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Biomedical subjects

R Lande

Publications and source records attributed to R Lande.

52 records · Page 3Linked to original sources
PubMed1988

Genetics and demography in biological conservation.

Predicting the extinction of single populations or species requires ecological and evolutionary information. Primary demographic factors affecting population dynamics include social structure, life history variation caused by environmental fluctuation, dispersal in spatially heterogeneous environments, and local extinction and colonization. In small populations, inbreeding can greatly reduce the average individual fitness, and loss of genetic variability from random genetic drift can diminish future adaptability to a changing environment. Theory and empirical examples suggest that demography is usually of more immediate importance than population genetics in determining the minimum viable sizes of wild populations. The practical need in biological conservation for understanding the interaction of demographic and genetic factors in extinction may provide a focus for fundamental advances at the interface of ecology and evolution.

Animals↗
PubMed1988

Ecological speciation by sexual selection.

Quantitative genetic models are used to investigate a mechanism of speciation involving natural and sexual selection on a population with more than one ecological niche available. Female choice of mates, based on ecologically important characters, can initiate a sudden shift into a new niche. Whether males alone or both sexes make the transition depends strongly on the genetic correlation between homologous male and female characters. This mode of speciation rapidly produces premating and postmating isolating barriers, as well as ecological separation, between populations that can then coexist in the same area as distinct species.

Ecology↗
PubMed1988

Extinction dynamics of age-structured populations in a fluctuating environment.

We model density-independent growth of an age- (or stage-) structured population, assuming that mortality and reproductive rates fluctuate as stationary time series. Analytical formulas are derived for the distribution of time to extinction and the cumulative probability of extinction before a certain time, which are determined by the initial age distribution, and by the infinitesimal mean and variance, mu and sigma 2, of a diffusion approximation for the logarithm of total population size. These parameters can be estimated from the average life history and the pattern of environmental fluctuations in the vital rates. We also show that the distribution of time to extinction (conditional on the event) depends on the magnitude but not the sign of mu. When the environmental fluctuations in vital rates are small or moderate, the diffusion approximation gives accurate estimates of cumulative extinction probabilities obtained from computer simulations.

Aging↗
PubMed1986

Pararosaniline or acriflavine-Schiff staining of epoxy embedded tissue after periodic acid oxidation in ethanol: a method suitable for morphometric and fluorometric analysis of glycogen.

A method for preparing tissue sections for automatic image analysis of glycogen is described. Large semithin sections of epoxy embedded tissue fixed in glutaraldehyde-osmium were stained with Schiff reagent and acriflavine (fluorescent staining) after resin removal and periodic acid oxidation in ethanol. We found it essential to avoid tissue rehydration before final staining. The Schiff stain permits an assessment of the cellular volume of glycogen, and the acriflavine allows a fluorometric evaluation of glycogen density.

Acriflavine↗
PubMed1985

Evolution of mating preference and sexual dimorphism.

A quantitative genetic model of the joint evolution of female mating preferences and sexual dimorphism in homologous characters of the sexes is described for polygamous species with no male parental effort, such that mating preferences are selectively neutral and evolve only by indirect selection on genetically correlated characters. The male character and the homologous female character are each under stabilizing natural selection toward an optimum phenotype. At an evolutionary equilibrium the female character under natural selection is at its optimum, whereas there is a line of possible equilibria between female mating preferences and the male character. The line of equilibria may be stable or unstable, depending on the intensity of natural selection, the type of mating preferences, and the inheritance of the characters. Various mechanisms for maladaptive evolution of mating preferences and sexual dimorphism are discussed.

Animals↗
PubMed1985

The fixation of chromosomal rearrangements in a subdivided population with local extinction and colonization.

The fixation of major chromosomal rearrangements with a heterozygote disadvantage is modelled as a simple example of Wright's shifting balance process of evolution in a strongly subdivided population. Chromosomal mutations with an inferior heterozygote become fixed in a local population (or deme) by random genetic drift and spread by migration and colonization. Wright postulated a process of selective diffusion in which the numbers of emigrants and colonizers dispersed from a deme increase with the mean fitness of individuals in it. The present models show that interdeme selection during the spread of a mutation depends more on the capacity of the mutant to invade and become established in other demes than on selective diffusion, unless there is rapid local extinction and colonization. The intensity of interdeme selection is reduced by random local extinction and colonization, and when these processes are rapid (with no selective diffusion) the expected fixation rate of spontaneous mutations with a heterozygote disadvantage approaches that in a single isolated deme. Local extinction and colonization, and selection on the homozygotes, accelerate the spread of chromosomal mutations which are destined to be fixed.

Animals↗
PubMed1985

Expected time for random genetic drift of a population between stable phenotypic states.

Natural selection and random genetic drift are modeled by using diffusion equations for the mean phenotype of a quantitative (polygenic) character in a finite population with two available adaptive zones or ecological niches. When there is appreciable selection, the population is likely to spend a very long time drifting around the peak in its original adaptive zone. With the mean phenotype initially anywhere near the local optimum, the expected time until a shift between phenotypic adaptive peaks increases approximately exponentially with the effective population size. In comparison, the expected duration of intermediate forms in the actual transition between adaptive peaks is extremely short, generally below the level of resolution in the fossil record, and increases approximately logarithmically with the effective population size. The evolutionary dynamics of this model conform to the pattern of current paleontological concepts of morphological "stasis" and "punctuated equilibria."

