Influence of temporal fluctuations in seed abundance on the diet of harvester ants (Pogonomyrmex spp.) in the central Monte desert,Argentina

Harvester ants usually go through temporal fluctuations in environmental seed abundance and composition which could influence their behaviour and ecology. The aim of this study was to evaluate how these fluctuations influence the diet of Pogonomyrmex rastratus, P. pronotalis and P. inermis (Hymenoptera, Formicidae) in the central Monte desert during three consecutive growing seasons. Although seeds were the main item in the diet, these ants turned more generalist when seed abundance of the most consumed species (grasses Aristida spp., Trichloris crinita, Pappophorum spp., Digitaria californica and Stipa ichu) was low. Accordingly, diversity of items in the diet decreased with seed abundance in a logarithmical fashion, showing higher foraging efficiency for seeds at higher seed abundance. Seed diversity, however, was not related to seed abundance as ants always included several species in their diet, with alternating prevalence. The proportion of the most consumed species increased logarithmically in the diet of P. rastratus and P. pronotalis along with their abundance in the environment probably as a consequence of diet switching (from forb and shrub seeds to grass seeds) and by an increase in foraging efficiency at higher seed densities. In contrast, foraging activity of P. inermis was very low at low seed abundance and its diet included only the five grasses. Among the most consumed species, proportion in the diet was not associated with relative abundance in the environment. Aristida spp., Pappophorum spp. and D. californica were overall highly selected. However, the flexibility in the diet of P. pronotalis and P. rastratus and the low foraging activity of P. inermis during periods of low resource abundance could attenuate potential top‐down effects in the central Monte desert. This study shows that bottom‐up effects are important in ant‐seed interactions and should be considered when predicting and evaluating ants' effects on seed resources.     

Ribosomal DNA of Leishmania brasiliensis: Number of Ribosomal Copies and Gene Isolation1

ABSTRACT. The DNA content of the hemoflagellate Leishmania brasiliensis. strain Y, has been determined by colorimetric reactions and found to be nearly 0.226 pg/cell. When this DNA is bound to filters and hybridized with labeled rRNA from the same organism, saturation is reached at 0.47% of the DNA, corresponding to an estimated 160 ribosomal gene copies. When the DNA is sheared and centrifuged to equilibrium in CsCl gradients, two major satellites of the main band (p = 1.712 g/cm³) are observed: a heavy one (1.720 g/cm³), which hybridizes with labeled rRNA, and a light one (1.699 g/cm³) with the electron microscopic characteristics of the kinetoplast DNA network.     

Comparative response of δ13C, δ18O and δ15N in durum wheat exposed to salinity at the vegetative and reproductive stages

This study compared the performance of the stable isotope composition of carbon (δ¹³C), oxygen (δ¹⁸O) and nitrogen (δ¹⁵N) by tracking plant response and genotypic variability of durum wheat to different salinity conditions. To that end, δ¹³C, δ¹⁸O and δ¹⁵N were analysed in dry matter (dm) and the water‐soluble fraction (wsf) of leaves from plants exposed to salinity, either soon after plant emergence or at anthesis. The δ¹³C and δ¹⁸O of the wsf recorded the recent growing conditions, including changes in evaporative conditions. Regardless of the plant part (dm or wsf), δ¹³C and δ¹⁸O increased and δ¹⁵N decreased in response to stress. When the stress conditions were established just after emergence, δ¹⁵N and δ¹³C correlated positively with genotypic differences in biomass, whereas δ¹⁸O correlated negatively in the most severe treatment. When the stress conditions were imposed at anthesis, relationships between the three isotope signatures and biomass were only significant and positive within the most severe treatments. The results show that nitrogen metabolism, together with stomatal limitation, is involved in the genotypic response to salinity, with the relative importance of each factor depending on the severity and duration of the stress as well as the phenological stage that the stress occurs.     

First Miocene fossils of Vivianiaceae shed new light on phylogeny,divergence times,and historical biogeography of Geraniales

