Some Other Amazonians: Perspectives on Modern Amazonia

Some Other Amazonians: Perspectives on Modern Amazonia . Stephen Nugent and Mark Harris, eds. London: Institute for the Study of the Americas, 2004. 211 pp.     

Genome‐wide association mapping and biochemical markers reveal that seed ageing and longevity are intricately affected by genetic background and developmental and environmental conditions in barley

Globally, over 7.4 million accessions of crop seeds are stored in gene banks, and conservation of genotypic variation is pivotal for breeding. We combined genetic and biochemical approaches to obtain a broad overview of factors that influence seed storability and ageing in barley (Hordeum vulgare). Seeds from a germplasm collection of 175 genotypes from four continents grown in field plots with different nutrient supply were subjected to two artificial ageing regimes. Genome‐wide association mapping revealed 107 marker trait associations, and hence, genotypic effects on seed ageing. Abiotic and biotic stresses were found to affect seed longevity. To address aspects of abiotic, including oxidative, stress, two major antioxidant groups were analysed. No correlation was found between seed deterioration and the lipid‐soluble tocochromanols, nor with oil, starch and protein contents. Conversely, the water‐soluble glutathione and related thiols were converted to disulphides, indicating a strong shift towards more oxidizing intracellular conditions, in seeds subjected to long‐term dry storage at two temperatures or to two artificial ageing treatments. The data suggest that intracellular pH and (bio)chemical processes leading to seed deterioration were influenced by the type of ageing or storage. Moreover, seed response to ageing or storage treatment appears to be significantly influenced by both maternal environment and genetic background.     

Cross‐species amplification of 105 Lolium perenne SSR loci in 23 species within the Poaceae

Amplification of 105 Lolium perenne SSR markers was studied in 23 grass species representing seven tribes from three subfamilies of Poaceae. Twelve of the SSR markers are published for the first time. Between 2% and 96% of the SSR markers could be amplified within a given species. A subset of eight SSR markers was evaluated for polymorphism across nine of the 23 grass species. Four to seven of the markers were polymorphic within each species, with an average detection of 2.4 alleles per species.     

Effects of experience on parasitoid movement in odour plumes

Abstract. Insects commonly improve the effectiveness with which they locate biotic resources through learning, but the mechanism by which experience exerts its effects has rarely been studied in detail. The effect of oviposition experience on upwind movement of the eucoilid parasitoid, Leptopilina heterotoma (Thomson) (Hym.: Eucoilidae), in odour plumes of host microhabitats, was quantified with the use of a Kramer-type locomotion compensator. A 2h exposure to host Drosophila melanogaster larvae in either fermenting apple-yeast or decaying mushroom substrate (known to affect their preference for these odours in glasshouse and field choice experiments) had a number of effects on movement in plumes of each substrate. Females experienced with a particular substrate walked faster and straighter, made narrower turns and spent more time in upwind movement (i.e. toward the source) in a plume of odour from that substrate than in odour from an alternative substrate. Inexperienced females, by contrast, generally showed little or no significant difference in responses to alternative odours. In addition to affecting the mean values of movement parameters, experience also affected variability around those means. When walking speed or path straightness in an odour plume was increased by experience, variability among individuals was correspondingly decreased. The consequences of odour learning for microhabitat choice is discussed briefly.     

Multilocus DNA fingerprinting and RAPD reveal similar genetic relationships between strains of Oreochromis niloticus (Pisces: Cichlidae)

Two molecular techniques which reveal highly variable DNA polymorphisms, RAPD and multilocus DNA fingerprinting, were used to evaluate genetic diversity between six aquacultural strains of Oreochromis niloticus (tilapia) from the Philippines. The results using both techniques were in close agreement Within-strain heterozygosity values were similar and were correlated between the two data sets, but statistical errors associated with the RAPD data set were lower. Although genetic distances between strains were greater using DNA fingerprinting, the distances measured using both methods were significantly correlated. Both methods were useful in estimating variation between strains, but they offered different advantages. RAPD was technically easier to perform and produced results with low statistical error, whereas DNA fingerprinting detected greater genetic differentiation between strains. The theoretical basis for using RAPD and multilocus minisatellite markers for population studies is discussed.     

