RESTRICTED MIGRATION AND THE EVOLUTION OF ALTRUISM

A suggestion that limited migration, i.e., population viscosity, should favor the evolution of altruism has been challenged by recent kin selection models explicitly incorporating restricted migration. It is demonstrated that these models compound two distinct elements of population structure, spatial-genotypic variation and density regulation. These two characteristics are often determined by distinct biological processes. While they may be linked under certain circumstances, this is not invariably true. A simple modification of the migration system employed in these studies decouples migration and population regulation thus favoring inter-group selection. At least in some cases, restricted migration will facilitate the evolution of altruism.     

THE FINE STRUCTURE OF TWO PHOTOSYNTHETIC SPECIES OF DINOPHYSIS (DINOPHYSIALES,DINOPHYCEAE)1

Two closely related, photosynthetic species belonging to the genus Dinophysis were examined, D. acuminata Claparède et Lachmann and D. fortii Pavillard. Typical dinoflagellate features include the amphiesmal covering enclosing the cells and the structure of the nucleus and mitochondria. Many other characteristics seem to be specific to the order Dinophysiales. Many rhabdosomes are present, and complex mucocysts are found beneath the amphiesma. The thecal pores are unusual with the base of the pore occluded by a thin disc that is continuous with the main amphiesmal plate. The structure of the apical pore is also distinctive. Chloroplasts are grouped together in chromatospheres, enclosed by a double membrane, and contain paired thylakoids with electron dense contents in the lumen. The two pusules are extensive, each branching off the flagellar canal, and consisting of a large antechamber and a number of convoluted sacs. The entrance of each antechamber, and site of an emerging flagellum, is surrounded by a striated fibrous collar. Near the flagellar pore is a prominent microtubular/microbody complex which penetrates deep into the cell cytoplasm. Consideration is given to taxonomic position of the Dinophysiales and also to the nature and origins of the chloroplasts.     

Cigarette advertising and onset of smoking in children: questionnaire survey.

OBJECTIVE: To investigate uptake of smoking in a cohort of 11 to 12 year olds related to awareness of advertised cigarette brands named. DESIGN: Self completed questionnaires administered to whole classes of schoolchildren in June 1993 and June 1994. SETTING: Primary, middle, and secondary schools in the north and south of England. SUBJECTS: 1450 pupils aged 11 and 12 years at the time of the first survey. MAIN OUTCOME MEASURES: Onset of smoking and brands smoked by the second survey related to cigarette brands named in the first one. Less advertised brands were used as the base for calculating odds ratios. RESULTS: Girls who named the most advertised brands-namely, Benson and Hedges alone (odds ratio = 2.50, 95% confidence interval = 1.18 to 5.30) or Benson and Hedges and Silk Cut (2.15, 1.04 to 4.42) in the first survey were at greatest risk of taking up smoking by the second one. The difference was similar but not significant for boys. Boys and girls who named the least advertised brands in the first survey were at no greater risk of taking up smoking by the second survey than those who named no brands (boys odds ratio = 0.49 (0.24 to 1.01); girls 0.79 (0.38 to 1.62)). New smokers were more likely to smoke any available brand (29.5%) or a less advertised brand such as Embassy (24.6%) than the most advertised ones, Benson and Hedges (19.7%) and Silk Cut (14.8%). Established smokers were more selective, only 15% smoking any available brand and 38.3% smoking Benson and Hedges. CONCLUSIONS: Cigarette advertising appears to increase children''s awareness of smoking at a generic level and encourages them to take up the behaviour, beginning with any cigarettes which are available and affordable.     

Absence of plasma membrane H+-ATPase in plasmodesmata located in pit-fields of the young reactive pulvinus ofMimosa pudica L.

Summary Immunocytochemical techniques were employed to study the spatial distribution of the plasma membrane H⁺-ATPase within various cell types of the young reactive primary pulvinus ofMimosa pudica L. These cells were interconnected by large numbers of plasmodesmata, being concentrated within pit-fields. Although we could routinely detect evidence of the H⁺-ATPase along the plasma membrane, immunolabelling was rarely, if ever, observed along the plasma membranes of the plasmodesmata. This finding is discussed with respect to the likely specialized supramolecular structure of the plasmodesma.Abbreviations SEL size exclusion limit of plasmodesmata     

Characterization of diverse primary herpes simplex virus type 1 gB-specific cytotoxic T-cell response showing a preferential V beta bias.

