VARIABLE SELECTION ON EUROSTA'S GALL SIZE,I: THE EXTENT AND NATURE OF VARIATION IN PHENOTYPIC SELECTION

Natural fluctuations in environmental conditions are likely to induce variation in the intensity or direction of natural selection. A long-term study of the insect, Eurosta solidaginins Fitch (Diptera; Tephritidae), which induces stem galls on the perennial herb Solidago altissima (Asteraceae) was performed to explore the patterns of variation in phenotypic selection. The intensity of selection imposed by parasitoids and predators on gallmaking larvae, for gall size, was measured across 16 populations over the course of 4 generations, for a total of 64 population-generations. Directional selection was quantified by i, the selection intensity, and variance selection by j‘, a measure of the intensity of selection on phenotypic variance. Size-dependent attack by parasitoids caused upward directional selection (mean i_p = 0.42; SE = 0.023), while size-dependent bird attack favored larvae that induced smaller galls (mean i_b = -0.07; SE = 0.013. The mean net directional selection intensity was 0.35 (SE = 0.030), which indicates that insects inducing larger galls are generally favored by selection. The opposing patterns of size-dependent attack resulted in stabilizing selection in half the population generations, with an overall average. j‘ of -0.11 (SE = 0.078). The magnitude of directional selection was strongly influenced by the population mean gall size and weakly by the optimal gall size. The intensity of variance selection was strongly influenced by the shape of the fitness function, with sigmoidal and Gaussian-like shapes causing greater depletion of phenotypic variance.     

BIOLOGICAL INVASIONS IN EUROPE

Books reviewed:
Kowarik I., Biologische Invasionen: Neophyten und Neozoen in Mitteleuropa .     

Antigenic structure and variation in an influenza virus N9 neuraminidase.

We previously determined, by X-ray crystallography, the three-dimensional structure of a complex between influenza virus N9 neuraminidase (NA) and the Fab fragments of monoclonal antibody NC-41 [P. M. Colman, W. G. Laver, J. N. Varghese, A. T. Baker, P. A. Tulloch, G. M. Air, and R. G. Webster, Nature (London) 326:358-363, 1987]. This antibody binds to an epitope on the upper surface of the NA which is made up of four polypeptide loops over an area of approximately 600 A2 (60 nm2). We now describe properties of NC-41 and other monoclonal antibodies to N9 NA and the properties of variants selected with these antibodies (escape mutants). All except one of the escape mutants had single amino acid sequence changes which affected the binding of NC-41 and which therefore are located within the NC-41 epitope. The other one had a change outside the epitope which did not affect the binding of any of the other antibodies. All the antibodies which selected variants inhibited enzyme activity with fetuin (molecular weight, 50,000) as the substrate, but only five, including NC-41, also inhibited enzyme activity with the small substrate N-acetylneuramin-lactose (molecular weight, 600). These five probably inhibited enzyme activity by distorting the catalytic site of the NA. Isolated, intact N9 NA molecules form rosettes in the absence of detergent, and these possess high levels of hemagglutinin activity (W.G. Laver, P.M. Colman, R.G. Webster, V.S. Hinshaw, and G.M. Air, Virology 137:314-323, 1984). The enzyme activity of N9 NA was inhibited efficiently by 2-deoxy-2,3-dehydro-N-acetylneuraminic acid, whereas hemagglutinin activity was unaffected. The NAs of several variants with sequence changes in the NC-41 epitope lost hemagglutinin activity without any loss of enzyme activity, suggesting that the two activities are associated with separate sites on the N9 NA head.     

