Phenotypic plasticity of Brevicoryne brassicae in responses to nutritional quality of two related host plants

Abstract 1. The host species used by a herbivorous insect may impose different selective pressures promoting host race formation, yet the presence of plasticity can potentially constrain host race formation. 2. The goal of this study is to determine if there is phenotypic plasticity in life history traits of Brevicoryne brassicae in response to host and nutritional quality of two host species, Brassica oleraceae and Brassica campestris, and to what extent there are genetic differences among genotypes in plasticity. 3. Plants of B. oleraceae and B. campestris were fertilised with three different nitrogen doses (with nutritive solutions of 50, 200 and 400 ppm of soluble nitrogen) to produce plants with different nutritional qualities. Eight clones of B. brassicae were reared on those plants, and days to reproduction (DTR), number of nymphs, and fitness (r_m) were recorded. 4. A significant genotype × host interaction was detected in days to reproduction. Genotype × nitrogen interaction (plasticity) was detected in the number of nymphs when aphids were raised on B. campestris. Aphids showed plasticity in DTR and marginal plasticity in r_m in reaction to the varying nitrogen content of B. oleraceae. 5. The phenotypic plasticity to fine‐scale variation of host (nutritional quality) documented here may be an important source of phenotypic variation and may potentially constrain host race formation.     

Global spatial patterns and temporal trends of burned area between 1981 and 2000 using NOAA-NASA Pathfinder

An analysis of the spatial and temporal patterns of global burned area with the Daily Tile US National Oceanic and Atmospheric Administration-Advanced Very High-Resolution Radiometer Pathfinder 8 km Land dataset between 1981 and 2000 is presented. Nine distinct temporal and spatial fire patterns were identified at the global scale using principal components and cluster analysis. Three major fire seasons were identified from June to December and from February to June for different areas of the northern hemisphere and from October to March for the southern hemisphere. The area burned primarily followed the annual cycle and secondarily, an important 6-month cycle. Temporal cycles were unimportant in some equatorial and tropical areas in the northern hemisphere. The total annual burned area has not increased in the last 20 years but a significant increase was found in the mid-latitude and subtropical areas of the northern hemisphere which was offset by a slight decrease in burned area in tropical southeast Asia and Central America. Additionally, burned area has significantly increased during the summer in the mid-latitudes of the northern hemisphere and in the boreal region, and the fire season starts earlier in the mid-latitudes. Total burned area was explained by the extent of savanna (wooded grassland) cover. Latitude was not determinative as divergent fire patterns were encountered and did not have an impact on extent of burned area at our spatial level of analysis.     

Randomly Amplified Polymorphic DNA (RAPD) and Isoenzyme Analysis of Trypanosoma rangeli Strains

ABSTRACT. Sixteen Trypanosoma rangeli strains were compared by isoenzyme and randomly amplified polymorphic DNA (RAPD) analysis. Eight strains were isolated from either Rhodnius prolixus or Homo sapiens from Honduras, Colombia and Venezuela. Another eight strains were isolated from either Panstrongylus megistus or the rodent Echimys dasythrix from the State of Santa Catarina, southern Brazil. All six T. rangeli strains isolated from P. megistus were co-infections with Trypanosoma cruzi , demonstrating an overlap of the sylvatic cycles of these parasites and that the accurate identification of species is of utmost importance. Both isoenzyme and RAPD analysis revealed two distinct groups of T. rangeli strains, one formed by the strains from Santa Catarina and the other, by the strains from Honduras, Colombia and Venezuela. With the five enzymes used, all the strains from Santa Catarina had identical profiles which overlapped with those of the other regions only in the pattern obtained with malic enzyme. Analysis of 138 RAPD bands by means of an unweighted pair group method analysis (UPGMA) phenogram using the Dice similarity coefficient allowed the separation of the two groups based on their divergence at a lower level of similarity than the phenon line. We show that the identification of T. cruzi and T. rangeli in naturally mixed infections is readily achieved by either RAPD or isoenzyme analysis.     

Monovalent Cations Induce Microsporidian Spore Germination In Vitro

ABSTRACT The relative capacity of Na⁺, K⁺ and Cl^- to stimulate germination of spores of the microsporidian Nosema algerae, a pathogen of mosquitoes, was examined by ion substitution experiments. Sodium at 0.1 M was ineffective to produce the high percentage of germination that typically occurs with 0.1 M NaCl (the normal stimulation solution) if Cl^- was substituted with the usually impermeant anions SO₄^2-, HPO₄^2-, or the organic acids oxalate, cacodylate, EGTA, MES and HEPES. However, substantial concentration- and pH-dependent germination was seen with Na₂SO₄ in the 0.2-0.8 M Na⁺ range. Similar results were obtained with solutions of K⁺ accompanied by impermeant anions. In contrast, the chloride salts of usually impermeant cations, like choline and triethanolamine, failed to germinate spores even at 0.8 M unless Na⁺ or K⁺ was independently added. The presence of 0.5 M choline chloride in the medium reduced the levels of Na₂SO₄ required to produce germination down to equivalence with those of Na⁺ in the normal stimulation solution. Monensin, a Na⁺ ionophore, facilitated the germination induced by a medium-level stimulus (0.04 M NaCl) in sonicated samples. These findings indicate that N. algerae spores germinate in response to the alkali metal cations, while CI^- plays a passive role by diffusing to maintain internal electroneutrality during cation influx. A possible mechanism of cation action in spore germination is suggested on the basis of these results and observations on other systems of intracellular motility.     

