date in Phlox drummondii were determined for three populations in central Texas (USA) over 3 yr (1990-1992). Mean fitness (seed set) always decreased with the later initiation of flowering. The likelihood of a plant fruiting differed with flowering date in five of the six instances (population by year combinations). Though plants that initiated flowering later tended to have spent more time in the vegetative stage and tended to die later in the year than did earlier flowering plants, this was not sufficient to overcome the reproductive penalties of flowering late. Plants that initiated flowering later in the season spent less time in the adult phase and were smaller. The mean number of flowers, fruits, and seeds per flowering plant always decreased with later flowering. Fruit set was negatively correlated with flowering date in four of the six population by year combinations. Nonparametric fitness functions were used to summarize predicted fitness among different initial flowering dates for each population on a yearly basis. Predicted mean fitness always declined nonlinearly with later flowering; the earliest flowering plants always had the highest predicted fitness. These fitness functions describe directional selection for the early initiation of flowering.

Journal Article↗
PubMed2000

Beta-adrenergic receptor blockade by propranolol enhances retention in a multitrial passive-avoidance procedure.

The effect of beta-adrenergic receptor blockade on retention in a mildly aversive passive-avoidance procedure was investigated. Rats were given passive-avoidance training--1 trial per day for 4 days-and were administered saline, the centrally and peripherally acting beta-adrenergic blocker propranolol (4 or 10 mg/kg ip), or the peripherally acting beta-adrenergic blocker sotalol (4 or 10 mg/kg ip) immediately or 2 hr after the 1st trial. Enhanced retention occurred only with the higher dose (10 mg/kg) of propranolol and only when it was administered immediately after training. The enhanced retention produced by propranolol is discussed in terms of opposing, regionally specific actions of beta-adrenergic receptor-mediated neural circuits on modulation of memory.

Adrenergic beta-Antagonists↗
PubMed1979

Alcohol dehydrogenase activity in diploid and autotetraploid Phlox.

The effect of polyploidy on the activity of alcohol dehydrogenase was examined in a series of diploid and synthetic autotetraploid Phlox drummondii. In most cases autotetraploids had about twice as much activity as the corresponding diploids, in two cases autotetraploids had about 1.5 times more activity, and in one wild seed pair the activity of the tetraploid was somewhat lower.

Alcohol Oxidoreductases↗
PubMed1976

Rates of evolution in seed plants: Net increase in diversity of chromosome numbers and species numbers through time.

An approach was made to the problem of estimating rates of chromosomal evolution in plants. This was done by considering variability in chromosome number within genera whose ages are known approximately from fossil and biogeographic evidence. The relative increases in chromosome number diversity per lineage per unit time were as follows: herbaceous angiosperms, 100; woody angiosperms, 14; conifers, 2; and cycads, 0. Rates of increase in species diversity were estimated in an analogous way. These rates were strongly correlated with the karyotypic rates.These evolutionary rate differences between major groups of seed plants are largely explicable in terms of the breeding structures of populations. Herbs usually have small to moderate effective population sizes, and relatively high dispersability. By contrast, woody angiosperms and gymnosperms are usually obligate outbreeders with large effective population sizes and low dispersability. Thus the probability of fixing and dispersing new karyotypes or novel character ensembles is higher in herbs than in other seed plants.

Journal Article↗
PubMed1975

Allozyme genetics in permanent translocation heterozygotes of the Oenothera biennis complex.

Allozyme inheritance and transmission genetics of 11 enzyme systems were determined in the permanent translocation heterozygotes Oenothera biennis, Oe. strigosa, and Oe. parviflora. Electrophoretic variation was examined first among 164 strains of structural heterozygotes. Allelic configurations were then judged from inheritance patterns in reciprocal F1 hybrids between each of 22 ring-forming strains and tester strains of the related bivalent-formers, Oe. hookeri and Oe. grandiflora. Allozymes are inherited as codominant markers, and, as dictated by the genetic system, within a strain individual allelic variants are generally transmitted through only one germ line. Of the 20 loci resolved, only eight are polymorphic in any species, and, within species, generally only two alleles are present at each polymorphic locus. Despite the relatively meager allelic array, each of the 22 strains whose chromosome complexes were characterized is genotypically unique. Generally, within taxa, alpha (egg) and beta (sperm) complexes differ in allele frequency at several polymorphic loci. Such variability is correlated with differences in the phylogenetic origins of complexes and not with differences in segmental arrangement within a group of related complexes.

Alleles↗
PubMed1975

Species richness of the parasitic fungi of british trees.

The species richness of fungi associated with British trees is described by a significant species/area curve (r = 0.53, 0.01 > P > 0.001). Introduced tree species cannot be shown to have fewer fungal species than natives, per unit distributional range about Britain. Also, among natives and among introductions, older host taxa do not have more fungal species than do younger ones. This indicates the species richness of fungi to rapidly reach the limit set by host range, within ecological time. The slope of the species/area relationship for fungi is one-fourth that for insects; we propose that this is due to the inherently greater dispersability of fungi. Finally, the species/area regression residuals for fungi are correlated with those for insects (r = 0.65, 0.001 > P), suggesting plant defense mechanisms may be generally effective to plant parasites, be they insects or fungi.

Journal Article↗
PubMed1973

Polymorphism for interspecific cross-compatibility in phlox.