Electrical Characteristics of the Tonoplast of Cham corallincr. A Study Using Permeabilised Cells

Use of permeabilised cells of Chara corallina provides a uniqueopportunity to study the electrical characteristics of the tonoplastwhilst being able to control ionic conditions on the outsideof the membrane. Current-voltage (I/V) analysis over wide voltagespans, and admittance measurements at 5 Hz showed that manypermeabilised cells had a similar conductance and capacitanceto the tonoplast of intact cells. Cells developed two regionsof negative-slope conductance upon addition of external Cl^–,which suggests the existence of potential-dependent Cl^–channels in the Chara tonoplast. With Cl^– concentrationssimilar to those expected in vivo, the resting potential wasmore sensitive to changes in external K⁺ than Cl^–; however,a decrease in external K⁺ did not significantly alter the shapeof the I/V relation. ¹Present address: Biopysics Laboratory, School of BiologicalSciences, A12, University of Sydney, Sydney, N.S.W., 2006, Australia ²Permanent address: Department of botany, Faculty of Science,University of Tokyo, Hongo, Tokyo 113, Japan (Received May 6, 1987; Accepted September 21, 1987)     

Polymorphism and Gene Conversion in Mouse α-Globin Haplotypes

We have cloned and characterized three distinct alpha-globin haplotypes obtained from inbred strains of the mouse, Mus domesticus. We report here the complete nucleotide sequence of the six alpha-globin genes that the haplotypes contain. Our analysis of these genes and those from one other previously described haplotype indicates that recurrent gene conversion events have played a major role in their history. The pattern of nucleotide substitutions suggests that conversions have occurred both within and between haplotypes. Limited segments of coding and noncoding DNA have been involved in these gene conversion events. In two of the haplotypes, the nonallelic genes of each maintain DNA sequence identity over discrete intervals and encode the same alpha-globin polypeptide. On the other hand, the coding regions of some genes have accumulated replacement changes that result in distinct alpha-globins. In one instance, these changes appear to reflect positive selection of advantageous mutations.     

Nucleotide sequence of a gene cluster involved in entry of E colicins and single-stranded DNA of infecting filamentous bacteriophages into Escherichia coli.

Mutations in fii or tolA of the fii-tolA-tolB gene cluster at 17 min on the Escherichia coli map render cells tolerant to high concentrations of the E colicins and do not allow the DNA of infecting single-stranded filamentous bacteriophages to enter the bacterial cytoplasm. The nucleotide sequence of a 1,854-base-pair DNA fragment carrying the fii region was determined. This sequence predicts three open reading frames sequentially coding for proteins of 134, 230, and 142 amino acids, followed by the potential start of the tolA gene. Oligonucleotide mutagenesis of each open reading frame and maxicell analysis demonstrated that all open reading frames are expressed in vivo. Sequence analysis of mutant fii genes identified the 230-amino acid protein as the fii gene product. Chromosomal insertion mutations were constructed in each of the two remaining open reading frames. The phenotype resulting from an insertion of the chloramphenicol gene into the gene coding for the 142-amino acid protein is identical to that of mutations in fii and tolA. This gene is located between fii and tolA, and we propose the designation of tolQRA for this cluster in which tolQ is the former fii gene and tolR is the new open reading frame. The protein products of this gene cluster play an important role in the transport of large molecules such as the E colicins and filamentous phage DNA into the bacterium.     

Use of a biotinylated probe and in situ hybridization for light and electron microscopic localization of P 0 mRNA in myelin-forming Schwann cells

Summary A biotinylated P ₀ glycoprotein cDNA was hybridized in situ to aldehyde-fixed vibratome sections and to aldehyde-fixed thin sections of Lowicryl-embedded trigeminal ganglia of 15 day old rats. Alkaline phosphatase and peroxidase detectors were used for light microscopic (LM) studies and peroxidase or colloidal gold were employed for electron microscopic (EM) detection. In both LM and EM sections, probe was found in cytoplasmic areas of myelinforming Schwann cells that were enriched in granular endoplasmic reticulum, demonstrating that these regions contain P ₀ mRNA. Interestingly, P ₀ mRNA tended to cluster in regions close to the developing myelin sheath. Relatively simple methods are here described for EM detection of mRNA with reasonable tissue preservation and high resolution. These methods may be useful for developmental and disease-related studies of specific mRNAs in mammalian tissues.