Direct and indirect pathways of fitness-impact in a protozoan-infected kissing bug

Abstract.  Parasites can reduce host fitness through short-term mortality, complete or partial castration, or slight reductions in host fecundity. Hosts may reduce reproductive effort as an adaptive strategy to tolerate parasitism. However, host fitness reduction may be unrelated to host adaptation but represent a pathological side-effect of infection. The present study evaluates experimentally the direct and indirect impact of the protozoan parasite Trypanosoma cruzi on the investment of female kissing bugs in reproductive tissue. The presence of the parasite decreases gonad weight but this effect disappears when body size is included as covariate. To examine in more detail the set of causal relationships involved, a structural equation modelling analysis is performed using body size, moulting time and nutrition as predictor variables on gonad weight in the presence and absence of the protozoan. The results obtained indicate that, irrespective of the pathway and status of infection, female kissing bugs showing a slow development tend to have lighter gonads. On the other hand, the importance of blood ingestion for gonad weight is dependent on body size and contingent on the status of infection. Uninfected individuals tend to invest more in reproductive tissue when ingesting more blood during their ontogeny, and the opposite situation is observed for infected insects. These results indicate that gonad weight reduction in T. cruzi -infected Mepraia spinolai (Porter, 1934) is a consequence of nutrition curtailment and body size reduction rather than an adaptive strategy to cope with infection.     

Leaf carbon management in slow-growing plants exposed to elevated CO2

Two slow‐growing plant species (Chamaerops humilis, L. and Cycas revoluta Thunb.) were exposed to elevated CO₂ conditions over a 20‐month period in order to study the CO₂ effect on growth, photosynthetic capacity and leaf carbon (C) management. The ambient isotopic ¹³C/¹²C composition (δ¹³C) of the greenhouse module corresponding to elevated CO₂ (800 μmol mol^?1 CO₂) conditions was changed from δ¹³C ca. ?12.8±0.3‰ to ca. ?19.2±0.2‰. Exposure of these plants to elevated CO₂ enhanced dry mass (DM) by 82% and 152% in Chamerops and Cycas, respectively, mainly as a consequence of increases in plant level photosynthetic rates. However, analyses of A–C_i curve parameters revealed that elevated CO₂ diminished leaf photosynthetic rates of Chamaerops whereas in Cycas, no photosynthetic acclimation was detected. The fact that Chamaerops plants had a lower DM increase, together with a longer leaf C residence time and a diminished capacity to respire recently fixed C, suggests that this species was unable to increase C sink strength. Furthermore, the consequent C source/sink imbalance in Chamaerops might have induced the downregulation of Rubisco. Cycas plants were capable of avoiding photosynthetic downregulation due to a greater ability to increase C sink strength, as was confirmed by DM values, and ¹²C‐enriched CO₂ labeling data. Cycas developed the ability to respire a larger proportion of recently fixed C and to reallocate the recently fixed C away from leaves to other plant tissues. These findings suggest that leaf C management is a key factor in the responsiveness of slow‐growing plants to future CO₂ scenarios.     

Tomato yellow leaf curl viruses: ménage à trois between the virus complex,the plant and the whitefly vector

Tomato yellow leaf curl disease (TYLCD) is one of the most devastating viral diseases affecting tomato crops in tropical, subtropical and temperate regions of the world. Here, we focus on the interactions through recombination between the different begomovirus species causing TYLCD, provide an overview of the interactions with the cellular genes involved in viral replication, and highlight recent progress on the relationships between these viruses and their vector, the whitefly Bemisia tabaci. Taxonomy: The tomato yellow leaf curl virus‐like viruses (TYLCVs) are a complex of begomoviruses (family Geminiviridae, genus Begomovirus) including 10 accepted species: Tomato yellow leaf curl Axarquia virus (TYLCAxV), Tomato yellow leaf curl China virus (TYLCCNV), Tomato yellow leaf curl Guangdong virus (TYLCGuV), Tomato yellow leaf curl Indonesia virus (TYLCIDV), Tomato yellow leaf curl Kanchanaburi virus (TYLVKaV), Tomato yellow leaf curl Malaga virus (TYLCMalV), Tomato yellow leaf curl Mali virus (TYLCMLV), Tomato yellow leaf curl Sardinia virus (TYLCSV), Tomato yellow leaf curl Thailand virus (TYLCTHV), Tomato yellow leaf curl Vietnam virus (TYLCVNV) and Tomato yellow leaf curl virus(TYLCV). We follow the species demarcation criteria of the International Committee on Taxonomy of Viruses (ICTV), the most important of which is an 89% nucleotide identity threshold between full‐length DNA‐A component nucleotide sequences for begomovirus species. Strains of a species are defined by a 93% nucleotide identity threshold. Host range: The primary host of TYLCVs is tomato (Solanum lycopersicum), but they can also naturally infect other crops [common bean (Phaseolus vulgaris), sweet pepper (Capsicum annuum), chilli pepper (C. chinense) and tobacco (Nicotiana tabacum)], a number of ornamentals [petunia (Petunia×hybrida) and lisianthus (Eustoma grandiflora)], as well as common weeds (Solanum nigrum and Datura stramonium). TYLCVs also infect the experimental host Nicotiana benthamiana. Disease symptoms: Infected tomato plants are stunted or dwarfed, with leaflets rolled upwards and inwards; young leaves are slightly chlorotic; in recently infected plants, fruits might not be produced or, if produced, are small and unmarketable. In common bean, some TYLCVs produce the bean leaf crumple disease, with thickening, epinasty, crumpling, blade reduction and upward curling of leaves, as well as abnormal shoot proliferation and internode reduction; the very small leaves result in a bushy appearance.     