Biological Evolution↗
PubMed1984

Inheritance of a secondary sexual character in Drosophila silvestris.

Reciprocal crosses were carried out between laboratory stock specimens obtained from two races of Drosophila silvestris from the island of Hawaii that differ in a quantitative secondary sexual character. The race from the Hilo side of the island has a novel attribute, consisting of an extra row of cilia on the tibia of males, which is used during courtship. With regard to this character, sex-linked genes contribute about 30% of the difference, and the remaining 70% of the difference between the races is produced by genes on at least two autosomes. The novel character appears to have been the outcome of altered sexual selection in the Hilo-side race. In an altered genetic environment, resulting from a founder event or random genetic drift, sexual selection may take a new direction. Such a shift may serve as a model for incipient speciation.

Animals↗
PubMed1981

Models of speciation by sexual selection on polygenic traits.

The joint evolution of female mating preferences and secondary sexual characters of males is modeled for polygamous species in which males provide only genetic material to the next generation and females have many potential mates to choose among. Despite stabilizing natural selection on males, various types of mating preferences may create a runaway process in which the outcome of phenotypic evolution depends critically on the genetic variation parameters and initial conditions of a population. Even in the absence of genetic instability, rapid evolution can result from an interaction of natural and sexual selection with random genetic drift along lines of equilibria. The models elucidate genetic mechanisms that can initiate or contribute to rapid speciation by sexual isolation and divergence of secondary sexual characters.

Journal Article↗
PubMed1977

The influence of the mating system on the maintenance of genetic variability in polygenic characters.

The traditional models of the effect of assortative mating and inbreeding on the genetic variance of polygenic characters (FISHER 1918; WRIGHT 1921) presume that there is no natural selection or mutation. In a large population, the genetic variance determined by additive genes may then increase by up to a factor of two with local inbreeding, and even more with assortative mating. The classical models are still used to interpret data from natural populations. But contrary to their assumptions, most metrical characters in natural populations are usually thought to be under a type of selection which depletes polygenic variation. Mutation is then necessary to maintain genetic variation. The present models show that with the additional features of mutation and selection, in a large population, the mating system has no influence on the amount of genetic variability maintained by additive genes.

Animals↗
PubMedDate not supplied

The minimum number of genes contributing to quantitative variation between and within populations.

A procedure is outlined for estimating the minimum number of freely segregating genetic factors, nE, contributing to the difference in a quantitative character between two populations that have diverged by artificial or natural selection. If certain simple criteria are satisfied approximately on an appropriate scale of measurement, nE can be estimated by comparing the phenotypic means and variances in the two parental populations and in their F1 and F2 hybrids (and backcrosses). This generalizes the method of Wright to genetically heterogeneous (or wild) parental populations, as well as inbred lines. Standard errors of the estimates are derived for large samples. The minimum number of genes involved in producing a large difference between populations in a quantitative trait is typically estimated to be about 5 or 10, with occasional values up to 20. This strongly supports the neo-Darwinian theory that large evolutionary changes usually occur by the accumulation of multiple genetic factors with relatively small effects.

Alleles↗
PubMedDate not supplied

60-kDa heat shock protein of Chlamydia pneumoniae is a target of T-cell immune response.

Inflammatory processes contribute to the pathogenesis and complications of atherosclerosis and coronary heart disease (CHD). Several findings indicate that chlamydial heat shock proteins (HSP) may represent a particularly strong antigenic stimulus, able to induce specific humoral (Ab) and T-cell-mediated immune responses (CMI) linking infection by Chlamydia pneumoniae (CP) to immuno-pathological sequelae such as atherosclerosis and CHD. We have here evaluated the ability of chlamydial recombinant (r) HSP60 and rHSP10 to induce specific immune responses in human peripheral blood lymphocytes and in murine models. rHSP60, but not rHSP10, was shown to induce proliferation and Interferon-gamma secretion in lymphocytes of randomly selected blood donors, as well as to generate and detect delayed-type hypersensitivity response in HSP60-vaccinated mice. Overall, the present study provides new hints to evaluate a previous exposition to CP using rHSP60 in humans. Thus the evaluation of specific HSP60 CMI response in healthy subject could be useful to monitor the reactivity to Chlamydia pneumoniae possibly providing a link to CHD pathologies.

Animals↗
PubMedDate not supplied

Decreased DTH response to recall antigens in mice injected with human immunodeficiency virus type 1-infected U937 cells and infected with Candida albicans.

In previous studies, we have reported that the intraperitoneal (i.p.) injection of HIV-1 infected human U937 cells into normal mice resulted in long-term persistence of anti-HIV antibodies and in a small percentage (10-20%) of HIV-1 infected animals at 6-12 months after the injection. The study reported here was undertaken to detect T immune defects in U937-HIV-1-injected mice. Eight months after the initial injection, a marked decrease in DTH response against U937 cells was detected in HIV injected animals. In addition, a consistent decrease in DTH response against a soluble mannoprotein antigen of Candida albicans cell wall (MP-F2) was also observed in U937-HIV-1-injected mice, chronically infected with low-virulent strain of the fungus. No decreases in DTH response was observed in control-injected animals. These data indicate that U937-HIV-1-injected mice become unable to mount a normal antigen-specific immune response. Although the mechanisms involved in the generation of these T cell defects remain unclear, these events appear to be somehow related to the HIV-1 infection and should be considered in the current studies of HIV-1 infection with transgenic mice.

Animals↗