Heavy Water and Hydrostatic Pressure Effects on Tetrahymena pyriformis1

SYNOPSIS. Heat-synchronized cultures of Tetrahymena pyriformis strain GL subjected to pulses of high hydrostatic pressure (10,000 psi for 2 min) had increasing division delays during the 1st 40 min after the last heat shock (40 min after heat treatment). Pressure treatment during the subsequent 10-min interval disrupted cell synchrony. Comparable pressures applied to the cells at later stages, before the 1st synchronous division, caused negligible division delay. Continuous exposure to 10% (v/v) heavy water hardly affected division; higher concentrations delayed or blocked division. Ten-min pulses with heavy water (40%, 50%, 70%) resulted in increasing division delays depending on the stage of the cell cycle during which the heavy water was applied. Amelioration of the division-delaying effects of pressure was observed in cells treated simultaneously with pressure (3,000 psi for 30 min), and 30% D₂O. The results are consistent with the hypothesis that some of the pressure and D₂O effects could be attributed to changes in the sol-gel state of the cytoplasm.     

The Size of Macronuclear DNA and Its Relationship to Models for Maintaining Genic Balance*†

Synopsis.
A considerable amount of evidence is now available to indicate that the DNA in the ciliates Oxytricha and Stylonychia undergoes fragmentation when the micronucleus forms a macronucleus. Some evidence suggests that fragmentation may also occur in Tetrahymena and possibly in Paramecium . It is shown that some regulatory or nonrandom segregational mechanism must operate during cell divisions to maintain genic balance in Tetrahymena . Both the hypothesis of macronuclear subunits and also a new hypothesis based on replicative control of DNA are capable of explaining the currently know biochemical, cytological, and genetic facts.     

Behaviour of male and female parasitoids in the field: influence of patch size,host density,and habitat complexity

1. Two field experiments were carried out to examine the role of patch size, host density, and complexity of the surrounding habitat, on the foraging behaviour of the parasitoid wasp Cotesia glomerata in the field. 2. First, released parasitoids were recaptured on patches of one or four Brassica nigra plants, each containing 10 hosts that were placed in a mown grassland area. Recaptures of females were higher than males, and males and females aggregated at patches with four plants. 3. In experiment 2, plants containing 0, 5 or 10 hosts were placed in unmown grassland plots that differed in plant species composition, on bare soil, and on mown grassland. Very low numbers of parasitoids were recaptured in the vegetated plots, while high numbers of parasitoids were recaptured on plants placed on bare soil or in mown grassland. Recaptures were higher on plants on bare soil than on mown grassland, and highest on plants containing 10 hosts. The host density effect was significantly more apparent in mown grassland than on bare soil. 4. Cotesia glomerata responds in an aggregative way to host density in the field. However, host location success is determined mostly by habitat characteristics, and stronger host or host‐plant cues are required when habitat complexity increases.     

LATE HETTANGIAN (EARLY JURASSIC) AMMONITES FROM TASEKO LAKES, BRITISH COLUMBIA, CANADA

Abstract: The Taseko Lakes area yields the most diverse and well‐preserved late Hettangian ammonite assemblage in British Columbia. In total, 27 ammonite taxa are described, of which Fergusonites hendersonae, Eolytoceras constrictum and Pseudaetomoceras victoriense are new. Based on this study, Phylloceras cf. asperaense Hillebrandt, Togaticeras togatum (Neumayr), T. aff. goisernense Rakús, Eolytoceras aff. guexi Taylor, Discamphiceras aff. silberlingi Guex, Schlotheimia cf. cuevitensis Hillebrandt and Franziceras aff. graylockense Taylor are newly recognized in the North American Mineralense Zone whereas Nevadaphyllites psilomorphus (Neumayr), N. aff. compressus Guex, Fergusonites hendersonae sp. nov., Eolytoceras chongi Hillebrandt, E. constrictum sp. nov., Paracaloceras spp. A and B, P.? spp., Metophioceras? sp. and Schreinbachites? aff. laqueoides (Hyatt) are newly recognized in the Rursicostatum Zone. Discamphiceras silberlingi, D. sp. nov., Alsatites aff. bipartitus (Hillebrandt), Alsatites sp., Pseudaetomoceras victoriense sp. nov. and Paracaloceras aff. varaense Hillebrandt are newly recognized in both the Mineralense and Rursicostatum zones. The Taseko Lakes fauna allows clear correlations with contemporaneous strata in other areas of North America as well as with the Canadensis Zone and probably the Arcuatum horizon of the South American succession. Broad correlations are also possible with Hettangian or lowest Sinemurian strata in New Zealand and the eastern Tethys. Furthermore, the Taseko Lakes fauna permits correlation of the Mineralense and Rursicostatum zones with the circum‐Mediterranean Marmoreum Zone. Finally, this fauna suggests that the Mineralense Zone and the lower to middle portion of the Rursicostatum Zone in Taseko Lakes are equivalent to the Complanata Subzone whereas the upper portion of the Rursicostatum Zone correlates with the Depressa Subzone of the north‐west European Angulata Zone.