The use of canonical analysis for selection within a population of spring barley

A selection method is described involving the application of canonical analysis to data for a number of measured traits in a composite population of spring barley grown in two seasons. Lines were selected which fell within the Euclidean space defined by the range, for a number of standard cultivars, on each significant canonical variate. Alternatively, limits were fixed for an acceptable range for each trait and transformed to canonical variates. Lines were selected which fell nearest to the centroid of this acceptable space. The method might be used as an alternative to the selection index method where difficulty is often encountered in assigning appropriate economic weightings to the traits measured.     

The realized effect of postpollination sexual selection in a natural plant population

The ultimate importance of postpollination sexual selection has remained elusive, largely because of the difficulty of assigning paternity in the field. Here I use a powerful new molecular marker (AFLP) for paternity analysis in a natural population of the outcrossing angiosperm Persoonia mollis (Proteaceae) to assess male reproductive success following equal pollination of 15 pollen donors on each of 6310 pistils. These results were contrasted with male reproductive success of these same plants following natural mating. Following equal pollination, there was a significant departure from equal siring success, indicating a potential for postpollination sexual selection. The most successful pollen donor sired more than twice the expected number of seeds, and this was largely consistent across recipient plants. However, siring success following natural mating was significantly different from siring success following artificial pollination and showed that the reproductive gains to be made from superior pollen performance did not translate into increased reproductive success following natural mating. As the ecological context for post-pollination sexual selection is strong in P. mollis, I suggest that pollen competition may ultimately have only a weak effect on non-random male mating success under natural conditions because the realized opportunities for pollen competition within pistils are limited.     

Clinal variation and selection on MDH allozymes in honeybees in Chile

Evidence of clinal variation and selection on Mdh-1 locus was observed in 27 samples from 22 sites in a 2800 km north-south transect across Chile. We found a negative correlation among F allele normalized frequency and mean temperature, and minimum temperature of January and July, as well as a positive correlation among S allele normalized frequency and annual mean, and minimum January temperatures. Our results lend weight to the idea that Chilean honeybee populations of colder areas have higher F allele frequencies, supporting previous claims that Mdh-1 allozymes of Apis mellifera are subject to temperature-mediated selection.     

Genetic changes in a barley population analyzed in terms of some life cycle components of selection

A bulk-hybrid population of barley (CC-XXI) was investigated for changes over a period of six generations, in (1) generation means and variances for three quantitative characters (2) phenotypic and genotypic frequencies at several marker loci and (3) the components of selection at several life cycle stages (germination and seedling survival, fertility, fecundity) for the dominant-recessive phenotypic classes at three of the above loci. The changes in mean and variance for the quantitative characters appeared to be due to both directional and stabilizing types of selection. The estimates of selective values from frequency data suggested heterozygote advantage along with unequal homozygote fitnesses at locuss and heterozygote disadvantage at locibl, r andv, from computations based on higher outcrossing rates in the presence of male-steriles.Of the components studied, fertility and fecundity appeared to account for a larger portion of the total selective differential than the pre-adult stages (germination and seedling establishment). Net selective values based on component analysis approximated the selective values obtained from the frequency data for locusr. For locis, andv, however, the two estimates were often quite different, although they generally agreed in direction. The discrepancies between the two sets of estimates were discussed in terms of the complexity of overall measures of fitness.     

The effect of selection on genetic balance when the population size is varying

It is known that a reformulation for variable population size of the classical Sewall Wright model for balance between two genotypes can lead, under some circumstances, to a situation of balanced polymorphism when there is no selection present. In this note it is shown that the presence of selection prohibits the possibility of balance and assures ultimate homozygosity with probability one.     

Analysis of complex allozyme polymorphisms in a barley population

Genotypes of 68,230 individuals taken from 10 generations (F₄–F₆, F₁₄–F₁₇, F₂₄–F₂₆) of an experimental population of barley were determined for four esterase loci. The results show that frequencies of gametic ditypes changed significantly over generations and that striking gametic phase disequilibrium developed within a few generations for each of the six pairwise combinations of loci which were monitored. The complex behavior of these four enzyme loci in the population is attributed to interactions between selection and restriction of recombination resulting from the effects of linkage and/or inbreeding.     