The origin of Geraniales (approximately 900 species in three families: Geraniaceae, Melianthaceae, and Vivianiaceae) is traced back to the Cretaceous of Gondwana, yet their geotemporal history is largely unknown because of a limited fossil record and incomplete phylogenies. In the present study, we provide the first fossil record of Vivianiaceae and a highly resolved molecular phylogeny for all extant Geraniales genera. Our results support the hypothesis that five (instead of three) families should be recognized in the order Geraniales: Francoaceae A. Juss. (Francoa, Greyia, Tetilla), Geraniaceae Juss. (Erodium, Geranium, Monsonia, Pelargonium), Hypseocharitaceae Wedd. (monogeneric), Melianthaceae Horan. (Bersama, Melianthus), and Vivianiaceae Klotzsch (Balbisia, Rhynchotheca, Viviania). The four major lineages (i.e. Geraniaceae, Francoaceae + Melianthaceae, Hypseocharitaceae, Vivianiaceae) all originated within a narrow time frame during the Eocene (36.9–49.9 Mya) based on the five fossil calibration points. The divergence of most of the extant genera occurred much later, from the Miocene onwards. The South American–South African disjunction in Francoaceae apparently goes back to long distance dispersal with an estimated divergence time of the lineages in the Middle Miocene [11.2 (5.9–17.7) Mya]. Diversification in Melianthus appears to be much more recent than previously assumed [starting approximately 3.4 (1.9–5.2) Mya rather than approximately 8–20 Mya]. However, divergence of the Andean Hypseocharis lineage [36.9 (31.9–42.8) Mya] significantly predates the main Andean uplift: Current distributions likely go back to northward migrations and subsequent extinctions in Patagonia. Similarly, Rhynchotheca, Balbisia, and Viviania have a current southern distribution limit > 10°N of the fossil finds, indicating a massive northward displacement. The present evidence suggests that niche conservatism likely played a major role in the historical biogeography of Geraniales. © 2012 The Linnean Society of London, Biological Journal of the Linnean Society, 2012, ?? , ??–??.     

CONSUMER ATTITUDES AND OPINIONS TOWARD FUNCTIONAL FOODS: A FOCUS GROUP STUDY

Acceptance of foods with specific health characteristics depends largely on the consumers' opinion. The objective of this work was to investigate Spanish consumers' opinions, attitudes and beliefs regarding functional foods in general, and one of the most popular foods, yogurt, in particular. Six consumer focus group interviews were conducted, involving a total of 59 participants. Each group profile was chosen to either complement or contrast the other groups according to previously established criteria (gender, age and educational level). The youngest consumers (18–30 years old) proved, in general, to have a fairly negative attitude toward these types of products, although this attitude varied according to the type of food. For the consumers participating in this study, the most acceptable functional foods were low-fat foods and some fermented dairy products. Purchase and consumption of yogurt were more dependent on its sensorial qualities and its price than on the nutritional information printed on the label.

PRACTICAL APPLICATIONS

The influence of attitudes, beliefs and opinions on food choice and purchase is specially important in the acceptance of some types of foods (organic or ecological, genetically modified or functional) that are presented to the consumer as a possible alternative to the conventional foods. The application of focus groups can help not only in explaining consumer behavior, but also in designing more effective nutritional education rules and products that satisfy consumer needs and expectations.     

The origin and paleoecologic significance of the trace fossil Asteriacites in the Pennsylvanian of Kansas and Missouri

The trace fossil Asteriacites, recorded in Cambrian to Recent shallow- and deep-marine facies, is traditionally interpreted as the resting trace of asterozoans. Well-preserved specimens of A. lumbricalis are abundant in Pennsylvanian (Upper Carboniferous) shallow- and marginal-marine siliciclastic deposits of eastern Kansas and western Missouri. Detailed morphologic analysis of these specimens suggests that they record the activities of mobile epifaunal ophiuroids. Evidence of a brittle star (ophiuroid) producer rather than sea star (asteroid) is provided by (1) trace-fossil morphologic features reflecting the anatomy of the producer (e.g., well-differentiated central structure, slender vermiform arms) and ophiuroid burrowing technique (e.g., proximal arm expansion, arm branching), and (2) mode of occurrence (e.g., gregarious behavior, horizontal and vertical repetition). Vertical and horizontal repetition produces complex aggregates of A. lumbricalis that are interpreted either as escape structures (fugichnia) or as feeding structures, respectively. Ophiura texturata is proposed as a modern analogue for the A. lumbricalis producer, based on inferred life habit and feeding behavior. Asteriacites lumbricalis is present in two different intertidal trace-fossil assemblages. The first assemblage is characterized by high diversity and records tidal flats developed outside of embayments under normal marine conditions. The second assemblage consists of A. lumbricalis together with a few other ichnotaxa and represents a depauperate association that developed in restricted tidal flats within an embayment or estuarine setting. This challenges the conventional view of Asteriacites as a normal-marine salinity indicator. Some echinoderms, and particularly asterozoans, penetrate and inhabit modern environments of depressed salinity. The presence of Asteriacites in Pennsylvanian marginal-marine facies of Kansas and Missouri provides evidence that ophiuroids had adapted to brackish-water conditions by the late Paleozoic.     