The glycoprotein B (gB) from herpes simplex virus type I is a major target of cytotoxic T lymphocytes (CTL) in C57BL/6 mice. The majority of these T cells are directed to a single Kb-restricted determinant, gB498-505. We have analyzed the T-cell receptor (TCR) usage in gB-specific CTL lines derived shortly after virus infection. The CTL populations preferentially used two V beta regions, a dominant V beta 10 element and a subdominant V beta 8 element. Detailed sequence analysis revealed considerable TCR beta-chain heterogeneity despite a striking level of predicted amino acid conservation at the V beta-D beta junction. This junction forms part of the third hypervariable loop of the TCR thought to directly contact the major histocompatibility complex-bound antigenic peptide. The results reveal considerable diversity within the primary T cells responding to a single viral determinant while still maintaining a high degree of TCR V beta bias and sequence conservation at the V-D-J junction.     

Partial restoration of impaired alpha1-adrenergic responsiveness in parotid cells of aged rats by S-adenosylmethionine treatment

The age related decrease in alpha₁-adrenergic stimulated inositol 1,4,5 trisphosphate (IP₃) production in parotid cells of aged rats can be partially restored by treatment with S-adenosylmethionine (SAM). This effect is completely blocked by S-adenosyl homocysteine (SAH) and occurs in association with an increase in the conversion of phosphatidylethanolamine to phosphatidylcholine and a decrease in membrane viscosity. In contrast, SAM treatment actually inhibits stimulated IP₃ production in cells of young rats. The membrane viscosity of these cells is lower than that of those from aged rats. Although conversion of phosphatidylethanolamine to phosphatidylcholine is enhanced, no further decrease in membrane viscosity is elicited in young cell preparations. These findings suggest that age changes in the membrane environment may result in impaired alpha₁-adrenergic signal transduction and that such alterations may be at least partially reversible by SAM treatment.     

Role of arginine-43 and arginine-69 of the Hin recombinase catalytic domain in the binding of Hin to the hix DNA recombination sites

The Hin recombinase mediates the site-specific inversion of a segment of the Salmonella chromosome between two flanking 26 bp hix DNA recombination sites. Mutations in two amino acid residues, R43 and R69 of the catalytic domain of the Hin recombinase, were identified that can compensate for loss of binding resulting from elimination of certain major and minor groove contacts within the hix recombination sites. With one exception, the R43 and R69 mutants were also able to bind a hix sequence with an additional 4 bp added to the centre of the site, unlike wild-type Hin. Purified Hin mutants R43H and R69C had both partial cleavage and inversion activities in vitro while mutants R43L, R43C, R69S, and R69P had no detectable cleavage and inversion activities. These data support a model in which the catalytic domain plays a role in DNA-binding specificity, and suggest that the arginine residues at positions 43 and 69 function to position the Hin recombinase on the DNA for a step in the recombination reaction which occurs either at and/or prior to DNA cleavage.     

Distinct Requirements for Somatic and Germline Expression of a Generally Expressed Caernorhabditis Elegans Gene

In screening for embryonic-lethal mutations in Caenorhabditis elegans, we defined an essential gene (let-858) that encodes a nuclear protein rich in acidic and basic residues. We have named this product nucampholin. Closely homologous sequences in yeast, plants, and mammals demonstrate strong evolutionary conservation in eukaryotes. Nucampholin resides in all nuclei of C. elegans and is essential in early development and in differentiating tissue. Antisense-mediated depletion of LET-858 activity in early embryos causes a lethal phenotype similar to characterized treatments blocking embryonic gene expression. Using transgene-rescue, we demonstrated the additional requirement for let-858 in the larval germline. The broad requirements allowed investigation of soma-germline differences in gene expression. When introduced into standard transgene arrays, let-858 (like many other C. elegans genes) functions well in soma but poorly in germline. We observed incremental silencing of simple let-858 arrays in the first few generations following transformation and hypothesized that silencing might reflect recognition of arrays as repetitive or heterochromatin-like. To give the transgene a more physiological context, we included an excess of random genomic fragments with the injected DNA. The resulting transgenes show robust expression in both germline and soma. Our results suggest the possibility of concerted mechanisms for silencing unwanted germline expression of repetitive sequences.     

A Test of Neutrality Based on Interlocus Associations

The evolutionary processes governing variability within genomic regions of low recombination have been the focus of many studies. Here, I investigate the statistical properties of a measure of intrlocus genetic associations under the assumption that mutations are selectively neutral and sites are completely linked. This measure, denoted Z(nS), is based on the squared correlation of allelic identity at pairs of polymorphic sites. Upper bounds for Z(nS) are determined by simulations. Various deviations from the neutral model, including several different forms of natural selection, will inflate the value of Z(nS) relative to its neutral theory expectations. Larger than expected values of Z(nS) are observed in genetic samples from the yellow-ac-scute and Adh regions of Drosophila melanogaster.