The effect of directed and stabilizing selection on the population size of Drosophila melanogaster

Population size as a measure of population fitness was assayed in laboratory lines of Drosophila melanogaster subjected to directional selection for positive photoactivity and stabilizing selection for a complex of metric wing characters. Three experimental designs were used: directional and stabilizing selection (DS); directional selection (D); unselected controls (C). Population size increased under all three experimental designs. The population size of DS and C lines as well as the rate of increase of the DS lines were higher as compared to the D lines. The results suggest that stabilizing selection maintains population fitness at the higher level.     

Phenotypic assortment mediates the effect of social selection in a wild beetle population

Social interactions often have major fitness consequences, but little is known about how specific interacting phenotypes affect the strength of natural selection. Social influences on the evolutionary process can be assessed using a multilevel selection approach that partitions the effects of social partner phenotypes on fitness (referred to as social or group selection) from those of the traits of a focal individual (nonsocial or individual selection). To quantify the contribution of social selection to total selection affecting a trait, the patterns of phenotypic association among interactants must also be considered. We estimated selection gradients on male body size in a wild population of forked fungus beetles (Bolitotherus cornutus). We detected positive nonsocial selection and negative social selection on body size operating through differences in copulation success, indicating that large males with small social partners had highest fitness. In addition, we found that, in low-density demes, the phenotypes of focal individuals were negatively correlated with those of their social partners. This pattern reversed the negative effect of group selection on body size and led to stronger positive selection for body size. Our results demonstrate multilevel selection in nature and stress the importance of considering social selection whenever conspecific interactions occur nonrandomly.     

Genetic variation in the acorn barnacle from allozymes to population genomics

Understanding the patterns of genetic variation within and among populations is a central problem in population and evolutionary genetics. We examine this question in the acorn barnacle, Semibalanus balanoides, in which the allozyme loci Mpi and Gpi have been implicated in balancing selection due to varying selective pressures at different spatial scales. We review the patterns of genetic variation at the Mpi locus, compare this to levels of population differentiation at mtDNA and microsatellites, and place these data in the context of genome-wide variation from high-throughput sequencing of population samples spanning the North Atlantic. Despite considerable geographic variation in the patterns of selection at the Mpi allozyme, this locus shows rather low levels of population differentiation at ecological and trans-oceanic scales (F(ST)?～?5%). Pooled population sequencing was performed on samples from Rhode Island (RI), Maine (ME), and Southwold, England (UK). Analysis of more than 650 million reads identified approximately 335,000 high-quality SNPs in 19 million base pairs of the S. balanoides genome. Much variation is shared across the Atlantic, but there are significant examples of strong population differentiation among samples from RI, ME, and UK. An F(ST) outlier screen of more than 22,000 contigs provided a genome-wide context for interpretation of earlier studies on allozymes, mtDNA, and microsatellites. F(ST) values for allozymes, mtDNA and microsatellites are close to the genome-wide average for random SNPs, with the exception of the trans-Atlantic F(ST) for mtDNA. The majority of F(ST) outliers were unique between individual pairs of populations, but some genes show shared patterns of excess differentiation. These data indicate that gene flow is high, that selection is strong on a subset of genes, and that a variety of genes are experiencing diversifying selection at large spatial scales. This survey of polymorphism in S. balanoides provides a number of genomic tools that promise to make this a powerful model for ecological genomics of the rocky intertidal.     

The inhibitory effect of NaCl on barley germination

Abstract The possibility that the nature of the inhibitory effect of NaCl is different during imbibition compared to germination was investigated. Germination in both NaCl and betaine (a non-toxic solute) improved with pre-imbibition in water. Seeds imbibed in inhibitory concentrations of either solute could be induced to germinate by brief exposure to water. Electron micrographs of tissue from seeds imbibed in 0.5 kmol m^?3 NaCl for 25 h showed cells identical to those in seeds imbibed in water for only 1 h, but seeds imbibed for 6 h in water exhibited many changes in ultrastructure. These results are consistent with the hypothesis that seed hydration must reach a critical value before germination can proceed, and that the inhibitory effect of NaCl is primarily osmotic in barley seeds that have not reached this hydration threshold. Although isotonic solutions of betaine and NaCl were equally inhibitory to germination, isotonic solutions of betaine and NaCl were not equally inhibitory to continued development in seeds which had been pre-imbibed in water. Calcium ions improved both germination and plumule emergence of pre-imbibed seeds in NaCl solutions, but calcium had little effect on pre-imbibed seeds placed in betaine. Very high concentrations of NaCl or betaine inhibited germination, but did not kill dry seeds. Both solutes, on the other hand, were lethal at high concentrations to germinating seeds. NaCl killed germinating seeds more rapidly than betaine, but calcium reduced the rate of killing to nearly that of betaine. We conclude that hydrated seeds are sensitive to both osmotic and toxic effects of NaCl and that calcium mitigates the toxic effect of NaCl, but not the osmotic effect.     