Extensive polymorphism for the cross-compatibility of Phlox pilosa with P. glaberrima occurs within Illinois populations. The polymorphism is genetically determined. Thus, there is an opportunity for selection to enhance existing cross-compatibility barriers in areas of species contact. There is no evidence that selection has favored the reinforcement of such barriers.

Journal Article↗
PubMed1972

Protein polymorphism and genic heterozygosity in a population of the permanent translocation heterozygote, Oenothera biennis.

Genic allozyme polymorphism and heterozygosity was studied in a large population of the evening primrose, Oenothera biennis, growing in North Haven, Connecticut. This species is a permanent structural heterozygote for the entire complement of 14 chromosomes, and is thus capable of accumulating and maintaining genic heterozygosity. A total of 11 protein species were examined, and these were judged to be controlled by 19 loci. Polymorphism occurs at 26% of the loci, with only two alleles being present at each locus. The proportion of polymorphic loci per population in organisms with normal meiotic systems is no less than in Oe. biennis, indicating that structural heterozygosity is not necessarily accompanied by a greater proportion of polymorphic loci. On the other hand, the average Oe. biennis was heterozygous at 26% of its loci, an amount considerably greater than in most other organisms. With few exceptions, all plants in the North Haven population had the same genotype. Since the species is a colonizer, it is likely that the population was founded by a single individual and retained this genotype by virtue of the genetic system.

Alleles↗
PubMed1971

The origin of novel flavonoids in Phlox allotetraploids.

The flavonoids of two diploid species of Phlox and two of their allotetraploid derivatives were characterized. The tetraploids accumulate five flavonoids not observed in the parental species. Generally, novel compounds are less highly glycosidated than, but otherwise similar to, parental compounds that they partially or totally replace. We propose that hybridity and polyploidy have repressed or suppressed the activity of certain ancestral genes responsible for the production of glycosidating enzymes. Accordingly, the novel compounds are merely the accumulated or modified precursors of parental compounds.

Chromatography, Paper↗
PubMed1970

Temporal phenotypic heterogeneity as a substrate for selection.

The interaction of temporal phenotypic heterogeneity with a population level fitness function was explored through the use of a simple model. The model, based upon experimental data, assumes that the exploitation of pollinators, and seed-set within plant populations are dependent upon the frequency of a pink flower morph in populations composed of pink and white morphs. An increase in pink frequency is accompanied by an increase in seed-set for both morphs. The model also assumes that seed-set within a population is the same for pink and white individuals. In perennials and annuals with long-lived seeds, fluctuations in morph balance from one season to another may lead to reproductive pulses or drags, depending upon which morph was in excess. The reproductive differential which stems from different levels of pollinator service leads to an increase in pink frequency and an attendant fitness gain. The perennial habit and long-lived seeds provide a population with a memory which permits the current population image to compete with images of previous years. As a consequence, fitness gains may be achieved in the absence of interplant or interpopulation selection.

Journal Article↗
PubMed1970

Chloroplast aldolase is controlled by a nuclear gene.

Variant chloroplast fructose 1,6-diphosphate aldolases were found in Pisum sativum when 10 commercial varieties were examined for electrophoretically distinct species of chloroplast triose phosphate isomerase, phosphoglyceric acid kinase, glyceraldehyde 3-phosphate dehydrogenase, and aldolase. When reciprocal crosses are made, both aldolases appear in individuals in the F(1) generation. Backcrossing gives offspring having aldolases characteristic of the homozygous or of the heterozygous parent; the inheritance is therefore not maternal but Mendelian. Clearly this chloroplast reductive pentose phosphate cycle enzyme is under nuclear gene control in P. sativum.

Cell Nucleus↗
PubMed1968

Multiple chromosome triplication in Liatris.

A plant with four and one with six extra A chromosomes were discovered in a hybrid swarm involving Liatris aspera and Liatris spicata. In each plant, the extra chromosomes formed trivalents with chromosomes of the normal complement. This pairing behavior indicates that of the ten chromosomes in the complement the plants are triplicate for four and six chromosomes, respectively.

Aneuploidy↗
PubMedDate not supplied

Profound hypothermia with alpha-stat pH management during open-heart surgery is associated with choreoathetosis.

A retrospective chart review was conducted to examine risk factors associated with the occurrence of choreoathetosis, a rare but significant complication of open-heart surgery in children. Ten children were identified as having developed choreoathetosis after cardiac surgery. Their charts were reviewed and compared with 33 age- and diagnosis-matched controls who underwent open-heart surgery during the same time period. Children with choreoathetosis reached lower rectal and esophageal temperatures (p = 0.0018 for both) and spent a greater portion of total bypass time at lower rectal and esophageal temperatures (p < 0.001 for both). Duration of cooling below 20 degrees C esophageal temperature and PaCO2 at the end of the cooling period were significant predictors of choreoathetosis (p = 0.023 and p = 0.0497, respectively) in a logistic regression model, and a greater fraction of choreoathetosis patients had prior developmental delays (p = 0.017). No difference was found in the age at surgery, duration of bypass, aortic cross-clamp time, arterial pH, PaCO2 or mean arterial pressure. The combination of extended exposure to profound hypothermia and alpha-stat pH management strategy and preexisting developmental delay are associated with the development of choreoathetosis following open-heart surgery 61 in children.

Acid-Base Equilibrium↗