Biomedical subjects

JA Shykoff

Publications and source records attributed to JA Shykoff.

4 recordsLinked to original sources

PubMed2000

Is There a Genetic Basis for Fluctuating Asymmetry and Does it Predict Fitness in the Plant Lotus corniculatus Grown in Different Environmental Conditions?

Fluctuating asymmetry (FA) is considered to be a good measure of developmental stability. We measured the asymmetry of leaves and flowers of 16 different genotypes of Lotus corniculatus grown in four different experimental environments to estimate the plasticity or developmental stability of asymmetry itself. We found that an index of FA (absolute difference between size of left and right sides, corrected for trait size) differed significantly across environments, with the treatment CO2+/N+ inducing the greatest FA for both flowers and leaves. Genotypes did not differ in FAs. Individual plants showed significantly different FAs only for flowers. At the individual level, we found no significant relationship between flower FA and fitness. Previous work indicates that change in asymmetry in a poor or perturbing environment versus a good environment could reflect the intrinsic quality of a particular genotype. However, in our experiment, genotype effect was significant only for change in asymmetry of leaves, and this last trait was not significantly correlated with our fitness estimate for each genotype in either the most or the least perturbing environment.

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PubMed1999

Host and parasite population structure in a natural plant-pathogen system

We investigated the genetic population structure in a metapopulation of the plant Silene latifolia (Caryophyllaceae) and its fungal pathogen Microbotryum violaceum (Ustilaginales), a pollinator-borne disease. Population structure of the host plant was estimated using allozyme markers and that of the fungus by microsatellites. Both host and parasite showed significant differentiation, but parasite populations were 12 times more strongly differentiated than those of the hosts. We found significant isolation by distance for host populations but not for parasite populations. Higher population differentiation for the parasite may result from small effective population size, high selfing rates, or low migration rate. In this system, hosts are obligate outcrossers and they migrate by seeds and pollen, whereas parasites can self-fertilize and migrate only on pollinating insects. We discuss the effect of limited gene flow in this parasite on its coevolutionary interaction with its host, and its potential for local adaptation on sympatric host populations.

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PubMed1999

Genetic Isolation among Host Races of the Anther Smut Fungus Microbotryum violaceum on Three Host Plant Species.

Genetic isolation among strains of the plant pathogenic fungus Microbotryum violaceum on three species of its host plants was examined. Fungal strains collected from a sympatric population of all three host plant species were examined for their ability to infect the other host plant species and to cross-conjugate among each other. Genetic isolation was investigated from the distribution of neutral microsatellite alleles. Since this is a pollinator-transmitted disease, we examined movement patterns and flower-visitation behavior of pollinators to investigate whether they transfer fungal spores between different host species. Low infection success from the cross-inoculation experiment limits interpretability of the results, but fungus collected from Silene vulgaris was capable of infecting Dianthus carthusianorum. Different fungal strains were able to conjugate and form the infectious dikaryon in most combinations, so hybridization between different fungal host races is possible. The distribution of neutral genetic variation, however, revealed little successful genetic exchange among the fungal host races that were clearly differentiated by host plant species. Pollinators, while showing partial constancy, moved between plants of different host species. Pollinator behavior is therefore not adequate to explain the lack of gene flow among the different fungal races. This indicates that the divergence among these fungal races that has produced incipient species sharing almost no alleles may have occurred in allopatry, unless disruptive selection can outweigh gene flow among fungal races in sympatry.

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PubMed1999

Morphological Developmental Stability in Plants: Patterns and Causes.

Minor bilateral or radial asymmetry of leaves or flowers, the frequency of phenodeviants, intraindividual variation in repeated characters, and fractal dimensions of morphology are considered to represent measures of developmental instability since deviations from regularity of the phenotype constitute a measure of the inability to maintain developmental precision during ontogeny. First, we review patterns of fluctuating asymmetry in plants and show that levels of asymmetry are considerably greater than in animals. While petal asymmetry tends to decrease with petal size within species, leaf asymmetry tends to increase with leaf size. Intraspecific correlations of petal asymmetry and leaf asymmetry are weakly positive. Second, a meta-analysis of the effects of environmental factors hypothesized to increase asymmetry in leaves and flowers, such as radiation, ultraviolet light, excess artificial fertilizer, pollutants, extreme saline conditions, herbivory, and competition, showed intermediate (i.e., explaining 10% of the variance) to large (i.e., explaining 25% of the variance) effects. Third, a meta-analysis of the effects of genetic factors hypothesized to contribute to increased asymmetry in plants, such as homozygosity, hybridization, mutation, and quantitative genetic differences among individuals, showed variable but usually significant effects, although the number of studies generally was small. Controlled experimental studies of environmental and genetic effects on developmental instability of plants may increase our understanding of the mechanisms causing developmental instability.

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