In planta measurements of oxidative bursts elicited by avirulent and virulent bacterial pathogens suggests that H2O2 is insufficient to elicit cell death in tobacco

A rapid and localized programmed cell death – the hypersensitive response (HR) – is a widely utilized plant resistance mechanism against pathogens. Studies have implicated H₂O₂ generation as a key elicitory mechanism in the HR. The causal relationship between the kinetics of the in planta oxidative burst, the HR and certain defence gene expression was examined. H₂O₂ generation following challenge with avirulent strains of Pseudomonas syringae pv. (P. s. pv.) syringae occurred in two phases. The effects of ROS generation were investigated using the H₂O₂-responsive transgene AoPR10-GUS, the dually responsive (H₂O₂ and salicylic acid) PR1a-GUS as well as measures of cell death. Co-application of catalase with P. s. pv. syringae into tobacco leaf panels suppressed AoPR10- and PR1a-GUS expression and cell death. Conversely, varying H₂O₂ generation with glucose: glucose oxidase influenced both defence gene expression and cell death. AoPR10-GUS proved to be primarily responsive to apoplastic not intracellular oxidative stress, suggesting that the apoplasm was a distinctive source of oxidative signals. A biphasic oxidative burst was also observed with virulent P. s. pv. tabaci, which, although delayed compared to that observed during HR, persisted at equivalent levels for a longer period. Taking all these data together we suggest that either (1) additional factors to the apoplastic oxidative burst are required to explain the rapid kinetics of defence signalling and cell death associated with the HR or (2) P. s. pv. tabaci successfully suppresses the effects of H₂O₂ generation by an unknown mechanism.     

SIMULTANEOUS PCR DETECTION OF BACTERIA AND MOLD DNA SEQUENCES IN PHARMACEUTICAL SAMPLES BY USING A GRADIENT THERMOCYCLER

A gradient thermocycler, the Stratagene RoboCycler 96-Gradient, was evaluated for the simultaneous PCR amplification of microbial genes which indicated the presence of Escherichia coli, Staphylococcus aureus, Pseudomonas aeruginosa, and Aspergillus niger in pharmaceutical samples. Suspensions of pharmaceutical products were inoculated with pure cultures of bacteria and mold. After a 24 h incubation, bacterial DNA was extracted from each enrichment broth using a mild lysis in Tris-EDTA-Tween 20 buffer containing proteinase K while mold DNA was extracted by boiling the samples in Tris-EDTA-SDS buffer for 1 h. A 10 μL aliquots of extracted DNA was added to Ready-To-Go PCR beads and specific primers for E. coli, S. aureus, and P. aeruginosa. However, 50 μL aliquots of extracted mold DNA were used for amplification of specific A. niger DNA sequences. The individual samples were loaded into the RoboCycler 96-Gradient thermocycler. Simultaneous detection of all microbial genes was performed by using a gradient profile that allowed the use of DNA primers with different annealing temperatures. Standard methods for quality control evaluation of pharmaceutical products required 6–8 days while simultaneous PCR detection of bacteria and mold DNA sequences was completed within 27 h.     

Carbon dioxide exchange above a Mediterranean C3/C4 grassland during two climatologically contrasting years

Eddy‐covariance measurements of net ecosystem carbon exchange (NEE) were carried out above a grazed Mediterranean C3/C4 grassland in southern Portugal, during two hydrological years, 2004–2005 and 2005–2006, of contrasting rainfall. Here, we examine the seasonal and interannual variation in NEE and its major components, gross primary production (GPP) and ecosystem respiration (R_eco), in terms of the relevant biophysical controls. The first hydrological year was dry, with total precipitation 45% below the long‐term mean (669 mm) and the second was normal, with total precipitation only 12% above the long‐term mean. The drought conditions during the winter and early spring of the dry year limited grass production and the leaf area index (LAI) was very low. Hence, during the peak of the growth period, the maximum daily rate of NEE and the light‐use and water‐use efficiencies were approximately half of those observed in the normal year. In the summer of 2006, the warm‐season C4 grass, Cynodon dactylon L., exerted an evident positive effect on NEE by converting the ecosystem into a carbon sink after strong rain events and extending the carbon sequestration for several days, after the end of senescence of the C3 grasses. On an annual basis, the GPP and NEE were 524 and 49 g C m^?2, respectively, for the dry year, and 1261 and ?190 g C m^?2 for the normal year. Therefore, the grassland was a moderate net source of carbon to the atmosphere, in the dry year, and a considerable net carbon sink, in the normal year. In these 2 years of experiment the total amount of precipitation was the main factor determining the interannual variation in NEE. In terms of relevant controls, GPP and NEE were strongly related to incident photosynthetic photon flux density on short‐term time scales. Changes in LAI explained 84% and 77% of the variation found in GPP and NEE, respectively. Variations in R_eco were mainly controlled by canopy photosynthesis. After each grazing event, the reduction in LAI affected negatively the NEE.