BROODING AND NON-BROODING DACRYDIUM (BIVALVIA: MYTILIDAE): A REVIEW OF THE ATLANTIC SPECIES

The Atlantic species of the marine bivalve genus Dacrydium arereviewed, with particular emphasis on their hinge and protoconchcharacters. The basic groundplan of a Dacrydium comprises afunctional primary ligament, a paired series of primary teeth,and a posterior row of secondary teeth separated from the latterby a secondary ligament; this can be transformed into a singleseries either by loss of the secondary ligament and mergingprimary and secondary teeth, or by loss of secondary teeth andligament through paedomorphosis. Twelve species are recognized, of which eleven are illustrated.One abyssal species is not separable morphologically from theIndian Ocean D. speculum Poutiers, 1989 and is new to the Atlantic;four new species (D. wareni, D. dauvini, D. filiferum and D.balgimi) are described; a Caribbean form which is hardly distinctfrom the Eastern Pacific D. elegantu-lum Soot-Ryen, 1955, isdescribed as a new subspecies D. e. hendersoni. The larvae are brooded in D. hyalinum (Mon-terosato, 1875),D. viviparum Ockelmann, 1983 and D. balgimi. The brooding specieshave larger larvae (protoconch 210 to 315 µm long) thanthe non-brooding (protoconch 120 to 150 µm long), andreach a smaller adult size (1.4 to 3 mm instead of 4.5–5mm). A phylogenetic reconstruction is attempted using parsimonyanalysis of hinge and shell characters as well as the brooding/nonbrooding character. (Received 22 October 1996; accepted 28 November 1996)     

Multivariate hierarchical analyses of Early Jurassic Ostracoda assemblages

Palaeobiogeographic patterns of Early Jurassic ostracods from the northern and southern hemispheres (96 sections located in Europe, North Africa, Western Australia and North and South America) based on 243 species-level records document global patterns of distribution that can be compared to those previously published on ostracods from the European Epicontinental Sea and Tethyan and South Panthalassa areas. All described records of ostracods from both hemispheres spanning the Hettangian to Early Toarcian have been compiled and verified, and their patterns of origin and distribution have been interpreted. Jaccard coefficient of similarity was used to asses similarities among European, American and Tethyan ostracod shelf faunas. The numerical analysis shows a progressive longitudinal gradient in provincialism through the Early Jurassic, consistent with the northward drift of Tethyan ostracod faunas towards the European Epicontinental Sea and the southward movement of European taxa into Tethys and Panthalassa oceans. The spread of cosmopolitan species and extinction of endemic species, allied to the disappearance of geographical barriers, warmer climate conditions and rising sea levels can explain the reduction in ostracod diversity and the east-west provincialism throughout the Early Jurassic. Interchange between hemispheres, including bipolar distributions, are recognized from the Sinemurian time, pointing out that for most of the studied period, the climate worldwide was warm and tropical.     

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.     

Comparative Aspects of Energy Metabolism in Plant Trypanosomatids

ABSTRACT. The energy metabolism was compared among four different representatives of the genus Phytomonas isolated from different plants and localities: the sieve tubes of the hartrot-infected coconut palm in French Guyana, the latex fluid of Euphorbia hyssopifolia in French Guyana and the fruits of tomato and cherimoya in Spain. All four isolates produced acetate, ethanol, glycerol and glycine as metabolic end-products. In addition, small amount of succinate and pyruvate were excreted. Only minor quantitative differences were observed in the four isolates. Glycosomes, harboring the glycolytic enzymes, were present in all isolates. No evidence was found for an active involvement of the mitochondrion in metabolism. Respiration was insensitive to the classical inhibitors of the respiratory chain, such as antimycin and potassium cyanide, but inhibited by salicylhydroxamic acid. No evidence was found for the functioning of a citric-acid cycle. It is concluded that representative of this genus share the same highly active carbohydrate metabolism combined with a complete suppression of mitochondrial activity.