Low Levels of Genetic Diversity within Populations of Hosta clausa (Liliaceae)

Abstract Genetic diversity of Korean populations in Hosta clausa was investigated using starch gel electrophoresis. Hosta clausa is widespread, grows only along streamsides, and has both sexual and asexual reproduction. Populations of the species are small and isolated. Thirty-two percent of the loci examined were polymorphic, and mean genetic diversity within populations (He_p=0.082) was lower than mean estimates for species with very similar life history characteristics (0.131), particularly for its congener H. yingeri (0.250). The mean number of multilocus genotypes per population was 8.7, and genotypic diversity index (D_G) was 0.84. Significant differences in allele frequencies among populations were found in all seven polymorphic loci (P < 0.001). About one-fifth of the total allozyme variation was among populations (G_ST=0.192). Indirect estimate of the number of migrants per generation (Nm=0.48, calculated from mean G_ST) and nine private alleles found indicate that gene movement among populations was low. The low levels of genetic diversity within populations and the relatively high levels of genetic diversity among populations suggest that strong moist habitat preferences, clonal reproduction, low level of gene flow among populations, genetic drift, and historical events may have played roles in the genetic structuring of the species.     

Cassava leaf harvesting as vegetables; a cause of vulnerability of cassava plant to cassava mosaic disease and eventual yield reduction: Ernte von cassavablättern als gemüse; eine ursache für die anfälligkeit der cassavapflanze für die cassava-mosaikkrankheit und für spätere ertragseinbußen

The consequence of harvesting young leaves of cassava as vegetable on the vulnerability of the crop to cassava mosaic disease (CMD) and on storage root yield was investigated using 30 cassava genotypes planted in IITA fields located in the humid forest (Port Harcourt?:?Onne), forest-savannah transition (Ibadan), southern guinea savannah (Mokwa) and northern guinea savannah (Zaria) agroecologies in Nigeria. Tender apical leaves and shoots of the cassava genotypes were removed from forty plants per cassava genotype with the same number of plants considered as control. Whitefly infestation, disease incidence (DI) and symptom severity (ISS) of the disease were assessed at monthly interval for six months and also at the ninth month after planting (MAP). Yield reduction due to this treatment was calculated as percentage harvest index (HI). Whitefly population fluctuated throughout the period of observation at all locations with higher population obtained generally for treated plants compared to control plants. Sprouting leaves of some treated genotypes were observed with severe mosaic symptoms, while corresponding control showed no mosaic symptoms. Contrarily, no remarkable difference was observed in Zaria between the mean ISS of treated and control cassava genotypes. There was a highly significant difference (P?<?0.01) in DI and ISS among cassava genotypes across all locations. Also, there was a highly significant interaction (P?<?0.01) in symptom severity between location (loc) and genotype, genotype and treatment (trt), loc and trt. Interaction between loc, genotypes and trt with regard to DI was highly significant at 2, 3 and 4 MAP, while with ISS, the interaction was highly significant all through the counting period. There was a positive relationship between DI and ISS on plants of genotypes 96/1039 and ISU. The percentage HI (27.4) of treated plants of genotype 95/0166 in Ibadan was remarkably lower than the value obtained for corresponding control (41.9) plants. Also, sharp distinction in% HI of treated (39.5) and control (43.8) ISU was observed in Onne with their respective ISS values as 3.7 and 3.2. Therefore, harvesting tender apical leaves and shoots of cassava as vegetables should be discouraged as it increases the severity of CMD infection in the regenerating shoots of cassava with attendant storage root yield reduction.     

Criteria for the assessment of radon potential risk in territories

The detailed analysis of criteria used in the different countries for an assessment of radon potential risk in territories was made. Such criteria as radon flux density from earth surface, radon concentration in soil air, specific activity of 226Ra in superficial soils were chosen. The analysis has revealed that the most reliable criterion is the value of equilibrium radon concentration in the soil air. The method of measurement of this value is specified.     

Seasonal mortality trends in tree‐feeding insects: a field experiment

Abstract 1. The majority of general life‐history models treat the environment as being invariable through time, even though temporal variation in selective agents could dramatically change the outcomes, e.g. in terms of optimal size and time at maturity. For herbivorous insects, seasonal differences in food quality are reasonably well described, but seasonal dynamics of top‐down selective forces are poorly documented. 2. The present study attempted to quantify seasonal changes in predation risk of folivorous insect larvae in temperate forest habitats. In a series of field experiments, artificial larvae were exposed to predators, and the resulting bird‐inflicted damage was recorded. The trials were repeated regularly throughout the course of two summers. 3. A distinct peak of larval mortality was recorded in mid‐June (the nestling period for most insectivorous passerine birds), after which predation risk declined to a plateau of 20–30% below the peak value. 4. The recorded pattern is interpreted as a consequence of seasonal changes in the number and behaviour of insectivorous birds, and the abundance of alternative food resources for these predators. 5. A quantitative analysis based on field data indicated that considering temporal variation in mortality in life‐history models is crucial for obtaining realistic predictions concerning central life‐history traits, such as final body size in different generations.     