Immunodetection of Botrytis-specific Invertase in Infected Grapes

Invertase (β-fructofuranosidase, EC 3.2.1.26) activity was shown to be stimulated in grape berries after infection with Botrytis cinerea . By using organism-specific extraction methods, evidence was found proving that both partners contribute to the increase in activity. Qualitative analysis of the extracts by SDS–PAGE showed a new invertase species in the botrytised material, with a molecular weight similar to that of Botrytis invertase (BIT). A method allowing the preparative isolation of homogeneous invertase from liquid cultures of B. cinerea in only three steps (ethanol precipitation, DEAE anion exchange and hydroxyapatite chromatography) with 50% recovery was developed. BIT appeared to be strongly glycosylated; interestingly, the amount of glycan seemed to vary and had a remarkable influence on the chromatographic behaviour of the enzyme. After chemical deglycosylation with TFMS, the BIT peptide was used for the production of polyclonal antibodies in chickens (anti-BIT-IgY). The antibodies recognised glycosylated as well as deglycosylated BIT, a partial denaturation of the protein being necessary for reaction. This indicates that the deglycosylation procedure had been successful and that the antibodies were in fact directed to the peptide moiety. However, after a short incubation at 70°C, native BIT was detectable by anti-BIT-IgY, while still active. Western blotting with extracts of diseased berries confirmed the fungal origin of the new invertase form. The anti-BIT-IgY proved highly specific, although some cross-reaction with a protein in Monilia laxa extracts occurred. The importance of careful immunogen preparation in the production of specific antibodies, and the potential of BIT as a target molecule for the immunological detection of B. cinerea are discussed.     

Analysis of enamel-line length as a morphometric parameter and its application to Quaternary arvicolids

This paper proposes a methodology for taxonomic, phylogenetic and ecological analyses based on enamel distribution in the crown of the tooth. Enamel units (EU) and morphological units (MU) are defined, which can be used to identify both genera and species, and also morphotypes in populations closely located in time. The biological character of the enamel units allows us to propose hypotheses on the genetic characteristics of fossil populations. Mammals, herbivores, Arvicolidae, enamel, methodology, taxonomy, biostratigraphy.     

Distribution of Carbohydrates Recognized by the Lectins Euonymus europaeus and Concanavalin A in Monoxenic and Heteroxenic Trypanosomatids

We observed a wide distribution of the carbohydrate epitopes galactosylα(1–3) galactose (galα1–3 gal), α-glucoside, and α-mannoside in mono- and heteroxenic trypanosomatids by using fluorescein-labelled lectins of Euonymus europaeus (EE) and Concanavalin A (Con A) as well as sera from acute chagasic patients who have very high levels of anti-galα(1–3) gal antibodies. The direct fluorescence test for galα1–3 gal with EE was positive at minimum concentrations of 6 μg/ml for heteroxenic trypanosomatids and 0.7 μg/ml for monoxenic ones and for the plant parasite, Phytomonas. On the other hand, heteroxenic trypanosomatids that infect vertebrates bound ten-fold more Con A than monoxenic flagellates and Phytomonas. These data were confirmed in ELISA and Western Blot assays carried out with peroxidase-labelled EE and Con A. Euonymus europaeus recognized several glycoproteins in all trypanosomatids that we tested. Con A, however, recognized a glycoprotein cluster in heteroxenic protozoa, which ranging from 60–120 kDa, seemed to lack monoxenic parasites and Phytomonas. These findings suggest that α-D-mannose and α-D-glucose might play an important role in the interaction between trypanosomatids and vertebrate hosts.     

Enhancement of root hydraulic conductivity by methyl jasmonate and the role of calcium and abscisic acid in this process

The role of jasmonic acid in the induction of stomatal closure is well known. However, its role in regulating root hydraulic conductivity (L) has not yet been explored. The objectives of the present research were to evaluate how JA regulates L and how calcium and abscisic acid (ABA) could be involved in such regulation. We found that exogenous methyl jasmonate (MeJA) increased L of Phaseolus vulgaris, Solanum lycopersicum and Arabidopsis thaliana roots. Tomato plants defective in JA biosynthesis had lower values of L than wild‐type plants, and that L was restored by addition of MeJA. The increase of L by MeJA was accompanied by an increase of the phosphorylation state of the aquaporin PIP2. We observed that MeJA addition increased the concentration of cytosolic calcium and that calcium channel blockers inhibited the rise of L caused by MeJA. Treatment with fluoridone, an inhibitor of ABA biosynthesis, partially inhibited the increase of L caused by MeJA, and tomato plants defective in ABA biosynthesis increased their L after application of MeJA. It is concluded that JA enhances L and that this enhancement is linked to calcium and ABA dependent and independent signalling pathways.