The effect of proline insertions on the thermostability of a barley alpha-glucosidase

The thermal stability of alpha-glucosidase is important because the conversion of starch to fermentable sugars during industrial production of ethanol (e.g. brewing, fuel ethanol production) typically takes place at temperatures of 65-73 degrees C. In this study we investigate the thermostability of alpha-glucosidases from four plant species, compare their deduced amino acid sequences, and test the effect of substituting a proline for the residue present in the wild-type enzyme on the thermostability of alpha-glucosidase. The alpha-glucosidase from barley (Hordeum vulgare) was significantly less thermostable than the other three alpha-glucosidases. A comparison of the published deduced amino acid sequences of these four alpha-glucosidases revealed conserved proline residues in the three most thermostable alpha-glucosidases that were not found in the barley enzyme. Site-directed mutagenesis was done on recombinant barley alpha-glucosidase to create proteins with prolines at these conserved positions. The thermostability (T(50)) of one of these mutant enzymes, T340P, was 10 degrees C higher than the non-mutated enzyme.     

The effect of genotype on a barley scutella culture. Histological aspects

Cereals are known to be recalcitrant to the induction of morphogenesis in vitro and the majority of the methods used are callus-mediated and species/genotype-dependent. In the present investigation, a method of morphogenesis induction from immature scutella of selected barley cultivars was used, and particular attention was paid to histology in the initial stages of the regeneration process in order to confirm whether it occurs directly or indirectly (via callus formation). The length of the period from inoculating scutella on the medium to obtaining plantlets depended on the cultivar and the individual scutellum of the barley and varied between 2.5–4 months. The regeneration efficiency and viability of barley scutella was revealed to be highly genotype dependent. The average number of regenerated plants per regenerating scutellum was highest in the case of cv Granal (3.7). A histological analysis of the cultured explants showed both non-morphogenic and morphogenic callus formation. Two types of indirect morphogenetic response were observed: organogenesis (shoot bud formation) and somatic embryogenesis. This is the first report concerning an analysis of in vitro regeneration from immature scutella of barley cultivars (Stratus, Ryton, Granal and Binal).     

The effect of haem on chlorophyll synthesis in barley leaves

Exogenously supplied bovine haemin, fed to etiolated barley leaves, inhibited chlorophyll synthesis in leaves exposed to light. Haemin inhibited the regeneration of protochlorophyllide (P650) and the conversion of exogenously supplied δ-aminolaevulinate (ALA) to protochlorophyll (P630). The effect of haemin on chlorophyll production was overcome by incubating the leaves in water in the dark before light treatment, suggesting the operation of a rapid haem destruction mechanism in leaves. Protohaem turnover in dark-grown leaves was between 8 and 9 hr, based on the rate of degradation of erogenous haemin and the rate of protohaem breakdown in laevulinic acid (LA) treated leaves. The rate constant for haem destruction was 85 pmol/nmol/hr in the dark and 45 pmol/nmol/hr after 4 hr light. There was no evidence that light affects the synthesis of protohaem. It appears that the regulation of endogenous levels of protohaem is by breakdown and it is this mechanism which is under light control. Haem considerably decreased the incorporation of radioactivity from glycollate-[¹⁴C], glycine-[¹⁴C] and glutamate-[¹⁴C] into accumulated ALA in the presence of LA.     

Further analysis of complex allozyme polymorphisms in a barley population

New theory has recently been developed for two-locus models. In the light of this theory, an earlier analysis of esterase allozyme data from an experimental barley population has been modified to take proper account of initial gametic phase (linkage) disequilibria. The results show that the directions in which two-locus genotypic frequencies deviated from products of one-locus frequencies in this population followed those predicted by neutral descent theory. The observed departures were, however, much larger in size than predicted by the new descent measure theory, indicating that selection is operating in the population.