Functional activity of transposase of Bordetella pertussis IS element in Escherichia coli cells

An Escherichia coli strain producing transposase of a repeated sequence of Bordetella pertussis chromosome (RSBP) was constructed. A defective MGE-helper plasmid method, which allowed the determination of transposase functional activity was developed. It was shown that transposase synthesized in E. coli cells ensures transposition of “defective” RSBP into the host chromosome. Overexpression of transposase was shown to markedly decrease the vital activity of E. coli cells under selective cultivation conditions. Reasons for a decrease in viability transposase-producing cells are discussed. Results showing the impact of transposase on replication of recombinant plasmids and E. coli cell division were obtained.     

Molecular evidence for the lysogenic state of microorganisms belonging to the genus Bordetella and characterization of Bordetella parapertussis temperate bacteriophage 662-2

A new bacteriophage ?K of microorganisms belonging to the genus Bordetella was isolated from cells of the earlier characterized strains 66_2-2 (1 and 2) obtained upon phage conversion of B. parapertussis 17 903 cells by B. pertussis bacteriophage ?134. Bacteriophage ?K is identical to previously described Bordetella bacteriophages ?T, ?134, and ?214 in morphology and some biological properties but has a permuted genome different from all other phages. DNA of bacteriophage ?K is not integrated in the chromosome of B. parapertussis 17 903, similar to DNA of bacteriophages ?T, ?134, and ?214 that are not integrated into B. pertussis and B. bronchiseptica chromosomes, but may be present in a small part of the bacterial population as linear plasmids. Sequences homologous to DNA of bacteriophage ?K were detected in the chromosome of strain 66_2-2 (1 and 2) and in chromosomes of all tested strains B. pertussis and B. bronchiseptica. Prophage integration in chromosomes of microorganisms of the genus Bordetella may vary in different bacterial strains and species. An assumption about abortive lysogeny of B. parapertussis bacteria for ?K phage and of B. pertussis and B. bronchiseptica for closely related phages ?T, ?134, and ?214 has been advanced. The possibility of involvement of B. pertussis insertion sequences in the formation of the chromosomal structure in 66_2-2 convertants and in phage genomes is considered.     

Construction of recombinant plasmids encoding the biosynthesis of the beta-subunit of cholera toxin

The structure of the cholera toxin operon and the location of A and B toxin subunits have been studied by the Southern blot hybridization on filters. The gene coding for the synthesis of the cholera toxin B-subunit has been cloned in the vector plasmid pBR322. The structural gene of A-subunit has been partially deleted by the restriction endonuclease Bal31 digestion. The size of the 250 b. p. deletion has been defined by electron microscopy. The production of the cholera toxin B-subunit in Escherichia coli K12 cells has been studied.     

Lysogeny and conversion characteristics of microbes in the genus Bordetella

The genomes of B. pertussis bacteriophages 134 and 41405 and B. bronchiseptica bacteriophage 214 have been studied. As revealed by the methods of heteroduplex and restriction analyses, the populations of these bacteriophages are heterogeneous and their DNAs differ in size and location of inserts. The study carried out with the use of blot hybridization techniques has shown that in lysogenic cells the genome is not integrated into the chromosome, but exists as an autonomous plasmid replicon. Only partial incorporation of the phage genome into the recipient chromosome takes place in the process of conversion, the phage genome continuing its existence as an autonomous replicon.     

Changes in sperm stores, ejaculate size, fertilization success, and sexual motivation over repeated matings in the common toad, Bufo bufo (Anura: Bufonidae)

Fertilization is of central importance in the determination of reproductive success for both males and females. In species where males have the chance to mate repeatedly within a short period of time, sperm stocks may become depleted and males may have to carefully economize on their sperm reserves. Also, intensive intrasexual competition for females and repeated matings may lead to exhaustion on the behavioural level. To determine whether the reproductive potential of males is limited and if such a limitation is due to behavioural exhaustion or sperm depletion, we experimentally investigated changes in sperm stores, sperm expenditure, fertilization success, and sexual motivation over three repeated matings in the common toad, Bufo bufo , where the breeding season is short and sequential polygyny occurs. At the end of the breeding season, the number of sperm stored in the testes of males mated repeatedly was close to 50% lower than in testes of unmated males. Ejaculate size, which was estimated by applying a novel method allowing direct quantification, decreased by 88% from first to third matings. We also observed a drop in fertilization success from the first two to third matings by 65%, which was largest in males that had started the reproductive season in bad body condition. Some of these males also showed a decreased interest in females in the third mating round. Our results suggest that sperm depletion and loss of sexual motivation may together set a limit to the reproductive potential of common toad males. The present study draws attention to a limitation in reproductive potential, which may occur more often than currently anticipated and has the potential to strongly influence several aspects of reproductive behaviour.  © 2009 The Linnean Society of London, Biological Journal of the Linnean Society , 2009, 96 , 361–371.